This document summarizes a research paper that models and simulates a coplanar patch antenna for X-band satellite communication applications. It begins by introducing coplanar patch antennas and their advantages over microstrip patch antennas, such as higher radiation efficiency and wider bandwidth. It then describes the design and simulation of a coplanar patch antenna using inset feeding technique at 10GHz. Simulation results show the coplanar patch antenna achieves a radiation efficiency of 98% and bandwidth of 17.8%, outperforming a comparable microstrip patch antenna. A brief comparison of the antenna types is also provided.

1. International Journal of Electronics and Communication Engineering & Technology (IJECET),
INTERNATIONAL JOURNAL OF ELECTRONICS AND
ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME
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ISSN 0976 – 6472(Online)
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IJECET
©IAEME
Coplanar Rectangular Patch Antenna for X Band Applications Using
Inset Fed Technique
Arvind Singh Jadon1, Jalaj Sharma2, Ajay Prajapat3, Avanish Bhadauria4
1,3Department
2,4MEMS
of Electronics & Communication,BKBIET, Pilani, India
and Microsensors Group,Central Electronics Engineering Research Institute, Pilani, India
1avanish@ceeri.ernet.in
ABSTRACT: This paper presents the simulation model of an inset fed Coplanar Patch Antenna
for X band satellite communication. Inset feed provides an easy impedance matching and
better return loss value. The simulated results show that coplanar patch antenna has high
radiation efficiency and comprises of a wider bandwidth as compared to a microstrip patch
antenna. A radiation efficiency of approximately 98% and an impedance bandwidth equal to
17.8% is obtained for a coplanar patch antenna. There is an increment of 10.5% in radiation
efficiency of the coplanar patch antenna then microstrip patch antenna. A brief comparison
between Coplanar and Microstrip Patch Antenna is also presented. All the designs presented in
this paper are simulated using electromagnetic simulation software Ansoft HFSS v13.
KEYWORDS: Coplanar Patch Antenna, Impedance Bandwidth, Inset Fed Technique, Microstrip
Patch Antenna, Radiation Efficiency.
I.
INTRODUCTION
From last few decades, planar antennas have been a field of interest for many researchers and
scholars. With the revolution in electronic circuit miniaturization and large scale integration in
the early 70’s, demand for a compact antenna with small size, which can be integrated with
MMIC designs increased. Since planar antennas are substrate based antennas and their
properties like ease in fabrication, and easy integration with MMIC and PCB designs, increased
popularity of planar antennas and influenced large number of research in this field. Planar
patch antennas have advantages like low profile, light weight and ease of fabrication.
Microstrip patch antenna is the most popular of all the other type of planar antennas. It
consists of a grounded substrate with a conducting patch above the substrate. But they have
certain disadvantages too like low gain, narrow bandwidth and low efficiency [1].
A large number of articles and papers have been published showing different methods to
increase the performance parameters of a microstrip patch antenna such as gain, bandwidth,
efficiency, and polarization etc. Different type of patch shapes such as rectangular, circular,
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2. International Journal of Electronics and Communication Engineering & Technology (IJECET),
ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME
triangular, square and different polyhedron shapes have been designed and studied [2-5].
Different feed techniques and impedance matching circuits have been used so that maximum
excitation power should be coupled through the feed line to the patch [6, 7].
Coplanar patch antenna is a new and better alternative of microstrip patch antennas. A
coplanar patch antenna has ground and patch on the same side of the substrate with a gap
width s as shown in fig.1. Since the effective dielectric constant for a coplanar antenna design is
lower than microstrip antenna design, the surface wave excitation is reduced to a large extent
and due to the reason coplanar antennas have high radiation efficiency and wider bandwidth.
Also, coplanar patch antennas are easy to fabricate, have low radiation loss, less dispersion,
uniplanar configuration and easy MEMS based reconfigurable antennas can be designed
without using via holes as used in case of microstrip designs.
