Interference cancellation system having noise reduction features and method

• US 5,117,505 A
• Filed: 02/22/1990
• Issued: 05/26/1992
• Est. Priority Date: 02/22/1990
• Status: Expired due to Term

• Current Assignee: Exelis Incorporated (L3Harris Technologies, Inc.)
• Original Assignee: American Nucleonics Corp. (Eaton Corporation PLC.)
• Inventors: Talwar, Ashok K.
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Belzer, Christine K.
• Application Number:
  US07/483,543
• Time in Patent Office: 824 Days
• Field of Search: 455/278, 455/272, 455/136, 455/273, 455/277, 343/713, 343/841, 343/853
• US Class Current: 455/278.1
• CPC Class Codes: H04B 1/126 having multiple inputs, e.g. auxiliary antenna for receiving interfering signal aerials in general H01Q

Abstract

An interference cancellation system automatically couples and decouples intself from a radio receiver system when no interfering signals are present. The interference cancellation system, which is adapted to be connected to the radio receiver system having a receiver antenna, a receiver and a receiver transmission line interconnecting the receiver antenna and the receiver, includes an auxiliary antenna, a first directional coupler connected to the auxiliary antenna, a second directional coupler connected to the receiver transmission line, a third directional coupler connected to the first directional coupler, a synchronous detector connected to the third and second directional couplers, a signal controller connected to the synchronous detector and a subtractor connected to the receiver transmission line and to the signal controller. A detector is connected to the third directional coupler, and a comparator is connected to the detector and is provided with a predetermined threshold voltage level. The comparator compares the detected output signal from the detector with the predetermined threshold voltage level, and provides an output signal to a switch circuit interposed between the signal controller and the subtractor. When an interfering signal is detected, the switch circuit provides an electrical path from the signal controller to the subtractor so that a cancellation signal may be injected into the receiver transmission line. If no interfering signal is detected, the switch circuit opens the connection between the signal controller and the subtractor so that no noise from the interference cancellation system is injected into the radio receiver system.

Claims

1. An interference cancellation system for connection to a radio receiver system having a receiver antenna, a receiver and a receiver transmission line electrically coupling the receiver antenna to the receiver, the interference cancellation system comprising:

an auxiliary antenna for receiving an interfering signal, the auxiliary antenna providing a reference signal corresponding to the interfering signal received by the auxiliary antenna;

a first directional coupler, the reference signal being provided to the first directional coupler, the first directional coupler having first and second outputs and respectively providing thereon first and second output signals each corresponding to the reference signal;

a second directional coupler, the second directional coupler being electrically coupled to the receiver transmission line, the second directional coupler having an output and providing thereon a sample signal corresponding to an interfering signal and desired signal received by the receiver antenna;

a third directional coupler, the third directional coupler being electrically coupled to the first directional coupler and having first and second outputs and respectively providing thereon first and second output signals each corresponding to the reference signal;

a first detector, the first detector being electrically coupled to the third directional coupler and providing a first detected output signal in response to the first output signal of the third directional coupler;

a synchronous detector, the synchronous detector having at least two inputs respectively electrically coupled to the third and second directional couplers and being responsive to the second output signal of the third coupler and the sample signal of the second coupler, the synchronous detector comparing the third coupler second output signal and the sample signal and providing at least one synchronous detector output signal in response thereto;

a signal controller, the signal controller having a first input electrically coupled to the first directional coupler and being responsive to the first output signal of the first coupler, and at least a second input electrically coupled to the synchronous detector, the signal controller having an output and providing thereon a cancellation signal in response to the synchronous detector output signal;

a subtractor, the subtractor being electrically coupled to the receiver transmission line and being further electrically coupled to the signal controller, the subtractor having an input on which is provided the cancellation signal, the subtractor effectively injecting the cancellation signal onto the receiver transmission line carrying the received interfering and desired signals, the cancellation signal injected into the receiver transmission line being equal in amplitude and opposite in phase to the interfering signal received by the receiver antenna and carried by the receiver transmission line so as to cancel the interfering signal on the receiver line;

a comparator, the comparator being provided with the first detected output signal of the first detector and with a predetermined threshold signal, the comparator comparing the first detected output signal and the predetermined threshold signal and providing an output signal in response thereto; and

switch means for coupling and decoupling at least a portion of the interference cancellation system from the radio receiver system, the switch means being electrically coupled to the comparator and being responsive to the output signal therefrom, the switch means including a first switch circuit, the first switch circuit being electrically coupled to the signal controller and to the subtractor and providing an electrical path between the signal controller and the subtractor in response to the output signal from the comparator.

