Miniaturized lowpass filter with ultra-wide stopband using dual-plane defected structures

A miniaturized lowpss filter (LPF) with ultra-wide stopband is proposed by using the complementary rectangle split ring defected microstrip structure (CRSR-DMS) and the quad U-shaped defected ground structure (QU-DGS). The presented CRSR-DMS can provide a sharp rejection rate and two obvious attenuation poles while the QU-DGS can produce four independently controlled transmission zeros. Based on the characteristics of the defected structures, the proposed LPF is constructed by using four cascaded CRSR-DMS units and four cascaded QU-DGS units. The measurement result of the designed filter with 3 dB cut-off frequency at 2.0 GHz shows that the obtained 20 dB rejection band ranges from 2.12 GHz to more than 20 GHz within a small circuit area of 0.73 lambda g * 0.13 lambda g, lambda g being the guided wavelength at 2.12 GHz.