Design and Development of a Hybrid-Coupled Waveguide Multiplexer for a Multiband Receiver

This paper describes a waveguide hybrid-coupled multiplexer for frequencies around 400 GHz. The designed multiplexer has three bands with 25-GHz bandwidth and no frequency gap between channels. The multiplexer is composed of two identical waveguide branch-line quadrature hybrid couplers and two identical bandpass filters based on waveguide inductive iris windows. In order to find the critical element of the multiplexer, network analysis was carried out using signal flow graphs. The multiplexer was fabricated based on direct machining technology with machining accuracy in the order of a few microns. S-parameters measured with a vector network analyzer show excellent agreement with simulations.