AN-SOF Antenna Simulation Software | User Guide
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The document is a user guide for the an-sof antenna simulator, a software tool designed for modeling, analyzing, and designing antennas and wire structures. It provides detailed instructions covering setup, simulation processes, graphical tools, and results visualization, emphasizing the capabilities of an-sof in achieving accurate electromagnetic simulations through the conformal method of moments technique. Additional features include handling complex antenna designs, various input parameters, and the ability to simulate wire structures over different ground conditions.
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4.4 FAR FIELD PARAMETERS
Go to the Setup tab in the main window and select the Far-Field panel, Fig. 4.10.
Fig. 4.10: Far-Field panel in the Setup tabsheet.
The far field can be computed after having calculated the current distribution previously.
Thus, the parameters set in the Far-Field panel have no effect in the determination of the
currents and can be modified at any time. However, the far field must be recalculated every
time these parameters are modified.
There are four options for radiation pattern calculations:
FULL 3D
The far field is calculated in angular ranges that cover the entire 3D space, which allows us
to obtain 3D radiation lobes. The steps for the Theta (zenith) and Phi (azimuth) angles can
be set in the Theta [deg] and Phi [deg] boxes.
VERTICAL
The far field is calculated at a vertical slice for a given Phi (azimuth) angle. The step for the
Theta (zenith) angle can be set in the Theta [deg] box, while the fixed Phi can be set in the
Phi [deg] box.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-76-320.jpg)
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HORIZONTAL
The far field is calculated at a horizontal slice for a given Theta (zenith) angle. The step for
the Phi (azimuth) angle can be set in the Phi [deg] box, while the fixed Theta can be set in
the Theta [deg] box.
CUSTOM
The far field is calculated for the specified ranges of angles Theta (zenith) and Phi
(azimuth). The start, step, and stop values for Theta and Phi can be set in the Theta [deg]
and Phi [deg] boxes.
Additionally, the following parameters can be set:
ORIGIN (X0,Y0,Z0)
This can be any point used as a phase reference, its coordinates do not affect the shape of
the radiation pattern. The 3D radiation pattern will be plotted centered at this point.
DISTANCE
It is the distance from (X0,Y0,Z0) to an observation point in the far-field region. A
normalized far-field pattern can be obtained by setting Distance = 1.
The zenith and azimuth angles, (Theta) and (Phi), are shown in Fig. 4.11, where it is also
shown de Distance R from the structure to an observation point in the far-field zone. These
three numbers (R,,) define the spherical coordinates of the far-field point.
Fig. 4.11: Spherical coordinates (R,,) of a far-field point.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-77-320.jpg)
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than the first one. Check this option if you need to change the amplitude values of
voltage/current sources frequently.
If Load Impedances is checked, lumped impedances will be considered in the simulation.
With this option all the lumped loads can be disabled or enabled at the same time.
If Wire Resistivity is checked, the finite resistivity of the wires will be considered in the
simulation. Any wire has its own resistivity in [Ohm meter] that can be set when the wire is
drawn. This option allows us considering the whole structure as a perfect electric conductor
when it is unchecked.
If Wire Coating is checked, the coating materials of the wires will be considered in the
simulation. Any wire has its own coating specified by a dielectric permittivity, magnetic
permeability, and thickness, which can be set when the wire is drawn. When this option is
unchecked, the wire coating will not be considered in the simulation.
Fig. 4.18: Settings panel in the Setup tabsheet.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-87-320.jpg)
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5.9 WIRE MATERIALS
The Materials page belongs to the Draw dialog box of the chosen wire type, Fig. 5.33. In the
Materials page the following attributes can be specified:
WIRE RESISTIVITY
A resistivity in [Ohm meter] can be specified for the wire. This value is used for computing a
distributed impedance along the wire, considering the skin effect. The equivalent radius for
wires of non-circular cross section will be used to compute the impedance per unit length
along the wires.
Resistivity values for most common conductive materials are the following:
Material Resistivity [ m]
Aluminum (Pure) 2.65E-8
Aluminum (6061-T6) 4.01E-8
Aluminum (6063-T832) 3.25E-8
Brass 6.41E-8
Copper 1.74E-8
Phosphor Bronze 1.10E-7
Silver 1.59E-8
Stainless Steel 302 7.19E-7
Tin 1.14E-7
Zinc 5.90E-8
The resistivity of wires is considered in the simulation if the option Wire Resistivity is
checked in the Settings panel of the Setup tabsheet.
WIRE COATING
Wires can have an insulation or coating material. The cross section of a coated wire is
circular, so the equivalent radius will be used for wires having a non-circular cross section.
In this case, the material the coating is made of can be set by the following parameters:
RELATIVE PERMITTIVITY
It is the dielectric constant of the coating material relative to the permittivity of
vacuum.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-111-320.jpg)
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GW – Linear Wire
One linear wire per line must be set beginning with “GW” and ending with an Enter as
follows:
GW Tag Segments X1 Y1 Z1 X2 Y2 Z2 Radius
[Enter]
Tag > 0. Tag number for the linear wire. The space between “GW” and Tag is optional. A
single tab or comma can also be used as a separator between the command name and the
first data field.
Segments = Number of segments for the wire. If a zero is entered, the minimum
recommended number of segments will be computed.
X1 Y1 Z1 = Cartesian coordinates of the start point of the linear wire.
X2 Y2 Z2 = Cartesian coordinates of the end point of the linear wire.
Radius = Wire radius.
Fields can be separated by up to two spaces, a single tab, a single comma, or a comma and
space. Each GW line, including the last one in a set of linear wires to be imported, must end
with an Enter (press Enter in the keyboard for a carriage return). The text lines above the
GW lines will be ignored, so comments can be added at the beginning of the file.
The following are equivalent examples:
Write comments here
GW 1 12 5.42 0.38 1.262 5.425 -0.378 1.261 0.01[Enter]
GW 2 5 7.45 0 1.122 7.45 0 1.49 0.015[Enter]
GW 3 2 8.3 0.0 1.12 8.37 0.0 1.595 0.01[Enter]
Write comments here
GW1,12,5.42,0.38,1.262,5.425,-0.378,1.261,0.01[Enter]
GW2,5,7.45,0,1.122,7.45,0,1.49,0.015[Enter]
GW3,2,8.3,0.0,1.12,8.37,0.0,1.595,0.01[Enter]](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-119-320.jpg)
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CM and Other Commands
The CM (comment lines), GH (helical wire), GA (arc), GM (coordinate transformation), GS
(scale dimensions), FR (frequency), EX (excitation), LD (load impedances and wire
conductivity), EK (exact kernel), RP (radiation pattern), GE (ground connections) and GN (real
ground parameters) commands will also be read.
The CM lines will be added to the Note panel of the Setup tabsheet after the NEC file is
imported. The comment termination card, “CE”, is not needed in AN-SOF. Comments
without the CM command at the beginning of the file will be ignored and not imported. The
command names, “CM”, “GW”, “GH”, etc., are reserved words in AN-SOF and they are used to
recognize the fields between these commands and the final Enter in each text line, so the
command names should not be used in comments.
The rest of the AN-SOF commands must have the following formats, where all the indicated
fields are mandatory:
GH – Helix
GH Tag Segments Spacing Length R R R R Radius
[Enter]
Tag > 0. Tag number for the helix. The space between “GH” and Tag is optional. The helix
begins at the origin at develops along the positive z-axis. To rotate and/or move the helix,
use the GM command described below. This GH command corresponds to the NEC-2 helix
specification. Consider that the GH command is different in NEC-4.
Segments = Number of segments for the helix. If a zero is entered, the minimum
recommended number of segments will be computed. We must point out that unlike NEC,
AN-SOF uses conformal segments that exactly follow the helix contour.
Spacing = Spacing between turns.
Length = Total length of the helix. Length > 0 gives a right-handed helix, and Length < 0
gives a left-handed helix.
R = Radius of the helix (it must appear four times).
Radius = Wire radius.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-120-320.jpg)
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GA – Arc
GA Tag Segments R Ang1 Ang2 Radius
[Enter]
Tag > 0. Tag number for the arc. The space between “GA” and Tag is optional. The arc is on
the xz-plane, and it is centered at the origin, so the arc axis is the y-axis. To rotate and/or
move the arc, use the GM command described below.
Segments = Number of segments for the arc. If a zero is entered, the minimum
recommended number of segments will be computed. We must point out that unlike NEC,
AN-SOF uses conformal segments that exactly follow the arc contour.
R = Arc radius.
Ang1 = Angle of the first end of the arc measured from the x-axis in a left-handed direction
about the y-axis, in degrees.
Ang2 = Angle of the second end of the arc, in degrees.
Radius = Wire radius.
GM – Coordinate Transformation
GM 0 N rotX rotY rotZ DX DY DZ 0
[Enter]
N = 0 means that the whole structure above the GM command must be rotated and moved
using (rotX,rotY,rotZ) and (DX,DY,DZ). The coordinate transformations are applied
sequentially in that order. N = 1 means that the whole structure above the GM command
must be copied and the copy must be moved to a new position (DX,DY,DZ) from the origin.
The “GM” command can be used below the “GW”, “GH” and “GA” commands for rotating,
moving, and copying the desired linear wires, helices and arcs.
rotX = Angle of rotation about X-axis, in degrees.
rotY = Angle of rotation about Y-axis, in degrees.
rotZ = Angle of rotation about Z-axis, in degrees.
DX = Move the structure an amount DX along X-axis.
DY = Move the structure an amount DY along Y-axis.
DZ = Move the structure an amount DZ along Z-axis.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-121-320.jpg)
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GS – Scale Structure Dimensions
GS 0 0 Scale
[Enter]
Scale = Scaling factor. All structure dimensions, including wire radii, are multiplied by Scale.
FR – Frequencies
FR Type Num 0 0 Freq Df
[Enter]
Type = Type of frequency sweep. Linear -> Type = 0, Log -> Type = 1.
Num = Number of frequency steps.
Freq = Frequency in MHz or starting frequency in a range.
Df = If Type = 0, it is the frequency stepping increment in MHz. If Type = 1, it is the
multiplication factor of a log sweep.
EX – Excitation
EX Type Wire# Seg# 0 Real Imag
[Enter]
Type = Type of source. Only voltage sources are currently supported, so set Type = 0 or 5
(the “5” being an old source model only used in NEC).
Wire# = Wire tag number where the source is placed.
Seg# = Segment where the source is placed.
Real = Real part of the source voltage.
Imag = Imaginary part of the source voltage.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-122-320.jpg)
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LD – Load impedance
LD Type Wire# Seg# Seg# R L C
[Enter]
Type = Type of load. Only series RLC loads are currently supported, so set Type = 0 for a
RLC load. Set Type = 5 and Seg# = 0 to specify a wire conductivity [S/m] in the “R” field for
the wire number “Wire#”. Type LD 5 0 0 0 R 0 0 to set a conductivity "R [S/m]" on all wires.
Wire# = Wire tag number where the load or conductivity is placed.
Seg# = Segment tag number where the load is placed. It is a field that appears twice due to
a NEC convention that is not used in AN-SOF, so the second Seg# will be ignored. Set Seg#
= 0 if a wire conductivity is to be entered.
R = Resistance in Ohms or conductivity in S/m.
L = Inductance in Henries. It is ignored if R is a conductivity; enter a zero.
C = Capacitance in Farads; if none, enter zero. It is ignored if R is a conductivity, so enter a
zero.
GE – Ground connections
GE Type
[Enter]
Type = 0 -> No ground plane is present. A “GE” command without a type will be interpreted
as “GE 0”.
Type = 1 -> A PEC ground plane is placed at z = 0 and wires ending on the ground plane will
be connected to the ground. If a real ground plane has been chosen, Type = 1 means that
the wire connections to the ground must be considered as zero-Ohm connections.
Type = -1 -> The wire connections to the ground are imperfect and producing power losses
when a real ground plane has been chosen.
GN – Real ground
GN Type Screen 0 0 Epsilon Sigma Length WireRadius
[Enter]](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-123-320.jpg)
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Type = type of ground plane.
Type = -1 -> Free space simulation; all ground parameters are ignored. “GN -1” can be used
in this case.
Type = 0 -> Reflection Coefficients/Asymptotic option.
Type = 1 -> PEC ground plane at z = 0; the other parameters are ignored. “GN 1” can be used
in this case.
Type = 2 -> Sommerfeld-Wait/Asymptotic option.
Screen = Number of radials in a radial wire ground screen. Set Screen = 0 if no ground
screen is present.
Epsilon = Ground plane relative permittivity or dielectric constant.
Sigma = Ground plane conductivity in [S/m].
Length = Length of radial wires if a radial wire ground screen is used. Enter a zero if no
ground screen is used.
WireRadius = Radius of radial wires if a screen is used. Enter a zero if no ground screen is
used.
RP – Radiation pattern
RP 0 Ntheta Nphi 1001 Theta Phi Dtheta Dphi R
[Enter]
Ntheta = Number of values of at which the field is to be computed.
Nphi = Number of values of at which the field is to be computed.
1001 = It is a NEC variable which indicates that the average power gain must be computed.
This value will be ignored since AN-SOF always computes the average power gain.
Theta = Initial angle in degrees.
Phi = Initial angle in degrees.
Dtheta = Increment for in degrees.
Dphi = Increment for in degrees.
R = Radial distance in meters of the field point from the origin. R = 0 is taken as R = 1 m.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-124-320.jpg)
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MM FORMAT
One linear wire per line must be defined as follows:
X1,[TAB]Y1,[TAB]Z1,[TAB]X2,[TAB]Y2,[TAB]Z2,[TAB]Radius,[TAB]Segments
[Enter]
X1 Y1 Z1 = Cartesian coordinates of the wire start point.
X2 Y2 Z2 = Cartesian coordinates of the wire end point.
Radius = Wire radius.
Segments = Number of segments.
The last text line must end with an Enter (press Enter in the keyboard for a carriage return).
Example:
5.42, 0.38, 1.262, 5.425, -0.378, 1.261, 0.01, 12
7.45, 0, 1.122, 7.45, 0, 1.49, 0.015, 5
8.3, 0.0, 1.12, 8.37, 0.0, 1.595, 0.01, 2
[Enter]
In the MM format, automatic segmentation of a wire can be obtained by entering any
number equal or less than zero as the number of segments. The units for the coordinates of
the start and end points of any wire must be consistent with the length unit chosen in the
AN-SOF Preferences dialog box. Also, the wire radius or diameter of any imported wire must
be expressed in the unit chosen in the Preferences dialog box.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-126-320.jpg)
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THE MATERIALS PAGE
It shows the properties of the materials the selected wire is made of, Fig. 6.10, namely,
• Wire Resistivity: The resistivity of the selected wire in [Ohm m]. If the wire is coated,
it is the resistivity of the internal conductor.
• Wire Coating: The parameters of the coating shield of the selected wire.
• Relative Permittivity: The permittivity or dielectric constant of the coating material
relative to the permittivity of vacuum.
• Relative Permeability: The magnetic permeability of the coating material relative to
the permeability of vacuum.
• Thickness: The thickness of the coating shield.
Fig. 6.10: Wire Properties dialog box. The Materials page shows the material parameters of the
conductive wire and its coating shield or insulation.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-142-320.jpg)
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13.11 POWER BUDGET
Go to Results > Power Budget/RCS in the main menu to display the Power Budget dialog
box, Fig. 13.21. The following list of parameters versus frequency will be shown when
discrete sources are used as the excitation:
• The Input Power column shows the total input power provided by the discrete
sources in the structure.
• The Radiated Power column shows the total radiated power from the structure.
• The Structure Loss column shows the total consumed power (ohmic losses) in the
structure.
• The Efficiency column is the radiated power to the input power ratio. When the
structure is lossless, an efficiency of 100% is obtained.
• The Directivity column is the peak directivity (dimensionless) .
• The Directivity [dBi] column is the peak directivity in decibels with reference to an
isotropic source .
• The Gain column is the peak gain (dimensionless).
• The Gain [dBi] column is the peak gain in decibels with reference to an isotropic
source.
• The Pav column is the average power density. This value is calculated averaging
the power density over all directions in space.
• The Pmax column is the maximum value of the radiated power density.
• The Theta (max) and Phi (max) columns are the zenith and azimuth angles,
respectively, in the direction of maximum radiation.
• The Error column is the error in the power balance of the system. A necessary, but
not sufficient, condition for a model to be valid is that the input power must be
equal to the sum of the radiated and lost powers, so the Error is defined as follows:
Error % = 100 x (Input Power – Lost Power – Radiated Power) / (Input Power – Lost Power)](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-235-320.jpg)
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13.12 RADAR CROSS SECTION
Go to Results > Power Budget/RCS in the main menu to display the Radar Cross Section
dialog box, Fig. 13.22. The following list of parameters versus frequency will be shown
when an incident field is used as the excitation:
• The RCS [m2
] column shows the Radar Cross Section in square meters.
• The RCS [lambda2
] column shows the Radar Cross Section in square wavelengths.
• The RCS [dBsw] column shows the Radar Cross Section in decibels with reference
to a square wavelength.
• The Radiated Power column shows the total scattered power from the structure.
• The Structure Loss column shows the total consumed power (ohmic losses) in the
structure.
• The Pav column is the average power density scattered from the structure. This
value is computed averaging the scattered power density over all directions in
space.
• The Pmax column is the maximum value of the scattered power density.
• The Theta (max) and Phi (max) columns are the zenith and azimuth angles,
respectively, in the direction of maximum radiation.
Select an item from the list in the upper right corner of the window and then press the Plot
button to plot the selected item versus frequency.
Fig. 13.22: The Radar Cross Section dialog box.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-238-320.jpg)
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Fig. 15.2: Line page in the Draw dialog box. The wire will be drawn starting from point (0,0,-750)
[mm] and ending at point (0,0,750) [mm]. Thus, it lies along the z-axis and is 1500 mm long,
which corresponds to half-wavelength at 100 MHz. Press F7 to view the main axes.
Fig. 15.3: Attributes page in the Draw dialog box. The wire is divided into 17 segments, and it
has a circular cross-section with 5 mm in radius.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-255-320.jpg)
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Fig. 15.7: Gain [dBi] and total E-field patterns at 100 MHz.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-259-320.jpg)
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Fig. 15.9: Results tabsheet, where a peak gain of 8.9 dBi is obtained for the Yagi-Uda array.
Fig. 15.10: Gain pattern [dBi] for the Yagi-Uda array of Fig. 15.8 at 300 MHz.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-261-320.jpg)
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STEP 3 | RUN: Click on the Run Currents and Far-Field (F11) button on the toolbar. After
the calculations are complete, click on the Far-Field 3D Plot button on the toolbar to
display the radiation pattern. Choose Radiation Pattern under the Plot menu in AN-3D
Pattern to plot the normalized radiation pattern (dimensionless). Then, choose the
Radiation Pattern [dB] option to see the pattern in decibel scale. Note that the far field has
a null on the xy-plane due to the losses in the ground plane, Fig. 15.14.
The antenna efficiency is the radiated to the input power ratio. Go to the Results tabsheet
to see the input impedance, VSWR, Directivity, Gain, and Efficiency, Fig. 15.15. Note that the
efficiency is low and therefore the gain too since most of the input power is lost to the
ground. In this example we have chosen a Poor soil. Try different soils and increasing the
number of radial wires and their length to improve the antenna efficiency.
Fig. 15.14: Radiation pattern of a quarter-wave monopole over a radial wire ground screen.
Fig. 15.15: Results tabsheet for a quarter-wave monopole over a radial wire ground screen.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-264-320.jpg)
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18.2 THE ELECTRIC FIELD INTEGRAL EQUATION
The current distribution on metallic surfaces with ideal conductivity can be found by
solving an Electric Field Integral Equation (EFIE) expressed in the frequency domain [1]:
(1)
where:
Ei: Incident Electric Field on the surface S.
n: unit vector at point r on the surface S.
k: wave number.
J: unknown electric current density flowing on the surface.
G: Green's function, which in free space is given by:
(2)
The EFIE is an expression of a boundary condition on the surface, namely zero tangential
electric field. When we are dealing with a wire structure, the EFIE reduces to [2]:
(3)
where T is the tangential unit vector describing the contour of the curve , I(s) is the
unknown electric current on the wire, and K(s,s') is the integral equation Kernel defined as:
(4)
The EFIE is averaged about the wire circumference described by the angle , resulting in
the EFIE (3) with the Kernel (4). The current distribution I(s) is then the average value of the
current density J in the axial direction; the current in the direction is neglected. This is a
good assumption provided that the wire radius is small with respect to the wavelength.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-282-320.jpg)
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The wire axis is defined by its parametric equations that can be written in the compact
form [3]:
(5)
which points from the origin to any point on the wire, Fig. 18.1. The parameter s varies over
a real interval. The tangent unit vector can be obtained from the first derivative of (5):
(6)
Fig. 18.1: Parametric description of a curved wire. The tangent unit vector is obtained from the
first derivative of the position vector r(s).
This parametric description is the key for the accurate modeling of wire structures [3]. A
straight wire approximation to the geometry produces a loss of geometrical information
that can never be completely restored. However, this information is not lost if a parametric
representation is used to describe the wire locus [4], [5]. It is also possible to improve on
the straight wire approximation by using quadratic segments to model the geometry [6].
x
y
z
r(s)
T(s)](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-283-320.jpg)
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Thus, the definition of a wire must include its parametric description and its first derivative
if an exact representation of the geometry is required, as shown in Fig. 18.1.
The Kernel (4) can be approximated by the following generalized thin-wire approximation:
(7)
where a is the wire radius.
When the observation point r(s) and the source point r(s') are both in the same straight wire,
the distance R reduces to the usual thin-wire approximation:
(8)
Thus, the EFIE and its Kernel are also valid for straight wires.
It is well known that the thin-wire approximation produces numerical oscillations in the
computed current distribution near wire ends and near the position of discrete sources
when wire segments are relatively thick [7]. To avoid this undesired behavior and obtain the
maximum accuracy, the exact Kernel in (4) is used in AN-SOF by default instead of the thin-
wire approximation in (7). A closed-form expression for the exact Kernel has been found so
its use practically does not compromise the speed of the simulation. However, an extended
thin-wire Kernel has been calculated that also avoids the current distribution inaccuracies
for a thin-wire ratio (wire diameter/segment length) < 3, which is far better than the thin-
wire ratio < 1 that must be used when the standard thin-wire approximation is used.
In the Settings panel of the Setup tabsheet check the Exact Kernel option to use the exact
Kernel in (4). Uncheck this option to use the extended thin-wire Kernel.
The existence of a PEC ground plane is modeled in AN-SOF by means of image currents.
This method can be easily implemented by adding an image term to the Green's function,
resulting in an additional term for the Kernel.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-284-320.jpg)
![2 8 5 – A N - S O F U S E R G U I D E
18.3 THE CONFORMAL METHOD OF MOMENTS
The Method of Moments (MoM) is a technique used to convert the EFIE into a system of
linear equations that then can be solved by standard methods [1], [8]. For simplicity, the
integral (linear) operator in (3) will be denoted by L, then the EFIE takes the form:
(9)
where ET is the tangential component of the incident electric field. The current distribution
is approximated by a sum of N basis functions with unknown amplitudes In, giving:
(10)
With this expansion and using the linearity of the operator L, we can write:
(11)
To obtain a set of N equations, the functional equation (11) is weighted with a set of N
independent testing functions wm, giving:
(12)
where the integrals are calculated over the domain of L. Now we have as many independent
equations as unknowns, so (12) can be written as:
(13)
where
[Z]: impedance matrix with dimension NN and the elements
[I]: current matrix with dimension N1 and the elements In.
[U]: voltage matrix with dimension N1 and the elements
This fully occupied equation system must be solved for the unknown currents In. LU
decomposition is used in AN-SOF.
The MoM is applied by first dividing the wire structure into N segments, and then defining
the basis and testing functions on the segments. Triangular basis and pulse testing
functions are used in AN-SOF, Fig. 18.2.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-285-320.jpg)
![2 8 6 – A N - S O F U S E R G U I D E
Fig. 18.2: (a) Triangular basis functions, Fi(u), and pulse testing functions, Ti(u). (b) Current
distribution approximated by triangular functions.
When a curved wire is described parametrically by a vector function (5), the basis and
testing functions are curved in the sense that their support is a curved subset of the wire.
Therefore, when curved basis and testing functions are used, the Conformal Method of
Moments (CMoM) is obtained.
To fill the impedance matrix [Z], an adaptive Gauss-Legendre quadrature rule is applied to
compute the involved integrals. After having solved the equation system, the currents In are
known and other parameters of interest, such as input impedances, voltages, radiated
power, directivity, and gain can be computed.
The MoM can also be used to calculate the electromagnetic response of metallic surfaces,
which are modeled using wire grids [9]. In AN-SOF, with the CMoM the accuracy of the
calculation of wire grids is remarkably improved compared to the traditional MoM, as
demonstrated in this article.
Another extension of the calculation includes wires that do not have a circular cross section
[10]. In AN-SOF an equivalent radius is calculated for these wires.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-286-320.jpg)
![2 8 8 – A N - S O F U S E R G U I D E
18.5 CURVED VS. STRAIGHT SEGMENTS
Many examples show the advantages of using curved segments with respect to the stability
and convergence properties of the solutions [11], [12]. Due to the improved convergence
rate, accurate results can be obtained with reduced simulation time and memory space.
As an illustration, Figs. 18.5 and 18.6 show a comparison between AN-SOF, which uses
curved segments, and a straight wire approximation to a normal mode helix antenna, Fig.
18.4. The convergence properties of the input impedance and admittance versus the
number of unknowns are investigated.
Fig. 18.4: Center-fed helical antenna (normal mode) in free space. Helix radius = 0.0273. Pitch =
0.0363. Number of turns = 10. Wire radius = 0.001.
As can be seen from these results, by using curved segments significantly fewer unknowns
are needed to predict the input impedance. However, the admittance convergence is
questionable for the straight wire case, while it has a notorious convergent behavior for the
curved case.
The improvement depends on the geometry and frequency, but generally, if N straight
segments are needed to obtain a convergent value, then N/p curved segments are needed](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-288-320.jpg)
![2 9 1 – A N - S O F U S E R G U I D E
18.6 REFERENCES
[1] Harrington, R. F., Field Computation by Moment Methods, MacMillan, New York, 1968.
[2] K. K. Mei, "On the Integral Equations of Thin Wire Antennas," IEEE Trans. Antennas
Propagat., vol. AP-13, pp. 374-378, May 1965.
[3] Song, J. M. and Chew, W. C., "Moment method solutions using parametric geometry", J. of
Electromagnetic Waves and Appl., vol. 9, no. 1/2, pp. 71-83, January-February 1995.
[4] N. J. Champagne II, J. T. Williams, D. R. Wilton, "The Use of Curved Segments for
Numerically Modeling Thin Wire Antennas and Scatterers," IEEE Trans. Antennas Propagat., vol.
40, No. 6, pp. 682-689, June 1992.
[5] S. D. Rogers, C. M. Butler, "An Efficient Curved-Wire Integral Equation Solution Technique,"
IEEE Trans. Antennas Propagat., vol. 49, No. 1, pp. 70-79, January 2001.
[6] M. A. Jensen, Y. Rahmat-Samii, "Electromagnetic Characteristics of Superquadratic Wire
Loop Antennas," IEEE Trans. Antennas Propagat., vol. 42, No. 2, pp. 264-269, February 1994.
[7] R. Redlich, "On the Extended Boundary Condition as Applied to the Dipole Antenna Problem,"
IEEE Trans. Antennas Propagat., vol. AP-32, No. 4, pp. 403-404, April 1984.
[8] D. R. Wilton, C. M. Butler, "Efficient Numerical Techniques for Solving Pocklington's Equation
and Their Relationships to Other Methods," IEEE Trans. Antennas Propagat., (vol. AP-23, No.
5), pp. 83-86, January 1976.
[9] J. H. Richmond, "A Wire-Grid Model for Scattering by Conducting Bodies," IEEE Trans.
Antennas Propagat., vol. AP-14, No. 6, pp. 782-786, November 1966.
[10] D. L. Jaggard, "On Bounding the Equivalent Radius," IEEE Trans. Antennas Propagat., vol.
AP-28, No. 3, pp. 384-388, May 1980.
[11] G. Zhou, G. S. Smith, "An Accurate Theoretical Model for the Thin-Wire Circular Half-Loop
Antenna," IEEE Trans. Antennas Propagat., vol. 39, No. 8, pp. 1167-1177, August 1991.
[12] S. K. Khamas, G. G. Cook, "Moment-Method Analysis of Printed Wire Spirals Using Curved
Piecewise Sinusoidal Subdomain Basis and Testing Functions," IEEE Trans. Antennas Propagat.,
vol. 45, No. 6, pp. 1016-1022, June 1997.](https://image.slidesharecdn.com/an-sofuserguide-230219114448-3bd6a27f/85/AN-SOF-Antenna-Simulation-Software-User-Guide-291-320.jpg)
AN-SOF Antenna Simulation Software | User Guide
- 1. AN-SOF Antenna Simulator Fast and easy to use software to model, analyze, and design antennas Simulate accurately using the Conformal Method of Moments with Exact Kernel GOLDEN ENGINEERING www.ante nna si m ulat or .c o m 1. Setup 2. Draw 3. Run
- 2. 2 – A N - S O F U S E R G U I D E Welcome to AN-SOF! Congratulations for choosing AN-SOF, the best combination of ease of use and accuracy you can find in an electromagnetic simulator for the modeling and design of antennas and wire structures in general. This User Guide describes AN-SOF and its many features in detail. Here you will also find step-by-step examples and tips to help you quickly move forward with your antenna modeling projects.
