A Circularly Polarized Annular Patch Antenna and the Influence of a Conductive Protrusion on its Axis

An annular-ring microstrip patch antenna is fabricated considering an application to be loaded on a gear wheel with a certain sensor. This antenna is a single-point-fed type and radiates right-handed circular polarization by slightly perturbing the patch with slits. First, the basic characteristics of the fabricated antenna are shown, and then the influence on the antenna characteristics is investigate by simulations when a conductive protrusion exists inside the annular ring.