Design and simulation of broadband rectangular microstrip antenna

Eng.Tech.V0l.26,No1,2008
93
Design and Simulation of Broadband Rectangular
Microstrip Antenna
Adil Hameed Ahmad and Basim Khalaf Jar’alla
Received on:5 / 5/2005
Accepted on:5 / 3/ 2006
Abstract
In this work, many techniques are suggested and analyses for
rectangular microstrip antenna (RMSA) operating in X-band for 10 GHz
center frequency. These approaches are: lowering quality factor, shifting
feeding point , using reactive loading and modification of the patch shape.
The design of a RMSA is made to several dielectric materials, and the
selection is based upon which material gives a better antenna performance
with reduced surface wave loss. Duroid 5880 and Quartz are the best materials
for proposed design to achieve a broader Bandwidth (BW) and better
mechanical characteristics than using air. The overall antenna BW for RMSA
is increased by 11.6 % with Duroid 5880 with shifted feeding point and with
central shorting pin (Reactive loading) while that for Quartz is 17.4 %.
Modification of patch shape with similar improving techniques gives an
overall increasing VSWR bandwidth of 26.2 % for Duroid 5880 and a
bandwidth of 30.9 % for Quartz. These results are simulated using Microwave
Office package version 3.22, 2000.
‫اﻟﺨﻼﺻﺔ‬
‫ﺍﻟﺒﺤﺙ‬ ‫ﻫﺫﺍ‬ ‫ﻴﻘﺩﻡ‬‫ﺤﺯﻤﺔ‬ ‫ﻟﺘﻭﺴﻴﻊ‬ ‫ﺘﻘﻨﻴﺎﺕ‬ ‫ﻋﺩﺓ‬‫ﺍﻟﺘﺭﺩﺩ‬‫ﺫﻭ‬ ‫ﺍﻟﺩﻗﻴﻕ‬ ‫ﺍﻟﺸﺭﻴﻁﻲ‬ ‫ﺍﻟﻬﻭﺍﺌﻲ‬ ‫ﻟﻌﻤل‬
‫ﻭﺍﺤﺩﺓ‬ ‫ﻨﻘﻁﺔ‬ ‫ﻤﻥ‬ ‫ﻴﻐﺫﻯ‬ ‫ﻭﺍﻟﺫﻱ‬ ‫ﺍﻟﻤﺴﺘﻁﻴل‬ ‫ﺍﻟﺸﻜل‬,‫ﺍﻟﺘﺭﺩﺩﻴﺔ‬ ‫ﺍﻟﺤﺯﻤﺔ‬ ‫ﻓﻲ‬ ‫ﻋﻤﻠﻪ‬ ‫ﻴﻜﻭﻥ‬ ‫ﺒﺤﻴﺙ‬X‫ﻭ‬
‫ﻗﺩﺭﻩ‬ ‫ﻤﺭﻜﺯﻱ‬ ‫ﺒﺘﺭﺩﺩ‬)10 GHz(‫ﺍﻟﺴﻁﺤﻴﺔ‬ ‫ﺍﻟﻤﻭﺠﺔ‬ ‫ﺘﺎﺜﻴﺭ‬ ‫ﻭﺘﻀﺎﺅل‬‫ﺍﻟﻤﺴﺘﻭﻴﺎﺕ‬ ‫ﺍﺩﻨﻰ‬ ‫ﺍﻟﻰ‬.‫ﻭﻫﺫﻩ‬
‫ﻫﻲ‬ ‫ﺍﻟﺘﻘﻨﻴﺎﺕ‬:‫ﻟﻠﻬﻭﺍﺌﻲ‬ ‫ﺍﻟﺠﻭﺩﺓ‬ ‫ﻤﻌﺎﻤل‬ ‫ﺘﻘﻠﻴل‬)Q(‫ﻤﻭﻗ‬ ‫ﺘﻐﻴﻴﺭ‬ ‫ﻭ‬‫ﺍﻟﺤﻤل‬ ‫ﻭﺍﺴﺘﺨﺩﺍﻡ‬ ‫ﺍﻟﺘﻐﺫﻴﺔ‬ ‫ﻨﻘﻁﺔ‬ ‫ﻊ‬
‫ﻏﻴﺭ‬‫ﺍﻟ‬‫ﻟﻠﻬﻭﺍﺌﻲ‬ ‫ﺍﻟﺸﻜل‬ ‫ﺘﻌﺩﻴل‬ ‫ﻭ‬ ‫ﻔﻌﺎل‬.
‫ﻟﻌﺩﺓ‬ ‫ﺍﻟﻤﺴﺘﻁﻴل‬ ‫ﺍﻟﺸﻜل‬ ‫ﺫﻭ‬ ‫ﺍﻟﺩﻗﻴﻕ‬ ‫ﺍﻟﺸﺭﻴﻁﻲ‬ ‫ﻟﻠﻬﻭﺍﺌﻲ‬ ‫ﺘﺼﺎﻤﻴﻡ‬ ‫ﻨﻤﺎﺫﺝ‬ ‫ﻋﺩﺓ‬ ‫ﺘﻘﺩﻴﻡ‬ ‫ﺘﻡ‬ ‫ﻟﻘﺩ‬
‫ﻋﺎﺯﻟﺔ‬ ‫ﻤﻭﺍﺩ‬,‫ﺘﻘ‬ ‫ﻤﻊ‬ ‫ﻟﻠﻬﻭﺍﺌﻲ‬ ‫ﺍﺩﺍﺀ‬ ‫ﺍﻓﻀل‬ ‫ﺍﻋﻁﻰ‬ ‫ﺍﻟﺫﻱ‬ ‫ﺍﻟﺘﺼﻤﻴﻡ‬ ‫ﺍﺨﺘﻴﺎﺭ‬ ‫ﺘﻡ‬ ‫ﻗﺩ‬ ‫ﻭ‬‫ﺍﻟﺨﺴﺎﺌﺭ‬ ‫ﻨﺴﺒﺔ‬ ‫ﻠﻴل‬
‫ﺍﻟﺴﻁﺤﻴﺔ‬ ‫ﺍﻟﻤﻭﺠﺔ‬ ‫ﺘﻭﻟﻴﺩ‬ ‫ﺘﺎﺜﻴﺭ‬ ‫ﺒﺴﺒﺏ‬,‫ﺍل‬ ‫ﻫﻤﺎ‬ ‫ﺍﻟﻤﻌﺘﻤﺩ‬ ‫ﻟﻠﺘﺼﻤﻴﻡ‬ ‫ﻤﺎﺩﺘﻴﻥ‬ ‫ﺍﻓﻀل‬ ‫ﻜﺎﻨﺕ‬)Quartz(‫ﻭ‬
‫ﺍل‬)Duroid5880(,‫ﻋﻤ‬ ‫ﺤﺯﻤﺔ‬ ‫ﺍﻭﺴﻊ‬ ‫ﺍﻋﻁﺕ‬ ‫ﺍﻟﻤﺎﺩﺘﻴﻥ‬ ‫ﻫﺎﺘﻴﻥ‬ ‫ﺍﻥ‬ ‫ﺤﻴﺙ‬‫ﺘﺭﺩﺩﻱ‬ ‫ل‬‫ﺍﻟﻤﻭﺍﺩ‬ ‫ﻤﻥ‬
‫ﺍﻻﺨﺭﻯ‬‫ﺒ‬ ‫ﺍﻓﻀل‬ ‫ﻭﻜﺫﻟﻙ‬‫ﺨﻭﺍﺼ‬‫ﻬﺎ‬‫ﺍﻟﻤﻴﻜﺎﻨﻴﻜﻴﺔ‬.
‫ﺍﻋﻁى‬ ‫ﻟﻘﺩ‬‫ﺍ‬ ‫ﺫﻭ‬ ‫ﺍﻟﺩﻗﻴﻕ‬ ‫ﺍﻟﺸﺭﻴﻁﻲ‬ ‫ﺎﻟﻬﻭﺍﺌﻲ‬‫ﺍﻟﻤﺴﺘﻁﻴل‬ ‫ﻟﺸﻜل‬‫ﺍل‬ ‫ﻤﺎﺩﺓ‬ ‫ﻤﻊ‬)Duroid5880(
‫ﺯﻴﺎﺩﺓ‬‫ﺘﺭﺩﺩﻱ‬ ‫ﺍﺸﺘﻐﺎل‬ ‫ﺤﺯﻤﺔ‬ ‫ﻋﺭﺽ‬‫ﻜﻠﻲ‬‫ﺒﻤﻘﺩﺍﺭ‬)11.6 %(,‫ﺍﻤﺎ‬‫ﺘﻠﻙ‬‫ﺍل‬ ‫ﻤﺎﺩﺓ‬ ‫ﻤﻊ‬)Quartz(‫ﻓﻘﺩ‬
‫ﺒ‬ ‫ﺍﻟﺯﻴﺎﺩﺓ‬ ‫ﻜﺎﻨﺕ‬‫ﻌﺭﺽ‬‫ﺍﻷﺸﺘﻐﺎل‬ ‫ﺤﺯﻤﺔ‬‫ﺒﻤﻘﺩﺍ‬‫ﺭ‬( 17.4 %).‫ﻟﻠﺸﺭﻴﺤﺔ‬ ‫ﺍﻟﺸﻜل‬ ‫ﺘﻌﺩﻴل‬ ‫ﺘﻘﻨﻴﺔ‬ ‫ﺍﻤﺎ‬
‫ﻟﻬﻭﺍﺌﻲ‬ ‫ﺍﻟﺩﻗﻴﻘﺔ‬)Duroid5880(‫ﺍﻋﻁﻰ‬ ‫ﻗﺩ‬‫ﺯﻴﺎﺩﺓ‬‫ﺒﻤ‬ ‫ﺤﺯﻤﺔ‬ ‫ﻋﺭﺽ‬‫ﻘﺩﺍﺭ‬)26.2 %(‫ﻭ‬)30.9
%(‫ﻟﻬﻭﺍ‬‫ﺌ‬‫ﻲ‬Quartz)(.
‫ﺘﻡ‬‫ﺍﺴﺘﺨﺩﺍﻡ‬‫ﺒﺭﻨﺎﻤﺞ‬‫ﺍﻟﻤﺤﺎﻜﺎﺓ‬)(Microwave Office Package ver. 3.22, 2000
‫ﺍﻟﻨﺘﺎﺌﺞ‬ ‫ﻟﻤﺤﺎﻜﺎﺕ‬.