Fig.1: Schematic Diagram of Inset Fed Coplanar Patch Antenna
Impedance matching in a patch antenna is an important issue. Generally a 50Ω transmission
line is considered as a feed line, because 50Ω transmission line has a very low reflection
coefficient. However, impedance at the edge of the patch is generally more than 300Ω, which
requires some additional impedance matching techniques. Now to couple maximum power
from the feed to patch we can introduce a λ/4impedance transformer line between patch and
the feed line. In case of direct feeding, the feed line is shifted on either side of the patch along
the edge until an impedance of 50Ω is achieved.
One more technique used to match the impedance of the patch with respect to feed line is to
design an inset fed patch antenna. In general the impedance in a patch decreases from the edge
to the centre of the patch, at the centre of the patch impedance is zero. Now we make a cut
from the edge of the patch to that point where impedance of feed line and patch is matched and
we connect feed line from that point as shown in fig.1.
To our knowledge few design models of coplanar patch antenna has been reported, such as
rectangular patch coplanar antennas are designed and characterized by different authors at
different frequency bands [11,12], a bow tie coplanar patch antenna is also studied which gives
a wider bandwidth [10].
Here in this paper we are presenting a coplanar patch antenna using inset coplanar waveguide
(CPW) feed technique for X band applications. Due to its wider bandwidth and high radiation
efficiency it could be applicable in many X band satellite systems. In satellite system
transponder requires antenna with high radiation efficiency and wider bandwidth so as to
transmit (or receive) audio, video and data signal all together.
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For designing the coplanar patch antenna we have used a full wave EM simulation software
Ansoft HFSS v13, which works on the principle of Finite Element Method (FEM). FEM can be
divided into two different methods; one uses variational analysis, and the other weighted
residuals. However both the methods start with the partial differential equation form of
Maxwell’s equations. The unknown field is dicretized using a finite element mesh; typically
triangular elements are used for surface meshes and tetrahedrons for volumetric meshes. Both
these geometries are chosen as with these geometries two dimensional and three dimensional
regions respectively can be meshed [13].
II.
COPLANAR PATCH ANTENNA
A coplanar line is a structure in which all the conductors supporting wave propagation are
located on the same plane, i.e. generally the top of a dielectric substrate. Coplanar Waveguide
(CPW) is composed of a median metallic strip separated by two narrow slits from an infinite
ground plane. The characteristic dimensions of a CPW are the central strip width Wand the
width of the slots s. The structure is obviously symmetrical along a vertical plane running in
the middle of the central strip (as shown in Fig. 2) [9].
Fig. 2: Side view of a Coplanar Waveguide [9]
A CPW can be quasi-statically analyzed by the use of conformal mappings. Since the substrate
has a finite thickness h, to carry out the analysis of this conformation, a preliminary conformal
mapping transforms the finite thickness dielectric into an infinite thickness. In this analysis, the
CPW conductors and the dielectric substrates are assumed to have perfect conductivity and
relative permittivity respectively. Hence the structure is considered to be loss less. Further the
dielectric substrate material is considered to be isotropic. In this analysis, expressions for
determining εreff and Z0 using conformal mapping techniques are presented. The assumptions
made are that the conductor thickness t is negligible and magnetic walls are present along all
the dielectric boundaries including the CPW slots. The CPW is then divided into several partial
regions and the electric field is assumed to exist only in that partial region. In this manner the
capacitance of each partial region is determined separately. The total capacitance (CCPW) is
then the sum of the partial capacitances. In this case the partial capacitances are capacitance
due to substrate (C1) and capacitance due to air (Cair). Therefore, the total capacitance can be
given as [9]:
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Where C1 and Cair is given as [9]:
and
(2)
Hence the total Capacitance as given in equation 1 can be written as:
Now using above capacitances values, effective dielectric constant can be given as [9]:
Here K(k) and K’(k) represents the complete elliptical integral of the first kind and it’s
complement, and
and
(5)
The impedance of such a coplanar transmission line is given as [9]:
Where, c is the velocity of light in free space. The guided wavelength λg for a coplanar
waveguide is given as:
Using above equation for guided wavelength, dimension of the coplanar patch design are
calculated. The length of the coplanar patch is approximately taken as λ g/4 whereas the width
of the patch is taken such that the length and width summation of the patch dimensions should
not exceed λg. Here in this design the width is approximately taken as λ g/2. And the ground
dimension around the patch is taken 5 times the dimension of the patch.
