Design and simulation of printed micro strip low pass filter based on the electromagnetic models 18 ghz printed microstrip lowpass filter using x models

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Issue: 05 | May-2014, Available @ http://www.ijret.org 312
DESIGN AND SIMULATION OF PRINTED MICRO STRIP LOW PASS
FILTER BASED ON THE ELECTROMAGNETIC MODELS 18GHZ
PRINTED MICROSTRIP LOWPASS FILTER USING X-MODELS
Arfiya Kouser1
, Pramod K B2
, Kumaraswamy H.V3
, Jayaraj N4
1
Department of Electronics and Communication Engineering, The Oxford College of Engineering, Bangalore, Karnataka,
India
2
Department of Electronics Engineering, Jain University, Bangalore, Karnataka, India
3
Department of Telecommunication, R. V. College of Engineering, Bangalore, India
4
Department of Electronics and Communication Engineering, The Oxford College of Engineering, Bangalore, India
Abstract
This paper presents the Design, Simulation and characterization of Printed Micro strip Low Pass Filter based on 15 mil Alumina
substrate. Simulations show a comparison between a pure EM simulation with EM Sight and a more efficient hybrid approach that
combines EM analysis (using X-Models) with conventional circuit simulations and both approaches match the measured data.
Furthermore, the proposed paper has four different low pass filter designs, lumped design; basic designs uses only micro strip lines;
advanced design uses multiple edge coupled micro strip lines, EM sight design provides a very sharp cut-off frequency response with
low insertion loss, results having great agreement with excellent correlation. Tuning and Optimization of the design is carried out
using AWR Microwave office tool.
Keywords— EM sight, AWR, MMIC, X-Models, I-Filter
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1. INTRODUCTION
A low-pass filter (LPF) offers easy passage to low-frequency
signals and difficult passage to high-frequency signals. It is
highly demanded in modern microwave communication
systems, especially in wireless and mobile communications in
order to suppress harmonics and spurious signals [1]. The
amount of insertion loss and phase shift encountered by a signal
passing through the filter and the amount of rejection of an
undesired signal is a function of the filter design. Filters are
networks that process signals in a frequency-dependent manner
and they can be explained by examining the frequency
dependent nature of the impedance of capacitors and inductors.
With the advent of printed-circuit board (PCB) technology,
microwave system also develop a strip line components and
system with a technique of integrated circuit, called MMIC. It is
a type of Integrated circuit device that operates at microwave
frequencies (300MHz - 300GHz). Inputs and outputs on MMIC
devices are frequently matched to a characteristic impedance of
50 ohms. In advanced filter design, micro strip edge-coupled
filters are used, they have advantages such as easy design
procedures and simple integration into circuits. A general
structure of parallel-coupled (or edge-coupled) micro strip filters
that use half-wavelength line resonators. They are positioned so
that adjacent resonators are parallel to each other along half of
their length. This parallel arrangement gives relatively large
coupling for a given spacing between resonators, therefore this
filter structure is particularly convenient for constructing filters
having a wider bandwidth as compared to the structure for the
end coupled microstrip filters. For the creation of EM waves we
need specific structures with time-varying charges and currents.
At high frequencies hollow waveguides are used to transmit
energy because they do not radiate at any frequency. There are
new design methodologies for EM analysis such as topological
partitioning, functional partitioning, and tuning methodology. In
this filter design topological partitioning method is applied since
it has advantage of gain in speed and also one can make certain
changes very quickly.
This paper deals with the designing and fabrication of microstrip
low pass filters. The designing is done using AWR Microwave
Office simulation program developed by Applied Wave
Research USA. This is a user-friendly software with all of the
capabilities necessary for the accurate modelling and design of
microwave components. It contains a linear, harmonic-balance,
time domain, EM simulation, physical layout and includes linear
and nonlinear noise analysis and can model nonlinear behavior
existing in microwave devices.
2. I-FILTER
I-Filter is specifically developed for synthesis of lumped
element and distributed filters, it brings useful ﬁlter synthesis to
the integrated desktop. The module plugs directly into the

