Multiband waveguide filters with advanced filtering characteristics based on an in‐band transmission zeros method and stacked cylindrical resonators

This paper significantly improves the previously proposed novel multiband waveguide filter implementation employing cylindrical resonators. The improved model has the advantages of a further reduced footprint using stacking shunt resonators horizontally and vertically and the ability to realise advanced filtering functions, including transmission zeros below and above the passbands. The coupling matrix synthesis with a brief example and a detailed filter design with considerations for additional coupling and in‐line and folded topologies is given. Several filter prototypes, namely third‐order quad‐band and quintuple‐band in‐line filters and a sixth‐order dual‐band folded filter in Ku‐band, were designed to validate the proposed model. Selective laser melting (SLM), a metal 3‐D printing technique where metal powder is selectively melted with a laser layer by layer, was used to fabricate a dual‐band folded filter prototype in copper to validate the proposed model since the model has a complex inner geometry. Additionally, selective laser melting has the advantage of monolithic near‐net shape fabrication, eliminating assembly, improving reliability, and reducing weight. The measured results show good agreement with the simulations.