A Technique for Spurious Suppression in Substrate Integrated Waveguide Filters

This paper presents an efficient technique for the broadband suppression of spurious frequency bands in substrate integrated waveguide (SIW) filters. The technique is based on the combined use of a regular SIW filter and a pre-filter, with a broader pass band and a much larger spurious-free band. The effect is a limitation of the spurious frequency bands of the SIW filter, which are attenuated according to an envelope corresponding to the transmission of the pre-filter. The proposed technique is validated through an example, consisting of a three-pole SIW inline filter combined with a two-pole pre-filter with shorted microstrip stubs.