New method to transform band-pass to low-pass filter using multilayer- and U-slotted ground structure-technique

A novel compact microstrip band-pass filter (BPF) with sharp rejection bands is proposed. The proposed filter structure is composed of U-shaped microstrip resonators, “U-strip,” backed by similarly shaped U-slots “U-slotted ground structure (U-SGS)” also called “U-defected ground structure (U-DGS).” By controlling the electrical coupling between the U-strip and the U-DGS, the band-pass filter's stopband is optimized for better rejection. The proposed filter has low insertion loss and compact size due to 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 center 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. Finally a new simple method, on the basis of the elimination of the admittance inverter (gap) J, will be used to transform the band-pass to compact low-pass filter. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2427–2433, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26263