2. An interference cancellation system for connection to a radio receiver system having a receiver antenna, a receiver and a receiver transmission line electrically coupling the receiver antenna to the receiver, the interference cancellation system comprising:

an auxiliary antenna for receiving an interfering signal, the auxiliary antenna providing a reference signal corresponding to the interfering signal received by the auxiliary antenna;

a first directional coupler, the reference signal being provided to the first directional coupler, the first directional coupler having first and second outputs and respectively providing thereon first and second output signals each corresponding to the reference signal;

a second directional coupler, the second directional coupler being electrically coupled to the receiver transmission line, the second directional coupler having an output and providing thereon a sample signal corresponding to an interfering signal and desired signal received by the receiver antenna;

a third directional coupler, the third directional coupler being electrically coupled to the first directional coupler and having first and second outputs and respectively providing thereon first and second output signals each corresponding to the reference signal;

a first detector, the first detector being electrically coupled to the third directional coupler and providing a first detected output signal in response to the first output signal of the third directional coupler;

a synchronous detector, the synchronous detector having at least two inputs respectively electrically coupled to the third and second directional couplers and being responsive to the second output signal of the third coupler and the sample signal of the second coupler, the synchronous detector comparing the third coupler second output signal and the sample signal and providing at least one synchronous detector output signal in response thereto;

a signal controller, the signal controller having a first input electrically coupled to the first directional coupler and being responsive to the first output signal of the first coupler, and at least a second input electrically coupled to the synchronous detector, the signal controller having an output and providing thereon a cancellation signal in response to the synchronous detector output signal;

a subtractor, the subtractor being electrically coupled to the receiver transmission line and being further electrically coupled to the signal controller, the subtractor having an input on which is provided the cancellation signal, the subtractor effectively injecting the cancellation signal onto the receiver transmission line carrying the received interfering and desired signals, the cancellation signal injected into the receiver transmission line being equal in amplitude and opposite in phase to the interfering signal received by the receiver antenna and carried by the receiver transmission line so as to cancel the interfering signal on the receiver line;

a comparator, the comparator being provided with the first detected output signal of the first detector and with a predetermined threshold signal, the comparator comparing the first detected output signal and the predetermined threshold signal and providing an output signal in response thereto; and

switch means for coupling and decoupling at least a portion of the interference cancellation system from the radio receiver system, the switch means being electrically coupled to the comparator and being responsive to the output signal therefrom, the switch means including first and second switch circuits, the first switch circuit being electrically coupled to the receiver transmission line and electrically interposed between the receiver antenna and the subtractor, the second switch circuit being electrially coupled to the receiver transmission line and electrically interposed between the subtractor and the receiver, each of the first and second switch circuits being operable in at least first and second states in response to the output signal of the comparator, wherein the first and second switch circuits provide an electrical path from the receiver antenna to the receiver when the switch circuits are in the first state, thereby effectively decoupling the interference cancellation system from the radio receiver system, and wherein the first and second switch circuits provide an electrical path from the receiver antenna to the subtractor and from the subtractor to the radio receiver when the switch circuits are in the second state, thereby effectively coupling the interference cancellation system to the radio receiver system.

