Electronically tunable, absorptive, low-loss notch filter
First Claim
1. 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.
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Abstract
An electronically tuned, absorptive, low-loss notch filter with high RF power handling capability is obtained using a four-port quadrature hybrid coupler connected to a matched pair of band pass resonator devices and resistive terminations. The notch filter design uses series-only tuning elements for the band pass resonator devices to raise the RF power handling of the band pass resonators far above conventional techniques while also being tunable at high speeds. The notch filter architecture and method can be used for interference cancellation in a wide range of wireless technologies, such as cellular phone, wireless routers, hand-held radios, satellite communications, and any other environments where there are a number of wireless technologies in close signal proximity.
43 Citations
18 Claims
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1. An electronic tunable, absorptive, low-loss notch filter comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method of operating a notch filter comprising:
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providing 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 split an incoming signal at the first terminal to 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; providing a matched pair of electronically tuned band pass resonators connected to respective ones of the second and third terminals of the quadrature hybrid coupler and having respective resistive terminations each of which has an impedance matched to an overall impedance of the notch filter; tuning the first and second electronically tuned band pass resonators to a frequency to be notched by the notch filter; wherein an incoming signal at the frequency to be notched by said notch filter injected to the first terminal of the quadrature hybrid coupler results in signals passed by the first and second electronically tuned band pass resonators and absorbed into the first and second resistive terminations, and wherein an incoming signal at an out-of-notch frequency injected to the first terminal of the quadrature hybrid coupler results in reflected signals reflected back from the first and second band pass resonators that undergo a second phase shift through the quadrature hybrid coupler, resulting in the reflected signals being passed to the first terminal that are 180 degrees out-of-phase and which cancel each other, and the reflected signals being passed to the fourth terminal that are in-phase and which reinforce each other so as to pass a full out-of-notch frequency signal from the notch filter with little or no loss. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification