Compact H-Antenna with Shorting Post for GSM Using Genetic Algorithm and Moment Method

Abstract

Emails: (1) n_Komjani@iust.ac.ir, (2) m_ostadrahimi@ee.iust.ac.ir INTRODUCTION y increasing demand for multi-frequency services in communication, the need for compact and multi-band antennas has been growing recently. Microstrip patch antennas for their special characteristics such as low profile, light weight, conformity and ease of fabrication are widely used. They are manufactured in many different shapes and geometries. Among them, H-shaped microstrip antennas are one of compact structures which have been investigated by Palanisamy and Garg [1]. By using shorting post between the surface patch and ground plane, more miniaturization plus dual-band operation is attainable. This paper presents our computational and experimental studies of the performance of these antennas. Optimized dimensions, Feed and shorting post positions are investigated using genetic algorithm as one of the best engines for thorough searching in problems of many parameters [2]. This very compact H-shaped antenna is optimized to operate in 900 MHz and 1800 MHz for GSM application. We also proposed a flexible and accurate model of coaxial and shorting post in prob-fed microstrip antennas discussed in [3] and is useful for optimization process. The method of analysis is moment with RWG basis functions. More information is provided in [3]. A prototype was designed, fabricated and tested to be used in GSM systems. Good agreement has been obtained between theoretical and experimental results. MINIATURIZD AND DUAL BAND H-SHAPED ANTENNAGenerally, the dual band microstrip antennas found in the literature may be divided into two categories, namely, multiresonator antennas and reactive loading antennas. By using multiple shorting posts located symmetrically with respect to the patch axis, dual band operation can also be realized with low cross polarization [4]. In this design, we used a shorting post as reactive loading. The position of shorting post(s) is very important. Shorting post(s) places on the node lines of a specific mode electric field, has weak effect on that mode and if it removes from these nodes, shows an inductance (or capacitance) depending on its position and dimension. In [5] a rectangular patch antenna is designed for GSM application with eight shorting posts that works in TM 10 and TM 30 modes. Appearing this new reactance from shorting post in antenna equivalent circuit changes resonance frequency of the perturbed mode. In inductive case, as the result of new inductor, resonance frequency goes higher and to achieve that resonance frequency again, dimension of antenna should be decreased. Therefore shorting posts can be an essential tool for compact antennas in spite of their disadvantages like decreasing the antenna gain and bandwidth as the result of decreasing the surface of antenna [10]. We optimized the shorting post to perturb both TM 10 and TM 30 simultaneously in H antenna. In these modes, broadside pattern as the result of current distribution appeared. A simplified equivalent model for H-shaped antennas is presented in...