A Compact Ridge-Waveguide Contiguous-Channel Frequency Multiplexer

The experimental 4-6.25-GHz contiguous-channel frequency multiplexer being presented comprises three equal-bandwidth four-pole ridge-waveguide channel filters that are series-connected through a quasi-low-pass ridge-waveguide manifold. To minimize insertion loss, the multiplexer´s port impedance-matching networks are also realized in ridge-waveguide, limiting the use of strip-type transmission line segments to short uniform-width microstrip feeder lines for linking to the multiplexer´s external coaxial ports. The three channel filters are stacked with their waveguide broadsides adjacent to each other, separated only by the thicknesses of the filters´ walls to achieve maximum compactness. Quasi-lumped waveguide elements are employed to properly couple the filters to the manifold. The multiplexer design methodology relies on the use of commercial general-purpose software, and on equivalent-circuit models of waveguide multiplexer subcomponents derived therewith. The observed good agreement between measured and predicted multiplexer response characteristics helps to validate the approach.