A sharp-rejection dual-bandstop filter with multiple transmission poles and zeros based on transversal signal-interaction concepts

A new sharp-rejection dual-bandstop filter is proposed in this paper. Two wide stopbands are realized by Path 1 composed of a T-type structure. Three transmission poles in each stop-band and nine transmission zeros out of band within 2f0 are achieved by the signal interaction of Path 1 and Path 2, guaranteeing sharp rejection and high filtering performance. In addition, the extraction process of the transmission poles and zeros is presented based on S-parameters theory. The 3-dB fractional bandwidths of 67.8% and 33.0% with the center frequency 0.575 and 1.425 GHz are obtained. The measured results agrees well with those of simulation.