Increase Bandwidth for Circular Microstrip Patch Antenna

ISSN 2249-6343
International Journal of Computer Technology and Electronics Engineering (IJCTEE)
Volume 2, Issue 1
Increase Bandwidth for Circular Microstrip Patch Antenna
Sonali Jain, Rajesh Nema
Abstract— In this paper a design and performance of a
circularly microstrip patch antenna, for the application in
Wireless Local Area Network (WLAN), are reported here. The
antenna is a proximity coupled microstrip patch antenna where
the radiating patch is loadedby a V-slot. This miniaturized
microstrip antenna has wide bandwidth in the frequency band
of WLAN and exhibits circularly far field with very good axial
ratio bandwidth. The simulated results using IE3D software are
verified by measurement.
I. INTRODUCTION
This article introduces some of the basic concepts of patch
antennas. The main focus will be on explaining the general
properties of patch antennas by using the simple rectangular
probefed patch. It will cover topics including: principles of
operation, impedance matching, radiationpattern and related
aspects, bandwidth, and efficiency.Microstrip antennas have
profound applications especially in the field of medical,
military, mobile and satellite communications. Their
utilization has become diverse because of their small size and
light weight. Rapid and cost effective fabrication is especially
important when it comes to the prototyping of antennas for
their performance evaluation. As wireless applications
require more and more bandwidth, the demand for wideband
antennas operating at higher frequencies becomes inevitable.
Inherently microstrip antennas have narrow bandwidth and
low efficiency and their performance greatly depends on the
substrate parameters i.e. its dielectric constant, uniformity
and loss tangent.
Microstrip patch antennas are attractive for their
well-known efficient features such as compatibility with
monolithic microwave integrated circuits (MMIC), light
weight, less fragile, low profile etc. The main disadvantage
associated with microstrip patch antennas is the narrow
bandwidth, which is due to the resonant characteristics of the
patch structure. But on the other hand modern
communication systems, such as those for wireless local area
networks (WLAN), as well as emerging applications such as
satellite links (vehicular, GPS,etc.) often require antennas
with low cost and compactness, thus requiring planar
technology. Due to the light weight of the microstrip patch
antennas, they are appropriate for the systems to be mounted
on the airborne platforms such as synthetic aperture radars
(SAR) and scatterometers. Because of these applications of
the microstrip patch antenna, a new motivation is evolved for
research and development on indigenous solutions that
overcome the bandwidth limitations of the patch antennas.
In applications in which bandwidth enhancement is
required for the operation of two separate subbands, an
appropriate alternative to the broadening of the total
bandwidth is represented by dual-frequency microstrip
antenna, which exhibits a dual-resonant behavior in a single
radiating element. The radius of the antenna is 100 mm.
II. ANTENNA STRUCTURE AND RESULTS
Antenna element structure is shown in Fig.1. Using the
form of cutting H Shape of Circular microstrip patch
antenna. This antenna design a multi layer used, first layer a
glass epoxy and 2nd layer duroid layer.The antenna
fabricated on an h=1.5mm glass eproxy substrate with the
dielectric constant ξr =4.3 and loss tangent tanδ=.019.and
other layer used of antenna fabricated an h=.508mm duroide
epoxy substrate with the dielectric constant ξr=2.33 and loss
tangent tanδ=.0005.
Simulated and measured curves of Return loss (db) vs
Frequency of antenna shown in fig 2.
III. ANALYSIS OF CIRCULAR PATCH MICROSTRIP ANTENNA.
1. Equivalent dielectric
r1 r2( h1 h2
)
eq
h ( h h )
r1 r2 1 1 2
2. Circular Patch Radius and Effective Radius
K
a
2
f
a
e
nm
C
eq
2h
a
a{1 [ln( ) 1.7726]}
a 2h
eq
1
2
169

ISSN 2249-6343
International Journal of Computer Technology and Electronics Engineering (IJCTEE)
Volume 2, Issue 1
Fig1. Geometry of Circular Microstrip Patch Antenna
170

