Accurate Modeling of Stubs Used as Resonant Coupling Elements in SIW Filters

This letter presents an accurate model for the stubs used as frequency-dependent coupling elements in substrate integrated waveguide (SIW) filters, with the aim to generate transmission zeros (TZs) in the frequency response. The model is based on the actual modes excited in the stub, differently from the single-mode (equivalent circuit) representation used in previous works. A procedure to determine the geometrical dimensions of the stub, depending on the synthesized filters parameters, is also presented, based on the full-wave characterization of the structure. The proposed model is validated by the design and the fabrication of an SIW filter.