Wideband Bandpass Filter with High Selectivity and an Adjustable Notched-band Adopting a Multi-mode Resonator

Abstract

AbstractA wideband bandpass filter (BPF) with an adjustable notched-band and high selectivity is proposed. The proposed BPF consists of a multi-mode resonator (MMR), twoλ/2 resonators, and I/O feed lines with 50 ohm characteristic impedance. The MMR, connected as a whole by a wide stub, is composed of one I-shaped resonator and two open-loop resonators. Tightly coupling is built between MMR andλ/2 resonators. I/O feed lines are directly connected with twoλ/2 resonators, respectively. Due to the use of tapped-line coupling, one transmission zero (TZ) is formed near low-edge of aim passband. High-edge of passband with one attendant TZ can be tuned to desired location by adjusting bottom-side position of used wide stub or bottom-side length of I-shaped resonator in MMR. The top-side length of I-shaped resonator is applied to improve upper stopband performance and shift undesired resonant mode of MMR near high-edge of aim passband to proper frequency point. The notched-band in aim passband is dominated by top-side position of wide stub in MMR. Good agreement is observed between simulated and measured results.