Single channel interferometer with optical delay lines
View Patent ↗Systems and methods are provided in which a direction of arrival of a radio frequency (RF) signal received by a plurality of antennas is determined. A plurality of first converter receives RF signals from the plurality of antennas and outputs a minimum of a first optical signal and a second optical signal each modulated by their corresponding RF signal. A plurality of second converters receives a minimum of the first optical signal via a first optical channel that introduces a first delay and the second optical signal via a second optical channel that introduces a second delay. The second converter outputs a first RF signal that corresponds to the RF modulation on the first optical signal and a second RF signal that corresponds to the RF modulation on the second optical signal. A switch serially receives, from the second converter outputs, the first RF signal and the second RF signal. A direction finding subsystem determines a direction of arrival using a phase difference between the first RF signal and the second RF signal.
1. A method for determining a direction of arrival of a radio frequency (RF) signal, the method including:
receiving, by a plurality of radio frequency (RF) antennas including a first antenna and a second antenna, an RF signal;
outputting, by the plurality of RF antennas, a plurality of antenna signals including a first antenna signal and a second antenna signal;
receiving, by a first converter, the plurality of antenna signals including the first antenna signal and the second antenna signal;
outputting, by the first converter, a plurality of optical signals, including a first optical signal converted from the first antenna signal and a second optical signal converted from the second antenna signal;
receiving, by a second converter, the plurality of optical signals, wherein:
the first optical signal of the plurality of optical signals is received by the second converter from the first converter via a first optical channel with a first length, wherein the first optical channel introduces a first delay that is proportional to the length of the first optical channel, and
the second optical signal of the plurality of optical signals is received via a second optical channel with a second length that is longer than the first length, wherein the second optical channel introduces a second delay that is proportional to the length of the second optical channel;
outputting, by the second converter, a plurality of RF signals, including:
outputting, via a first RF signal output of the second converter, a first RF signal that corresponds to the first optical signal as delayed by the first delay, and
outputting, via a second RF signal output of the second converter, a second RF signal that corresponds to the second optical signal as delayed by the second delay;
electronically coupling a first switch to the first RF signal output of the second converter to receive the first RF signal;
after receiving the first RF signal, electronically coupling the first switch to the second RF signal output of the second converter to receive the second RF signal;
receiving, by a direction finding subsystem communicatively coupled to the first switch, the first RF signal and the second RF signal; and
determining, by the direction finding subsystem, a direction of arrival of the RF signal received by the plurality of antennas using a phase difference between the first RF signal and the second RF signal.
2. The method of claim 1 , wherein at least one of the first optical channel or the second optical channel includes optical fiber.
3. The method of claim 1 , wherein the plurality of RF antennas include a third RF antenna, and the method includes:
receiving, by the third RF antenna, the RF signal;
outputting, by the third RF antenna, a third antenna signal;
receiving, by the first converter, the third antenna signal;
outputting, by the first converter, a third optical signal converted from the third antenna signal;
receiving, by the second converter, the third optical signal via a third optical channel, wherein:
the third optical channel is longer than the second optical channel, and
the third optical channel introduces a third delay that is proportional to the length of the third optical channel;
outputting, via a third RF signal output of the second converter, a third RF signal that corresponds to the third optical signal as delayed by the third delay;
after receiving the second RF signal, electronically coupling the first switch to the third RF signal output of the second converter to receive the third RF signal;
receiving, by a direction finding subsystem communicatively coupled to the first switch, the third RF signal; and
determining, by the direction finding subsystem, a phase difference between the first RF signal and the third RF signal, wherein the phase difference between the first RF signal and the third RF signal and the phase difference between the first RF signal and the third RF signal are used to determine the direction of arrival of the received RF signal.
4. The method of claim 3 , wherein the plurality of RF antennas are arranged in a one-dimensional array.
5. The method of claim 3 , wherein the plurality of RF antennas are arranged in a two-dimensional or three dimensional array.
6. The method of claim 1 , wherein electronically coupling the first switch to the second RF signal output of the second converter to receive the second RF signal occurs a predetermined amount of time after electronically coupling the first switch to the first RF signal output of the second converter to receive the first RF signal.
7. The method of claim 6 , including:
receiving, by a second switch that is communicatively coupled to the direction finding subsystem, the first RF signal;
outputting, by the second switch, the first RF signal;
after the predetermined amount of time, receiving, by the second switch, the second RF signal; and
outputting, by the second switch, the second RF signal.
8. The method of claim 7 , including applying, by a delay device, a delay to the first RF signal.
9. The method of claim 8 , wherein the delay device includes optical fiber.
10. The method of claim 7 , including:
applying, by a digital delay device, a delay to a reference signal generated by a reference signal generator; and
wherein the phase difference between the first RF signal and the second RF signal is determined using:
a phase difference between the first RF signal and the reference signal, and
a phase difference between the second RF signal and the delayed reference signal.
11. The method of claim 7 , including:
storing, by a memory device, a digitized representation of the first RF signal output of the second switch; and
storing, by the memory device, a digitized representation of the second RF signal output of the second switch, wherein a digital delay is applied to the second RF signal stored by the memory device.