3. An interference cancellation system for connection to a radio receiver system having a receiver antenna, a receiver and a receiver transmission line electrically coupling the receiver antenna to the receiver, the interference cancellation system comprising:

an auxiliary antenna for receiving an interfering signal, the auxiliary antenna providing a reference signal corresponding to the interfering signal received by the auxiliary antenna;

a first directional coupler, the reference signal being provided to the first directional coupler, the first directional coupler having first and second outputs and respectively providing thereon first and second output signals each corresponding to the reference signal;

a second directional coupler, the second directional coupler being electrically coupled to the receiver transmission line, the second directional coupler having an output and providing thereon a first sample signal corresponding to an interfering signal and desired signal received by the receiver antenna;

a third directional coupler, the third directional coupler being electrically coupled to the first directional coupler and having first and second outputs and respectively providing thereon first and second output signals each corresponding to the reference signal;

a first detector, the first detector being electrically coupled to the third directional coupler and providing a first detected output signal in response to the first output signal of the third directional coupler;

a synchronous detector, the synchronous detector having at least two inputs respectively electrically coupled to the third and second directional couplers and being responsive to the second output signal of the third coupler and the first sample signal of the second coupler, the synchronous detector comparing the third coupler second output signal and the first sample signal and providing at least one synchronous detector output signal in response thereto;

a signal controller, the signal controller having a first input electrically coupled to the first directional coupler and being responsive to the first output signal of the first coupler, and at least a second input electrically coupled to the synchronous detector, the signal controller having an output and providing thereon a cancellation signal in response to the synchronous detector output signal; and

a subtractor, the subtractor being electrically coupled to the receiver transmission line and being further electrically coupled to the signal controller, the subtractor having an input on which is provided the cancellation signal, the subtractor effectively injecting the cancellation signal onto the receiver transmission line carrying the received interfering and desired signals, the cancellation signal injected into the receiver transmission line being equal in amplitude and opposite in phase to the interfering signal received by the receiver antenna and carried by the receiver transmission line so as to cancel the interfering signal on the receiver line;

a fourth directional coupler, the fourth directional coupler being electrically coupled to the receiver transmission line and electrically interposed between the receiver antenna and the subtractor, the fourth directional coupler having at least one output and providing thereon a second sample signal corresponding to the interfering signal and desired signal received by the receiver antenna;

a second detector, the second detector being electrically coupled to the fourth directional coupler and providing a second detected output signal in response to the second sample signal of the fourth directional coupler;

divider and comparator means, the divider and comparator means being provided with the first detected output signal of the first detector and with the second detected output signal of the second detector, the divider and comparator means dividing the second detected output signal with the first detected output signal and determining the ratio of the signal magnitudes thereof, and comparing the ratio with a predetermined value and providing an output signal in response to the comparison thereof; and

switch means for coupling and decoupling at least a portion of the interference cancellation system from the radio receiver system, the switch means being electrically coupled to the divider and comparator means and being responsive to the output signal therefrom, the switch means including a first switch circuit, the first switch circuit being electrically coupled to the signal controller and to the subtractor and providing an electrical path between the signal controller and the subtractor in response to the output signal from the divider and comparator means.

4. An interference cancellation system for connection to a radio receiver system having a receiver antenna, a receiver and a receiver transmission line electrically coupling the receiver antenna to the receiver, the interference cancellation system comprising:

an auxiliary antenna for receiving an interfering signal, the auxiliary antenna providing a reference signal corresponding to the interfering signal received by the auxiliary antenna;

a first directional coupler, the reference signal being provided to the first directional coupler, the first directional coupler having first and second outputs and respectively providing thereon first and second output signals each corresponding to the reference signal;

a second directional coupler, the second directional coupler being electrically coupled to the receiver transmission line, the second directional coupler having an output and providing thereon a first sample signal corresponding to an interfering signal and desired signal received by the receiver antenna;

a third directional coupler, the third directional coupler being electrically coupled to the first directional coupler and having first and second outputs and respectively providing thereon first and second output signals each corresponding to the reference signal;

a first detector, the first detector being electrically coupled to the third directional coupler and providing a first detected output signal in response to the first output signal of the third directional coupler;

a synchronous detector, the synchronous detector having at least two inputs respectively electrically coupled to the third and second directional couplers and being responsive to the second output signal of the third coupler and the first sample signal of the second coupler, the synchronous detector comparing the third coupler second output signal and the first sample signal and providing at least one synchronous detector output signal in response thereto;