- 3. 3 – A N - S O F U S E R G U I D E Contents AN-SOF Antenna Simulator About AN-SOF................................................................................................................................................... 9 A Brief Summary.............................................................................................................................................11 1. Introduction ................................................................................................................................................13 1.1 Application description....................................................................................................................13 1.2 Integrated graphical tools..............................................................................................................20 1.3 Intended users ....................................................................................................................................24 1.4 Installation...........................................................................................................................................25 1.5 Activation..............................................................................................................................................29 1.6 Versions.................................................................................................................................................30 2. Getting Started with AN-SOF................................................................................................................31 2.1 Antenna modeling software ..........................................................................................................31 2.2 Fundamentals of simulation..........................................................................................................32 2.3 Conformal Moment Method with exact Kernel......................................................................38 2.4 Performing the first simulation ....................................................................................................40 3. The AN-SOF Interface..............................................................................................................................47 3.1 Main window and menu..................................................................................................................47 3.2 Main toolbar ........................................................................................................................................61 3.3 Preferences ..........................................................................................................................................65 4. Setting Up a Simulation .........................................................................................................................67 4.1 The Setup tab......................................................................................................................................67 4.2 Specifying the frequencies.............................................................................................................69 4.3 Defining the environment ..............................................................................................................71 4.4 Far field parameters..........................................................................................................................76 4.5 Near field parameters ......................................................................................................................79
- 4. 4 – A N - S O F U S E R G U I D E 4.6 Defining the excitation....................................................................................................................83 4.7 The Settings panel ............................................................................................................................86 5. Drawing Wires............................................................................................................................................89 5.1 Line .........................................................................................................................................................90 5.2 Arc ...........................................................................................................................................................93 5.3 Circle.......................................................................................................................................................96 5.4 Helix .................................................................................................................................................... 100 5.5 Quadratic ........................................................................................................................................... 104 5.6 Archimedean spiral ........................................................................................................................ 106 5.7 Logarithmic spiral........................................................................................................................... 108 5.8 Wire attributes ................................................................................................................................. 110 5.9 Wire materials.................................................................................................................................. 111 5.10 Enabling/Disabling resistivity.................................................................................................. 113 5.11 Enabling/Disabling coating...................................................................................................... 114 5.12 Cross-section equivalent radius.............................................................................................. 115 5.13 Importing wires............................................................................................................................. 118 5.14 Exporting wires............................................................................................................................. 127 5.15 Dragging lines ............................................................................................................................... 128 5.16 Tabular input of linear wires ................................................................................................... 129 6. Editing Wires............................................................................................................................................ 131 6.1 Selecting a wire............................................................................................................................... 131 6.2 The pop-up menu........................................................................................................................... 132 6.3 Modifying a wire ............................................................................................................................. 133 6.4 Deleting a wire ................................................................................................................................ 134 6.5 Modifying a group of wires ......................................................................................................... 135 6.6 Deleting a group of wires............................................................................................................ 137 6.7 Wire color .......................................................................................................................................... 138 6.8 Viewing wire properties ............................................................................................................... 139 6.9 Connecting wires ............................................................................................................................ 143 6.10 Project details................................................................................................................................ 145
- 5. 5 – A N - S O F U S E R G U I D E 6.11 Tapered wires................................................................................................................................ 146 6.12 Moving, rotating and scaling wires ....................................................................................... 149 6.13 Copying and stacking wires...................................................................................................... 151 7. Wire Grids.................................................................................................................................................. 153 7.1 Patch.................................................................................................................................................... 154 7.2 Plate..................................................................................................................................................... 156 7.3 Disc....................................................................................................................................................... 158 7.4 Flat ring.............................................................................................................................................. 160 7.5 Cone..................................................................................................................................................... 162 7.6 Truncated cone................................................................................................................................ 164 7.7 Cylinder .............................................................................................................................................. 166 7.8 Sphere................................................................................................................................................. 168 7.9 Paraboloid ......................................................................................................................................... 170 7.10 Wire grid attributes...................................................................................................................... 172 7.11 Modifying a wire grid.................................................................................................................. 173 7.12 Deleting a wire grid..................................................................................................................... 174 7.13 Wire grid color............................................................................................................................... 175 8. Sources and Loads................................................................................................................................. 177 8.1 Choosing sources as the excitation ......................................................................................... 178 8.2 The Source/Load toolbar ............................................................................................................. 179 8.3 Adding sources ................................................................................................................................ 183 8.4 Editing sources ................................................................................................................................ 184 8.5 Adding loads..................................................................................................................................... 185 8.6 Editing loads..................................................................................................................................... 186 8.7 Enabling/Disabling loads............................................................................................................. 187 9. Excitation by an Incident Field......................................................................................................... 189 9.1 Choosing an incident field as excitation................................................................................ 189 9.2 Incident field parameters............................................................................................................. 190 9.3 The 3D-View interface.................................................................................................................. 192 10. Ground Planes....................................................................................................................................... 195
- 6. 6 – A N - S O F U S E R G U I D E 10.1 Adding a PEC ground plane...................................................................................................... 195 10.2 Adding a real ground plane...................................................................................................... 196 10.3 Adding a dielectric substrate................................................................................................... 197 10.4 Connecting wires to the ground............................................................................................. 198 10.5 Removing the ground plane..................................................................................................... 199 11. Tools in the Workspace..................................................................................................................... 201 11.1 Display options ............................................................................................................................. 201 11.2 Viewing 3D axes........................................................................................................................... 202 11.3 Zooming the view ........................................................................................................................ 203 11.4 Rotating the view......................................................................................................................... 204 11.5 Moving the view........................................................................................................................... 205 12. Running the Calculations ................................................................................................................. 207 12.1 The Run ALL command.............................................................................................................. 207 12.2 Calculating the current distribution...................................................................................... 208 12.3 Calculating the far field............................................................................................................. 209 12.4 Calculating the near E-Field .................................................................................................... 210 12.5 Calculating the near H-Field.................................................................................................... 211 12.6 Aborting the calculations.......................................................................................................... 212 12.7 Numerical Green’s function...................................................................................................... 213 12.8 Running a bulk simulation........................................................................................................ 214 13. Displaying Results............................................................................................................................... 217 13.1 Plotting the current distribution............................................................................................. 218 13.2 The List Currents toolbar .......................................................................................................... 220 13.3 Listing the currents in a segment .......................................................................................... 223 13.4 Listing the input impedances.................................................................................................. 224 13.5 Displaying Smith charts............................................................................................................. 225 13.6 Listing the internal impedance of a source........................................................................ 226 13.7 Listing load impedances............................................................................................................ 227 13.8 Plotting 2D far-field patterns .................................................................................................. 228 13.9 Plotting 3D far-field patterns .................................................................................................. 231
- 7. 7 – A N - S O F U S E R G U I D E 13.10 Plotting the far-field spectrum............................................................................................. 233 13.11 Power budget.............................................................................................................................. 235 13.12 Radar Cross Section.................................................................................................................. 238 13.13 Plotting near-field patterns................................................................................................... 240 13.14 Plotting the near-field spectrum ......................................................................................... 242 13.15 Exporting the far and near fields......................................................................................... 243 13.16 The Results tab........................................................................................................................... 245 13.17 The Plots tab ............................................................................................................................... 246 14. Adding a Feed Line............................................................................................................................. 247 14.1 Feed line parameters.................................................................................................................. 247 14.2 Feed line results........................................................................................................................... 249 14.3 Custom line options .................................................................................................................... 251 15. Step-By-Step Examples..................................................................................................................... 253 15.1 Cylindrical antenna...................................................................................................................... 254 15.2 Yagi-Uda array............................................................................................................................... 260 15.3 Monopole over a real ground plane...................................................................................... 262 15.4 Helix antenna in axial mode.................................................................................................... 265 15.5 Loop antenna................................................................................................................................. 268 15.6 A transmission line...................................................................................................................... 270 15.7 An RLC circuit................................................................................................................................ 273 16. Shortcut Keys........................................................................................................................................ 277 17. File Formats........................................................................................................................................... 279 18. Background Theory............................................................................................................................. 281 18.1 The calculation engine............................................................................................................... 281 18.2 The Electric Field Integral Equation ..................................................................................... 282 18.3 The Conformal Method of Moments..................................................................................... 285 18.4 Excitation of the structure........................................................................................................ 287 18.5 Curved vs. straight segments................................................................................................... 288 18.6 References ...................................................................................................................................... 291 19. Disclaimer of Warranty...................................................................................................................... 293
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- 9. 9 – A N - S O F U S E R G U I D E ABOUT AN-SOF AN-SOF is a comprehensive software tool for the modeling and simulation of antenna systems and radiating structures in general. Transmitting and receiving antennas can be designed and many antenna parameters can be obtained as a function of frequency: input impedance, standing wave ratio (SWR), efficiency, radiated and consumed powers, directivity, gain, beamwidth, front-to-rear/back ratios, radar cross section (RCS), linearly and circularly polarized field components, to mention a few. The radiation and scattering properties of a structure can be represented in fully angle- resolved 3D patterns. Colored mesh and surface for the clear visualization of radiation lobes are available as well as the traditional polar graphs. Other remarkable features include near-fields in 2D and 3D-colored plots, current distributions, reflection coefficients in Smith charts, tapered and insulated wires, large and short antennas over lossy ground, transmission line modeling, planar antennas on dielectric substrates and printed circuit boards (PCB). Simulations of curved wire antennas, like helices, spirals and loops can be efficiently performed by means of the Conformal Method of Moments (CMoM), which has been exclusively implemented in AN-SOF. To stay informed about new releases and advances in electromagnetic simulation tools, visit our site at www.antennasimulator.com. Latest release: AN-SOF 8.20 | April 2023.
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- 11. 1 1 – A N - S O F U S E R G U I D E A BRIEF SUMMARY What can we Model and what Results can we obtain? WHAT IS AN-SOF? It’s a comprehensive software tool for the modeling, analysis, and design of antenna systems and radiating structures in general. In the case of antennas, a lot of parameters can be obtained as a function of frequency, such as input impedance, standing wave ratio (SWR), efficiency, radiated and consumed powers, directivity, gain, beamwidth, front-to-back ratio, radar cross section (RCS), linearly and circularly polarized fields, etc. THE SIMULATION METHOD AN-SOF calculates the electric currents flowing on metallic wires by means of an improved version of the so-called Method of Moments (MoM). In this method, metallic structures like antennas are described by a set of wires and wire grids. Then, the wires are decomposed into small pieces that are short compared to the wavelength: the segments. An individual segment has usually the form of a short cylindrical wire that approaches the electromagnetic behavior of an electric dipole. Thus, any antenna or metallic structure can be thought of as made of short electric dipoles. When a source is placed at some position on the structure, a current is forced to flow over the wires. This induced current distribution is the first quantity calculated by AN-SOF in any simulation. Afterwards, the radiated field can be computed as well as the input impedance at the position of the source. The situation described above is the most common one that can be encountered in the simulation of a transmitting antenna. However, there are many more possibilities that can be handled with AN-SOF, such as transmitting antennas with multiple voltage and current sources, receiving antennas illuminated by incoming waves, complex antenna arrays, planar antennas printed on dielectric substrates, antennas with loading impedances, wires coated with an insulation material, scattered waves by arbitrarily shaped obstacles, ground waves traveling over the soil surface, and virtually any scenario where electromagnetic waves are interacting with metallic objects.
- 12. 1 2 – A N - S O F U S E R G U I D E WHAT ELSE? The geometry of the wire structure can be easily drawn on the screen using dialog boxes for the input data. All wires are placed in 3D space where several 3D-tools with mouse support have been implemented, including zoom, motion, and rotation features. Lumped impedances representing resistors, inductors and capacitors can be placed at arbitrary locations on the structure. Voltage and current generators can be used as sources in the transmitting case, while an incident plane wave of arbitrary incoming direction and polarization can be defined to illuminate an object in the receiving case. AN-SOF provides a suite of dedicated graphical tools that allow for the representation of the results in 2D and 3D plots. The electric currents flowing on a structure can be visualized directly on the wires as a colored intensity map. The radiation pattern in the far-field zone can be displayed either as a rectangular plot, as a traditional polar plot or as a fully angle- resolved 3D pattern. The radiation lobes in a 3D plot are shown as smooth surfaces with a colored scale that can be superimposed to the antenna geometry for a better interpretation of its directional properties. Near-fields in the proximity of a structure can also be represented with color maps for the electric and magnetic field intensities. Input impedances, admittances, SWR and reflection coefficients can be plotted as a function of frequency in a Smith chart representation. The AN-SOF capabilities are not only limited to bare metallic structures, but wires coated with a general material having dielectric and/or magnetic properties can also be simulated. Besides, the skin effect is considered when the metallic materials have a non-zero resistivity. Different resistivities at different locations on the structure can be defined. In the case of curved antennas like loops, helices and spirals, the wire segments composing the structure have a curvature that follows the exact shape of the antenna geometry. Usually, a curved antenna is roughly approximated by a broken line with straight segments, thus introducing an input error to the simulation that can never be fixed. Instead of straight wire segments, conformal segments are used in AN-SOF to exactly follow the contour of curved antennas. This innovation has been coined as the Conformal Method of Moments (CMoM). AN-SOF is the only electromagnetic simulator that implements the CMoM. Antennas over an imperfect or real ground plane can be simulated by setting the ground conductivity and dielectric constant. Power losses in the ground are calculated to obtain a realistic antenna input impedance. The real ground parameters also affect the near and far fields, so the ground wave attenuation along the ground surface can be calculated. A radial wire ground screen having the specified radial length and number of radials can be added below an antenna, this being of great interest to those who simulate monopole radio masts for broadcasting applications in LF and MF frequency bands. Finally, AN-SOF includes a dielectric substrate backed up by a perfect ground plane. The dielectric slab and ground plane can be infinite in two dimensions (xy-plane) with a finite thickness (along z-axis) or finite in three dimensions. The substrate can be used to simulate printed circuit boards (PCBs) as well as patch or microstrip antennas.
- 13. 1 3 – A N - S O F U S E R G U I D E 1. INTRODUCTION Description of AN-SOF Features and Capabilities 1.1 APPLICATION DESCRIPTION AN-SOF is a comprehensive software tool for the modeling and simulation of antenna systems and radiating structures in general. AN-SOF is intended for solving problems in the following areas: • Modeling and design of wire antennas. • Antennas above a lossy ground plane. • Broadcast antennas over radial wire ground screens. • Single layer microstrip patch antennas. • Radiated emissions from printed circuit boards (PCBs). • Electromagnetic Compatibility (EMC) applications. • Passive circuits, transmission lines, and non-radiating networks. AN-SOF is based on an improved version of the so-called Method of Moments (MoM) for wire structures. Metallic objects like antennas can be modeled by a set of conductive wires and wire grids, as it is illustrated in Fig. 1.1. In the MoM formulation, the wires composing the structure are divided into segments that must be short compared to the wavelength. If a source is placed at a given location on the structure, an electric current will be forced to flow on the segments. The induced current on each individual segment is the first quantity calculated by AN-SOF. Once the current distribution has been obtained, the radiated electromagnetic field can be computed in the far- and near-field zones. Input parameters at the position of the source or generator can also be obtained, such as the input impedance, input power, standing wave ratio (SWR), reflection coefficient, transmission loss, etc. The modeling of the structure can be performed by means of the AN-SOF specific 3D CAD interface. Electromagnetic fields, currents, voltages, input impedances, consumed and radiated powers, directivity, gain and many more parameters can be computed in a frequency sweep and plotted in 2D and 3D graphical representations.
- 14. 1 4 – A N - S O F U S E R G U I D E Fig. 1.1: Antennas modeled by means of wires and wire grids. In the case of curved antennas like loops, helices and spirals, the MoM has been improved to account for the exact curvature of wires. In traditional calculations, curved antennas are modeled using straight-line segments with a lot of discontinuous wire junctions. This linear approximation to the geometry can be very inefficient in terms of computer memory and the number of calculations to be performed, since several straight segments must be used to reproduce the curvature of smooth curved wires. To overcome this inaccuracy, curved segments that exactly follow the contour of curved antennas are used in AN-SOF. This innovative technique has been coined as the Conformal Method of Moments (CMoM). As an example, Fig. 1.2 shows the different approaches to a circular disc obtained by means of the MoM and CMoM methods. Both methods are available in AN-SOF since the MoM is a special case of the more general CMoM. Fig. 1.2: Modeling of a disc by means of the MoM and CMoM methods.
- 15. 1 5 – A N - S O F U S E R G U I D E In addition to the CMoM capabilities, advanced mathematical techniques have been implemented in the calculation engine making possible simulations from extremely low frequencies (e.g., electric circuits at 50-60 Hz) to very high ones (e.g., microwave antennas above 1 GHz). In what follows, a summary of the modeling options and the simulation results that can be obtained from AN-SOF is presented. MODELING OF METALLIC STRUCTURES Metallic structures can be modeled by combining different types of wires and wire grids: WIRES • Straight wire • Circular arc • Circular loop • Helix • Quadratic wire • Archimedean spiral • Logarithmic spiral WIRE GRIDS • Patch • Plate • Disc • Flat ring • Cone • Truncated cone • Cylinder • Sphere • Paraboloid
- 16. 1 6 – A N - S O F U S E R G U I D E 1. All types of curved wires can be modeled by means of arced or quadratic segments. 2. Wire grids can be defined using either curved or straight wire segments. Curved segments follow the exact curvature of discs, rings, cones, cylinders, spheres, and parabolic surfaces. Wire grids can be used to model grids and approximate conductive surfaces. 3. Tapered wires with stepped radii can be defined. 4. All wires can be loaded or excited at any segment. 5. The structure can also have finite non-zero resistivities (skin effect). 6. Electrical connections of different wires and connections of several wires at one point are possible. 7. Metallic wires in either dielectric or magnetic media can be analyzed. 8. Wires with insulation can be modeled. Dielectric and magnetic coatings are available. 9. The structures can be placed in free space, above a perfectly conducting ground plane or over an imperfect ground plane. 10. Flat strip lines can be defined on a dielectric substrate for modeling planar antennas and printed circuit boards (PCB). 11. Vias in microstrip antennas and printed circuit boards can also be modeled. 12. The wire cross-section can either be Circular, Square, Flat, Elliptical, Rectangular or Triangular. 13. The geometry modeling can be performed in suitable unit systems (um, cm, mm, m, in, ft). Different unit systems can also be chosen for inductance (pH, nH, uH, mH, H) and capacitance (pF, nF, uF, mF, F). EXCITATION METHODS 1. Voltage sources can be placed on the wires, as many as there are segments, with equal or different amplitudes (RMS values) and phases. 2. Current sources (e.g., representing impressed currents) can also be arranged at any segments.
- 17. 1 7 – A N - S O F U S E R G U I D E 3. The voltage and current sources can have internal impedances. 4. An incident plane wave of arbitrary polarization (linear, circular, or elliptical) and direction of incidence can also be used as the excitation. 5. Hertzian electric and magnetic dipoles can also be modeled and used as the excitation. 6. The antenna input power can be set to obtain the results (current distribution, near and far fields) scaled accordingly. FREQUENCY OPTIONS 1. The simulation can either be performed for a single frequency, for frequencies taken from a list or for a frequency sweep. 2. The list of frequencies can either be created inside the program or loaded from a text file. It can also be saved to a txt file. 3. Linear and logarithmic frequency sweeps are possible. 4. A suitable unit system can be selected (Hz, KHz, MHz, GHz). DATA INPUT 1. 3D CAD tools are implemented for drawing the structure geometry. Wires, wire grids, discrete generators and lumped loads can easily be added, modified, or deleted. 2. The segmentation of the wire geometry is done automatically but can also be set manually. 3. Any wire can be selected and highlighted by left clicking on it. 4. Right clicking on a wire shows a pop-up menu with several options. 5. Wire connections can easily be performed by means of a copy/paste function for the end points of the wires. 6. The source, load element and ground point positions are shown with special 3D- symbols. 7. All dialog boxes check for valid inputs.
- 18. 1 8 – A N - S O F U S E R G U I D E 8. Rotation, move and zoom functions with mouse support are implemented. 9. Text files containing geometrical data can be imported into the program. Three different file formats for importing wires are supported, including the still-in-use NEC (Numerical Electromagnetics Code) cards. With this feature, old antenna projects can be leveraged and updated. Importation of DXF files having 3D LINE entities is also supported. 10. Powerful numerical methods are integrated into the AN-SOF architecture for getting the fastest calculation speed and, at the same time, the most accurate results. DATA OUTPUT 1. All computed data is written to storage files for a subsequent graphical evaluation. 2. Input impedances, currents, voltages, VSWR, return and transmission losses, radiated and consumed powers, efficiency, directivity, gain and other system responses are shown as lists in text format and can be plotted vs. frequency. A Smith chart is available for representing impedances and admittances as well as for showing the reflection coefficient and VSWR at the mouse selected point in the graph. 3. The current distribution on a selected wire can be plotted in amplitude, phase, real and imaginary parts vs. position in a 2D representation. The currents flowing on a structure can also be plotted as a color map on the wires. 4. Radiation and scattering fields are obtained, such as power density, directivity and gain patterns, total electric field, linearly and circularly polarized components, and Radar Cross Section (RCS). The surface-wave field can be obtained as a function of distance in the case of a real ground with finite conductivity. 5. The near-field components can be calculated in Cartesian, cylindrical and spherical coordinates. The field intensities can be plotted in 2D and 3D graphical representations and visualized as color maps in the proximity of a structure. 6. A 2D representation of radiated fields is available in Cartesian and polar coordinates. The ARRL-style log scale is available in polar diagrams. 7. 3D radiation patterns can be viewed with arbitrary viewing angles, zoom functions and colored mesh and surface, including a color bar-scale. 3D patterns can be plotted with specially designed lighting and illumination for an enhanced visualization of the simulation results.
- 19. 1 9 – A N - S O F U S E R G U I D E 8. Far-field patterns can be resolved into theta (vertical) and phi (horizontal) linearly polarized components, or right and left circularly polarized components. 9. The frequency spectrum of near- and far-fields can be seen in a 2D representation for all the field components versus frequency. 10. An average radiated power test, also known as AGT (Average Gain Test), is performed for checking the accuracy of the simulation. 11. The computed data can be exported to .csv, .dat or .txt files to load the results in other software programs. 12. An embedded transmission line calculator is included to facilitate the feed line design of transmitting antennas. Actual cable part numbers can be chosen from a lot of manufacturers since the data from the cable datasheets has been extracted and added to the calculator. 13. A Bulk Simulation feature allows us to run the calculation of multiple files, each with a different geometry description, automatically. This is used to obtain results based on a variable geometric parameter. The results are automatically exported to .csv files for further processing. 14. Suitable unit systems can be chosen for the plotted results (current scaling in KA, A, mA, uA; voltage scaling in KV, V, mV, uV; electric field scaling in KV/m, V/m, mV/m, uV/m; magnetic field scaling in KA/m, A/m, mA/m, uA/m; decibel scales, etc.).
- 20. 2 0 – A N - S O F U S E R G U I D E 1.2 INTEGRATED GRAPHICAL TOOLS AN-SOF has a suite of integrated graphical tools for the convenient visualization of the simulation results. The following applications are installed automatically and used by the main program, AN-SOF: AN-XY CHART A friendly 2D chart for plotting two related quantities, Y versus X. Use AN-XY Chart to plot parameters that depend on frequency, such as currents, voltages, impedances, reflection coefficient, VSWR, radiated power, consumed power, directivity, gain, radiation efficiency, radar cross section, and many more. Also plot the current distribution along wires as a function of position, 2D slices of radiation lobes and near fields as a function of distance from an antenna. Choose different units to display results and use the mouse to easily zoom and scroll graphs.
- 21. 2 1 – A N - S O F U S E R G U I D E AN-SMITH Plot impedance or admittance curves on the Smith chart with this tool. Just click on the graph to get the frequency, impedance, reflection coefficient, and VSWR that correspond to each point on the curve. Plots can be stored in independent files and opened later for a graphical analysis with AN-Smith.
- 22. 2 2 – A N - S O F U S E R G U I D E AN-POLAR Plot on a polar diagram the radiation pattern versus the azimuth (horizontal) or zenith (vertical) angles. The maximum, -3dB and minimum radiation levels are shown within the chart as well as the beam width and front-to-rear/back ratio. Click on the graph to quickly obtain the values of the radiated field. The represented quantities include power density, directivity, gain, normalized radiation pattern, total electric field, linearly and circularly polarized components, and radar cross section (RCS).
- 23. 2 3 – A N - S O F U S E R G U I D E AN-3D PATTERN Get a complete view of the radiation properties of a structure by plotting a 3D radiation pattern. AN-3D Pattern implements colored mesh and surface for the clear visualization of radiation lobes, including a color bar-scale indicating the field intensities over the lobes. Quickly rotate, move, and zoom the graph using the mouse. The 3D radiation pattern can be superimposed to the structure geometry to gain more insight into the directional properties of antennas. The represented quantities include the power density, normalized radiation pattern, directivity, gain, total field, linearly and circularly polarized components, and radar cross section (RCS). Choose between linear or decibel scales. Display near fields as color maps in the proximity of antennas in three different representations: Cartesian, cylindrical and spherical plots. Also plot the current distribution on the structure as a colored intensity map.
- 24. 2 4 – A N - S O F U S E R G U I D E 1.3 INTENDED USERS The main purpose of AN-SOF is making simulation easy and affordable to a wide audience, so the software tool is designed for everyone interested in Electromagnetics and Electronics. No previous expertise in electromagnetic simulation is required to begin using this tool. AN-SOF is used by students, teachers, technicians, engineers, ham radio operators, and everyone involved in the research and design of metallic antennas and passive circuits, from the very low frequency range to microwaves, as well as those dealing with radio engineering, microwaves, radar techniques, electromagnetic compatibility and communications. AN-SOF can also be used for teaching purposes, research activities, and demonstration of antenna and scatterer phenomena.
- 25. 2 5 – A N - S O F U S E R G U I D E 1.4 INSTALLATION AN-SOF can be installed on a PC running Microsoft Windows Vista/7/8/10/11 (32 and 64 bits). The minimum recommended hardware requirements are the following: • 2 GHz processor • 2 GB RAM • 1 GB free disk space The procedure for installing AN-SOF is straightforward. Execute the SETUP.EXE program and follow the instructions on the screen. Follow these steps to install AN-SOF: 1. When the AN-SOF installer startup screen appears, click Next to begin the installation. 2. The setup wizard starts, and the license agreement is shown. If you accept the terms in the license agreement, click on this option and then press Next.
- 26. 2 6 – A N - S O F U S E R G U I D E 3. In the information screen a username and organization can be entered.
- 27. 2 7 – A N - S O F U S E R G U I D E 4. Choose the destination folder where AN-SOF will be installed and click Next to continue. 5. The wizard is ready to install AN-SOF. Click Install to begin the process.
- 28. 2 8 – A N - S O F U S E R G U I D E 6. The installation begins. 7. If AN-SOF has successfully been installed, click Finish. 8. A folder with sample project files, called “Examples”, will also be installed in the AN-SOF installation directory.
- 29. 2 9 – A N - S O F U S E R G U I D E 1.5 ACTIVATION A license must be activated on each PC. After installing AN-SOF, it can be run as a trial version. To activate a licensed version, perform the following steps: 1. Execute the AN-Key application. It is accessible from the AN-SOF program folder on the Windows Start menu. 2. A Serial Number will be shown in the AN-Key window, which is a unique number per machine. 3. If you have purchased a licensed version, send the Serial Number to info@antennasimulator.com and you will receive an Activation Key. 4. Copy the received Key in the field indicated in the AN-Key window and click on the Activate button. To activate the Trial version, use this key (type number “1” twenty times): 11111111111111111111 or click on the “Trial Key” button. 5. Restart AN-SOF.
- 30. 3 0 – A N - S O F U S E R G U I D E 1.6 VERSIONS AN-SOF is provided in two versions: AN-SOF TRIAL Fully featured, up to 50 unknowns for small sized structures. FREE Edition for evaluating the capabilities of AN-SOF AN-SOF PROFESSIONAL Fully featured, unlimited number of unknowns* for large and very large structures. Fully featured Edition NOTE: If you have installed AN-SOF Trial, the software tool is free and ready to be used. If you are upgrading to a new version, uninstall the previous version of AN-SOF before installing the new version. AN-SOF Trial must also be uninstalled before installing a Professional version. *Limited by the available computer memory and resources.
- 31. 3 1 – A N - S O F U S E R G U I D E 2. GETTING STARTED WITH AN-SOF Taking the First Steps in Antenna Simulation 2.1 ANTENNA MODELING SOFTWARE An antenna model is a representation of a real-world antenna in a computer program. This kind of model should not be confused with a scale model that sometimes is built to measure the radiation characteristics of an identical antenna with a larger physical size. Due to the complexity of the math involved in a model, a computer software is often programmed to predict and analyze antenna performance. AN-SOF CAN BE USED TO… • design better antennas • predict antenna performance • tune for performance • account for environment effects • optimize a design using scripts • get insight into the behavior of an antenna • try many times before building the real model • learn more about antennas and share our findings with colleagues. • enjoy this exciting field! Wires are drawn in 3D space where tools are available to zoom, move, and rotate the structure. Computer simulation in industry is used to overcome challenges and drive innovation in the product creation and development processes. A computer model has the advantage that it can be modified, redesigned, broken, destroyed, and built again many times without wasting materials. Therefore, a considerable reduction in the cost of building successive physical models can be obtained during the design process with the help of a simulation software. The geometry of the structure can be easily drawn in AN-SOF using the mouse, menus, and friendly dialog windows. To plot the results from a simulation, a suite of applications has been integrated that allow us to display graphs: AN-XY Chart, AN-3D Pattern, AN-Polar and AN-Smith. These tools can also be executed independently for a subsequent processing of graphics. AN-SOF is the easiest to use software tool for the simulation of wire antennas and, at the same time, it is the most accurate one. The key advantages can be summarized as follows: • Fast and easy input and output graphical interfaces. • Extended frequency range. • Conformal Method of Moments with Exact Kernel for higher accuracy and speed.
- 32. 3 2 – A N - S O F U S E R G U I D E 2.2 FUNDAMENTALS OF SIMULATION AN-SOF computes the electric currents flowing on metallic structures, including antennas in transmitting and receiving modes as well as scatterers. A scatterer is any object that can reflect and/or diffract radiofrequency waves. For example, the scattering of waves could be analyzed on the surface of an aircraft to investigate the best placement of an antenna, on a parabolic reflector to analyze gain as a function of the reflector shape, on the chassis of a car to predict interference effects, etc. AN-SOF ALLOWS US… • to describe the geometry of the antenna • to choose construction materials • to describe the environment and ground conditions • to describe the antenna height above ground • to analyze the radiation pattern and front-to-back ratio • to plot directivity and gain • to analyze impedance and SWR (Standing Wave Ratio) • to predict bandwidth • and to get many more parameters and plots. One of the most validated methods for antenna simulation is the so-called Method of Moments (MoM). An improved and advanced form of this method has been implemented in AN-SOF to overcome various well-known difficulties of the traditional MoM. According to the MoM, any metallic structure can be modeled using conductive wires, as Fig. 2.1 shows. These wires must be divided into small pieces called segments. A wire segment has the shape of a cylindrical tube whose length should be short compared to the wavelength, , to get accurate results, Fig. 2.2. However, this is not a matter to worry about in a first simulation since automatic segmentation of wires is set by default in AN-SOF. Electric currents can be forced to flow on the structure by placing a voltage generator at some position that works at a given frequency. Current generators can also be used as the excitation, as well as a plane wave impinging on the structure that comes from a far or distant source. Once the structure geometry, materials and sources have been defined, the calculation can be run to obtain the currents flowing on the wire segments. In general, the electric currents will have varying intensities along and across the structure, so they are collectively referred to as a current distribution. Figure 2.3 shows an example of the current distribution on a log-periodic antenna. The electromagnetic field radiated by the current distribution can be calculated in a second step of the simulation process. However, the current distribution itself gives a lot of information about the behavior of the structure, especially if a frequency sweep has been performed. In the case of antennas, the feed point impedance can be obtained as a function
- 33. 3 3 – A N - S O F U S E R G U I D E of frequency to analyze the bandwidth. The VSWR (Voltage Standing Wave Ratio) can be plotted in a Smith chart for a better interpretation of the results, Fig. 2.4. Fig. 2.1: Computer models of a car, a parabolic reflector, a plane, and a ship using wire grids. Fig. 2.2: A straight wire divided into short segments.
- 34. 3 4 – A N - S O F U S E R G U I D E Fig. 2.3: Current distribution on a log-periodic antenna. The color map on the structure indicates the amplitudes of the electric currents. Fig. 2.4: Impedance plotted as a function of frequency in a Smith Chart, where the VSWR can be obtained by clicking on the curve.
- 35. 3 5 – A N - S O F U S E R G U I D E The electric and magnetic fields can be obtained in the proximity of the structure, in the so- called near-field zone, and plotted as a color map whose intensities sometimes resemble the temperature maps in weather forecasts, Fig. 2.5. Fig. 2.5: Near electric field in the proximity of a Horn antenna. Far away from the structure, at several wavelengths, the magnetic field becomes proportional to the electric field, so only the electric field intensities are often used to analyze the results. This is the so-called far-field zone, where the radiated field is usually plotted as a function of direction in a polar diagram, Fig. 2.6. A more complete representation is obtained plotting a 3D pattern, where radiation lobes can be superimposed to the structure geometry for a better visualization of its directional properties, Fig. 2.7. The application of the MoM is not only limited to wire structures but can also be extended to patches and strip lines. AN-SOF is the only electromagnetic simulation software of its kind that includes the modeling of dielectric substrates besides the standard perfectly conducting and real ground planes. This innovation allows us to predict the radiation properties and susceptibility features of microstrip antennas and printed circuit boards (PCBs), Fig. 2.8.
- 36. 3 6 – A N - S O F U S E R G U I D E Fig. 2.6: Far-field pattern represented in a polar diagram. Beamwidth, front-to-rear, and front-to- back ratios are indicated. Fig. 2.7: Far-field pattern represented in a 3D plot and superimposed to the antenna geometry.
- 37. 3 7 – A N - S O F U S E R G U I D E Fig. 2.8: Modeling a microstrip antenna and a PCB. In summary, simulating a wire structure is a three-step procedure: 1. SETUP > Set frequencies, environment, and desired results. 2. DRAW > Draw geometry, specify materials and sources. 3. RUN > Run the calculation and visualize the results. A convenient unit system for the frequencies and lengths can be chosen at the beginning of the simulation and can then be changed at any time by going to Tools > Preferences. For example, the wire lengths are often measured either in meters (m) or feet (ft) at frequencies below 100 MHz, while either millimeters (mm) or inches (in) are preferred at higher frequencies.
- 38. 3 8 – A N - S O F U S E R G U I D E 2.3 CONFORMAL MOMENT METHOD WITH EXACT KERNEL In the traditional Method of Moments (MoM) the structures to be modeled are divided into straight wire segments. Straight segments fit well the shape of linear antennas like dipoles and arrays constructed using dipoles. However, there are many antennas and structures that have curved shapes. In these cases, a curved wire is approximated using a string of straight- line segments, Fig. 2.9(a). Sharp junctions between adjacent wires introduce a modeling error at the very beginning of the simulation that can never be fixed. Poor results for curved antennas like loops, helices and spirals are often obtained when the linear approximation is applied, especially large errors in the feed point impedances. Furthermore, in the traditional MoM other problems arise due to the use of the so-called thin-wire Kernel. The Kernel is the heart of the integral equation to be solved by the MoM, and the thin-wire approximation, which considers that the currents are concentrated as a filament along the wire axes, produces large errors in the results. For the math involved, refer to Section “18. Background Theory”. One of the problems that appears due to the thin-wire Kernel is erratic numerical oscillations when there are wires bent at right angles or for angles less than 30 degrees between adjacent segments, Fig. 2.9(b). Fig. 2.9: Limitations of the traditional Method of Moments with thin-wire Kernel. Another problem that should be pointed out is about the spacing between parallel wires. Segments cannot be very close to each other since misleading results are obtained when the spacing between them is less than a quarter of a segment length, Fig. 2.9(c). The segment length itself has a limitation, it must be greater than 0.001 of a wavelength, and consequently the traditional MoM cannot be applied at very low frequencies, Fig. 2.9(d). For example, consider an electric circuit around 1 meter in size operating at 60 Hz. The free space wavelength can be calculated as (300/60) x 1,000,000 = 5,000,000 meters. Thus, the size of the circuit measured in wavelengths is 1/5,000,000 = 0.0000002, so segments shorter than 0.0000002 of a wavelength are needed to model the circuit. This segment length is at least 5,000 times shorter than the minimum segment length supported by the
- 39. 3 9 – A N - S O F U S E R G U I D E MoM. Therefore, an electric circuit at low frequencies cannot be modeled using the traditional implementation of the MoM for wire antennas. The limitations of the traditional MoM have been removed in its improved version: the Conformal Method of Moments (CMoM) with Exact Kernel. In the CMoM, conformal segments are used that exactly follow the contour of the structure, so an exact description of geometry details is achieved, Fig. 2.10. A conformal segment is a curved cylindrical tube that correctly fit the shape of curved wires. The limitations regarding bent wires, small spacings between wires, and segment length have been removed in AN-SOF by using the exact Kernel instead of the thin-wire approximation, which allows us to perform calculations with much higher accuracy than the traditional method. Fig. 2.10: A circular loop and a disc modeled using the traditional MoM and the Conformal MoM. Therefore, with the CMoM with exact Kernel we remove the limitations of the old MoM and obtain the following advantages: • Decreased number of calculations and increased accuracy of results. • Decreased simulation time and computer memory usage, allowing us to model larger and more complex designs. • Ability to simulate from extremely low frequencies (circuits at 60 Hz) to very high ones (microwave antennas). AN-SOF is the only antenna modeling software that offers a calculation engine based on the Conformal Method of Moments with Exact Kernel.