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Microwave Office design environment and is integrated as a
wizard within the AWR Design Environment (AWRDE), it is
completely integrated into AWRDE and easily accessible.
Limits for minimum line width and minimum line spacing are
specified in iFilter - which are typical dimensions for modern
printed circuit board processes.
I-Filter also provides the ability to adjust secondary parameters
in real time and see the results, in the case of hairpin filters,
includes adjustment of the filter’s nominal impedance. The short
connecting lines between the resonators (in the U-turns), will
have this impedance and the resonator lines will share this line
width. If the area is assumed to be limited to 0.36 x 0.30 inches,
the nominal impedance of the resonators can be adjusted to
examine the effects of line width on performance and required
area. Additionally, I-Filter performs accurate synthesis through
electromagnetic verification with for instance, AWR’s AXIEM
3D planar EM simulator. This is especially important when
designing distributed filters.
Fig 1: Schematic showing ifilter design
2.1 Features:
 Simplicity.
 Power – ideal or real, lumped or distributed, wide variety
 Ease-of-use.
 Integrated – works directly with AWR layout, EM, and
optimization.
 Upgradeable – options for your design needs.
3. MICROSTRIP
Microstrip line consists of thin strip conductor suspended over
ground plane by a low-loss dielectric material. Waves traveling
in microstrip line not only travels in the dielectric medium they
also travel in the air media above the microstrip line. Thus they
don’t support pure TEM waves, rather it supports quasi TEM
approximation.
Fig 2: A basic Microstrip structure
The effective dielectric constant in terms of W (width of the
Microstrip), h (height of the substrate) and εr (relative dielectric
constant) given by Hammerstad and Jensen [11] is:
εre =
εr + 1
2
+
εr − 1
2
1
1 +
12h
W
1
Characteristic impedance of the microstrip line is given by
Zc =
1
c CaCd
(2)
Where c is the velocity of electromagnetic waves in free space
c=2.99x108
m/s. The accuracy of Zc√εre is better than 0.01 %.
4. INITIAL LUMPED DESIGN:
Insertion loss method is used in designing lumped element
filter. It provides ways to shape pass band and stop band of the
filter, although its design theory is much more complex. The
order N of a filter can be found as follows:
𝑁 =
cosh−1
(100.1×𝐼𝐿 − 1)/(100.1×𝛼 − 1)
cosh−1(𝜔/𝜔𝑐)
(3)
The filter design specification has cut-off frequency of 18GHz.
From the above equation order of the filter is found to be 7. For
this design prototype parameters are as follows:
g0 = g8 = 1
g1 = g7 = 1.3722
g2 = g6 = 1.3781
g3 = g5 = 2.2756
g4 = 1.5001
5. IMPLEMENTATION:
5.1 Basic Design:
Basic filter is designed using microstrip lines such as MLIN,
MLEF and MTEE$ microstrips which are available in AWR
tool. Input/Output ports are matched to 50ohms, these are also
available in AWR tool. Microstrip has relative dielectric
constant, ɛᵣ=9.8, substrate thickness H=15mil, conductor