12. An interferometer, comprising:
a plurality of radio frequency (RF) antennas including a first antenna and a second antenna, the plurality of RF antennas configured to receive an RF signal and output a plurality of antenna signals including a first antenna signal output by the first antenna and a second antenna signal output by the second antenna;
a first converter configured to receive the plurality of antenna signals including the first antenna signal and the second antenna signal and output a plurality of optical signals including a first optical signal converted from the first antenna signal and a second optical signal converted from the second antenna signal;
a second converter configured to receive the plurality of optical signals and output a plurality of RF signals including a first RF signal that corresponds to the first optical signal and a second RF signal that corresponds to the second optical signal;
a first optical channel that is optically coupled to the first converter and the second converter, wherein the first optical channel:
has a first length, and
introduces a first delay that is proportional to the first length of the first optical channel;
a second optical channel that is optically coupled to the first converter and the second converter, wherein the second optical channel:
has a second length that is longer than the first length, and
introduces a second delay that is proportional to the length of the second optical channel;
a first switch configured to:
electronically couple to a first RF signal output of the second converter to receive the first RF signal, and
after receiving the first RF signal, electronically couple to the second RF signal output of the second converter to receive the second RF signal; and
a direction finding subsystem communicatively coupled to the output of the first switch, the direction finding subsystem configured to:
receive the first RF signal and the second RF signal, and
determine a direction of arrival of the RF signal received by the plurality of antennas using a phase difference between the first RF signal and the second RF signal.
13. The interferometer of claim 12 , wherein at least one of the first optical channel or the second optical channel includes optical fiber.
14. The interferometer of claim 12 , wherein:
the plurality of RF antennas include a third RF antenna that is configured to receive the RF signal and output a third antenna signal,
the first converter is configured to receive the third antenna signal and output a third optical signal converted from the third antenna signal;
the second converter receives the third optical signal via a third optical channel, wherein:
the third optical channel is longer than the second optical channel, and
the third optical channel introduces a third delay that is proportional to the length of the third optical channel;
the second converter outputs a third RF signal that corresponds to the third optical signal as delayed by the third delay;
after receiving the second RF signal, the first switch receives the third RF signal by electronically coupling the first switch to a third RF signal output of the second converter;
the direction finding subsystem receives the third RF signal; and
the direction finding subsystem uses a phase difference between the first RF signal and the third RF signal and the phase difference between the first RF signal and the third RF signal to determine the direction of arrival of the received RF signal.
15. The interferometer of claim 14 , wherein the plurality of RF antennas are arranged in a one-dimensional array.
16. The interferometer of claim 14 , wherein the plurality of RF antennas are arranged in a two-dimensional array or three-dimensional.
17. The interferometer of claim 12 , wherein electronically coupling the first switch to the second RF signal output of the second converter to receive the second RF signal occurs a predetermined amount of time after electronically coupling the first switch to the first RF signal output of the second converter to receive the first RF signal.
18. The interferometer of claim 17 , including a second switch communicatively coupled to the direction finding subsystem, wherein the second switch is configured to:
receive the first RF signal;
output the first RF signal;
receive the second RF signal; and
after the predetermined amount of time, output the second RF signal.
19. The interferometer of claim 18 , including a delay device configured to apply a delay to the first RF signal.
20. The interferometer of claim 19 , wherein the delay device includes optical fiber.
21. The interferometer of claim 18 , including:
a reference signal generator configured to generate a reference signal; and
a digital delay device configured to apply a delay to the reference signal;
wherein the phase difference between the first RF signal and the second RF signal is determined using:
a phase difference between the first RF signal and the reference signal, and
a phase difference between the second RF signal and the delayed reference signal.
22. The interferometer of claim 18 , including a memory device configured to store a digitized representation of the first RF signal output of the second switch; and wherein:
the memory device stores a digitized representation of the second RF signal output of the second switch; and
a digital delay is applied to the second RF signal stored by the memory device.
23. A method for determining a direction of arrival of a radio frequency (RF) signal, the method including:
receiving, by a plurality of radio frequency (RF) antennas including a first antenna and a second antenna, an RF signal;
outputting, by the plurality of RF antennas, a plurality of antenna signals including a first antenna signal and a second antenna signal;
receiving, by a first converter that is electrically coupled to the plurality of RF antennas, the second antenna signal;
outputting, by the first converter, an optical signal converted from the second antenna signal;
receiving, by a second converter, the optical signal, wherein the optical signal is received via an optical channel that introduces a delay that is proportional to the length of the optical channel;
outputting, by an RF signal output of the second converter, an optically delayed RF signal that corresponds to the second antenna;
electronically coupling a first switch to a first output of the first antenna to receive the first antenna signal;
after receiving the first antenna signal, electronically coupling the first switch to the RF signal output of the second converter to receive the optically delayed RF signal that corresponds to the second antenna;
receiving, by a direction finding subsystem communicatively coupled to the first switch, the first antenna signal and the optically delayed RF signal that corresponds to the second antenna, and
determining, by the direction finding subsystem, a direction of arrival of the received RF signal using a phase difference between the first antenna signal and the optically delayed RF signal.