Broadband microwave filters based on metamaterial concepts

The paper presents new results on the design of broad-band microwave band pass filters based on a combination of open split ring resonators (OSRRs) and open complementary split ring resonators (OCSRRs). Essentially, OSRRs and OCSRRs behave as series and parallel resonant elements, respectively. Thus by series connecting OSRRs and shunt connecting OCSSRs to a host line, a composite right/left handed (CRLH) transmission line results. By balancing the lines, broadband filter responses result. However, better performance and standard responses can be achieved by sacrificing periodicity. In a first order approximation, the equivalent circuit model of the structures is the canonical circuit model of a band pass filter. However, parasitics must be taken into account for an accurate modeling and design. The detailed models of the structures as well as an illustrative example corresponding to an order-5 wideband band pass filter is reported. Small size, wide bands and good stop band performance are the key advantages of the reported filters. In spite that the design of the filters can be made without invoking metamaterials, these filters are implemented by using the open version of the split ring resonator (SRR) and its complementary counterpart (CSRR), and they have been conceived from the synthesis of CRLH transmission lines based on these open particles. For this reason the filters can be considered to be based on metamaterial concepts.