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.