Generating a pure circularly polarised axial beam from a pattern reconfigurable square loop antenna

Abstract

A pattern reconfigurable square loop antenna (SLA) is capable of generating tilted and doughnut beam patterns. In this study, it is demonstrated that the same antenna can be used to generate a circularly polarised axial beam if all four feeds are excited simultaneously with equal amplitude and a sequential phasing of 90°. Thus, the same square loop is capable of generating three distinct unit patterns by changing its feed excitation mechanism. This phenomenon makes the SLA an exceptional candidate for integration in the unit pattern reconfigurable antenna array. The study presents a complete design of SLA in conjunction with the feeding network and validates the computed and experimental results for a test band from 4.3 to 5 GHz. The antenna provides an axial beam of a maximum directivity of 7.4 dBi over the test band and yields near to ideal circular polarisation at broadsight. Using current distributions an explanation for the mechanism of generation of circularly polarised axial beam is also presented.