Radar limiter distortion cancellation
A full duplex radio apparatus comprising: a transmit path configured to transmit a first signal; a receive path configured to receive a received signal; a near-receive path for observing a first period of the received signal; a far-receive path for observing a second period of the received signal, the far-receive path comprising a radio frequency limiter; a self-interference cancellation circuit coupled between the transmit path and the near receive path; a variable impedance component; and a directional coupler comprising a first port, a second port, a third port, and a fourth port, wherein: the first port is coupled to the receive path; the second port is coupled to the radio frequency limiter of the far-receive path; the third port is coupled to the self-interference cancellation circuit; and the fourth port is coupled to the variable impedance component.
1. A full duplex radio apparatus comprising:
a transmit path configured to transmit a transmit signal including a first pulse having a pulse width less than a predetermined time and a second pulse having a pulse period more than the predetermined time, the transmit path being coupled to an antenna;
a receive path configured to receive a received signal, the receive path being coupled to the antenna;
a first receive path for observing the first pulse from the received signal, the first receive path branching from the receive path;
a second receive path for observing the second pulse from the received signal, the second receive path comprising a radio frequency limiter, the second receive path branching from the receive path, and the receive path being divided into the first receive path and the second receive path;
a variable impedance component;
a first directional coupler comprising a first port, a second port, a third port, and a fourth port;
a second directional coupler comprising a fifth port, a sixth port, and a seventh port; and
a self-interference cancellation circuit configured to input a signal from the receive path via the first directional coupler and a signal from the transmit path via the second directional coupler, cancel at least a portion of a self-interference in the received signal, and output the canceled signal to the first receive path, wherein:
the first port is coupled to the second port;
the third port is coupled to the fourth port;
the first port is coupled to the receive path;
the second port is coupled to the radio frequency limiter of the second receive path;
the third port is coupled to the self-interference cancellation circuit;
the fourth port is coupled to the variable impedance component;
the fifth port is coupled to the sixth port;
the fifth port is coupled to the transmit path;
the sixth port is coupled to the antenna; and
the seventh port is coupled to the self-interference cancellation circuit.
2. The full duplex radio apparatus according to claim 1 , wherein the variable impedance component comprises at least one of:
a variable phase shifter configured to control a phase of the variable impedance component; or
a variable resistance configured to control an amplitude of the variable impedance component.
3. The full duplex radio apparatus according to claim 2 , further comprising:
a controller configured to tune the variable impedance of the variable impedance component by at least one of:
varying a phase shift provided by the variable phase shifter; or
varying an amount of attenuation provided by the variable resistance.
4. The full duplex radio apparatus according to claim 3 , wherein:
the variable impedance component comprises the variable phase shifter and the variable resistance;
the variable phase shifter comprises:
a hybrid coupler comprising an eighth port, a ninth port, a tenth port, and an eleventh port;
a first varactor diode; and
a second varactor diode;
the eighth port of the hybrid coupler is coupled to the fourth port of the first directional coupler;
the ninth port of the hybrid coupler is coupled to an anode of the first varactor diode;
the tenth port of the hybrid coupler is coupled to an anode of the second varactor diode;
a cathode of the first varactor diode and a cathode of the second varactor diode are coupled to a phase control input;
the variable resistance comprises:
a capacitor comprising a first terminal and a second terminal, the first terminal being coupled to the eleventh port of the hybrid coupler; and
a PIN diode;
the anode of the PIN diode is coupled to the second terminal of the capacitor and an amplitude control input; and
the cathode of the PIN diode is coupled to ground.
5. The full duplex radio apparatus according to claim 2 , wherein:
the variable impedance component comprises the variable phase shifter and the variable resistance;
an input of the variable phase shifter is coupled to the fourth port of the first directional coupler;
an input of the variable resistance is coupled to an output of the variable phase shifter; and
an output of the variable resistance is coupled to ground.
6. The full duplex radio apparatus according to claim 4 , wherein:
the controller is configured to tune the variable impedance of the variable impedance component by at least one of:
adjusting an amplitude of a phase control signal applied to the phase control input; or
adjusting an amplitude of a voltage control signal applied to the amplitude control input.
7. The full duplex radio apparatus according to claim 1 , wherein:
the variable impedance component comprises a variable delay line and a variable attenuator;
an input of the variable delay line is coupled to the fourth port of the first directional coupler;
an output of the variable delay line is coupled to an input of the variable attenuator; and
an output of the variable attenuator is connected to ground.
8. The full duplex radio apparatus according to claim 1 , wherein:
the variable impedance component comprises:
a power splitter comprising: an eighth port, a ninth port, and a tenth port;
a variable delay line; and
a variable attenuator;
the eighth port of the power splitter is coupled to the fourth port of the first directional coupler;
the ninth port of the power splitter is coupled to an input of the variable delay line;
the tenth port of the power splitter is coupled to an input of the variable attenuator; and
an output of the variable delay line is coupled to an output of the variable attenuator.
9. The full duplex radio apparatus according to claim 1 , wherein:
the transmit path is configured to transmit the transmit signal via the antenna; and
the receive path is configured to receive the received signal via the antenna.
10. The full duplex radio apparatus according to claim 9 , wherein:
the self-interference cancellation circuit comprises:
a variable attenuator;
a variable phase shifter; and
a signal combiner comprising a first input, a second input, and a first output;
the seventh port of the second directional coupler is coupled to an input of the variable attenuator;
an output of the variable attenuator is coupled to an input of the variable phase shifter;
an output of the variable phase shifter is coupled to the first input of the signal combiner;
the third port of the first directional coupler is coupled to the second input of the signal combiner; and
the first output of the signal combiner is coupled to the first receive path.
11. The full duplex radio apparatus according to claim 10 , further comprising a circulator, the circulator comprising an eighth port, a ninth port, and a tenth port, wherein:
the eighth port of the circulator is coupled to the sixth port of the second directional coupler;
the ninth port of the circulator is coupled to the antenna; and
the tenth port of the circulator is coupled to the first port of the first directional coupler.
12. The full duplex radio apparatus according to claim 10 , wherein:
the transmit path comprises a power amplifier;
the first receive path comprises a second radio frequency limiter and a first low noise amplifier; and
the second receive path further comprises a second low noise amplifier.
13. The full duplex radio apparatus according to claim 1 , wherein the first receive path is used for full duplex operation.
14. A radar comprising the full duplex radio apparatus according to claim 1 .
15. A weather radar comprising the full duplex radio apparatus according to claim 1 .