- 40. 4 0 – A N - S O F U S E R G U I D E 2.4 PERFORMING THE FIRST SIMULATION Several example files are included in the AN-SOF installation directory within a folder named “Examples”. Opening a file with extension “.emm” will show the wire structure on the screen. The calculation can be run by clicking on the Run ALL button on the toolbar. The main results can be plotted by clicking on the Plot Current Distribution button , the Far-Field 3D Plot button , and the Far-Field Polar 1 Slice button . As a first experience using AN-SOF, a simulation of a standard half-wave dipole could be performed since this is one of the simplest antennas that can be modeled. A dipole is just a straight wire fed at its center. When the wire cross-section is circular, the dipole is called a cylindrical antenna. Since the material the wire is made of is usually a very good conductor, the wire can be considered a perfect conductor, that is, a material that has zero resistivity. Therefore, a cylindrical antenna with zero resistivity will be modeled in this example. The first step is to set the operating frequency. Go to the Setup tabsheet in the AN-SOF main window. In the Frequency panel, three options can be chosen. Select Single and then write the operating frequency for the antenna, Fig. 2.11. In this case, the frequency is given in megahertz (MHz) and lengths are measured in meters (m). Go to Section “3.3 Preferences” to change the unit system for frequencies and lengths if desired. Note that for a frequency of 300 MHz, the wavelength practically equals 1 meter (0.999308 m). Once the operating frequency has been set, the antenna geometry can be drawn in the Workspace tabsheet. The workspace is the place on the screen where the wire structure is drawn; it represents the 3D space where the structure can be zoomed, rotated, and moved. Fig. 2.11: Single Frequency option in the Setup tabsheet where a frequency of 300 MHz is set.
- 41. 4 1 – A N - S O F U S E R G U I D E A straight wire is called a Line in AN-SOF. Go to Draw > Line in the main menu. The Draw dialog box will be shown. In the Line tab, the coordinates of two distinct points can be set. In this example, the line will be along the z-axis and will be 0.5 meters long, which corresponds to half a wavelength at 300 MHz. Figure 2.12 shows that the starting point of the line is chosen at (X1,Y1,Z1) = (0,0,-0.25) m while the ending point is at (X2,Y2,Z2) = (0,0,0.25) m. Fig. 2.12: Line tab in the Draw dialog box for drawing a straight line. Then, go to the Attributes tab, Fig. 2.13. The line must be divided into segments, which must be short compared to the wavelength. Basically, if the segment length is equal or less than a tenth of a wavelength, it is considered as a short segment. AN-SOF automatically suggests a minimum number of segments to achieve reliable results. To get more resolution, the number of segments can be increased. In this case, the line will be divided into 17 segments. The wire cross-section will be circular with 5 millimeters in radius. In the Materials tab the wire resistivity will be set to zero, Fig. 2.14. The next step is to feed the dipole. Right click on the wire and select the Source/Load command from the displayed pop-up menu. A toolbar with a slider will be displayed at the bottom of the screen. Move the slider to the segment at the wire center. Then, press the Add Source button. Add a voltage source 1 Volt in amplitude and zero phase, Fig. 2.15.
- 42. 4 2 – A N - S O F U S E R G U I D E Fig. 2.13: Attributes tab in the Draw dialog box where the number of segments and wire radius can be set. Fig. 2.14: Materials tab in the Draw dialog box for setting the wire resistivity.
- 43. 4 3 – A N - S O F U S E R G U I D E Fig. 2.15: Add Source dialog box shown after pressing the Add Source button in the Source/Load toolbar at the bottom of the screen. Go to Run > Run Currents in the main menu to run the calculation. Once the calculations are done, go to Run > Run Far-Field in the main menu. In this way, the current distribution on the dipole antenna and the radiated field will be calculated. AN-SOF has integrated graphical tools for the visualization of the results. Right click on the wire and select Plot Currents in the displayed pop-up menu. A plot of the current distribution in amplitude and phase along the dipole antenna will be shown, Fig. 2.16. Since a half-wave dipole has been drawn, the resulting current distribution is a semi-cycle approaching a sine function. Several parameters from the point of view of the voltage source connected to the antenna terminals can be obtained. Right click on the wire and select List Currents in the pop-up menu. Move the slider to the position of the voltage source and click on the Input List button. The input impedance of the dipole antenna will be shown and many other parameters, Fig. 2.17. The input impedance can also be obtained by just clicking on the List Input Impedances button in the main toolbar.
- 44. 4 4 – A N - S O F U S E R G U I D E Fig. 2.16: Current distribution in amplitude and phase along a half-wave dipole. Fig. 2.17: Input List dialog box where the input impedance can be seen.
- 45. 4 5 – A N - S O F U S E R G U I D E The radiation pattern can be represented in a 3D plot. Go to Results > Plot Far-Field Pattern > 3D Plot in the main menu. The normalized radiation pattern will be displayed in the AN- 3D Pattern application. A color bar-scale indicates the field intensities over the radiation lobes. The directivity, gain and electric field patterns can also be plotted by going to the Plot menu in AN-3D Pattern. The half-wave dipole is an omnidirectional antenna in the plane perpendicular to the dipole axis (xy-plane), Fig. 2.18. Fig. 2.18: Radiation pattern of a half-wave dipole. For more examples, refer to Section “15. Examples”. The following sections describes AN- SOF and its many functions in detail. The guide is organized according to the steps that should be followed when performing a simulation. Technical support can be requested at info@antennasimulator.com.
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- 47. 4 7 – A N - S O F U S E R G U I D E 3. THE AN-SOF INTERFACE Recognizing the Main Windows and Menus 3.1 MAIN WINDOW AND MENU When AN-SOF is started, the initial screen contains the following components: Fig. 3.1: The AN-SOF interface. The title bar contains the name of the currently active project (.emm file). The main menu bar contains the File, Edit, Draw, View, Tools, Run, Results, and Help menus. The main toolbar contains icons that represent commands. The tab sheets allow us to quickly switch between pages, from Setup to Plots. The workspace is the page where the wire structure can be drawn in a 3D space. The status bar contains information about the number of segments, connections, and ground points.
- 48. 4 8 – A N - S O F U S E R G U I D E FILE MENU Use the File menu to open, save, close, and print new or existing projects. This menu has the following commands: New... (Ctrl + N) Creates a new project. Open... (Ctrl + O) Displays the Open dialog box for opening an existing project (.emm file). Save (Ctrl + S) Saves the currently active project using its current name. Save As... Saves the currently active project using a new name. Also saves a new project using a name specified by the user. Import Wires Displays the Import dialog box for importing a list of wires in either AN-SOF (.wre files), NEC, DXF (CAD files) or MM format. Export Wires Displays the Export dialog box for exporting wires to a NEC or DXF file. Copy Workspace Sends the project workspace to the clipboard as a bitmap image. Print... (Ctrl + P) Sends the project workspace to the printer. Exit (Ctrl + Q) Closes the project that is open and then exits AN-SOF. Fig. 3.2: File menu.
- 49. 4 9 – A N - S O F U S E R G U I D E EDIT MENU Use the Edit menu commands to edit and handle wires and wire grids. This menu has the following commands: Undo (Ctrl + Z) Returns the project to the status before a command was executed. Source/Load (Ctrl + Ins) Displays the Source/Load toolbar for exciting or loading the selected wire. This command is enabled when a wire is selected. Modify (Ctrl + M) Displays the Modify dialog box for modifying the selected wire or wire grid. This command is enabled when a wire or wire grid is selected. Wire Color Displays a Windows dialog box for changing the color of the selected wires. This command is enabled when a wire or group of wires is selected. Delete (Ctrl + Del) Deletes the selected wire, wire grid or group of wires with all sources and loads placed on it. This command is enabled when a wire, wire grid or group of wires is selected. Copy Start Point Copies the starting point of the selected wire. This point can then be used as the starting point of a second wire, which will be connected to the first one. This command is enabled when a wire is selected. Copy End Point Copies the ending point of the selected wire. This point can then be used as the starting point of a second wire, which will be connected to the first one. This command is enabled when a wire is selected. Start Point to GND Draws a vertical wire between the start point of the selected wire and the ground plane. This command is shown when a ground plane is included in the model, and it is enabled when a wire is selected. End Point to GND Draws a vertical wire between the end point of the selected wire and the ground plane. This command is shown when a ground plane is included in the model, and it is enabled when a wire is selected.
- 50. 5 0 – A N - S O F U S E R G U I D E Copy Wires Displays the Copy Wires dialog box for copying the selected wire or group of wires. The copied wires can then be pasted in a different position. This command is enabled when a wire or group of wires is selected. Move Wires Displays the Move Wires dialog box for moving the selected wire or group of wires to a different position. This command is enabled when a wire or group of wires is selected. Rotate Wires Displays the Rotate Wires dialog box for rotating the selected wire or group of wires around the chosen axis. This command is enabled when a wire or group of wires is selected. Scale Wires Displays the Scale Wires dialog box for scaling the selected wire or group of wires according to the specified scale factor. This command is enabled when a wire or group of wires is selected. Stack Wires Displays the Stack Wires dialog box for stacking the selected wire or group of wires along the specified direction and according to the given number of wires in the stack. This command is enabled when a wire or group of wires is selected. Fig. 3.3: Edit menu.
- 51. 5 1 – A N - S O F U S E R G U I D E DRAW MENU Use the Draw menu commands to create and draw wires and wire grids. This menu has the following commands: Line Opens the Line dialog box for drawing a line or straight wire. Arc Opens the Arc dialog box for drawing an arc. Circle Opens the Circle dialog box for drawing a circle or circular loop. Helix Opens the Helix dialog box for drawing a helix or helical wire. Quadratic Opens the Quadratic dialog box for drawing a quadratic wire. Archimedean Spiral Opens the Archimedean Spiral dialog box for drawing an Archimedean spiral. Logarithmic Spiral Opens the Logarithmic Spiral dialog box for drawing a logarithmic spiral. Wire Grid Creates a new wire grid in the workspace. This option has a sub-menu with the following commands: Patch Opens the Draw dialog box for drawing a rectangular grid on the xy-plane. Plate Opens the Draw dialog box for drawing a plate or bilinear surface. Disc Opens the Draw dialog box for drawing a disc. Flat Ring Opens the Draw dialog box for drawing a flat ring or a disc with a hole at its center.
- 52. 5 2 – A N - S O F U S E R G U I D E Cone Opens the Draw dialog box for drawing a cone. Truncated Cone Opens the Draw dialog box for drawing a truncated cone. Cylinder Opens the Draw dialog box for drawing a cylinder. Sphere Opens the Draw dialog box for drawing a sphere. Paraboloid Opens the Draw dialog box for drawing a parabolic surface. Tapered Wire Creates a new tapered wire in workspace. This option has a sub-menu with the same commands as the wire options described above, but each wire can have a stepped radius along its length. Tabular Input (Ctrl + T) Opens a table to enter linear wires, sources and loads in spreadsheet format. Fig. 3.4: Draw menu.
- 53. 5 3 – A N - S O F U S E R G U I D E VIEW MENU Use the View menu commands to display or hide different elements of the AN-SOF interface, zoom the wire structure, and view additional information about the project and wires. This menu has the following commands: Wire Properties... (Ctrl + W) Displays the Wire Properties dialog box for viewing information about the selected wire. This command is enabled when a wire is selected. Project Details... Displays the Project Details dialog box for viewing information about the project that is open. Zoom In (Ctrl + I) Increases the size of the view in the workspace (also roll the mouse wheel to zoom). Zoom Out (Ctrl + K) Decreases the size of the view in the workspace (also roll the mouse wheel to zoom). Reset Zoom Scale Resets the zoom and resizes the view of the structure in the workspace. Axes (Ctrl + A) Displays the Axes dialog box for changing the appearance of the axes in the workspace. Press F7 to switch between small and main axes. X-Y Plane / Y-Z Plane / Z-X Plane Shows a view of the xy-plane/ yz-plane/ zx-plane parallel to the screen. Center Centers the view of the structure in the workspace (double click on the workspace to center the view). Initial View (Home) Returns the workspace to the initial view. Drawing Panel Displays a panel to the left of the workspace that contains buttons for quicker access to commands for drawing wires and wire grids.
- 54. 5 4 – A N - S O F U S E R G U I D E Fig. 3.5: View menu. TOOLS MENU Use the Tools menu commands to display 3D, polar, rectangular, and Smith charts and to check the wires. This menu has the following commands: 3D Chart Executes the AN-3D Pattern application for opening 3D plot files (.p3d). Polar Chart Executes the AN-Polar application for opening polar plot files (.plr). Rectangular Chart Executes the AN-XY Chart application for opening rectangular plot files (.plt). Smith Chart Executes the AN-Smith application for opening Smith chart files (.sth). Check Individual Wires Checks the segment length, cross-section size and thin-wire ratio of each wire. Wires in warning/error will be highlighted in yellow/red. Check Wire Spacing Checks the spacing between wires. Wires in warning/error will be highlighted in yellow/red. Delete Duplicate Wires Deletes duplicate or overlapping wires. Calculator Executes the Microsoft Windows Calculator application.
- 55. 5 5 – A N - S O F U S E R G U I D E Preferences Displays the Preferences dialog box for setting up the preferred options for unit systems, workspace color, pen width, confirmation questions, etc. Fig. 3.6: Tools menu. RUN MENU Use the Run menu commands to run the calculations. This menu has the following commands: Run ALL (F10) Runs the calculation of the current distribution, far- and near-fields. Run Currents and Far-Field (F11) Runs the calculation of the current distribution and far-fields. Run Currents and Near-Field (F12) Runs the calculation of the current distribution and near electric and magnetic fields. Run Currents Runs the calculation of the current distribution on the wire structure. This command is disabled when the currents are already computed. Run Far-Field Runs the calculation of the far-field generated by the currents flowing on the wire structure. This command is enabled when the currents are already computed. Run Near E-Field Runs the calculation of the near electric field generated by the currents flowing on the wire structure. This command is enabled when the currents are already computed.
- 56. 5 6 – A N - S O F U S E R G U I D E Run Near H-Field Runs the calculation of the near magnetic field generated by the currents flowing on the wire structure. This command is enabled when the currents are already computed. Run Bulk Simulation Opens a dialog box for choosing multiple files in NEC format at the same time. The file extension must be “.nec”. AN-SOF will import these input files and compute the corresponding output results. The results will be saved as CSV files in the same directory as the NEC input files. Fig. 3.7: Run menu. RESULTS MENU Use the Results menu commands to visualize the results from a simulation. This menu has the following commands: Plot Current Distribution Executes the AN-3D Pattern application for plotting the current distribution as a colored pattern on the wire structure. Plot Currents Executes the AN-XY Chart application for plotting the currents vs. position along the selected wire. This command is enabled when a wire has been selected. List Currents Displays the List Currents toolbar for listing the currents vs. frequency at the chosen segment on the selected wire. If the segment has a source on it, the list of input impedances, voltages, and powers as a function of frequency can be shown. This command is enabled when a wire has been selected.
- 57. 5 7 – A N - S O F U S E R G U I D E List Input Impedances Displays a table with the list of input impedances vs. frequency, including reflection coefficient, VSWR, return loss and transmission loss at the antenna terminals. Plot Far-Field Pattern This option has a sub-menu with the following commands: 3D Plot Executes the AN-3D Pattern application for plotting a 3D view of the radiation patterns. Polar Plot 1 Slice Displays the Radiation Pattern Cut dialog box for selecting a 2D slice of the 3D far-field pattern. Then, the selected 2D pattern cut will be plotted in polar coordinates by the AN-Polar application. Polar Plot 2 Slices Displays a dialog box for selecting two slices of the 3D far-field pattern. Then, the selected 2D patterns will be plotted in polar coordinates by the AN-Polar application. 2D Rectangular Plot Displays the Radiation Pattern Cut dialog box for selecting a 2D cut of the 3D far- field pattern. Then, the selected 2D pattern cut will be plotted in rectangular coordinates by the AN-XY Chart application. Plot Far-Field Spectrum Displays the Select Far-Field Point dialog box for selecting a point in space where the far- field components will be shown versus frequency. Then, the far-field spectrum will be plotted in rectangular coordinates by the AN-XY Chart application. List Far-Field Pattern Displays a table showing the total E-field and its components (E-theta, E-phi, E-right, E-left) at the grid of angles theta and phi specified in the Far-Field panel of the Setup tabsheet. This table can be exported as a CSV file. List Far-Field Spectrum Displays the Select Far-Field Point dialog box for selecting a point in space where the far- field components will be shown versus frequency. Then, this far-field spectrum will be listed in a table with different columns for the total E-field and the field components: E- theta and E-phi (spherical components) and the right and left polarized components.
- 58. 5 8 – A N - S O F U S E R G U I D E Power Budget/RCS Displays the Power Budget dialog box for listing the total input power, consumed and radiated powers, power densities, efficiency, directivity and gain vs. frequency. In the case of plane wave excitation, the Radar Cross Section (RCS) vs. frequency will be displayed. Plot Near E-Field Pattern This option has a sub-menu with the following commands: 3D Plot Executes the AN-3D Pattern application for plotting a 3D view of the near electric field components. 2D Plot Displays the Near-Field Cut dialog box for selecting a 2D cut of the near electric field pattern. Then, the selected 2D pattern cut will be plotted by the AN-XY Chart application. Plot Near E-Field Spectrum Displays the Select Near-Field Point dialog box for selecting a point where the near electric field components will be shown versus frequency. Then, this near-field spectrum will be plotted in rectangular coordinates by the AN-XY Chart application. List Near E-Field Pattern Displays a table showing the total near E-field and its components at the grid of points specified in the Near-Field panel of the Setup tabsheet. This table can be exported as a CSV file. List Near E-Field Spectrum Displays the Select Near-Field Point dialog box for selecting a point where the near electric field components will be shown versus frequency. Then, this near-field spectrum will be listed in a table with different columns for the field components. Plot Near H-Field Pattern This option has a sub-menu with the following commands: 3D Plot Executes the AN-3D Pattern application for plotting a 3D view of the near magnetic field components.
- 59. 5 9 – A N - S O F U S E R G U I D E 2D Plot Displays the Near-Field Cut dialog box for selecting a 2D cut of the near magnetic field pattern. Then, the selected 2D pattern cut will be plotted by the AN-XY Chart application. Plot Near H-Field Spectrum Displays the Select Near-Field Point dialog box for selecting a point where the near magnetic field components will be shown versus frequency. Then, the near-field spectrum will be plotted in rectangular coordinates by the AN-XY Chart application. List Near H-Field Pattern Displays a table showing the total near H-field and its components at the grid of points specified in the Near-Field panel of the Setup tabsheet. This table can be exported as a CSV file. List Near H-Field Spectrum Displays the Select Near-Field Point dialog box for selecting a point where the near magnetic field components will be shown versus frequency. Then, the near-field spectrum will be listed in a table with different columns for the field components. Fig. 3.8: Results menu.
- 60. 6 0 – A N - S O F U S E R G U I D E HELP MENU Use the Help menu to access the user guide, request technical support, activate a license, or view the version of AN-SOF. This menu has the following commands: User Guide Displays the AN-SOF user guide in PDF format. AN-SOF Home Page Goes to the AN-SOF web page at www.antennasimulator.com in the default web browser. Knowledge Base Goes to the knowledge base where you can search for categorized information. Email to Tech Support Executes the default e-mail client to send a technical support request to info@antennasimulator.com. Chat to Tech Support Goes to the live chat* page in the default web browser. Activation Key Executes the AN-Key application to activate a license. Check for Updates Goes to the website where the latest AN-SOF releases are posted. About AN-SOF Shows copyright and version information. Fig. 3.9: Help menu. *Live chat is not an instant service, please consider delays in responses depending on demand and schedules. You can leave your message in the chat indicating your e-mail address and we will respond as soon as possible. This service is available from Monday to Friday from 6 a.m. to 3 p.m. CST and only for those users who have purchased a license and a Platinum plan.
- 61. 6 1 – A N - S O F U S E R G U I D E 3.2 MAIN TOOLBAR The main toolbar has the following icons and associated commands: Fig. 3.10: Main Toolbar. New (Ctrl + N) Creates a new project. Open (Ctrl + O) Displays the Open dialog box to open an existing project (.emm file). Save (Ctrl + S) Saves the currently active project using its current name. Undo (Ctrl + Z) Returns the project to the status before a command was executed. Source/Load (Ctrl + Ins) Displays the Source/Load toolbar for adding a source or load to the selected wire. This command is enabled when a wire has been selected. Modify (Ctrl + M) Displays the Modify dialog box for modifying the selected wire or group of wires. This command is enabled when a wire or group of wires has been selected. Wire color Displays a Windows dialog box for changing the color of the selected wire or group of wires. This command is enabled when a wire or group of wires has been selected.
- 62. 6 2 – A N - S O F U S E R G U I D E Delete (Ctrl + Del) Deletes the selected wire, wire grid or group of wires with all sources and loads placed on it. This command is enabled when a wire, wire grid or group of wires has been selected. Preferences Displays the Preferences dialog box for setting up the preferred options for unit systems, workspace color, pen width, confirmation questions, etc. Wire Properties (Ctrl + W) Displays the Wire Properties dialog box for viewing information about the selected wire. This command is enabled when a wire has been selected. Project Details Displays the Project Details dialog box for viewing information about the currently active project. Select Wire Enables the selection mode where a wire can be selected individually by left clicking on it. Selection Box Enables the selection mode where a group of wires can be selected expanding a box with the mouse (left mouse button pressed). Draw Line Enables the drawing mode where a line can be dragged with the mouse (left mouse button pressed). This mode is enabled when the X-Y, Y-Z or Z-X view has been chosen. The coordinates of the starting and ending points of the line will be shown in the status bar. Rotate around X/Y/Z/3D Enables the 3D rotation of the view or around the x/y/z-axis by moving the mouse.
- 63. 6 3 – A N - S O F U S E R G U I D E Move Enables the movement of the view by moving the mouse (left mouse button pressed). Zoom Enables the zoom of the view by moving the mouse with the left button pressed. The mouse wheel can also be moved to zoom the view of the structure. X-Y / Y-Z / Z-X Plane Shows a view of the xy/yz/zx-plane parallel to the screen. Center Centers the view of the structure on the workspace. Initial View (Home) Returns the workspace to the initial view. Run ALL (F10) Runs the calculation of the current distribution, far- and near-fields. Run Currents and Far-Field (F11) Runs the calculation of the current distribution and far-fields. Run Currents and Near-Field (F12) Runs the calculation of the current distribution and near-fields. List Input Impedances Shows a table with the input impedances vs. frequency. Reflection coefficient, VSWR, return and transmission losses at the antenna terminals are also tabulated.
- 64. 6 4 – A N - S O F U S E R G U I D E Plot Current Distribution Executes the AN-3D Pattern application for plotting the current distribution as a colored pattern on the wire structure. Far-Field 3D Plot Executes the AN-3D Pattern application for plotting a 3D view of the radiation pattern. Far-Field Polar 1 Slice Displays the Radiation Pattern Cut dialog box for selecting a 2D cut of the 3D far-field pattern. Then, the selected 2D pattern cut will be plotted in a polar chart by the AN-Polar application. Far-Field Polar 2 Slices Displays a dialog box for selecting two slices of the 3D far-field pattern. Then, the selected 2D patterns will be plotted in a polar chart by the AN-Polar application. Far-Field 2D Plot Displays the Radiation Pattern Cut dialog box for selecting a 2D cut of the 3D far-field pattern. Then, the selected 2D pattern cut will be plotted in rectangular coordinates by the AN-XY Chart application. Export Results Opens a dialog box to save the results displayed in the "Results" tab as a CSV file. User Guide Opens the user guide file in PDF format.
- 65. 6 5 – A N - S O F U S E R G U I D E 3.3 PREFERENCES Preferences include the unit system to be used for showing input and output data, the workspace appearance, and several miscellaneous options. Preferences can be accessed via Tools > Preferences from the main menu. A suitable unit for frequencies, lengths, wire cross-section, inductances and capacitances can be selected in the Units page of the Preferences dialog box, Fig. 3.11. In the cases of lengths and cross-section, inches (in) and feet (ft) can be chosen apart from the standard SI units. Fig. 3.11: Units tab in Preferences dialog box. The units for frequencies, lengths, wire cross- section, inductances and capacitances can be set. The workspace background color can be switched between black and white in the Workspace tab, Fig. 3.12. Also, there are three levels for the pen width used to draw objects on the workspace: Thin, Medium, and Thick. The pen width option applies to axes, wires, and wire grids. The size of the source symbol can also be edited as well as its color and the color of loads. Check the Show Segments option to display the segments in the workspace. In the Options page, check the Show Main Toolbar option to see this toolbar, Fig. 3.13. Two “Ask before…” questions can be set to avoid mistakes. If the option “Run ALL” also calculates the H-field is checked, the near H-field will also be calculated after clicking on the “Run ALL” button. Here you can also choose to close the chart windows after exiting AN-SOF. Select the option "The comma is set as the decimal symbol" if you use the comma as decimal separator in your Windows regional settings. The number of significant digits shown in results can also be set (this option does not modify the double precision used in the internal algorithms).
- 66. 6 6 – A N - S O F U S E R G U I D E All the preferences can be configured at any time, either before or after performing a calculation. Fig. 3.12: Preferences dialog box. The Workspace tab is chosen, where the workspace background color, pen width, and appearance of sources/loads can be set. Fig. 3.13: Options page in the Preferences dialog box.
- 67. 6 7 – A N - S O F U S E R G U I D E 4. SETTING UP A SIMULATION Parameters to Configure before Running the Calculations 4.1 THE SETUP TAB The simulation parameters can be set in the Setup tabsheet. This page has the following panels: Frequency, Environment, Far-Field, Near-Field, Excitation, and Settings, Fig. 4.1. Fig. 4.1: Setup tab where the simulation parameters can be set. • In the Frequency panel, the project operating frequencies can be specified. • In the Environment panel, the relative permittivity and permeability of the surrounding medium and the type of ground plane can be set. • In the Far-Field panel, the angular ranges for the calculation of the far-field can be set.
- 68. 6 8 – A N - S O F U S E R G U I D E • In the Near-Field panel, the observation points for the calculation of the near-field can be set. • In the Excitation panel, the type of excitation for the structure can be set. When discrete sources are chosen as excitation, the total input power can be specified. When an incident field is chosen as excitation, the incoming direction and polarization for the incident wave can be specified. • In the Settings panel, additional parameters can be set, such as the reference impedance for VSWR and the accuracy of the calculations. • On the right side of the Setup page there is a Note panel to write notes associated to the project. These notes will be saved in a text file in the same path as the project file and with the same name as the project.
- 69. 6 9 – A N - S O F U S E R G U I D E 4.2 SPECIFYING THE FREQUENCIES Go to the Setup tab in the main window and select the Frequency panel. The Frequency panel has three options: Single, List and Sweep. By choosing one of these options the simulation can either be performed for a single frequency, for frequencies taken from a list or for a frequency sweep. • If Single is chosen, enter the frequency in the Single Frequency box, as shown in Fig. 4.1. The wavelength will be shown below the frequency. • If List is chosen, write the list of frequencies in the Frequency List box, Fig. 4.2. A list from a text file can be read by pressing the Open button. The frequency list can also be saved to a text file by pressing the Save button. • If Sweep is selected, it can either be linear or logarithmic. For a linear sweep the start, step and stop frequencies must be set, Fig. 4.3. For a logarithmic frequency sweep the start, stop and a multiplication factor must be set, Fig. 4.4. The frequency unit can be changed going to Tools > Preferences in the main menu and choosing a suitable unit in the Units page of the Preferences dialog box. Refer to Section “3.3 Preferences”. Fig. 4.2: Frequency panel in the Setup tabsheet. A list of frequencies is set.
- 70. 7 0 – A N - S O F U S E R G U I D E Fig. 4.3: Frequency panel in the Setup tabsheet. A linear frequency sweep is set. Fig. 4.4: Frequency panel in the Setup tabsheet. A logarithmic frequency sweep is set.
- 71. 7 1 – A N - S O F U S E R G U I D E 4.3 DEFINING THE ENVIRONMENT Go to the Setup tab in the main window and select the Environment panel. The relative permittivity and permeability of the surrounding medium can be set in the Medium box, Fig. 4.5. Four options are available for the ground plane: NONE None ground plane is used. The simulation will be performed in free space with the permittivity and permeability set in the Medium box, Fig. 4.5. PERFECT An infinite perfectly electric conducting (PEC) ground plane will be placed at the specified height from the xy-plane, Fig. 4.6. Thus, the ground plane will be parallel to the xy-plane. The Z value defines the ground plane height above the xy-plane. A negative Z defines the ground plane below the xy-plane. REAL A real ground plane having the conductivity and the relative permittivity (relative permeability is 1) set by the user will be placed on the xy-plane (z = 0), Fig 4.7. There are three options for the real ground calculations, namely, SOMMERFELD-WAIT/ASYMPTOTIC The currents flowing on the antenna/wire structure are computed using a model that consists of a PEC ground plane and the addition of equivalent loss impedances that account for the power dissipated in the ground plane when there are connections to ground. This is a very good model, developed by Prof. James R. Wait, to obtain the input impedance of low (LF) and medium frequency (MF) antennas, where the ground conductivity is high at those bands. The ground finite conductivity and permittivity are also used to compute the near- and far-fields radiated from the structure using the Sommerfeld-Norton asymptotic expressions and the Fresnel’s reflection coefficients, respectively. Connections to ground are allowed (start or end point of a wire having z = 0) and will be considered imperfect by default (currents flowing between ground and the grounded wires produce power losses in the ground). If the option “Zero-Ohm connections to ground” is checked, the wire connections to ground will be considered perfect (no ground power dissipation about the connection point).
- 72. 7 2 – A N - S O F U S E R G U I D E REFLECTION COEFFICIENTS/ASYMPTOTIC The ground parameters will affect the current distribution on the antenna or wire structure above ground via a generalization of the Fresnel’s reflection coefficients, so the input impedance of a transmitting antenna will also be affected by the real ground. The near and far fields will also be affected by the finite ground conductivity and its dielectric constant. Near fields are computed using the Sommerfeld-Norton asymptotic expressions, so the electric/magnetic field can be calculated as a function of distance from a transmitting antenna to observe the attenuation due to ground losses. The far-field is computed using the standard Fresnel’s reflection coefficients. Wire connections to ground are allowed, but they will be considered as lossless connections. RADIAL WIRE GROUND SCREEN A ground screen composed of buried radial wires will be placed below the ground plane. The screen is centered at the origin of coordinates and has the number of radial wires, wire length (or radius of the circular screen) and wire radius specified by the user. The ground screen model affects the current distribution on the antenna/wire structure by computing the power dissipated in the ground plane- wire screen system, so the input impedance of a transmitting antenna above the ground screen will be influenced by the presence of the screen and the finite ground conductivity. The ground finite conductivity and permittivity are also used to compute the near- and far-fields radiated from the structure using the Sommerfeld-Norton expressions and the Fresnel’s reflection coefficients, respectively. Connections to ground are allowed (start or end point of a wire having z = 0) and will be considered imperfect by default (currents flowing between ground and the grounded wires produce power losses in the ground). If the option “Zero-Ohm connections to ground” is checked, the wire connections to ground will be considered perfect (no ground power dissipation about the connection point). SUBSTRATE A dielectric substrate having the permittivity set by the user will be placed below the xy- plane (z = 0), Fig. 4.8. The substrate can either be infinite or finite in the xy-plane. The slab thickness, h, along the z-axis must be specified. A perfectly electric conducting (PEC) ground plane will be placed at z = -h (just below the dielectric slab), Fig. 4.9.