93
1. Introduction
The arrangement of an arbitrary
shaped patch microstrip antenna is
given in Figure 1. It consists of patch,
substrate, ground plane and feeding
point. A patch is a two-dimensional
antenna element, which is often
rectangular in shape. It is of a very
thin thickness (t) of metallic strip on
top of a material known as the
substrate with thickness h (h«λo,
usually 0.003λo≤h≤0.05λo, where λo is
free space wavelength) above a
ground plane[1].The microstrip
antenna (MSA) can be excited
directly either by a coaxial probe or
by a microstrip line. It can also be
excited indirectly using
electromagnetic coupling or aperture
coupling and a coplanar waveguide
feed, in which case there is no direct
metallic contact between the feed line
and the patch. The microstrip patch is
designed so that its pattern has
maximum normal to the patch plane
(broadside radiator) by choosing a
certain field configuration mode. For
rectangular patch, the length L of the
element is usually λo/3<L<λo/2. The
strip (patch) and the ground plane are
separated by a dielectric (substrate).
Microstrip antennas have a very
high antenna quality factor (Q). This
factor represents the losses associated
with the antenna and a large quality
factor leads to narrow bandwidth and
low efficiency. Quality factor can be
reduced by increasing the thickness of
the dielectric substrate. But as the
thickness increases, an increasing
fraction of the total power delivered
by the source goes into a surface
wave. This surface wave contribution
can be counted as an unwanted power
loss since it is ultimately scattered at
the dielectric bends and causes
degradation of the antenna
characteristics. However, surface
waves can be minimized by the use of
photonic bandgap structures [2].
Other problems such as lower gain
and lower power handling capacity
can be overcome by using an array
configuration for the elements. The
patch is generally square, rectangular,
circular, triangular, and elliptical or
some other common shapes .
Microstrip antennas have narrow
bandwidth, typically 1-5%, which is
the major limiting factor for the
widespread application of these
antennas. Increasing the bandwidth of
MSA has been the major thrust of
researches in this field [3,4 ].
2. Analyses and Modeling of
RMSA
Three methods of analysis are
commonly used to calculate
microstrip antenna (MSA) parameters
[5,6]. These are:Transmission line
model, cavity model, and full wave
analysis.
It is useful to model the microstrip
antenna as a transmission line . This
model is the simplest of all and it
gives good physical insight but it is
less accurate. It represents the MSA by
two slots of width W and height h,
separated by a transmission line of
length L. The microstrip is essentially
a non homogeneous line of two
dielectrics, typically the substrate and
air. An effective dielectric constant
(εreff) must be obtained in order to
account for the fringing and the wave
propagation in the line. The
expression for εreff is given by [1]:
2
1
121
2
1
2
1
−
⎥
⎦
⎤
⎢
⎣
⎡
+
−
+
+
=
W
hrr
reff
εε
ε
……
(1)

