Design of wideband/dual-band bandpass filter using a vias and slots loaded sector circular patch resonator

In this paper, a novel patch resonator is proposed to realize wideband and dual-band bandpass filter (BPF) with small frequency ratio. The introduction of metallic vias and slots on the patch enables the flexible control of the resonant frequencies of TM₀₁, two degenerated modes of TM₁₁, and TM₂₁. Two stubs loaded on the patch and coupled with I/O feeding line can introduce two additional resonant modes, and facilitate the control of input/output coupling strength. Owing to the different coupling relationships between the stub modes and two degenerated modes of TM₁₁, the transmission zeros (TZs) located at the center of passband can be eliminated or generated by altering their resonant order, thus realizing wideband or dual-band operation. For demonstration, two prototypes are simulated, fabricated and measured. Good agreement can be observed between simulation and measurement. The implemented wideband BPF has a passband from 1.85 GHz to 3.03 GHz with six transmission poles (TPs). While the implemented dual-band BPF operates at 1.8/2.45 GHz with three TPs within each band and two TZs between two bands. Small frequency ratio of 1.33 is achieved. Wide upper stopband and low insertion loss can be observed for both prototypes.