Stop‐band and band‐pass characteristics in coplanar waveguides coupled to spiral resonators

Coplanar waveguide (CPW) transmission lines periodically coupled to spiral resonators (SRs) are proposed to obtain very compact band‐pass or rejection‐band structures. The devices consist of a CPW with SRs etched on the back substrate side, underneath the slots. Due to inductive coupling between the line and the spirals, signal propagation is inhibited in the vicinity of the resonant frequency, resulting in a stop‐band structure. However, by periodically loading the line with narrow wires, this behavior is switched to a band‐pass characteristic. This has been interpreted as being due to the coexistence of a negative effective permittivity and permeability in a narrow band above resonance for the composite structure. Since the dimensions of the spirals are very small in comparison to the signal wavelength at resonance, these devices are very compact and can be of interest in applications where miniaturization is mandatory.