2
Fig. 2 shows a RMSA of length L,
width W resting on a substrate of
height h. The co-ordinate axis is
selected such that the length is along
the y direction, width is along the x
direction .
In order to operate in the
fundamental TM10 mode, the length of
the patch must be slightly less than λ/2
where λ is the wavelength in the
dielectric medium and is equal to
λo/√εreff where λo is the free space
wavelength.
In Fig. 2a, the MSA is represented
by two slots, separated by a
transmission line of length L and open
circuited at both ends. Along the
width of the patch, the voltage is max
and current is minimum due to the
open ends. The fields at the edges can
be resolved into normal and tangential
components with respect to the
ground plane as in Fig.2b.
The dimensions of the patch along
its length have now been extended on
each end by a distance ∆L, which is
given empirically by [7]:
)8.0)(258.0(
)264.0)(3.0(
412.0
+−
++
=∆
h
W
h
W
L
reff
reff
ε
ε h
.
(2)
The effective length of the patch Leff
now becomes:
Leff = L+2∆L
…. (3)
For a given resonance frequency fo,
the effective length is given as:
reffo
eff
f
c
L
ε2
= …. (4)
Where c is the speed of light.
For a rectangular Microstrip patch
antenna, the resonance frequency for
any TMmn mode is given as:
2
1
22
2 ⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
⎟
⎠
⎞
⎜
⎝
⎛
+⎟
⎠
⎞
⎜
⎝
⎛
=
W
n
L
mc
f
reff
o
ε
…. (5)
Where m and n are modes along L and
W respectively.
For efficient radiation, the width W is
given as [8] :
( )
2
1
2
+
=
r
of
c
W
ε
…. (6)
The cavity model is more accurate
and gives good physical insight but is
complex in nature. The full wave
models are extremely accurate,
versatile and can treat single elements,
finite and infinite arrays, stacked
elements, arbitrary shaped elements
and coupling .
The four most popular feed
techniques used in MSA are the
microstrip line, coaxial probe ,
aperture coupling and proximity
coupling [1, 7].
The input impedance should be
accurately known so that a good
match between the element and the
feed can be designed. Referring to
Fig. 3, the input impedance at the feed
point (xo ) is [1,9]:
)(cos
)cos(
1
)( 2
o
mr
oin x
nGG
xZ β
π+
=
Where Gr is the self conductance
given by the following three relations,
depending on
W/λo :
2
2
90 o
r
W
G
λ
= , for W<0.35λo
2
60
1
120 πλ
−=
o
r
W
G , for 0.35λo
≤ W ≤ 2 λo

