Substrate integrated waveguide filters with face-to-face broadside-coupled complementary split ring resonators

Novel substrate integrated waveguide (SIW) filters using face-to-face oriented broadside-coupled complementary split ring resonators (BC-CSRRs) are presented in this paper. The SIW with the conventional BC-CSRR resonator pairs is first investigated. By removing the metal strip between the two back-to-back rings of the BC-CSRR pair, a modified BC-CSRR pair which shows a significantly improved spurious suppression and a wider rejection bandwidth is then proposed. SIW bandpass filters based on the resonator pairs have been designed, fabricated and measured. The SIW filter with modified BC-CSRR pairs exhibits a great improvement in the stopband performance. The proposed filters work below the cutoff frequency of the main mode of the SIW. They have the usual advantages of the SIW and the BC-CSRR such as compact size, easy fabrication and easy integration with other electronic circuits.