Manifold Frequency Division Multiplexer With Narrowband SIW–SSPP Hybrid Filters

A manifold-coupled multiplexer comprising substrate integrated waveguide (SIW)–spoof surface plasmon polariton (SSPP) hybrid filters and a microstrip line network is proposed for Ka-band applications, achieving a compact profile and low insertion loss. The narrowband hybrid filter is designed by converging the cut-off frequencies of SIWs and SSPPs, which may avoid the high-order modes of the resonant filters, and two SSPP slots are chosen for filter miniaturization without significantly sacrificing the cut-off response. A short taper is designed to connect the hybrid filter and microstrip lines, and the microstrip line network is carefully optimized to match the manifold phase configuration with a compact size. A prototype is fabricated and characterized for demonstration. The experimental insertion loss is 2.10, 2.49, and 2.61 dB at 28.2, 29.7, and 31.2 GHz, respectively, and the corresponding 3 dB bandwidth is 4.1%, 4.7%, and 4.8%, respectively, showing a good match with the simulation. The reflection loss is larger than 10 dB from 27.8 to 31.4 GHz. Considering the promising out-of-band rejection of the hybrid filters, such a configuration should be suitable for multiplexers with large channel numbers and may find many applications in ultra-wideband and multifunctional communication systems.