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International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME
324
DESIGN OF CIRCULARLY POLARIZED MICROSTRIP SQUARE-
PATCH ANTENNA FOR IMPROVED BANDWIDTH AND
DIRECTIVE GAIN WITH LOW RETURN LOSS
Sandeep Kumar1, Suresh Sahni
2, Ugra Mohan Kumar
3, Devendra Singh
4
1(Assistant Professor, Uttaranchal University, Dehradun, India,)
2(M.Tech Scholar, Uttarakhand Technical University, Dehradun,)
3(M.Tech Scholar, Uttarakhand Technical University, Dehradun,)
4(Assistant Professor, Uttaranchal University, Dehradun,)
ABSTRACT
This paper presents a circularly polarized microstrip square patch antenna with single
feed technique that operates in wireless local area network. Compact circularly polarized
(CP) microstrip antenna with inserted thin slots is proposed to reduce the size and widen the
bandwidth. The antenna is operated at 3.55 GHz frequency. The impedance bandwidth
(VSWR < 2) is 180 MHz and the directive gain is 5.81 dB. The proposed antenna also
provides low return loss (S11=-31.53dB). The proposed structure is designed and simulated
by Ansoft HFSS software. The simulated results give significant improvement in terms of
directive gain and bandwidth.
Keywords: Bandwidth, Directive Gain, VSWR, Radiation pattern, Return loss.
I. INTRODUCTION
Designing a circularly polarized microstrip antenna is challenging; it requires
combination of design steps. The first step involves designing an antenna to operate at a
given frequency. In the second step circular polarization is achieved by either introducing a
perturbation segment to a basic single fed microstrip antenna, or by feeding the antenna with
dual feeds equal in magnitude but having 90° physical phase shift[6,7]. The shape and the
dimensions of the perturbation have to be optimized to ensure that the antenna achieves an
axial ratio that is below 3 dB at the desired design frequency.
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Now a day’s circular polarization is very important in the antenna design industry, it
eliminates the importance of antenna orientation in the plane perpendicular to the propagation
direction, it gives much more flexibility to the angle between transmitting & receiving
antennas, also it enhances weather penetration and mobility. It is used in a bunch of
commercial and militarily applications [3, 6]. However it is difficult to build good circularly
polarized antenna.
In a typical wireless communication system increasing the gain of antennas used for
transmission increases the wireless coverage range, decreases errors, increases achievable bit
rates and decreases the battery consumption of wireless communication devices. One of the
main factors in increasing this gain is matching the polarization of the transmitting and
receiving antenna [1, 3].
The microstrip antenna is one of the most commonly used antennas in applications
that require circular polarization. This paper is concerned with the design of a circularly
polarized microstrip antenna that would operate in the 3.6 GHz range. This range is
commonly used by wireless local area devices and wireless personal area devices such as the
802.11 WIFI and the 802.15.4 Zigbee wireless systems [2, 5].
For circular polarization to be generated in microstrip antenna two modes equal in magnitude
and 90 out of phase are required. Microstrip antenna on its own doesn’t generate circular
polarization; subsequently some changes should be done to the patch antenna to be able to
generate the circular polarization
2. FEED TECHNIQUES
The most commonly used feeding techniques in circular polarization generation are
dual feed and single feed [5, 6, and 7].
2.1 Dual Feed Circularly Polarized Microstrip Antenna
As 90° phase shift between the fields in the microstrip antenna is a perquisite for
having circular polarization, dual feed is an easy way to generate circular polarization in
microstrip antenna. The two feed points are chosen perpendicular to each other as shown in
Figure1. With the help of external polarizer the microstrip patch antenna is fed by equal in
magnitude and orthogonal feed. Dual feed can be carried out using quadrature hybrid, ring
hybrid, Wilkinson power divider, T-junction power splitter or two coaxial feeds with physical
phase shift 90°.
Fig.(1) Examples for dual fed CP patches [1, 2, 3]
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International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
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2.2 Single feed circularly polarized microstrip antenna
Single fed microstrip antennas are simple, easy to manufacture, low cost and compact
in structure as shown in Figure(2
very complicated to be used in antenna a
antennas are considered to be one of the simplest antennas that can p
polarization[2, 6].
