Tri-band Pass Filter Using Optimized Psi-shaped Resonators

In this paper, a tri-band pass filter (BPF) at 0.75 GHz, 2.1 GHz, and 3.5 GHz is designed using a modified tri-mode Psi shape resonator whose parameters are optimized using particle swarm optimization algorithm (PSO). The Psi shape resonator input impedance has three resonance frequencies with two transmission zeroes which improve the isolation between passbands. A mathematical analysis is performed to calculate the center resonance frequencies of the proposed design for the tri-band pass filter (BPF). The implemented design is simulated, fabricated, and measured. All measured results are consistent with the analysis and the simulations.