We numerically and experimentally evaluate different designs of coplanar waveguides (CPWs) loaded with split ring resonators (SRRs) and complementary split ring resonators (CSRRs), respectively. In particular, we are interested in their stop-band performance. Starting from structures which consist of two concentric rings, we study devices with only an outer ring, an inner ring or multiple concentric rings. Furthermore, our study shows that introducing slots in the proximity of the SRR or CSRR will modify the stop-band considerably. Single and multiple unit cells for both designs are fabricated and measured. Our results demonstrate the potential of the CSRR/CPW structure for filter applications.