Active reflector with oscillation inhibition
Disclosed active reflector apparatus and methods that inhibit self-induced oscillation. One illustrative apparatus embodiment includes an amplifier and an adjustable phase shifter. The amplifier amplifies a receive signal to generate a transmit signal, the transmit signal causing interference with the receive signal. The adjustable phase shifter modifies the phase of the transmit signal relative to that of the receive signal to inhibit oscillation. A controller may periodically test a range of settings for the adjustable phase shifter to identify undesirable phase shifts prone to self-induced oscillation, and may maintain the phase shift setting at a value that inhibits oscillation.
1. An active reflector comprising:
an antenna;
a bidirectional signal path coupled to the antenna;
a directional coupler, coupled to the bidirectional signal path, a unidirectional receive signal path and a unidirectional transmit signal path, configured to convey a receive signal from the antenna to the unidirectional receive signal path and to convey a transmit signal from the unidirectional transmit signal path to the antenna;
the unidirectional receive signal path configured to convey the receive signal;
the unidirectional transmit signal path configured to convey the transmit signal;
an active reflector circuit, coupled to the unidirectional receive signal path and the unidirectional transmit signal path, configured to generate the transmit signal by amplifying the receive signal and applying a phase shift in a range of phase shifts; and
a calibration circuit, coupled to the active reflector circuit, configured to select the phase shift based at least in part on one or more measurements at different phase shifts in the range of phase shifts, wherein the calibration circuit is configured to sweep the phase shift over the range of phase shifts, and
wherein the phase shift is selected to inhibit or reduce oscillation of the transmit signal associated with interference with the receive signal.
2. The active reflector of claim 1 , wherein the active reflector circuit comprises:
an amplifier coupled to the unidirectional receive signal path;
an adjustable phase shifter, coupled to the amplifier, configured to apply the phase shift in the range of phase shifts;
a variable gain amplifier coupled to the adjustable phase shifter; and
a second amplifier coupled to the variable gain amplifier and the unidirectional transmit signal path.
3. The active reflector of claim 1 , wherein the active reflector further comprises a power splitter, coupled to the active reflector circuit and the calibration circuit, configured to couple a portion of the receive signal to the calibration circuit.
4. The active reflector of claim 1 , wherein the calibration circuit comprises a power detector configured to measure a power of the receive signal.
5. The active reflector of claim 4 , wherein the calibration circuit comprises control logic, coupled to the power detector, configured to select the phase shift based at least in part on one or more measurements of the power at different phase shifts in the range of phase shifts, and configured to sweep the phase shift over the range of phase shifts.
6. The active reflector of claim 5 , wherein the active reflector circuit comprises an adjustable phase shifter, coupled to the calibration circuit, configured to apply the phase shift in the range of phase shifts.
7. The active reflector of claim 5 , wherein the control logic is configured to select the phase shift based at least in part on a phase margin of the active reflector when oscillation of the transmit signal exceeds threshold value.
8. The active reflector of claim 1 , wherein the active reflector is configured to sweep the phase shift over the range of phase shifts once per period of the transmit signal.
9. The active reflector of claim 1 , wherein the directional coupler comprises a quasi-circulator.
10. The active reflector of claim 1 , wherein the receive signal and the transmit signal have a carrier frequency in a band of frequencies corresponding to: radar, sonar, lidar, ultrasound, or radio frequency identification (RFID).
11. A vehicle, comprising:
an active reflector, wherein the active reflector comprises:
an antenna;
a bidirectional signal path coupled to the antenna;
a directional coupler, coupled to the bidirectional signal path, a unidirectional receive signal path and a unidirectional transmit signal path, configured to convey a receive signal from the antenna to the unidirectional receive signal path and to convey a transmit signal from the unidirectional transmit signal path to the antenna;
the unidirectional receive signal path configured to convey the receive signal;
the unidirectional transmit signal path configured to convey the transmit signal;
an active reflector circuit, coupled to the unidirectional receive signal path and the unidirectional transmit signal path, configured to generate the transmit signal by amplifying the receive signal and applying a phase shift in a range of phase shifts; and
a calibration circuit, coupled to the active reflector circuit, configured to select the phase shift based at least in part on one or more measurements at different phase shifts in the range of phase shifts, wherein the calibration circuit is configured to sweep the phase shift over the range of phase shifts, and
wherein the phase shift is selected to inhibit or reduce oscillation of the transmit signal associated with interference with the receive signal.
12. The vehicle of claim 11 , wherein the active reflector circuit comprises:
an amplifier coupled to the unidirectional receive signal path;
an adjustable phase shifter, coupled to the amplifier, configured to apply the phase shift in the range of phase shifts;
a variable gain amplifier coupled to the adjustable phase shifter; and
a second amplifier coupled to the variable gain amplifier and the unidirectional transmit signal path.
13. The vehicle of claim 11 , wherein the active reflector further comprises a power splitter, coupled to the active reflector circuit and the calibration circuit, configured to couple a portion of the receive signal to the calibration circuit.
14. The vehicle of claim 11 , wherein the calibration circuit comprises a power detector configured to measure a power of the receive signal.
15. The vehicle of claim 14 , wherein the calibration circuit comprises control logic, coupled to the power detector, configured to select the phase shift based at least in part on one or more measurements of the power at different phase shifts in the range of phase shifts, and configured to sweep the phase shift over the range of phase shifts.
16. The vehicle of claim 15 , wherein the active reflector circuit comprises an adjustable phase shifter, coupled to the calibration circuit, configured to apply the phase shift in the range of phase shifts.
17. The vehicle of claim 15 , wherein the control logic is configured to select the phase shift based at least in part on a phase margin of the active reflector when oscillation of the transmit signal exceeds threshold value.
18. A method for applying a phase shift, comprising:
by an active reflector:
receive, via a bidirectional signal path, a receive signal from an antenna;
conveying, via a directional coupler and a unidirectional receive signal path, the receive signal to an active reflector circuit;
generating, using the active reflector circuit, a transmit signal by amplifying the receive signal and applying the phase shift in a range of phase shifts;
selecting, using a calibration circuit, the phase shift based at least in part on one or more measurements at different phase shifts in the range of phase shifts, wherein the selecting comprises sweeping the phase shift over the range of phase shifts, and wherein the phase shift is selected to inhibit or reduce oscillation of the transmit signal associated with interference with the receive signal;
conveying, via a unidirectional transmit signal path, the directional coupler, the transmit signal to the bidirectional signal path; and
providing, via the bidirectional signal path, the receive signal to the antenna.
19. The vehicle of claim 18 , wherein the phase shift is selected based at least in part on a phase margin of the active reflector when oscillation of the transmit signal exceeds threshold value.
20. The method of claim 18 , wherein the receive signal and the transmit signal have a carrier frequency in a band of frequencies corresponding to: radar, sonar, lidar, ultrasound, or radio frequency identification (RFID).