Sensing signals that include radio frequency pulses
In a general aspect, a radar system includes a vapor cell sensor system and a radio frequency (RF) optic. The vapor cell sensor system includes a vapor cell sensor, and the RF optic is configured to direct an RF field onto the vapor cell sensor. The RF field includes one or more RF pulses that define a radar signal. The radar system also includes a signal processing system configured to perform operations that include generating a digital signal based on a signal from the vapor cell sensor system. The digital signal represents a measured response of the vapor to the RF field over a time period. The operations also include applying a matched filter to the digital signal to generate a filtered signal and processing the filtered signal to determine properties of the RF field sensed by the vapor cell sensor over the time period.
1. A radar system, comprising:
a vapor cell sensor system comprising a vapor cell sensor;
a radio frequency (RF) optic configured to direct an RF field onto the vapor cell sensor, the RF field comprising one or more RF pulses that define a radar signal; and
a signal processing system configured to perform operations that comprise:
generating a digital signal based on a signal from the vapor cell sensor system, the digital signal representing a measured response of a vapor of the vapor cell sensor to the RF field over a time period,
applying a matched filter to the digital signal to generate a filtered signal, the filtered signal generated based on a comparison of the digital signal with a response template, the response template representing a known response of the vapor to a target RF pulse, and
processing the filtered signal to determine properties of the RF field sensed by the vapor cell sensor over the time period.
2. The radar system of claim 1 , wherein processing the filtered signal comprises detecting a sequence of RF pulses.
3. The radar system of claim 2 , wherein the signal processing system is configured to identify an aircraft as a source of the sequence of RF pulses.
4. The radar system of claim 1 , wherein the operations comprise:
determining at least one of a start time, a duration, or an amplitude of an RF pulse sensed by the vapor cell sensor in the time period.
5. The radar system of claim 1 , wherein the response template is based on a plurality of reference RF pulses generated by an RF source over a reference time period, the plurality of reference RF pulses sharing a common pulse shape.
6. The radar system of claim 1 , wherein the response template is based on a computer simulation of a response of the vapor to the target RF pulse.
7. The radar system of claim 1 ,
wherein the response template is a first response template that represents a first known response of the vapor to a first type of target RF pulse; and
wherein the filtered signal is generated based on a comparison of the digital signal with:
the first response template, and
a second response template that represents a second known response of the vapor to a second type of target RF pulse.
8. The radar system of claim 7 , wherein the first and second types of target RF pulses have different, non-overlapping ranges of field strength.
9. The radar system of claim 1 , wherein the vapor comprises a vapor of Group IA atoms.
10. The radar system of claim 1 , wherein the vapor cell sensor system comprises a laser system configured to generate beams of light that pass through the vapor of the vapor cell sensor, the beams of light comprising a probe beam of light.
11. The radar system of claim 10 , wherein the signal from the vapor cell sensor system is based on at least one of an amplitude, a polarization, or a phase of the probe beam of light.
12. The radar system of claim 1 ,
wherein the vapor cell sensor system comprises an optical detector and the signal from the vapor cell sensor system is a detector signal generated by the optical detector; and
wherein the operations comprise receiving the detector signal at the signal processing system over the time period, the detector signal based on a probe beam of light that passes through a vapor of the vapor cell sensor.
13. A method of operating a radar system, comprising:
directing a radio frequency (RF) field onto a vapor cell sensor of a vapor cell sensor system, the vapor cell sensor comprising a vapor, the RF field comprising one or more RF pulses that define a radar signal; and
by operation of the signal processing system:
generating a digital signal based on a signal from the vapor cell sensor system, the digital signal representing a measured response of the vapor to the RF field over a time period,
applying a matched filter to the digital signal to generate a filtered signal, the filtered signal generated based on a comparison of the digital signal with a response template, the response template representing a known response of the vapor to a target RF pulse, and
processing the filtered signal to determine properties of the RF field experienced by the vapor over the time period.
14. The method of claim 13 , wherein directing the RF field comprises:
directing, by operation of a dish, the RF field onto a focal point of the dish, the vapor cell sensor being disposed at the focal point of the dish.
15. The method of claim 13 , wherein directing the RF field comprises:
directing the RF field onto the vapor cell sensor by operation of an RF lens.
16. The method of claim 13 , wherein processing the filtered signal comprises detecting a sequence of RF pulses.
17. The method of claim 16 , comprising:
identifying, by operation of the signal processing system, an aircraft as a source of the sequence of RF pulses.
18. The method of claim 13 , wherein applying a matched filter comprises applying a convolution function to the digital signal and the response template to generate the filtered signal.
19. The method of claim 18 , wherein a period for the convolution function is greater than an expected duration of an RF pulse of the RF field.
20. The method of claim 13 , comprising determining at least one of a start time, a duration, or an amplitude of an RF pulse sensed by the vapor cell sensor in the time period.
21. The method of claim 13 , comprising:
receiving reference pulses of the RF field at the vapor cell sensor over a reference time period, the reference pulses sharing a common pulse shape; and
generating, by operation of the signal processing system, the response template based on the digital signal associated with the reference pulses over the reference time period.
22. The method of claim 21 , wherein generating the pulse template comprises:
determining, for each reference pulse, a pulse shape based on a portion of the digital signal associated with a duration of the reference pulse; and
averaging the pulse shapes to generate the response template.
23. The method of claim 13 , comprising:
generating the response template based on a computer simulation of a response of the vapor to the target RF pulse.
24. The method of claim 13 ,
wherein the vapor cell sensor system comprises a laser system;
wherein the method comprises:
generating beams of light by operation of the laser system, and
passing the beams of light through the vapor in the vapor cell sensor, the beams of light comprising a probe beam of light; and
wherein the signal from the vapor cell sensor system is based on the probe beam of light after the probe beam has passed through the vapor.
25. The method of claim 24 , wherein directing the RF field comprises:
altering, by operation of the RF field on the vapor, an optical transmission the probe beam of light through the vapor as the beams of light pass through the vapor.
26. The method of claim 13 , wherein the signal from the vapor cell sensor system is based on at least one of an amplitude, a polarization, or a phase of the probe beam of light.
27. The method of claim 13 ,
wherein the vapor cell sensor system comprises an optical detector;
wherein the signal from the vapor cell sensor system is a detector signal from the optical detector, the detector signal based on the probe beam of light after the probe beam has passed through the vapor; and
wherein the method comprises receiving the detector signal at the signal processing system over the time period.
28. The method of claim 13 , wherein the vapor comprises a vapor of Group IA atoms.
29. The method of claim 13 ,
wherein the response template is a first response template that represents a first known response of the vapor to a first type of target RF pulse; and
wherein the filtered signal is generated based on a comparison of the digital signal with:
the first response template, and
a second response template that represents a second known response of the vapor to a second type of target RF pulse.
30. The method of claim 29 , wherein the first and second types of target RF pulses have different, non-overlapping ranges of field strength.