Tunable channelised bandstop passive filter using reconfigurable phase shifter

A novel tunable channelised two-branches passive bandstop filter using a reconfigurable parallel-coupled-line-based phase shifter (PS) is presented. The filter topology uses the signal destructive principle and aims to protect the receiver against an unwanted interference signal received by the antenna. The global filter topology contains two branches, each of which has a different function. The bandpass tunable branch selects the frequency to be rejected while the reconfigurable PS plays the signal inverter role. The simultaneous tunabilities of both bandpass and PS branches are ensured by using identical varactor diodes and features 550–700 MHz tuning range. In addition to having a constant and relatively high rejection level over all the tuning range and low insertion loss in the passband area, the filter guaranties ultra-low power consumption. Moreover, synthesis equations are proposed and used to illustrate the operating principle, and finally validated by comparing simulations results to measurements.