Study and Analysis of Bandwidth Enhancement for Circular Shaped Circularly Polarized Microstrip Antennas for Wireless Communication

Study and Analysis of Bandwidth Enhancement for Circular Shaped Circularly Polarized Microstrip Antennas for Wireless Communication

Uma Kumari

Tapan V. Nahar

Archana Mewara

Laxmi Narayan Balai

1

M. Tech Scholar

Assistant Professor

Head of Department

1,2,3,4

Department of Electronics & Communication Engineering

1,3,4

Yagyavalkaya Institute of Technology, India

Global Institute of Technology, India

Abstract— This paper presents analysis of bandwidth enhancement by cutting the slots in patch and by changing ground plane length. Proposed antennas are simulated on HFSS virtual tool. Optimized ring shaped antenna provides 31.46 % impedance bandwidth at 2.16 GHz resonant frequency. It provides less than 10 dB return loss from frequencies 1.8 GHz to 2.48 GHz and provides circular polarization which is suitable for wireless applications.

Antenna finds its applications such as MSS (Mobile Satellite Services), Bluetooth, wireless networking etc.

Keywords: Microstrip Patch Antenna, Impedance Bandwidth, HFSS Circular Polarization, Wireless Communication

I. INTRODUCTION

Present wireless communication system requires compact, low cost antenna with ease of fabrication. Microstrip Antennas are widely used. Microstrip antenna was firstly theoretically represented by Deschamps since 1953 [1].

Microstrip antenna was patented in 1955 but was firstly fabricated during the 1970’s after availability of suitable substrate. At that time, for wide range of microwave systems, Microstrip antenna was very good choice after continuous development by researchers [2]. Due to wide range of applications and uses, characteristics of microstrip antenna continuously improved by efforts of scientists [3-5]. It can be easily fabricated on printed circuit Board so it is simple and inexpensive. But low bandwidth, small gain, small power handling characteristics and small efficiency is major drawbacks of this antenna. Many scientists have done the research for increasing the bandwidth and gain. The gain of antenna can be increased by using the array configuration [6].

Bandwidth can be increased by various techniques like quarter wave transformers [7], aperture coupled feeding technique [8] and slotted patches. Different shapes of slots like H shape [4], U shape [7], annular ring shape [8], L shape [8], Bow Tie Shape [9], C shape [10] and inverted F shape [10] are popular. Bandwidth can also be increased by stacking of patches [11].

Antenna is main element of communication systems which defines system performance and size. It must be provide three main requirements: i) Design characteristics (small size, light weight, circuit integration, and no obstructive to customer), ii) Electrical properties (wide bandwidth, high efficiency, good radiation characteristics, reconfigurability, and compatibility in terms diversity), and iii) Fabrication factors (optimized cost, reliable, good packagability) [12-14].

Polarization matching is a key factor to improve transmission efficiency, Polarization of Antenna should be matched at transmitters and receivers [15]. Attractive solutions for polarization matching is circularly polarized

antennas which allows flexible behavior between antennas at transmitters and receivers [16]. Effects of multipath propagations can be reduced with improvement in weather penetration and mobility between the sender and the receiver [17]. Designing of microstrip antenna with circular polarization is a challenging task. Following steps are needed for circularly polarized antenna. The first step is to obtain design parameters of antenna at a specific operating frequency. In second step, using perturbation segment to a basic single fed microstrip antenna or by exciting the antenna with double feed lines having equal in magnitude but orthogonally physical phase shift [18-20]. The structure and the size of the perturbation have to be optimized to achieve axial ratio less than 3 dB at operating frequency [21-22].

In this paper, Circular Shaped Microstrip Antenna is designed, than circular slot is designed on the patch and length of ground plane is optimized to meet the requirements in terms of the return loss, bandwidth and polarization.

This Paper is divided into five sections. Section I describes the introduction and literature survey. Antenna designing fundamentals and formulations are explained in section II.

Section III consists different antenna geometries and their simulation results. The comparison of different geometries is discussed in section IV. Paper is concluded in section V.

II. ANTENNA DESIGN CONSIDERATIONS

A circular shape is considered as the basic antenna geometry shape for the proposed antenna model. Hence, the radius of the circular patch [20-22] is calculated from the following equation:

where a = radius of the patch (m), c = velocity of light in vacuum = 3 * 10^8 m/s, fr =resonant frequency (GHz), and εr =relative permittivity = 4.4 (no unit).

