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, 1Satyabratamaiti12@gmail.com

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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