Design of radiating edge gap-coupled broadband

International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
INTERNATIONAL JOURNAL OF ELECTRONICS AND
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEME
COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)
ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 3, Issue 3, October- December (2012), pp. 303-313
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DESIGN OF RADIATING-EDGE GAP-COUPLED BROADBAND
MICROSTRIP ANTENNA FOR GPS APPLICATION

Rahul T. Dahatonde1, Shankar B. Deosarkar2
1. Assistant Professor, Electrical Engineering, Sardar Patel College of Engineering, Andheri
(W), Mumbai, INDIA.
2. Professor & Head, Dept. of E & TC, Dr. Babasaheb Ambedkar Technological University,
Lonere, Mangaon, INDIA.

ABSTRACT

This paper discusses design and testing of gap-coupled broadband Microstrip antenna
(MSA) for Global Positioning System (GPS) application. A simple Rectangular Microstrip
Patch Antenna (RMSA) was designed and tested at GPS frequency of 1.57 GHz. This
RMSA was found to have bandwidth (BW) of 26 MHz. The bandwidth of this RMSA was
increased up to 35.5 MHz, by placing two parasitic patches along both the radiating edges of
this RMSA. Both the MSA configurations were simulated using Zeland’s MoM based EM
Simulation Package IE3D. The simulation results were experimentally verified by
fabricating these configurations using FR4 substrate. The gap-coupled MSA yielded better
gain and 36% more BW than basic RMSA. The other performance parameters of the RMSA,
such as return loss, VSWR and input impedance were also improved in the proposed design.
The effects of finite ground plane on the performance of gap coupled MSA were also studied
and experimentally verified. It was found that, gap coupled MSA with finite ground plane
performs similar to MSA with infinite ground plane and achieves 33% over all size reduction.

Keywords: Rectangular Microstrip Antenna, gap-coupled Microstrip antenna, Bandwidth
Enhancement, Gain Enhancement, Finite Ground plane, Size reduction.

I. INTRODUCTION

These days, MSAs are widely used in many applications due to their inherent
advantages such as low profile, light weight, planer configuration and ease of fabrication.
However, main limitation of MSAs is their inherently narrow bandwidth (BW) [1].

Most of the Wireless Communication Applications need antenna with broad bandwidth.
Therefore, most of the recent research activities in MSA are aiming towards development of

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MSAs with wide impedance BW without sacrificing return loss of the antenna. Many such
techniques are proposed in literature [2].

However, techniques such as use of an electronically thick substrate also introduce a large
inductance due to increased length of the probe feed, resulting in a maximum BW of less than
10% of the resonance frequency. Also, though the designs consisting of stacked patches
yield little higher bandwidths (10% to 20% of the resonance frequency); these designs are
complex for fabrication.

The easiest way to increase BW of MSA would be to place a parasitic patch near the
radiating patch. This patch is placed sufficiently close to the active patch so that it gets
excited through the coupling between the two patches. Both the patches are designed such
that their resonance frequencies are close to each other, yielding broad BW. The overall
input VSWR is superposition of the responses of both the patches resulting in broad
bandwidth [1].

In this paper, we have presented a MSA with two parasitically coupled patches placed along
both the radiating edges of simple RMSA. This configuration yielded approximately 30%
more BW than simple RMSA resonating at the same frequency. Both these MSA
configurations, (i) simple RMSA and (ii) MSA with gap-coupled parasitically excited patches
placed along radiating edges of RMSA, were designed, simulated and tested. It was observed
that the second configuration, yielded considerable improvement in BW without much
sacrifice on other performance parameters of MSA such as, return loss, VSWR and its input
impedance.

II. DESIGN OF RMSA

According to Transmission Line Model, MSA is represented as two slots separated by
a transmission line. The Microstrip separates two dielectrics, i.e. air and substrate. Hence
most of the electric field lines reside inside the substrate and some extend to air. This
transmission line cannot support pure TEM mode of propagation since the phase velocities
would be different in air and the substrate. Hence, effective dielectric constant must be
obtained in order to account for fringing fields. The value of effective dielectric constant is
less than dielectric constant of the substrate, because the fringing fields around the periphery
of the patch are not confined in the dielectric substrate, but are also spread in the air. The
value of this effective dielectric constant is given by [4],
1
(ε + 1) + (ε r − 1) 1 + 12h  − 2
ε eff = r
2 2   W  
where, ε eff is effective dielectric constant and ε r , h, W represent dielectric constant, height
and width of the substrate, respectively.

