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

Four designs of substrate integrated waveguide (SIW) filter employing integrated broadside-coupled complementary split-ring resonators are compared. By changing the orientation of the rings, four types of SIW unit cell are proposed and investigated and it is shown that, for one particular topology, two poles and two zeros can be realised with a single unit cell. Bandpass filters based on the proposed resonators coupled by evanescent-mode SIW sections have been fabricated and tested. The proposed filters have the advantages of compact size, high selectivity and ease of integration.