ANALYSIS OF CAVITY BACKING ON SIMPLE RECTANGULAR MICROSTRIP PATCH ANTENNA.

Rajneesh Verma & P.K. Singhal

Microwave Laboratory

Department of Electronics & Communication

Madhav Institute of Technology & Science

Gwalior-474005,

India.

ABSTRACT

This paper presents simple square patch antenna representing the effects of cavity backing by two side walls as well as four side walls. Impedance bandwidth of 42.00 % has been obtained from the proposed antenna over the desired frequency band.

INTRODUCTION

A metallic surface supported by ground dielectric substrate represents a microstrip antenna. Microstrip antennas have many interesting features such as small size, low weight, easy and cheap to manufacture. The most serious limitation of the microstrip antenna is its narrow bandwidth [1]. The traditional microstrip antenna has bandwidth of only a few percent, for this reason large volume of research and development in the area of microstrip antenna in the last fifteen years has been devoted to various techniques for the enhancement of microstrip antenna bandwidth [2-7].

This paper describes an alternative method of obtaining enhanced bandwidth from a microstrip antenna, using cavity backing with two and the four side walls on a square patch microstrip antenna. Also the affects of two side & four side backing are compared in this paper. This antenna being cavity backed one, which can increase the bandwidth and suppress the surface wave propagating, so as to increase the radiation efficiency. Simulation of the proposed antenna has been carried out using IE3D software [9] and various characteristics have been investigated.

ANTENNA DESIGN

Proposed antenna is shown in figure 1. In the proposed antenna one square patch of dimensions of 28x28 mm is placed on the substrate having thickness 4.4m and dielectric constant of 2.55 .The probe feeding is done at the corner of the square patch .Frequency of design being taken is 4Ghz. First of all the simple patch without wall is taken in accordance to above parameters, then two side walls opposite to each other are added to the patch and effects studied, then after two more side walls added to cover the substrate. The side walls of height equal to the thickness of the substrate being taken.

RESULTS AND DISCUSSIONS

The simulations of the proposed antenna has been carried out by using IE3D software. Figures 2(a-c) shows the variation of VSWR with frequency for the proposed configuration. From fig. 2(a), it is clear that a bandwidth of only 6.00 % for VSWR £ 2 has been obtained. Similarly, from fig. 2(b), and 2(c), it is 42.00 % i.e., same for two sidewalls and four sidewalls. Therefore, using cavity backing, bandwidth increases by a large amount. The simulated impedance loci of the designed antennas are shown in fig. 3(a-c), respectively. Figures 4(a-c) show radiations patterns at center frequencies of the designed antennas, fig. 5(a-c) shows variation of radiation efficiencies of the proposed antennas with frequency and it has been obtained that efficiency gets improved drastically. The number of walls increases the radiation efficiency. Figure 6(a-c) shows directivity variation for the corresponding geometries. It is observed that the antenna gives similar radiation pattern at all frequencies along the band for two and four side walls.

CONCLUDING REMARKS

The effects of cavity backing with two side walls and four side walls on a square patch microstrip antenna have been analyzed. It is obtained that radiation efficiency is enhanced using cavity backing, bandwidth is improved to 42.00 % and also the gain increases. The proposed design has similar radiation characteristics through out the operating band for two as well as four side walls and the gain for the small configuration has increased with side walls. So the compact design with high gain and improved bandwidth is possible with cavity walls.

ACKNOWLEDGEMENT

The authors thankfully acknowledge the financial support provided by the university grant commission, New Delhi & also the authorities of Madhav Institute of Technology & science, Gwalior, India.

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[9] IE3D software Release8 Developed by M/S Zeland Software, Inc.

Figure 1: Geometry under consideration

Figure 2: Analysis of VSWR vs Frequency

Figure 3: Smith Chart Analysis

Figure 4: Analysis of polar elevation pattern

Figure 5 : Analysis of Efficiency vs Frequency

Figure 6: Analysis of Directivity vs Frequency