For RMSA to be an efficient radiator, W should be taken equal to a half wavelength
corresponding to the average of the two dielectric mediums (i.e., substrate and air) [1]
c
W =
ε +1
2 f0 r
2

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The fringing fields along the width can be modeled as radiating slots increasing electrical
length of patch than physical length. This increase in length is given as,
 W  
 (ε eff + 0.3) h + 0.264  
∆L = 0.412h    
 (ε − 0.258) W + 0.813  
 eff  
 h 

Thus at resonance frequency, effective length of the patch is,
Le = L + 2∆L
From these equations, dimensions of RMSA for GPS application frequency of 1.57 GHz
were obtained. The optimized length and width of the RMSA was found to be 58 mm and
44.5 mm, respectively.

This design was simulated using Zeland’s MoM based EM Simulation Package, IE3D [5].
For simulations, the FR4 substrate with dielectric constant of 4.47 with thickness of 1.59 mm
was considered. This patch was fed by a 50 coaxial feed line. The feed point location was
optimized using IE3D for better performance of this RMSA.

Figure 1-a indicates that the minimized value of return loss, –15.73 dB, occurs at resonance
frequency of 1.57 GHz. The impedance BW of this RMSA is around 26 MHz. Figure 1-b
shows that the VSWR BW of this RMSA is around 25 MHz which is very close to
impedance BW of RMSA. At resonance frequency of 1.57 GHz VSWR is almost 1, which
shows close to perfect matching of antenna with the feed line.

Figure 1-a. Return loss Vs Frequency for Figure 1-b. VSWR Vs Frequency for RMSA
RMSA (Simulated)
(Simulated)

From Smith Chart obtained using software IE3D, the simulated value of input impedance for
this RMSA was found to be 39.1 .

III. Design of Gap-coupled RMSA [6-8]

The RMSA designed in earlier section can be used for GPS application. However, it
has comparatively narrow BW. The BW of this RMSA can be increased by placing either
one or two parasitic patches along one or both of the radiating edges of the active patch with

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a small spacing between them [1]. The edges along the width and length of the RMSA are
known as radiating and non-radiating edges, respectively. The parasitic patches get excited
due to coupling with fringing fields along the width of the active rectangular patch.

Using commercially available software IE3D various configurations of MSA with gap
coupled parasitic patches, were analyzed. It was observed that performance of MSA with
two gap coupled patches along both the radiating edges is better than MSA with one gap
coupled patch along one of the radiating edge of MSA. The further details about these
observations are discussed in the section of results and discussion.

Based on these observations, a MSA with two gap coupled patches placed along both the
radiating edges of RMSA was proposed. The dimensions of the RMSA were kept same as
that of RMSA discussed in earlier section. The length and width of parasitically coupled
patches was kept as 10 mm and 58 mm, respectively. The spacing between fed RMSA and
parasitic patches on both the sides was kept 5.75 mm. Keeping the substrate parameters same
as RMSA, this modified design was analyzed using IE3D.
It can be seen from Figure 2-a that, for gap coupled MSA, the return loss is almost –37 dB, at
resonance frequency of 1.57 GHz, is much better than simple RMSA, indicating better
radiation from proposed configuration. The impedance BW of this configuration is around
35.5 MHz. Figure 2-b shows that the VSWR BW of this configuration is 33.21 MHz which
is very close to its impedance BW. At resonance frequency of 1.57 GHz VSWR is almost 1,
which shows close to perfect matching of antenna with the feed line.

Figure 2-a. Return loss Vs Frequency for Figure 2-b. VSWR Vs Frequency for
Gap-coupled MSA (Simulated) Gap-coupled MSA (Simulated)

From Smith Chart obtained using software IE3D, the simulated value of input impedance for
this gap coupled MSA was found to be 49.87 .

IV. EXPERIMENTAL VERIFICATION

Both the MSA configurations discussed in earlier sections were fabricated on FR4
substrate, since it’s easily available and not much expensive for experimental purpose.
Figures 3-a and 3-b, show the photographs of fabricated RMSA and gap coupled MSA,
respectively.

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Figure 3-a. Photograph of fabricated Figure 3-b. Photograph of fabricated gap coupled
RMSA MSA

These fabricated antennas were tested on Agilent Marconi Scalar Network Analyzer 6204
available at Antenna Laboratory of Dr. Babasaheb Ambedkar Technological University,
Lonere, Maharashtra.
Figure 4-a shows measured values of return loss Vs frequency for RMSA. It can be seen that
the measured value of impedance BW for RMSA is 25.82 MHz which is very close to
simulated value of 26 MHz. Figure 4-b, shows the measured value of VSWR Vs frequency.
It can be observed that the measured value of VSWR BW of RMSA is 27.12 MHz.

