Control of Higher Order Harmonics and Spurious Modes for Microstrip Patch Antennas

In rectifying or active antenna systems, the higher order modes can hamper the system efficiency, and thus, the filter antennas are used to eliminate the harmonic radiation. In this paper, the distribution of standing wave fields in patch antenna having been presented and then the characteristic mode theory having been employed, the influences of feeding location and the indentation of patch edges on the suppression of higher order harmonics and their spurious modes are investigated. It is indicated that indenting the radiating edges of the patch element works more effectively on the control of spurious modes while indenting the non-radiating edges can eliminate the harmonics by shifting down the fundamental mode. By selecting feed position and indenting the patch edges, a microstrip patch antenna with both harmonic and spurious mode controls is proposed.