a signal controller, the signal controller having a first input electrically coupled to the first directional coupler and being responsive to the first output signal of the first coupler, and at least a second input electrically coupled to the synchronous detector, the signal controller having an output and providing thereon a cancellation signal in response to the synchronous detector output signal; and

a subtractor, the subtractor being electrically coupled to the receiver transmission line and being further electrically coupled to the signal controller, the subtractor having an input on which is provided the cancellation signal, the subtractor effectively injecting the cancellation signal onto the receiver transmission line carrying the received interfering and desired signals, the cancellation signal injected into the receiver transmission line being equal in amplitude and opposite in phase to the interfering signal received by the receiver antenna and carried by the receiver transmission line so as to cancel the interfering signal on the receiver line;

a fourth directional coupler, the fourth directional coupler being electrically coupled to the receiver transmission line and electrically interposed between the receiver antenna and the subtractor, the fourth directional coupler having at least one output and providing thereon a second sample signal corresponding to the interfering signal and desired signal received by the receiver antenna;

a second detector, the second detector being electrically coupled to the fourth directional coupler and providing a second detected output signal in response to the second sample signal of the fourth directional coupler;

divider and comparator means, the divider and comparator means being provided with the first detected output signal of the first detector and with the second detected output signal of the second detector, the divider and comparator means dividing the second detected output signal with the first detected output signal and determining the ratio of the signal magnitudes thereof, and comparing the ratio with a predetermined value and providing an output signal in response to the comparison thereof; and

switch means for coupling and decoupling at least a portion of the interference cancellation system from the radio receiver system, the switch means being electrically coupled to the divider and comparator means and being responsive to the output signal therefrom, the switch means including first and second switch circuits, the first switch circuit being electrically coupled to the receiver transmission line and electrically interposed between the receiver antenna and the subtractor, the second switch circuit being electrically coupled to the receiver transmission line and electrically interposed between the subtractor and the receiver, each of the first and second switch circuits being operable in at least first and second states in response to the output signal of the divider and comparator means, wherein the first and second switch circuits provide an electrical path from the receiver antenna to the receiver when the switch circuits are in the first state, thereby effectively decoupling the interference cancellation system from the radio receiver system, and wherein the first and second switch circuits provide an electrical path from the receiver antenna to the subtractor and from the subtractor to the radio receiver when the switch circuits are in the second state, thereby effectively coupling the interference cancellation system to the radio receiver system.

5. An interference cancellation system for connection to a radio receiver system having a receiver antenna, a receiver and a receiver transmission line electrically coupling the receiver antenna to the receiver, the interference cancellation system comprising:

an auxiliary antenna for receiving an interfering signal, the auxiliary antenna providing a reference signal corresponding to the interfering signal received by the auxiliary antenna;

a first directional coupler, the reference signal being provided to the first directional coupler, the first directional coupler having first and second outputs and respectively providing therein first and second output signals each corresponding to the reference signal;

a second directional coupler, the second directional coupler being electrically coupled to the receiver transmission line, the second directional coupler having an output and providing thereon a first sample signal corresponding to an interfering signal and desired signal received by the receiver antenna;

a synchronous detector, the synchronous detector having at least two inputs respectively electrically coupled to the first and second directional couplers and being responsive to the second output signal of the first coupler and the first sample signal of the second coupler, the synchronous detector comparing the first coupler second output signal and the sample signal and providing at least one synchronous detector output signal in response thereto;

a signal controller, the signal controller having a first input electrically coupled to the first directional coupler and being responsive to the first output signal of the first coupler, and at least a second input electrically coupled to the synchronous detector, the signal controller having an output and providing thereon a cancellation signal in response to the synchronous detector output signal;

a subtractor, the subtractor being electrically coupled to the receiver transmission line and being further electrically coupled to the signal controller, the subtractor having an input on which is provided the cancellation signal, the subtractor effectively injecting the cancellation signal onto the receiver transmission line carrying the received interfering and desired signals, the cancellation signal injected into the receiver transmission line being equal in amplitude and opposite in phase to the interfering signal received by the receiver antenna and carried by the receiver transmission line so as to cancel the interfering signal on the receiver transmission line;