Figure 4-a. Return loss Vs Frequency of Figure 4-b. VSWR Vs Frequency of RMSA
RMSA (Measured) (Measured)

Figure 5-a and 5-b, show the measured values of return loss Vs frequency and VSWR Vs
frequency, respectively, for gap coupled MSA. It can be observed that the measured value of
impedance BW and VSWR BW for gap coupled MSA is exactly same, i.e. 31.1 MHz. This
value is slightly less than simulated value due to practical constraints during fabrication of
MSA.

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Figure 5-a. Return loss Vs Frequency for Figure 5-b. VSWR Vs Frequency for Gap
Gap coupled MSA (Measured) coupled MSA (Measured)

The value of input impedance for simple RMSA and gap coupled MSA was measured to be
40.10 and 51.23 , respectively from the Smith Chart shown in Figure 6-a and –b,
respectively. It can be observed that the measured values of input impedance for both the
MSAs are fairly close to the simulated values.

Figure 6-a. Smith Chart of RMSA Figure 6-b Smith Chart of gap-coupled MSA
(Measured) (Measured)

Table 1 summarizes simulated and measured values of various performance parameters for
these two configurations of MSA. It can be observed that the simulated and measured values
of all the performance parameters of MSA for both the configurations are matching fairly
well. Also the gap coupled MSA shows considerable improvement in impedance BW over
RMSA. Other performance parameters such as return loss, VSWR and input impedance are
also improved.

308


Table 1. Summary of simulated and measured values of various performance parameters of
RMSA and gap coupled MSA

Return Loss Input
VSWR Impedance
MSA (dB) Impedance ( )
At 1.57 GHz Bandwidth (MHz)
Configuration at 1.57 GHz At 1.57 GHz
Simulated Measured Simulated Measured Simulated Measured Simulated Measured

Basic RMSA -15.74 -17.12 1.39 1.31 39.10 40.10 26.00 25.82
MSA with
gap-coupled
-36.98 -36.36 1.02 1.03 49.87 51.23 35.50 31.10
parasitic
patches

V. EFFECT OF FINITE GROUND PLANE

For all the simulations and measurements discussed in earlier sections, we have
considered MSAs with infinite ground plane, because the transmission line model used for
designing basic RMSA is based on assumption of infinite ground plane [1]. However, in
practice, MSAs are designed and fabricated with ground plane of sufficiently larger size but
still this is not infinite. It is proved in [1] that when the size of the ground plane is greater
than the patch dimensions by approximately six times the substrate thickness all around the
periphery, the results are similar to that of the infinite ground plane.

The advantage of having finite ground plane for MSA is that the over all size of MSA
reduces since the dimensions of finite ground plane are comparatively smaller than that of
(assumed to be) infinite ground plane. So as to reduce the size of the gap coupled MSA
shown in Figure 3-b, another configuration of gap coupled MSA with finite ground plane was
designed and fabricated. The photograph of this gap coupled MSA with finite ground plane
is shown in Figure 7.

Figure 7. Photograph of fabricated gap coupled MSA with finite ground plane

The length and width of the finite ground plane are chosen as 115 mm and 100 mm,
respectively. Thus for the same gap coupled MSA, the area of finite ground plane is 33%
less than infinite ground plane. The dimensions of fed and parasitic patches and location of

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feed point are not change. This gap coupled MSA with finite ground plane was analyzed
using IE3D and the simulation results were verified experimentally. The measured values of
return loss Vs frequency, VSWR Vs frequency and Smith Chart are shown in Figure 8-a, -b, -
c, respectively.

Figure 8-a. Return loss Vs Frequency for Figure 8-b. VSWR Vs Frequency for gap
gap coupled MSA with finite ground plane coupled MSA with finite ground plane
(Measured) (Measured)

Figure 8-a and –b show that the measured value of return loss and VSWR for gap coupled
MSA with finite ground plane, at the resonance frequency of 1.57 GHz is –29.04 dB and
1.07, respectively. Its impedance BW and VSWR BW are exactly equal to 31.80 MHz.

Figure 8-c. Smith Chart for gap coupled MSA with finite ground plane (Measured)

The Smith Chart in Figure 8-c shows that the measured value of input impedance for gap
coupled MSA with finite ground plane, at resonance frequency of 1.57 GHz is 47.5 .

