1,190,888. Aerials. PHILCO-FORD CORP. 17 May, 1968 [19 May, 1967], No. 23707/68. Heading H4A. A radio horn assembly comprises a central circular conical horn which is surrounded by four outer flared horns 16, 18, 20, 22 of nominally rectangular cross-sections, a portion of the inner corner of each rectangular horn being replaced by a tapering arcuate sector corresponding to the shape of the central horn. Dielectric plates 34, 36, 38, 40 are provided inside the horns 16, 18, 20, 22 to compensate electrically for the effect of changing their cross-sections from rectangular over the lengths of the said arcuate sectors. Circular to linear polarization converters 26, 28, 30, 32 are provided at the feed ends of the outer horns and the dielectric plates are made with pointed ends to improve matching to the said converters. The assembly may be used at a ground station of a satellite communications system. Tracking is effected by means of signals received by the outer horns, and main communication signals are sent and received by means of the central horn, with separation by cross-polarization if required. The assembly may operate as the feed of a Cassegrain-type aerial with a hyperboloidal sub-reflector and a paraboloidal main reflector.