Novel W‐Band Star‐Junction Diplexer Based on All Resonators

A novel W‐band narrowband waveguide diplexer based on an all‐resonant structure is proposed, designed for high‐performance integrated transceiver systems in the millimeter‐wave and sub‐terahertz bands. Unlike conventional manifold‐based diplexers, the diplexer employs a common resonant junction to directly connect the two channel filters, enabling a compact configuration with high channel isolation and steep roll‐off. The synthesis is based on the coupling matrix principle, and the main novelty lies in a hybrid coupling mechanism, in which different inverter types are introduced at different locations to suppress spurious modes. An E‐plane stub is adopted in the strong‐coupling sections to facilitate high‐yield CNC milling. Experimental results of the aluminum diplexer show center frequencies at 85.6 and 93.4 GHz with fractional bandwidths of 3.5% and 3.2%. The measured insertion losses are 0.9 and 0.85 dB, respectively. These results demonstrate that the proposed design provides an effective solution for high‐frequency electronics and millimeter‐wave system applications.