Broadband Omnidirectional Circularly Polarized Antenna With Asymmetric Power Divider

Broadband omnidirectional circularly polarized (CP) antenna has a unique advantage of reducing multipath effect over linear polarized antenna for wideband communication or radar applications. This article presents such antenna design based on broadband omnidirectional vertically polarized (VP) and horizontally polarized (HP) radiators, and a dedicated designed broadband asymmetric power divider and a phase shifter. The asymmetric power divider is analyzed systematically and an optimization process similar to particle swarm optimization (PSO) is employed in optimizing the feeding network. The proposed antenna is omnidirectional on azimuth plane, and has 66.7% impedance bandwidth, 57.7% axial ratio (AR) bandwidth and 53.4% (1.215-2.1 GHz) usable bandwidth, which is the overlapping bandwidth of 10 dB return loss and 3 dB AR band. The peak gain of right-handed CP for this antenna is 0.9 dBi and the average gain over all azimuth direction and frequencies within the band is better than -1 dBi.