S-Shaped Complementary Split Ring Resonators and Their Application to Compact Differential Bandpass Filters With Common-Mode Suppression

This letter presents an S-shaped complementary split ring resonator (S-CSRR) for application in compact differential filters. The working principle of the proposed S-CSRR is explained and a circuit model is developed and validated through electromagnetic simulations. It is shown that an S-CSRR-loaded differential microstrip line with series gaps can be used in the design of compact differential bandpass filters (BPFs) with common-mode suppression. The filter design procedure is explained and the theoretical concept is validated through fabrication and measurement of a compact (0.09λ_g ×0.25 λ_g) third-order differential BPF with common-mode suppression.