Ultra-narrow bandwidth filters based on highly dispersive metamaterial basic cells

Two narrow pass-band filters with an out-of-band rejection in excess of 30 dB was designed for an operation in the C-band (operating frequency @ 4.5 GHz). These potential performances were achieved by cascading three double-split ring resonator cells magnetically coupled to a coplanar waveguide line and six shunt wires placed between the central strip and the ground metal layers. This configuration, directly inspired from the so-called metamaterial technology, takes advantage of the high dispersion induced by a negative magnetic response via the resonators and of a negative permittivity effect via the shunt wires. The design of the basic cell was achieved by a proper engineering of the plasma frequencies of the electrical and magnetic systems. In a second stage, the optimization of the out-of-band rejection, while preserving the narrow band, was carried out by optimizing the dimension of the SRR´s aiming at the overlap of individual responses.