Substrate-integrated waveguide filters based on mushroom-shaped resonators

This paper presents a new class of quasi-elliptic pass-band filters in substrate-integrated waveguide technology, which exhibits compact size and modular geometry. These filters are based on mushroom-shaped metallic resonators, and they can be easily implemented using a standard dual-layer printed circuit board manufacturing process. The presented filters exploit non-resonating modes to obtain coupling between non-adjacent nodes in the case of in-line geometry. The resulting structure is very compact and capable of transmission zeros. In this work, the singlet configuration is preliminarily investigated, and a parametric study is performed. The design of three-pole, four-pole, and higher-order filters is illustrated with examples and thoroughly discussed. A four-pole filter operating at the frequency of 4 GHz has been manufactured and experimentally verified, to validate the proposed technique.