Optimization of Circular Probe Fed Microstrip Patch Antenna
Amit Kumar Jaiswal
Electronics and communication engineering
MANIT, Bhopal, India
Email: jaiswal.amit121@gmail.com
Abstract- In this paper, I have focus on the
design and simulation of Microstrip patch
antennas (which are widely used in cell phone
today) with an emphasis on optimization of a
2.4 GHz circular probe fed patch antenna. I
have found that different parameter like
substrate dimension,µ, 𝜺, patch radius, feed
radius etc. affects the directivty, radiation
efficiency, total efficiency and return loss
curve of the patch antenna. I have analysed
the simulation result for far-field of different
patch antenna and on comparing the
parameter values of different patch antenna.
I found an optimized patch antenna. In this
paper, I have designed and studied the
simulated performance result of an optimized
microstrip patch antenna using CST
simulator.
Keywords- Microstrip patch antenna,
directivity, Radiation efficiency, Total
efficiency, CST simulator.
Introduction- The software simulations of our
project focused on designing and testing of patch
antennas using software called Computer
Simulation Technology (CST). Before the
software results are presented the theory behind
patch antennas is described.
Microstrip antennas are planar resonant cavities
that radiate electromagnetic radiation and it
leaks some part of it from their edges[1]. For
etching the antennas on soft substrates to
produce repeatable antennas in a low profile
with low cost printed circuit techniques can be
Prof. D. K. Raghuvanshi
Electronics and communication engineering
MANIT, Bhopal, India
Email: dkraghuvanshi3@gmail.com
used [2]. The antennas fabricated on compliant
substrates withstand tremendous shock and
vibration environments. mobile communication
base stations manufacturers frequently fabricate
these antennas directly in sheet metal and mount
them on dielectric posts or foam in a variety of
ways to eliminate the cost of substrates and
etching and also eliminates the problem of
radiation from surface waves excited in a thick
dielectric substrate which increases bandwidth
of antenna[3-4].
Most of the electric field lines reside in the
substrate and parts of some lines in air. Because
of which the transmission line cannot support
pure transverse electric- magnetic (TEM)
transmission mode, since the phase velocities in
the substrate and the phase velocities in the air
would be different. Thus, the dominant
propagation mode would be the quasi-TEM
mode[5]. Which requires to obtain an effective
dielectric constant (εreff) in order to think that the
wave propagation and the fringing field in the
line. The value of εreff is slightly less then εr
because the fringing fields around the periphery
of the patch are not restricted in the dielectric
substrate but are also spread in the air[7].
The expression for εreff is given as:
⁄2
𝜀𝑟𝑒𝑓𝑓
𝜀𝑟 + 1 𝜀𝑟 − 1
12ℎ −1
=
+
[1 +
]
2
2
𝑊
Where, εreff = Effective dielectric constant
εr = Dielectric constant of substrate
h = Dielectric substrate height
Feed
Radius = 0.05 mm
Co-ordinate = (0,9.2 mm)
Height =2.8 mm
Ground
Ground material = PEC
Dimension = 56 mm×56 mm
Height =2.1 mm
W = Patch width.
As shown in Fig 5 ,The lowest return loss
magnitude is obtained at 𝜀𝑟 = 2 , 𝜇𝑟 = 1 return
loss magnitude is equal to -39dB at resonant
frequency is equal to 2.575 GHz. From Fig 6,
The best return loss curve obtained at feed
radius = 0.05 mm and return loss is equal to 24dB. From Fig 7, When patch radius increases
return loss curve starts shifting leftwards and
decreases continuously. At 2.4 GHz return loss
is equal to -24dB. The minimum return loss is
obtained as -34dB at 2.21GHz for patch radius is
equal to 20.2mm. From Fig 8, At substrate
length is equal to 56, the return loss is minimum
and equal to -39dB.
Since 1986, FCC rules have provided for
unlicensed spread-spectrum operation in the 915
MHz (902–928 MHz), 2.4 GHz (2400–2483.5
MHz), and 5.7 GHz (5725–5850 MHz) bands.
But a vast number of RF devices currently
operate in the 2.4 GHz band (like microwave
ovens, cordless telephones, medical devices
etc.). Recently there has been proliferation of
"Wi-Fi" hotspots and wireless computers
permitting undeterred internet access by the
public
and
RF
identification
(RFID)
technology[6].
