Patent ID: 8013690

Claim:
An electronic tunable, absorptive, low-loss notch filter comprising: a quadrature hybrid coupler with first, second, third, and fourth terminals, wherein the first terminal is a signal input terminal, the fourth terminal is a signal output terminal, and the second and third terminals are connected to respective electronically tuned band pass resonators in tandem, wherein the quadrature hybrid coupler operates to convert an incoming signal to the first terminal into two outgoing signals of equal amplitude and 90 degrees out of phase with the other which are passed to respective ones of the second and third terminals; a first electronically tuned band pass resonator having first and second terminals, wherein the second terminal of the quadrature hybrid coupler is connected to the first terminal of the first electronically tuned band pass resonator; a first resistive termination whose impedance is matched to an overall impedance of the notch filter, having a high side terminal connected to the second terminal of the first electronically tuned band pass resonator, and a low side terminal connected to a ground termination; a second electronically tuned band pass resonator having first and second terminals, wherein the third terminal of the quadrature hybrid coupler is connected to the first terminal of the second electronically tuned band pass resonator; and a second resistive termination whose impedance is matched to the overall impedance of the notch filter, having a high side terminal connected to the second terminal of the second electronically tuned band pass resonator, and a low side terminal connected to the ground termination, wherein both the first and second electronically tuned band pass resonators are a matching pair and are tuned to respective frequencies equal to a notch frequency to be notched by the notch filter.