- 73. 7 3 – A N - S O F U S E R G U I D E Fig. 4.5: Medium and Ground Plane boxes in the Environment Panel. None ground plane is chosen (free space). Fig. 4.6: A perfect ground plane is placed at Z = 0 (xy-plane).
- 74. 7 4 – A N - S O F U S E R G U I D E Fig. 4.7: The parameters of a real ground plane are set. Fig. 4.8: The parameters of a finite dielectric substrate are set. A perfect ground plane will be placed at z = -h.
- 75. 7 5 – A N - S O F U S E R G U I D E Fig. 4.9: Dielectric substrate below the xy-plane. A microstrip line is set over the xy-plane.
- 76. 7 6 – A N - S O F U S E R G U I D E 4.4 FAR FIELD PARAMETERS Go to the Setup tab in the main window and select the Far-Field panel, Fig. 4.10. Fig. 4.10: Far-Field panel in the Setup tabsheet. The far field can be computed after having calculated the current distribution previously. Thus, the parameters set in the Far-Field panel have no effect in the determination of the currents and can be modified at any time. However, the far field must be recalculated every time these parameters are modified. There are four options for radiation pattern calculations: FULL 3D The far field is calculated in angular ranges that cover the entire 3D space, which allows us to obtain 3D radiation lobes. The steps for the Theta (zenith) and Phi (azimuth) angles can be set in the Theta [deg] and Phi [deg] boxes. VERTICAL The far field is calculated at a vertical slice for a given Phi (azimuth) angle. The step for the Theta (zenith) angle can be set in the Theta [deg] box, while the fixed Phi can be set in the Phi [deg] box.
- 77. 7 7 – A N - S O F U S E R G U I D E HORIZONTAL The far field is calculated at a horizontal slice for a given Theta (zenith) angle. The step for the Phi (azimuth) angle can be set in the Phi [deg] box, while the fixed Theta can be set in the Theta [deg] box. CUSTOM The far field is calculated for the specified ranges of angles Theta (zenith) and Phi (azimuth). The start, step, and stop values for Theta and Phi can be set in the Theta [deg] and Phi [deg] boxes. Additionally, the following parameters can be set: ORIGIN (X0,Y0,Z0) This can be any point used as a phase reference, its coordinates do not affect the shape of the radiation pattern. The 3D radiation pattern will be plotted centered at this point. DISTANCE It is the distance from (X0,Y0,Z0) to an observation point in the far-field region. A normalized far-field pattern can be obtained by setting Distance = 1. The zenith and azimuth angles, (Theta) and (Phi), are shown in Fig. 4.11, where it is also shown de Distance R from the structure to an observation point in the far-field zone. These three numbers (R,,) define the spherical coordinates of the far-field point. Fig. 4.11: Spherical coordinates (R,,) of a far-field point.
- 78. 7 8 – A N - S O F U S E R G U I D E IMPORTANT INFORMATION To check the average radiated power of a structure or compute the Radar Cross Section (RCS) in the case of plane wave excitation, a full radiation pattern covering the whole of space should be defined. For this reason, the Theta and Phi angles should vary in the following ranges when the Custom option is chosen: If the environment is free space (there is no ground plane): 0 Theta 180 deg. and 0 Phi 360 deg. If the environment has a ground plane: 0 Theta 90 deg. and 0 Phi 360 deg. These angular ranges allow the Average Power Density to be computed averaging the power density or Poynting vector in all directions in 3D space. If there is a ground plane, directions must be considered in half-space. When a real ground plane or an infinite substrate slab is set, and the Vertical, Horizontal or Custom option is chosen not in the ranges mentioned above, the calculated directivity, average power density and RCS will be meaningless quantities.
- 79. 7 9 – A N - S O F U S E R G U I D E 4.5 NEAR FIELD PARAMETERS Go to the Setup tab in the main window. Then, select the Near-Field panel, Fig. 4.12. Fig. 4.12: Near-Field panel in the Setup tabsheet. The Cartesian option is selected. The near field can be computed after having calculated the current distribution previously. Thus, the parameters set in the Near-Field panel have no effect in the determination of the currents and can be set at any time. However, the near field must be recalculated every time these parameters are modified. The Near-Field panel has three options: Cartesian, Cylindrical, and Spherical. By choosing one of these options near-fields can either be calculated in Cartesian, Cylindrical or Spherical coordinates. If the Cartesian option is chosen, the following parameters can be set for near-field calculations, Fig. 4.12: ORIGIN (X0,Y0,Z0) It is the origin of the Cartesian coordinates used to define the observation points where near fields will be calculated.
- 80. 8 0 – A N - S O F U S E R G U I D E X This box is used to set x-coordinates of the observation points where near-fields will be calculated. The start, step and stop x-coordinates must be set. Start and stop x-coordinates are measured from X0. Y This box is used to set y-coordinates of the observation points where near-fields will be calculated. The start, step and stop y-coordinates must be set. Start and stop y-coordinates are measured from Y0. Z This box is used to set z-coordinates of the observation points where near-fields will be calculated. The start, step and stop z-coordinates must be set. Start and stop z-coordinates are measured from Z0. If the Cylindrical option is chosen, the following parameters can be set for near-field calculations, Fig. 4.13: ORIGIN (X0,Y0,Z0) It is the origin of the Cylindrical coordinates used to define the observation points where near fields will be calculated. R This box is used to set the distances or R-coordinates of the observation points where near- fields will be calculated. The start, step and stop R-coordinates must be set. Start and stop distances or R-coordinates are measured from the origin (X0,Y0,Z0). PHI This box is used to set the azimuth angles or phi-coordinates of the observation points where near-fields will be calculated. The start, step and stop phi-coordinates must be set in degrees. Z This box is used to set the z-coordinates of the observation points where near-fields will be calculated. The start, step and stop z-coordinates must be set.
- 81. 8 1 – A N - S O F U S E R G U I D E Fig. 4.13: Near-Field panel in the Setup tabsheet. The Cylindrical option is selected. If the Spherical option is chosen, the following parameters can be set for near-field calculations, Fig. 4.14: ORIGIN (X0,Y0,Z0) It is the origin of the Spherical coordinates used to define the observation points where near fields will be calculated. R This box is used to set the distances or R-coordinates of the observation points where near- fields will be calculated. The start, step and stop R-coordinates must be set. Start and stop distances or R-coordinates are measured from the origin (X0,Y0,Z0). THETA This box is used to set zenith angles or theta-coordinates of the observation points where near-fields will be calculated. The start, step and stop theta-coordinates must be set in degrees. PHI This box is used to set azimuth angles or phi-coordinates of the observation points where near-fields will be calculated. The start, step and stop phi-coordinates must be set in degrees.
- 82. 8 2 – A N - S O F U S E R G U I D E Fig. 4.14: Near-Field panel in the Setup tabsheet. The Spherical option is selected.
- 83. 8 3 – A N - S O F U S E R G U I D E 4.6 DEFINING THE EXCITATION Go to the Setup tab in the main window and select the Excitation panel, Fig. 4.15. There are two types of excitations: DISCRETE SOURCES The discrete generators placed at the wire structure will be used to calculate the current distribution. The total input power in Watts can be specified, so the voltage/current sources will be adjusted accordingly to achieve the specified input power. If the input power is not specified, then the voltage/current sources will be constant, and the input power will be an output result from calculations. INCIDENT FIELD An incident plane wave will be used as the excitation of the structure. The direction of incidence and polarization of the incoming field can be set in this panel. When an incident plane wave is used as excitation, all discrete sources, if any, will not be considered in the simulation. The following parameters must be set for the incident wave excitation: E-FIELD MAJOR AXIS In the case of linear polarization, it is the amplitude, in Volts per meter (rms value), of the incoming electric field. For an elliptically polarized plane wave, it is the major axis of the polarization ellipse. AXIAL RATIO It is the ratio of the minor axis to the major axis of the polarization ellipse. If the axial ratio is positive (negative) a right-handed (left-handed) ellipse is obtained. If the axial ratio is set to zero, a linearly polarized wave will be obtained. PHASE REFERENCE It is the phase, in degrees, of the incident plane wave at the origin of coordinates. Its value only shifts all phases in the structure by the same amount. GAMMA For a linearly polarized wave, it is the polarization angle, in degrees, of the incident electric field measured from the plane of incidence to the direction of the electric field vector, as it is shown in Fig. 4.16. For an elliptically polarized wave, Gamma is the angle between the plane of incidence and the major ellipse axis.
- 84. 8 4 – A N - S O F U S E R G U I D E THETA It is the zenith angle, in degrees, of the incident direction. PHI It is the azimuth angle, in degrees, of the incident direction. The definition of these parameters is illustrated in Fig. 4.16. Fig. 4.15: Excitation panel in the Setup tabsheet. Fig. 4.16: Definition of the incident plane wave.
- 85. 8 5 – A N - S O F U S E R G U I D E When the 3D View button is pressed a user interface is enabled in the workspace, where the direction of arrival of the plane wave and its polarization can be specified easily, Fig. 4.17. Fig. 4.17: 3D View user interface for the incident field definition. In the case of elliptical polarization, the electric field vector Einc indicates the major ellipse axis.
- 86. 8 6 – A N - S O F U S E R G U I D E 4.7 THE SETTINGS PANEL Go to the Setup tab in the main window and select the Settings panel. The accuracy of the integrals involved in the calculations can be set in the Settings panel. The Quadrature Tolerance is the error in the evaluation of interactions between wire segments which are separated by a distance less than the Interaction Distance. The Interaction Distance is the maximum distance in wavelengths between segments for which an error less than the Quadrature Tolerance is guaranteed in the integrations. The interaction between all wire segments further apart than the Interaction Distance is computed using a third-degree polynomial approximation to the involved integrals, which is more accurate for curved segments than the Hertzian dipole approximation used in the traditional Method of Moments. Therefore, the Interaction Distance could be set to zero for a faster simulation when wire segments are not too close to each other, but results will be less accurate. A convergence test for various values of this parameter is recommended. For most cases, a quadrature tolerance between 0.1% and 1% and an interaction distance between 0.25 and 1.0 wavelengths will be enough for obtaining accurate results. In AN-SOF, all calculations are done with double precision. The Matrix Size Threshold allows us to simulate big antenna problems when the size of the structure compromises the available memory space. For instance, by setting the Matrix Size Threshold to 4,000, the set of linear equations associated to the Z-matrix of the antenna system will be computed using single precision for a matrix size bigger than 4,000 x 4,000. This will impact the accuracy of the calculations but will save memory. In practice, the error will be not significant. The Exact Kernel option allows us to use the exact Kernel for the Electric Field Integral Equation associated to the structure. This option must be chosen when relatively thick wire segments are used to describe the wire structure. If the Exact Kernel option is unchecked, an extended thin-wire approximation will be used for the kernel. If all wire segments are thin enough, then the computation will be a little faster using the extended thin-wire kernel. See chapter “18. Background Theory” for further information. In the Settings panel, the Reference Impedance for VSWR calculations can also be set. A default value of 50 Ohm is set, Fig 4.18. Besides, four options for the type of simulation are available in the Options box, Fig. 4.18. If NGF is checked, the Numerical Green’s Function calculation is performed in the simulation, that is, the LU-decomposed matrix of the system is stored in a file in the first simulation. Then, by using the stored information, new simulations are performed faster
- 87. 8 7 – A N - S O F U S E R G U I D E than the first one. Check this option if you need to change the amplitude values of voltage/current sources frequently. If Load Impedances is checked, lumped impedances will be considered in the simulation. With this option all the lumped loads can be disabled or enabled at the same time. If Wire Resistivity is checked, the finite resistivity of the wires will be considered in the simulation. Any wire has its own resistivity in [Ohm meter] that can be set when the wire is drawn. This option allows us considering the whole structure as a perfect electric conductor when it is unchecked. If Wire Coating is checked, the coating materials of the wires will be considered in the simulation. Any wire has its own coating specified by a dielectric permittivity, magnetic permeability, and thickness, which can be set when the wire is drawn. When this option is unchecked, the wire coating will not be considered in the simulation. Fig. 4.18: Settings panel in the Setup tabsheet.
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- 89. 8 9 – A N - S O F U S E R G U I D E 5. DRAWING WIRES Wires in the Workspace and their Features MENU OPTIONS The commands to draw wires can be accessed from three menus: • Main menu > Draw • Popup menu by right clicking on the workspace • Main menu > View > Drawing Panel TYPES OF WIRES AN-SOF has different types of wires. Each wire type has its own geometrical parameters, attributes and materials that can be set in a specific Draw dialog box. This dialog box allows us drawing a new wire in the workspace. Choosing Draw in the main menu shows the following commands: • Line: Displays the Draw dialog box for drawing a linear or straight wire. • Arc: Displays the Draw dialog box for drawing an arc . • Circle: Displays the Draw dialog box for drawing a circular loop. • Helix: Displays the Draw dialog box for drawing a helix or helical wire. • Quadratic: Displays the Draw dialog box for drawing a quadratic wire. • Archimedean Spiral: Displays the Draw dialog box for drawing an Archimedean spiral. • Logarithmic Spiral: Displays the Draw dialog box for drawing a logarithmic spiral.
- 90. 9 0 – A N - S O F U S E R G U I D E 5.1 LINE The Line refers to a linear or straight wire. Go to Draw > Line in the main menu to display the Draw dialog box for the Line, Fig. 5.1. This dialog box has three pages: Line, Attributes, and Materials, Fig. 5.2. THE LINE PAGE In the Line page the geometrical parameters for the Line can be set. There are two options: 2 Points and Start - Direction - Length. The 2 Points option allows us entering the Line by giving two points: “From Point” and "To Point", as shown in Figs. 5.2 and 5.3. If Start - Direction - Length is chosen, the line will be drawn starting from Start Point, in the direction given by the Theta and Phi angles in spherical coordinates and ending at a point defined by the wire Length measured along that direction, Figs. 5.4 and 5.5. Once the geometrical parameters in the Line page have been set, the Attributes page can be selected. Section 5.8 describes the parameters that can be set in the Attributes page. The wire resistivity and coating can be set in the Materials page described in Section 5.9. Fig. 5.1: The Draw/Line command in the main menu displays the Draw dialog box for the Line.
- 91. 9 1 – A N - S O F U S E R G U I D E Fig. 5.2: "2 Points" option in the Line page of the Draw dialog box. Fig. 5.3: A Line drawn using the "2 Points" option.
- 92. 9 2 – A N - S O F U S E R G U I D E Fig. 5.4: "Start - Direction - Length" option in the Line page of the Draw dialog box. Fig. 5.5: A Line drawn using the "Start - Direction - Length" option.
- 93. 9 3 – A N - S O F U S E R G U I D E 5.2 ARC The Arc refers to a circular arc. Go to Draw > Arc in the main menu to display the Draw dialog box for the Arc, Fig. 5.6. This dialog box has three pages: Arc, Attributes, and Materials, Fig. 5.7. THE ARC PAGE In the Arc page the geometrical parameters for the Arc can be set. There are two options: 3 Points and Start - Center - End. The 3 Points option allows us entering the Arc by giving three points. An arc starting from Start Point, passing through Second Point and ending at End Point will be drawn on the workspace, Figs. 5.7 and 5.8. If Start - Center - End is chosen, the Arc will be drawn starting from Start Point, with the center given by Center and ending at a point determined by End Point, Figs. 5.9 and 5.10. The End Point determines the arc aperture angle and the plane where it will be on, so this point could not coincide with the actual ending point of the arc. Once the geometrical parameters in the Arc page have been set, the Attributes page can be selected. Section 5.8 describes the parameters that can be set in the Attributes page. The wire resistivity and coating can be set in the Materials page described in Section 5.9. Fig. 5.6: The Draw/Arc command in the main menu displays the Draw dialog box for the Arc.
- 94. 9 4 – A N - S O F U S E R G U I D E Fig. 5.7: "3 Points" option in the Arc page of the Draw dialog box. Fig. 5.8: An Arc drawn using the "3 Points" option.
- 95. 9 5 – A N - S O F U S E R G U I D E Fig. 5.9: "Start - Center - End" option in the Arc page of the Draw dialog box. Fig. 5.10: An Arc drawn using the "Start - Center - End" option.
- 96. 9 6 – A N - S O F U S E R G U I D E 5.3 CIRCLE The Circle refers to a circular loop. Go to Draw > Circle in the main menu to display the Draw dialog box for the Circle, Fig. 5.11. This dialog box has four pages: Circle, Orientation, Attributes and Materials, Fig. 5.12. THE CIRCLE PAGE In the Circle page the geometrical parameters for the Circle can be set. There are two options: Center - Radius - Orientation and 3 Points. The Center - Radius - Orientation option allows us entering the Circle by giving its Center, Radius, and axis, Figs. 5.13 and 5.14. The circle axis can be set in the Orientation page. If the 3 Points option is chosen, the Circle will be drawn starting from First Point, passing through Second Point and Third Point, and ending at First Point, Figs. 5.15 and 5.16. Thus, the circle starts and ends at the same point. The Orientation page will be invisible when the 3 Points option is chosen. Once the geometrical parameters in the Circle and Orientation pages have been set the Attributes page can be selected. Section 5.8 describes the parameters that can be set in the Attributes page. The wire resistivity and coating can be set in the Materials page described in Section 5.9. THE ORIENTATION PAGE In the Orientation page the orientation for the Circle can be set. There is a box with two options: Angles and Vector. If Angles is selected, the circle axis can be defined by given an orthogonal direction to the rest plane of the circle. Thus, the Theta and Phi angles determine the axis direction in spherical coordinates, Fig. 5.12. If Vector is selected, the circle axis can be defined by given an orthogonal vector to the rest plane of the circle. Thus, the Nx, Ny, and Nz components of that vector determine the axis direction. The circle can be rotated around its axis by given the Rotation Angle, Fig. 5.12.
- 97. 9 7 – A N - S O F U S E R G U I D E Fig. 5.11: The Draw/Circle command in the main menu displays the Draw dialog box for the Circle. Fig. 5.12: "Angles" option in the Orientation page of the Draw dialog box.
- 98. 9 8 – A N - S O F U S E R G U I D E Fig. 5.13: "Center - Radius - Orientation" option in the Circle page of the Draw dialog box. Fig. 5.14: A Circle drawn using the "Center - Radius - Orientation" option.
- 99. 9 9 – A N - S O F U S E R G U I D E Fig. 5.15: "3 Points" option in the Circle page of the Draw dialog box. Fig. 5.16: A Circle drawn using the "3 Points" option.
- 100. 1 0 0 – A N - S O F U S E R G U I D E 5.4 HELIX The Helix refers to a helical wire. Go to Draw > Helix in the main menu to display the Draw dialog box for the Helix, Fig. 5.17. This dialog box has four pages: Helix, Orientation, Attributes and Materials, Fig. 5.18. THE HELIX PAGE In the Helix page the geometrical parameters for the Helix can be set. There are two options: Start - Radius - Pitch - Turns and Start - End - Radius - Turns. The Start - Radius - Pitch - Turns option allows us entering the Helix by setting its Start Point, Radius, Pitch and Number of turns, Figs. 5.19 and 5.20. If Pitch is positive (negative) the helix will be right-handed (left-handed). The helix axis can be set in the Orientation page. If Start - End - Radius - Turns is chosen, the helix will be drawn starting from Start Point and ending at End Point, with the given Radius and Number of turns, Figs. 5.21 and 5.22. The Number of turns must be an integer number, if it is positive (negative) the helix will be right-handed (left-handed). The orientation of the helix axis is determined by the starting and ending points. The helix can be rotated around its axis by given the Rotation Angle. The Orientation page will be invisible when the Start - End - Radius - Turns option is chosen. Once the geometrical parameters in the Helix and Orientation pages have been set the Attributes page can be selected. Section 5.8 describes the parameters that can be set in the Attributes page. The wire resistivity and coating can be set in the Materials page described in Section 5.9. THE ORIENTATION PAGE In the Orientation page the orientation for the Helix can be set. There is a box with two options: Angles and Vector. If Angles is selected, the helix axis can be defined by given its direction in 3D space. This direction is determined by the Theta and Phi angles in spherical coordinates, Fig. 5.18. If Vector is selected, the helix axis can be defined by given a vector in the axis direction. Its Nx, Ny, and Nz components define this vector. The helix can be rotated around its axis by given the Rotation Angle, Fig. 5.18.
- 101. 1 0 1 – A N - S O F U S E R G U I D E Fig. 5.17: The Draw/Helix command in the main menu displays the Draw dialog box for the Helix. Fig. 5.18: "Angles" option in the Orientation page of the Draw dialog box.
- 102. 1 0 2 – A N - S O F U S E R G U I D E Fig. 5.19: "Start - Radius - Pitch - Turns" option in the Helix page of the Draw dialog box. Fig. 5.20: A Helix drawn using the "Start - Radius - Pitch - Turns" option.
- 103. 1 0 3 – A N - S O F U S E R G U I D E Fig. 5.21: "Start - End - Radius - Turns" option in the Helix page of the Draw dialog box. Fig. 5.22: A Helix drawn using the "Start - End - Radius - Turns" option.
- 104. 1 0 4 – A N - S O F U S E R G U I D E 5.5 QUADRATIC The Quadratic refers to a quadratic wire or parabola. Go to Draw > Quadratic in the main menu to display the Draw dialog box for the Quadratic, Fig. 5.23. This dialog box has three pages: Quadratic, Attributes, and Materials, Fig. 5.24. THE QUADRATIC PAGE In the Quadratic page the geometrical parameters for the Quadratic can be set. The Quadratic is entered by giving three points. A quadratic curve starting from Start Point, passing through Second Point and ending at End Point will be drawn on the workspace, as shown in Figs. 5.25. Once the geometrical parameters in the Quadratic page have been set, the Attributes page can be selected. Section 5.8 describes the parameters that can be set in the Attributes page. The wire resistivity and coating can be set in the Materials page described in Section 5.9. Fig. 5.23: The Draw/Quadratic command in the main menu displays the Draw dialog box for the Quadratic.
- 105. 1 0 5 – A N - S O F U S E R G U I D E Fig. 5.24: Quadratic page of the Draw dialog box. Fig. 5.25: A Quadratic drawn using the points shown in Fig. 5.24.
- 106. 1 0 6 – A N - S O F U S E R G U I D E 5.6 ARCHIMEDEAN SPIRAL The Archimedean Spiral refers to the Archimedes’ spiral with polar equation r() = r0 + p/(2) , where r0 is the starting radius and p is the pitch. For a spiral with an integer number of turns, M, we have = 2M at its end point, so rend = r0 + pM, the pitch p being the separation between turns. Besides, we have that the pitch equals the constant growth rate of the spiral radius r() per turn, that is p = 2dr/d. Go to Draw > Archimedean Spiral in the main menu to display the Draw dialog box for the Archimedean Spiral, Fig. 5.26. This dialog box has three pages: Archimedean Spiral, Attributes, and Materials, Fig. 5.27. THE ARCHIMEDEAN SPIRAL PAGE In the Archimedean Spiral page, the geometrical parameters for the Archimedean Spiral can be set. The Archimedean spiral is entered by giving the Start Point, Start Radius r0, Pitch p (positive or negative) and Number of Turns M (complete turns and fractions of a turn can be set). The spiral lies on a plane given by the Orientation Angles Theta and Phi (normal to the plane in spherical coordinates) and can be rotated by setting a Rotation Angle, Fig. 5.28. Once the geometrical parameters in the Archimedean Spiral page have been set, the Attributes page can be selected. Section 5.8 describes the parameters that can be set in the Attributes page. The wire resistivity and coating can be set in the Materials page described in Section 5.9. Fig. 5.26: The Draw/Archimedean Spiral command in the main menu displays the Draw dialog box for the Archimedean Spiral.
- 107. 1 0 7 – A N - S O F U S E R G U I D E Fig. 5.27: Archimedean Spiral page of the Draw dialog box. Fig. 5.28: An Archimedean Spiral drawn using the data shown in Fig. 5.27.
- 108. 1 0 8 – A N - S O F U S E R G U I D E 5.7 LOGARITHMIC SPIRAL The Logarithmic Spiral refers to a spiral with polar equation r() = r0 exp(b), where r0 is the starting radius (r at = 0), b = p/(2r0) and p is the starting pitch, that is, the derivative 2dr/d at = 0 (starting growth rate of the spiral radius r() per turn). The first two terms of the Taylor expansion r() = r0 + p/(2) + r0(b)2 /2 + … give the polar equation of an Archimedean spiral, which is described in Section 5.6. Go to Draw > Logarithmic Spiral in the main menu to display the Draw dialog box for the Logarithmic Spiral, Fig. 5.29. This dialog box has three pages: Logarithmic Spiral, Attributes, and Materials, Fig. 5.30. THE LOGARITHMIC SPIRAL PAGE In the Logarithmic Spiral page, the geometrical parameters for the Logarithmic Spiral can be set. The logarithmic spiral is entered by giving the Start Point, Start Radius r0, Start Pitch p (positive or negative) and Number of Turns (complete turns and fractions of a turn can be defined). The spiral lies on a plane given by the Orientation Angles Theta and Phi (normal to the plane in spherical coordinates) and can be rotated by setting a Rotation Angle, Fig. 5.31. Once the geometrical parameters in the Logarithmic Spiral page have been set, the Attributes page can be selected. Section 5.8 describes the parameters that can be set in the Attributes page. The wire resistivity and coating can be set in the Materials page described in Section 5.9. Fig. 5.29: The Draw/Logarithmic Spiral command in the main menu displays the Draw dialog box for the Logarithmic Spiral.
- 109. 1 0 9 – A N - S O F U S E R G U I D E Fig. 5.30: Logarithmic Spiral page of the Draw dialog box. Fig. 5.31: A Logarithmic Spiral drawn using the data shown in Fig. 5.30.
- 110. 1 1 0 – A N - S O F U S E R G U I D E 5.8 WIRE ATTRIBUTES The Attributes page belongs to the Draw dialog box of the chosen wire type, Fig. 5.32. In the Attributes page the following attributes can be specified: NUMBER OF SEGMENTS Any wire must be divided into a given number of segments. An unknown current on each segment must be found in the simulation process. A default Number of Segments will be shown when the Attributes page is chosen. This number is obtained from the ratio between the wire length and the shortest wavelength, but it can be modified by the user. If the Number of Segments is set to zero, AN-SOF will compute the number of segments consistent with the highest frequency or shortest wavelength. Fig. 5.32: Attributes page in the Draw dialog box for the Line. CROSS-SECTION The Cross-Section of the wire can be chosen from a combo-box. There are six cross-section types available: Circular, Square, Flat, Elliptical, Rectangular, and Triangular. AN-SOF computes an equivalent radius for the five last cases. Infinitesimally thin wires are not allowed, so the cross-section radius must be greater than zero. The Draw dialog box for any wire type has its own Attributes page with the same features as those described here.
- 111. 1 1 1 – A N - S O F U S E R G U I D E 5.9 WIRE MATERIALS The Materials page belongs to the Draw dialog box of the chosen wire type, Fig. 5.33. In the Materials page the following attributes can be specified: WIRE RESISTIVITY A resistivity in [Ohm meter] can be specified for the wire. This value is used for computing a distributed impedance along the wire, considering the skin effect. The equivalent radius for wires of non-circular cross section will be used to compute the impedance per unit length along the wires. Resistivity values for most common conductive materials are the following: Material Resistivity [ m] Aluminum (Pure) 2.65E-8 Aluminum (6061-T6) 4.01E-8 Aluminum (6063-T832) 3.25E-8 Brass 6.41E-8 Copper 1.74E-8 Phosphor Bronze 1.10E-7 Silver 1.59E-8 Stainless Steel 302 7.19E-7 Tin 1.14E-7 Zinc 5.90E-8 The resistivity of wires is considered in the simulation if the option Wire Resistivity is checked in the Settings panel of the Setup tabsheet. WIRE COATING Wires can have an insulation or coating material. The cross section of a coated wire is circular, so the equivalent radius will be used for wires having a non-circular cross section. In this case, the material the coating is made of can be set by the following parameters: RELATIVE PERMITTIVITY It is the dielectric constant of the coating material relative to the permittivity of vacuum.
- 112. 1 1 2 – A N - S O F U S E R G U I D E RELATIVE PERMEABILITY It is the magnetic permeability of the coating material relative to the permeability of vacuum. THICKNESS It is the thickness of the coating shield. It can be set to zero when no coating is used. Fig. 5.33: Materials page in the Draw dialog box for the Line.
- 113. 1 1 3 – A N - S O F U S E R G U I D E 5.10 ENABLING/DISABLING RESISTIVITY If wires with non-zero resistivity have been drawn previously and the whole structure must now be considered as a perfect electric conductor, all resistivities can be disabled without modifying the definitions of the wires. Go to the Setup tabsheet in the main window and select the Settings panel, Fig. 5.34. If the option Wire Resistivity in this panel is checked, the resistivities are enabled. Uncheck the Wire Resistivity option to disable all of them. Fig. 5.34: Wire Resistivity option in the Settings panel of the Setup tabsheet. If this option is checked, all resistivities are enabled, otherwise they are disabled.
- 114. 1 1 4 – A N - S O F U S E R G U I D E 5.11 ENABLING/DISABLING COATING If wires with a coating shield or insulation have been drawn previously and the whole structure must now be considered as composed of bare conductive wires, all coatings can be disabled without modifying the definitions of the wires. Go to the Setup tabsheet in the main window and select the Settings panel, Fig. 5.35. If the option Wire Coating in this panel is checked, the coatings are enabled. Uncheck the Wire Coating option to disable all of them. Fig. 5.35: Wire Coating option in the Settings panel of the Setup tabsheet. If this option is checked, all coatings are enabled, otherwise they are disabled.
- 115. 1 1 5 – A N - S O F U S E R G U I D E 5.12 CROSS-SECTION EQUIVALENT RADIUS The wire cross-section can be chosen from a combo-box in the Attributes page of the Draw dialog box for the chosen wire type, Fig. 5.36. Fig. 5.36: Cross-section combo-box in the Attributes page of the Draw dialog box. A circular cross section of radius “a” is chosen. There are six cross-section types available: Circular, Square, Flat, Elliptical, Rectangular, and Triangular. AN-SOF computes an equivalent radius for the non-circular cross-sections. The equivalent radius is the radius of a circular cross-section that produces the same average electromagnetic fields around the wire and on its surface. The cross-sections and their equivalent radii are: CIRCULAR A positive and non-zero radius “a” must be set. The equivalent radius is “a”.
- 116. 1 1 6 – A N - S O F U S E R G U I D E SQUARE A positive and non-zero width “w” must be set. The equivalent radius is 0.59017 w. FLAT A positive and non-zero width “w” must be set. The equivalent radius is w/4. ELLIPTICAL The semi-axes “a” and “b” must be positive and non-zero. The equivalent radius is (a + b)/2. RECTANGULAR The widths “w” and “t” must be positive and non-zero. The equivalent radius is computed using a polynomial and logarithmic approximation to the solution of an integral equation.
- 117. 1 1 7 – A N - S O F U S E R G U I D E TRIANGULAR A positive and non-zero width “w” must be set. The equivalent radius is 0.42w.
- 118. 1 1 8 – A N - S O F U S E R G U I D E 5.13 IMPORTING WIRES Wires in an external file can be imported into AN-SOF by going to File > Import Wires in the main menu, Fig. 5.37. A sub-menu having four options will be displayed: AN-SOF, NEC, DXF, and MM formats. The DXF and MM formats must contain only linear wires written in ASCII text format. Fig. 5.37: File/Import Wires option in the main menu. AN-SOF FORMAT Wires can be imported into AN-SOF from another AN-SOF project. When a project is saved, a file having extension “.wre” will also be saved. This file contains the geometrical description of the structure. To import wires into a project, just find and select the .wre file that you want to import. NEC FORMAT There are slight differences between the commands supported by AN-SOF and the standard NEC cards. To maintain compatibility with the NEC format, which was originally created for entering data using punch cards, some fields appear repeating, and others must be entered with a zero with no meaning. Lengths and wire radii are assumed to be in meters. If errors are found while importing a file, an error report will be shown in the Note panel of the Setup tab.
