International Journal of Engineering Trends and Technology (IJETT) – Volume 5 Number 7- Nov 2013
Design of compact Polygon Slot CPW Fed Antenna
for Broadband/UWB Applications
Abhishek kumar#1, T.Shanmuganantham*2,
#1
M.Tech scholar, Department of Electronics Engineering
# Assistant professor, Department of Electronics Engineering
Pondicherry University, Puducherry, India-605014
2
Abstract— In this paper a low profile, small size polygon slot
CPW fed antenna for broadband application is presented. The
proposed antenna comprises of simple polygon radiator and
rectangular ground plane. It resonates at 4.9 and 8.4 GHz
frequency where return loss is well below to -10 dB. The
proposed antenna is designed with FR4 epoxy substrate having
dielectric constant of 4.4 and loss tangent of 0.02 and overall size
19x 21x 0.8 mm3. The antenna is designed using simulation tool
Mentor graphics 15.10 version which is based on method of
moments (MoM). Simulation results show that the axial ratio
(AR) bandwidth is as large as 115.4% (4.1 GHZ- 15.3 GHz) with
VSWR≤ 2, which makes the antenna be used for broad band and
ultra wideband (UWB) applications also.
Keywords—Broad band network, Coplanar waveguide (CPW),
gain, radiation pattern, ultra wideband (UWB)
I. INTRODUCTION
With the development of modern wireless communication,
the design of the polygon slot antenna is getting more and
more popular. Microstrip printed antennas attract much
attention in the recent years by its light weight, low profile,
small size and easy of fabrication. Though they have narrow
bandwidth it can be eliminated by use of slot antennas [1].
Due to the high Q nature, the obtained bandwidth is usually
small. Thus, the need for broadband slot antennas is
inevitable. In the last decades, owing to the slot antennas,
especially wide slot antenna which can provide much wider
impedance bandwidth, many slot antennas have been used for
the broad band and UWB applications [2-4]. Moreover, due to
attractive features such as wide impedance bandwidth, single
metallic layer, low profile, and easy integration with active
device or MMICs, printed wide slot antennas with a coplanar
wave- guide (CPW) feed have been increasingly investigated
in the design of the CP antennas for axial ratio (AR)
bandwidth enhancement [5]. In an early research, the
conventional CP CPW-fed antenna has been capacitive
coupled in the feeding network [6]. Broadband axial ratio
(AR) bandwidth can be obtained by embedding square slots
appropriate perturbation Structures which can be constructed
by loading a cross patch [7] or a ground T-shaped metallic
strip [8] or a pair of inverted-L grounded strips [9]. It can also
be constructed by an inverted-L tuning stub extended from the
signal line and a pair of grounded strips [10]. The slot antenna
with enhanced impedance and AR bandwidth was obtained by
using the lightening-shaped feed line. The antenna has
introduced vertical and horizontal tuning stubs to widen the
VSWR≤ 2 impedance band effectively. The design antenna of
ISSN: 2231-5381
[11] has been measured to exhibit an impedance bandwidth
larger than 45%.
The proposed antenna is designed with a wide polygon slot,
having octagonal metal patch feeding structure. The slot is
introduced at the ground planes to increase the bandwidth and
to get better impedance matching. The antenna has less
number of design parameters compared to the existing
wideband antennas in the literature [3-7] which makes its
design simple. The characteristics of polygon slot antenna
including return loss (S11), radiation patterns, efficiency and
gain are simulated and parametric analysis is done with
respect to the length (Ls) and width (Ws) which is shown in
section III. The paper is organized as follows: Section II
brings out the geometry of the antenna. In Section III
simulation results and analysis are discussed. Section IV
concludes the work.
II. ANTENNA DESIGN PARAMETERS
The geometry of antenna is shown in Figure1. The antenna
is printed on FR4 dielectric substrate with dielectric constant
 r =4.4, loss tangent tanδ=0.02and thickness of 0.8mm. The
antenna has compact size of 19 × 21 mm2 and it is fed by
CPW for a 50Ω characteristic impedance with fixed 1.6mm
feed line width and 0.3 mm ground gap. Since the patch and
feed structure are constructed on the same plane, one metallic
layer only is present. Hence, the antenna can be easily
fabricated and it has low cost. By properly adjusting the
dimensions of the slot and feeding structure, the impedance
matching of the proposed antenna is improved, which
produces wide impedance bandwidth with relatively stable
radiation pattern. The wide impedance matching with reduced
size of the antenna shows the novelty compared to the existing
antenna.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 5 Number 7- Nov 2013
III. SIMULATION RESULTS AND DISCUSSIONS
Figure2 shows the simulated return loss characteristics of
proposed CPW fed octagonal patched UWB antenna. From
the figure it can be seen that, proposed antenna resonates at
4.9 GHZ, 8.4 GHz frequency having -43 dB and -23 dB return
loss respectively.
Figure1. Geometry of the proposed antenna
The optimized values of proposed antenna structure are
obtained using Zealand IE3D electromagnetic solver. These
values are shown in table 1. Details of the antenna design and
the simulation results of the proposed antenna are presented
and discussed.
