Switchable circularly-polarised square ring antenna controlled by dual-loaded dual-loop

A new switchable perturbing method is presented for a microstrip square ring antenna with a circular-polarisation diversity. The proposed antenna consists of three identical loops at the back ground side and one diagonal dual-loop at the front patch side for obtaining switchable circular-polarisation senses with a simple DC bias circuit. By control of the states of the two pin diodes in the front-sided dual-loop, both the left-handed and the right-handed circular polarisations can be easily alternated. The implemented antenna employing the dual-loop perturbation shows a good agreement with the simulation results and symmetrical circular polarisation characteristics at the resonant frequencies.