Multimode Propagation and Complex Waves in CSRR-Based Transmission-Line Metamaterials

Transmission-line metamaterials based on complementary split-ring resonators (CSRRs) are shown to support forward, backward, electroinductive, and complex waves. Two CSRR-based lines are considered: 1) stopband microstrip lines simply loaded with CSRRs, and 2) passband microstrip lines loaded with CSRRs and series gaps. The effects of interresonator coupling on bandwidth enhancement are analyzed on the basis of Bloch mode theory by considering the lumped-element equivalent 4-port circuit model of the unit cell. All the propagation modes are captured by the proposed multiterminal Bloch mode theory, from an eigenmode analysis. The results are validated through a commercial eigenmode solver and supported by experimental data.