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This paper presents a design of compact elliptical shaped CPW fed planer UWB fractal antenna. A novel planer UWB antenna using a fifth itera-tion elliptical fractal shape is presented in this paper. The frequency characteris-tics of antenna consist of UWB properties in the range 2.0 GHz-16 GHz corre-sponding to the impedance bandwidth of 140%. The antenna has nearly good Omni-directional radiation pattern and peak gain of 4.9 dBi. The group delay profile of the proposed antenna lies within 1ns. The areas of applications are medical imaging, wireless communication, and vehicular radar.
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adfa, p. 1, 2011.
Springer-Verlag Berlin Heidelberg 2011
On the Design An Enhanced
Bandwidth of Elliptical Shape
CPW-Fed Fractal monopole An-
tenna for UWB Application
Satyabrata Maiti1, Naikatmana Pani
2
School of Electronics Engineering, [email protected]
Abstract. This paper presents a design of compact elliptical shaped CPW fed
planer UWB fractal antenna. A novel planer UWB antenna using a fifth itera-
tion elliptical fractal shape is presented in this paper. The frequency characteris-
tics of antenna consist of UWB properties in the range 2.0 GHz-16 GHz corre-
sponding to the impedance bandwidth of 140%. The antenna has nearly good
Omni-directional radiation pattern and peak gain of 4.9 dBi. The group delay
profile of the proposed antenna lies within 1ns. The areas of applications are
medical imaging, wireless communication, and vehicular radar.
Keywords: Fractal Geometry, Ultra Wide Band, coplanar wave guide, Im-
pedance Bandwidth
1. Introduction
In recent years, the area of UWB system has created a lot of heed among RF and mi-
crowave engineers. In February 2002 the frequency band between 3.1 GHz to 10.6 GHz was assigned as the ultra wide band (UWB) usable frequency by the Federal
Communication Commission (FCC) [1], USA, since it provides high data rate at very
high speeds[2-3]. This has increased the demand for smaller size antenna having
broadband features. One of the many technological challenges of ultra wide band
system lies in the high level of integration that UWB products require at low cost and
low power consumption. However, antenna design is a challenging task in UWB sys-
tems due to a 140% impedance bandwidth. The antenna used in warfare applications
for UWB systems, e.g. 'Archimedean antenna' and 'frequency independent spiral
antenna' are huge and hence cannot be used easily in MIC/MMIC devices. Thus, it is
clear that an antenna should be packed compactly and should have ultra wide band-
width along with Omni-directional radiation patterns. Various designs of UWB an-
tenna have been accounted for, where sub-wavelength structures as SRR and electro-magnetic band gap structures are used to create notch bands. If both the time and
frequency domains are accounted for, then the 'CPW-fed elliptical disc fractal mono-
pole antenna presents good performance and has a simple structure. The printed mon-
opole antennas have been developed in current years catering ultra wide band range
[4-6]. Various matching techniques are reported to increase the bandwidth and there-
by depletion of size. Optimization beveling of ground planes [7], feed gap etc are
used to increase the bandwidth and hence to obtain UWB [8-9]. Currently the self
recursive nature of the fractal geometries has been utilized to design electrically
smaller ultra wide band antennas. A novel approach to obtain multiband miniaturized
antenna was to include fractal geometry.
2. Antenna design And parametric study
The geometry of proposed antenna structure is designed on a substrate of 3.4r ,
thickness 1.53 mm with a dimension of 45 x 48 mm2 (Wsub x Lsub), loss tangent of
0.025 and coplanar wave guide feed. The impendence bandwidth of the designed
antenna covers the range from 2.0 GHZ to 16 GHz unlike a elliptical co planer wave
guide feed monopole of same size whose operating bandwidth ranges from 3.1 GHz
to 14 GHz.
Fig. 1. a) Initial elliptical monopole b) Construction of beveled ground
Fig. 2. Fig. 2 Proposed elliptical fractal antenna
The initial height dg of the two ground planes is taken to be 14.5 mm Fig.1 (a) and
then beveled to the height as depicted in fig. 1 (b). At first, the planar antenna was
designed such that it covers the entire UWB range. The proposed antenna structure is
shown in fig.2. The effect of the various parameters of the feed gap and radiating
patch gap between ground planes is studied. It can be that there is a shift to lower frequency, for S11 dB better than 10 dB, as iteration increases. Introduction of fractal
shape enhances the effective electrical path of surface current which in turn increases
the effective impedance bandwidth [10-13]. This fine tunes the desired impedance
bandwidth frequency range of UWB antenna.