a third directional coupler, the third directional coupler being electrically coupled to the receiver transmission line and electrically interposed between the receiver antenna and the subtractor, the third directional coupler having at least one output and providing thereon a second sample signal corresponding to the interfering signal and desired signal received by the receiver antenna;

a first detector, the first detector being electrically coupled to the third directional coupler and providing a first detected output signal in response to the second sample signal of the third directional coupler;

a comparator, the comparator being provided with the first detected output signal of the first detector and with a predetermined threshold signal, the comparator comparing the first detected output signal and the predetermined threshold signal and providing an output signal in response thereto; and

switch means for coupling and decoupling at least a portion of the interference cancellation system from the radio receiver system, the switch means being electrically coupled to the comparator and being responsive to the output signal therefrom, the switch means including a first switch circuit, the first switch circuit being electrically coupled to the signal controller and to the subtractor and providing an electrical path between the signal controller and the subtractor in response to the output signal from the comparator.

6. An interference cancellation system for connection to a radio receiver system having a receiver antenna, a receiver and a receiver transmission line electrically coupling the receiver antenna to the receiver, the interference cancellation system comprising:

an auxiliary antenna for receiving an interfering signal, the auxiliary antenna providing a reference signal corresponding to the interfering signal received by the auxiliary antenna;

a first directional coupler, the reference signal being provided to the first directional coupler, the first directional coupler having first and second outputs and respectively providing therein first and second output signals each corresponding to the reference signal;

a second directional coupler, the second directional coupler being electrically coupled to the receiver transmission line, the second directional coupler having an output and providing thereon a first sample signal corresponding to an interfering signal and desired signal received by the receiver antenna;

a synchronous detector, the synchronous detector having at least two inputs respectively electrically coupled to the first and second directional couplers and being responsive to the second output signal of the first coupler and the first sample signal of the second coupler, the synchronous detector comparing the first coupler second output signal and the sample signal and providing at least one synchronous detector output signal in response thereto;

a signal controller, the signal controller having a first input electrically coupled to the first directional coupler and being responsive to the first output signal of the first coupler, and at least a second input electrically coupled to the synchronus detector, the signal controller having an output and providing thereon a cancellation signal in response to the synchronous detector output signal;

a subtractor, the subtractor being electrically coupled to the receiver transmission line and being further electrically coupled to the signal controller, the subtractor having an input on which is provided the cancellation signal, the subtractor effectively injecting the cancellation signal onto the receiver transmission line carrying the received interfering and desired signals, the cancellation signal injected into the receiver transmission line being equal in amplitude and opposite in phase to the interfering signal received by the receiver antenna and carried by the receiver transmission line so as to cancel the interfering signal on the receiver transmission line;

a third directional coupler, the third directional coupler being electrically coupled to the receiver transmission line and electrically interposed between the receiver antenna and the subtractor, the third directional coupler having at least one output and providing thereon a second sample signal corresponding to the interfering signal and desired signal received by the receiver antenna;

a first detector, the first detector being electrically coupled to the third directional coupler and providing a first detected output signal in response to the second sample signal of the third directional coupler;

a comparator, the comparator being provided with the first detected output signal of the first detector and with a predetermined threshold signal, the comparator comparing the first detected output signal and the predetermined threshold signal and providing an output signal in response thereto; and

switch means for coupling and decoupling at least a portion of the interference cancellation system from the radio receiver system, the switch means being electrically coupled to the comparator and being responsive to the output signal therefrom, the switch means including first and second switch circuits, the first switch circuit being electrically coupled to the receiver transmission line and electrically interposed between the receiver antenna and the subtractor, the second switch circuit being electrically coupled to the receiver transmission line and electrically interposed between the subtractor and the receiver, each of the first and second switch circuits being operable in at least first and second states in response to the output signal of the comparator, wherein the first and second switch circuits provide an electrical path from the receiver antenna to the receiver when the switch circuits are in the first state, thereby effectively decoupling the interference cancellation system from the radio receiver system, and wherein the first and second switch circuits provide an electrical path from the receiver antenna to the subtractor and from the subtractor to the radio receiver when the switch circuits are in the second state, thereby effectively coupling the interference cancellation system to the radio receiver system.