- 119. 1 1 9 – A N - S O F U S E R G U I D E GW – Linear Wire One linear wire per line must be set beginning with “GW” and ending with an Enter as follows: GW Tag Segments X1 Y1 Z1 X2 Y2 Z2 Radius [Enter] Tag > 0. Tag number for the linear wire. The space between “GW” and Tag is optional. A single tab or comma can also be used as a separator between the command name and the first data field. Segments = Number of segments for the wire. If a zero is entered, the minimum recommended number of segments will be computed. X1 Y1 Z1 = Cartesian coordinates of the start point of the linear wire. X2 Y2 Z2 = Cartesian coordinates of the end point of the linear wire. Radius = Wire radius. Fields can be separated by up to two spaces, a single tab, a single comma, or a comma and space. Each GW line, including the last one in a set of linear wires to be imported, must end with an Enter (press Enter in the keyboard for a carriage return). The text lines above the GW lines will be ignored, so comments can be added at the beginning of the file. The following are equivalent examples: Write comments here GW 1 12 5.42 0.38 1.262 5.425 -0.378 1.261 0.01[Enter] GW 2 5 7.45 0 1.122 7.45 0 1.49 0.015[Enter] GW 3 2 8.3 0.0 1.12 8.37 0.0 1.595 0.01[Enter] Write comments here GW1,12,5.42,0.38,1.262,5.425,-0.378,1.261,0.01[Enter] GW2,5,7.45,0,1.122,7.45,0,1.49,0.015[Enter] GW3,2,8.3,0.0,1.12,8.37,0.0,1.595,0.01[Enter]
- 120. 1 2 0 – A N - S O F U S E R G U I D E CM and Other Commands The CM (comment lines), GH (helical wire), GA (arc), GM (coordinate transformation), GS (scale dimensions), FR (frequency), EX (excitation), LD (load impedances and wire conductivity), EK (exact kernel), RP (radiation pattern), GE (ground connections) and GN (real ground parameters) commands will also be read. The CM lines will be added to the Note panel of the Setup tabsheet after the NEC file is imported. The comment termination card, “CE”, is not needed in AN-SOF. Comments without the CM command at the beginning of the file will be ignored and not imported. The command names, “CM”, “GW”, “GH”, etc., are reserved words in AN-SOF and they are used to recognize the fields between these commands and the final Enter in each text line, so the command names should not be used in comments. The rest of the AN-SOF commands must have the following formats, where all the indicated fields are mandatory: GH – Helix GH Tag Segments Spacing Length R R R R Radius [Enter] Tag > 0. Tag number for the helix. The space between “GH” and Tag is optional. The helix begins at the origin at develops along the positive z-axis. To rotate and/or move the helix, use the GM command described below. This GH command corresponds to the NEC-2 helix specification. Consider that the GH command is different in NEC-4. Segments = Number of segments for the helix. If a zero is entered, the minimum recommended number of segments will be computed. We must point out that unlike NEC, AN-SOF uses conformal segments that exactly follow the helix contour. Spacing = Spacing between turns. Length = Total length of the helix. Length > 0 gives a right-handed helix, and Length < 0 gives a left-handed helix. R = Radius of the helix (it must appear four times). Radius = Wire radius.
- 121. 1 2 1 – A N - S O F U S E R G U I D E GA – Arc GA Tag Segments R Ang1 Ang2 Radius [Enter] Tag > 0. Tag number for the arc. The space between “GA” and Tag is optional. The arc is on the xz-plane, and it is centered at the origin, so the arc axis is the y-axis. To rotate and/or move the arc, use the GM command described below. Segments = Number of segments for the arc. If a zero is entered, the minimum recommended number of segments will be computed. We must point out that unlike NEC, AN-SOF uses conformal segments that exactly follow the arc contour. R = Arc radius. Ang1 = Angle of the first end of the arc measured from the x-axis in a left-handed direction about the y-axis, in degrees. Ang2 = Angle of the second end of the arc, in degrees. Radius = Wire radius. GM – Coordinate Transformation GM 0 N rotX rotY rotZ DX DY DZ 0 [Enter] N = 0 means that the whole structure above the GM command must be rotated and moved using (rotX,rotY,rotZ) and (DX,DY,DZ). The coordinate transformations are applied sequentially in that order. N = 1 means that the whole structure above the GM command must be copied and the copy must be moved to a new position (DX,DY,DZ) from the origin. The “GM” command can be used below the “GW”, “GH” and “GA” commands for rotating, moving, and copying the desired linear wires, helices and arcs. rotX = Angle of rotation about X-axis, in degrees. rotY = Angle of rotation about Y-axis, in degrees. rotZ = Angle of rotation about Z-axis, in degrees. DX = Move the structure an amount DX along X-axis. DY = Move the structure an amount DY along Y-axis. DZ = Move the structure an amount DZ along Z-axis.
- 122. 1 2 2 – A N - S O F U S E R G U I D E GS – Scale Structure Dimensions GS 0 0 Scale [Enter] Scale = Scaling factor. All structure dimensions, including wire radii, are multiplied by Scale. FR – Frequencies FR Type Num 0 0 Freq Df [Enter] Type = Type of frequency sweep. Linear -> Type = 0, Log -> Type = 1. Num = Number of frequency steps. Freq = Frequency in MHz or starting frequency in a range. Df = If Type = 0, it is the frequency stepping increment in MHz. If Type = 1, it is the multiplication factor of a log sweep. EX – Excitation EX Type Wire# Seg# 0 Real Imag [Enter] Type = Type of source. Only voltage sources are currently supported, so set Type = 0 or 5 (the “5” being an old source model only used in NEC). Wire# = Wire tag number where the source is placed. Seg# = Segment where the source is placed. Real = Real part of the source voltage. Imag = Imaginary part of the source voltage.
- 123. 1 2 3 – A N - S O F U S E R G U I D E LD – Load impedance LD Type Wire# Seg# Seg# R L C [Enter] Type = Type of load. Only series RLC loads are currently supported, so set Type = 0 for a RLC load. Set Type = 5 and Seg# = 0 to specify a wire conductivity [S/m] in the “R” field for the wire number “Wire#”. Type LD 5 0 0 0 R 0 0 to set a conductivity "R [S/m]" on all wires. Wire# = Wire tag number where the load or conductivity is placed. Seg# = Segment tag number where the load is placed. It is a field that appears twice due to a NEC convention that is not used in AN-SOF, so the second Seg# will be ignored. Set Seg# = 0 if a wire conductivity is to be entered. R = Resistance in Ohms or conductivity in S/m. L = Inductance in Henries. It is ignored if R is a conductivity; enter a zero. C = Capacitance in Farads; if none, enter zero. It is ignored if R is a conductivity, so enter a zero. GE – Ground connections GE Type [Enter] Type = 0 -> No ground plane is present. A “GE” command without a type will be interpreted as “GE 0”. Type = 1 -> A PEC ground plane is placed at z = 0 and wires ending on the ground plane will be connected to the ground. If a real ground plane has been chosen, Type = 1 means that the wire connections to the ground must be considered as zero-Ohm connections. Type = -1 -> The wire connections to the ground are imperfect and producing power losses when a real ground plane has been chosen. GN – Real ground GN Type Screen 0 0 Epsilon Sigma Length WireRadius [Enter]
- 124. 1 2 4 – A N - S O F U S E R G U I D E Type = type of ground plane. Type = -1 -> Free space simulation; all ground parameters are ignored. “GN -1” can be used in this case. Type = 0 -> Reflection Coefficients/Asymptotic option. Type = 1 -> PEC ground plane at z = 0; the other parameters are ignored. “GN 1” can be used in this case. Type = 2 -> Sommerfeld-Wait/Asymptotic option. Screen = Number of radials in a radial wire ground screen. Set Screen = 0 if no ground screen is present. Epsilon = Ground plane relative permittivity or dielectric constant. Sigma = Ground plane conductivity in [S/m]. Length = Length of radial wires if a radial wire ground screen is used. Enter a zero if no ground screen is used. WireRadius = Radius of radial wires if a screen is used. Enter a zero if no ground screen is used. RP – Radiation pattern RP 0 Ntheta Nphi 1001 Theta Phi Dtheta Dphi R [Enter] Ntheta = Number of values of at which the field is to be computed. Nphi = Number of values of at which the field is to be computed. 1001 = It is a NEC variable which indicates that the average power gain must be computed. This value will be ignored since AN-SOF always computes the average power gain. Theta = Initial angle in degrees. Phi = Initial angle in degrees. Dtheta = Increment for in degrees. Dphi = Increment for in degrees. R = Radial distance in meters of the field point from the origin. R = 0 is taken as R = 1 m.
- 125. 1 2 5 – A N - S O F U S E R G U I D E DXF FORMAT The DXF file format is a standard format for storing CAD (Computer Aided Design) geometrical data as ASCII text lines. Only DXF files containing LINE objects can be imported into AN-SOF. The structure of a LINE entity is as follows, where only the (X,Y,Z) coordinates of the starting and ending points are read: LINE 8 // Subclass marker. Not read 0 // Thickness (default = 0). Not read 10 // Starting point – 10, 20, 30 are tags – Not read -0.5000 // X value 20 // Not read -0.5000 // Y value 30 // Not read 1.000 // Z value 11 // Ending point – 11, 21, 31 are tags – Not read 0.5000 // X value 21 // Not read -0.5000 // Y value 31 // Not read 1.000 // Z value 0 // Extrusion direction (default = 0) – Not read Since LINE objects have zero thickness, AN-SOF will set a wire radius equal to 0.5% of the wire length. The LINE coordinates in the DXF file are in meters. AN-SOF will also set the number of segments for each wire according to the operating frequency, so it is recommended to set the frequencies before importing the DXF file. Wire radii and the number of segments can be modified after importing the DXF file using the Modify option in the main menu.
- 126. 1 2 6 – A N - S O F U S E R G U I D E MM FORMAT One linear wire per line must be defined as follows: X1,[TAB]Y1,[TAB]Z1,[TAB]X2,[TAB]Y2,[TAB]Z2,[TAB]Radius,[TAB]Segments [Enter] X1 Y1 Z1 = Cartesian coordinates of the wire start point. X2 Y2 Z2 = Cartesian coordinates of the wire end point. Radius = Wire radius. Segments = Number of segments. The last text line must end with an Enter (press Enter in the keyboard for a carriage return). Example: 5.42, 0.38, 1.262, 5.425, -0.378, 1.261, 0.01, 12 7.45, 0, 1.122, 7.45, 0, 1.49, 0.015, 5 8.3, 0.0, 1.12, 8.37, 0.0, 1.595, 0.01, 2 [Enter] In the MM format, automatic segmentation of a wire can be obtained by entering any number equal or less than zero as the number of segments. The units for the coordinates of the start and end points of any wire must be consistent with the length unit chosen in the AN-SOF Preferences dialog box. Also, the wire radius or diameter of any imported wire must be expressed in the unit chosen in the Preferences dialog box.
- 127. 1 2 7 – A N - S O F U S E R G U I D E 5.14 EXPORTING WIRES Linear wires can be exported from AN-SOF to a text file in NEC format (extension .nec) by going to File > Export Wires in the main menu, Fig. 5.38. Linear wires will be stored as GW lines. FR (frequency), EX (excitation), LD (load impedances and wire conductivity), RP (radiation pattern), GE (ground connections) and GN (ground plane) cards will also be saved in the exported file. The exported file can also be saved as a Scilab script, a .sce file. The exported file will have programming code that can be modified to create a new project with varying parameters, such as the wire lengths and positions, frequencies, and ground conditions. Fig. 5.38: File/Export Wires option in the main menu.
- 128. 1 2 8 – A N - S O F U S E R G U I D E 5.15 DRAGGING LINES Lines can be dragged in the workspace using the mouse with the left button pressed. Select the Draw Line button in the main toolbar to enable the dragging line mode, Fig. 5.39. Then, select the plane where the lines will be drawn by pressing the x-y, y-z or z-x buttons in the main toolbar. Left click on the workspace and drag a line. When the mouse button is released, the Draw dialog box for the Line wire will be shown. Adjust the line parameters as needed and press the OK button. When drawing the first line in the workspace, its starting and ending points will be shown with zero coordinates in the Draw dialog box. Once these coordinates are set for the first time, they will be used to scale the subsequent lines and the Draw dialog box will show the correct coordinates. The start and end point coordinates are shown in the status bar while dragging the line. Fig. 5.39: Dragging a line in the xy-plane.
- 129. 1 2 9 – A N - S O F U S E R G U I D E 5.16 TABULAR INPUT OF LINEAR WIRES Lines or linear wires can be entered and edited in a table as follows: 1. Go to Draw > Tabular Input (Ctrl + T) in the main menu to show the table, Fig. 5.40. 2. Choose the Wires tab and enter the values as it is specified in the column titles. Each row corresponds to a linear wire. Enter the number of segments in Segs, the coordinates of the starting (X1,Y1,Z1) and ending (X2,Y2,Z2) points and the wire radius. Only wires with circular cross-section can be entered. The wire resistivity can also be set. The wire coating can be set by selecting the wires in groups (Section 6.5). 3. Right click on the table and a pop-up menu will be displayed with the standard Cut (Ctrl + X), Copy (Ctrl + C) and Paste (Ctrl + V) options. 4. A single cell can be selected by left clicking on it or using the TAB and arrows keys on the keyboard. 5. A row can be selected by clicking on the row number in the left column (the No. column). Use the mouse or the up and down arrows in the keyboard to select a single row. Double click on a single cell to exit the row selection mode. 6. The Cut (Ctrl + X), Copy (Ctrl + C) and Paste (Ctrl + V) options also apply to a selected row. Besides, the Insert (Ins key) and Delete (Del key) options can be used to insert and delete rows. 7. The Clear Contents (Ctrl + Del) option in the pop-up menu clears the content of a selected cell or row. 8. Use the Sources and Loads tabs to enter sources and loads. The Wire No. column specifies which wire the source or load is placed on. Fig. 5.40: Tabular input of linear wires.
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- 131. 1 3 1 – A N - S O F U S E R G U I D E 6. EDITING WIRES A Variety of Tools to Modify Wires 6.1 SELECTING A WIRE Any wire in the workspace can be selected in three different ways: 1. By clicking on the Select Wire button (arrow icon) on the toolbar and then left clicking on the wire. 2. By right clicking on the wire. In this case, a pop-up menu will be displayed, Fig. 6.1. 3. By pressing F8 or F9 on the keyboard. In this case, the wires will be selected one by one, forwards or backwards, in the order in which they were created. A wire is highlighted in light blue when it is selected. Fig. 6.1: Pop-up menu displayed when a wire is selected by right clicking on it.
- 132. 1 3 2 – A N - S O F U S E R G U I D E 6.2 THE POP-UP MENU Right-clicking on a wire brings up a menu with the following commands: Source/Load (Ctrl + Ins) Displays the Source/Load toolbar for exciting or loading the selected wire. Modify (Ctrl + M) Displays the Modify dialog box for modifying the selected wire. Wire Color Displays a Windows dialog box for changing the color of the selected wire. Delete (Ctrl + Del) Deletes the selected wire with all sources and loads placed on it. Copy Start Point Copies the start point of the selected wire to connect this point to the start point of another wire. Copy End Point Copies the end point of the selected wire to connect this point to the start point of another wire. Plot Currents Executes the AN-XY Chart application for plotting the currents vs. position along the selected wire. This command is enabled when the currents are already computed. List Currents Displays the List Currents toolbar for listing the currents vs. frequency at the selected wire segment. This command is enabled when the currents are already computed. Wire Properties (Ctrl + W) Displays the Wire Properties dialog box where information about the selected wire is shown. Draw Contains a sub-menu with the Line, Arc, Circle, Helix, Quadratic, Archimedean Spiral, and Logarithmic Spiral commands to draw these types of wires.
- 133. 1 3 3 – A N - S O F U S E R G U I D E 6.3 MODIFYING A WIRE Right-clicking on a wire brings up a menu, Fig. 6.1. Choosing the Modify command from the pop-up menu shows the Modify dialog box, where the geometrical parameters and attributes of the selected wire can be modified. The Modify command can also be chosen by first selecting a wire by left clicking on it, and next going to Edit > Modify in the main menu, Fig. 6.2. This option is enabled when the Select Wire button (arrow icon) in the main toolbar is pressed. When a wire is modified, all sources and loads placed on it are removed. To modify a wire without removing the sources and loads, select the wire using the selection box, as explained in Section “6.5 Modifying a group of wires”. Fig. 6.2: Modify command in the Edit menu. This command is enabled when a wire is selected.
- 134. 1 3 4 – A N - S O F U S E R G U I D E 6.4 DELETING A WIRE Right-clicking on a wire brings up a menu, Fig. 6.1. Choosing the Delete command from the pop-up menu deletes the selected wire with all sources and loads placed on it. The Delete command can also be chosen by first selecting a wire by left clicking on it, and next going to Edit > Delete in the main menu, Fig. 6.3. This option is enabled when the Select Wire button (arrow icon) in the main toolbar is pressed. Fig. 6.3: Delete command in the Edit menu. This command is enabled when a wire is selected.
- 135. 1 3 5 – A N - S O F U S E R G U I D E 6.5 MODIFYING A GROUP OF WIRES AN-SOF allows us to select a group of wires to edit them all at once. Click on the Selection Box button on the main toolbar. By left clicking on the workspace and dragging a box with the mouse, multiple wires can be selected, Fig. 6.4. All wires inside the selection box will be highlighted in light blue. Go to Edit > Modify in the main menu to modify the selected wires. Fig. 6.4: Box to select a group of wires. The Modify command will display the dialog box shown in Fig. 6.5. There are three tabs: Attributes, Materials, and Sources / Loads. Use the check boxes to choose the parameters you want to modify. In this case, the sources and loads will not be removed unless these options are checked in the Sources / Loads tab.
- 136. 1 3 6 – A N - S O F U S E R G U I D E Fig. 6.5: The three tabs in the “Modify Wires” dialog box.
- 137. 1 3 7 – A N - S O F U S E R G U I D E 6.6 DELETING A GROUP OF WIRES Click on the Selection Box button in the main toolbar. Then, left clicking on the workspace a box to select multiple wires can be expanded, as shown in Fig. 6.4. The selected group of wires will be highlighted in light blue. Go to Edit > Delete in the main menu to delete the selected group of wires. The Delete command can also be executed by pressing Ctrl + Del or the Delete button on the toolbar.
- 138. 1 3 8 – A N - S O F U S E R G U I D E 6.7 WIRE COLOR Right clicking on a wire shows a pop-up menu, Fig. 6.1. Choose the Wire Color command to display a dialog box that allows us to select a color for the wire. This command is enabled when a wire is selected. The Wire Color command can also be accessed by first pressing the Select Wire button (arrow icon) on the toolbar, then left clicking on the wire to select it, and finally going to Edit > Wire Color in the main menu, Fig. 6.6. The Wire Color command is also available as a button on the toolbar. The color of a group of wires can be changed by first selecting the wires and next clicking on Edit > Wire Color in the main menu. A group of wires can be selected by expanding a selection box as explained in Section “6.5 Modifying a group of wires”. Fig. 6.6: Wire Color command in the Edit menu. This command is enabled when a wire or group of wires is selected.
- 139. 1 3 9 – A N - S O F U S E R G U I D E 6.8 VIEWING WIRE PROPERTIES Right clicking on a wire will display a pop-up menu, Fig. 6.1, where the Wire Properties command can be selected. The Wire Properties command can also be accessed by first pressing the Select Wire button (arrow icon) on the toolbar, then left clicking on the wire to select it, and finally going to Edit > Wire Properties in the main menu, Fig. 6.7. The Wire Properties command is also available as a button on the toolbar. Execute the Wire Properties command to display the Wire Properties dialog box, Fig. 6.8. There are three pages: Geometry, Attributes, and Materials. Fig. 6.7: Wire Properties command in the main menu. THE GEOMETRY PAGE It shows the geometrical properties of the selected wire, Fig. 6.8, namely, • Start Point: Coordinates of the start point of the selected wire. • End Point: Coordinates of the end point of the selected wire.
- 140. 1 4 0 – A N - S O F U S E R G U I D E • Length: Wire length. • Longest Segment: The length of the longest segment. • Shortest Segment: The length of the shortest segment. • Shortest Wavelength : The wavelength related to the highest frequency. • Length/: Wire length in wavelengths. The wavelength corresponds to the highest frequency. • Longest Segment/: Length of the longest wire segment in wavelengths. The wavelength corresponds to the highest frequency. • Shortest Segment/: Length of the shortest wire segment in wavelengths. The wavelength corresponds to the highest frequency. Fig. 6.8: Wire Properties dialog box. The Geometry page shows the geometrical properties of the selected wire.
- 141. 1 4 1 – A N - S O F U S E R G U I D E THE ATTRIBUTES PAGE It shows the electrical properties of the selected wire, Fig. 6.9, namely, • Number of Segments: The number of segments into which the selected wire has been divided. • Number of Sources: The number of sources placed on the wire. • Number of Loads: The number of loads placed on the wire. • Cross-Section: The cross-section type and its dimensions. • Equivalent Radius: The cross-section equivalent radius. • Equivalent Radius/: The cross-section equivalent radius as a fraction of the shortest wavelength. • Thin-Wire ratio: The wire diameter to the shortest segment length ratio. It must be less than 3 when the Exact Kernel option is unchecked in the Settings panel of the Setup tabsheet. Check the Exact Kernel option to be able to calculate with any value of the thin-wire ratio. For a non-circular cross-section, the wire diameter is two times the equivalent radius of the cross-section. Fig. 6.9: Wire Properties dialog box. The Attributes page shows the segmentation used for the selected wire, the number of sources and loads placed on the wire, and the type of cross section.
- 142. 1 4 2 – A N - S O F U S E R G U I D E THE MATERIALS PAGE It shows the properties of the materials the selected wire is made of, Fig. 6.10, namely, • Wire Resistivity: The resistivity of the selected wire in [Ohm m]. If the wire is coated, it is the resistivity of the internal conductor. • Wire Coating: The parameters of the coating shield of the selected wire. • Relative Permittivity: The permittivity or dielectric constant of the coating material relative to the permittivity of vacuum. • Relative Permeability: The magnetic permeability of the coating material relative to the permeability of vacuum. • Thickness: The thickness of the coating shield. Fig. 6.10: Wire Properties dialog box. The Materials page shows the material parameters of the conductive wire and its coating shield or insulation.
- 143. 1 4 3 – A N - S O F U S E R G U I D E 6.9 CONNECTING WIRES A wire junction is automatically established whenever the coordinates of a wire end are identical to the end coordinates of a wire previously specified. However, two wires will be also connected automatically when their ends are spaced one tenth of the wire radius. Wire junctions must be established to satisfy Kirchhoff's current law at the connection point. Figure 6.11 shows the correct and incorrect ways to connect two wires. To connect the end of wire 1 to a point on another wire 2 that is not another end, you must split wire 2 into two wires. So, three wires will be needed instead of two to make the connection. Fig. 6.11: Wrong and right ways to connect wires. Two wires can be connected by copying and pasting their ends. The following procedure will show how to connect the Start Point of a wire #1 to the Start Point of a wire #2. PROCEDURE FOR CONNECTING TWO WIRES AT THEIR ENDS 1. Right clicking on wire #1 will display a pop-up menu. 2. Choose the Copy Start Point or Copy End Point command from the pop-up menu. This command is also available in the Wire Properties window of the selected wire, Fig. 6.12. 3. In this example, wire #2 will be a Line. Then, choose Draw/Line in the main menu to display the Draw dialog box for the Line. 4. Press the From Point button to paste the copied point, Fig. 6.13. Then, complete the definition of wire #2.
- 144. 1 4 4 – A N - S O F U S E R G U I D E By means of this procedure, any number of wires can be connected at the same point. Fig. 6.12: Wire Properties dialog box. Click on the “Start Point” or “End Point” button to copy a wire end. Fig. 6.13: Draw dialog box for wire #2. Click on the “From Point” button to paste the copied end of wire #1.
- 145. 1 4 5 – A N - S O F U S E R G U I D E 6.10 PROJECT DETAILS Go to View > Project Details in the main menu to display the Project Details window, where a summary of the project information is shown, Figs. 6.14 and 6.15. There is also a button on the toolbar to access this window. The text in the Project Details window can be selected and copied to the clipboard in the usual way (Ctrl+C and Ctrl+V commands). Fig. 6.14: Project Details command in the main menu. Fig. 6.15: Project Details window.
- 146. 1 4 6 – A N - S O F U S E R G U I D E 6.11 TAPERED WIRES A tapered wire is a wire with a variable radius along its length. The cross section of tapered wires is always circular. The radius is varied linearly along the wire and in defined steps, then a wire with a stepped radius is obtained, as shown in Fig. 6.16. Fig. 6.16: Example of a tapered wire divided into 5 wire portions. Each portion is divided into 2 segments. Fig. 6.17: Draw/Tapered Wire option in the main menu.
- 147. 1 4 7 – A N - S O F U S E R G U I D E Go to Draw > Tapered Wire in the main menu and select a wire type for drawing, Fig. 6.17. The wire types available are the same as in the Draw menu. As an example, Fig. 6.18 shows the Line page of the Draw dialog box when a linear wire is selected. The wire must be divided into wire portions according to the desired steps in radius, as it is indicated in Fig. 6.16. Also, each wire portion having a uniform radius must be divided into segments as it is required by the Method of Moments used for the simulation. The number of wire portions and the number of segments per wire can be set by going to the Attributes tab, Fig. 6.19. In this page, the Start and End radii can be set. The resistivity for the conductive wire and its coating material can be set in the Materials tab, Fig. 6.20. In this case, a tapered coating shield can also be set by giving a Start and End thickness. The wire portions will be displayed in alternating colors for easy identification in the workspace. Fig. 6.18: Tapered Line page in the Draw dialog box. Go to main menu > Draw > Tapered Wire > Tapered Line.
- 148. 1 4 8 – A N - S O F U S E R G U I D E Fig. 6.19: Attributes page where the number of wire portions and segments per wire can be set, as well as Start and End radii. Fig. 6.20: Materials page where the wire resistivity and coating can be set. A tapered coating can be defined by giving the Start and End thicknesses.
- 149. 1 4 9 – A N - S O F U S E R G U I D E 6.12 MOVING, ROTATING AND SCALING WIRES After drawing the wire structure, we may need to modify the position or size of one wire or a group of them. To modify wires, we must first select them. Click on the Selection Box button on the toolbar and then expand a box using the mouse with the left button pressed. Enclose the wires you want to modify inside the box, Fig. 6.21. Fig. 6.21: “Selection Box” button on the toolbar to select a group of wires and commands in the Edit menu to move, rotate and scale the selected wires. After selecting the wires, go to the Edit menu, and choose one of these commands: Move Wires Displays the Move Wires dialog box for moving the selected wire or group of wires to a different position, Fig. 6.22. Rotate Wires Displays the Rotate Wires dialog box for rotating the selected wire or group of wires around the chosen axis, Fig. 6.23. Scale Wires Displays the Scale Wires dialog box for scaling the selected wire or group of wires according to the specified scale factor, Fig. 6.24.
- 150. 1 5 0 – A N - S O F U S E R G U I D E Fig. 6.22: Move Wires dialog box. Enter the desired offset at each coordinate. Fig. 6.23: Rotate Wires dialog box. Enter the axis of rotation, the center around which the wires will be rotated, and the desired angle. Fig. 6.24: Scale Wires dialog box. Enter the scale factor, which can be greater or less than 1 and if you want to scale the cross section of the wires as well.
- 151. 1 5 1 – A N - S O F U S E R G U I D E 6.13 COPYING AND STACKING WIRES When drawing a wire structure, it is often necessary to copy wires from one position to another. An antenna array is an example where this situation occurs. To copy wires, we must first select them by first pressing the Selection Box button on the toolbar and then expanding a box using the mouse to enclose the wires we wish to copy, as indicated in Fig. 6.21. In the Edit menu there are the following commands to copy the selected wires: Copy Wires Displays the Copy Wires dialog box for copying the selected wire or group of wires. The copied wires can then be pasted in a different position, Fig. 6.25. Stack Wires Displays the Stack Wires dialog box for stacking the selected wire or group of wires along the specified direction and according to the given number of wires in the stack, Fig. 6.26. Fig. 6.25: Copy Wires dialog box. Enter the offset of the copy relative to the original wires. Fig. 6.26: Stack Wires dialog box. Enter the axis, position, spacing and number of wires.
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- 153. 1 5 3 – A N - S O F U S E R G U I D E 7. WIRE GRIDS Build Metal Surfaces using Wire Grids WHAT ARE GRIDS? Wire grids can be composed of curved or straight wires and can be used to model grids and approximate conductive surfaces. The wires of a grid do not overlap but are connected to each other. See in this report the excellent accuracy obtained when modeling surfaces using grids. Go to View > Drawing Panel in the main menu to quickly access the wire grids. A VARIETY OF SHAPES AN-SOF offers different types of wire grids. Each type of grid has its own geometric parameters and attributes that can be set in a specific Draw dialog box. Go to Draw > Wire Grid in the main menu to see the following grid options: • Patch: Displays the Draw dialog box for drawing a rectangular patch on the xy-plane (z = 0). • Plate: Displays the Draw dialog box for drawing a plate or bilinear surface. • Disc: Displays the Draw dialog box for drawing a disc. • Flat Ring: Displays the Draw dialog box for drawing a flat ring or a disc with a hole at its center. • Cone: Displays the Draw dialog box for drawing a cone. • Truncated Cone: Displays the Draw dialog box for drawing a truncated cone. • Cylinder: Displays the Draw dialog box for drawing a cylinder. • Sphere: Displays the Draw dialog box for drawing a sphere. • Paraboloid: Displays the Draw dialog box for drawing a paraboloid.
- 154. 1 5 4 – A N - S O F U S E R G U I D E 7.1 PATCH The Patch refers to a rectangular patch on the xy-plane composed of wires having a flat or rectangular cross-section. Use this wire grid to model patch and microstrip antennas. Go to Draw > Wire Grid > Patch in the main menu to display the Draw dialog box for the Patch, Fig 7.1. There are three pages: Patch, Attributes and Materials, Fig. 7.2. THE PATCH PAGE In the Patch page the geometrical parameters for the Patch can be set. The Patch is defined by giving the coordinates of two opposite corner points in the xy-plane (z = 0), as shown in Fig. 7.3. Once the geometrical parameters in the Patch page have been set, the Attributes page can be chosen, where the number of facets of the Patch can be entered. Section 7.10 describes other parameters that can be set in the Attributes page. Section “5.9 Wire materials” describes the parameters that can be set in the Materials page. Fig. 7.1: The Draw/Wire Grid/Patch command in the main menu displays the Draw dialog box for the Patch.
- 155. 1 5 5 – A N - S O F U S E R G U I D E Fig. 7.2: Patch page of the Draw dialog box. Fig. 7.3: A Patch drawn using the input data of Fig. 7.2.
- 156. 1 5 6 – A N - S O F U S E R G U I D E 7.2 PLATE The Plate refers to a plate or bilinear surface. Go to Draw > Wire Grid > Plate in the main menu to display the Draw dialog box for the Plate, Fig 7.4. There are three pages: Plate, Attributes and Materials, Fig. 7.5. THE PLATE PAGE In the Plate page the geometrical parameters for the Plate can be set. The Plate is defined by giving the coordinates of four corner points. In general, a plate or bilinear surface is a non-planar quadrilateral, which is defined uniquely by its four vertices, as shown in Fig. 7.6. In this case, the bilinear surface degenerates into a flat quadrilateral. Once the geometrical parameters in the Plate page have been set, the Attributes page can be chosen, where the number of facets of the Plate can be entered. Section 7.10 describes other parameters that can be set in the Attributes page. Section “5.9 Wire materials” describes the parameters that can be set in the Materials page. Fig. 7.4: The Draw > Wire Grid > Plate command in the main menu displays the Draw dialog box for the Plate.
- 157. 1 5 7 – A N - S O F U S E R G U I D E Fig. 7.5: Plate page of the Draw dialog box. Fig. 7.6: A Plate drawn using the input data of Fig. 7.5.
- 158. 1 5 8 – A N - S O F U S E R G U I D E 7.3 DISC The Disc refers to a disc or circular surface. Go to Draw > Wire Grid > Disc in the main menu to display the Draw dialog box for the Disc, Fig 7.7. There are three pages: Disc, Attributes and Materials, Fig. 7.8. THE DISC PAGE In the Disc page the geometrical parameters for the Disc can be set. There is a combo-box with two options: Curved segments and Straight segments. Choose Curved segments for an exact representation of the disc curvature. The Straight segments option is an approximation using linear wires. The Disc is defined by giving the Center coordinates, Radius and orientation angles, Theta and Phi. A disc is a planar surface, which is defined uniquely by these parameters, as shown in Fig. 7.9. Once the geometrical parameters in the Disc page have been set, the Attributes page can be chosen, where the number of facets of the Disc can be entered. Section 7.10 describes other parameters that can be set in the Attributes page. Section “5.9 Wire materials” describes the parameters that can be set in the Materials page. Fig. 7.7: The Draw > Wire Grid > Disc command in the main menu displays the Draw dialog box for the Disc.
- 159. 1 5 9 – A N - S O F U S E R G U I D E Fig. 7.8: Disc page of the Draw dialog box. Fig. 7.9: A Disc drawn using the input data of Fig. 7.8.
