Design of a new bandpass filter with sharp transition band using multilayer-technique and U-defected ground structure

A novel compact microstrip bandpass filter with sharp rejection bands is proposed. The proposed filter structure is composed of U-shape microstrip resonators, ´U-strip´, backed by similarly shaped U-slots ´U-defected ground structure´ (U-DGS). By controlling the electrical coupling between the U-strip and the U-DGS, the bandpass filter´s stopband is optimised for better rejection. The proposed filter has low insertionloss and compact size because of the slow-wave effect. Meanwhile, sharp rejection bands induced by the presence of two transmission zeros on both sides of its passband are achieved. The measured centre frequency, bandwidth and passband insertion loss are 3.6 GHz, 40 and 0.5 dB, respectively. The simulated and measured results show good agreement and validate the proposed approach.