Simultaneous transmit and receive (STAR) subsystem with external noise canceller

• US 10,649,067 B1
• Filed: 10/26/2016
• Issued: 05/12/2020
• Est. Priority Date: 10/26/2016
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Inventors: Yang, Jeffrey M., Nakamura, Eric B., Parker, A. Dale
• Primary Examiner(s): Bythrow, Peter M
• Application Number:
  US15/335,283
• Time in Patent Office: 1,294 Days
• CPC Class Codes: G01S 13/0209 Systems with very large relative bandwidth, i.e. larger than 10 %, e.g. baseband, pulse, carrier-free, ultrawideband
• CPC Class Codes: G01S 2013/0245 Radar with phased array antenna
• CPC Class Codes: G01S 7/038 Feedthrough nulling circuits

Abstract

A wideband simultaneous transmit and receive (STAR) subsystem for a radar or communications system including self-interference cancellation and external noise cancellation. The STAR subsystem includes a canceller circuit which digitally prepares a cancellation signal to cancel out leaked or reflected portions of the transmit signal and correlated noise in the receiver signal. The self-interference cancellation can be adaptively configured in a closed-loop mode, and operated open loop in real time to minimize bandwidth limitations and achieve wideband performance. The STAR subsystem also includes an external noise active canceller which greatly diminishes high-power external noise in the receiver signal. The external noise canceller digitally synthesizes a cancellation signal which dramatically improves the signal-to-noise ratio in the receiver. Together, the combined cancellation techniques prevent receiver saturation and preserve receiver sensitivity.

Claims

1. A simultaneous transmit and receive (STAR) system with self-cancellation of transmit signal interference and external noise cancellation, said system comprising:

an antenna aperture;

a transmitter circuit for transmitting signals over a frequency band through the antenna aperture;

a receiver circuit for receiving signals from the antenna aperture, where the receiver circuit uses the same frequency band as the transmitter circuit at the same time;

a circulator for directing transmit signals from the transmitter circuit to the antenna aperture and a received signal from the antenna aperture to the receiver circuit;

a transmit signal self-canceller circuit including a plurality of tuners that operate on the transmit signals and digitally synthesize a self-cancellation signal which is applied to the received signal, where the self-cancellation signal cancels out components which are present in the received signal due to antenna reflection and circulator leakage of the transmit signals and correlated noise, and where the plurality of tuners include true time delay tuners which apply a true time delay to a leakage component and a reflection component of each of one or more digital transmit signals, and amplitude tuners which apply an amplitude scale factor to the leakage component and the reflection component of each of the digital transmit signals; and

an external noise canceller circuit including a signal processor which applies a 180 degree phase offset to a digitized form of the received signal to synthesize a noise cancellation signal which is converted to analog and applied to the received signal, where the noise cancellation signal decreases external noise power in the received signal.

2. The system of claim 1 wherein the self-canceller circuit includes the tuners which synthesize the self-cancellation signal, a summer which sums components of the self-cancellation signal from all of the tuners, a digital to analog converter, a low-pass filter, a mixer for up-converting from intermediate frequency to radio frequency, a band-pass filter and a power amplifier.

3. The system of claim 1 wherein the true time delays are calculated based on expected elapsed times for leaked and reflected signals to travel from the transmitter circuit to the receiver circuit, and the amplitude scale factors are calculated based on a transmission coefficient of the circulator and a reflection coefficient of the antenna aperture.

4. The system of claim 3 further comprising a feedback loop from the receiver circuit to the self-canceller circuit for separately calibrating the true time delays and the amplitude scale factors for the leakage components and the reflection components, where calibration values for the true time delays and the amplitude scale factors, at a range of temperatures, are stored in a look-up table, and the calibration values from the look-up table are used during operations of the system.

5. The system of claim 1 wherein the external noise canceller circuit includes a first coupler which splits the received signal into a first path and a second path, where the first path includes the signal processor which synthesizes the noise cancellation signal, and a second coupler which injects the noise cancellation signal into the received signal.

6. The system of claim 5 wherein the first coupler applies a weighted split of power of the received signal, where over half of the power of the received signal passes through the second path and a low-power copy of the received signal passes through the first path.

7. The system of claim 5 wherein the first path includes a variable attenuator which attenuates the received signal in the first path, an RF-IF down-converter, an analog-to-digital converter (ADC), the signal processor, a digital-to-analog converter (DAC), an IF-RF up-converter, and an amplifier.

