Compact and wideband filtenna for circularly polarised application

Abstract

A compact single M-shaped probe fed circularly polarised filtenna (filtering antenna) without extra filtering circuit is presented in this study, in which three pair slots with different lengths are etched on its parasitic patch to produce radiation nulls at both band edges of its operating band. Furthermore, a single M-shaped probe feeding structure is used to improve the selectivity, especially for the lower band edge. By merging the filtering circuit into a radiating element, a good selectivity in the gain response can be realised without influencing the operation band aperture efficiency. A sample is fabricated and results show that the proposed filtenna has an operating bandwidth of 13% (| S 11 | < −10 dB, AR < 3 dB) with a centre frequency of 5 GHz, a peak gain of 8.9 dBic, and an average gain of 8.3 dBic within its operating bandwidth. Radiation nulls at 3.93, 5.97 and 6.36 GHz introduced by the three pairs of slots have been successfully generated. The radiation patterns are stable within the whole wide operating band.