Microstrip bandpass filters based on zeroth-order resonators with complementary split ring resonators

The zeroth-order resonant (ZOR) properties of the left-handed material (LHM) unit cells composed of complementary split ring resonators and series gaps are analysed. The method to determine the resonant frequency and susceptance slope parameter is proposed. A bandpass filter (BPF) is designed by connecting the ZORs with admittance inverters. Experimental verification is provided and a good agreement has been found between the simulation and measurement. Compared with the bandpass structure fabricated by simply cascading the same amount of LHM unit cells, the proposed BPF has much better selectivity, more symmetrical responses and controllable bandwidth.