Design of Tri-Band Bandpass Filter Using Stub-Loaded Multimode Resonators

A newly tri-band bandpass filter (BPF) based on two stub-loaded multimode resonators is proposed in this paper. The filter is constructed by the combination of a stub-loaded quadruple-mode resonator (SLQMR), a T-shaped dual-mode resonator (DMR) and a pair of parallel coupled lines. The resonant characteristics of the SLQMR and T-shaped DMR are analyzed by using odd- and even-mode method. The SLQMR constructs the first and third passbands, and T-shaped DMR forms the second passband, which provide high design flexibility and satisfy various design specifications. The tri-band BPF is well designed and simulated. The results show that three passbands are centered at 1.84 GHz, 2.64 GHz, and 3.24 GHz with fractional bandwidths of 10.95%, 11.24%, and 4.88%, respectively, which is a potential application in modern wireless communication systems.