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.