Abstract: Broadband (8-18 GHz) operation of a horn antenna with broadband corrugations is achieved by provision of dissipative TM.sub.11 mode suppressor means in the input waveguide feed to the horn. For a conical horn the input feed waveguide is circular and the mode suppressor means comprises a pair of axially extending diametrically spaced conductive wires or rods supported within the waveguide in dielectric foam, or alternatively, a cylindrical resistance card similarly supported coaxially with the waveguide. For a square corrugated horn of this type, the input waveguide is square and the mode suppressor means comprises a pair of parallel spaced axially extending resistance cards located in the planes of the magnetic field nulls in the waveguide.