A Compact Bandpass Filter with Source-Load Coupling by Using Short-Circuited Coupled Lines Between Ports

Abstract

A compact filter with a T-shaped resonator and short-circuited coupled lines between two ports is presented. The frequency response of filter has four extra controllable transmission zeros in the stopband because of the multiple signal transmission paths and controllable source-load coupling strength. The positions of the transmission zeros in the stopband are controllable by adjusting the length of coupled lines. At the same time, the center frequency and bandwidth are both not changed. The bandwidth of filter can be adjusted by the different lengths of short-circuited stub of T-shaped resonator. In addition, the second harmonic is suppressed. Good skirt selectivity and controllable stopband characteristics can be achieved simultaneously.