On the circular polarization operation of annular-ring microstrip antennas

Circular polarization (CP) operation of an annular-ring microstrip antenna with a pair of inserted slits at its fundamental TM₁₁ mode is proposed and experimentally investigated. Two examples of the proposed antenna fed using a microstrip line at the inner and outer patch boundaries are studied. Results show that the proposed antenna can have good CP performance and, moreover, the required antenna size at a fixed CP operation can be much less than that of a conventional circularly polarized circular microstrip antenna operated at the TM₁₁ mode. Details of the proposed antenna for CP operation are described and experimental results of the CP performance are presented and discussed