Bidirectional Circularly Polarized Microstrip Antenna Fed by Coplanar Waveguide

A novel bidirectional microstrip antenna fed by coplanar waveguide (CPW) is proposed to obtain circular polarization (CP) radiation. Two radiating patches, located on the front and back sides of the CPW respectively, are fed by coupling through the CPW open stub. Same rotation CP radiations in two opposite directions are achieved by adding perturbation segments at different sides of the square patches. The symmetrical characteristics of the antenna suppress the even mode in the CPW line. Measured results show that the proposed antenna can have an input impedance bandwidth of 11.6% and CP bandwidth of 1.86%. Left-hand circular polarization (LHCP) is found on both sides of the antenna. This bidirectional CP antenna is suited to be a reader antenna for the radio frequency identification (RFID) system.