Compact Broadband Dual-Sense Circularly-Polarized Microstrip Antenna/Array with Enhanced Isolation

This paper presents a novel method of designing the compact dual-sense circularly polarized (CP) microstrip antenna/array with improved impedance bandwidth, axial ratio (AR) bandwidth, and interpolarization isolation. The lefthand and right-hand CP characteristics are achieved simultaneously by conceiving a vertically coupled resonant structure for the first time. Different from traditional methods, the antenna shows a compact size but exhibits the wide impedance and 3 dB AR bandwidths. For each input, two coupling paths are purposely designed to excite the TM10 and TM01-mode of the patch, respectively. By composing different coupling units in the two paths, an intrinsic ±90° phase difference over a broadband can be obtained, resulting in the broadband CP characteristics. In addition, a novel method of using the neutralization line between the two feeds is investigated to improve the isolation between the polarizations. Based on the dual-sense CP element, a 1 × 4 dual-sense CP array is composed to exemplify its potential applications in large arrays. Compared with traditional CP antennas, the proposed antennas have the advantages of compact size, simplified feed, broad impedance and 3 dB AR bandwidths, and improved isolation. Experimental results verify the predictions.