Fig. 3. (a) simulated result of proposed antenna gap variation between feed and groun
Fig. 3 (b) simulated result of proposed antenna gap variation between patch and ground
The gap between the patch and the ground plane, wp, and the gap between the feed
line and the ground plane, g, are the two most important parameters which determine
the UWB characteristics of the antenna as shown in Fig. 3(a) & 3(b). By varying these
two parameters the antenna is made to cover the entire UWB range from 3.1 GHz to
10.6 GHz. It is observed that the bandwidth of the antenna increases as the gap g de-creases. So the optimized value of the gap, g, is fixed at 0.5 mm. Then Elliptical patch
contains fifth iterative structure. In first iteration, a horizontal ellipse having its major
axis=15mm and minor axis= 10.5 mm is intersected with the vertical ellipse having
same dimension. Then a horizontal and vertical ellipse having major axis=9.5mm and
minor axis=8mm is subtracted from it. The same process is repeated for each iteration
using the scaling down of 1.0 on both axis. The full procedure is repeated five times
and it gives the final iterative structure of elliptical shape antenna. Fig.4
Fig. 4. Elliptical iteration
TABLE 1
PARAMETERS OF ANTENNA (UNIT: MM)
3. RESULTS AND DISCUSSION
Return loss
The proposed antenna is evaluated by finite integration method by using time domain
solver of CST microwave studio. The designed antenna has a compact size of 45x
48mm2. The optimized dimensions are listed in Table 1. The simulated characteristic
of the designed antenna is shown in fig.5 and it is notice that the impedance band-
width ranges from 2GHz to 16GHz.
Fig. 5. Comparison of s11 with and without beveling the ground and with fractal slots cut in the patch
Antenna
Parameter
Lsub Wsub Lg wp g dg W r
Value(mm) 48 45 3 0.4 0.4 14.5 3.2 1
Slot pa-
rameters
Rx Ry d 1st
Rx
1st
Ry
2nd
Rx
2nd
Ry
Value(mm) 15 10.5 17.5 8 9.5 7 7.5
Current Distribution
The current distribution at four frequencies, 3.0GHz.5.5GHz, 7.5GHz, and 10GHz,
are shown in fig.6 Antenna behaves as a radiating slot which can be formed between
ground plane and radiating patch .The current distribution at 5.5 GHz is shown in fig
that shows it results in standing wave due to the concentration of current near the slot.
Fig. 6. Simulated current distribution on proposed antenna at
(a) 3.0 GHz, (b) 5.5 GHz,(c) 7.5 GHz and (d)10.0 GHz
Radiation Pattern
The radiation patterns of this proposed antenna at selective frequencies 2.0 to 16 GHz
in E-plane and H-plane. H-plane radiation patterns are depicted in fig.7 which show
that it is nearly good Omni direction and E-plane is bidirectional. The simulated ra-
diation patterns at 2.1GHZ, 5.0GHz, and 10GHz are plotted shown below.
Fig. 7. Simulated radiation patterns in H-plane and E-plane at 3.0 GHz, 5.0 GHz and 10.0 GHz
H-plane radiation patterns are depicted in fig.7 which show that it is nearly good Om-
ni direction and E-plane is bidirectional. The simulated radiation patterns at 3.0GHZ,
5.0 GHz, and 10GHz are plotted shown below.
Peak gain & Group delay
The peak gain of the proposed antenna is simulated 4.9 dBi with in band as shown in
fig.8. The peak gain increase as the higher frequency but it almost constant. Fig.9.
shows group delay of the proposed antenna which is within 1ns, confirming the pro-
posed antenna to be non-dispersive. The proposed antenna shows a nearly flat feed-
(a)
(b)
(c)
back in 3.1 to 10.6 GHz ultra wide band, where the group delays makes large outing.
Fig. 8. . Simulated peak gain of this proposed antenna Fig.9. Simulated Group Delay
This outing satisfactory TDM characteristics and distortion free transmission.
dttsdtts
tsts
)()(
)(2)(1max
2
2
2
1
is the delay which is which is change to make the numerator in the equation maxi-mum. It obtain the correlation between the electric field signals s1(t) and s2 (t). The input signal is 5th derivative Gaussian pulse and its 5th derivative. The elevated pulses
are chosen as the signal s1(t), while the received pulse as signal s2 (t), it indicates the
similarity between the original pulse and the received pulse. When the 2 signal wave-
forms are identical, this means that the antenna system does not distort the input sig-
nal at all. The correlation coefficient found from the slotted fractal antenna is 0.83 and
from the unslotted fractal from antenna is 0.89.
4. CONCLUTION
A novel CPW-fed elliptical fractal antenna is proposed .The fractal monopole antenna
with elliptical fractal slots in the radiating patch having characteristics. The simulated
radiation pattern of this antenna is very close to bi directional in E-plane and Omni
directional in H-plane. The gain of the antenna varies from -2 dBi to 4.9 dBi. Imped-
ance bandwidth of the antenna ranges from 2 GHz to 16 GHz which affinity 140%
impedance bandwidth. The simulated group delay exhibits within 1ns over the desired
frequency. Total antenna dimension is 48 mm x 45 mm. This specifies the proposed
antenna potential for use in military application. The antenna is simple to design,
compact size of the antenna and easy to fabricate and it suitable for MIC/MMIC cir-
cuits.
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