Abstract: Beam waveguide (BWG) feed system, composed of a series of flat reflectors, conicoid mirrors and lens can use conicoid mirror and flat mirror as rotating joint to implement mechanical scan of antenna in electromagnetic wave transmission.In this paper, the operating principle of the Cassegrain antenna fed by beam waveguide is analyzed, and the design method of the beam waveguide for the HPM radiating antenna is discussed. Emphasis is placed on a practical HPM radiating antenna fed by beam waveguide. In the antenna system, a dual-reflector antenna with two paraboloids is fed by the beam waveguide feeding system formed by three reflectors, realizing quick scanning of the beam. The antenna can operate at X-band with more than 1 GW power capacity, and its gain is greater than 50 dB.