Signal-Interference Planar Bandpass Filters and Diplexers with Frequency-Symmetrical/Asymmetrical Stopband-Attenuation Profiles Using Filtering Cascading Networks

A family of transversal-signal-interference planar bandpass filters (BPFs) with frequency-symmetrical and asymmetrical filtering transfer functions is reported. These RF BPFs are shaped by two dissimilar bi-path in-parallel-transmission-line-based transversal filtering sections (TFSs) and a filtering cascading network to interconnect them. In this manner, overall high-selectivity BPF actions can be realized from the composition of the BPF response of the cascading network and the plurality of out-of-band transmission zeros (TZs) generated by the TFSs. For experimental-validation purposes, two proof-of-concept microstrip prototypes consisting of a 2-GHz frequency-symmetrical multi-TZ BPF and a 1.78/2.24-GHz sharp-rejection diplexer with spectrally-adjacent channels are designed, built, and measured.