Abstract: A microwave transmit/receive terminal having an antenna and associated feed for receiving vertically and horizontally polarized signals and for transmitting a horizontally polarized signal employs a diplexer to be inserted between the feed and an orthomode coupler. The diplexer is formed of a cylindrical waveguide main body, a first port of which is coupled to the feed for receiving the orthogonally polarized receive signals and for coupling thereto the (horizontally polarized) transmit signal. A second port of the main body is coupled to the orthomode coupler for receiving the horizontally polarized signal to be transmitted and for coupling thereto the vertically polarized receive signals. A rectangular waveguide section is coupled to the cylindrical waveguide main body and forms a third port for coupling the horizontally polarized received signal away from said cylindrical waveguide main body.