Tri-mode stub-loaded ring resonator and its application to miniaturized wideband bandpass filter design

Stub-loaded ring resonator and its application to miniaturized wideband BPF are presented in the paper. Detail analysis shows that the presented stub-loaded ring resonator can allocate three resonant modes within the desired frequency range, and due to the dual path effect of the ring resonator, two transmission zeros can be introduced at the upper and lower cut-off frequencies, resulting high passband selectivity. A tri-mode wideband BPF is simulated, fabricated, and measured. The EM simulated and measured results are presented, and an excellent agreement is obtained.