A centrosymmetric-coupled tri-band bandpass filter constituted by loaded bar and embedded S-shaped resonator

In this study, a novel tri-band bandpass filter supported by five resonant modes is developed on the basis of two coupled open-loop resonators with center-loaded bars (CLBs). Embedding the S-shaped resonator into the open-loop structure generates a new passband while keeping the same layout area. Also, another LB located between the open-loop resonator and the CLB is introduced to provide the perturbation for generating new resonances. The final design is realized by the structure optimization via adjusting the coupling coefficients and external quality factors. The measurements match well with the simulation which proves its practicability in (0.45–6 GHz) 5G frequency range-1 (FR-1).