8. The system of claim 7 wherein the signal processor is an application specific integrated circuit (ASIC) including a waveform adjustment module and a calibration table, where the waveform adjustment module applies the 180 degree phase offset to the received signal to produce the noise cancellation signal.

9. The system of claim 8 further comprising a feedback loop from the receiver circuit to the calibration table, where the waveform adjustment module makes adjustments to the noise cancellation signal to reduce noise in the received signal detected via the feedback loop.

10. The system of claim 5 wherein the second path includes a true time delay module which adds a time delay to the received signal in the second path to compensate for a processing time of the signal processor.

11. The system of claim 1 wherein the system is a multi-beam electronically steerable phased array antenna radar system.

12. A radio receiver system with external noise cancellation, said receiver system comprising:

an external noise canceller circuit including a first coupler which splits a received signal from an antenna into a first path and a second path, where the first path includes a signal processor which applies a 180-degree phase offset to a digitized form of the received signal to synthesize a noise cancellation signal, and a second coupler which injects the noise cancellation signal into a time-delayed form of the received signal from the second path to produce a modified received signal; and

a receiver circuit which receives the modified received signal from the external noise canceller circuit, said receiver circuit including a low noise amplifier, a radio frequency to intermediate frequency (RF-IF) down-converter, an IF amplifier, and an analog-to-digital converter (ADC), where the receiver circuit provides a digital receiver output signal.

13. The receiver system of claim 12 wherein the first coupler applies a weighted split of power of the received signal, where over half of the power of the received signal passes through the second path and a low-power copy of the received signal passes through the first path.

14. The receiver system of claim 12 wherein the first path includes a variable attenuator which attenuates the received signal in the first path, an RF-IF down-converter, an ADC, the signal processor, a digital-to-analog converter (DAC), an IF-RF up-converter, and a power amplifier, where the signal processor is an application specific integrated circuit (ASIC) including a waveform adjustment module and a calibration table, and where the waveform adjustment module applies the 180-degree phase offset and other adjustments designated by the calibration table to the received signal to produce the noise cancellation signal.

15. The receiver system of claim 14 further comprising a feedback loop coupling the digital receiver output signal from the receiver circuit to the calibration table of the signal processor, where the waveform adjustment module makes further adjustments to the noise cancellation signal to minimize noise in the modified received signal detected via the feedback loop.

16. A method for cancelling interference in a simultaneous transmit and receive (STAR) system, said method comprising:

providing one or more digital transmit signals to a transmitter circuit;

creating, by the transmitter circuit, an analog transmit signal for transmission from the digital transmit signals;

providing the analog transmit signal to a phased array antenna via a circulator;

preparing, in a self-canceller circuit, a self-cancellation signal from the digital transmit signals, including applying a true time delay to a leakage component and a reflection component of each of the digital transmit signals, applying an amplitude scale factor to the leakage component and the reflection component of each of the digital transmit signals, and summing the leakage components and the reflection components after the true time delays and the amplitude scale factors have been applied;

receiving a primary received signal from the antenna via the circulator;

combining the self-cancellation signal with the primary received signal into a secondary received signal;

preparing, in an external noise canceller circuit, a noise cancellation signal by applying a 180 degree phase offset to a digitized form of the secondary received signal;

combining the noise cancellation signal with the secondary received signal to produce a tertiary received signal, where the noise cancellation signal decreases external noise power in the tertiary received signal; and

cancelling, in a receiver circuit, leaked and reflected components of uncorrelated transmit signal noise from the tertiary received signal to create a final received signal.

17. The method of claim 16 wherein the external noise canceller circuit includes a first coupler which splits the secondary received signal into a first path and a second path, where the first path includes a signal processor which synthesizes the noise cancellation signal, and a second coupler which injects the noise cancellation signal into the secondary received signal to produce the tertiary received signal.

18. The method of claim 17 wherein the first path includes a variable attenuator which attenuates the secondary received signal in the first path, an RF-IF down-converter, an analog-to-digital converter (ADC), the signal processor, a digital-to-analog converter (DAC), an IF-RF up-converter, and an amplifier, and the second path includes a true time delay module which adds a time delay to the secondary received signal in the second path to compensate for a processing time of the signal processor.

19. The method of claim 17 wherein the signal processor is an application specific integrated circuit (ASIC) including a waveform adjustment module and a calibration table, where the waveform adjustment module applies the 180 degree phase offset to the secondary received signal to produce the noise cancellation signal.

20. The method of claim 19 further comprising a feedback loop from the receiver circuit to the calibration table, where the waveform adjustment module makes adjustments to the noise cancellation signal to reduce noise in the tertiary received signal detected via the feedback loop.