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IJETR, 2012; Vol 1(2): July-2012 (009 - 013) International Standard Serial Number: 2278 - 6082
Available online on www.ijetr.com
9
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COMPACT BROADBAND COPLANAR CAPACITIVE COUPLED PROBE FED MICROSTRIP
ANTENNA FOR WIRELESS APPLICATIONS
Dr. Ravi M. Yadahalli1*
,
Nandini Ammanagi2, Neelamma K Patil
3
1P.E.S. Institute of Technology & Management, Shivamogga, Karnataka, India
2V.E.S. Institute of Technology, Mumbai, India
3K.L.Es College of Engineering & Technology, Belgaum, Karnataka, India
ABSTRACT
In this paper, the design of a compact broadband capacitive feed
microstrip antenna with open end meandering slots in the radiating
patch is presented. The three identical narrow open end meandering
slots are embedded in the radiating patch of the antenna. Effects of
varying the length of meandering slots on the input characteristics of
the antenna have been investigated and discussed.
KEYWORDS: Microstrip Patch Antenna; Coplanar Capacitive Coupled
feed; Impedance bandwidth; meandering slot.
INTRODUCTION
In modern wireless communication systems,
more and more attention is paid for the
development of small size, broadband antennas.
Printed Microstrip antennas (MSAs) are attractive,
as they are small in size, low in cost, and easy to
integrate with printed circuit configuration.
Many studies to increase the bandwidth of the
microstrip patch antennas have been extensively
investigated [1, 2]. Recently, an ultra-wideband
microstrip antenna was achieved by using a
capacitive coupled probe feed [3, 4]. To
accommodate such antennas in wireless
communication systems, it is necessary to reduce
the size of such antennas. Many techniques have
been reported for reducing the size of microstrip
antennas [5, 6, 7]. Meandering of the radiating
patch by loading several slits in the non-radiating
edge is proven to be one of the effective methods
in reducing the size of the microstrip antennas [8,
9, 10]. It is found that the narrow meandering slots
increase the effective electrical length of the patch,
which in turn reduces the size of the antenna
operated at a given frequency.
In this paper, a capacitive fed compact
broadband microstrip antenna with meandered
slots in its radiating patch for wireless applications
Correspondence Author
Dr. Ravi M. Yadahalli
P.E.S. Institute of Technology &
Management, Shivamogga,
Karnataka, India
Email: ravimyadahalli@yahoo.com
International Journal of Engineering & Technology Research
Available online on www.ijetr.com
is presented. The proposed antenna consists of a
rectangular patch which is fed by a capacitive
probe feed. Three identical narrow open
are embedded in the antenna’s radiating patch.
These meandered slots are aligned with an equal
spacing of L/4 parallel to the rectangular patch’s
radiating patch. Parametric study was carried out
by varying the length of meandered slots. The
proposed antenna is simulated using IE3D which is
Method of Moments (MOM) based
Electromagnetic (EM) software [11].
2. Antenna Design
Initially a reference antenna (RA) which is a
rectangular microstrip antenna was designed for 6
GHz using a coplanar capacitive coupled probe
feed. Reference antenna uses glass epoxy substrate
having εr = 4.4 and h = 1.56 mm and Fig.1 shows
the geometry of the reference antenna. Table 1
shows the optimized dimensions of reference
antenna. The configuration is basically a suspended
microstrip antenna in which radiating patch and
the feed strip are etched on the substrate of
thickness “h” mm. A long pin SMA connector is
used to connect the feed strip which is capacitively
coupled to the radiating patch. The length and
width of the radiating patch is designed for center
frequency of 6 GHz. The Capacitive feed strip is
basically a rectangular microstrip capacitor formed
from a truncated microstrip transmission
all its open ends are represented by terminal or
edge capacitances.
International Journal of Engineering & Technology Research
is presented. The proposed antenna consists of a
tch which is fed by a capacitive
probe feed. Three identical narrow open-end slots
are embedded in the antenna’s radiating patch.
