IRJET- Improving Performance of Circularly Polarized Patch Antenna by Varying Stub Positions

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 06 Issue: 08 | Aug 2019 www.irjet.net p-ISSN: 2395-0072
© 2019, IRJET | Impact Factor value: 7.34 | ISO 9001:2008 Certified Journal | Page 1270
Improving Performance of Circularly Polarized Patch Antenna by
Varying Stub Positions
Gulshanpreet Singh1, Sehaj Rattan Singh2, Kuldeep Singh3
1Student, Department of Electronics & Communication Engineering, University Institute of Engineering and
Technology, Panjab University, Chandigarh, India
2Student, Department of Electrical & Electronics Engineering, University Institute of Engineering and Technology,
Panjab University, Chandigarh, India
3Assistant Professor, Department of Electrical and Electronics Engineering, University Institute of Engineering and
Technology, Panjab University, Chandigarh, India
---------------------------------------------------------------------***----------------------------------------------------------------------
Abstract - In this paper, we analysed the stacked
microstrip planar antenna and improved its performance by
implementing circular polarization through change in stub
position. Circular polarization is necessary to have constant
receiving power levels. In order to create circularly
polarized radiation, it is required to excite two orthogonal
patch modes on the antenna with 90° phase difference. The
extent of improvement is measured through some
parameters like return loss, axial ratio and radiation
efficiency of antenna using IE3D software.
Key Words: Axial ratio, Circular polarization, Return
Loss, Radiation efficiency, Stub, Bandwidth
1. INTRODUCTION
A three layer stacked microstrip planner antenna with air
sandwiched in them is used. The outer layers are equally
thick and have the same dielectric constant. Circular
polarization [1] can be obtained by a number of methods
[2] such as:
1. 3-dB hybrid
2. Truncated corner
3. Stub on radiating edge
4. Corner fed
5. Slot centre
(Refer to Figure 1). An antenna mostly radiates an
elliptical polarization defined by parameters such as axial
ratio, tilt angle and sense of rotation. In our experiment we
have used the Stub position method in order to generate
unity axial ratio i.e.0 dB for a perfect circular polarization.
2. PROPOSED ANTENNA DESIGN
The simple structure of single-feed circularly polarized
microstrip antennas [3] does not require an external
polarizer. Although this offer some advantages but the
main weakness of an ordinary microstrip antenna is its
narrow bandwidth. There are several techniques [4] to
overcome this problem. We have used the method of
stacked microstrip patch as shown below (Figure 2):
Fig-1: (a) 3-db hybrid (b) Truncated corner (c) Stub
on radiating edge (d) corner fed (e) Slot centre
Fig-2: A patch antenna in a three layers dielectric
The stacked microstrip patch method for the multilayer
(three Layers) microstrip antenna structure involves
addition of a superstrate layer [5] over the patch. With the
addition of superstrate, effective permittivity of all the
substrate reduces. Hence, the length of the patch is
decreased than the original length required for the
resonance at 2.4 GHz. We will use the following quasi-
static equation [6] for the multilayer dielectric structure

shown in Fig 2. Equation (1) can still be used provided
that the proper effective permittivity is determined.
√
[( ) ( ) ] (1)
Th xpr ssio or eff [7] is:
r r
q q
r q r q r
-q -q
( -q -q -q ) q
(2)
Where, eff = Effective dielectric constant
r1, r2, r3 = Dielectric constant of substrate 1 and
substrate 2, substrate 3 respectively,
q1, q2 and q3 = filler constants.
It is necessary to calculate filler constants q1, q2 for
calculating effective dielectric constant for given stack of
dielectric layer as given by equation (2). Hence filler
constants can be calculated as follows -
, 〖* ( ) ( )〗+-
(3)
(4)
( )
(5)
With
( ) (6)
Where,
h12= h1 + h2, and h13= h1 + h2 + h3.
Dielectric constant is calculated according to the values
given in table 1 below. The stacked multilayer antenna can
be treated as a single substrate patch antenna having
effective dielectric constant as calculated above. The
effective dielectric constant using above formula is eff
=1.03.
Table 1: Substrate specification for Fabrication
LAYER Substrate
Dielectric
constant
(εr)
Height
(h) mm
layer 1 DSWT 1.07 1.6
layer 2 Air 1 5
layer 3 DSWT 1.07 1.6
Fig-3: Patch of three layered Reference antenna
Fig-4: Circular Polarization using Stub at radiating
edge of patch of three layered antenna
3. RESULT AND DISCUSSION
Initially in our research, we simulated the three layered
antenna without stub. The simulation was designed using
IE3D software and results were analysed. The results were
unsatisfactory as antenna seemed to be randomly
polarized showing poor return loss and axial ratio. The
return loss of reference antenna was obtained around -9
dB, as shown in figure 5 and 6, indicating poor matching
with antenna impedance. The axial ratio was also found to
be outside the 3dB in three layers reference antenna as
per figure 7. Then stub was introduced in the antenna
system to improve parameters such as axial ratio,
bandwidth, antenna efficiency etc. Using the stub at
different position, the performance of antenna improved
as discussed next.
Fig-5: Return Loss of Multilayered reference Antenna

