A Simple-Topology Compact Broadband Circularly Polarized Antenna With Unidirectional Radiation Pattern

In this letter, a geometrically simple, reflector-backed single-point-fed circularly polarized (CP) antenna with unidirectional radiation pattern is presented. The structure comprises a simple coplanar waveguide feeding circuit with an open slot etched on one side of the coplanar ground. The enhanced CP bandwidth is obtained by combining the loop mode, the slot mode, and the asymmetrical configuration of the coplanar ground planes along the feedline. All parameters are optimized at the full-wave level of description for the best impedance and axial-ratio (AR) bandwidth. The antenna footprint is only 0.35λ
_o
× 0.39λ
_o
at the lowest CP operating frequency of 3.1 GHz. The measurement results indicate 82% impedance bandwidth (from 3 to 7.2 GHz) and 80% AR bandwidth (from 3.1 to 7.2 GHz). A unidirectional right-hand circular polarization radiation pattern in the +z-direction is also achieved by adding a reflector. The peak realized gain of the antenna is 6.7 dBic, and the peak radiation efficiency is 98%.