3
o
r
W
G
λ120
= , for 2 λo≤ W
and Gm is the mutual conductance
between the patch ends. At resonance
and Gr>>Gm then the input
impedance becomes:
⎟
⎠
⎞
⎜
⎝
⎛
== o
r
inoin x
LG
RxZ
π2
cos
1
)(
…. (7)
A microstrip antenna is basically a
broadside
radiator, which has a relatively large
beam width and low gain
characteristics. The formulas for the E
and H plane radiation patterns are
given by [10]:
E-plane:
F(Φ) = { sin[ (koh/2)cosΦ]
/(koh/2)cosΦ}.cos[ (koL/2)cosΦ]
…. (8)
H-plane:
F(θ) = { sin[ (kow/2)cosθ]
/(kow/2)cos θ }.sin θ
…. (9)
Where:
o
ok
λ
π2= (free space wave
number)
The half power beam widths in the
H and E planes are given by [ 11]:
__________
θ BH = 2 cos – 1
[ | 1 . . ]
√ ( 2 + ko W )
….. (10)
___________________
|
7.03______
θ BE = 2 cos – 1
[ √ ( 3 ko
2
Le
2
+
ko
2
h2
) ]
….. (11)
Thus beam width can be increased
by choosing a smaller element, thus
reducing W and L. For a given
resonant frequency these dimensions
may be changed, by selecting a
substrate having a higher relative
permittivity. As beam width increases,
element gain and directivity decrease,
however, efficiency is unaffected .
The expression for approximately
calculating the directivity D of the
rectangular microstrip antenna is
given by [10] :
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
++≅
r
WD
ε
6.1log106.62.0
dB
…….
(12)
For other geometries, the values of
equivalent W can be obtained by
equating its area with that of the
rectangular microstrip antenna [12].
The most serious limitation of the
microstrip antenna is its narrow BW.
The BW could be defined in terms of
its VSWR or input impedance
variation with frequency or in terms
of radiation parameters. For the
circularly polarized antenna, BW is
defined in terms of the Axial Ratio .
VSWR is a very popular parameter for
determining the BW of a particular
antenna configuration(1≤ VSWR ≤ 2 )

4
as an acceptable interval for
determining the BW of the antenna.
BW is presented more concisely as a
percentage where:
%100% ×
∆
=
of
f
BW
…. (13)
Where ∆f is the width of the range of
acceptable frequencies, and fo is the
resonant frequency of the antenna
[10].
The expressions for approximately
calculating the percentage BW of the
(RMSA) antenna in terms of patch
dimensions and substrate parameters
is given by[13]:
%
L
WhA
BW
ro ελ
×
=
…. (14)
Where A is constant:
A = 180 for
045.0≤
ro
h
ελ
A = 200 for
075.0045.0 ≤≤
ro
h
ελ
A = 220 for
07.0≥
ro
h
ελ
With an increase in W, bandwidth
increases. However, W should be
taken less than λ to avoid excitation of
higher order modes.
The BW of the (MSA) can also
inversely proportional to its quality
factor Q and is given by [1].
BW=(VSWR-1)/(Q√VSWR) ….
(15)
The BW is usually specified as
frequency range over which VSWR ≤
2.
3. Design
considerations and
Process of Broadband
MSA
The methods for increasing
the BW of (MSA)'s are continuously
getting upgraded. The search for an
ideal broadband (MSA) is still
continuing. Perhaps a combination of
various approaches would lead to an
optimum broadband configuration
[3,5].
There are various techniques for
increasing the bandwidth BW of
(MSA)'s. The main techniques used to
increase the bandwidth are presented
briefly as[14]:
a) Low Quality Factor :
The principle of introducing low
quality factor of the cavity below the
patch can be achieved by:
. Low dielectric constant .
. Larger thickness of the substrate
but it is restricted by the surface wave
generation leading to low gain and
low efficiency of the antenna .
b) Modified Shape Patches :
The regular (MSA) configurations,
such as rectangular and circular
patches have been modified to
rectangular ring and circular ring,
respectively, to enhance the BW. The
larger BW is because of a reduction in
the quality factor of the patch
resonator, which is due to less energy
stored beneath the patch and higher
radiation. In this work the modified
shape is developed as a compact
model; it has nearly a trapezoidal
shape, its dimension consist of a

5
combination from three rectangular
patches one at resonance (center
frequency of the operating band)
which gives the length of the patch
and the other two at beginning
frequency and end frequency of the
operating bandwidth which gives the
two widths of the trapezoidal
shape[12].
c) Multilayer Configurations :
In the multilayer configuration, two
or more patches on different layers of
the dielectric substrate are stacked on
each other. Based on the coupling
mechanism, these configurations are
categorized as electromagnetically
coupled or aperture-coupled
microstrip antennas [12].
The design process of broadband
MSA is based mainly on the
measurements acquired from the
narrowband rectangular antenna using
single layer configuration. The
antenna is assumed passive, linearly
polarized, fed by a coaxial probe with
input impedance nearly of 50 ohms.
The patch antenna element is
designed to radiate or operate with a
narrow impedance bandwidth.
The narrow bandwidth of the
microstrip antenna can be widened by
using combination between lowering
Q-factor, modified shaped patches,
and reactive loading approaches.
To achieve the broad banding of
the microstrip antenna, it is important
to determine the requirement arises
with such design. The requirements
needed to start the design process of a
broadband microstrip antenna are:
a- Type of substrate material to be
choosen.
b- The center frequency, and
c- The operating bandwidth.
The substrate material is important
in the successful design, where a low
quality factor of the cavity below the
patch can be achieved by proper
choice of the substrate material. The
center frequency of the antenna is 10
GHz designed to operate at whole X-
band .
The substrate height is limited by the
excitation of surface wave, and then
choice is based on Woods criterion
which depends on the operated
frequency and substrate material [7]:
h<0.07λo for εr≈ 2.3 , and h<0.023λo
for εr≈10
Assuming the antenna is operating to
cover the whole X-band range from 8
GHz to 12 GHz. For each frequency
there is a desired substrate height
associated with it. This height is based
on the above criterion. For f = 12
GHz then λo = 2.5 cm , the calculated
heights for both dielectrics are:
h = 0.07 λo = 0.175 cm for εr≈ 2.3,
and h = 0.023λo = 0.0575 cm for
εr≈10.
Therefore for εr≈ 2.3 the height
must be 0.175 cm or less, and for
εr≈10 the height must be 0.0575 cm or
less. For proper design, the choice is
made for εr≈ 2.3 is 0.17 cm and for
εr≈10 is 0.057 cm, since the antenna is
assumed to cover the X-band, i.e. to
stay in the safe side if antenna is
operating in the upper frequency limit
at 12 GHz.
The flow chart in Figure 4 explains
the design process. During phase 1 of
the work, the permittivity of the
substrate will be tested. This process
had to be carried out several times to
reach an optimal value of substrate
permittivity that gives a wider BW
using accurate permittivity values.
Phase one also oversaw the selection
of substrate heights to reduce surface
wave excitation. In phase two, three
narrowband patches were designed.
The first one was at the center
frequency of the band, the second was
at the beginning frequency of the band