ISSN 2249-6343
International Journal of Computer Technology and Electronics Engineering (IJCTEE)
Volume 2, Issue 1
Conductance
The conductance due to the radiated power of the circular
microstrip patch antenna can be computed based on the the
radiated power expressed as;
2 2 2
V0 ( K0ae
) 2 2 2
Prad
[ J '
02
cos J02]sind
960
0
K 0 is the free space phase constant. The conductance across
the gap between the patch and the ground plane at φ’=0o is
given as
2
( Ka
0 e) 3 2 2 1 4 4 7 6 6
3 3 10
Grad
{[1 sin sin sin ]
480 2 32 122
3 2 2 1 4 4 7 6 6
0.333[1 sin sin sin ]}
3 3 10
2 32 122
Grad accounts for radiation and dielectric losses and are
expressed as
3 3
2
c
m0 0 r 10 0 e
2
G ( ( f ) ) [( K a ) ]
G
d
tan
4 ( )
m0
2
[( Kae) ]
0h fr
10
as where G c is the conductance due to conduction losses, G d
is the conductance due to dielectric losses and f r is the
resonant frequency of the dominant mode. The total
conductance can be expressed
Gt Grad Gc Gd
4.Directivity
D
0
( Ka
0 e)
120G
2
rad
This directivity is not strongly influenced by height of
substrate as long as it is maintained electrically small. It is a
function of patch radius.
III.
RESONANT INPUT IMPEDANCE
The input impedance of a circular patch at resonance is real
and the input power is independent of the feed point position
on the circumference (Balanis, 1982). Taking the reference of
the feed point at , the input resistance at any radial distance
from the center of the patch can be written as (Balanis, 1982)
J ( K
)
Rin
G J Ka
2
1 [
m 0
2 ]
t m( e)
For the circular patch antenna, the resonant input resistance
with an inset feed is
2
m
in( ' 0)
in( '
e)
2
Jm
R R a
J
( K0)
( Ka )
PROGRAM DESIGN AND SIMULATION
The program written in FORTRAN using WATFORT g77
compiler was developed based on equations (17) to (35). The
program was run on the DOS mode and results exported to
Microsoft word.The main program reads in the microstrip
parameters then determines the ideal radiation characteristics
Input Parameters
ξ eq = dielectric constant
h= height of substrate
C = Speed due to free space
Output Parameters
a = radius of patch
a e = effective radius of patch
G rad = Conductance between gap & ground
G d = conductance due to dielectric
G t = total conductance
D 0 = directivity of slot
R in = resonant of input resistance
The calculate parameters for different antennas designed at
various feeding point at a 5Ghz frequency are given in table:-
Circular microstrip patch antenna results in table
S.NO
Co-Ordinates Result in dB Bandwidth Directivity
1 -170,-292 -12db 7.6% 9.33db
2 -122,-307 -18db 12% 6.88db
3 -301,-149 -16db 12% 7.76db
4 92,-2 -22db 28% 5.95db
5 -140,-360 -14db 12% 9.57db
6 -68,-323 -14db 22% 7.34db
7 -81,-328 -14db 23% 6.71db
8 95,0 -30db 34% 8.33db
e
171

ISSN 2249-6343
International Journal of Computer Technology and Electronics Engineering (IJCTEE)
Volume 2, Issue 1
IV. RESULTS
The simulated results of the antenna comprise of return loss(db).Fabricated antenna at frequency 5GHz.
simulated
Frequency GHz
Fig2.-GHz Antenna Results
Fig3.-Simulated VSWR vs.Frequency of antenna
172

ISSN 2249-6343
International Journal of Computer Technology and Electronics Engineering (IJCTEE)
Volume 2, Issue 1
V. CONCLUSION
This study provided an insight in determining the
performance of microstrip patch antenna. From the results
presented it is observed that glass epoxy and duroid epoxy
for X-band antenna designs . However,first theoretically
calculated parametric dimensions and simulated results
should be properly analyzed. Then based on the
analysis,predesign calibrating corrections may be
incorporated in the bandwidth development
process.predesign bandwidth are maximum 15% and this
paper of bandwidth 34% .It means 19%bandwidth
improvement this paper.
ACKNOWLEDGEMENTS
The authors, for this work, deeply acknowledge the
professional guidance provided by Mr. Rajesh Nema , and
financial support by NIIST. The authors also sincerely
recognize technical help and day to day supported.
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