BROADBAND CIRCULARLY POLARIZED PRINTED MONOPOLE ANTENNA WITH UNIDIRECTIONAL RADIATION PATTERNS

摘要

This article proposes a new broadband circularly polarized (CP) printed monopole antenna (PMA) with unidirectional radiation patterns. The simple structure consists of only a circular patch, a tuning rectangular patch, and an inverted-L strip protruded from the signal line of a feeding asymmetric coplanar waveguide (CPW). Through simple design procedures, a CP PMA with bidirectional radiation patterns and with a fractional CP bandwidth (CPBW) of larger than 35% can be obtained. By placing an open metal cavity underneath the bidirectional PMA without changing the PMA's structural dimensions, one can obtain unidirectional radiation patterns without downgrading the CPBW. In addition, the peak antenna gain can be raised by about 6 dB.