Miniature coplanar waveguide and microstrip stop-band filters using spiral resonators

We propose in this paper three new stop-band filters made of metamaterials, which main characteristic is their small size compared to the filters fabricated with traditional techniques. The first configuration consists of a dual-substrate coplanar waveguide (CPW) line with double-spiral resonators (DSRs) etched on one side of each substrate, the line and the ground plane being situated between both substrates. The resonant frequency of this miniature filter is 2.5 GHz. The second structure is also a CPW line with the same layer distribution as the first one, but the DSRs are substituted by broadside-coupled split-ring resonators (BC-SRRs). In this configuration, the orientation of the resonators, whose slits are aligned in parallel with the line, is the key factor to obtain a wide relative bandwidth (44%) at 7.1 GHz. Finally, the third filter is composed of a microstrip line and some rectangular DSRs etched in the ground plane. This filter is destined for low frequency applications, since a resonant frequency of 1.25 GHz is achieved. The main characteristics of these filters have been studied numerically, and the results are exposed in this paper.