In order to achieve circular polarization using only single feed two degenerate modes
should be exited with equal amplitude and 90° difference. Since basic shapes microstrip
antenna produce linear polarization there must be some changes in the patch design to
produce circular polarization. Perturbation segments are used to split the field into two
orthogonal modes with equal magnitude and 90° phase shift. Therefore the circular
polarization requirements are met
Fig.
3. DESIGN OF MICROSTRIP
POLARIZATION
Design of microstrip patch antenna depends mainly upon three parameters, namely substrate
and its dielectric constant, height of the substrate and resonant frequency. In this paper,
selected three parameters are: Resonant Frequency (f
2.2, Height of the dielectric substrate (h)
Microstrip Patch antenna with square patch
Fig. (3) Microstrip square patch antenna
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326
larly polarized microstrip antenna
Single fed microstrip antennas are simple, easy to manufacture, low cost and compact
2). It eliminates the use of complex hybrid polarizer, which is
very complicated to be used in antenna array [17]. Single fed circularly polarized microstrip
antennas are considered to be one of the simplest antennas that can produce circular
In order to achieve circular polarization using only single feed two degenerate modes
exited with equal amplitude and 90° difference. Since basic shapes microstrip
antenna produce linear polarization there must be some changes in the patch design to
produce circular polarization. Perturbation segments are used to split the field into two
thogonal modes with equal magnitude and 90° phase shift. Therefore the circular
polarization requirements are met[3, 6].
Fig. (2) Single fed patches [1, 2]
MICROSTRIP SQUARE PATCH ANTENNA WITH
antenna depends mainly upon three parameters, namely substrate
and its dielectric constant, height of the substrate and resonant frequency. In this paper,
selected three parameters are: Resonant Frequency (fr) = 3.55 GHz, Dielectric constant (
2.2, Height of the dielectric substrate (h) = 1.57 mm. Fig.(3) represents the designed
with square patch. Designed antenna has linear polarization.
Microstrip square patch antenna Fig. (4) Circularly polarized microstrip antenna
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
April (2013), © IAEME
Single fed microstrip antennas are simple, easy to manufacture, low cost and compact
. It eliminates the use of complex hybrid polarizer, which is
]. Single fed circularly polarized microstrip
roduce circular
In order to achieve circular polarization using only single feed two degenerate modes
exited with equal amplitude and 90° difference. Since basic shapes microstrip
antenna produce linear polarization there must be some changes in the patch design to
produce circular polarization. Perturbation segments are used to split the field into two
thogonal modes with equal magnitude and 90° phase shift. Therefore the circular
LINEAR
antenna depends mainly upon three parameters, namely substrate
and its dielectric constant, height of the substrate and resonant frequency. In this paper,
GHz, Dielectric constant (εr) =
represents the designed
Designed antenna has linear polarization.
microstrip antenna
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3.1 Calculation of Width The width of the Microstrip patch antenna is given by equation (1) [1, 2]:
1
2
2 +=
rf
cW
ε (1)
The calculated width of proposed square patch antenna from equation (1) is W= 32.94 mm,
where c is the speed of light.
3.2 Calculation of Effective dielectric constant (εeff): 2/1
1012
1
2
1
+
−+
+=
W
hrr
reff
εεε (2)
The calculated effective dielectric constant from equation (2) [1], ε reff = 2.329.
3.3 Calculation of the Effective length (Leff):
eff
efff
cL
ε2= (3)
From above equation the effective length is comes out to be [1, 3], Leff=27.30mm
3.4 Calculation of the Length Extension (∆L):
)8.0/).(258.0(
)264.0/).(3.0(412.0
+−
++=∆
hW
hWhL
eff
eff
ε
ε (4)
Which comes out to be [1, 2] ∆L =0.8008mm.
3.5 Calculation of the resonant length of patch (L):
L = LEFF – 2 ∆L (5)
This comes out to be 25.698mm.
