Substrate integrated waveguide filters with stopband performance improvement

This paper introduces effective approaches to improve the stopband response of substrate integrated waveguide filter. First, a filter is constructed by using different resonators which resonate at the same fundamental mode but at different high order modes. As second resonant mode of the circular cavities is more than rectangular ones, we cascade circular and rectangular cavities to separate high order modes. Then by inserting radiating slots at the proper positions of cavities, their second longitudinal resonant modes are strongly rejected. Comparison between results verifies the effectiveness of the proposed idea.