Compact Second-Order Bandstop Filter Based on Dual-Mode Complementary Split-Ring Resonator

Abstract

A compact dual-mode bandstop filter is presented in this letter. From an equivalent circuit viewpoint, a second-order response is obtained by designing a two-pole notch filter with inductive coupling. This equivalent circuit is then implemented by using a dual-mode complementary split-ring resonator. The proposed bandstop filter prototype has dimensions of $0.1\lambda_{g}\times 0.18\lambda_{g}$ , where $\lambda_{g}$ defines the guided-wave wavelength. An experimental validation at the center frequency $f_{0}$ of 2 GHz shows that the proposed filter can extend the harmonic-free upper passband up to $4.2f_{0}$ .