Balanced Right/Left-Handed Coplanar Waveguide With Stub-Loaded Split-Ring Resonators

In this letter, a host coplanar waveguide (CPW) loaded with modified split-ring resonators (SRR) is presented. In recent publications, it has been demonstrated that the capacitive interaction between the host CPW line and the SRRs is the cause of a right-handed band, which degrades the selectivity of the response. Consequently, an open-ended microstrip stub connected to the rings is used to modify this interaction, and thus has an effective control of the rejection above the passband. Fortunately, these stubs only affect the frequency position of the right-handed band. As a result, it is quite straightforward to obtain balanced composite right/left-handed (CRLH) transmission lines with increased transmission bandwidth and improved rejection levels, which are the main drawbacks of traditional SRR-loaded CPW lines. Moreover, the response of the modified cell shows a pair of transmission zeros at both sides of the passband. Therefore, this new cell is a very interesting choice for designing balanced CRLH lines and is very attractive for filter applications.