Hybrid mode feed horn having funnel-shaped horn flange with grooved conical inner surface

A feed horn for use as a primary focus feed of a reflector antenna, the feed horn having a horn flange located at a free end portion of a tubular TE.sub.11 -mode feeding waveguide, the horn flange widening in a funnel shape radially outwardly from a horn throat fitted on the feeding waveguide and which horn flange has a conical inner surface which is provided with grooves therein of uniform axial depth extending parallel to and coaxially with a central longitudinal axis of the feeding waveguide, the grooves being radially separated by concentric ring-shaped walls therebetween, the walls extending parallel to said central longitudinal axis, characterized in that a half opening angle .theta..degree. of the horn flange (7) defined between the central longitudinal axis (11) of the feeding waveguide (2) and the inner surface of the horn flange lies in the region 70.degree.<.theta..degree.<80.degree. and in that a free end of the feeding waveguide (2) is protrudingly offset axially relative to the intersection between a straight line connecting free axial ends of said walls separating the grooves in the horn flange inner surface and the feeding waveguide, means being provided on the free end portion of the feeding waveguide and on the feed horn for axially shifting the feed horn on the free end portion of the feeding waveguide for adjusting said offset.