An annular patch circularly polarized antenna in 920-MHz band

A circularly polarized microstrip patch antenna in 920-MHz band was designed and fabricated. This antenna has an annular-ring patch as the radiating conductor and radiates circular polarization by making two slits on the patch. The simulation and measurement results were shown, and then the effect of a conductor protrusion was analyzed when it was inserted in the center of the ring patch. This antenna is intended for applications in which a conductor protrusion exists inside the ring like a gear wheel.