Abstract
A broadband H-plane horn antenna with suppressed back lobes is designed based on the ridge gap waveguide (RGW). A broader bandgap is achieved by introducing two cascaded bandgap structures based on which the RGW H-plane horn is designed. Moreover, a broadband soft surface is designed at the exterior horn walls to prevent undesired radiation and to increase the front-to-back ratio (FBR). A transmission line model is also presented to better explain the soft surface operation. The antenna is fed through a double-ridge waveguide (DRW), and to have a broadband transmission between the two structures, a DRW-to-RGW transition is designed. Furthermore, a coaxial impedance transition is designed to ensure safe power transmission between the coaxial line and the DRW. The antenna is fabricated, and a good agreement between the simulation and measured results is observed. This work achieves a significantly broader bandwidth of 120%. In addition, a wideband corrugated surface has been designed to improve the antenna's FBR. Measured results show that the FBR ratio is better than 20 dB, indicating the excellent performance of the added corrugations, and a gain of 11.3-14.2 dBi is achieved.