A Lowpass Filter Based on Microstrip Splitter-Combiner Section loaded With Multiple CSRR Coupled Units

In this paper, a lowpass filter (LPF) with N-controllable transmission zeros in stopband is proposed. It is consisting of N-stage complementary split ring resonator (CSRR) coupled units and a microstrip splitter-combiner section. The equivalent circuit of the proposed filter and relevant lumped parameters are summarized and applied to predict the resonance frequencies in stopband. The resonance frequencies can be controlled arbitrarily through adjusting the physical parameters of CSRR units. As an example, an LPF with four CSRR coupled units is designed, simulated, experimentally fabricated and measured. The stopband rejection level is suppressed to be better than 17.7 dB within the passband. The measured results compare well with the EM simulated results, which validates the configuration and corresponding equivalent circuit of the proposed class of filter.