Abstract: A feed system for an antenna has a set of inner and outer coaxial waveguides which apply, respectively, both higher and lower frequency radiations to a common radiating aperture provided by a horn and shroud which envelops radiating apertures of the individual feed waveguides. Each of the feed waveguides carries signals having a bandwidth of an octave. Lower frequency radiation to be transmitted by the outer coaxial feed waveguide is applied thereto by a set of four waveguides of a launcher which launches a wave with a desired propagation mode into the outer feed waveguide. Each of the launch waveguides is initially a rectangular double-ridged waveguide for increase bandwidth. The ridging is reduced to a condition of no ridging in the outer feed waveguide by a transition to a single inner ridge which terminates in a tapered star-shaped combination ridge within the outer feed waveguide.