A tunable X-band active notch filter with low-distortion passband response

The tunable channelized active notch filter presented distinguishes itself through its ability to maintain forward signal flow in its three parallel-connected branches without an amplifier in the one branch that determines passband performance, resulting in extremely low signal distortion and very low noise levels at passband frequencies. The practicability of the new approach has been experimentally verified with a filter whose 40-dB-deep notch tunes, with the help of varactors, from 9.5 to 10.5 GHz.