Table 1: Optimal parameter values of the antenna
Figure2 Return loss characteristics of proposed antenna
Parameters
Description
L
Length of the antenna
21 mm
W
Width of the antenna
19 mm
L1
Length of the patch
4.5 mm
W1
Width of the slot
11.2 mm
W2
Width of the one side ground
plane
8.4 mm
A
Horizontal value of the lower part
of Patch
2.65 mm
B
Vertical value of the lower part of
Patch
2 mm
C
Horizontal value of the lower part
of Patch
3.2 mm
D
Vertical value of the lower part of
slot
2.5 mm
d
Distance between ground plane
and patch
1.5 mm
ISSN: 2231-5381
Optimum
Value
3.1 Parametric Analysis
In this section, the effects of different geometric parameters
of antenna on return loss and bandwidth are investigated for
the proposed antenna. This helps to design broad band or
UWB antenna with wider bandwidth. The parametric study is
performed and the performance of antenna is analyzed with
IE3D electromagnetic solver. The analysis is done by varying
one parameter at a time, keeping all other parameters constant.
3.1.1 Effect of side Length Ws of Polygon slot
Figure3 shows that, the variation of resonance
characteristics of proposed antenna with bottom length Ws.
When it increases from 0.7 to 1.3 mm, from the figure 3 it can
be seen that, there is a down shift in return loss at the
resonating frequency. The return loss values also changes due
to inductive and capacitive effects, which are produced by
electromagnetic coupling between ground and patch. Since
change in Ws affects impedance matching at resonant
frequencies, so this parameter plays an important role in
improving bandwidth. Hence, the simulated analysis shows
that the antenna has better return loss at 4.9 GHZ and 8.4 GHz
for the optimum value Ws = 0.7 mm.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 5 Number 7- Nov 2013
Figure 3: comparison of return loss characteristics by various Ws
3.1.2 Effect of feed length Ls
Figure 5: VSWR characteristics of proposed antenna
The parameter Ls has great effect on performance of
antenna as shown in Figure 4. This parameter is optimized
such that there is proper coupling between feed lines to the
patch. The antenna is simulated for various values of Ls
starting from 5.3 to 5.9 mm.
From simulation results, it is observed that the impedance
matching is poor at Ls =5.9 mm. As Ls increases from 5.3 to
5.9 mm, the simulated lowest and highest resonating
frequency shifted. The impedance bandwidth also changes.
Hence, it is concluded that the Ls affects more on lowest,
highest resonating frequencies and impedance bandwidth. The
antenna has better impedance matching at the optimum value
Ls = 5.3 mm.
Figure 6 shows the simulated radiation patterns with
Elevation and azimuthal plane at 4.9 GHz and 8.4 GHZ
resonating frequency by using ZELAND IE3D software. The
antenna has bi-directional radiation patterns in E-plane at both
resonant frequencies. In H-plane, the antenna has
omnidirectional radiation patterns, which indicates that it can
receive the signals in all directions. The patterns and other
curves are obtained at the time of simulation. We observed
relatively stable radiation by taking 20 cells per wavelength.
Figure 4: comparison of return loss characteristics by various Ls
Figure 5 shows the simulated voltage standing wave ratio
(VSWR) of the proposed antenna is less than 2 for entire
frequency range of 4.1 to 15.3 GHz. From figure it is clear
that, standing wave ratio is around 1.5 for entire operating
band which satisfies 2:1 VSWR bandwidth.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 5 Number 7- Nov 2013
distribution is mainly on the lower and upper edge of the
ground plane, middle portion of patch. At the top of ground
plane, the strong current distribution indicates that this part of
the ground plane which is nearer to patch acts as a part of
radiating structure. Hence, the distance Ls or distance between
lower part of the radiating patch and ground plane and also
feed gap ‘g’ strongly affect the return loss of antenna.
(a)
(b)
Figure 7: 3D current distribution of antenna (a) 4.9 GHz (b 8.4 GHz)
Figure 8 shows total field gain of the antenna as a function
of frequency. The antenna gain varies between 2.4 dBi to 4.5
dBi in the operating band 4.1-15.3 GHz and has peak gain 4.5
dBi at 10 GHz. These characteristics can make sure the ability
of the proposed antenna to operate in broad band and UWB
band effectively.
Figure 6: E and H-plane radiation patterns at 4.9 and 8.4 GHZ
Figure 7 shows the current distribution at resonant frequency
4.9 GHz and 8.4 GHZ. At 4.9 GHz, the electric current
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International Journal of Engineering Trends and Technology (IJETT) – Volume 5 Number 7- Nov 2013
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
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Figure 8: Gain characteristics of proposed antenna
[8]
IV. CONCLUSIONS
In this paper, a compact CPW fed polygon slot antenna is
proposed. The octagonal turning stub is introduced at the
interior portion of the slot to enhance the coupling between
the ground and feed. Thus results, the proposed antenna shows
better impedance matching. The impedance bandwidth of the
proposed antenna is over 4.1-15.3 GHz, and the AR
bandwidth is about 115.4% which proves the proposed
antenna uses for broad band as well as UWB application.
ISSN: 2231-5381
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