Motion compensated synthetic aperture imaging system and methods for imaging

• US 6,970,128 B1
• Filed: 10/06/2004
• Issued: 11/29/2005
• Est. Priority Date: 10/06/2004
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Beylor, Michael R., Dwelly, Wesley H., Adams, Vinh N.
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US10/959,794
• Time in Patent Office: 419 Days
• Field of Search: 342/22, 342/25.R, 342 25 A- 25 F, 342/27, 342/28, 342/59, 342/175, 342/176, 342/179, 342191-197, 34235701-35717, 342/89, 342/90, 342128-147, 342450-465
• US Class Current: 342/25.00F
• CPC Class Codes: G01S 13/888 through wall detection
• CPC Class Codes: G01S 13/9019 Auto-focussing of the SAR signals
• CPC Class Codes: G01S 13/904 SAR modes
• CPC Class Codes: G01S 13/9089 SAR having an irregular aperture
• CPC Class Codes: G01S 5/0247 Determining attitude

Abstract

A see-through-the-wall (STTW) imaging system uses a plurality of geographically separated positioning transmitters to transmit non-interfering positioning signals. An imaging unit generates a synthetic aperture image of a target by compensating for complex movement of the imaging unit using the positioning signals. The imaging unit includes forward and aft positioning antennas to receive at least three of the positioning signals, an imaging antenna to receive radar return signals from the target, and a signal processor to compensate the return signals for position and orientation of the imaging antenna using the positioning signals. The signal processor may construct the synthetic aperture image of a target from the compensated return signals as the imaging unit is moved with respect to the target. The signal processor may determine the position and the orientation of the imaging unit by measuring a relative phase of the positioning signals.

Claims

1. A synthetic aperture radar imaging unit comprising:

forward and aft positioning antennas to receive at least three positioning signals that are transmitted from different locations;

an imaging antenna to receive radar return signals; and

a signal processor to compensate the return signals for position and orientation of the imaging antenna using the positioning signals.

2. The imaging unit of claim 1 wherein the signal processor is to further construct a synthetic aperture radar image of a target from the compensated radar return signals as the imaging unit is moved with respect to the target.

3. The imaging unit of claim 2 wherein the imaging antenna transmits and receives one or more radar frequencies selected to allow the signal processor to generate the image of the target through an obstacle.

4. The imaging unit of claim 3 wherein the forward and the aft positioning antennas are patch antennas and have a separation distance therebetween.

5. The imaging unit of claim 4 further comprising an image classifier to classify the image and provide an image output to a user.

6. The imaging unit of claim 5 wherein the image classifier is to further detect, identify and locate the image of the target either behind, through or within the obstacle.

7. The imaging unit of claim 1 wherein the signal processor is to determine the position and the orientation of the imaging unit by measuring a phase of the positioning signals when received by the forward and aft antennas as the imaging unit is moved with respect to the target.

8. The imaging unit of claim 7 wherein when the positioning signals are phase-locked, the signal processor uses at least three of the positioning signals to determine the position and orientation of the imaging unit.

9. The imaging unit of claim 7 wherein the signal processor determines the position of the imaging unit based on a phase history of corresponding positioning signals received by the forward and aft antennas as the imaging unit is moved with respect to the target.

10. The imaging unit of claim 9 wherein the signal processor determines the orientation based on phase differences between the return signals received by the forward and aft antennas from corresponding positioning signals.

11. The imaging unit of claim 7 wherein a transmission and reception direction of the imaging antenna is positionally fixed with respect to the locations of the forward and aft positioning antennas allowing a relative pitch and yaw of the imaging antenna to be determined from phases of the positioning signals received through the forward and aft positioning antennas.

12. The imaging unit of claim 1 wherein the positioning signals are generated by corresponding positioning transmitters separate from the imaging unit, the positioning transmitters being separated from each other in azimuth, and

wherein at least one of the positioning transmitters is separated in elevation with respect to the other positioning transmitters.

13. The imaging unit of claim 12 wherein the positioning signals comprise substantially non-interfering signals.

14. The imaging unit of claim 13 wherein the positioning signals comprise carrier-wave (CW) tones.

15. The imaging unit of claim 13 wherein the positioning signals comprise at least one of time-division multiplexed signals, code-division multiplexed signals and frequency division multiplexed signals.