3.6 Calculation of radiation conductance (G):
The radiation conductance for a parallel-plate radiator as [1, 2]
−=
24
)(1
2
0
khWG
ηλ
π= 3.2944mS. (6)
3.7 Calculation of input resistance of the patch (R):
GR
2
1= =151.768Ohms (7)
4. DESIGN OF SINGLE FED CIRCULARLY POLARIZED MICROSTRIP SQUARE PATCH
ANTENNA
Single feeding techniques are very common with microstrip antennas as they are
simple, easy to manufacture, low in cost and compact in structure. Several techniques were
used to achieve circular polarization in single fed microstrip antenna. Among these
techniques: fractal boundary, square patch with shaped slots , embedding cross slot in
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International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME
328
metallic patch or the ground plane, staking antennas, annular ring with strip line inside the
inner ring , and truncated edges patches.
In this paper proposed technique is square patch with shaped slot utilized. this is the
type of single fed circularly polarized microstrip antenna. Now, for achieving circular
polarization cut a thin slot in square patch with dimensions given below and the structure is
shown in above Fig.4.
C=L/2.72 [1]=W/2.72=25.702/2.72
=9.449mm
D=C/10 [1]=L/27.2=W/27.2=25.702/27.2
=0.9449mm
5. ANALYSIS AND RESULTS:
Starting with the values we get from theoretical design, we prepared a model of
antenna in Ansoft HFSS. Since the theoretical design is based on closed loop formulas and
the software is based on open loop formulas, the resonant frequency of the patch designed
with theoretical values shifted to a lower frequency.
Therefore to correct the value of frequency to 3.55GHz, we changed the dimensions
of the patch and the quarter wave transformer. We iteratively simulate the design to get the
resonant dimensions of the patch. The results of the circularly polarized square patch antenna
are given below in Table (1):
Table (1): Results of circularly polarized microstrip antenna
Parameters Practical design
Frequency f 3.55Ghz
Return Loss -31.53dB
VSWR 1.05
Gain 5.721dB
Directivity 5.81dB
Bandwidth VSWR < 2 180Mhz
5.1 Simulated Results of a Circularly Polarized Microstrip Antenna The proposed antenna has been designed and simulated using Ansoft HFSS software.
Fig. (5) represents the variation of Return Loss with Frequency. Plot shows resonant
frequency at 3.55 GHz with minimum -31.53 dB returns loss available at resonant
frequency.
The bandwidth of the antenna depends on the patch shape, resonant frequency,
dielectric constant and the thickness of the substrate [4, 7]. The bandwidth enhancement of a
microstrip antenna has been directed towards improving the impedance bandwidth of the
antenna element. Impedance bandwidth is usually specified in terms of a return loss. The
VSWR of microstrip square patch antenna is shown in Fig. (6).
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International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
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Fig. (5)
Fig. (6)
Fig. (7) Radiation pattern of
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
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Fig. (5) Return Loss vs. Frequency
Fig. (6) VSWR vs. frequency
Radiation pattern of circularly polarized microstrip antenna
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
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circularly polarized microstrip antenna
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International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
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Fig. (8) Directivity of
6. CONCLUSION
A square patch circularly polarized microstrip antenna design has been proposed and
successfully implemented. The
HFSS software. The square patch circularly polarized antenna
bandwidth, directive gain and return loss (S11 parameters) of
with broad side radiation pattern. The circularly polarized microstrip antenna can be used for
wireless local area network (WLAN, IEEE 802.11), as
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International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME
330
Directivity of circularly polarized microstrip antenna
A square patch circularly polarized microstrip antenna design has been proposed and
successfully implemented. The proposed structure has been simulated by using the Ansoft
HFSS software. The square patch circularly polarized antenna provides enhancement in
return loss (S11 parameters) of -31.53dB is achieved along
n pattern. The circularly polarized microstrip antenna can be used for
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International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
April (2013), © IAEME
A square patch circularly polarized microstrip antenna design has been proposed and
proposed structure has been simulated by using the Ansoft
provides enhancement in
31.53dB is achieved along
n pattern. The circularly polarized microstrip antenna can be used for
well as military applications.
ong Hee Park,Design of circularly polarized microstrip patch antenna with wide band
CIRCULARLY POLARIZED BROADBAND ANTENNA
, Progress In
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