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thickness T=0.3mil, metal bulk resistivity normalized to gold
ρ=2 and loss tangent dielectric, Tand=0.002. Basic filter design
has insertion-loss of -1.0896dB and return loss of -42.441dB at
18.95GHz.
Fig 3: Basic schematic of LPF
5.2 Advanced Filter Design:
Advanced filter is designed using edge coupled microstrip line.
The following figure shows the cross section of a coupled line.
They support two modes of excitation, even and odd mode.
Fig 4: A Coupled Line Structure.
5.3 Even Mode:
In even mode excitation both the microstrip coupled lines have
the same voltage potential resulting in a magnetic wall at the
symmetry plane.
Fig 5: Quasi-TEM, Even Mode of a Pair of Coupled Microstrip
Lines
The Odd mode Impedances can be calculated using the
following formulae
(𝑍 𝑜𝑒 )𝑗 ,𝑗+1 =
1
𝑌0
1 +
𝐽01
𝑌0
+
𝐽01
𝑌0
2
(4)
Where,
𝐽01
𝑌0
=
𝜋∆
2𝑔0 𝑔1
(5)
Jj.j+1
Y0 j=1 to n−1
=
𝜋∆
2ω1
′ 2𝑔𝑗 𝑔𝑗 +1
(6)
𝐽𝑛,𝑛+1
𝑌0
=
𝜋∆
2𝑔 𝑛 𝑔 𝑛+1
(7)
5.4 Odd Mode
In odd mode the coupled microstrip line possess opposite
potential. This results into an electric wall at the symmetry. The
following cross section diagram shows the same.
Fig 6: Quasi-TEM, Odd Mode of a Pair of Coupled Microstrip
Lines
The Odd mode impedances can be calculated as same as Even
mode impedances using the following formulae.
(𝑍 𝑜𝑜 )𝑗,𝑗+1 =
1
𝑌0
1 −
𝐽01
𝑌0
+
𝐽01
𝑌0
2
(8)
Where,
𝐽01
𝑌0
=
𝜋∆
2𝑔0 𝑔1
(9)
Jj.j+1
Y0 j=1 to n−1
=
𝜋∆
2ω1
′ 2𝑔𝑗 𝑔𝑗+1
(10)
𝐽𝑛,𝑛+1
𝑌0
=
𝜋∆
2𝑔 𝑛 𝑔 𝑛+1
11
Table 1: Odd and Even Impedances values obtained from the
admittance inverter parameters
J
Even – mode
impedance
(Zoe)j , j+1
Odd – mode
impedance
(Zoo)j , j+1
Characteristic
Impedance Zo
Zo2
 (Zoe)(Zoo)
0 78.777 37.9177 54.6514
1 59.7244 43.0544 50.7089
2 57.3072 44.3672 50.4238
3 56.9688 44.5688 50.3888

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Applied Wave Research has developed accurate advanced
numerical models for microstrip edge coupled lines, which are
labelled MXCLIN elements. “X,” which can range from 3 to 16,
represents the number of parallel edge-coupled microstrip lines.
Figure.7 shows AWR MXCLIN with 8 coupled lines.
Fig 7: AWR MXCLIN advanced numerical element model
where X=8.
5.5 Electromagnetic Model:
At frequency greater than 3GHz it is compulsory for any
microstrip design to undergo EM simulation. EM simulation
considers all the dielectric effect so the response of the
schematic will lose some of its characteristics and as the
frequency goes higher and higher these responses may vary
enormously. So at the higher frequency the EM Simulation is
very necessary simultaneously it is difficulty to meet the
specification. To increase the length of all resonators by
connecting a multiple coupled line in between the two halves.
The multiple coupled lines can come from a good circuit theory
model, or it can be generated from an EM analysis. Increase the
length of the added line to decrease the center frequency of the
filter. To shorten all the resonators, connect a negative length
line. While not physical, circuit theory and EM analysis
programs both have no trouble doing this just connect a multiple
coupled line in between the two halves. No need to repeat the
entire EM analysis. Tune up your layout with circuit theory, do
one more EM analysis to confirm the changes, and then
fabricate. Design closure, quick and easy: a tunable EM
analysis.
Fig 8: EM sight filter.
EM sight is designed using EM layer= 2, a perfect conductor
material, drawing layer of top copper conductor, input port of
impedance 50ohms and reference plane distance= 30mil, and
output port of impedance 50ohms and reference plane distance=
34mil.
Fig 9: Three dimensional EM Structure design with enclosure
box
An EM simulation is recommended to confirm the design
accuracy fig 9 shows the simulation of planar 3D structures
containing multiple metallization and dielectric layers. The
structures can have interconnecting vias between layers or to
ground. EMSight uses the Galerkin Method of Moments (MoM)
in the spectral domain, an extremely accurate method for
analyzing micro strip, this technique can provide accurate
simulation results up to 100 GHz and beyond.
6. RESULT AND ANALYSIS:
Insertion loss plot of lumped element low pass filter is shown in
figure 10. Here the insertion loss at 18.14GHz is -2.999dB.
Fig 10: Insertion loss of Lumped design.
Return loss of lumped element low pass filter is shown in fig 11.
Here the return loss at 18.011GHz is -16.029dB.
W1
W2
W3
W4
W5
W6
W7
W8
1 2 3 4 5 6 7 8
9 10 11 12 13 14 15 16
M8CLIN
ID=TL1
W1=W2 mil
W2=W4 mil
W3=W6 mil
W4=W6 mil
W5=W6 mil
W6=W6 mil
W7=W4 mil
W8=W2 mil
S1=L3 mil
S2=L5 mil
S3=L7 mil
S4=L9 mil
S5=L7 mil
S6=L5 mil
S7=L3 mil
L=24 mil
Acc=1

