Synthesis of compact and highly selective filters via metamaterial-inspired coplanar waveguide line technologies

In this study, two split ring resonator-based coplanar waveguide cells operating in C-band are studied. Particularly, the lines have been loaded with double shunt strips or series gaps. The use of double strips allows controlling the electric plasma frequency, and at the same time permits one to have a good excitation of the resonators. On the other hand, the employment of double series gaps provides a right-handed behaviour, contrary to conventional metamaterial structures for which a backward propagation is obtained. Several parametric studies show the possibility to significantly increase the selectivity, and in particular the possibility to have an effective control on the out-of-band rejection levels by means of the loading elements characteristics. In a second stage, enhanced out-of-band rejection properties have been obtained by the use of cascaded basic cells and rigorous optimization processes. As a consequence, the proposed filters can be foreseen for practical applications relying on the trade-off found between selectivity, insertion losses and out-of-band rejection.