III.
DESIGN AND SIMULATION
The coplanar patch antenna is designed on Rogers/RT duroid 5880 substrate with dielectric
constant, εr = 2.2, dielectric loss tangent = 0.0009 and thickness of the substrate is 0.508mm.
The strip gap (s) is taken as 0.2mm and width (W) of the coplanar waveguide feed is 1.252mm.
The antenna is designed for an operating frequency of 10GHz. Using these design parameters
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5. International Journal of Electronics and Communication Engineering & Technology (IJECET),
ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME
and equation 1 to 7, the length and width of the coplanar patch is calculated as 4.3mm and
10.5mm respectively. The coplanar patch antenna modeled in HFSS software is shown in Fig. 3.
Fig.3:Model of Coplanar Patch Antenna in HFSS software
A microstrip patch antenna is designed for the same operating frequency and on the same
substrate as that of the coplanar patch antenna so as to analyze the differences between a
microstrip and coplanar patch antenna. The patch length and width calculated for the
microstrip patch antenna are 9.24015mm and 11.9mm respectively. The feed width for
microstrip patch antenna is 1.6mm. The Microstrip Patch Antenna modeled in HFSS software is
shown in Fig. 4.
Fig. 4: Model of Microstrip Patch Antenna in HFSS Software.
IV.
RESULTS AND DISCUSSION
Full wave electromagnetic simulation of both the antenna models in HFSS software yield
various antenna parameters such as return loss, radiation efficiency, directivity, bandwidth etc.
Both the designs are simulated at 10GHz operating frequency. However, coplanar patch
antenna model has a resonance frequency at 10.0557GHz and has a return loss of -32.2009dB,
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whereas microstrip patch antenna has resonance frequency at 9.9585GHz and return loss
value of -40dB. The ‫׀‬S11‫ ׀‬plots with respect to frequency for both the design are shown in Fig.
5.
Fig. 5: Simulation Results of ‫׀‬S11‫ ׀‬plot versus frequency
The radiation efficiency obtained for coplanar antenna is 97.84% and that for a microstrip
patch antenna is 88.63% i.e. 10.5% more than the efficiency of the microstrip patch antenna.
Similarly, coplanar patch antenna has an impedance bandwidth of 17.75% (i.e. 1.785GHz)
whereas that for a microstrip patch antenna is approximately 2%. However microstrip patch
antenna has 5.35dB directivity whereas coplanar patch antenna has 2.79dB directivity value.
The reason for the low directivity in case of coplanar patch antenna is that it has patch and
ground on the same plane so the electric field below the patch also form a lobe on the other
side of the patch forming a broadside pattern, whereas in case of microstrip patch the fields
below the patch are shorted by the lower ground making a single lobe in one direction above
the patch forming a unidirectional pattern. The radiation pattern plot for coplanar and
microstrip patch antenna are shown in Fig. 6.
(a)
(b)
Fig. 6: Radiation Pattern of: (a) Coplanar Patch Antenna; (b) Microstrip Patch Antenna.
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7. International Journal of Electronics and Communication Engineering & Technology (IJECET),
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V.
CONCLUSION
Full wave EM simulation of coplanar and microstrip patch antenna models shows that for same
operating frequency and same substrate coplanar patch antenna gives wider impedance
bandwidth and high radiation efficiency than microstrip patch antenna. An impedance
bandwidth of 17.75% and a radiation efficiency of 97.84% are achieved in case of a coplanar
patch antenna. However, the directivity is higher in case of microstrip patch antenna and also
the size of the microstrip patch antenna is smaller than the coplanar patch antenna. But the
directivity of the coplanar patch antenna can be improved by providing another conductor (or
ground) below the substrate; such designs are called as Conductor Backed Coplanar Patch
Antennas. These type of antennas have unidirectional pattern and have better directivity then
coplanar patch antenna. Due to its high radiation efficiency and wide bandwidth it can be
applicable in satellite transponders and in military RADAR and satellite communication
systems.
VI.
ACKNOWLEDGEMENT
Authors are thankful for financial support obtained from CSIR India.
