Fourth-order tri-band bandpass filter using square ring loaded resonators

A tri-band bandpass filter (BPF) using a novel square ring loaded resonator (SRLR) is presented. The SRLR can generate a tri-band response by tuning its geometric parameters. Moreover, it can build the high-order tri-band BPFs using the proposed resonators because of the sufficient coupling between adjacent resonators. A fourth-order Chebyshev tri-band BPF centred at 2.4, 3.5 and 5.2 GHz is designed and fabricated. Measurement results agree well with the full-wave EM simulated results.