Ultra-Wideband H-Plane Horn Antenna with Chamfered Ridge Feed and AMC Reflectors using Ridge Gap Waveguide Technology

We present a broadband H-plane horn antenna using ridge gap waveguide (RGW). A wide electromagnetic bandgap is achieved by designing a mushroom-shaped high-impedance unit cell structure, which forms the basis for the RGW and supports leakage-free wave propagation. The antenna is excited using a vertical coaxial feed and includes coaxial-to-RGW transitions along with free-space matching sections to minimize reflection. To enhance impedance matching, we use a chamfered ridge tuning technique, optimizing the transition input impedance. An artificial magnetic conductor (AMC)-based reflector is integrated along the outer horn walls to suppress backward waves and improve the front-to-back ratio (FBR). The proposed design achieves an ultra-wide fractional bandwidth of 82.5% from 19.8 to 47.6 GHz. The antenna exhibits a high FBR exceeding 22 dB, with a gain ranging from 11 to 14.8 dBi. Moreover, stable H-plane radiation patterns are maintained across the entire operating band, with side lobe levels consistently below −22 dB. This antenna is well-suited for millimeter-wave wideband applications.