Miniaturised multi-band substrate integrated waveguide filters using complementary split-ring resonators

A novel method for designing miniaturised multi-band filters using the complementary split-ring resonators (CSRRs) is proposed and demonstrated on the basis of substrate integrated waveguide (SIW) technology. By loading different types of CSRRs on the waveguide surface, multiple passbands propagating below the waveguide cutoff frequency can be generated separately. The proposed structures allow relatively independent control over the centre frequency and the coupling coefficient. The working principle is illustrated by the equivalent circuit and the filter coupling methodology is introduced for design purpose. Two types of dual-passband filters, a triple-band and a quadruple-band filter are designed and fabricated to validate the proposed concept. These filters are showing advantages in terms of compact size, good selectivity and stopband rejection, as well as the easy integration capability with other circuits.