A compact utral-wideband bandpass filter with broad stopband based on step-impedance stub-loaded tri-mode resonator

Abstract

A five-pole ultra-wideband (UWB) bandpass filter (BPF) with broad stopband for FCC UWB indoor communication application is developed. It employs a step-impedance stub-loaded tri-mode resonator, by properly selecting the impedance ratio of the stub, the proposed resonator is able to be downsized without changing significantly its tri-mode characteristics. The advantages of such resonator are easy control of its frequency response and highly compact in structure compared with other resonators. Moreover, a lowpass filter (LPF) is utilized to suppress the unwanted highfrequency harmonics of the proposed UWB BPF. Design and synthesis procedures with details are provided, and good agreement between simulated and measured results is also observed. Due to the fact that the introduced filter structure is simple and all the geometrical parameters are larger than 0.1 mm, the UWB BPF is feasible for low-cost fabrication using conventional printed circuit fabricating techniques.