Tunable, Substrate Integrated, High Q Filter Cascade for High Isolation

A combination of tunable bandpass/bandstop filter substrate integrated cavity filters is shown for high spectral isolation. Greater than 90 dB of isolation is shown, which is potentially useful for isolating small signals in the presence of large interferers. Both filters are created using the same substrate integrated evanescent-mode cavity resonators which are placed in series or in shunt by changing the cavity feeds. The resonators are tuned using deformation of a copper membrane induced by a piezo electric actuator. The bandstop filter is able to place deep nulls on the skirt of the bandpass filter function on both the high and low frequency sides. The notch can be tuned from 2.1% to 9.6% away from the center frequency of the bandpass filter. The bandstop filter is also designed with a tunable shape which allows for wider bandwidth isolation on demand.