Circularly Polarized 1 x 4 Square Slot Array Antenna by Utilizing Compacted Modified Butler Matrix and Branch Line Coupler

Abstract

Circularly polarized (CP), beam steering antennas are preferred to reduce the disruptive effects such as multi-path fading and co-channel interference in wireless communications systems. Nowadays, intensive studies have been carried out not only on the specific antenna array design but also their feeding networks to achieve circular polarization and beam steering characteristics. A compact broadband CP antenna array with a low loss feed network design is aimed in this work. To improve impedance and CP bandwidth, a feed network with modified Butler matrix and a compact ultra-wideband square slot antenna element are designed. With this novel design, more than 3 GHz axial ratio BW is achieved. In this study, a broadband meander line compact double box coupler with impedance bandwidth over 4.8-7 GHz frequency and the phase error less than 38 is used. Also the measured impedance bandwidth of the proposed beam steering array antenna is 60% (from 4.2 to 7.8 GHz). The minimum 3 dB axial ratio bandwidth between ports, support 4.6-6.8 GHz frequency range. The measured peak gain of the proposed array antenna is 8.9 dBic that could scan solid angle about similar to 91 degree. (C) 2015 Wiley Periodicals, Inc.