Novel substrate integrated waveguide filter based on mushroom resonators

This paper presents a novel substrate integrated waveguide (SIW) filter topology, based on mushroom-shaped resonators. By exploiting non-resonant nodes, this structure allows the coupling between non adjacent nodes, resulting in the presence of transmission zeros with in-line geometry. This filter exhibits a very compact footprint and requires a double-layer configuration. The operation principle of SIW filters based on mushroom-shaped resonators is discussed in detail, and the design of three-pole filters is presented as an example. The extension to higher-order filters is also outlined. The prototype of a three-pole filter is fabricated and measured.