Design of Circularly Polarized Microstrip Antenna Using Truncated Corner Method
Design of Circularly Polarized Microstrip Antenna Using Truncated Corner Method
Design of Circularly Polarized Microstrip Antenna Using Truncated Corner Method
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∆s =
2Q
3. INPUT RETURN LOSS (S11) (1)
Input return loss or S parameter is known as Where, Δs is the areas of the perturbations with x
scattering parameters. S parameter is a set of length and Q is the quality factor for a square
parameters describing the scattering and patch with dimension a. Figure 1 shows the
reflection of traveling waves when a network is geometry of CP antenna.
inserted into transmission line. S parameters are
normally used to characterize high frequency
network, where simple models valid at lower
frequencies cannot be applied.
4. BANDWIDTH
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In this paper single fed CP antenna are designed
There are many materials can be used in order to with using FR-4 as substrate layer with εr=4.5,
design a microstrip antenna, for example, dielectric thickness 1.6 mm. The antenna is
RT/DUROID 5880, R3003, R04003, and FR4. fabricated at UTHM Printed Circuit Board
However, FR-4 is decided to be used since the (PCB) Fabrication Laboratory. The SMA
cost is cheaper rather than others. The FR-4 has connector is soldered near the edge of the patch
the dielectric constant 4.5 and thickness 1.6 mm. and a radiation characteristic for this element is
measured. Figure 4 shows the CP antenna after
B. Design parameters fabricated process.
E. Testing
There are two types of testing or measurements
involve in this project. One is the return loss,
input impedance, vswr, test using network
analyzer. The other part is the antenna radiation
pattern test which involves the use of equipments
like rotating antenna platform, transmitter, and
using CASSY Lab software. Figure 5 shows the
measurement of CP microstrip antenna.
C. Simulation
The simulation process of the antenna is using
CST microwave studio. Using software, the
truncated segments as well as the patch
dimension is adjusted to yield a peak axial ratio
at the desired frequency.
Figure 5: Radiation pattern setup
D. Fabrication
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7. RESULT AND ANALYSIS
In figures 6 and 7 simulated and measured
results of return loss of antenna have been
represented. In simulation process the antenna
has been considered lossless and therefore
minimum of measured return loss is different
from simulated result. Based on figure 6, the
input return loss of the antenna at 2.4 GHz
operating frequency is -26.81 dB, this value is
larger than -10 db and it’s accepted in order to
fabricate an antenna. Besides that, this value also
shows the feeder point is the optimum feeder
point. In figure 7, the input return loss for this
antenna is -23.785 db at 2.4 GHz. Figure 8 show
the Comparison input return loss (dB) from Figure 6: Simulated input return loss
simulation and measurement. it is clearly seen
that there is a frequency shift between the
measured and simulation of the microstrip
antenna. The exact value is 2.415 GHz which is
the value of return loss is -27.3 dB. This means
that the measured resonant frequency is shifted
15 MHz over the operating frequency. It is
mainly due to the size of the patch especially the
length (L) and the perturbation segments for the
microstrip antenna. Due to inaccuracy in
fabrication process, the size of patch will either
increase or decrease. This will definitely bring to
the shifting in the resonant frequency which the
increase in the length of the patch will decrease
the resonant frequency or vice versa. The
difference in return loss reading between the Figure 7: Measured input return loss
measured and simulated result is mainly caused
by the feed-point location. The effect of the feed-
point location will bring to the condition where
the antenna is either matched or mismatched
with the feed line. If the antenna is mismatch,
not all the available power from the source is
delivered to antenna. This loss is called return
loss (RL). the variation of return loss value
indicates the variation in the reflection
coefficient value. The decrease in return loss
(<negative) also indicates increase in the
mismatch between the antenna and the
transmission line.
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Figure 10: voltage standing wave ratio
(measured)
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Figure 14: Right polarization (RHCP)
The antenna gain of this microstrip antenna is
Figure 12: Input impedance (measurement) defined in far-field region. From simulation at
figure 15, the gain of this antenna is 6.293 dB at
operating frequency of 2.4 GHz.
Figure 13 and 14 shows the polarization of this
antenna. This antenna has two type polarizations,
which is left polarization and right polarization.
From figure 4.12, at frequency 2.4 GHz, this
antenna has angular width (3db) about 81.3
degrees and for right polarization, the angular
width (3db) about 92.3 deg.
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Figure 18: Radiation pattern for PHI component.
8. CONCLUSION
The circularly polarized truncated square
microstrip antenna at 2.4 GHz has been
designed, fabricated and tested. Measured results
of resonant frequency, return loss, radiation
pattern, bandwidth were presented. The objective
of this project not fulfilled reached because the
resonant frequency is shifted 15 MHz over the
2.4 GHz. Since bandwidth is related to quality
factor of the square patch. By comparing the
simulated values obtained from the CST
microwave studio with the measured values of
Figure 16: Radiation pattern for theta component the fabricated microstrip antenna, it ca be seen
that the real antenna actually have better
performance than predicted by the simulation
software. Through this project, much experience
and knowledge about microstrip antenna have
gained. From the design process, the knowledge
of using CST microwave studio to design the
microstrip antenna would be an invaluable tool
for my future career as an engineer. During the
testing process, the experience of using network
analyzer, CASSY Lab, will enhance my hand on
skills.
ACKNOWLEDGMENT
Figure 17: Radiation pattern for ABS component
The author would like to thank to his
supervisor Puan Elfarizanis Bt Baharudin who
throughout the year has been advising, guiding,
supporting and keep motivating him till the
completion of the project and for all companions
and friends for supporting the author till the
completion of the project.
REFERENCES
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[1] Ramesh Garg, Prakash Bhartia, Inder Bhal,
and Apisak Ittipiboon (2000),
“Microstrip Antenna Design Handbook.”
London : Attach House Boston.
[2] Sadiku M.N.O (1995). “Elements of
electromagnetics” . 3 nd ed. US : Oxford
University Press.
[3] Lee, Kai Fong. and Chen, Wei. (1997). “
Advances In Microstrip And Printed
Antennas.” Wiley
[4] Doris I.Wu, John Huang. “CAD and
Optimization of Circularly-Polarized
Microstrip Arrays”. Proc, IEEE, 1840