Fig.1. Proposed Microstrip patch antenna
Specification of optimized Microstrip Patch
Antenna –
Substrate
ϵ𝑟 = 2.33
µ𝑟 = 1.00
Material = Rogers RT5870
(lossy)
Dimension = 56 mm×56 mm
Height = 0.7 mm
Patch
Material = PEC
Radius = 23.2 mm
Height = 0.07 mm
Fig.2. Farfield pattern of proposed microstrip
patch antenna
Table for different values of 𝛜𝒓 and µ𝒓
Fig 3 : Polar plot of Directivity for constant
phi(𝜙 = 90)
S. Permi
No ttivity
.
𝜀𝑟
Perme
ability
𝜇𝑟
Direct
ivity
(dB)
Radiati
on
efficien
cy (dB)
Total
efficien
cy (dB)
1
1.00
1.00
3.162
0.051
-24.29
2
2.00
1.00
7.048
2.11
-14.35
3
2.33
1.00
7.166
-0.157
-0.527
4
2.50
1.00
7.055
0.213
-9.059
5
2.33
0.90
7.139
1.529
-10.77
6
2.33
1.25
6.747
0.397
-17.28
Table no.- 1
Table for different values of different value of
substrate dimension
Fig 4 : Polar plot of Directivity for constant
theta(𝜃 = 90)
Simulated result-
S.
No
.
Substrat
e length
(mm)
Directi
vity
(dB)
Radiation
efficiency
(dB)
Total
efficiency
(dB)
1
52
7.455
-0.184
-1.583
2
56
7.166
-0.157
-0.527
3
60
7.150
-0.164
-1.608
4
64
7.075
-0.203
-1.558
5
68
7.081
-0.019
-1.617
Table no.- 2
Table for different values of different value of
Feed radius
S.N
o.
Patch
Radius
(mm)
Directi
vity
(dB)
Radiation
efficiency
(dB)
Total
efficienc
y (dB)
1
20.2
6.286
-1.799
-17.66
2
22.2
6.897
-0.6843
-8.944
3
23.2
7.166
-0.157
-0.527
4
24.2
7.317
0.7902
-10.84
5
25.2
7.370
0.1776
-15.94
Table no. - 3
Fig : 5
Table for different values of different values
of feed radius
S.
Feed
No. radius
(mm)
Directivi
ty (dB)
Radiation
efficiency
(dB)
Total
efficienc
y (dB)
1
0.05
7.166
-0.157
-0.527
2
0.1
7.169
-0.1210
-0.7006
3
0.2
7.170
-0.1199
-0.7851
4
0.4
7.172
-0.1417
-0.8280
5
0.8
7.148
-0.0367
-1.562
Table no.- 4
Return Loss Curve for variation in𝜺𝒓 and 𝝁𝒓
Return Loss Curve for variation in feed
radius
Fig : 6
Return Loss Curve for variation in Patch
Radius
ConclusionI have designed large number of patch antenna
by varying different parameters like µ𝒓 , 𝛜𝒓 ,
substrate dimension ,patch radius and feed
radius. I have studied the simulation result for
far-field for different patch antenna and on
comparing the parameters values for different
patch antenna we found an optimised patch
antenna. I have found directivity = 7.166 dB,
radiation efficiency = -0.157 dB and total
efficiency = -0.5268 dB.
References [1] Constantine A. Balanis, “Antenna Theory:
Analysis Design,” Third Edition, 2005 John
Wiley & Sons, Inc.
Fig :7
Return Loss curve for variation in substrate
length
[2] R. B. Waterhouse,"Design of probe-fed
stacked patches," IEEE Trans. Antennas Pmp.,
vol. 47, no. 12, pp. 1780-1784, Dec. 1999.
[3] Bhal and Bhartia,” Microstrip antenna
Design-Handbook ”, Chapters –3 &4, Artech
House, Boston, London, 2001.
[4] S. Zavosh, “Analysis of circular microstrip
patch antennas backed by circular cavities,”
Department of Electrical, Computer and Energy
Engineering,ASU,Tempe,AZ,USA,1993.
[5] L.Greetis and E.Rothwell, “A self structuring
patch antenna,” in Proc. IEEE Antennas Propg.
Soc. Int. Symp., Jul. 2008,pp.1-4.
[6] C. A. Balanis, Advanced Engineering
Electromagnetics, 2nd ed. NewYork,USA:
Wiley,2012.
[7] Harrington, R.F.: ‘Effects of antenna size on
gain, bandwidth, and efficiency’, J. Res. Natl.
Bur. Stand. D, Radio Propag. , 1960, 64, (1),pp.
1 – 12.
Fig : 8