Analysis of coupled microstrip lines loaded with complementary split ring resonators (CSRRs) and applications

This paper is focused on the analysis of pairs of microstrip lines loaded with complementary split ring resonators (CSRRs). The distance between the CSRRs is considered to be small, so that the loaded lines are coupled through the resonant elements. Moreover, the pair of lines is cascaded in between a power divider and combiner, resulting in a two-port device that can be fed and characterized by means of single-ended ports. We will consider the effects of coupling in symmetric structures, and the effects of asymmetry as well. In the former case, the single resonance frequency, which manifests as a notch in the transmission coefficient, varies with the coupling level. In the second case, asymmetry (e.g., by considering different CSRRs) produces a frequency split, and two different notches separated a distance that depends on the coupling level appear. A method to extract the reactive parameters in the proposed equivalent circuit model is presented, and the model is validated by comparison to electromagnetic simulation. These structures can be useful for sensing purposes, where the operation principle is based on symmetry disruption, as well as for the implementation of dual notched filters.