A class of differential-mode single/dual-band bandpass planar filters based on signal-interference techniques

The design of RF/microwave planar differential-mode single/dual-band bandpass filters (BPFs) based on signal-interference principles is addressed in this work. To this aim, transversal filtering sections (TFSs) that consist of bi-path in-parallel-transmission-line-type cells are embedded into the two identical parts of a balanced circuit. The engineered filtering devices feature sharp-rejection capabilities in their differential-mode transfer function through multi-transmission-zero (TZ) generation along with higher in-band power attenuation levels in their common mode of operation when compared to most of the related prior-art architectures. Furthermore, the proposed concept of balanced BPF can be extrapolated to other classes of signal-interference TFSs as well as to configurations with more-than-two passbands. For experimental verification, a demonstrative two-stage single-band balanced BPF centered at 2 GHz is synthesized, manufactured in microstrip technology, and characterized.