Tunable bandpass-bandstop filter cascade for VHF applications

A lumped-element bandpass-bandstop filter cascade with the capability of independently allocating its poles and zeros is demonstrated with commercially available components. The filter cascade consists of 14 tunable resonators to form advanced filtering functions. Eight resonators implement a reconfigurable fourth-order band-pass filter with tunable resonant-couplings, while the remaining six are used to form three second-order absorptive band-stop filters to create deep isolation levels. The filter cascade can be continuously tuned from 100 to 255MHz with high isolation (70dB at 5% away from the pass-band edge). Resonant coupling structures act as intrinsic switches to achieve reconfigurable signal routing. Therefore, switchless multi-band filter bank operation is also achieved.