A feed system for an antenna has a set of inner an outer coaxial waveguides (70, 60) which apply, respectively, both higher and lower frequency radiations to a common radiating aperture provided by a horn (68) and a shroud (62). Lower frequency radiation to be transmitted by the outer waveguide is applied thereto by a set of four waveguides (74) of a launcher (72). Each of the launching waveguides is a rectangular double-ridged waveguide (94A, 94B). Impedance matching rings (160) are slidable within the space between the inner and outer surfaces of the coaxial waveguide for development of a desired standing wave ratio. A dielectric rod (144) is disposed in a forward end of the tube of the inner feed waveguide and protrudes therefrom into the horn for shaping a beam of the higher frequency radiation.
