Highly Selective Broadband mm-Wave Diplexer Design

This letter presents a novel broadband diplexer design that is capable of achieving highly stringent rejection characteristics through the use of singlets whose interconnecting irises are formulated as resonant slot irises. The combination of these two resonant-cavity types allows for a unique filtering solution with increased filter order, wide available bandwidth, low geometric complexity, and simple milling requirements, which can be suitably applied to millimeter-wave and submillimeter-wave applications. A prototype is fabricated for operation in the $W$ -band (75–110 GHz) in order to cover a 10% fractional bandwidth in each passband. Measurement of the prototype denotes highly accurate results and exemplifies the use of all resonator and coupling elements in order to support ten poles and four transmission zeros in an elegant diplexer solution.