Moving receive beam method and apparatus for synthetic aperture radar

• US 6,175,326 B1
• Filed: 06/29/1998
• Issued: 01/16/2001
• Est. Priority Date: 06/29/1998
• Status: Expired due to Fees

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Kare, Jordin T.
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US09/106,406
• Time in Patent Office: 932 Days
• Field of Search: 342/25, 342/371, 342/157, 367/123
• US Class Current: 342/25.00R
• CPC Class Codes: G01S 13/904 SAR modes
• CPC Class Codes: H01Q 3/26 varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture H01Q3/12, H01Q3/22, H01Q3/24 take precedence
• CPC Class Codes: H01Q 3/2658 Phased-array fed focussing structure

Abstract

A method and apparatus for improving the performance of Synthetic Aperture Radar (SAR) systems by reducing the effect of “edge losses” associated with nonuniform receiver antenna gain. By moving the receiver antenna pattern in synchrony with the apparent motion of the transmitted pulse along the ground, the maximum available receiver antenna gain can be used at all times. Also, the receiver antenna gain for range-ambiguous return signals may be reduced, in some cases, by a large factor. The beam motion can be implemented by real-time adjustment of phase shifters in an electronically-steered phased-array antenna or by electronic switching of feed horns in a reflector antenna system.

Claims

1. In a Synthetic Aperture Radar the improvement comprising;

a receiver antenna having a receiver antenna pattern, and means for moving the receiver antenna pattern in synchrony with the apparent motion of the transmitted pulse along the ground thus at least reducing the edge losses associated with nonuniform receiver antenna gain,

said means for moving the receiver antenna pattern including means selected from the group consisting of means for real-time adjustment of phase shifters in an electronically-steered phased-array antenna, means for electronic switching of feed horns in a reflector antenna system, and means for electronic switching among two or more fixed delay networks, or fixed ports on a single delay network, connected to a phased array antenna.

2. A method for improving the performance of Synthetic Aperture Radar systems comprising:

providing a receiver antenna pattern, and

moving the receiver antenna pattern in synchrony with apparent motion of the transmitted pulse along the ground thus at least reducing the effect of edge losses associated with nonuniform receiver antenna gain.

3. The method of claim 2, wherein moving the receiver antenna pattern in synchrony with apparent motion of the transmitted pulse along the ground additionally produces the maximum available receiver antenna gain.

4. The method of claim 2, additionally including adjusting the position of the receiver antenna pattern for reducing the receiver antenna gain for range-ambiguous signals.

5. The method of claim 2, wherein moving the receiver antenna pattern is implemented by real-time adjustment of phase shifters in an electronically-steered phased-array antenna.

6. The method of claim 2, wherein moving the receiver antenna pattern is implemented by electronic switching of feed horns in a reflector antenna system or a spaced-fed phased array.

7. The method of claim 2, wherein moving the receiver antenna pattern is implemented by electronic switching among two or more fixed delay networks, or fixed ports on a single delay network, connected to a phased array antenna.

8. The method of claim 2, wherein moving the receiver antenna pattern is carried out by electronically steering a receive antenna in the elevation direction over an angle equal to the angular width of the useful part of the transmitter beam.

9. The method of claim 8, additionally including providing approximate timing and synchronizing circuitry such that the center of the receiver antenna pattern is moved in synchrony with the apparent position of the illuminated portion of the target area.

10. The method of claim 8, wherein the steering is implemented by continuous rapid adjustment of the phase shift or time delay networks of a phased-array antenna.

11. The method of claim 8, wherein the steering is implemented by rapidly switching among several fixed phase shift or time delay networks.

12. The method of claim 8, wherein the steering is implemented by rapidly switching among several fixed ports on a single delay network connected to a phased array antenna.

13. The method of claim 12, wherein the single delay network comprises a Blass feed system.

14. The method of claim 8, wherein the steering is implemented by switching among several closely-spaced fixed feed horns for a reflector antenna or a space-fed phased array.

15. The method of claim 8, wherein the steering is implemented by rapid mechanical motion of a reflector or other beam-steering component.

16. The method of claim 9, additionally including providing a mechanism for measuring the signal strength at multiple feed networks or multiple ports of a single feed network, and automatically selecting the port which provides maximum instantaneous gain.

17. The method of claim 2, wherein the transmitted signal varies in frequency as a function of time, and the position of the receiver antenna pattern is made a function of the frequency of the received signal, such that the peak of the receiver antenna gain at a particular frequency is aligned with the apparent position of the point on the ground illuminated by the corresponding frequency component of the transmitted pulse.