These meandered slots are aligned with an equal
spacing of L/4 parallel to the rectangular patch’s
study was carried out
by varying the length of meandered slots. The
IE3D which is
Method of Moments (MOM) based
Initially a reference antenna (RA) which is a
angular microstrip antenna was designed for 6
GHz using a coplanar capacitive coupled probe
feed. Reference antenna uses glass epoxy substrate
= 4.4 and h = 1.56 mm and Fig.1 shows
the geometry of the reference antenna. Table 1
d dimensions of reference
antenna. The configuration is basically a suspended
microstrip antenna in which radiating patch and
the feed strip are etched on the substrate of
thickness “h” mm. A long pin SMA connector is
s capacitively
coupled to the radiating patch. The length and
width of the radiating patch is designed for center
frequency of 6 GHz. The Capacitive feed strip is
basically a rectangular microstrip capacitor formed
from a truncated microstrip transmission line and
all its open ends are represented by terminal or
Fig.1. Geometry of Coplanar Capacitive fed
microstrip antenna.
(a) Top View (b) Cross-sectional View
Table1. Dimensions of capacitive coupled probe
feed microstrip antenna
Parameter
Length of the radiator patch (L)
Width of the radiator patch (W)
Length of the feed strip (s)
Width of the feed strip (t)
Separation of the feed strip from
the patch (d)
Air gap between substrate (g)
Relative dielectric constant (
Thickness of substrate (h)
Later, the radiating patch is meandered using
three identical narrow meandering slots (L
Fig. 2 shows coplanar capacitive coupled probe fed
microstrip antenna with meandered slots in its
radiator patch. The meandered slots are aligned
with an equal spacing of L/4 parallel to the
radiating edge. The width of the meandering slot is
Ws = 1 mm.
Fig. 2. Geometry of coplanar capacitive coupled
probe fed microstrip antenna with meandering
slots in its radiating patch
(a) Top View (b) Cross-sectional View
ISSN: 2278 - 6082
10
Fig.1. Geometry of Coplanar Capacitive fed
sectional View
Table1. Dimensions of capacitive coupled probe
feed microstrip antenna
Dimension
Length of the radiator patch (L) 11.33 mm
Width of the radiator patch (W) 15.21 mm
Length of the feed strip (s) 1.2 mm
Width of the feed strip (t) 3.7 mm
Separation of the feed strip from 1.7 mm
substrate (g) 4 mm
Relative dielectric constant ( ) 4.4 mm
1.56 mm
the radiating patch is meandered using
three identical narrow meandering slots (Ls, Ws).
Fig. 2 shows coplanar capacitive coupled probe fed
microstrip antenna with meandered slots in its
The meandered slots are aligned
with an equal spacing of L/4 parallel to the
radiating edge. The width of the meandering slot is
Fig. 2. Geometry of coplanar capacitive coupled
probe fed microstrip antenna with meandering
sectional View
International Journal of Engineering & Technology Research ISSN: 2278 - 6082
Available online on www.ijetr.com
11
3. PARAMETRIC STUDY
To understand how dimension of the
meandered slots will affect the center frequency,
impedance bandwidth and size reduction of
antenna, a parametric study was carried out using
IE3D simulation software version 14.1. The
simulated data of the proposed antenna were
noted by varying the Ls from the 9.21 mm to 14.21
mm, which are tabulated in Table 2. It may be
noted from the table that the reference antenna
(RA) with Ls = 0 mm resonates for 6.2 GHz having a
bandwidth of 2.6% (−10 dB return loss) and this
may confirmed from Fig.3. Also, it is also amply
evident from the table that the resonant frequency
of the antenna decreases gradually with the
increase in the slot length from 9.21 mm to 14.21
mm.
Table 2. Dimensions of capacitive coupled probe
feed microstrip antenna
Length of
meandering
slot
Ls (mm)
Resonant
frequency
fr (GHz)
Bandwidth
(MHz)
Size
Reduction
(%)
0 6.2 2600 -
9.21 5.39 192 14.55
10.21 5.36 202 15.07
11.21 5.2 226 17.60
12.21 5.34 258 13.39
13.21 5.34 264 13.39
14.21 5.33 267 13.42
Initially, as the slot length Ls increases from 0 to
9.21 mm, the resonant frequency of the antenna
slightly lowers from 6.2 GHz to 5.39 GHz giving a
size reduction of 14.55 % when compared to RA.
