Improved equivalent circuits for complementary split-ring resonator-based high-pass filter with C-shaped couplings

The authors modify the complementary split-ring resonator (CSRR) with dual C-shaped couplings for high-pass filter (HPF) design and propose improved equivalent circuits as a means to analyse the filter. The pi-type circuit of the dual C-shaped coupling in the CSRR-based HPF is presented to have the improved equivalent circuit in contrast to the conventional equivalent circuit. At 3 dB, the cut-off frequency f_c = 1.74 GHz, the maximum IL is within 0.33 dB up to 8 GHz and the 65.81 dB rejection extends down to 0.53 GHz. Simulation and measurement results including surface current distributions and frequency responses are presented and discussed.