A tunable notch filter/amplifier based on the non-reciprocal operation of distributedly modulated capacitors (DMC) formed for an RF front end. In one embodiment within the DMC is formed into a ring resonator with a filter between its ends to allow resonance to build up only at an up-converted frequency, and tune the frequency of the whole received band instead of the resonant frequency of the filter alone. In addition a circulator is described for passing different signals in different directions, but at the same frequency, while maintaining signal separation.