Quasi-elliptic SIW band-pass filter based on mushroom-shaped resonators

This paper present a new class of quasi-elliptic pass-band filters, which exhibit compact size and modular geometry. They are based on the use of mushroom-shaped resonators, and find easy application in double-layer substrate integrated waveguide (SIW) structures. The filter exploits 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. The singlet configuration is first studied, and a simple way to obtain higher order filters design is shown. A 3-pole filter has been designed and manufactured to show the feasibility of the proposed technique.