A 50Ω Microstrip Line Fed Shorted Hexagonal Microstrip Antennas with Reduced Cross-Polarization

Abstract A Hexagonal Microstrip Antenna (HMSA) is an approximation to a Circular MSA (CMSA), which is not symmetrical over two principal planes, unlike a CMSA. Consequently, two types of feed positions are feasible for each X and Y-axes. When a quarter-wave transformer or inset feed is used to match the edge impedance of the HMSA, it becomes asymmetrical over the feed axis (E-plane), which leads to increase in the crosspolarization level in the H-plane. In this paper, to reduce the crosspolarization level of HMSA along H-plane and to match the edge impedance of the HMSA on each X and Y-axes with the 50Ω-Microstrip (MS)-line-feed, a single and a pair of shorting posts have been used. The current distribution of the shorted HMSA is changed due to the loading of shorting posts into the patch, which in-turns help to match the edge input impedance. A detailed investigation on the characteristics of the shorted HMSA with modified fundamental mode frequencies has been presented. The co-polarization to crosspolarization ratios (CTCR) in H-plane of the HMSA with a pair of shorting posts has been reduced substantially by more than 20 dB at the broadsight direction in comparison with that of an HMSA with a single shorting post or with an inset. The simulated results of the HMSA with direct 50Ω-MS-line-feed are in good agreement with measured ones.