Complementary automatic gain control for anti-jam communications
View Patent ↗Anti-jamming techniques are provided for RF receivers, such as those that operate in hostile environments. In some embodiments, the techniques are embodied in an anti-jam communications system configured with automatic gain control (AGC) that is complementary. The system includes a first AGC circuit prior to an interference suppression circuit and a second AGC circuit after the interference suppression circuit. The first AGC circuit operates to adjust the power level presented to the interference suppression circuit to facilitate interference cancellation. The second AGC circuit operates to maintain the original power level of the desired communications signal and prevent amplitude errors as the first AGC circuit responds to fluctuations in jammer signal power. The second AGC can be slaved to the first AGC circuit such that the sum of two gain values is held constant, according to some embodiments. In this manner, the first and second AGC circuits provide a complementary-AGC system.
1. An anti-jam communications system, comprising:
a first automatic gain control (AGC) circuit having an input to receive RF signals captured by an antenna, and an output to provide a first gain adjusted version of the received RF signals, the received RF signals including a desired signal and a jammer signal;
an interference suppression circuit having an input to the first gain adjusted version of the received RF signals, and to suppress the jammer signal, thereby providing a second gain adjusted version of the received RF signals; and
a second AGC circuit having an input to receive the second gain adjusted version of the received RF signals, and an output to provide a third gain adjusted version of the received RF signals;
wherein the sum of the gain provided by the first AGC circuit and the gain provided by the second AGC is within the range of −1.0 dB to +1.0 dB.
2. The anti-jam communications system of claim 1 , further comprising:
the antenna operatively coupled to the input of the first AGC circuit; and
a radio frequency (RF) receiver operatively coupled to the output of the second AGC circuit.
3. The anti-jam communications system of claim 2 , wherein the antenna is an adaptive antenna array.
4. The anti-jam communications system of claim 1 , wherein the interference suppression circuit includes an adaptive analog nulling circuit.
5. The anti-jam communications system of claim 1 , wherein the interference suppression circuit includes a notch filter.
6. The anti-jam communications system of claim 1 , wherein the sum of the gain provided by the first AGC circuit and the gain provided by the second AGC is within the range of −0.5 dB to +0.5 dB.
7. The anti-jam communications system of claim 1 , wherein the first AGC circuit comprises:
a first variable gain amplifier having a gain that is adjustable based on a first control signal;
a sampling circuit to generate a representation of the first gain adjusted version of the received RF signals; and
a first control circuit to receive the representation of the first gain adjusted version of the received RF signals and to provide the first control signal to the first variable gain amplifier.
8. The anti-jam communications system of claim 7 , wherein the second AGC circuit comprises:
a second variable gain amplifier having a gain that is adjustable based on a second control signal; and
a second control circuit to provide the second control signal to the second variable gain amplifier, the second control signal being substantially complementary to the first control signal.
9. The anti-jam communications system of claim 8 , wherein the first and second control circuits each includes an inverting amplifier circuit, the second control circuit to receive the first control signal, and the first and second control signals are analog control signals.
10. The anti-jam communications system of claim 8 , wherein the first and second control circuits each provides a variable gain ratio G (0 and 1) digital output, and the first and second control signals are digital control signals.
11. The anti-jam communications system of claim 7 , wherein the sampling circuit includes one or more of a coupler, a power detector, and/or a low pass filter.
12. The anti-jam communications system of claim 11 , wherein the sampling circuit further includes an analog to digital converter (ADC).
13. An anti-jam communications system, comprising:
a first automatic gain control (AGC) circuit having an input to receive RF signals captured by an adaptive antenna array, and an output to provide a first gain adjusted version of the received RF signals, the received RF signals including a desired signal and a jammer signal, wherein the first AGC circuit includes
a first variable gain amplifier having a gain that is adjustable based on a first analog control signal;
a sampling circuit to generate a representation of the first gain adjusted version of the received RF signals; and
a first control circuit to receive the representation of the first gain adjusted version of the received RF signals and to provide the first analog control signal to the first variable gain amplifier;
an interference suppression circuit having an input to the first gain adjusted version of the received RF signals, and to suppress the jammer signal, thereby providing a second gain adjusted version of the received RF signals; and
a second AGC circuit having an input to receive the second gain adjusted version of the received RF signals, and an output to provide a third gain adjusted version of the received RF signals, wherein the second AGC circuit includes
a second variable gain amplifier having a gain that is adjustable based on a second analog control signal; and
a second control circuit to receive the first analog control signal and to provide the second analog control signal to the second variable gain amplifier, the second analog control signal being substantially complementary to the first analog control signal;
wherein gain provided by the first AGC circuit is substantially complementary to gain provided by the second AGC circuit.
14. The anti-jam communications system of claim 13 , further comprising:
the adaptive antenna array operatively coupled to the input of the first AGC circuit; and
a radio frequency (RF) receiver operatively coupled to the output of the second AGC circuit.
15. The anti-jam communications system of claim 13 , wherein the interference suppression circuit includes one or more of an adaptive analog nulling circuit and/or a notch filter.
16. The anti-jam communications system of claim 13 , wherein the sum of the gain provided by the first AGC circuit and the gain provided by the second AGC is within the range of −1.0 dB to +1.0 dB.
17. An anti-jam communications system, comprising:
a first automatic gain control (AGC) circuit having an input to receive RF signals captured by an adaptive antenna array, and an output to provide a first gain adjusted version of the received RF signals, the received RF signals including a desired signal and a jammer signal, wherein the first AGC circuit includes
a first variable gain amplifier having a gain that is adjustable based on a first digital control signal;
a sampling circuit to generate a representation of the first gain adjusted version of the received RF signals; and
a first control circuit to receive the representation of the first gain adjusted version of the received RF signals and to provide the first digital control signal to the first variable gain amplifier;
an interference suppression circuit having an input to the first gain adjusted version of the received RF signals, and to suppress the jammer signal, thereby providing a second gain adjusted version of the received RF signals; and
a second AGC circuit having an input to receive the second gain adjusted version of the received RF signals, and an output to provide a third gain adjusted version of the received RF signals, wherein the second AGC circuit includes
a second variable gain amplifier having a gain that is adjustable based on a second digital control signal; and
a second control circuit to provide the second digital control signal to the second variable gain amplifier, the second digital control signal being substantially complementary to the first digital control signal;
wherein gain provided by the first AGC circuit is substantially complementary to gain provided by the second AGC circuit.
18. The anti-jam communications system of claim 17 , further comprising:
the adaptive antenna array operatively coupled to the input of the first AGC circuit; and
a radio frequency (RF) receiver operatively coupled to the output of the second AGC circuit.
19. The anti-jam communications system of claim 17 , wherein the interference suppression circuit includes one or more of an adaptive analog nulling circuit and/or a notch filter.