EVANESCENT-MODE SUBSTRATE INTEGRATED WAVEGUIDE (SIW) FILTERS IMPLEMENTED WITH COMPLEMENTARY SPLIT RING RESONATORS

A new type of evanescent-mode substrate integrated waveguide (SIW) bandpass filter is presented in this paper, with complementary split ring resonators (CSRRs) introduced on the top or bottom metal planes of the waveguide. Both positive and negative couplings are obtained between the CSRRs by changing their locations and orientations. In comparison with conventional SIW filters, the proposed filters are compact since their passbands are below the cutoff frequency of SIW. A third- and a fourth-order cross-coupled filter prototypes were designed using standard PCB technology. They operate at the same central frequency of 3.8 GHz, with their fractional bandwidths of 15% and 20%. The proposed filters have a wide upper stopband as the cutoff frequency of TE10-mode in the SIW is much higher than the central frequency. Their good performance is demonstrated by both the simulated and measured S-parameters.