Design of multimode tracking system for earth station antenna

This paper presents the design of a unique multimode extractor and converter of higher order modes of a circular waveguide. The multi-mode extractor couples first five circular waveguide propagation modes TE11, orthogonal TE11(o), TM01, TE21, and TE21(o) that includes the three tracking signals (i.e. sum signal, elevation signal, and azimuth signal) used in a high-frequency monopulse tracking system and two communication channels for transmitting and receiving signal at Ka band. This design is based on amplitude and phase characteristics of the higher-order modes TM01, TE21, and TE21(o) excited in circular waveguide. TE21 and TE21 (o) modes are extracted from circular waveguide to TE10 mode in rectangular waveguide by two longitudinal slots milled in the circular waveguide. TE11 mode is coupled using two coupling slots and H-plane power combiner. A turnstile junction is used to extract TM01 and TE11(o) mode. This multimode tracking system is designed both for linear or circular polarized ground earth station antennas to track orbiting satellites.