Synthetic aperture radar using alternating beams and associated methods

Patent metadata

Field	Value
Publication number	US-12596191-B2
Application number	US-202318179721-A
Country	US
Kind code	B2
Filing date	Mar 7, 2023
Priority date	Mar 7, 2023
Publication date	Apr 7, 2026
Grant date	Apr 7, 2026

Abstract

A synthetic aperture radar (SAR) for a flight vehicle may include an elongate phased array antenna oriented with a long axis in an elevation direction. The elevation direction is normal to a direction of flight of the flight vehicle. A transmitter is coupled to the elongate phased array antenna, and a receiver is coupled to the elongate phased array antenna. A controller is coupled to the transmitter and receiver and is configured to generate temporally alternating sets of receive beams for respective swaths to be used to form a SAR image across a surface below the flight vehicle. The same center frequency is used to create consistent SARs for all swaths, allowing for coherent combination between subsequent passes over the same swath.

First claim

The invention claimed is:

1 . A synthetic aperture radar (SAR) for a flight vehicle, the SAR comprising: an elongate phased array antenna oriented with a long axis in an elevation direction, the elevation direction being normal to a direction of flight of the flight vehicle, the elongate phased array antenna comprising a plurality of steerable elements forming a one-dimensional array along the long axis; a transmitter coupled to the elongate phased array antenna; a receiver coupled to the elongate phased array antenna; and a controller configured to cooperate with the transmitter and receiver to generate temporally alternating sets of receive beams for respective first and second swaths to be used to form a SAR image across a surface below the flight vehicle, the alternating sets of receive beams comprising a first set of receive beams for the first swath and comprising a plurality of first subswaths, with adjacent first subswaths being separated by a respective first gap, and a second set of receive beams for the second swath and comprising a plurality of second subswaths, with adjacent second subswaths being separated by a respective second gap, wherein the plurality of second subswaths overlap with the respective first gaps in the plurality of first subswaths.

2 . The SAR according to claim 1 wherein the controller is configured to operate the receiver to receive the first set of receive beams before receiving the second set of receive beams.

3 . The SAR according to claim 1 wherein the controller is configured to operate the transmitter to: generate pulses at a first pulse repetition frequency (PRF) to be received by the first set of receive beams; and generate pulses at a second PRF to be received by the second set of receive beams; the second PRF being higher than the first PRF to shift the respective second gaps in the second set of receive-3-beams to overlap the plurality of first subswaths in the first set of receive beams.

4 . The SAR according to claim 1 wherein the controller is configured to operate the transmitter to transmit during the respective first and second gaps in the first and second sets of receive beams.

5 . The SAR according to claim 1 wherein the elongate phased array antenna comprises M adjustable elements positioned along the long axis, the receiver comprises N channel inputs, the first and second set of receive beams each comprise N beams, and the plurality of first and second subswaths each comprise N subswaths, the SAR further comprising: a beam forming network (BFN) comprising M inputs coupled to the M adjustable elements in the elongate phased array antenna and N outputs coupled to the N channel inputs in the receiver, and configured to adjust the M adjustable elements for forming the N receive beams in the first and second swaths, with each channel input in the receiver corresponding to a respective subswath in the first set of receive beams and to a respective subswath in the second set of receive beams.

6 . The SAR according to claim 5 further comprising a distribution network comprising M outputs coupled to the M adjustable elements in the elongate phased array antenna and an input coupled to an output of the transmitter, and configured to spread out the single beam by adjusting the M adjustable elements.

7 . The SAR according to claim 1 wherein the transmitter is configured to operate at a fixed center frequency.

8 . The SAR according to claim 1 wherein the elongate phased array antenna has a short axis oriented in an azimuth direction, and is configured to transmit a single beam across the respective swaths in the same azimuth direction.

9 . The SAR according to claim 1 wherein the elongate phased array antenna comprises a reflector oriented with a long axis in the elevation direction opposite the plurality of steerable elements.

10 . The SAR according to claim 1 wherein the controller is configured to transmit data to a remote image processor to form the SAR image across the surface below the flight vehicle.

11 . A synthetic aperture radar (SAR) for a flight vehicle, the SAR comprising: an elongate phased array antenna oriented with a long axis in an elevation direction, the elevation direction being normal to a direction of flight of the flight vehicle, the elongate phased array antenna comprising a plurality of steerable elements forming a one-dimensional array along the long axis; a transmitter coupled to the elongate phased array antenna; a receiver coupled to the elongate phased array antenna; and a controller coupled to the transmitter and receiver and configured to generate a first set of receive beams for a first swath and comprising a plurality of first subswaths, with adjacent first subswaths being separated by a respective first gap; generate a second set of receive beams for a second swath and comprising a plurality of second subswaths, with adjacent second subswaths being separated by a respective second gap, and with the plurality of second subswaths overlapping with the respective first gaps in the plurality of first subswaths; the first and second set of receive beams to be used to form a SAR image across a surface below the flight vehicle; and operate the transmitter to transmit during the respective first and second gaps in the first and second sets of receive beams.

12 . The SAR according to claim 11 wherein the controller is configured to operate the receiver to receive the first set of receive beams before receiving the second set of receive beams.

13 . The SAR according to claim 11 wherein the controller is configured to operate the transmitter to generate pulses at a first pulse repetition frequency (PRF) to be received by the first set of receive beams; and generate pulses at a second PRF to be received by the second set of receive beams; the second PRF being higher than the first PRF to shift the respective second gaps in the second set of receive beams to overlap the plurality of first subswaths in the first set of receive beams.

14 . The SAR according to claim 11 wherein the transmitter is configured to operate at a fixed center frequency.

15 . The SAR according to claim 11 wherein the elongate phased array antenna has a short axis oriented in an azimuth direction, and is configured to transmit a single beam across the respective swaths in the same azimuth direction.

16 . The SAR according to claim 11 wherein the elongate phased array antenna comprises a reflector oriented with a long axis in the elevation direction opposite the plurality of steerable elements.

17 . A method for operating a synthetic aperture radar (SAR) for a flight vehicle, the SAR comprising an elongate phased array antenna oriented with a long axis in an elevation direction, the elevation direction being normal to a direction of flight of the flight vehicle, the elongate phased array antenna comprising a plurality of steerable elements forming a one-dimensional array along the long axis, a transmitter coupled to the elongate phased array antenna, and a receiver coupled to the elongate phased array antenna, the method comprising: operating a controller coupled to the transmitter and receiver to generate temporally alternating sets of receive beams for respective first and second swaths to be used to form a SAR image across a surface below the flight vehicle, the alternating sets of receive beams comprising a first set of receive beams for the first swath and comprising a plurality of first subswaths, with adjacent first subswaths being separated by a respective first gap, and a second set of receive beams for the second swa

Assignees

• Eagle Tech Llc

Inventors

• Lieb Donald A
• Riley Robert
• Taylor Robert M
• Speed Kerry T
• Durham Timothy E

Classifications

• G01S2013/0245

  Radar with phased array antenna · CPC title

• G01S13/9054

  Stripmap mode · CPC title

• G01S13/225

  with cyclic repetition of a non-uniform pulse sequence, e.g. staggered PRF · CPC title

• G01S13/9056 Primary

  Scan SAR mode · CPC title

• G01S13/904 Primary

  SAR modes · CPC title