- 160. 1 6 0 – A N - S O F U S E R G U I D E 7.4 FLAT RING The Flat Ring refers to a disc with a hole at its center. Go to Draw > Wire Grid > Flat Ring in the main menu to display the Draw dialog box for the Flat Ring, Fig 7.10. There are three pages: Flat Ring, Attributes and Materials, Fig. 7.11. THE FLAT RING PAGE In the Flat Ring page, the geometrical parameters for the Flat Ring can be set. There is a combo-box with two options: Curved segments and Straight segments. Choose Curved segments for an exact representation of the flat ring curvature. The Straight segments option is an approximation using linear wires. The Flat Ring is defined by giving the Center coordinates, Inner Radius (hole radius), Outer Radius and orientation angles, Theta and Phi. A flat ring is a planar surface, which is defined uniquely by these parameters, as shown in Fig. 7.12. Once the geometrical parameters in the Flat Ring page have been set, the Attributes page can be chosen, where the number of facets of the Flat Ring can be entered. Section 7.10 describes other parameters that can be set in the Attributes page. Section “5.9 Wire materials” describes the parameters that can be set in the Materials page. Fig. 7.10: The Draw > Wire Grid > Flat Ring command in the main menu displays the Draw dialog box for the Flat Ring.
- 161. 1 6 1 – A N - S O F U S E R G U I D E Fig. 7.11: Flat Ring page of the Draw dialog box. Fig. 7.12: A Flat Ring drawn using the input data of Fig. 7.11.
- 162. 1 6 2 – A N - S O F U S E R G U I D E 7.5 CONE Go to Draw > Wire Grid > Cone in the main menu to display the Draw dialog box for the Cone, Fig 7.13. There are three pages: Cone, Attributes and Materials, Fig. 7.14. THE CONE PAGE In the Cone page the geometrical parameters for the Cone can be set. There is a combo-box with two options: Curved segments and Straight segments. Choose Curved segments for an exact representation of the cone curvature. The Straight segments option is an approximation using linear wires. The Cone is defined by giving the Vertex coordinates, Aperture Angle, Aperture Radius and orientation angles, Theta and Phi. A cone is a surface which is defined uniquely by these parameters, as shown in Fig. 7.15. Once the geometrical parameters in the Cone page have been set, the Attributes page can be chosen, where the number of facets of the Cone can be entered. Section 7.10 describes other parameters that can be set in the Attributes page. Section “5.9 Wire materials” describes the parameters that can be set in the Materials page. Fig. 7.13: The Draw > Wire Grid > Cone command in the main menu displays the Draw dialog box for the Cone.
- 163. 1 6 3 – A N - S O F U S E R G U I D E Fig. 7.14: Cone page of the Draw dialog box. Fig. 7.15: A Cone drawn using the input data of Fig. 7.14.
- 164. 1 6 4 – A N - S O F U S E R G U I D E 7.6 TRUNCATED CONE Go to Draw > Wire Grid > Truncated Cone in the main menu to display the Draw dialog box for the Truncated Cone, Fig 7.16. There are three pages: Truncated Cone, Attributes and Materials, Fig. 7.17. THE TRUNCATED CONE PAGE In the Truncated Cone page, the geometrical parameters for the Truncated Cone can be set. There is a combo-box with two options: Curved segments and Straight segments. Choose Curved segments for an exact representation of the truncated cone curvature. The Straight segments option is an approximation using linear wires. The Truncated Cone is defined by giving the Base Point coordinates, Base Radius, Top Radius, Aperture angle and orientation angles, Theta and Phi. A truncated cone is a surface which is defined uniquely by these parameters, as shown in Fig. 7.18. A truncated cone can degenerate into a cylinder, a cone, a disc, or a flat ring. Once the geometrical parameters in the Truncated Cone page have been set, the Attributes page can be chosen, where the number of facets of the Truncated Cone can be entered. Section 7.10 describes other parameters that can be set in the Attributes page. Section “5.9 Wire materials” describes the parameters that can be set in the Materials page. Fig. 7.16: The Draw > Wire Grid > Truncated Cone command in the main menu displays the Draw dialog box for the Truncated Cone.
- 165. 1 6 5 – A N - S O F U S E R G U I D E Fig. 7.17: Truncated Cone page of the Draw dialog box. Fig. 7.18: A Truncated Cone drawn using the input data of Fig. 7.17.
- 166. 1 6 6 – A N - S O F U S E R G U I D E 7.7 CYLINDER Go to Draw > Wire Grid > Cylinder in the main menu to display the Draw dialog box for the Cylinder, Fig 7.19. There are three pages: Cylinder, Attributes and Materials, Fig. 7.20. THE CYLINDER PAGE In the Cylinder page the geometrical parameters for the Cylinder can be set. There is a combo-box with two options: Curved segments and Straight segments. Choose Curved segments for an exact representation of the cylinder curvature. The Straight segments option is an approximation using linear wires. The Cylinder is defined by giving the Base Point coordinates, Length, Radius and orientation angles, Theta and Phi. A cylinder is a surface which is defined uniquely by these parameters, as shown in Fig. 7.21. Once the geometrical parameters in the Cylinder page have been set, the Attributes page can be chosen, where the number of facets of the Cylinder can be entered. Section 7.10 describes other parameters that can be set in the Attributes page. Section “5.9 Wire materials” describes the parameters that can be set in the Materials page. Fig. 7.19: The Draw > Wire Grid > Cylinder command in the main menu displays the Draw dialog box for the Cylinder.
- 167. 1 6 7 – A N - S O F U S E R G U I D E Fig. 7.20: Cylinder page of the Draw dialog box. Fig. 7.21: A Cylinder drawn using the input data of Fig. 7.20.
- 168. 1 6 8 – A N - S O F U S E R G U I D E 7.8 SPHERE Go to Draw > Wire Grid > Sphere in the main menu to display the Draw dialog box for the Sphere, Fig 7.22. There are three pages: Sphere, Attributes and Materials, Fig. 7.23. THE SPHERE PAGE In the Sphere page the geometrical parameters for the Sphere can be set. There is a combo- box with two options: Curved segments and Straight segments. Choose Curved segments for an exact representation of the sphere curvature. The Straight segments option is an approximation using linear wires. The Sphere is defined by giving the Center coordinates, Radius and orientation angles, Theta and Phi. A sphere is a surface which is defined uniquely by these parameters, as shown in Fig. 7.24. Once the geometrical parameters in the Sphere page have been set, the Attributes page can be chosen, where the number of facets of the Sphere can be entered. Section 7.10 describes other parameters that can be set in the Attributes page. Section “5.9 Wire materials” describes the parameters that can be set in the Materials page. Fig. 7.22: The Draw > Wire Grid > Sphere command in the main menu displays the Draw dialog box for the Sphere.
- 169. 1 6 9 – A N - S O F U S E R G U I D E Fig. 7.23: Sphere page of the Draw dialog box. Fig. 7.24: A Sphere drawn using the input data of Fig. 7.23.
- 170. 1 7 0 – A N - S O F U S E R G U I D E 7.9 PARABOLOID Go to Draw > Wire Grid > Paraboloid in the main menu to display the Draw dialog box for the Paraboloid, Fig 7.25. There are three pages: Paraboloid, Attributes and Materials, Fig. 7.26. THE PARABOLOID PAGE In the Paraboloid page the geometrical parameters for the Paraboloid can be set. There is a combo-box with two options: Curved segments and Straight segments. Choose Curved segments for an exact representation of the paraboloid curvature. The Straight segments option is an approximation using linear wires. The Paraboloid is defined by giving the Vertex coordinates, Focal Distance, Aperture Radius and orientation angles, Theta and Phi. A paraboloid is a curved surface which is defined uniquely by these parameters, as shown in Fig. 7.27. Once the geometrical parameters in the Paraboloid page have been set, the Attributes page can be chosen, where the number of facets of the Paraboloid can be entered. Section 7.10 describes other parameters that can be set in the Attributes page. Section “5.9 Wire materials” describes the parameters that can be set in the Materials page. Fig. 7.25: The Draw > Wire Grid > Paraboloid command in the main menu displays the Draw dialog box for the Paraboloid.
- 171. 1 7 1 – A N - S O F U S E R G U I D E Fig. 7.26: Paraboloid page of the Draw dialog box. Fig. 7.27: A Paraboloid drawn using the input data of Fig. 7.26.
- 172. 1 7 2 – A N - S O F U S E R G U I D E 7.10 WIRE GRID ATTRIBUTES The Attributes page belongs to the Draw dialog box of the chosen wire grid type. As an example, Fig. 7.28 shows the Attributes page for the Plate, but all wire grids have the same Attributes page. In this page the following parameters can be set: NUMBER OF FACETS Every wire grid has a certain number of facets. For instance, the plate in Fig. 7.6 has 10x10 facets and the disc in Fig 7.9 has 6x12 facets. Each facet is a quadrilateral made up of four wires, and each wire is divided into segments. An unknown current on each wire segment must be found in the simulation process. Any curved or straight wire that makes up a grid can be edited individually. Refer to chapter “6. Editing Wires” to edit wires. SEGMENTS PER WIRE It sets the number of segments for each wire in the grid. If the Segments per Wire is set to zero, each wire will be divided into segments according to the shortest wavelength or highest frequency. Fig. 7.28: Attributes page in the Draw dialog box for the Plate. CROSS-SECTION The cross-section of the wires in a grid is circular. Infinitesimally thin wires are not allowed, so the cross-section radius “a” must be greater than zero.
- 173. 1 7 3 – A N - S O F U S E R G U I D E 7.11 MODIFYING A WIRE GRID A wire grid can be modified by the procedure described in Section 6.5 for a group of wires. Click on the Selection Box button on the main toolbar. By left clicking on the workspace and dragging a box with the mouse, a wire grid can be selected, Fig. 7.29. All wires inside the selection box will be highlighted in light blue. Go to Edit > Modify (Ctrl + M) in the main menu to modify the selected wires. There is also a button on the toolbar with the Modify command. This command is enabled when a wire grid is selected. Refer to Section "6.5 Modifying a group of wires" to see the description of the dialog window that allows us to modify the selected wires. Refer to Sections "6.12 Moving, rotating and scaling wires" and "6.13 Copying and stacking wires" to move, rotate, resize, copy, or stack wire grids. Fig. 7.29: A wire grid selected by the Selection Box.
- 174. 1 7 4 – A N - S O F U S E R G U I D E 7.12 DELETING A WIRE GRID Click on the Selection Box button in the main toolbar. By left clicking on the workspace and dragging a box with the mouse, a wire grid can be selected, as shown in Fig. 7.29. All wires inside the selection box will be highlighted in light blue. Got to Edit > Delete (Ctrl +Del) in the main menu to delete the selected wire grid. There is also a button on the toolbar with the Delete command. This command is enabled when a wire grid is selected.
- 175. 1 7 5 – A N - S O F U S E R G U I D E 7.13 WIRE GRID COLOR Click on the Selection Box button in the main toolbar. By left clicking on the workspace and dragging a box with the mouse, a wire grid can be selected, as shown in Fig. 7.29. All wires inside the selection box will be highlighted in light blue. Got to Edit > Wire Color in the main menu to change the color of the selected wire grid. A dialog window will be opened where a color can be chosen. There is also a button on the toolbar with the Wire Color command. This command is enabled when a wire grid is selected.
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- 177. 1 7 7 – A N - S O F U S E R G U I D E 8. SOURCES AND LOADS How to Excite the Structure and Connect Load Impedances SYMBOLS AND TIPS Sources are displayed as a yellow circle in the workspace, while loads are displayed as a green highlighted segment. To change the default colors, go to main menu > Tools > Preferences > Workspace tab. Voltage sources have their internal impedance in series, so set a null impedance to model a perfect source. Current sources have their internal impedance in parallel, so set a very large impedance (1E6 Ohm) to model a nearly perfect source. TYPES OF EXCITATIONS AND LOADS A structure can be excited by discrete sources or an incident field. Refer to chapter 9 for the second case. Discrete sources can be located on any wire segment and there can be more than one source, as many as there are segments. A source is used to model the feed point of a transmitting antenna or generator in an electrical circuit. There are two types of sources: • Voltage sources • Current sources Current sources can be used to model impressed currents. For each source, its amplitude and phase must be set. Internal impedances can also be added to model imperfect sources, which can be series RL or RC impedances. Lumped loads can also be added to any wire segment, representing resistors, inductors, or capacitors. There are two types of loads: • Inductive (series RL impedance) • Capacitive (series RC impedance) To model a pure resistor, add an inductive impedance with L = 0. The unit of inductance can be pH, nH, uH, mH or H, while that of capacitance can be pF, nF, uF, mF or F. These units can be set going to main menu > Tools > Preferences.
- 178. 1 7 8 – A N - S O F U S E R G U I D E 8.1 CHOOSING SOURCES AS THE EXCITATION To excite the wire structure with discrete sources, go to the Setup tab > Excitation panel and select the Discrete Sources option, Fig. 8.1. If the Set Input Power option is checked, the total input power to the structure can be set. So, the amplitudes of the voltage and current sources will be adjusted to achieve the specified input power. Fig. 8.1: Discrete Sources option in the Excitation panel of the Setup tabsheet.
- 179. 1 7 9 – A N - S O F U S E R G U I D E 8.2 THE SOURCE/LOAD TOOLBAR The Source/Load toolbar is used to place a source or load in a selected segment on a given wire. Sources and loads can also be edited with this toolbar. By right clicking on any part of a wire a pop-up menu will be displayed, Fig. 8.2. Click on the Source/Load command from the pop-up menu to display the Source/Load toolbar, Fig. 8.4. The Source/Load command can also be accessed from the main toolbar or going to main menu > Edit > Source/Load (Ctrl + Ins), Fig. 8.3. For this command to be enabled, first click on the Select Wire button (arrow icon) on the main toolbar and then left click on the wire where you want to place the source or load. Fig. 8.2: Source/Load command in the pop-up menu.
- 180. 1 8 0 – A N - S O F U S E R G U I D E Fig. 8.3: Source/Load command in the main menu. The Source/Load toolbar has the following components: Fig. 8.4: Source/Load toolbar. THE SLIDER Each position of the slider corresponds to the position of a segment in the selected wire. So, the slider allows us selecting a particular segment on the wire. At the right corner of this toolbar, the position of the selected segment is shown. The segment position as a percentage of the wire length is also shown. It is measured from the starting point of the wire to the middle point of the selected segment, and it is defined as follows: % position = 100 (position / wire length)
- 181. 1 8 1 – A N - S O F U S E R G U I D E THE 50% BUTTON This button positions the slider at the middle of the wire. Often discrete sources and loads are added at the center of wires, so click on this button to select the segment at the wire center quickly. Note that the wire must have an odd number of segments for it to have a segment at its center. THE ADD SOURCE BUTTON Click on the Add Source button to display a dialog box for adding a source to the selected wire segment, Fig. 8.5. This dialog box allows us setting the type of source, its amplitude, phase and internal impedance. Fig. 8.5: Add Source dialog box. THE ADD LOAD BUTTON Click on the Add Load button to display a dialog box for adding a load to the selected wire segment, Fig. 8.6. A load can represent a resistor in series with an inductor (RL) or a resistor in series with a capacitor (RC).
- 182. 1 8 2 – A N - S O F U S E R G U I D E Fig. 8.6: Add Load dialog box. THE DELETE BUTTON If the selected segment has a source or a load on it, the Delete button will be enabled. Click on this button to delete the source or load placed in the segment. THE MODIFY BUTTON If the selected segment has a source or a load on it, the Modify button will be enabled. Click on this button to display the Modify dialog box, where the source or load can be edited. THE EXIT BUTTON Click on the Exit button to close the Source/Load toolbar.
- 183. 1 8 3 – A N - S O F U S E R G U I D E 8.3 ADDING SOURCES A source can be added to a selected wire segment by means of the following steps: 1. Right click on any part of a wire to display the pop-up menu, Fig. 8.2. 2. Choose the Source/Load command from the pop-up menu to display the Source/Load toolbar, Fig. 8.4. 3. Move the slider to select the desired segment. 4. Click on the Add Source button to display the Add Source dialog box, Fig. 8.5. 5. Set the type of source, its amplitude (rms value), phase and internal impedance. Then, press the OK button. 6. Click on the Exit button to close the Source/Load toolbar.
- 184. 1 8 4 – A N - S O F U S E R G U I D E 8.4 EDITING SOURCES A source can be edited by means of the following steps: 1. Right click on any part of a wire to display the pop-up menu, Fig. 8.2. 2. Choose the Source/Load command from the pop-up menu to display the Source/Load toolbar, Fig. 8.4. 3. Move the slider to select the segment where the source is placed. 4. Click on the Modify button to display a dialog box where the source can be edited. The source can be deleted by clicking on the Delete button. 5. Click on the Exit button to close the Source/Load toolbar.
- 185. 1 8 5 – A N - S O F U S E R G U I D E 8.5 ADDING LOADS A load can be added to a selected wire segment by means of the following steps: 1. Right click on any part of a wire to display the pop-up menu, Fig. 8.2. 2. Choose the Source/Load command from the pop-up menu to display the Source/Load toolbar, Fig. 8.4. 3. Move the slider to select the desired segment. 4. Click on the Add Load button to display the Add Load dialog box, Fig. 8.6. 5. Set the type of load and the values of resistance and inductance or capacitance. Then, press the OK button. 6. Click on the Exit button to close the Source/Load toolbar.
- 186. 1 8 6 – A N - S O F U S E R G U I D E 8.6 EDITING LOADS A load can be edited by means of the following steps: 1. Right click on any part of a wire to display the pop-up menu, Fig. 8.2. 2. Choose the Source/Load command from the pop-up menu to display the Source/Load toolbar, Fig. 8.4. 3. Move the slider to select the segment where the load is placed. 4. Click on the Modify button to display a dialog box where the load can be edited. The load can be deleted by clicking on the Delete button. 5. Click on the Exit button to close the Source/Load toolbar.
- 187. 1 8 7 – A N - S O F U S E R G U I D E 8.7 ENABLING/DISABLING LOADS All the loads can be enabled or disabled at the same time. This option avoids deleting the load impedances when loads must not be considered in a simulation. Go to Setup tab > Settings panel in the main window. If the option Load Impedances is checked, the loads are enabled, otherwise they are disabled, Fig. 8.7 Fig. 8.7: Load impedances option in the Settings panel of the Setup tabsheet.
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- 189. 1 8 9 – A N - S O F U S E R G U I D E 9. EXCITATION BY AN INCIDENT FIELD Illuminating the Structure with a Plane Wave 9.1 CHOOSING AN INCIDENT FIELD AS EXCITATION To choose an incident plane wave as excitation of the structure, go to the Setup tab/ Excitation panel and select the Incident Field option, Fig. 9.1. When this option is selected, if there are discrete sources on the structure, none will be considered in the simulation. Fig. 9.1: Incident Field option in the Excitation panel of the Setup tabsheet.
- 190. 1 9 0 – A N - S O F U S E R G U I D E 9.2 INCIDENT FIELD PARAMETERS The following incident field parameters can be set in the Excitation panel of the Setup tabsheet after clicking on the Incident Field option: • E-FIELD MAJOR AXIS: Amplitude, in V/m (Volts rms per meter), of the linearly polarized incoming electric field. For elliptical polarization, it is the length of the major ellipse axis. • AXIAL RATIO: For an elliptically polarized plane wave, it is the ratio of the minor axis to the major axis of the ellipse. A positive (negative) axial ratio defines a right-handed (left-handed) ellipse. If the axial ratio is set to zero, a linearly polarized plane wave is defined. • PHASE REFERENCE: Phase, in degrees, of the incident plane wave at the origin of coordinates. It can be used to change the phase reference in the calculation. Its value only shifts all phases in the structure by the given amount. • GAMMA: Polarization angle of the incident electric field in degrees. For a linearly polarized wave, Gamma is measured from the plane of incidence to the direction of the electric field vector, Fig. 9.2. For an elliptically polarized wave, Gamma is the angle between the plane of incidence and the major ellipse axis. • THETA: Zenith angle of the incident direction in degrees, Fig. 9.2. • PHI: Azimuth angle of the incident direction in degrees, Fig. 9.2. IMPORTANT INFORMATION When an incident plane wave is used as excitation, all discrete sources, if any, will not be considered in the simulation.
- 191. 1 9 1 – A N - S O F U S E R G U I D E Fig. 9.2: Parameters of an incident field.
- 192. 1 9 2 – A N - S O F U S E R G U I D E 9.3 THE 3D-VIEW INTERFACE The 3D-View interface allows us entering the parameters of the incident field in a graphical way. Follow these steps: 1. Go to the Setup tabsheet and select the Incident Field option in the Excitation panel. 2. Click on the 3D View button to open the interface and display the Incident Wave dialog box, Fig. 9.3. 3. Set the Gamma, Theta and Phi angles and press ENTER. You can also use the small arrows to change these angles. 4. Close the Incident Wave dialog box. The angles that have been entered in the dialog box will appear in the Excitation panel, Fig. 9.4. Fig. 9.3: 3D-View interface for the definition of the incident field. The Incident Wave dialog box is also shown. Gamma, Theta, and Phi are set to –45, 45 and –100 deg., respectively.
- 193. 1 9 3 – A N - S O F U S E R G U I D E Fig. 9.4: The Gamma, Theta and Phi angles entered in the Incident Wave dialog box will appear in the Excitation panel of the Setup tabsheet.
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- 195. 1 9 5 – A N - S O F U S E R G U I D E 10. GROUND PLANES Adding a Ground Plane to the Antenna Environment 10.1 ADDING A PEC GROUND PLANE A perfectly electric conducting (PEC) ground plane, parallel to the xy-plane, can be added to the model by means of the following procedure: 1. Go to Setup tab > Environment panel. 2. Select the Perfect option in the Ground Plane box, Fig. 10.1. 3. Set the ground plane position under the Position label (Z-coordinate). When the perfect ground is selected, an infinite PEC ground plane will be placed at the specified position, Z, from the xy-plane. • If Z is positive, the PEC ground plane will be above the xy-plane. • If Z is zero, the PEC ground plane will be the xy-plane. • If Z is negative, the PEC ground plane will be below the xy-plane. Fig. 10.1: Perfect option in the Ground plane box of the Environment panel.
- 196. 1 9 6 – A N - S O F U S E R G U I D E 10.2 ADDING A REAL GROUND PLANE A real ground plane, located on the xy-plane (Z = 0), can be added to the model by means of the following procedure: 1. Go to Setup tab > Environment panel. 2. Select the Real option in the Ground Plane box, Fig. 10.2. 3. Specify the Real Ground Option: Sommerfeld-Wait/Asymptotic, Reflection Coefficients/Asymptotic, or Radial Wire Ground Screen. Refer to Section “4.3 Defining the Environment”. 4. Set the ground Permittivity and Conductivity. Also, set the radial length, number of radials and wire radius if a ground screen has been chosen. Fig. 10.2: Real option in the Ground Plane box of the Environment panel.
- 197. 1 9 7 – A N - S O F U S E R G U I D E 10.3 ADDING A DIELECTRIC SUBSTRATE A dielectric substrate, located below the xy-plane (Z < 0), can be added to the model by means of the following procedure: 1. Go to Setup tab > Environment panel. 2. Select the Substrate option in the Ground Plane box, Fig. 10.3. 3. Choose an infinite or finite slab in the Substrate Slab Options box. 4. Specify the substrate Permittivity and Thickness (h). Also set the widths along the X and Y axes if a finite slab has been chosen. The substrate slab is backed up by a PEC ground plane parallel to the xy-plane and located at Z = -h. This ground plane cannot be removed from the simulation. Fig. 10.3: Substrate option in the Ground Plane box of the Environment panel.
- 198. 1 9 8 – A N - S O F U S E R G U I D E 10.4 CONNECTING WIRES TO THE GROUND A wire will automatically connect to the ground plane when the z coordinate of one of its ends coincides with the position of the ground plane. • When a PEC ground plane is chosen, the ground position is specified by the value of Z in the Environment panel > Ground Plane box (refer to Section “10.1 Adding a PEC ground plane”). • When a real ground is chosen, the ground position is Z = 0 (xy-plane). • When a substrate is chosen, a PEC ground plane is placed at Z = -h (h: substrate thickness). Wire connections to the ground plane are shown with 3D symbols, Fig. 10.4. Fig. 10.4: 3D symbols showing ground connections. IMPORTANT INFORMATION All wires must be above the ground plane. Wires that cross the ground plane from one side to the other are not allowed.
- 199. 1 9 9 – A N - S O F U S E R G U I D E 10.5 REMOVING THE GROUND PLANE To remove the ground plane, do the following: 1. Go to Setup tab > Environment panel. 2. Choose the None option in the Ground Plane box, Fig. 10.5. Fig. 10.5: None option in the Ground Plane box of the Environment panel.
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- 201. 2 0 1 – A N - S O F U S E R G U I D E 11. TOOLS IN THE WORKSPACE How to Control the 3D View of the Structure 11.1 DISPLAY OPTIONS The background of the workspace can be white or black. When a white (black) background is chosen, all wires will default to black (white) unless a different color is specified for certain wires. The workspace color can be set by going to Tools > Preferences > Workspace tab. The color of selected wires and wire grids can be changed at any time via Edit > Wire Color in the main menu. The width of the line used for drawing wires and axes in the workspace can be changed by selecting a Pen Width option in the Workspace tab of the Preferences dialog box. There are three levels: Thin, Medium, and Thick. Figure 11.1 illustrates the different combinations between the workspace color and pen width that can be obtained. Fig. 11.1: Display options in the workspace.
- 202. 2 0 2 – A N - S O F U S E R G U I D E 11.2 VIEWING 3D AXES To change the appearance of the X, Y, Z axes in the workspace go to View > Axes (Ctrl + A) in the main menu to display the Axes dialog box, Fig. 11.2. There are two types of axes, the Small Axes, and the Main Axes. The small axes are displayed in the lower left corner of the workspace, while the main axes are displayed in the center of the screen. Fig. 11.2: Axes dialog box. Positive and negative axes can be displayed. Both positive and negative axes can be displayed. The color of the main axes can be changed by pressing the Color button. Check the Show Ticks option to add the specified number of ticks to the Main Axes. TIP Press F7 to switch between small and main axes.
- 203. 2 0 3 – A N - S O F U S E R G U I D E 11.3 ZOOMING THE VIEW Move the mouse wheel to zoom in/out the view of the structure in the workspace or use two fingers on a laptop touchpad as it is usual when zooming an image. You can also use the Zoom In (Ctrl + I) and Zoom Out (Ctrl + K) commands from the View menu. You can also zoom by first pressing the Zoom button on the toolbar and then moving the mouse over the workspace with the left button pressed.
- 204. 2 0 4 – A N - S O F U S E R G U I D E 11.4 ROTATING THE VIEW To rotate the view of the structure around the desired axis, first press one of these buttons on the toolbar: Rotate around X/Y/Z/3D Rotation Then, move the mouse over the screen with the left button pressed. The view can also be rotated by pressing the following keys: • F1: Right-handed rotation around the x-axis. • F2: Left-handed rotation around the x-axis. • F3: Right-handed rotation around the y-axis. • F4: Left-handed rotation around the y-axis. • F5: Right-handed rotation around the z-axis. • F6: Left-handed rotation around the z-axis.
- 205. 2 0 5 – A N - S O F U S E R G U I D E 11.5 MOVING THE VIEW The view of the structure can be moved in the workspace. First press the Move button on the toolbar and then move the mouse over the screen with the left button pressed. TIP Double-click on the workspace to center the view of the structure on the screen.
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- 207. 2 0 7 – A N - S O F U S E R G U I D E 12. RUNNING THE CALCULATIONS Commands to Start the Calculation Engine 12.1 THE RUN ALL COMMAND Once the frequencies, the environment, the geometry of the structure, the excitation, and the points of observation of the radiated field have been set, AN-SOF is ready to execute the calculations. First, the current distribution on the wire segments will be calculated, which allows us to obtain the input impedance when we have a transmitting antenna. Later, the far and near fields can be calculated from the currents in the segments. The Run ALL (F10) command allows us to run the calculation of the current distribution and the near and far fields sequentially and automatically. Go to main menu > Run > Run ALL to run this command, Fig. 12.1, or click on the Run ALL button on the toolbar. Fig. 12.1: The Run ALL command in the main menu. There are also buttons on the toolbar to run the calculations. If the near field is not required, the calculation can only be run for currents and far fields by clicking on the Run > Run Currents and Far-Field (F11) command. This command is also available on the toolbar. If the far field is not required, the calculation can only be run for currents and near fields by clicking on the Run > Run Currents and Near-Field (F12) command. This command is also available on the toolbar. The currents, far and near fields can be computed separately as it is explained in the next sections.
- 208. 2 0 8 – A N - S O F U S E R G U I D E 12.2 CALCULATING THE CURRENT DISTRIBUTION When the frequencies, the environment, the geometry, and the excitation are set, AN-SOF is ready to compute the currents flowing on the wire segments. Go to Run > Run Currents in the main menu to run the calculation of the current distribution, Fig. 12.2. Fig. 12.2: The Run Currents command in the main menu. TIP When we are modeling a transmitting antenna and we only need the input impedance, this command allows us to save time since the radiated field is not calculated.
- 209. 2 0 9 – A N - S O F U S E R G U I D E 12.3 CALCULATING THE FAR FIELD Once the current distribution on the structure has been obtained, the far-field in the angular ranges set in the Far-Field panel of the Setup tabsheet can be computed. Go to Run > Run Far-Field in the main menu to run the calculation of the far-field, Fig. 12.3. This command is only enabled when the current distribution has already been calculated. Fig. 12.3: The Run Far-Field command in the main menu. TIP To run the calculation of the current distribution and the far field sequentially and automatically, click on the Run Currents and Far-Field (F11) button on the toolbar.
- 210. 2 1 0 – A N - S O F U S E R G U I D E 12.4 CALCULATING THE NEAR E-FIELD Once the current distribution on the structure has been obtained, the near electric field at those points in space set in the Near-Field panel of the Setup tabsheet can be computed. Go to Run > Run Near E-Field in the main menu to run the calculation of the near electric field, Fig. 12.4. This command is only enabled when the current distribution has already been calculated. Fig. 12.4: The Run Near E-Field command in the main menu. TIP To run the calculation of the current distribution and the near fields sequentially and automatically, click on the Run Currents and Near-Field (F12) button on the toolbar. This command also runs the calculation of the near magnetic field. To avoid this calculation, go to main menu > Tools > Preferences > Options and uncheck the “Run ALL” also calculates the H-field option.
- 211. 2 1 1 – A N - S O F U S E R G U I D E 12.5 CALCULATING THE NEAR H-FIELD Once the current distribution on the structure has been obtained, the near magnetic field at those points in space set in the Near-Field panel of the Setup tabsheet can be computed. Go to Run > Run Near H-Field in the main menu to run the calculation of the near magnetic field, Fig. 12.5. This command is only enabled when the current distribution has already been calculated. Fig. 12.5: The Run Near H-Field command in the main menu. TIP To run the calculation of the current distribution and the near fields sequentially and automatically, click on the Run Currents and Near-Field (F12) button on the toolbar. This command also runs the calculation of the near electric field. Go to Tools > Preferences > Options in the main menu and check the “Run ALL” also calculates the H-Field option to enable the calculation of the H-field.
- 212. 2 1 2 – A N - S O F U S E R G U I D E 12.6 ABORTING THE CALCULATIONS When a calculation is executed using the commands described in the previous sections, the Processing window will be displayed, Fig. 12.6. There is a button to abort the calculation at any time. Note that you will be prompted to save the project before aborting, as AN-SOF will restart. Fig. 12.6: The Processing window.
- 213. 2 1 3 – A N - S O F U S E R G U I D E 12.7 NUMERICAL GREEN’S FUNCTION There are simulations where we need to change the excitation of the structure frequently. For example, when we must often change the amplitudes of discrete sources or the direction of arrival of an incident field. In these cases, we can save a lot of time by checking the NGF (Numerical Green’s Function) option in the Settings panel of the Setup tab, Fig. 12.7. When a NGF calculation is performed, the LU-decomposed matrix of the system is stored in a file after the first calculation. Then, by reusing this stored matrix, new calculations are performed faster than the first one. Fig. 12.7: NGF option in the Settings panel of the Setup tabsheet.
- 214. 2 1 4 – A N - S O F U S E R G U I D E 12.8 RUNNING A BULK SIMULATION AN-SOF can import a sequence of input files to obtain a corresponding sequence of output files, without user intervention in the middle of the process. The input files must be in NEC format and have “.nec” extension. The NEC commands supported are described in Section “5.13 Importing wires”. The output data include power budget or RCS, input impedances, far field, and near fields in CSV format. An individual AN-SOF project is generated (.emm and .wre files) for each NEC input file, so each project can be opened separately after the bulk simulation is finished. To run a bulk simulation, go to main menu > Run > Run Bulk Simulation. A message will appear asking if you want to save the changes in the current project, since the bulk simulation requires closing the project that is currently open. Then, a dialog box will be displayed where a directory and the input .nec files can be selected. After selecting the desired files and clicking on the Open button, the bulk simulation will begin. The input files will be imported and computed one after another. Fig. 12.8: Run Bulk Simulation option in the main menu. As an example, for a given input file called “InputFile.nec”, the following files will be generated: FILES OF THE AN-SOF PROJECT InputFile.emm > main file of the project (it can be opened with AN-SOF) InputFile.wre > geometry data (wires, segments, connections) InputFile.txt > comments
- 215. 2 1 5 – A N - S O F U S E R G U I D E InputFile.cur > current distribution InputFile.pwr > input and radiated powers, directivity, gain, etc. InputFile.the > Theta component of the far field InputFile.phi > Phi component of the far field InputFile.nef > near electric field InputFile.nhf > near magnetic field OUTPUT CSV FILES WITH RESULTS InputFile_PowerBudget.csv > input and radiated power, efficiency, gain, etc. InputFile_Zin.csv > input impedances InputFile_FarFieldX.csv > E-theta and E-phi far field components InputFile_EFieldX.csv > near electric field components InputFile_HFieldX.csv > near magnetic field components where “X” is the frequency in Hz (e.g., X = 300000000 for a frequency of 300 MHz). So, a FarField, EField and HField file will be generated for each frequency if a frequency sweep simulation has been set.
