Parasitic mode suppression techniques for shielded Fabry-Perot cavity antennas

Small-size shielded Fabry-Perot (FP) cavity antennas suffer from higher-order parasitic modes. In this paper we investigate and compare three techniques implemented to suppress these modes and thus improve the antenna performance in terms of enlargement of the radiation and impedance bandwidths (BW), reduction of the side lobe level, and improvement of the stability of the radiation patterns versus frequency. It is shown that the optimum configuration is obtained when using a conical penetration inside the FP cavity antenna. In the optimized case, we show that the overall antenna BW (defined as the intersection between the -1 dB radiation BW and the -10 dB reflection coefficient BW) reaches 14.5% with side lobes lower than -15 dB over the entire BW.