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Fig 11: Return loss of Lumped design
Insertion loss of Basic low pass filter design is shown in fig 12.
Here the insertion loss at 18.95GHz is -1.0869dB.
Fig 12: Insertion loss of Basic low pass filter.
Return loss of basic low pass filter is shown in fig 13. Here the
return loss at 18GHz is -42.441dB.
Fig 13: Return loss of basic low pass filter.
Insertion loss of advanced low pass filter is shown in fig 14.
Fig 14: Insertion loss of advanced low pass filter.
Return loss of advanced low pass filter is shown in fig 15. Here
the return loss at 18GHz is -10.001dB.
Fig 15: Return loss of advanced low pass filter.
Insertion loss of EM sight low pass filter is shown in fig 16.
Fig 16: Insertion loss of EM sight low pass filter.

__________________________________________________________________________________________
Return loss of EM sight low pass filter is shown in fig 17. Here
the return loss at 18.124GHz is -20dB.
Fig 17: Return loss of EM sight low pass filter.
VSWR comparison between iFilter, basic LPF, advanced LPF
and EM sight design is shown in fig 18. The advanced design
and EM sight design having very good VSWR value. Variation
of VSWR curve is crazy in Lumped design which is shown in
fig 19.
Fig 18: VSWR comparison.
Fig 19: Variation of VSWR in lumped design.
7. SUMMARY
Table 2: Characteristics Comparison of all design types
Table 3: Parameters Comparison with previous designs
8. CONCLUSIONS
This paper shows the design of 18GHz printed micro strip low
pass filter on 15 mil Alumina substrate and simulation shows the
comparison between lumped , basic , advanced and EM sight
design successfully. The "LPF EMSight” shows the filter in the
EMSight 2.5D electromagnetic simulator, which is viewed in
three dimensions. This compares very closely to measured data.
The "LPF Advanced" schematic makes use of advanced X-
Models (EM-based models), coupled lines and other linear
schematic elements, including a substrate definition. This too
gives excellent correlation. The "LPF Basic" indicates potential
errors in schematic entry with the associated errors in results. A
good comparison is achieved among all four designs and
validated through circuits and EM sight in AWR MWO
Environment, furthermore particular design can be chosen based
on tradeoffs.
The design will be useful for Satellite and PTP Communications
Links, Marine and Pleasure Craft Radar, Port Vessel Traffic
Services etc…
Design Frequen
cy
Insertio
n loss
Return
loss
VSW
R
Lumped
design
18.14GH
z
-2.996dB -
16.067d
B
1.5
Measured
filter
18.659G
Hz
-
3.0573d
B
-
18.458d
B
10.24
Basic design 18.95GH
z
-
1.0869d
B
-
42.441d
B
1.029
Advanced
design
18.498G
Hz
-
3.0195d
B
-
10.001d
B
1.826
EM sight
design
18.586G
Hz
-3.039dB -
20.001d
B
1.081
References [2] [7] [10] This
work
Order of the
filter
5 4 3 7
Cut-off
frequency
2 &
3GHz
7.7GHz 1990MHz 18.95GHz
Insertion-
loss
-0.6dB 18dB <0.6dB -
1.0869dB

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REFERENCES
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Design and simulation of printed micro strip low pass filter based on the electromagnetic models 18 ghz printed microstrip lowpass filter using x models

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Design and simulation of printed micro strip low pass filter based on the electromagnetic models 18 ghz printed microstrip lowpass filter using x models