16. The imaging unit of claim 12 wherein the signal processor is to perform a calibration procedure to determine an initial position and orientation, and

wherein positions and orientations determined by the signal processor as the imaging unit is moved are relative positions and orientations based on the initial position and orientation.

17. The imaging unit of claim 1 further comprising:

multiplexing circuitry to multiplex the positioning signals received from the forward and aft positioning antennas with down-converted imaging return signals;

an analog-to-digital (A/D) converter to generate digital samples from the interleaved signals;

fast Fourier transform (FFT) circuitry within the signal processor to generate frequency domain samples from the digital samples;

signal processing circuitry within the signal processor to determine relative phase of each positioning signal based on the frequency domain samples to determine the position and orientation of the unit; and

image generating circuitry within the signal processor to generate a synthetic aperture radar image of a target by compensating the radar return signals for the orientation and position of the imaging unit.

18. A see-through-the-wall (STTW) synthetic aperture radar imaging system comprising:

a plurality of geographically separated positioning transmitters to transmit non-interfering positioning signals; and

a synthetic aperture radar imaging unit to generate a synthetic aperture radar image of a target based on receipt of radar return signals, wherein the imaging unit is to compensate the radar return signals for movement of the imaging unit using the positioning signals.

19. The system of claim 18 wherein the imaging unit comprises

forward and aft positioning antennas to receive at least three of the positioning signals;

an imaging antenna to receive radar return signals from the target; and

a signal processor to compensate the radar return signals for position and orientation of the imaging antenna using the positioning signals.

20. The system of claim 19 wherein the signal processor is to further construct a synthetic aperture radar image of the target from the compensated radar return signals as the imaging unit is moved with respect to the target,

wherein the imaging antenna transmits and receives one or more radar frequencies selected to allow the signal processor to generate the image of the target through an obstacle, and

wherein the signal processor is to determine the position and the orientation of the imaging unit by measuring a phase of the positioning signals when received by the forward and aft antennas as the imaging unit is moved with respect to the target.

21. The system of claim 20 wherein the positioning signals are generated by corresponding positioning transmitters that are separated in azimuth,

wherein at least one of the positioning transmitters is separated in elevation with respect to the other positioning transmitters, and

wherein the positioning signals comprise carrier-wave (CW) tones.

22. A method of synthetic aperture radar imaging a target comprising:

receiving at least three positioning signals that are separately transmitted from different locations, the positioning signals being received through forward and aft positioning antennas;

receiving radar return signals through an imaging antenna; and

compensating the return signals for position and orientation of the imaging antenna using the positioning signals.

23. The method of claim 22 further comprising constructing a synthetic aperture radar image of a target from the compensated radar return signals as the imaging antenna is moved with respect to the target.

24. The method of claim 23 further comprising transmitting and receiving one or more radar frequencies corresponding to the radar return signals with the imaging antenna, the one or more radar frequencies selected for generating the image of the target through an obstacle.

25. The method of claim 24 further comprising classifying the image and providing an image output.

26. The method of claim 25 further comprising detecting, identifying and locating the image of the target either behind, through or within the obstacle.

27. The method of claim 22 further comprising determining a relative position and orientation of the imaging antenna by measuring a phase of the positioning signals when received by the forward and aft antennas as the imaging antenna is moved with respect to the target.

28. The method of claim 27 wherein when the positioning signals are phase-locked, the method comprises using at least three of the positioning signals to determine the relative position and orientation of the imaging antenna.

29. The method of claim 27 wherein determining comprises determining the relative position of the imaging antenna based on a phase history of corresponding positioning signals received by the forward and aft antennas as the imaging antenna is moved with respect to the target.

30. The method of claim 29 wherein determining further comprises determining the orientation based on phase differences between the return signals received by the forward and aft antennas from corresponding positioning signals.

31. The method of claim 22 wherein the positioning signals are generated by corresponding positioning transmitters that are separated in azimuth, and

wherein at least one of the positioning transmitters is separated in elevation with respect to the other positioning transmitters.

32. The method of claim 31 wherein the positioning signals comprise carrier-wave (CW) tones.

33. The method of claim 31 further comprising:

performing a calibration procedure to determine an initial position and orientation with respect to the positioning transmitters; and

determining relative positions and orientations of the imaging antenna as the imaging antenna is moved based on the initial position and orientation.