III. ANTENNA SIMULATIONS & RESULTS A. Circular Shaped Microstrip Antenna

Circular shaped patch having radius of 17.39 mm is designed on grounded FR4 substrate of 60*50*1.6 cube mm which relative permittivity 4.4. Patch is fed using microstrip line of 8*2.4 square mm. A quarter wave line is used between feed line and patch having dimensions 12*.96 square mm.

Proposed antenna geometry is shown in figure 1.

Fig. 1: Geometry of Circular Shaped MSA

Return loss (S11) versus frequency plot is shown in figure 2. It is observed that antenna provides significant impedance bandwidth of 2.92% at 2.39 GHz frequency respectively.

Fig. 2: Plot between return losses (S11) versus frequency Return loss is logarithmic ratio measured in dB that compares the power reflected by the antenna to power that is fed into antenna. Minimum return loss of -14.07 dB is achieved at 2.39 GHz.

The radiation pattern in 2D is shown in figure 3.

Gain of 1.914 dB is achieved

Fig. 3: Radiation pattern of Circular shaped MSA Axial ratio plot is shown in figure 4. It is observed that axial ratio is greater than 3 dB which suggests linear polarization.

Fig. 4: Axial ratio plot of Circular shaped MSA

B. Circular Ring Shaped Microstrip Antenna

In the proposed antenna discussed previously, circular slot of 16.43 mm radius is cut from the patch and length of ground plane is optimized at 38.4 mm. Proposed antenna geometry is shown in figure 5.

Fig. 5: Geometry of Circular Ring Shaped Antenna Return loss versus frequency plot is shown in figure 6. It is observed that antenna provides less than -10 dB S11 from frequencies 2.22 to 2.61 GHz and provides 16.18 % impedance bandwidth and -22.05 dB return loss at 2.41 GHz resonant frequency.

Fig. 6: Plot between return loss and frequency The radiation pattern in 2D is shown in figure 7.

Maximum gain of 2.73 dB is achieved.

Fig. 7: Two dimensional Radiation pattern.

Axial ratio plot is shown in figure 8. Axial ratio is less than 3 dB which suggests circular polarization.

-200.00 -150.00 -100.00 -50.00 0.00 50.00 100.00 150.00 200.00

Theta [deg]

0.00 12.50 25.00 37.50 50.00 62.50 75.00 87.50

dB(AxialRatioValue)

HFSSDesign1

XY Plot 11 ANSOFT

m1 Curve Info dB(AxialRatioValue) Setup1 : LastAdaptive Freq='2.3GHz' Phi='0deg'

dB(AxialRatioValue) Setup1 : LastAdaptive Freq='2.3GHz' Phi='90deg'

Name X Y

m1 150.0000 8.9954

-30.00 -20.00 -10.00 0.00

90 60 30 0 -30

-60

-90

-120

-150 -180

150 120

HFSSDesign1

Radiation Pattern 11 ANSOFT

m 1

Curve Info dB(GainTotal) Setup1 : LastAdaptive Freq='2.38GHz' Phi='0deg'

dB(GainTotal) Setup1 : LastAdaptive Freq='2.38GHz' Phi='90deg'

Name Theta Ang Mag

m 1 -180.0000 -180.0000 2.7368

Fig. 8: Axial Ratio Plot.

C. Optimized Ring Shaped Microstrip Antenna

In the geometry of figure 1 some modification is done and circular slot of 15.43 mm is cut and ground plane length is optimized at 20mm. Proposed geometry is shown in figure 9.

Fig. 9: Geometry of Optimized Ring Shaped Antenna Return loss versus frequency plot is shown in figure 10. It is observed that antenna is tuned from 1.8 GHz to 2.48 GHz frequencies and providing bandwidth 31.46%.

Fig. 10: Plot between return loss and frequency The radiation pattern in 2D is shown in figure 11. Gain of 1.59 dB is achieved.

Fig. 11: Two dimensional radiation pattern

Axial ratio plot is shown in figure 12. Axial ratio is 2.37 dB which suggests circular polarization.

Fig. 12: Axial Ratio Plot.

