A tri-band bandpass filter using 2T4L2C-pattern multi-layer structure

This paper presents a tri-band bandpass filter (BPF) based on a multi-layer technology. A tri-layer structure is adopted for both a compact size and a high coupling effect. The proposed tri-band BPF consists of three layers which are two T-shaped transmission lines on the top layer, four symmetrical L-shaped resonators on the middle layer, and two back-to-back C-shaped open-loop resonators defected-ground structures on the bottom layer. The first and the second passbands of BPF are realized by the defected ground structure. The third passband is generated using four L-shape resonators. The substrate material for fabrication is an FR4 PCB with a dielectric constant of 4.4 and a thickness of 0.8mm. The proposed tri-band BPF can be operated at 1.5GHz, 3.5GHz, and 5.8GHz.