6
and the third one was at the end
frequency of the band. The patches
were thoroughly tested for bandwidth
and tuned to best match the input
impedance. Phase three involved in-
depth research regarding possible
broadband techniques. The best
scheme is chosen based on
manufacturing simplicity without
compromising performance over the
frequency band concerned. The
modified patch has nearly a
trapezoidal shape as shown in Fig. 5
with its new dimensions .
The feeding point is the same as that
point of the patch at the beginning
frequency of the band, with some
amount of offset to match Zin .
Central pin may improve the purity
of the resonant mode. An addition of a
shorting pin acts as an extra parameter
to control the mode excitation.
4. Design Examples
[15]
To achieve the requirements, two
design examples are considered for X-
band applications. The patch antenna
element is designed to operate at 10
GHz as center frequency, and to
widen the bandwidth as far as possible
to cover X-band. The calculations are
made step by step from dielectric
materials that have low dielectric
constant to higher one.
Example one: Rectangular patch
design, dielectric material RT Duroid
5880, dielectric constant εr=2.2, loss
tangent<0.0009, operating
frequency=10 GHz, λo=3 cm.
• The height (h) must be less
than 0.175 cm for εr≈ 2.3.
Then height should be
h=0.17 cm.
• The width of the MSA is
given by equation (6), where
W=1.1859 cm
• Eqn(1) gives the effective
dielectric constant as
εreff=1.9638
• Eqn (4) gives the effective
length as: Leff =1.0704 cm
• Eqn (2) gives the length
extension as: ∆L=0.0864 cm
The actual length is obtained
from eqn (3) as:
L = Leff -2∆L then
L=0.8976 cm
The ground plane dimensions are L
g=1.9176 cm and W g=2.2059 cm
Feed point location where the input
impedance is nearly 50 ohms is: Xf
= W /2 and Yf = L / (2√ εreff ) then
Xf=0.593 cm along the width, and
Yf=0.320 cm along the length.
• Eqns (8) and (9) give the E
and H plane radiation
patterns: ko=2π / λo=2.1
rad/cm
• The half power beamwidths
are given by eqns (10) and
(11) as: θBE=1.65 rad and
θBH=2.158 rad
• The directivity is calculated
from eqn(12) as: D= 6.933
dB
• Eqn (14) gives the BW as:
BW=7.9 %
This example can be extended
for all other materials. Table 1
gives the calculated parameters
associated with such materials.
It is clear from this table that Duroid
5880, Duroid 5870 and, Quartiz are
the best materials for proposed design
with broader bandwidth and better
mechanical characteristics than using
air.
Example two : Modified Shape
Microstrip Design (MSMSA)[16].

7
Dielectric material RT Duroid 5880,
dielectric constant εr=2.2, loss
tangent<0.0009, operating frequency
(8-12) GHz, λo=3 cm, h=0.17 cm.
From Figure 4 broadband antenna
design needs to choose L, W1 and W2.
This can be done by the following
steps design procedure:
From Table 1, the actual length
L at 10 GHz for this dielectric is
L=0.8976 cm
• Eqn (6) gives W1 at 8 GHz
W1=1.48232 cm and W2
at12GHz
W2=0.988212
cm
• The feed point location as:
Xf=W1/2=0.74116 cm, and
Yf=L/2√ εreff=0.320 cm
• The ground plane dimensions
as:
L g=6 h + L =1.9176 cm ,
and Wg=6 h+W1=2.50232 cm
Table 2 shows the calculated
dimensions for different materials
compared to air case. This table is
used to get all results for MSA
performance.
5. SIMULATION AND
RESULTS
In this section, a documentation of
results is presented. These results are
obtained by using a design package
called Microwave Office version 3.22,
2000. The microwave office results
are compared with their
corresponding theoretical results.
These results are separated into two
categories: The first category includes
the simulation and test of RMSA with
single layer, probe fed and its
performance calculations (VSWR,
bandwidth, HPBW and, field pattern).
While the second category, includes
the simulation and test of the
suggested modified shape microstrip
antenna (MSMSA) and the effect of
variation of the feeding point with and
without adding the central shorting
pins[15].
a) Consider the RMSA that were
designed in previous sections, and
whose results were given in Table 1,
are tested using microwave office
package .
The selection of the correct material
for the broadband design is made.
Three types of substrate materials are
chosen. These substrate materials are
Duroid 5880, Quartiz, and Duroid
6006 and their dielectric constants are
2.2, 3.78 and 6.15 respectively. The
test shows that the bandwidth (for
VSWR≤2) in the operating X - band,
for Duroid 5880 is 9.7% and for
Quartiz is 15.5%, while for Duroid
6006 it is 1.3% [15]. Therefore the
choice was made on Duroid 5880 and
Quartiz, because they have a broader
BW than Duroid 6006.
Referring to Table 1, the original
feeding point of RMSA with substrate
material Duroid 5880 is (Xf = 0.593
cm, Yf= 0.320 cm) and, for Quartz is
(Xf = 0.34 cm, Yf = 0.25 cm) with an
operating frequency of 10 GHz. The
feeding will be shifted along X and Y
axis. From the original feeding point,
for Duroid 5880 it is by amount of
±0.038952 cm along X and ±0.044118
cm along Y, and for Quartz it is by
amount of ±0.048515 cm along X and
±0.034425 cm along Y.This shifted
gives a gain in the BW of the RMSA ,
for Duroid 5880, it is enhanced from
(9.7%) to (10.8%). While for Quartz,
the VSWR BW is enhanced from
(15.5%) to (16.1%). The optimum
value of shifting for Duroid 5880 is
toward positive X, while for Quartz it
is toward negative X taking into