The simulated and measured values of various performance parameters of gap coupled MSA
with finite and infinite ground plane are summarized in Table 2.

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Table 2. Summary of simulated and measured values of performance parameters of gap
coupled MSA with finite and infinite ground plane

Return Loss Input
VSWR Impedance
MSA (dB) Impedance ( )
at 1.57 GHz Bandwidth (MHz)
Configuration at 1.57 GHz at 1.57 GHz
Simulated Measured Simulated Measured Simulated Measured Simulated Measured
Gap-coupled
MSA with
-36.98 -36.36 1.02 1.03 49.87 51.23 35.50 31.10
infinite ground
plane
Gap-coupled
MSA with
-31.12 -29.04 1.09 1.07 48.73 47.50 32.00 31.80
finite ground
plane

It can be observed from Table 2, that if dimensions of finite ground plane are chosen properly
then the overall size reduction of MSA can be obtained without much sacrifice on
performance parameters of MSA, such as return loss, VSWR, input impedance and BW.

VI. RESULTS AND DISCUSSION

In order to increase BW of RMSA, its various configurations with one or two
parasitic patches along one or both of the radiating and non-radiating edges of the active
patch with a small spacing between them, were analyzed using software IE3D.

It was observed that, if the parasitic patches are placed along the non-radiating edges, the
field coupling between fed patch and parasitic patch is very small, since the field variation
along non-radiating edge of MSA is sinusoidal. Therefore, to achieve better coupling, the
spacing between fed patch and parasitic patch has be sufficiently small. If the parasitic
patches are placed along the radiating edges of MSA, the coupling between fed patch and
parasitic patches is better since the field is uniform along the radiating edges of the MSA. In
this case, the parasitic patches get excited due to coupling with fringing fields along the width
of the active patch. Therefore, a configuration with parasitic patches along the radiating
edges was chosen.

When one parasitic patch is placed along one of the radiating edges of the RMSA, the BW of
the antenna increases. However, the radiation pattern is not symmetrical with respect to the
broadside direction, since the radiation from parasitic patch shifts beam maxima to the side
where it’s placed. If MSA configuration is made geometrically symmetric with two parasitic
patches along the two radiating edges of RMSA, the radiation pattern becomes symmetric in
the broadside direction. In this configuration, since both the parasitic patches are on the
opposite sides of the fed patch, they shift the beam maxima in the direction opposite to each
other. The overall pattern of three patches will be the superposition of the individual pattern,
and hence it will remain symmetrical with the broadside direction.

Due to addition of two parasitic patches along with single rectangular patch, size of gap
coupled MSA is more than that of simple RMSA. However, due to increase in effective

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aperture of MSA, its gain increases. Thus the gap coupled MSA gives better gain and BW
than that of simple RMSA. However, increase in gain could not be verified experimentally,
since gain measurement facilities are very expensive and were not available at the time of
experimentation.

In order to reduce over all size of antenna, effects of finite ground plane on the performance
of gap coupled MSA were studied and experimentally verified. It was observed that software
IE3D assumes infinite ground plane by default since it’s based on Method of Moment (MoM)
which considers only infinite ground plane. Therefore, during simulations, with infinite
ground plane, software performs meshing only on radiating patch and simulates it.
Therefore, the simulation time for gap coupled MSA with infinite ground plane is small
compared to simulation time for gap coupled MSA with finite ground plane.

In case of the MSA with finite ground plane, the ground plane with desirable dimensions is to
be defined in the software, which is treated as a patch on the opposite side of the actual
radiating patch. Therefore, during simulation, meshing is performed on radiating patch as
well as on the finite ground plane and both are simulated together, hence simulation time
increases. Also due to this, there are back lobes in the radiation pattern of MSA with finite
ground plane. However, advantage of finite ground plane is reduction in overall size of
MSA compared to MSA with infinite ground plane.

CONCLUSION

A RMSA and a gap coupled MSA with finite and infinite ground plane was designed
and analyzed using software IE3D. It was observed that the theoretical results obtained using
IE3D are in good agreement with measured results, for all three configurations of MSA. It
was observed and experimentally verified that the gap coupled MSA yielded better gain and
36% more BW than basic RMSA. The other performance parameters of the RMSA, such as
return loss, VSWR and input impedance were also improved in the proposed design. The
effects of finite ground plane on the performance of gap coupled MSA were also studied and
experimentally verified. It was found that, gap coupled MSA with finite ground plane
performs similar to MSA with infinite ground plane and achieves 33% over all size reduction.

