Twin cascaded-trisection coupling topology and its application to dielectric waveguide resonator diplexer

This article investigates the twin cascaded-trisection (TCT) coupling topology, based on which a dielectric waveguide resonator (DWR) diplexer is designed. The TCT topology is constructed by two traditional trisection structures with one coupling route being shared. By properly setting the polarities of the couplings, it can generate two transmission zeros (TZs) on one side of the passband, either the low side or the high side. In order to facilitate the TCT topology, a four-pole DWR unit is constructed by flexibly utilizing four hexagonal DWRs. A diplexer with two frequency bands of 3.4 GHz−3.5 GHz (Channel 1) and 3.6 GHz−3.7 GHz (Channel 2) is designed by using two four-pole DWR units. A printed circuit board (PCB) is employed to realize the feeding and matching network for the two units. Two TZs are generated on the high side of the Channel 1 and two TZs are generated on the low side of Channel 2, making the filtering selectivity improved. The designed diplexer is fabricated and measured. For the two measured channels, the minimum insertion losses are 0.85 dB and 0.94 dB, and the isolations are better than 44 dB and 31 dB.