Compact, high selectivity and wideband bandpass filter with multiple transmission zeros

This paper presents the design of a compact, high selectivity and wideband bandpass filter based on signal interference technique. The proposed filter consists of open coupled line and stepped impedance modified Π-type (SMΠ) transmission line with short circuited stubs in transmission path 1 and path 2, respectively. Due to the superposition of signals of the two transmission paths, a fourth-order wideband bandpass filter with six transmission zeros can be obtained from 0 to 2f0 (f0 is the operating frequency). A bandpass filter prototype centring at 0.9 GHz, with 3 dB fractional bandwidth of 50% is designed, fabricated and tested. Good agreement is found between the simulated and experimental results.