8
consideration the mismatching
problems.
The central shorting pin is added
to the rectangular patch, where its
feeding position is shifted. As can be
seen from Fig. 6 , there is a gain in
VSWR BW≤2 of the RMSA, when the
central shorting pin is used, because
the resonance size of the patch
increases. For substrate material
Duroid 5880 is enhanced the
bandwidth from 1080 MHz (10.8%) to
1160 MHz (11.6%) . It increases by an
amount of 80 MHz (0.8%). While
that for Quartz, the BW is enhanced
from 1610 MHz (16.1%) to 1740 MHz
(17.4%). It increases by an amount of
130 MHz (1.3%).
Figure 7 a,b shows the normalized
electric field in polar and rectangular
plots radiation pattern of the RMSA in
H-plane, with and without the central
shorting pin for Duroid 5880. HPBW
in H-plane which can be determined
from this figure as θBH= 69.3°. Fig
8a,b shows that in E-plane, with and
without the central shorting pin for
Duroid 5880. HPBW in E-plane is
θBE= 51.9° . Fig. 9 a,b shows the
correspond normalized radiated power
pattern in polar and rectangular plots.
It is clear, from these plots that the
central shorting pin, offers a small
degrading in the far field radiation
pattern, and gives a considerable
effects on bandwidth as seen in Fig. 6
.
b) Consider the proposed modified
shape microstrip antenna (MSMSA)
which gives improvement in the
radiation characteristics and
bandwidth over RMSA.
This MSMSA is also simulated and
tested using microwave office
package, with and without central
shorting pin, for the two substrate
materials the Duroid 5880 and
Quartz.
Fig. 10 shows the VSWR variation
with respect to frequency for the
modified shape patch with and
without central shorting pin, for
Duroid 5880 and Quartz . VSWR
BW≤2 of Duroid 5880 without central
shorting pin is 2.54 GHz (25.4%),
whereas with central shorting pin is
2.62 GHz (26.2%), while for Quartz
is enhanced from 2.39 GHz (23.9%),
to 3.09 GHz (30.9%)by using central
shorting pin.
Fig. 11a,b shows the electric field in
polar and rectangular plot, of the
Duroid 5880 (MSMSA) in H-plane,
with and without the central shorting
pin. HPBW are θBH= 57.4° and θBH=
59.6° respectively for the two cases.
Fig. 12 a,b shows the Electric field
plots in E-plane where θBE= 15.86°
for the two cases.
Fig. 13 a,b shows the normalized
radiated power pattern for MSMSA
in polar and rectangular plots, with
and without the central shorting pin
for Duroid 5880 .
It is clear that the central shorting
pin, gives a considerable effect on
bandwidth of MSA.
6. Conclusion
One of the main problems arises
with the operation of MSA is the
surface wave excitation. Reduction of
surface wave is done by adjusting the
substrate height with respect to the
dielectric constant substrate material.
The selection of substrate materials
used in this design processes is based

