Inexpensive multi-mode satellite tracking feed antenna

A design of an inexpensive multi-mode tracking feed antenna, for a circularly polarised signal is described. It uses the TE₁₁ and TM₀₁ modes, in a smooth circular waveguide, to obtain the sum and difference patterns. The higher order mode, TM₀₁ generated within the feed is separated from the dominant mode, TE₁₁ by using the resonant mode filter printed on a thin dielectric material. The design of the resonant mode filter is described in some detail. The use of a printed resonant ring with a dual mode horn makes the design particularly inexpensive. Sum and difference patterns with both the dual mode and the corrugated horn are presented for comparison.