Triple-Mode Bandpass Filters on CSRR-Loaded Substrate Integrated Waveguide Cavities

In this paper, a novel approach is proposed to design and explore a class of triple-mode bandpass filters on substrate integrated waveguide (SIW) structure. Two degenerate modes of an SIW rectangular cavity and one resonant mode of a complementary split-ring resonator (CSRR) are employed to implement these filters. As the primary advantage, the CSRR mode is utilized instead of the fundamental mode of the SIW cavity to provide us with an attractive capacity in easily controlling the frequency band of the designed SIW filters through the dimensions of this CSRR. Moreover, the positions of transmission zeros can be properly adjusted by the metallic vias. Finally, three examples of SIW multimode bandpass filters are designed, fabricated, and tested to verify the effectiveness of the proposed approach. The measured results are found in good agreement with the simulated ones, showing that these filters have achieved high out-of-band rejection and sharp skirt selectivity.