9
on two materials, Duroid 5880 and,
Quartiz.
Broadening the bandwidth of the
rectangular microstrip antenna was
achieved by using a method of
lowering quality factor, shift feeding
point position, reactive loading and
by modification of the patch shape.
For substrate material Duroid 5880,
initial with 9.7% bandwidth with low
quality factor RMSA fed at original
feeding point getting as overall of
26.2% bandwidth with modification
in patch shape where reactive loading
was used. While for Quartz, initial
with 15.5% a percentage to be
enhanced to 30.9% by using shape
modification and, insertion of central
shorting pin. Table 3 shows the
enhancement in BW% for the
proposed types of MSA .
7. References
[1] COSTANTINE A. BALANIS,
"ANTENNA THEORY ANALYSIS
AND DESIGN", Wiley, 2nd edition,
Chapter 14, 1997.
[2] K. Rambabu, M. Alam, J.
Bornemann and M. A. Stuchly,
"Compact Wideband Dual-Polarized
Microstrip Patch Antenna", IEEE.
2004.
www.ece.uvic.ca/~jbornema/Conferen
ces/102-04aps-kabs.pdf.
[3] Chang won Jung and Franco De
Flaviis, " A Dual-Band Antenna for
WLAN Applications by Double
Rectangular Patch with 4-Bridges",
University of California, Irvine, CA,
USA. 1998.
[4] J. Ollikainen, M. Fischer and P.
Vainikainen, "Thin dual-resonant
stacked shorted patch antenna for
mobile communications", IEE.
Electronics Letters 35, number 6, pp
437-438, 1999.
[5] Jani Ollikainen and Pertti
Vainikainen, "Radiation and
Bandwidth Characteristics of Two
Planar Multistrip Antennas for Mobile
Communication Systems", IEEE
Vehicular Technology Conference.
Ottawa, Ontario, Canada, , volume 2,
pp. 1186-1190, 1998.
[6] R. W. Dearnley, " A Broadband
Transmission Line Model for a
Rectangular Microstrip Antenna"
IEEE Trans. , Antennas and
propagation, Vol. AP 37, No. 1, pp. 6
- 15, January 1989.
[7] James I.J & Hall P.s.,"
HANDBOOK OF MICROSTRIP
ANTENNAS", Vol. 1, Peter
Peregrinus Ltd., 1989.
[8] David W. Green, "Broadbanding
of Microstrip Antenna", 2002.
www.cwnp.com/learning_center/searc
h_details.php?doc_id=jbM80iLL-12k
.
[9] M . D . Deshpande, " Input
Impedance of Microstrip Antenna"
IEEE Trans. , Antennas and
propagation, Vol. AP 30, No. 4, pp.
645 - 650, July 1982.
[10] I. J. Bahl & P. Bhartia, "
Microstrip Antennas" Artech House,
1980.
[11] Zurcher, J-Francois and Gardiol,
F; "Broadband Patch Antenna"
Artech House, 1995.
[12] G. Kumar. & K. P. Ray,
"Broadband Microstrip Antennas",
Artech House, antennas and
propagations library. 2003

10
[13] Ray, K. P., "Broadband, Dual-
Frequency and Compact Microstrip
Antennas",
Ph. D. thesis, Indian Institute of
Technology, Bombay, India, 1999.
[14] Debtosh Guha, "BROADBAND
DESIGN OF MICROSTRIP
ANTENNAS: Recent Trends and
Developments", Facta Universities
Series Vol. 3, No15, pp. 1083-1088,
2003.
[15] Basim K. Jar’alla "Design
Consideration, and Simulation of
Broadband Rectangular Microstrip
Antenna" M.Sc thesis , University of
Technology, Baghdad - Iraq, July
2005.
[16] S. Haider, "Microstrip Patch
Antennas for Broadband Indoor
Wireless Systems", University of
Auckland, USA, part 4, project report,
2003.
www.ece.auckland.ac.nz/p4p_2005/ar
chive/reports2003/pdfs/p11_iyou021.
pdf .

93
Fig. 1 Arrangement of arbitrary
shaped microstrip antenna (MSA)
(a) Top view
(b) Side view
Fig. 2 Top and side views of
rectangular microstrip antenna
(RMSA) with two Slots.
Substrate
Patch
Ground plane
Top View Side View
Feeding point
t
h
Substrate
Fig. 3 Feed positions on patch

10
Fig. 4 Flow Chart of the
Main Design Process
Fig. 5
Modified Shape Microstrip Antenna.
Fig. 6 VSWR variation with
frequency for RMSA with shifted
input
feeding point for both cases
with and without central shorting pin
and for substrate materials
Duroid 5880 and Quartiz.
9.25 9.75 10.25
Frequency (GHz)
1
1.5
2
2.5
VSWR
9.39 GHz
2
9.36 GHz
2.01
9.43 GHz
2
9.44 GHz
2 10.5 G
2
10.1 GH
1.15
10 GHz
1.12
QUARTIZ REC SHAPE DESIGNED AT 10 GHz & FEEDING POINT SH
QUARIZ REC SHAPE DESIGNED AT 10 GHz & FEEDING
DUROID 5580 REC SHAPE DESIGNED AT 10 GHz &
DUROID 5580 REC SHAPE DESIGNED AT 10 GHz & FEEDING POIN
Design narrow BW
rectangular antenna at
center frequency of the
working band
Compact design modified shape that gives broader bandwidth
DESIGN REQUIREMENTS
Design narrow BW
beginning frequency of
the working band
Design narrow BW
end frequency of the
working band
Selection of substrate
With specified height to reduce surface wave excitation
W2W1 L
W1
W2
L Lg
Wg
Feeding
point
Central shorting
pin

