Coplanar waveguide structures loaded with split-ring resonators

Coplanar waveguide (CPW) transmission lines periodically coupled to split-ring resonators (SRRs) are analyzed, designed, and characterized. Due to inductive coupling between the lines and SRRs, signal propagation is inhibited in the vicinity of the resonant frequency of the rings. The result is a stop-band behavior that can be of interest for the elimination of frequency parasitics in CPW-based devices. Two different approaches are envisaged: a uniplanar structure, where CPW and rings share the same metal level; and a bimetal structure with SRRs etched on the back side of the substrate. It has been found that the latter exhibits almost negligible insertion losses in the pass band, and sharp cutoff and a high level of rejection in the stop band, with few unit cells. Since ring dimensions are small compared to the signal wavelength at resonance, the proposed SRR-CPWs are very promising for the design of miniaturized microwave circuits.