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- 217. 2 1 7 – A N - S O F U S E R G U I D E 13. DISPLAYING RESULTS Display Tables and Graphs with the Output Data LISTS AND PLOTS Listing the currents or input impedances means tabulating them as a function of frequency. In the case of fields, they can be listed at a given point versus the frequency (Spectrum) or at a given frequency versus the observation point (Pattern). AN-SOF includes a suite of four tools for plotting results: AN-XY Chart, AN-Smith, AN- Polar and AN-3D Pattern. TYPES OF RESULTS The output data of a simulation can be listed in tables or displayed in graphs. All results are found under the Results menu, and are categorized into four groups: • Results related to current distribution • Results related to the far field • Results related to the near E-field • Results related to the near H-field TIP > See the most relevant results for transmitting antennas in the Results tab of the main window.
- 218. 2 1 8 – A N - S O F U S E R G U I D E 13.1 PLOTTING THE CURRENT DISTRIBUTION Go to Results > Plot Current Distribution in the main menu to display a 3D graph of the current distribution on the structure, Fig. 13.1. This command executes the AN-3D Pattern application where the amplitude of the currents is displayed on the structure using a color scale. Additionally, the currents in phase, real, and imaginary parts can be plotted selecting these options in the Plot menu of AN-3D Pattern, Fig. 13.2. Fig. 13.1: Plot Current Distribution command in the main menu and toolbar. Fig. 13.2: Current distribution in amplitude plotted by AN-3D Pattern.
- 219. 2 1 9 – A N - S O F U S E R G U I D E A 2D plot of the current distribution along a selected wire can be shown by right clicking on the wire and choosing Plot Currents from the pop-up menu, Fig. 13.3. The Plot Currents command executes the AN-XY Chart application, where the current is plotted in amplitude vs. position along the selected wire. The current distribution can also be plotted in phase, real and imaginary parts by choosing these commands under View in the AN-XY Chart main menu. A wire can also be selected by first clicking on the Select Wire button (arrow icon) on the toolbar and then left clicking on the wire. Once the wire is selected, go to Results > Plot Currents in the main menu to plot the current along that wire. This command is enabled when the current distribution has been calculated. Fig. 13.3: The Plot Currents command in the pop-up menu and the current distribution in amplitude plotted by AN-XY Chart. TIP The graph plotted by AN-XY Chart can be zoomed by expanding a box with the left mouse button pressed on the plot. Right click on the graph and drag the mouse to move it. Left click and expand a rectangle up to return to the original view. Note that there are options to change the units of the plotted magnitudes and to export data in the AN-XY Chart main menu.
- 220. 2 2 0 – A N - S O F U S E R G U I D E 13.2 THE LIST CURRENTS TOOLBAR Right clicking on a wire shows a pop-up menu. Click on the List Currents command to display the List Currents toolbar, Fig. 13.4. This toolbar allows us to select a wire segment to see the current flowing through that segment versus frequency. If the segment has a source or load, the list of input impedances, admittances, voltages, powers, reflection coefficient, VSWR, return and transmission losses can also be displayed. A wire can also be selected by first clicking on the Select Wire button (arrow icon) on the toolbar and then left clicking on the wire. Once the wire is selected, go to Results > List Currents in the main menu. This command is enabled when the current distribution has been calculated. The List Currents toolbar has the following components: Fig. 13.4: The List Currents toolbar. THE SLIDER Each position of the slider corresponds to the position of a segment along the selected wire. Thus, the slider allows us selecting the desired wire segment. The position of the selected segment is shown at the right corner of this toolbar. The segment position is shown as a number and as a percentage of the wire length. The percentage position is measured from the starting point of the wire to the middle point of the segment, namely, % position = 100 (position / wire length) THE 50% BUTTON Moves the slider towards the center of the wire. Note that there must be an odd number of segments for there to be a segment at the midpoint of the wire. THE CURRENT ON SEGMENT BUTTON Displays the Current on Segment dialog box, Fig. 13.5, showing a list of the current in the selected segment versus frequency. Click the Plot button to plot the current in the segment as a function of frequency.
- 221. 2 2 1 – A N - S O F U S E R G U I D E THE INPUT LIST BUTTON If the selected segment has a source on it, the Input List button will be enabled. Click this button to display the Input List dialog box, Fig. 13.6, where the list of input impedances, admittances, currents, voltages, and powers is shown. Select an item from the list in the upper right corner of the window and then press the Plot button to plot the selected item versus frequency. The input impedance can be plotted in a Smith chart by pressing the Smith button. Click the Export button to save the list in CSV format. THE SOURCE LIST BUTTON If the selected segment has a source on it, the Source List button will be enabled. Click this button to display the Source List dialog box, Fig. 13.7, where the list of currents, voltages, and powers in the source internal impedance is shown. Select an item from the list in the upper right corner of the window and then press the Plot button to plot the selected item versus frequency. Click the Export button to save the list in CSV format. THE LOAD LIST BUTTON If the selected segment has a load on it, the Load List button will be enabled. Click this button to display the Load List dialog box, Fig. 13.8, where the list of load impedances, currents, voltages, and powers in the segment is shown. Select an item from the list in the upper right corner of the window and then press the Plot button to plot the selected item versus frequency. Click the Export button to save the list in CSV format. THE EXIT BUTTON Closes the List Currents toolbar. Fig. 13.5: The Current on Segment dialog box.
- 222. 2 2 2 – A N - S O F U S E R G U I D E Fig. 13.6: The Input List dialog box. Fig. 13.7: The Source List dialog box. Fig. 13.8: The Load List dialog box.
- 223. 2 2 3 – A N - S O F U S E R G U I D E 13.3 LISTING THE CURRENTS IN A SEGMENT The following procedure allows us to select a wire segment to tabulate currents versus frequency: 1. Right click on the wire to display the pop-up menu. 2. Click on the List Currents command to display the List Currents toolbar, Fig. 13.4. 3. Move the slider and select the desired segment on the wire. 4. Click on the Current on Segment button to display the Current on Segment dialog box, Fig. 13.5, where a list of the currents versus frequency is shown. Currents are shown in amplitude, phase, real and imaginary parts. Click the Plot button to plot the current in the selected segment as a function of frequency.
- 224. 2 2 4 – A N - S O F U S E R G U I D E 13.4 LISTING THE INPUT IMPEDANCES The following procedure allows us to select a segment that has a source to tabulate input impedance versus frequency: 1. Right click on a wire that has a source to display the pop-up menu. 2. Click on the List Currents command to display the List Currents toolbar, Fig. 13.4. 3. Move the slider and select the segment where the source is placed. 4. Click on the Input List button to display the Input List dialog box, Fig. 13.6, where the list of input impedances, admittances, currents, voltages, powers, reflection coefficient, VSWR, return and transmission losses is shown. Select an item from the list in the upper right corner of the window and then press the Plot button to plot the selected item versus frequency. Click the Smith button to plot the input impedance in a Smith chart. TIPS The reference impedance for reflection and VSWR calculations can be set in the Settings panel of the Setup tabsheet. When there is a single source on the structure, the input impedance can be acceded quickly by going to main menu > Results > List Input Impedances or clicking on the List Input Impedances button on the toolbar.
- 225. 2 2 5 – A N - S O F U S E R G U I D E 13.5 DISPLAYING SMITH CHARTS The input impedance as a function of frequency can be plotted in a Smith chart by clicking the Smith button in the Input List dialog box, Fig. 13.6. Follow the procedure described in the previous section, 13.4 Listing the input impedances, for listing the input impedances versus frequency, and then click the Smith button in the opened dialog box. Left click on the impedance curve in the Smith chart to see the frequency, input impedance (Zin), reflection coefficient (Rho) and VSWR associated to the clicked point, Fig 13.9. Go to the AN-Smith main menu > Plot > Admittance to plot the input admittance curve. Go to Edit > Preferences to change the visualization options in AN-Smith. Fig. 13.9: Input impedance curve in the Smith chart plotted by AN-Smith.
- 226. 2 2 6 – A N - S O F U S E R G U I D E 13.6 LISTING THE INTERNAL IMPEDANCE OF A SOURCE Follow these steps to select a wire segment that has a source and to tabulate the source internal impedance versus frequency, 1. Right click on a wire that has a source to display the pop-up menu. 2. Click on the List Currents command to display the List Currents toolbar, Fig. 13.4. 3. Move the slider and select the segment where the source is placed. 4. Click on the Source List button to display the Source List dialog box, Fig. 13.7, where the list of currents, voltages, and powers in the internal impedance of the source versus frequency is shown. Select an item from the list in the upper right corner of the window and then press the Plot button to plot the selected item versus frequency.
- 227. 2 2 7 – A N - S O F U S E R G U I D E 13.7 LISTING LOAD IMPEDANCES Follow these steps to select a wire segment that has a load and to tabulate the load impedance versus frequency, 1. Right click on a wire that has a load to display the pop-up menu. 2. Click on the List Currents command to display the List Currents toolbar, Fig. 13.4. 3. Move the slider and select the segment where the load is placed. 4. Click on the Load List button to display the Load List dialog box, Fig. 13.8, where the list of currents, voltages, and powers in the load impedance versus frequency is shown. Select an item from the list in the upper right corner of the window and then press the Plot button to plot the selected item versus frequency.
- 228. 2 2 8 – A N - S O F U S E R G U I D E 13.8 PLOTTING 2D FAR-FIELD PATTERNS The radiation pattern can be shown as a 2D rectangular plot by going to Results > Plot Far- Field Pattern > 2D Rectangular Plot in the main menu, Fig. 13.10. This command displays the Radiation Pattern Cut dialog box, Fig. 13.11, where two types of plots can be produced, • Conical plots are obtained with fixed Theta and variable Phi. • Vertical plots are obtained with fixed Phi and variable Theta. Fig. 13.10: The 2D Rectangular Plot command in the main menu. Fig. 13.11: The Radiation Pattern Cut dialog box.
- 229. 2 2 9 – A N - S O F U S E R G U I D E Choose a radiation pattern cut and click the OK button to execute the AN-XY Chart application, Fig. 13.12, where the radiation pattern is plotted vs. Phi if a conical plot was chosen (for fixed Theta) or vs. Theta if a vertical plot was chosen (for fixed Phi). Go to the Plot menu in AN-XY Chart to plot the total E-field, the E-theta (vertical) and E-phi (horizontal) linearly polarized field components, the E-right and E-left circularly polarized components, the power density, directivity, and gain. In the case of plane wave excitation, the Radar Cross Section (RCS) will be plotted. Fig. 13.12: A Radiation Pattern Cut plotted by AN-XY Chart in a rectangular chart. The far-field pattern can also be plotted in a 2D polar chart by going to Results > Plot Far- Field Pattern > Polar Plot 1 Slice in the AN-SOF main menu, Fig. 13.13. In this case, the maximum radiation, beamwidth, and front-to-rear/back ratios will be shown. To plot two slices of a 3D far-field pattern in the same polar plot, go to Results > Plot Far- Field Pattern > Polar Plot 2 Slices in the AN-SOF main menu. A dialog box will be shown to choose the slices. Two vertical, two conical or vertical-conical combinations can be chosen, Fig. 13.14.
- 230. 2 3 0 – A N - S O F U S E R G U I D E Fig. 13.13: A radiation pattern cut plotted by AN-Polar. Fig. 13.14: Two slices of the radiation pattern plotted by AN-Polar.
- 231. 2 3 1 – A N - S O F U S E R G U I D E 13.9 PLOTTING 3D FAR-FIELD PATTERNS The far-field can be shown as a 3D plot by going to Results > Plot Far-Field Pattern > 3D Plot in the main menu. This command executes the AN-3D Pattern application, where the radiation pattern is plotted in a 3D view showing the radiation lobes. The power density, directivity, gain, total E-field, E-theta (vertical) and E-phi (horizontal) linearly polarized field components as well as the E-right and E-left circularly polarized field components can also be plotted by choosing these commands under Plot in the AN-3D Pattern main menu, Fig 13.15. In the case of plane wave excitation, the Radar Cross Section (RCS) will be plotted. The 3D graph can be rotated and moved by dragging the mouse with the left button pressed. Move the mouse wheel to zoom the graph. The main menu of AN-3D Pattern has options for changing the units of the magnitudes, showing a color bar, and exporting data. NOTE If discrete sources were used as the excitation of the structure, the plotted far-field is the total field, but if an incident plane wave was used as the excitation, the plotted far-field is the scattered field. Fig. 13.15: 3D far-field patterns plotted by AN-3D Pattern. Click on Edit > Preferences in the AN-3D Pattern main menu to display the Preferences dialog box, Fig. 13.16, where different options can be chosen for the colored surface and mesh of the radiation lobes, Fig. 13.17. The wire structure can be shown superimposed to the radiation pattern by selecting the Wires option in the Show box. We can also control the scale of the graph and display the main axes.
- 232. 2 3 2 – A N - S O F U S E R G U I D E The far-field pattern for a given frequency can also be tabulated going to Results > List Far- Field Pattern in the AN-SOF main menu. Fig. 13.16: Preferences dialog box of the AN-3D Pattern application. Fig. 13.17: Different options available for plotting radiation lobes.
- 233. 2 3 3 – A N - S O F U S E R G U I D E 13.10 PLOTTING THE FAR-FIELD SPECTRUM Far-field frequency spectra are obtained when a simulation is performed by specifying a list of frequencies or a frequency sweep. For each frequency, the far-field is calculated at the several directions given by the zenith (Theta) and azimuth (Phi) angular ranges and at the distance specified in the Far-Field panel of the Setup tabsheet. Therefore, a fixed direction (Theta, Phi) must be chosen to plot the far-field versus frequency. Go to Results > Plot Far-Field Spectrum in the main menu to plot the far-field spectrum. This command displays the Select Far-Field Point dialog box, Fig. 13.18, where the fixed Theta and Phi angles can be selected. After clicking the OK button, the AN-XY Chart application will show the frequency spectrum of the total E-field, Fig. 13.19. The linearly polarized field components, E-theta and E-phi, as well as the circularly polarized components, E-right and E-left, can be plotted in amplitude, phase, real and imaginary parts by choosing these options under Plot in the AN-XY Chart main menu. The far-field spectrum for a selected far-field point can also be tabulated. Go to Results > List Far-Field Spectrum in the AN-SOF main menu to display the Select Far-Field Point dialog box, where a fixed Phi and Theta can be selected. Then, the list of the far-field components versus frequency will be shown, which can be plotted by clicking the Plot button, Fig. 13.20. Fig. 13.18: Select Far-Field Point dialog box for selecting a fixed direction (Theta, Phi).
- 234. 2 3 4 – A N - S O F U S E R G U I D E Fig. 13.19: Far-field frequency spectrum plotted by AN-XY Chart. Fig 13.20: Far-Field List showing the far-field components vs. frequency.
- 235. 2 3 5 – A N - S O F U S E R G U I D E 13.11 POWER BUDGET Go to Results > Power Budget/RCS in the main menu to display the Power Budget dialog box, Fig. 13.21. The following list of parameters versus frequency will be shown when discrete sources are used as the excitation: • The Input Power column shows the total input power provided by the discrete sources in the structure. • The Radiated Power column shows the total radiated power from the structure. • The Structure Loss column shows the total consumed power (ohmic losses) in the structure. • The Efficiency column is the radiated power to the input power ratio. When the structure is lossless, an efficiency of 100% is obtained. • The Directivity column is the peak directivity (dimensionless) . • The Directivity [dBi] column is the peak directivity in decibels with reference to an isotropic source . • The Gain column is the peak gain (dimensionless). • The Gain [dBi] column is the peak gain in decibels with reference to an isotropic source. • The Pav column is the average power density. This value is calculated averaging the power density over all directions in space. • The Pmax column is the maximum value of the radiated power density. • The Theta (max) and Phi (max) columns are the zenith and azimuth angles, respectively, in the direction of maximum radiation. • The Error column is the error in the power balance of the system. A necessary, but not sufficient, condition for a model to be valid is that the input power must be equal to the sum of the radiated and lost powers, so the Error is defined as follows: Error % = 100 x (Input Power – Lost Power – Radiated Power) / (Input Power – Lost Power)
- 236. 2 3 6 – A N - S O F U S E R G U I D E • The Average Gain Test (AGT) column represents the same information as the Error column, but the AGT must be close to 1 to validate a model, since it is given by AGT = (Radiated Power + Lost Power) / Input Power Select an item from the list in the upper right corner of the window and then press the Plot button to plot the selected item versus frequency. Click on the Export button to export the list to a CSV file. Fig. 13.21: The Power Budget dialog box. TIPS A power budget error of about ±10% is permissible from the engineering point of view. When a real ground plane is used, this column shows the percentage of power lost in the ground due to its finite conductivity. When a substrate slab is used, this column shows the percentage of power transferred to the dielectric material in the substrate. AGT = 1 means that the power balance is exact. An AGT between 0.99 and 1.01 is comparable to achieving an error of ±1%.
- 237. 2 3 7 – A N - S O F U S E R G U I D E IMPORTANT INFORMATION The average power density (Pav), the error in the power budget, and the AGT are meaningful quantities only if the Theta and Phi angles in the Far-Field panel of the Setup tabsheet are set in the following ranges: If the environment is free space (there is no ground plane): 0 Theta 180 deg. and 0 Phi 360 deg. If the environment has a ground plane: 0 Theta 90 deg. and 0 Phi 360 deg. This is because the average power density must be computed averaging the power density or Poynting vector by considering all directions in free space. If there is a ground plane, directions must be considered in half-space.
- 238. 2 3 8 – A N - S O F U S E R G U I D E 13.12 RADAR CROSS SECTION Go to Results > Power Budget/RCS in the main menu to display the Radar Cross Section dialog box, Fig. 13.22. The following list of parameters versus frequency will be shown when an incident field is used as the excitation: • The RCS [m2 ] column shows the Radar Cross Section in square meters. • The RCS [lambda2 ] column shows the Radar Cross Section in square wavelengths. • The RCS [dBsw] column shows the Radar Cross Section in decibels with reference to a square wavelength. • The Radiated Power column shows the total scattered power from the structure. • The Structure Loss column shows the total consumed power (ohmic losses) in the structure. • The Pav column is the average power density scattered from the structure. This value is computed averaging the scattered power density over all directions in space. • The Pmax column is the maximum value of the scattered power density. • The Theta (max) and Phi (max) columns are the zenith and azimuth angles, respectively, in the direction of maximum radiation. Select an item from the list in the upper right corner of the window and then press the Plot button to plot the selected item versus frequency. Fig. 13.22: The Radar Cross Section dialog box.
- 239. 2 3 9 – A N - S O F U S E R G U I D E IMPORTANT INFORMATION The Radar Cross Section, the total scattered power and the average power density are meaningful quantities only if the Theta and Phi angles in the Far-Field panel of the Setup tabsheet are set in the following ranges: If the environment is free space (there is no ground plane): 0 Theta 180 deg. and 0 Phi 360 deg. If the environment has a ground plane: 0 Theta 90 deg. and 0 Phi 360 deg. This is because the average power density must be computed averaging the power density or Poynting vector by considering all directions in free space. If there is a ground plane, directions must be considered in half-space.
- 240. 2 4 0 – A N - S O F U S E R G U I D E 13.13 PLOTTING NEAR-FIELD PATTERNS Go to Results > Plot Near E-Field Pattern > 3D Plot in the main menu to plot the near electric field as a 3D graph with a color scale. This command executes the AN-3D Pattern application, Fig. 13.23. Go to Results > Plot Near H-Field Pattern > 3D Plot in the main menu to plot the near magnetic field. Fig. 13.23: Near-field 3D plot shown by AN-3D Pattern. Near-field 3D plots will be shown according to the type of coordinate system that was chosen in the Near-Field panel of the Setup tabsheet: Cartesian, Cylindrical or Spherical. If near-fields were calculated for more than one frequency, a dialog box asking for a fixed frequency will be shown before plotting the near-field pattern. The near electric field can also be plotted as a 2D rectangular plot by going to Results > Plot Near E-Field Pattern > 2D Plot in the main menu. The near magnetic field can be plotted by going to Results > Plot Near H-Field Pattern > 2D Plot. These commands execute the AN-XY Chart application, where the total rms electric or magnetic field is plotted in a 2D chart, Fig. 13.24. A near-field has always three components, which can be plotted individually by going to the Plot menu in the AN-XY Chart.
- 241. 2 4 1 – A N - S O F U S E R G U I D E REGARDING THE NEAR-FIELD COMPONENTS • If Cartesian coordinates have been set in the Near-Field panel of the Setup tabsheet, the Ex, Ey and Ez electric field components and the Hx, Hy and Hz magnetic field components will be calculated in a rectangular grid of points in space with coordinates (x,y,z). • If Cylindrical coordinates have been set in the Near-Field panel of the Setup tabsheet, the Er, E and Ez electric field components and the Hr, H and Hz magnetic field components will be calculated in a cylindrical grid of points in space with coordinates (r,,z). • If Spherical coordinates have been set in the Near-Field panel of the Setup tabsheet, the Er, E and E electric field components and the Hr, H and H magnetic field components will be calculated in a spherical grid of points in space with coordinates (r,,). Fig. 13.24: Near electric field plotted by AN-XY Chart as a function of the x-coordinate. The near-field patterns for a given frequency can also be tabulated going to Results > List Near E-Field Pattern or Results > List Near H-Field Pattern in the AN-SOF main menu.
- 242. 2 4 2 – A N - S O F U S E R G U I D E 13.14 PLOTTING THE NEAR-FIELD SPECTRUM Near-field frequency spectra are obtained when a simulation is performed by specifying a list of frequencies or a frequency sweep. For each frequency, the near-field is calculated at those points specified in the Near-Field panel of the Setup tabsheet. So, a fixed point in space must be selected to plot the near field versus frequency. Go to Results > Plot Near E-Field Spectrum or Results > Plot Near H-Field Spectrum in the main menu to plot the near E- or H-field spectrum. These commands display the Select Near-Field Point dialog box, where a fixed observation point can be selected, Figs. 13.25. The AN-XY Chart application will show the frequency spectrum of the total near electric or magnetic field, Fig. 13.26. The field components can be plotted in amplitude, phase, real and imaginary parts by choosing these options under Plot in the AN-XY Chart main menu. Fig. 13.25: Select Near-Field Point dialog box for selecting a fixed observation point. Fig. 13.26: Near E-field spectrum plotted by AN-XY Chart.
- 243. 2 4 3 – A N - S O F U S E R G U I D E 13.15 EXPORTING THE FAR AND NEAR FIELDS Far and near field patterns and spectra can be tabulated and exported by going to the following commands in the Results menu, Fig. 13.27: • List Far-Field Pattern • List Far-Field Spectrum • List Near E-Field Pattern • List Near E-Field Spectrum • List Near H-Field Pattern • List Near H-Field Spectrum Fig. 13.27: List Far-Field/Near E-Field/Near H-Field Pattern and Spectrum commands under the Results menu. A table with the results will be displayed after executing any of these commands, Fig. 13.28. The tabulated values can be exported to a CSV (Comma Separated Values) file by clicking the Export button.
- 244. 2 4 4 – A N - S O F U S E R G U I D E Fig. 13.28: Tabulated values of the far-field pattern. Click on the Export button to export the list to a CSV file.
- 245. 2 4 5 – A N - S O F U S E R G U I D E 13.16 THE RESULTS TAB In the AN-SOF main window there is a Results tab, Fig. 13.29, where a table with the main results for a transmitting antenna is shown: input impedance (Rin + jXin), VSWR, directivity, gain, efficiency, and the horizontal (H) and vertical (V) front-to-rear (F/R) and front-to-back (F/B) ratios. This table will be automatically filled only when the structure has been excited by a discrete source (it will not be filled when the excitation is an incident wave). Tabulated results persist until a new calculation is run, so we can refer to them at any time, even when we make changes to the project. To export these results to a CSV file, click the Export Results button on the toolbar. The column headings "Rin" through "Eff." are buttons you can press to display plots. The F/R and F/B ratios will be plotted as a function of frequency in the Plots tab. Fig. 13.29: Results tab in the main window. The Export Results button in the toolbar is highlighted.
- 246. 2 4 6 – A N - S O F U S E R G U I D E 13.17 THE PLOTS TAB Select the Plots tab in the AN-SOF main window to visualize the plots of the main results for a transmitting antenna as a function of frequency, Fig. 13.30. The left column presents the input impedance and VSWR. On the right are the gain and the front-to-rear (F/R) and front-to-back (F/B) ratios. The plots are aligned to make it easy to compare. Use the controls shown on the right of the window to change different aspects of the graphics. You can also maximize the plots. Fig. 13.30: Plots tab in the main window.
- 247. 2 4 7 – A N - S O F U S E R G U I D E 14. ADDING A FEED LINE Add Parameters from Actual Feed Line Datasheets 14.1 FEED LINE PARAMETERS In the case of a transmitting antenna that has a single feed port, the transmission line used to feed the antenna can be modeled in the Feed Line tabsheet, Fig. 14.1. Fig. 14.1: Feed Line tabsheet where the transmission line used to feed a transmitting antenna can be modeled. There is a list of cable types where real-life transmission lines are available, which include matched loss parameters adjusted to the cable datasheets. The cable types are ordered by part numbers, and they include the manufacturer name. For instance, type “RG-8” in the Cable Type option and this part number will be shown for different manufacturers, Fig. 14.2. The RG-8 Belden 8237 will show a set of K0, K1 and K2 parameters. The constants K0, K1 and K2 have been adjusted so that a matched loss curve is obtained as a function of frequency according to the matched loss vs. frequency table published in the cable datasheet. K0 is related to the DC losses in the transmission line
- 248. 2 4 8 – A N - S O F U S E R G U I D E conductors, K1 is related to the skin effect losses which depend on the square root of frequency and K2 is related to dielectric losses which increase linearly with frequency. These losses are then considered in the standard RLGC model of a lossy transmission line. The nominal values of the cable characteristic impedance Z0 and velocity factor will also be shown for the chosen part number and manufacturer. After the cable type has been chosen, the operating frequency and input power to the feed line can be set. The frequency can be selected from a list that shows the frequencies that have been set in the Setup tabsheet. Fig. 14.2: Cable Type option where the type of transmission line can be chosen. Then, the length of the cable can be set. The length is entered according to the length unit used for drawing wires in the workspace. Go to Tools > Preferences in the main menu to change the length unit. While typing the cable length, the length measured in wavelengths () and electrical degrees will be shown automatically. As a matter of fact, all the feed line results are calculated automatically by just modifying any of the feed line parameters. The load impedance of the feed line can then be chosen. The default option is to consider the antenna input impedance (Zin) as the load impedance of the transmission line, so the antenna input impedance at the chosen frequency will be shown automatically as a load for the line. However, any value for the line load impedance can be entered by choosing the “Custom Load” option. This allows us to use the Feed Line tabsheet as an independent calculator for transmission lines.
- 249. 2 4 9 – A N - S O F U S E R G U I D E 14.2 FEED LINE RESULTS After specifying the feed line parameters, the following results will be obtained: Characteristic Z0 It is the “true” characteristic impedance of the transmission line obtained from the RLGC model via the K0, K1 and K2 constants. The real part of Z0 may differ somewhat from the nominal Z0 depending on frequency and losses in the line. An imaginary part will always appear in Z0 due to the non-zero losses. So, note that the true characteristic Z0 will be generally different from the “Nominal Z0” (Z0 in the cable datasheet). True Velocity Factor It is the velocity factor obtained from the RLGC model of the transmission line, where the wavenumber (and wavelength inside the line) is affected by losses. The velocity factor will be modified relative to its nominal value accordingly. Therefore, the true velocity factor is a function of frequency and losses in the line. Matched Loss Any cable datasheet contains a table of matched loss values expressed in dB/100feet or dB/100m as a function of frequency. These values correspond to the attenuation of the line when it is matched (the line has a load impedance equal to Z0). So, the Matched Loss value that is shown in the Results panel is the attenuation of the line corresponding to the selected frequency. Total Matched Loss It is the matched loss that would be obtained for the specified length of the cable, so the Total Matched Loss equals the Matched Loss (dB/100feet or dB/100m) multiplied by the cable length. At Line Input The input impedance of the transmission line will be shown as well as the reflection coefficient (Rho), VSWR and return loss. This is the impedance at the line end opposite to the end where the load/antenna is connected. At Line Load / Antenna The load impedance connected to the transmission line will be shown as well as the reflection coefficient (Rho), VSWR and return loss at this line end. The load impedance will be the antenna input impedance if the “Antenna Zin” option was selected as a parameter for the feed line. Power at Load / Antenna It is the power in Watts consumed at the line load or effectively delivered to the antenna port. This power will be less than the input power specified as an input parameter for the
- 250. 2 5 0 – A N - S O F U S E R G U I D E feed line if the transmission line has losses. However, the power at load/antenna will be equal to the input power in the case of a lossless transmission line. Power Lost in Line It is the total power lost along the transmission line in Watts. Total Line Loss It is the total transmission line loss expressed in decibels. It will be different from the Total Matched Loss if the transmission line is not matched. Total Loss – Matched Loss It is the difference in decibels between the total loss obtained and the total loss that would be obtained if the line were matched. It can be interpreted as an additional loss due to a VSWR different from 1. Radiated Power It is the total power in Watts radiated by the antenna when it is fed using the power at the load/antenna end of the transmission line. The radiated power will be different from the power delivered by the feed line if the antenna itself has its own losses. The radiated power will be shown if the option “Antenna Zin” was selected as a line parameter. Antenna Loss It is the total power lost in the antenna structure. It will be shown if the option “Antenna Zin” was selected as a line parameter. Antenna Efficiency It is defined as the ratio of the antenna radiated power to the antenna input power (the power delivered by the feed line). It is expressed as a percentage as it is usual. It will be shown if the option “Antenna Zin” was selected as a line parameter. Total System Loss It is the total loss obtained in the antenna and feed line as a whole system.
- 251. 2 5 1 – A N - S O F U S E R G U I D E 14.3 CUSTOM LINE OPTIONS Besides the manufactured cables listed in the “Cable Type” option, the following custom line options can be chosen, Fig. 14.3: Custom lossless line It is an ideal transmission line having zero losses, so only the nominal Z0 and velocity factor can be specified in this case. Custom line low loss model It is a transmission line where the nominal Z0, velocity factor and matched loss curve can be specified. To define the matched loss curve, two values of attenuation must be entered at two different frequencies, the second frequency being greater than the first one. AN-SOF will adjust a low loss model to obtain a curve of attenuation vs. frequency to perform the subsequent calculations. The real part of the characteristic Z0 will be equal to the nominal Z0 in the low loss model, which is a good approximation in many cases, especially for higher frequencies. The “true” velocity factor is also assumed to be equal to the nominal velocity factor. Custom line RLGC model It is a transmission line model where the losses are accurately considered by adjusting a matched loss curve to the table of attenuation vs. frequency in the cable datasheet. The K0, K1 and K2 constants must be entered in this case. The definition of K0, K1 and K2 considers that the frequency is in Hz and lengths are in meters (SI metric units). This option allows us to enter the K0, K1, K2 obtained from other transmission line calculators. Fig. 14.3: Custom line options.
