Two-Branch Channelized Passive Filters for Lowpass and Bandpass Applications

Fully-passive two-branch channelized circuit configurations for high-selectivity planar filter realization are reported in this work. They exploit the in-parallel connection of two frequency-contiguous low-order passive filters-main and auxiliary channels-to synthesize an enhanced-selectivity filtering response by means of signal-interference principles. Added features of the channelized passive filter in relation to its building channels are: i) bandwidth enlargement of the overall transmission band and ii) the generation of reconfigurable notches in the transfer function of the main channel for dynamic interference suppression by detuning the poles of the auxiliary channel. As experimental proof-of-concept, two microstrip prototypes consisting of a frequency-static quasi-elliptic-type lowpass filter and a bandpass filter with tunable-dual-notch-creation capability through mechanically-adjustable capacitors are built and tested.