Half-mode SIW Filters with Resonant Couplings Implementing Transmission Zeros

This paper presents the basic structure for the implementation of compact half-mode SIW filters with transmission zeros. The proposed structure consists of two inline half-mode SIW cavities, coupled by an iris window, with a microstrip stub connected to the open boundary in the middle of a coupling iris. The open-circuit microstrip stub allows introducing an additional pole in the filter as well as a transmission zero, at the frequency where the length of the stub is quarter wavelength. A modal analysis of the structure has been performed, and a filter based on this structure, with three poles and a transmission zero, has been implemented. Simulation and measurement of the filter are reported.