Fig-6: Axial Ratio of three layered reference Antenna
Fig-7: Efficiency of Multilayered reference Antenna
A stub is introduced at one of radiating edge to bring the
result within the limit of all parameters. The dimension of
stub is taken constant as 10 mm x 8 mm but position of
stub is varied. The best result we obtained by varying the
stub’s positio is giv i igur 8,9, 0 or axial ratio,
return loss and efficiency. We observe that, with the
introduction of stub, the input impedance has been
changed remarkably which in turn changes the best return
loss and gives the better result of axial ratio indicating
polarization purity (introducing orthogonal component
having 900 phase shift). The different results we obtained
by varyi g th stub’s positio is giv i tabl or axial
ratio, return loss and efficiency.
Fig-8: Return Loss of Antenna using Stub
Fig-9: Axial Ratio of Multilayered Reference Antenna
Fig-10: Efficiency of Antenna using Stub
4. CONCLUSIONS
In our paper, three layers microstrip planar antenna with
dimensions 52.81x62.06 mm was taken as the base
antenna. In order to obtain circular-polarization we tried
to achieve 0 dB value of unity axial ratio for polarization
purity. Polarization purity is the ratio of major axis to the
minor axis in elliptical polarization. In our paper we have
used the stub position method to achieve circular
polarization in which the position of stub is varied and the
parameters such as Return loss, axial ratio, antenna
efficiency and radiation efficiency are measured. We were
able to achieve the value of return loss as -21.091, axial
ratio as 1.643 with 100% antenna efficiency which makes
our antenna design perfect for circular polarization.
Table 2: Variation of all the parameters with the stub
position
S
No.
d
(mm)
Resonant
Frequency
(GHz)
Return
Loss
Band-
width
Axial
Ratio
Radiation
Efficiency
1 5 2.4 -19.78 0.11 2.14 99.85
2 6 2.4 -21.09 0.11 2.19 100
3 7 2.4 -20.42 0.11 1.64 100
4 8 2.4 -20.28 0.11 1.64 100
5 9 2.4 -17.94 0.10 1.97 99.84

REFERENCES
[1] B. Y. Toh, R. Cahill and V. F. Fusco, "Understanding and
measuring circular polarization," in IEEE Transactions
on Education, vol. 46, no. 3, pp. 313-318, Aug. 2003.
[2] TY- BOOK, AU- Sahal, Madhuri PY- 2015/01/16, T1-
Review of Circular Polarization techniques for design
of Microstrip Patch Antenna
[3] Hyungrak Kim, Byoung Moo Lee and Young Joong
Yoon, "A single-feeding circularly polarized microstrip
antenna with the effect of hybrid feeding," in IEEE
Antennas and Wireless Propagation Letters, vol. 2, pp.
74-77, 2003.
[4] TY- CHAP, AU- Siakavara, Katherine PY- 2011/04/04,
SN - 978-953-307-247-0 T1 - Methods to Design
Microstrip Antennas for Modern Applications DO-
10.5772/14676
[5] Design of folded Rectangular Patch Antenna with
different multi-dielectric layer, International Research
Journal of Engineering and Technology (IRJET)e-
ISSN:2395-0056.
[6] J. Svacina, "A simple quasi-static determination of
basic parameters of multilayer microstrip and
coplanar waveguide," in IEEE Microwave and Guided
Wave Letters, vol. 2, no. 10, pp. 385-387, Oct. 1992
[7] Changhua Wan and A. Hoorfar, "Improved design
equations for multilayer microstrip lines," in IEEE
Microwave and Guided Wave Letters, vol. 10, no. 6, pp.
223-224, June 2000.

IRJET- Improving Performance of Circularly Polarized Patch Antenna by Varying Stub Positions

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