IV. COMPARATIVE ANALYSIS

The bandwidth comparison is shown in table I and figure 13.

It is observed that there is significant increment in impedence bandwidth when patch is slotted and partial ground plane is used. Optimized ring shaped antenna provides maximum bandwidth which is ten times of basic circular antenna. There is some shifting in the resonant frequencies when slot is cut and ground plane length is varied.

S.No Antenna Impedance

Bandwidth

Resonant Frequency 1 Circular

shaped 2.92 % 2.39 GHz

2 Circular Ring

shaped 16.18% 2.41 GHz

3 Optimized

Ring shaped 31.46% 2.15 GHz

Table 1: Bandwidth Comparison

Fig. 13: Bandwidth comparison chart

The return loss values are presented in table II and a comparative chart is plotted in figure 14. It may be observed that Optimized Ring Shaped antenna has minimum return loss at 2.15 GHz freq.

S.No Antenna S11

(dB)

Resonant Frequency 1 Circular shaped -14.07 2.39 GHz 2 Circular Ring

shaped -22.05 2.41 GHz

3 Optimized Ring

shaped -23.85 2.15 GHz

Table 2: Return Loss Comparison

-200.00 -150.00 -100.00 -50.00 0.00 50.00 100.00 150.00 200.00

Theta [deg]

0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00

dB(AxialRatioValue)

HFSSDesign1

XY Plot 69 ANSOFT

m1

Curve Info dB(AxialRatioValue) Setup1 : LastAdaptive Freq='2.38GHz' Phi='0deg'

dB(AxialRatioValue) Setup1 : LastAdaptive Freq='2.38GHz' Phi='90deg'

Name X Y

m182.0000 2.0708

-23.00 -16.00 -9.00 -2.00

90 60 30 0 -30

-60

-90

-120

-150 -180

150 120

HFSSDesign1

Radiation Pattern 10 ANSOFT

m1

Curve Info dB(GainTotal) Setup1 : LastAdaptive Freq='2.3GHz' Phi='0deg'

dB(GainTotal) Setup1 : LastAdaptive Freq='2.3GHz' Phi='90deg'

Name Theta AngMag

m1 0.00000.0000 1.5963

-200.00 -150.00 -100.00 -50.00 0.00 50.00 100.00 150.00 200.00

Theta [deg]

0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00

dB(AxialRatioValue)

HFSSDesign1

XY Plot 66 ANSOFT

m1

Curve Info dB(AxialRatioValue) Setup1 : LastAdaptive Freq='2.3GHz' Phi='0deg'

dB(AxialRatioValue) Setup1 : LastAdaptive Freq='2.3GHz' Phi='90deg'

Name X Y

m1 86.0000 2.3748

Fig. 14: Return Loss comparison chart

The axial ratio values are presented in table III and a comparative chart is plotted in figure 15. It may be observed that Circular Ring Shaped Antenna and Optimized Ring Shaped antenna has axial ratio less than 3 dB, so these antennas provide circular polarization and Circular Shaped antenna has axial ratio greater than 3 dB so it provides linear polarization.

S.No Antenna Axial Ratio

(dB) Polarization

1 Circular shaped 8.99 Linear

2 Circular Ring

shaped 2.07 Circular

3 Optimized Ring

shaped 2.37 Circular

Table 3: Axial Ratio Comparison

Fig. 15: Axial Ratio Comparison chart

The gain values are presented in table IV and a comparative chart is plotted in figure 16. It may be observed that Circular Ring Shaped Antenna has maximum gain than circular shaped antenna and then optimized ring shaped antenna.

S.No Antenna Gain (dB)

1 Circular shaped 1.914 2 Circular Ring shaped 2.73 3 Optimized Ring shaped 1.53

Table 4: Gain Comparison

Fig. 16: Gain comparison chart V. CONCLUSION

Three geometries of microstrip antennas are simulated and their performances are compared. It is observed that when circular slot is designed in the patch, bandwidth and gain is increased. Bandwidth is further enhanced by optimizing the slot radius and length of the ground plane. When bandwidth is enhanced after a specific limit, there is significant reduction in gain. Circular ring shaped antenna and Optimized ring shaped antenna provides circular polarization. Antenna finds its applications such as MSS (Mobile Satellite Services), Bluetooth, wireless networking etc.

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