SYSTEM AND METHOD FOR BISTATIC SAR IMAGE GENERATION WITH PHASE COMPENSATION

• US 20030151540A1
• Filed: 02/12/2002
• Published: 08/14/2003
• Est. Priority Date: 02/12/2002
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Faulkner, David A.
• Granted Patent: US 6,608,584 B1
• Time in Patent Office: Days
• US Class Current: 342/25R
• CPC Class Codes: G01S 13/003 Bistatic radar systems; Multistatic radar systems
• CPC Class Codes: G01S 13/904 SAR modes
• CPC Class Codes: G01S 13/9058 Bistatic or multistatic SAR
• CPC Class Codes: G01S 13/9092 combined with monopulse techniques

Abstract

A method and bistatic synthetic aperture radar (SAR) imaging system generate an image of a target area without knowledge of the position or velocity of the illuminator. The system includes an illuminator to illuminate a target area with a null-monopulse radiation pattern interleaved with a sum radiation pattern. The illuminator adjusts the phase terms of the sum radiation pattern to maintain a static electromagnetic field pattern at the target area. A receiver receives the radiation patterns reflected from the target area and generates phase compensation terms by correlating a measured electromagnetic vector field with the known static electromagnetic vector field. The phase compensation terms are used to generate an image of the target area.

Claims

1. A bistatic synthetic aperture radar (SAR) imaging system comprising:

an illuminator to illuminate a target area with a null-monopulse radiation pattern and a sum radiation pattern, wherein phase terms of the sum radiation pattern are adjusted to maintain a static electromagnetic vector field at the target area; and

a receiver to receive the radiation patterns reflected from the target area, to generate phase compensation terms by correlating a measured electromagnetic vector field with the static electromagnetic vector field, and to generate an image of the target area using the phase compensation terms.

2. The system of claim 1 wherein the illuminator adjusts the phase terms of the of the sum radiation pattern to compensate for an aspect angle of the illuminator relative to the target area.

3. The system of claim 1 wherein the receiver correlates the measured electromagnetic vector field with the static electromagnetic vector field to generate a two-dimensional phase compensation matrix comprised of phase compensation terms, the receiver adjusting phase terms of the received sum radiation pattern with the phase compensation terms to generate a bistatic SAR image of the target area.

4. The system of claim 1 wherein the illuminator observes energy reflected from the target area of the null-monopulse radiation pattern and the sum radiation pattern to maintain the static electromagnetic vector field at the target area, vectors of the vector field being determined from a ratio of the reflected null-monopulse radiation pattern and the reflected sum radiation pattern.

5. The system of claim 4 wherein the illuminator illuminates the target area with an illuminating antenna and also observes reflected energy through the illuminating antenna.

6. The system of claim 1 wherein the illuminator interleaves the null-monopulse radiation pattern with the sum radiation pattern.

7. The system of claim 1 wherein the target area is on a surface of Earth and the illuminator is moving substantially in a direction orthogonal to the target area.

8. The system of claim 7 wherein the illuminator is one of either an aircraft or a satellite.

9. The system of claim 1 wherein the receiver is stationary with respect to the target area.

10. The system of claim 1 wherein the receiver is moving substantially in a direction towards the target area.

11. The system of claim 10 wherein the receiver is a missile having vectors of the static electromagnetic vector field stored therein.

12. The system of claim 1 wherein the receiver is further configured to locate a target within the target area based on the generated image of the target area.

13. The system of claim 1 wherein the illuminator transmits the radiation patterns with a quadrant feed antenna.

14. A method of generating a bistatic SAR image of a target area comprising:

at a moving illuminator,

illuminating a target area with a null-monopulse radiation pattern and a sum radiation pattern; and

adjusting the phase terms of the sum radiation pattern to maintain a static electromagnetic vector field pattern at the target area,

and at a receiver,

generating phase compensation terms to adjust phase terms by correlating a measured electromagnetic vector field pattern with the static electromagnetic vector field pattern; and

generating an image of the target area using the phase compensation terms.

15. The method of claim 14 wherein a receiver is separately located from the illuminator, the method further comprises:

at the illuminator, adjusting the phase terms of the of the sum radiation pattern to compensate for an aspect angle of the illuminator relative to the target area.

16. The method of claim 14 wherein generating the phase compensation terms comprises correlating the measured electromagnetic vector field pattern with the static electromagnetic vector field pattern to generate a two-dimensional phase compensation matrix comprised of phase compensation terms, the receiver using the matrix to generate a bistatic SAR image of the target area.

17. The method of claim 14 further comprising observing, by the illuminator, energy reflected from the target area to maintain the static electromagnetic vector field pattern at the target area, vectors of the vector field being determined from a ratio of the reflected radiation patterns.

18. The method of claim 14 wherein illuminating comprises interleaving the null-monopulse radiation pattern with the sum radiation pattern.

19. The method of claim 14 wherein the target area is on a surface of Earth and the illuminator is moving substantially in a direction orthogonal to the target area.

20. A receiver for generating a bistatic synthetic aperture radar (SAR) image of a target area comprising:

an antenna to receive radiation patterns reflected from the target area; and

a processing element to generate phase compensation terms by correlating a measured electromagnetic vector field with a static electromagnetic vector field, and to generate an image of the target area using the phase compensation terms.

21. The receiver of claim 20 further comprising a memory to store components of the static electromagnetic vector field.

22. The receiver of claim 21 wherein an illuminator illuminates the target area with a null-monopulse radiation pattern interleaved with a sum radiation pattern, and dynamically adjusts the phase terms of the sum radiation pattern to maintain the static electromagnetic vector field at the target area.