Diagnosis and remedy of manifold spurious mode resonance in waveguide multiplexers

Output multiplexer (OMUX) is a key building block of a communication satellite payload system. One of the important concerns in an OMUX design is spurious free in the whole working bandwidth to ensure no interference to the high power signal integrity. Although some spurious resonances caused by the fundamental mode can be predicted at circuit level simulation, many hidden spurious resonances caused by the higher-order modes can only be revealed after either an OMUX is physically built or a complete OMUX is designed using a full-wave electromagnetic simulation tool. In this paper, first the possible spurious resonances that can affect a waveguide manifold OMUX are categorized, and then a wideband Ka-band OMUX is studied with special attention to the manifold spurious behavior. With the help of a full-wave EM model, the spurious modes are diagnosed and several counter measures are then successfully taken to remedy the original OMUX design.