A balanced tri-band BPF with high selectivity based on ASSLR

摘要

Abstract In this paper, a balanced second-order tri-band bandpass filter (BPF) with high selectivity is proposed. Three differential-mode (DM) passbands are formed by applying one pair of asymmetric short stub-loaded resonators (ASSLRs) and uniform impedance resonators (UIRs) into the design. Meanwhile, the frequencies and bandwidths of the DM passbands can be quasi-independently controlled by the lengths of resonators and the gaps between them. In addition, broadband common-mode (CM) suppression is achieved intrinsically without affecting the?DM parts based on the U-type balanced stepped-impedance microstrip-slotline transition (BSIMST) structures, thereby simplifying the design procedure significantly. In order to validate the practicability, a balanced tri-band BPF operating at 1.8, 3.5 and 4.45?GHz is fabricated and designed. A good agreement between the simulated and measured results is observed.