REFERENCES
[1]Ramesh Garg, PrakashBhartia, InderBahl and ApisakIttipiboon, “Microstrip Design Antenna
Handbook”, Artech House, Boston, London.
[2]Constantine A. Balanis, “Antenna Theory: Analysis and Design”, Third Edition, John Wiley &
Sons, Inc., Publication, New Jersey.
[3]D. Patel, and F. Raval, “Design and cavity model analysis of inset feed rectangular microstrip
patch antenna”, Published in IEEE Conference NUiCONE-2012, 06-08 December 2012, India.
[4]M. M. Abd- Elrazzak, and Ibrahim S. Al Nomay, “A Design of a Circular Microstrip Patch
Antenna for Bluetooth and HIPERLAN Applications”, 9th Asia Pasific Conference on
Communications 2003, Vol.3, 21-24 September 2003.
[5]J. P. Damiano, J. M. Ribero, and R. Staraj, “Original Simple and Accurate Model for Elliptical
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[6]P. J. Soh, M. K. A. Rahim, A. Asrokin, and M. Z. A. Abdul Aziz, “Comparative Radiation
Performance of Different Feeding Techniques for a Microstrip Patch Antenna”, 2005 Asia
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[7]Amit A. Deshmukh, K. P. Ray, and AmeyaKadam, “Proximity fed Circular Microstrip
Antennas”, Applied Electromagnetics Conference, (AEMC), 2011, IEEE Conference Proceedings,
18-22 December 2011, Kolkata, India.
[8]Horng-Dean Chen, Chow-Yen-Desmond, Jun-Yi Wu, and Tsung-Wen Chiu, “Broadband High
Gain Microstrip Array Antennas for WiMAX Base Station”, IEEE Transaction on Antenna and
Propagation, Vol.60, No.8, August 2012.
[9]Rainee N. Simons, “Coplanar Waveguide Circuits, Components, and Systems”, John Wiley &
Sons, Inc., Publication, New York.
[10]Paul L. Chin, Atef Z. Elsherbeni, and Charles E. Smith, “Characteristics of Coplanar Bow Tie
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[11]Rohith K. Raj, Manoj Joseph, C. K. Aanandan, K. Vasudevan, and P. Mohanan, “A New
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BIOGRAPHY
Avanish Bhadauria received the B.Sc (Hons). degree in physics from
Dayalbagh Educational Institute, Agra, M.Sc. degree in Electronics from
Jiwaji University, Gwalior and the PhD in Microwave Photonics from
University of Delhi in 1996, 1998 and 2005, respectively. During his PhD he
has been awarded Junior Research and Senior Research Fellowship by CSIR.
Currently, he is a scientist in CSIR- Central Electronics Engineering Research
Institute (CEERI), Pilani (Rajasthan) since 2005. His interests include RF
MEMS, RF reconfigurable antennae modelling of interconnect in High speed VLSI,
Optoelectronic, THz electronics and microwave-photonic component design. He is member of
IEEE, MTT, Optical Society of America, Fellow member of Optical Society of India and Life
member of Semiconductor Society of India. He is also in an editorial board of International
Journal of Advancement of Technology and International Journal of Advances in Engineering &
Technology.
Jalaj Sharma received his B.E. degree in Electronics and Communication
Engineering from Samrat Ashok Technological Institute, Vidisha and M.E.
degree in Microwave Engineering from Jabalpur Engineering College,
Jabalpur in 2009 and 2012 respectively. Presently, he is working as a Project
Fellow in CSIR- Central Electronics Engineering Research Institute (CEERI),
Pilani (Rajasthan). His areas of interest include RF MEMS based
reconfigurable antenna and RF circuits.
Arvind Singh Jadon received his B.Tech (Hons.) degree in Electronics and
Communication Engineering from B K Birla Institute of Engineering &
Technology, Pilani. Presently, he is working as a Lecturer in B K Birla
Institute OF Engineering & Technology (BKBIET), Pilani. His areas of interest
include RF MEMS based reconfigurable antennae.
Ajay Prajapat received his B.Tech degree in Electronics and Communication
Engineering from B K Birla Institute of Engineering & Technology, Pilani.
Presently, he is working as a quality engineer in autopal industries ltd.
Jaipur.
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