Abstract: A horn antenna for a radar device including a dielectric filling body arranged in a hollow horn section of a metal body and a dielectric cover attached to the filling body and sealingly closing the open end of the metal body. The filling body includes a first conical portion that is fittingly received in the hollow horn section, and a second conical portion that is situated away from the open end and dimensioned to leave a gap between itself and the wall of the hollow horn section. The dielectric filling body has a third portion between the first and second portions, where the third portion and the opposite portion of the wall of the hollow horn section are provided with circumferential grooves arranged in pairs opposite each other to provide a wear and maintenance-free attachment of the dielectric filling body in the horn antenna.