11
-90 -70 -50 -30 -10 10 30 50 70 90
phi (Deg)
ІEΦІn
0
0.16
0.33
0.49
0.67
1
E-Phi
DUROID 5880
SHIFTED POSITIVE X
E-Phi
0.83
-90 -70 -50 -30 -10 10 30 50 70 90
theta (Deg)
ІEθІn
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
E-Theta
DUROID 5880
SHIFTED POSITIVE X
E-Theta
DUROID 5880
SHIFTED POSITIVE X
WITH CENTRAL
SHORTING PIN
E-Phi
DUROID 5880
SHIFTED POSITIVE X
E-Phi
DUROID 5880
SHIFTED POSITIVE X
WITH CENTRAL
SHORTING PIN
0
-
-
-
-
-
-
-
-
-
-
-
-
- -
-
- -
1 1 1
1
1
1
1
1
1
9
8
7
6
5
4
3
21
0
-
-
-
-
-
-
-
-
-
-
-
-
- -
-
- -
1 1 16
1
1
1
12
1
10
9
8
7
6
5
4
3
21
E-Theta
DUROID 5880
SHIFTED POSITIVE X
E-Theta
DUROID 5880
SHIFTED POSITIVE X
WITH CENTRAL
SHORTING PIN
DUROID 5880
SHIFTED POSITIVE X
WITH CENTRAL
SHORTING PIN
Fig. 7 H-plane electric field radiation pattern E=f(θ) for RMSA for both
cases with and without central shorting pin and for substrate material
Duroid 5880 (a) normalized polar plot and, (b) normalized rectangular plot.
Fig. 8 E-plane, E=f(Φ) for RMSA for both cases with and without central shorting pin and
for substrate material Duroid 5880 (a)normalized polar plot, (b) normalized rectangular plot.
(a) (b)
(a) (b)
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
-110
-120
-130
-140
-150
-160
-170
180
170 160 150 140
130
120
110
100
90
80
70
60
50
30
2010
RADIATED POWER (normalized)
P_Rad[1,1]
DUROID 5880 SHIFTED POSITIVE X
P_Rad[1,1]
DUROID 5880 SHIFTED POSITIVE
WITH CENTRAL SHORTING PIN

12
8.25 8.75 9.25 9.75 10.25
Frequency (GHz)
1
1.5
2
2.5
9.5 GHz9.1 GHz8.37 GHz
8.75 GHz
1.4 10.2 GHz
1.32
QUARTIZ MODEFIED SHAPED WITH CENTR
QUARTIZ MODEFIED SHAPED, VSWR BW =
DUROID 5880 MODEFIED SHAPE, VSWR BW
DUROID 5880 MODEFIED SHAPE WITH CEN
Fig. 10 VSWR variations with frequency for mod
and without central shorting pin for substrate ma
-90 -70 -50 -30 -10 10 30 50 70 90
theta (Deg)
ІPrІn
0
0.154
0.31
0.4615
0.615
0.769
0.923
1 2.37 Deg
0.913
P_Rad[1,1]
P_Rad[1,1]
WITH CENTRAL SHORTING PINFig. 9 Radiated power pattern for RMSA for both cases with and without
central shorting pin and for Duroid 5880 (a) polar plot. (b) rectangular plot.
(b)

13
ІEθІn
0 2
0.6
0.4
0.8
1
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- -
1
1
1
9
8
7
6
5
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
-110
-120
-130
-140
-150
-160
-170
180 170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
RADIATED POWER (normalized)
P_Rad[1,1]
DUROID 5880 MODEFIED SHAPE
P_Rad[1,1]
Fig. 13 Radiated power pattern for MSMSA with and without central
shorting pin with substrate material Duroid 5880. (a) normalized polar plot.
(b) normalized rectangular plot.

14
Table 1 Results calculated for
various substrate materials at 10 GHz
for rectangular microstrip antenna.
Substrate εr h cm W cm εreff ∆L cm L cm Lg cm Wg cm %BW D dB
Duroid 5880 2.2 0.17 1.1859 1.9638 0.0864 0.8
Duroid 5870 2.33 0.17 1.1625 2.0657 0.0851 0.8
Quartz 3.78 0.17 0.9703 3.1792 0.0764 0.6
Duroid 6006 6.15 0.057 0.79333 5.462 0.025 0.
Alumina 9.8 0.057 0.6455 8.466 0.02395 0.4
Silicon 11.9 0.057 0.591 10.161 0.0236 0.4
Gallium
Arsenide
12.9 0.057 0.569 10.96 0.0235 0.4
Table 2 Calculated dimensions for
different materials
Table 3 Percentage bandwidth of
various types of MSA.
material εr h cm L cm W1 cm W2 cm Xf cm Yf cm Lg cm Wg cm
Air 1 0.17 1.268 1.875 1.25 0.9375 0.6340 2.288 2.895
Duroid
5880
2.2 0.17 0.8976 1.48232 0.988212 0.74116 0.3200 1.9176 2.50232
Duroid
5870
2.33 0.17 0.8735 1.4531 0.96873 0.72655 0.304 1.8935 2.4731
Quartiz 3.78 0.17 0.6885 1.213 0.809 0.6065 0.24 1.7085 2.233
Duroid6006 6.15 0.057 0.592 0.992 0.6611 0.496 0.127 0.934 1.334
Alumina 9.8 0.057 0.46764 0.8069 0.538 0.40345 0.0804 0.80964 1.1489
Silicon 11.9 0.057 0.4234 0.7383 0.4922 0.36915 0.066413 0.7654 1.0803
Gallium
Arsenide
12.9 0.057 0.4061 0.71123 0.4742 0.355615 0.06133 0.7481 1.05323
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
Angle (Deg)
IPrIn
0
0.125
0.25
0.375
0.5
0.625
0.75
0.875
1 -0.249 Deg
0.969
P_Rad[1,1]
P_Rad[1,1]

15
Substrate
material
Antenna type
Duroid
5880
Quartiz
Rectangular patch fed at original point
9.7%
BW
15.5%
BW
Rectangular patch shifted feeding point
10.8%
BW
16.1%
BW
Rectangular patch shifted feeding point
with central shorting pin
11.6%
BW
17.4%
BW
M o d i f i e d p a t c h s h a p e
25.4%
BW
23.9%
BW
M o d i f i e d p a t c h s h a p e
with central shorting pin
26.2%
BW
30.9%
BW

Design and simulation of broadband rectangular microstrip antenna

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