Improved compact microstrip low pass filter with novel distributions of complementary split ring resonators (CSRRs)

In this contribution, the coupling characteristics of three novel coupling structures for double CSRRs are applied. Firstly the concept of complementary split ring resonators (CSRRs) is utilized to improve the selectivity of a microwave low pass filter (LPF). To this end, a step-impedance low-pass filter (SILPF) is first optimized and then built. The proposed filters consist of an asymmetrical microstrip step discontinuity circuit with harmonic suppression and CSRRs to improve sharp rejection. Moreover, different coupling structures can cause different frequency responses, especially the stopband characteristics. In order to improve the optimized SILPF, a novel compact low pass filter using single and a pair of double CSRRs is proposed. Properties of these configurations are discussed, and two manufactured prototypes have been successfully tested. The results show the usefulness and validity of the new structures with high rejection capabilities.