REFERENCES

[1] Kumar G. and Ray K.P., Broadband Microstrip Antenna, Artech House, 2003.
[2] Kin Lu Wong, Compact and Broadband Microstrip Antennas, John Wiley & Sons, 2002.
[3] Bhartia P., Millimeter-Wave Microstrip and Printed Circuit Antennas, Artech House,
1991.
[4] Balanis C.A., Antenna Theory Analysis and Design,2nd Edi.,John Wiley & Sons,pp.730-
750,1997.
[5] IE3D 12.0, Zeland Software Inc., Fremont, CA, USA, 2008.
[6] Kumar, G., ‘‘Broadband Microstrip Antennas Using Coupled Resonators,’’ Ph.D.thesis,
Indian Institute of Technology, Kanpur, India, 1982.
[7] Kumar, G., and K. C. Gupta, ‘‘Broadband Microstrip Antennas Using Additional
Resonators Gap-Coupled to the Radiating Edges,’’IEEE Trans. Antennas Propagation,
Vol. AP-32, December 1984, pp. 1375–1379.

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[8] Kumar, G., and K. C. Gupta, ‘‘Nonradiating Edges and Four Edges Gap-Coupled with
Multiple Resonator, Broad Band Microstrip Antennas,’’IEEE Trans. Antennas
Propagation,Vol. AP-33, February 1985, pp. 173–178.
[9] Varun Shukla, Arti Saxena and Swati Jain, “A New Rectangular Dielectric Resonator
Antenna Compatible For Mobile Communication Or Broadband Applications”
International journal of Electronics and Communication Engineering &Technology
(IJECET), Volume3, Issue2, 2012, pp. 360 - 368, Published by IAEME
[10] Jagadeesha.S, Vani R.M and P.V Hunugund, “Size Reduction And Multiband Operation
Of Rhombusshaped Fractal Microstrip Antenna For Wireless Applications” International
journal of Electronics and Communication Engineering &Technology (IJECET),
Volume3, Issue2, 2012, pp. 445 - 450, Published by IAEME
[11] Nagraj Kulkarni and S. N. Mulgi, “Corner Truncated Inverted U - Slot Triple Band
Tunable Rectangular Microstrip Antenna for Wlan Applications” International journal of
Electronics and Communication Engineering &Technology (IJECET), Volume3, Issue1,
2012, pp. 1 - 9, Published by IAEME
[12] B.Ramarao, M.Aswini, D.Yugandhar and Dr.P.V.Sridevi, “Dominant Mode Resonant
Frequency Of Circular Microstrip Antennas With And Without Air Gap” International
journal of Electronics and Communication Engineering &Technology (IJECET),
Volume3, Issue1, 2012, pp. 111 - 122, Published by IAEME
[13] P.A Ambresh and P.M.Hadalgi,, “Slotted Inverted Patch - Rectangular Microstrip
Antenna For S And L - Band Frequency” International journal of Electronics and
Communication Engineering &Technology (IJECET), Volume1, Issue1, 2010, pp. 44-52,
Published by IAEME
Author Biography
Rahul T. Dahatonde, received his B. E. and M. Tech. degrees in Electronics
& Telecom. Engineering in the year 2001 and 2003 from North Maharashtra
University, Jalgaon and Dr. B. A. Technological University, Lonere,
respectively. He is currently a faculty in Dept. of Electrical Engineering at
Sardar Patel College of Engineering, Mumbai and is pursuing his Ph.D. from
Dr. B.A.T.U., Lonere in the area of Microstrip Patch Antennas.
His research interests include antennas, microwaves and EMI/EMC. He has published
around 10 research papers in various international and national journals/conferences. He is
life member of ISTE, India.

Dr. Shankar B. Deosarkar, obtained his M.E. degree in 1990 and Ph.D. in
2003 from S.R.T. Marathwada University, Nanded, India. He is a Professor
and Head of the E & TC Department at Dr. Babasaheb Ambedkar
Technological University, Lonere. Currently he is on lien and is associated
with V. P. College of Engineering, Baramati as Principal. He has teaching
experience of over 25 years. He has also worked as the Controller of
Examinations of the Dr. B. A. T. U. Lonere from 1990 to 2007.
His research interests include antennas, microwaves, EMI/EMC and signal integrity issues
in high speed circuits. He has around 50 research papers in various international and
national journals/conferences to his credit. Dr. Deosarkar is Fellow of IETE and life
member of ISTE, India. At present four research scholars are pursuing Ph.D. under his
guidance.

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Design of radiating edge gap-coupled broadband

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