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- 253. 2 5 3 – A N - S O F U S E R G U I D E 15. STEP-BY-STEP EXAMPLES Speed up the Learning Curve by doing these Examples AN-SOF TRIAL MODELS From this link > you can download 5 examples of antenna models that have less than 50 segments, so the calculations can be run with the trial version of AN-SOF: • 2 Element Quad • 2 Element Delta Loop • HF Skeleton Slot • Inverted V • 5 Element Yagi-Uda WHERE TO FIND EXAMPLES In the directory where AN-SOF was installed there is a folder called "Examples" which contains many examples of antennas and wire structures. The default directory is C:Program Files (x86)AN-SOF ProfessionalExamples We also recommend you visit our website where we are constantly uploading files with examples. You will find downloadable examples and modeling guidelines on our Resources and Blog pages. At the bottom of our website there are Categories and a Search bar to facilitate the search for information. We also invite you to subscribe to our newsletter here and to follow us on our social media channels: Google Group Facebook Group Twitter LinkedIn YouTube
- 254. 2 5 4 – A N - S O F U S E R G U I D E 15.1 CYLINDRICAL ANTENNA A center-fed cylindrical antenna is the simplest example that we can simulate. It consists of a straight wire with a source at its center and becomes a half-wave dipole when the frequency is such that the length of the antenna is half the wavelength. Follow the steps below to model this antenna. STEP 1 | SETUP: Go to Tools/Preferences in the main menu for selecting suitable units for frequencies and lengths. In this example, frequencies will be measured in MHz and lengths in mm. Then, go to the Setup tabsheet. In the Frequency panel choose Sweep and fill the Frequency Sweep box as shown in Fig. 15.1. Make sure None is selected in Environment panel > Ground Plane box and Discrete Sources in the Excitation panel. Fig. 15.1: A frequency sweep is set in the Frequency panel. The calculations will be performed at the frequencies: 50, 55,... ,295, 300 MHz. STEP 2 | DRAW: Right click on the workspace and choose Line from the displayed pop- up menu. The Draw dialog box for the Line will be shown. Fill the Line and Attributes pages as shown in Figs. 15.2 and 15.3. A straight wire with 17 segments and 5 mm in radius will be drawn in the workspace. Right click on the wire and choose the Source/Load command from the displayed pop-up menu. Follow the procedure described in Section “8.3 Adding sources” and put a voltage source in segment number 9 (at the wire center). The source voltage is 1 (0º) V. The center- fed cylindrical antenna in the workspace is shown in Fig. 15.4.
- 255. 2 5 5 – A N - S O F U S E R G U I D E Fig. 15.2: Line page in the Draw dialog box. The wire will be drawn starting from point (0,0,-750) [mm] and ending at point (0,0,750) [mm]. Thus, it lies along the z-axis and is 1500 mm long, which corresponds to half-wavelength at 100 MHz. Press F7 to view the main axes. Fig. 15.3: Attributes page in the Draw dialog box. The wire is divided into 17 segments, and it has a circular cross-section with 5 mm in radius.
- 256. 2 5 6 – A N - S O F U S E R G U I D E Fig. 15.4: Cylindrical antenna in the workspace. STEP 3 | RUN: Click on the Run Currents and Far-Field (F11) button on the toolbar. After the calculations are complete, right click on the wire and choose Plot Currents from the displayed pop-up menu and select the desired frequency. The current distribution along the wire will be plotted, Fig. 15.5. Follow the procedures described in chapter “13. Displaying Results” for obtaining other parameters of interest. As an example, the current distribution in amplitude and phase, the input impedance vs. frequency, the gain, and E-field patterns at 100 MHz are shown in the following figures. Note that the antenna length is half a wavelength at 100 MHz, so the current distribution approaches a semi cycle of a sine function, as expected for a half-wave dipole.
- 257. 2 5 7 – A N - S O F U S E R G U I D E Fig. 15.5: Current distribution in amplitude and phase along the cylindrical antenna at 100 MHz.
- 258. 2 5 8 – A N - S O F U S E R G U I D E Fig. 15.6: Real and imaginary parts of the input impedance vs. frequency.
- 259. 2 5 9 – A N - S O F U S E R G U I D E Fig. 15.7: Gain [dBi] and total E-field patterns at 100 MHz.
- 260. 2 6 0 – A N - S O F U S E R G U I D E 15.2 YAGI-UDA ARRAY After learning how to simulate a cylindrical antenna in Section 15.1, we are ready to build a dipole array. A 3-element Yagi-Uda antenna, consisting of a reflector, a driven element, and a director, is shown in Fig. 15.8, where the coordinates of the wire ends are indicated in meters. STEP 1 | SETUP: Go to the Setup tabsheet and set an operating frequency of 300 MHz in the Frequency panel. None must be selected in Environment panel > Ground Plane box and Discrete Sources in the Excitation panel. STEP 2 | DRAW: Follow the procedure described in Section “15.1 Cylindrical antenna” to draw one wire at a time. Set the coordinates of the ends of the wires indicated in Fig. 15.8. Set 15 segments for each wire and a radius of 5 mm. Then, right click on the driven element, select the Source/Load command, and connect a voltage source at the middle segment. STEP 3 | RUN: Click on the Run Currents and Far-Field (F11) button on the toolbar. Fig. 15.9 shows the table in the Results tabsheet, where a peak gain of 8.9 dBi is obtained. This can also be seen in the gain pattern of the Yagi-Uda array shown in Fig. 15.10. Click on the Far-Field 3D Plot button on the toolbar to plot the 3D radiation pattern. Fig. 15.8: Geometry definition for the Yagi-Uda array. The coordinates are in meters.
- 261. 2 6 1 – A N - S O F U S E R G U I D E Fig. 15.9: Results tabsheet, where a peak gain of 8.9 dBi is obtained for the Yagi-Uda array. Fig. 15.10: Gain pattern [dBi] for the Yagi-Uda array of Fig. 15.8 at 300 MHz.
- 262. 2 6 2 – A N - S O F U S E R G U I D E 15.3 MONOPOLE OVER A REAL GROUND PLANE A monopole is a vertical element connected to a ground plane and with the feed point at its base. In this example we will simulate a radio mast on an imperfect ground, which is used for broadcasting in the LF and MF bands. STEP 1 | SETUP: Go to the Setup tabsheet and set an operating frequency of 3 MHz in the Frequency panel. Then, go to the Environment panel > Ground Plane box and select Real, Fig. 15.11. Select Radial wire ground screen and the Poor ground options. Note that the soil conductivity will automatically be set to 0.001 S/m and the permittivity (dielectric constant) to 5. Finally, set the number of radials, their length and radius as shown in Fig. 15.11. In radio masts it is customary to use a constant input power as a reference, for example 1 kW. Go to the Excitation panel, select Discrete Sources, Set Input Power and enter 1,000 W, Fig. 15.12. Fig. 15.11: Setting a radial wire ground screen. STEP 2 | DRAW: Right click on the workspace and select Line from the displayed pop-up menu. Specify a vertical wire 25 m in height (1/4 of a wavelength at 3 MHz) and with a triangular cross section as shown in Fig. 15.13. Although the recommended minimum
- 263. 2 6 3 – A N - S O F U S E R G U I D E number of segments is 3, we will divide the wire into 10 segments to obtain greater resolution in the current distribution. Note that the wire will be automatically connected to the ground at the origin (0,0,0). Right click on the wire, select the Source/Load command from the displayed pop-up menu and put a voltage source on the first segment, so the source will be connected to the base of the mast. Fig. 15.12: Setting discrete sources as the excitation with 1,000 W of input power. Fig. 15.13: Specifying a vertical wire with a triangular cross section.
- 264. 2 6 4 – A N - S O F U S E R G U I D E STEP 3 | RUN: Click on the Run Currents and Far-Field (F11) button on the toolbar. After the calculations are complete, click on the Far-Field 3D Plot button on the toolbar to display the radiation pattern. Choose Radiation Pattern under the Plot menu in AN-3D Pattern to plot the normalized radiation pattern (dimensionless). Then, choose the Radiation Pattern [dB] option to see the pattern in decibel scale. Note that the far field has a null on the xy-plane due to the losses in the ground plane, Fig. 15.14. The antenna efficiency is the radiated to the input power ratio. Go to the Results tabsheet to see the input impedance, VSWR, Directivity, Gain, and Efficiency, Fig. 15.15. Note that the efficiency is low and therefore the gain too since most of the input power is lost to the ground. In this example we have chosen a Poor soil. Try different soils and increasing the number of radial wires and their length to improve the antenna efficiency. Fig. 15.14: Radiation pattern of a quarter-wave monopole over a radial wire ground screen. Fig. 15.15: Results tabsheet for a quarter-wave monopole over a radial wire ground screen.
- 265. 2 6 5 – A N - S O F U S E R G U I D E 15.4 HELIX ANTENNA IN AXIAL MODE The helix is a good example where we need curved segments to describe the geometry of the antenna. When the length of the helix is of the order of or greater than the wavelength, it can work in the so-called "axial mode". To do this, we need to add a ground plane as a reflector. STEP 1 | SETUP: Go to the Setup tabsheet and set an operating frequency of 100 MHz in the Frequency panel. Then, go to Environment panel > Ground Plane box, select Perfect, and set the ground plane position at Z = 0 (xy-plane), Fig. 15.16. Make sure the Discrete Sources option is selected in the Excitation panel. Fig. 15.16: Setting the operating frequency and ground plane for the helix antenna. STEP 2 | DRAW: Go to the Workspace tab, right click on the screen, and select Helix from the displayed pop-up menu. The Draw dialog box for the Helix will be shown, Fig. 15.17. The helix will start above the ground plane, at the point (0,0,0.3) m, and run along the Z axis. We will then add a vertical wire that will connect the helix to the ground plane and where we will place the source. The recommended helix dimensions for the axial mode can be obtained from any antenna book. Here we will set the helix radius, pitch (spacing between turns), and number of turns shown in Fig. 15.17. In the Attributes tab, we will leave the recommended number of segments of 103. The wire cross-section will be circular with 3 mm in radius. After drawing the helix, right click on the helix and choose the Start Point to GND command from the pop-up menu. The Draw dialog box for a Line will be displayed, where the coordinates of the ends of the wire are already set to connect the helix to the ground plane, Fig. 15.18. Set up 2 segments and a radius of 3 mm for this vertical wire.
- 266. 2 6 6 – A N - S O F U S E R G U I D E Finally, right click on the vertical wire, choose the Source/Load command, and connect a voltage source to the segment that is closest to the ground plane. Follow the instructions in Section “8.3 Adding sources” to add the source. Fig. 15.17: Specifying the helix dimensions, segmentation, and cross-section. Fig. 15.18: Specifying the vertical wire that connects the helix to the ground plane.
- 267. 2 6 7 – A N - S O F U S E R G U I D E STEP 3 | RUN: Click on the Run Currents and Far-Field (F11) button on the toolbar. After the calculations are complete, click on the Far-Field 3D Plot button on the toolbar to display the radiation pattern, Fig. 15.19(a). The main lobe is on the axis of the helix, hence the name "axial mode". Because the helix is right-handed, the radiated field is circularly polarized, and the right- handed component predominates. Go to the AN-3D Pattern Plot menu and choose E-right or E-left to see the difference between both components, Figs. 15.19(b) and 15.19(c). To make the comparison between the color scales meaningful, go to Edit > Preferences in AN-3D Pattern and set the maximum of E-left to the same value as the maximum of E-right. To draw a left-handed helix, specify a negative number of turns. Repeat the calculations and compare the E-right and E-left components. (a) (b) (c) Fig. 15.19: (a) Normalized radiation pattern of the helix. (b) Right-handed circularly polarized component of the far-field. (c) Left-handed circularly polarized component of the far-field.
- 268. 2 6 8 – A N - S O F U S E R G U I D E 15.5 LOOP ANTENNA Another example where we need curved segments to model an antenna is the circular loop case. When the loop is small compared to the wavelength, the radiation resistance is proportional to the square of the loop area. STEP 1 | SETUP: Go to the Setup tab and select Sweep in the Frequency panel. Choose Lin for a linear sweep and set the Start, Step, and Stop frequencies. The frequency sweep will start at 3 MHz and end at 30 MHz, incrementing by 1 MHz for each calculation, Fig. 15.20. Make sure None is selected in Environment panel > Ground Plane box and Discrete Sources is selected in the Excitation panel. Fig. 15.20: Setting a linear frequency sweep. STEP 2 | DRAW: Go to the Workspace tab, right click on the screen, and select Circle from the displayed pop-up menu. The Draw dialog box for the Circle will be shown, Fig. 15.21. Set a radius of 0.5 m, 8 segments, and a cross-section radius of 5 mm for the loop. At 30 MHz, which is the highest frequency, the wavelength is = 10 m. A loop of radius 0.5 m will then have a circumference of 3.14 m, or 0.314 . Measuring almost 1/3 of a wavelength in perimeter, this loop cannot be considered small. However, at the lower frequency of 3 MHz it will be. Right-click on the loop, choose the Source/Load command from the displayed pop-up menu, and put a voltage source in the first segment. Follow the instructions in Section “8.3 Adding sources” to add the source.
- 269. 2 6 9 – A N - S O F U S E R G U I D E Fig. 15.21: Setting the loop radius, number of segments and cross-section radius. STEP 3 | RUN: Click on the Run Currents and Far-Field (F11) button on the toolbar. After the calculations are complete, click on the Far-Field 3D Plot button on the toolbar to display the radiation pattern, Fig. 15.22. At the right of the AN-3D Pattern toolbar there is a dropdown menu to select the frequency. There are also buttons with arrows that allow us to raise or lower the frequency. Press the buttons to see how the radiation pattern changes with frequency. At low frequencies, the pattern is doughnut-shaped as expected. Go to the Results tab in AN-SOF to see that the input resistance is very small, only 0.000195 Ohm at 3 MHz. The radiation resistance is given by R = 31,200 (A/2 )2 for a small loop of area A. If we use this formula obtained from textbooks, the result is R = 0.000192 Ohm at 3 MHz. Therefore, the loop behaves according to the theory at low frequencies. Fig. 15.22: Radiation pattern of the loop at 3 MHz (left), 15 MHz (center), and 30 MHz (right).
- 270. 2 7 0 – A N - S O F U S E R G U I D E 15.6 A TRANSMISSION LINE Two-wire transmission lines can be modeled explicitly in AN-SOF. In this example, the line will have a single wire but there will be a ground plane below it, so we have the mirror image of the wire as the return of the line. STEP 1 | SETUP: Go to the Setup tab and select Single in the Frequency panel. Set a frequency of 100 MHz. Then, go to the Environment panel and set a perfect ground plane at Z = 0, Fig. 15.23. Fig. 15.23: Setting up the frequency and ground plane for the transmission line. STEP 2 | DRAW: Go to the Workspace tab, right click on the screen, and select Line from the pop-up menu. Draw a horizontal line with the coordinates indicated in Fig. 15.24. Next, connect the ends of the line to the ground plane by drawing two vertical wires. You can right click on the line and select the commands Start point to GND and End point to GND to connect the ends to ground. Fig. 15.24: Transmission line dimensions.
- 271. 2 7 1 – A N - S O F U S E R G U I D E Set 40 segments for the horizontal wire and 1 segment for each of the vertical wires. Note that dimensions in Fig. 15.24 are in millimeters. To change the unit of length, go to the Tools menu/Preferences/Units tab. Right click on the vertical wire at (0,0,0), select Source/Load from the displayed pop-up menu and put a 1 Volt voltage source on it. STEP 3 | RUN: Go to the Run menu and click on Run Currents. Since we are only interested in the current distribution and the input impedance, it is not necessary to calculate the radiated field (you can do it to check that it is practically negligible). Click on the Zin (List Input Impedances) button on the toolbar to display a table where the input impedance is shown as a function of frequency, Fig. 15.25. Fig. 15.25: Transmission line in the workspace and table of input impedances. The impedance obtained is practically reactive, j512 Ohm. The small real part is the radiation resistance, since the line radiates a small amount of power, which is negligible but not zero. This is a short-circuited line. Now right click on the vertical wire at (0,500,0) mm and select Delete from the pop-up menu to remove it. You will get an open-circuited line in this way. Rerun the calculations with the Run Currents command in the Run menu. The input impedance will now be -j105 Ohm. Summarizing, we have, • Zin (short-circuited line) = j512 Ohm. • Zin (open-circuited line) = -j105 Ohm. According to transmission line theory, the characteristic impedance can be calculated as the geometric mean of the short-circuit and open-circuit line input impedances, hence
- 272. 2 7 2 – A N - S O F U S E R G U I D E 𝑍𝑐 = √512 × 105 = 232 𝑂ℎ𝑚 On the other hand, the expression for the characteristic impedance of a line above a ground plane is given by: 𝑍𝑐 = 138 log ( 2ℎ 𝑎 ) = 138 log ( 2 × 40 2 ) = 221 𝑂ℎ𝑚 where a is the wire cross-section radius and h is the line height above the ground plane. As we can see, the agreement between the characteristic impedance obtained from AN-SOF and that from theory is quite good. The difference is since the theory neglects the radiation of the line, and the logarithmic formula is an approximation that is valid when h >> a.
- 273. 2 7 3 – A N - S O F U S E R G U I D E 15.7 AN RLC CIRCUIT The ability of AN-SOF to simulate at extremely low frequencies can be demonstrated with a model of an RLC circuit that will resonate at only 800 Hz, so the wavelength is 375 km! STEP 1 | SETUP: Go to Tools > Preferences in the main menu and select Hz, mm, mH and uF as the units for frequency, length, inductance, and capacitance, respectively. Then, go to the Setup tab and select Sweep in the Frequency panel. Choose Lin for a linear sweep and set the Start, Step, and Stop frequencies. The frequency sweep will start at 600 Hz and end at 1,000 Hz, incrementing by 10 Hz for each calculation, Fig. 15.26. In the Environment panel, set a perfect ground plane at Z = 0. Fig. 15.26: Setting up frequencies and the ground plane for the RLC circuit. STEP 2 | DRAW: Go to the Workspace tab, right click on the screen, and select Line from the pop-up menu. Draw the three wires with the coordinates indicated in Fig. 15.27 using the Line dialog box. The left vertical wire has 1 segment, the horizontal wire has 1 segment, and the right vertical wire has 2 segments. The wire radius is 0.5 mm. Right click on the left vertical wire, select the Source/Load command from the pop-up menu and put a 1 Volt voltage source. Then, right click on the horizontal wire, select Source/Load from the pop-up menu and connect a load impedance with R = 10 Ohm. Finally, right click on the right vertical wire, select Source/Load from then pop-up menu and put an inductance L = 20 mH on the first segment and a capacitance C = 2 uF on the second segment. Refer to Sections “8.3 Adding sources” and “8.5 Adding loads” for adding sources and load impedances.
- 274. 2 7 4 – A N - S O F U S E R G U I D E Fig. 15.27: RLC circuit dimensions. The coordinates are in millimeters. STEP 3 | RUN: Go to the Run menu and click on the Run Currents command. Since we are only interested in the input impedance, it is not necessary to calculate the radiated field (you can do it to check that it is practically negligible). Right click on any of the three wires composing the circuit, select the List Currents command and click on the Current on Segment button of the displayed toolbar. A table will be shown, where the current is tabulated vs. frequency. Next, press the Plot button to the right of the table to plot the current versus frequency, Fig. 15.28. Fig. 15.28: Current amplitude vs. frequency in the RLC circuit.
- 275. 2 7 5 – A N - S O F U S E R G U I D E Since this is a series RLC circuit, the current flowing must be the same in all three wires (check this). As can be seen, resonance occurs at a frequency near to 800 Hz. Repeat the calculation for frequencies around 800 Hz, with a step of 1 Hz, and verify that the resonant frequency is 796 Hz. On the other hand, according to circuit theory, the resonance frequency is given by 𝑓 𝑟 = 1 2𝜋√𝐿𝐶 = 1 2𝜋√20 × 10−3 × 2 × 10−6 = 796 𝐻𝑧 The agreement between AN-SOF and theory is remarkable!
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- 277. 2 7 7 – A N - S O F U S E R G U I D E 16. SHORTCUT KEYS Quickly Access Commands via the Keyboard Pressing ALT with the underlined letter of a menu item will execute the command associated with the item. The following keys and associated actions are available: Key Action Home Return the structure to the initial view ESC Unselect a wire F1 Rotate view around +X axis F2 Rotate view around -X axis F3 Rotate view around +Y axis F4 Rotate view around -Y axis F5 Rotate view around +Z axis F6 Rotate view around -Z axis F7 Show Main/Small axes F8 Select a wire in order of creation F9 Select a wire in reverse order of creation F10 Run ALL F11 Run currents and far-field F12 Run currents and near-field Ctrl + A Display the Axes dialog box Ctrl + I Zoom in Ctrl + K Zoom out Ctrl + M Modify the selected wire Ctrl + N Create a new project Ctrl + O Open a project file Ctrl + P Print the workspace Ctrl + Q Exit AN-SOF Ctrl + R Run Currents Ctrl + S Save the project Ctrl + T Tabular input of linear wires Ctrl + W Show properties of the selected wire Ctrl + Del Delete the selected wire or group of wires Ctrl + Ins Display the Source/Load toolbar
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- 279. 2 7 9 – A N - S O F U S E R G U I D E 17. FILE FORMATS About the AN-SOF File Types When a project is saved in AN-SOF, multiple files that have the same name as the project are saved. Each file has a unique extension that refers to its content. These files are the following: File type Description *.emm Main file with configuration data *.wre Geometric description of the wire structure *.cur Current distribution *.phi E-phi component of the far-field. *.the E-theta component of the far-field. *.pwr Radiation pattern data *.nef Near electric field *.nhf Near magnetic field *.ngf Numerical Green’s function *.txt Notes written by the user When requesting support, always attach the .emm and .wre files of your project.
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- 281. 2 8 1 – A N - S O F U S E R G U I D E 18. BACKGROUND THEORY On the Math Behind AN-SOF 18.1 THE CALCULATION ENGINE The AN-SOF engine is written in the C++ programming language using double-precision arithmetic and has been developed to improve the accuracy in the modeling of wire antennas and metallic structures in general. The computer code is based on an Electric Field Integral Equation (EFIE) expressed in the frequency domain. The current distribution on wire structures is computed by solving the EFIE using a Method of Moments (MoM) formulation with curved basis and testing functions, called the Conformal Method of Moments (CMoM). In this method, curved wires are modeled by means of conformal segments, which exactly follow the contour of the structure, instead of the traditional approximation based on straight wire segments. The linear approximation to the geometry can be a very inefficient method in terms of unknowns or computer memory. By using curved segments, the number of unknown currents, simulation time and memory space can be greatly reduced, allowing for the solution of bigger problems. Old MoM codes suffer from several drawbacks due to the linear approximation to geometry and the use of the so-called thin-wire Kernel, such as: divergent input impedance, poor convergence for curved antennas (helices, loops, spirals) and bent wires, and singularities that appear when two parallel wires are close to each other or close to a lossy ground plane. With the CMoM and an exact Kernel formulation we have removed these limitations and obtained the following advantages: • Decreased number of calculations and increased accuracy of results. • Decreased simulation time and computer memory usage, allowing us to model larger and more complex designs. • Ability to simulate from extremely low frequencies (circuits at 60 Hz) to very high ones (microwave antennas). Here is a brief explanation of the theoretical basis for the AN-SOF app.
- 282. 2 8 2 – A N - S O F U S E R G U I D E 18.2 THE ELECTRIC FIELD INTEGRAL EQUATION The current distribution on metallic surfaces with ideal conductivity can be found by solving an Electric Field Integral Equation (EFIE) expressed in the frequency domain [1]: (1) where: Ei: Incident Electric Field on the surface S. n: unit vector at point r on the surface S. k: wave number. J: unknown electric current density flowing on the surface. G: Green's function, which in free space is given by: (2) The EFIE is an expression of a boundary condition on the surface, namely zero tangential electric field. When we are dealing with a wire structure, the EFIE reduces to [2]: (3) where T is the tangential unit vector describing the contour of the curve , I(s) is the unknown electric current on the wire, and K(s,s') is the integral equation Kernel defined as: (4) The EFIE is averaged about the wire circumference described by the angle , resulting in the EFIE (3) with the Kernel (4). The current distribution I(s) is then the average value of the current density J in the axial direction; the current in the direction is neglected. This is a good assumption provided that the wire radius is small with respect to the wavelength.
- 283. 2 8 3 – A N - S O F U S E R G U I D E The wire axis is defined by its parametric equations that can be written in the compact form [3]: (5) which points from the origin to any point on the wire, Fig. 18.1. The parameter s varies over a real interval. The tangent unit vector can be obtained from the first derivative of (5): (6) Fig. 18.1: Parametric description of a curved wire. The tangent unit vector is obtained from the first derivative of the position vector r(s). This parametric description is the key for the accurate modeling of wire structures [3]. A straight wire approximation to the geometry produces a loss of geometrical information that can never be completely restored. However, this information is not lost if a parametric representation is used to describe the wire locus [4], [5]. It is also possible to improve on the straight wire approximation by using quadratic segments to model the geometry [6]. x y z r(s) T(s)
- 284. 2 8 4 – A N - S O F U S E R G U I D E Thus, the definition of a wire must include its parametric description and its first derivative if an exact representation of the geometry is required, as shown in Fig. 18.1. The Kernel (4) can be approximated by the following generalized thin-wire approximation: (7) where a is the wire radius. When the observation point r(s) and the source point r(s') are both in the same straight wire, the distance R reduces to the usual thin-wire approximation: (8) Thus, the EFIE and its Kernel are also valid for straight wires. It is well known that the thin-wire approximation produces numerical oscillations in the computed current distribution near wire ends and near the position of discrete sources when wire segments are relatively thick [7]. To avoid this undesired behavior and obtain the maximum accuracy, the exact Kernel in (4) is used in AN-SOF by default instead of the thin- wire approximation in (7). A closed-form expression for the exact Kernel has been found so its use practically does not compromise the speed of the simulation. However, an extended thin-wire Kernel has been calculated that also avoids the current distribution inaccuracies for a thin-wire ratio (wire diameter/segment length) < 3, which is far better than the thin- wire ratio < 1 that must be used when the standard thin-wire approximation is used. In the Settings panel of the Setup tabsheet check the Exact Kernel option to use the exact Kernel in (4). Uncheck this option to use the extended thin-wire Kernel. The existence of a PEC ground plane is modeled in AN-SOF by means of image currents. This method can be easily implemented by adding an image term to the Green's function, resulting in an additional term for the Kernel.
- 285. 2 8 5 – A N - S O F U S E R G U I D E 18.3 THE CONFORMAL METHOD OF MOMENTS The Method of Moments (MoM) is a technique used to convert the EFIE into a system of linear equations that then can be solved by standard methods [1], [8]. For simplicity, the integral (linear) operator in (3) will be denoted by L, then the EFIE takes the form: (9) where ET is the tangential component of the incident electric field. The current distribution is approximated by a sum of N basis functions with unknown amplitudes In, giving: (10) With this expansion and using the linearity of the operator L, we can write: (11) To obtain a set of N equations, the functional equation (11) is weighted with a set of N independent testing functions wm, giving: (12) where the integrals are calculated over the domain of L. Now we have as many independent equations as unknowns, so (12) can be written as: (13) where [Z]: impedance matrix with dimension NN and the elements [I]: current matrix with dimension N1 and the elements In. [U]: voltage matrix with dimension N1 and the elements This fully occupied equation system must be solved for the unknown currents In. LU decomposition is used in AN-SOF. The MoM is applied by first dividing the wire structure into N segments, and then defining the basis and testing functions on the segments. Triangular basis and pulse testing functions are used in AN-SOF, Fig. 18.2.
- 286. 2 8 6 – A N - S O F U S E R G U I D E Fig. 18.2: (a) Triangular basis functions, Fi(u), and pulse testing functions, Ti(u). (b) Current distribution approximated by triangular functions. When a curved wire is described parametrically by a vector function (5), the basis and testing functions are curved in the sense that their support is a curved subset of the wire. Therefore, when curved basis and testing functions are used, the Conformal Method of Moments (CMoM) is obtained. To fill the impedance matrix [Z], an adaptive Gauss-Legendre quadrature rule is applied to compute the involved integrals. After having solved the equation system, the currents In are known and other parameters of interest, such as input impedances, voltages, radiated power, directivity, and gain can be computed. The MoM can also be used to calculate the electromagnetic response of metallic surfaces, which are modeled using wire grids [9]. In AN-SOF, with the CMoM the accuracy of the calculation of wire grids is remarkably improved compared to the traditional MoM, as demonstrated in this article. Another extension of the calculation includes wires that do not have a circular cross section [10]. In AN-SOF an equivalent radius is calculated for these wires.
- 287. 2 8 7 – A N - S O F U S E R G U I D E 18.4 EXCITATION OF THE STRUCTURE If a discrete voltage source is placed at the i-th segment, the corresponding element in the voltage matrix is simply equal to the voltage of the generator. Thus, (14) When an incident plane wave is used as the excitation, each wire segment is excited by the incoming field, which has the form: (15) where k is defined by the direction of propagation, so that |k| = k is the wave number, and r is the evaluation point, Fig. 18.3. The elements of the voltage matrix are then defined by: (16) where the integration is performed over the m-th segment, and the vectors r(s) and T(s) are given by (5) and (6), respectively. Fig. 18.3: Incident plane wave exciting a wire.
- 288. 2 8 8 – A N - S O F U S E R G U I D E 18.5 CURVED VS. STRAIGHT SEGMENTS Many examples show the advantages of using curved segments with respect to the stability and convergence properties of the solutions [11], [12]. Due to the improved convergence rate, accurate results can be obtained with reduced simulation time and memory space. As an illustration, Figs. 18.5 and 18.6 show a comparison between AN-SOF, which uses curved segments, and a straight wire approximation to a normal mode helix antenna, Fig. 18.4. The convergence properties of the input impedance and admittance versus the number of unknowns are investigated. Fig. 18.4: Center-fed helical antenna (normal mode) in free space. Helix radius = 0.0273. Pitch = 0.0363. Number of turns = 10. Wire radius = 0.001. As can be seen from these results, by using curved segments significantly fewer unknowns are needed to predict the input impedance. However, the admittance convergence is questionable for the straight wire case, while it has a notorious convergent behavior for the curved case. The improvement depends on the geometry and frequency, but generally, if N straight segments are needed to obtain a convergent value, then N/p curved segments are needed
- 289. 2 8 9 – A N - S O F U S E R G U I D E to obtain the same value, with p = 2...10. For a straight geometry the improvement factor is p = 1, as can be expected, because there are no curved segments in this case. Fig. 18.5: Impedance convergence plot for the helix of Fig. 18.4.
- 290. 2 9 0 – A N - S O F U S E R G U I D E Fig. 18.6: Admittance convergence plot for the helix of Fig. 18.4.
- 291. 2 9 1 – A N - S O F U S E R G U I D E 18.6 REFERENCES [1] Harrington, R. F., Field Computation by Moment Methods, MacMillan, New York, 1968. [2] K. K. Mei, "On the Integral Equations of Thin Wire Antennas," IEEE Trans. Antennas Propagat., vol. AP-13, pp. 374-378, May 1965. [3] Song, J. M. and Chew, W. C., "Moment method solutions using parametric geometry", J. of Electromagnetic Waves and Appl., vol. 9, no. 1/2, pp. 71-83, January-February 1995. [4] N. J. Champagne II, J. T. Williams, D. R. Wilton, "The Use of Curved Segments for Numerically Modeling Thin Wire Antennas and Scatterers," IEEE Trans. Antennas Propagat., vol. 40, No. 6, pp. 682-689, June 1992. [5] S. D. Rogers, C. M. Butler, "An Efficient Curved-Wire Integral Equation Solution Technique," IEEE Trans. Antennas Propagat., vol. 49, No. 1, pp. 70-79, January 2001. [6] M. A. Jensen, Y. Rahmat-Samii, "Electromagnetic Characteristics of Superquadratic Wire Loop Antennas," IEEE Trans. Antennas Propagat., vol. 42, No. 2, pp. 264-269, February 1994. [7] R. Redlich, "On the Extended Boundary Condition as Applied to the Dipole Antenna Problem," IEEE Trans. Antennas Propagat., vol. AP-32, No. 4, pp. 403-404, April 1984. [8] D. R. Wilton, C. M. Butler, "Efficient Numerical Techniques for Solving Pocklington's Equation and Their Relationships to Other Methods," IEEE Trans. Antennas Propagat., (vol. AP-23, No. 5), pp. 83-86, January 1976. [9] J. H. Richmond, "A Wire-Grid Model for Scattering by Conducting Bodies," IEEE Trans. Antennas Propagat., vol. AP-14, No. 6, pp. 782-786, November 1966. [10] D. L. Jaggard, "On Bounding the Equivalent Radius," IEEE Trans. Antennas Propagat., vol. AP-28, No. 3, pp. 384-388, May 1980. [11] G. Zhou, G. S. Smith, "An Accurate Theoretical Model for the Thin-Wire Circular Half-Loop Antenna," IEEE Trans. Antennas Propagat., vol. 39, No. 8, pp. 1167-1177, August 1991. [12] S. K. Khamas, G. G. Cook, "Moment-Method Analysis of Printed Wire Spirals Using Curved Piecewise Sinusoidal Subdomain Basis and Testing Functions," IEEE Trans. Antennas Propagat., vol. 45, No. 6, pp. 1016-1022, June 1997.
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- 293. 2 9 3 – A N - S O F U S E R G U I D E 19. DISCLAIMER OF WARRANTY The technical descriptions, procedures and software included in this User’s Guide have been developed with the greatest care. They are provided without warranty of any kind. Golden Engineering Ltd. makes no warranties, expressed or implied, that the equations, programs and procedures in this guide or its associated software are free of error, consistent with any particular standard of merchantability, or will meet your requirements for any particular application. They should not be relied on for solving a problem whose incorrect solution could result in injury to a person or loss of property. Any use of the programs or procedures in such a manner is at the user’s own risk. Golden Engineering Ltd. disclaims all liability for direct, incidental, or consequential damages resulting from use of the programs or procedures in this guide or the associated software.
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