Wideband simultaneous transmit and receive (STAR) subsystem
A wideband simultaneous transmit and receive (STAR) subsystem for a radar or other two-way system. 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 STAR subsystem also performs a final cancellation of temperature-dependent or “thermal” transmit-signal noise in the receiver signal. Together, the combined cancellation techniques prevent receiver saturation and preserve receiver sensitivity. The digital cancellation can be adapted in a closed-loop mode to adjust time delays and amplitudes of cancellation signal components. The cancellation system is run open loop in real time to minimize bandwidth limitations and achieve wideband performance. The STAR subsystem can be implemented with discrete components, as a system-on-chip, or as any combination thereof.
1. A simultaneous transmit and receive (STAR) system, said system comprising:
a single 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 received signals from the antenna aperture to the receiver circuit; and
a canceller circuit including a plurality of tuners that operate on the transmit signals and digitally synthesize a cancellation signal which is injected into the receiver circuit, where the cancellation signal cancels out components of the transmit signals and correlated noise which are present in the received signals due to antenna reflection and circulator leakage, 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.
2. The system of claim 1 wherein the canceller circuit includes the tuners which synthesize the cancellation signal, a summer which sums components of the 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 1 further comprising a feedback loop from the receiver circuit to the canceller circuit for separately calibrating the true time delays and the amplitude scale factors for the leakage components and the reflection components.
5. The system of claim 4 wherein the true time delays are calibrated using digital time interpolation filters to achieve 0.1 degree phase accuracy and enable 60 dB suppression of self-interference present in the received signals from the antenna aperture.
6. The system of claim 4 wherein the calibrating is performed as a preparatory process before live operations of the system, 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 live, open-loop operations of the system.
7. The system of claim 1 wherein the transmitter circuit uses a solid state power amplifier to minimize amplification of uncorrelated noise, the circulator is an integrated nanowire magnetic circulator with high isolation to minimize leakage of the uncorrelated noise, and the receiver circuit uses a Gallium-Nitride differential low noise amplifier to maximize cancellation of the uncorrelated noise.
8. The system of claim 1 wherein the system is a multi-beam electronically steerable phased array antenna radar system.
9. A self-interference-cancelling simultaneous transmit and receive (STAR) system, said system comprising:
an antenna aperture;
a transmitter circuit for transmitting signals over a frequency band through the antenna aperture, said transmitter circuit including a solid state power amplifier to minimize amplification of uncorrelated noise;
a receiver circuit for receiving signals from the antenna aperture, said receiver circuit including a Gallium-Nitride differential low noise amplifier to maximize cancellation of the uncorrelated noise, 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 received signals from the antenna aperture to the receiver circuit, where the circulator is an integrated nanowire magnetic circulator with high isolation to minimize leakage of the uncorrelated noise; and
a canceller circuit including a plurality of tuners that operate on the transmit signals and synthesize a cancellation signal which is coupled into the receiver circuit, 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.
10. The system of claim 9 further comprising a feedback loop from the receiver circuit to the canceller circuit for separately calibrating the true time delays and the amplitude scale factors for the leakage components and the reflection components.
11. The system of claim 10 wherein the calibrating is performed as a preparatory process before live operations of the system, 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 live, open-loop operations of the system.
12. The system of claim 9 wherein the system is a millimeter-wave, multi-beam radar system onboard an aircraft using an electronically steerable phased array antenna and operating in a frequency range of 10-50 Gigahertz (GHz).
13. 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 canceller circuit, a 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 cancellation signal with the primary received signal into a modified received signal, where the cancellation signal cancels leaked and reflected components of the analog RF transmit signal and correlated noise which are present in the primary received signal; and
cancelling, in a receiver circuit, leaked and reflected components of uncorrelated noise from the modified received signal to create a final received signal.
14. The method of claim 13 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.
15. The method of claim 13 further comprising calibrating the true time delays and the amplitude scale factors for the leakage components and the reflection components separately using feedback from the final received signal.
16. The method of claim 15 wherein the true time delays are calibrated using digital time interpolation filters to achieve 0.1 degree phase accuracy and enable 60 dB suppression of interference present in the primary received signal.
17. The method of claim 15 wherein calibrating is performed as a preparatory process before live operations of the STAR system, where calibration values for the true time delay shifts and the amplitude scale factors, for a range of temperatures, are stored in a look-up table, and the calibration values from the look-up table are used during live, open-loop operations of the STAR system.
18. The method of claim 13 wherein the transmitter circuit uses a solid state power amplifier to minimize amplification of the uncorrelated noise, the circulator is an integrated nanowire magnetic circulator with high isolation to minimize leakage of the uncorrelated noise, and the receiver circuit uses a Gallium-Nitride differential low noise amplifier to maximize cancellation of the uncorrelated noise.
19. The method of claim 13 wherein the STAR system is used in a millimeter-wave, multi-beam radar system onboard an aircraft using an electronically steerable phased array antenna.