The bandwidth at this slot length is found to be
decreased from 90.32% to 3.56%. Again, as the slot
length increases from 9.21 mm to 10.21 mm, the
resonant frequency of the antenna decreases to
5.36 GHz giving a size reduction of 15.07%.
Moreover, it also observed that the bandwidth of
the antenna is 202 MHz.
Later when Ls = 11.21 mm, the resonant
frequency of the antenna lowers still further and
resonates at frequency, which is 1.19 times the
resonant frequency of the RA giving a size
reduction of 17.60%. However, the bandwidth of
the antenna is increased from 3.76 % to 4.23%.
This can be confirmed from Fig.4, which shows the
return loss characteristics of the proposed
antenna. Further increase in the length of the
meandered slots will not affect the center
frequency anymore.
Fig.3. Return loss characteristics of a capacitive
coupled microstrip antenna without meandering
slots
Fig.4. Return loss characteristics of a capacitive
coupled microstrip antenna with meandering slots
The radiation pattern at the resonant frequency 6.2
GHz of reference antenna has been taken for the
both H-plane and E-plane which are platted in
International Journal of Engineering & Technology Research ISSN: 2278 - 6082
Available online on www.ijetr.com
12
Fig.5. The co-polarised radiation pattern at the
resonant frequency of the proposed antenna has
been taken i.e., for 5.2 GHz which is as shown in
Fig.6.
Fig.5. Radiation pattern of the reference antenna
Fig.6. Radiation pattern of the proposed antenna
4. Conclusion
In this paper, the design of a compact capacitive
fed microstrip antenna suspended above the
ground plane is presented. The meandered slots
were etched in the radiating patch of the
microstrip patch antenna to achieve size reduction.
Simulation results show that the proposed antenna
with meandered slots in its radiating patch
resonates at 5.2 GHz providing a size reduction of
17.60% with a bandwidth of 226 MHz.
REFERENCES
[1] S N Mulgi, R M vani, B S Makal, P V Hunagung
and S F Farida, “Enhancement of bandwidth of
rectangular microstrip antenna by feeding and gap-
coupling techniques”, Progress in Electromagnetic
Research Symposium 2000. pp.623, 2000.
[2] Kumar G and Ray K P (2003), Broadband
Microstrip Antennas, Artech House, Norwood , MA
[3] “Design Studies of Ultra-WidebandMicrostrip
Antennas with a Small Capacitive Feed”, Veeresh G.
Kasabegoudar, Dibyant S. Upadhyay, and K. J. Vinoy;
International Journal of Antennas and Propagation,
Volume 2007, pp.1-8.
[4] “A Coplanar Capacitively Coupled Probe Fed
Microstrip Antenna for Wireless Applications”
Veeresh G. Kasabegoudar and K. J. Vinoy, The 2009
International Symposium on Antennas and
Propagation (ISAP 2009) October 20-23, 2009,
Bangkok, Thailand.
[5] Fujimutho K, Henderson A, Hirasawa K and
James J R (1987) , Small Antennas, Research Studies
Press, London, UK
[6] Kan H K and Waterhouse R B (1999), “Size
Reduction Technique for shorted patches”, Electron.
Lett., Vol. 35, pp.948-949
[7] Wong K L (2000), Compact and Broadband
Microstrip Antennas, John Wiley & Sons.
International Journal of Engineering & Technology Research ISSN: 2278 - 6082
Available online on www.ijetr.com
13
[8] S. Dey and R Mitra, Compact microstrip patch
antenna, Microwave Opt Technol Lett 13 (1996), 12-
14.
[9] Kuo J S and Wong K L. ‘A Compact microstrip
antenna with meandered slots in the ground plane’,
Microw. Opt. Technol. Lett., 2001, 29, pp. 95-97.
[10] Prabhakar H V, U K Kummuri, R. M. Yadahalli
and V Munnappa, ‘Effect of various meandering
slots in rectangular microstrip antenna ground plane
for compact broadband operation’, Electronics
Letters, 2007, 43, pp.
[11] IE3D release 14.1, Zeland Software Inc, 2011.
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