Multi-channel split-swath (MCSS) synthetic aperture radar (SAR)

Patent metadata

Field	Value
Publication number	US-11262446-B2
Application number	US-201916282763-A
Country	US
Kind code	B2
Filing date	Feb 22, 2019
Priority date	Feb 22, 2019
Publication date	Mar 1, 2022
Grant date	Mar 1, 2022

Abstract

A synthetic aperture radar (SAR) generates concurrent first radar pulses in first frequency channels. The SAR transmits, and receives returns of, the concurrent first radar pulses by first antenna feeds that form first beams in the first frequency channels and that are directed to respective first subswaths of a swath on the Earth separated by subswath gaps. The SAR generates concurrent second radar pulses in second frequency channels. The SAR transmits, and receives returns of, the concurrent second radar pulses by second antenna feeds configured to form second beams in the second frequency channels and that are directed to respective second subswaths of the swath on the Earth and that coincide with the subswath gaps. The SAR processes the returns of the first radar pulses from the first subswaths and the returns of the second radar pulses from the second subswaths to form a SAR image contiguous across the swath.

First claim

What is claimed is:

1. A method performed by a synthetic aperture radar (SAR) on a flight vehicle, the SAR including a transmit/receive (T/R) switch and a subswath switch to selectively couple the T/R switch to first antenna feeds over a first radio frequency (RF) path or to second antenna feeds over a second RF path, comprising:
generating concurrent first radar pulses in respective first frequency channels;
first controlling the subswath switch to couple the T/R switch to the first antenna feeds to perform transmitting, and receiving returns of, respective ones of the concurrent first radar pulses by respective ones of the first antenna feeds configured with respective first feed horns that are fed by RF energy to form respective first beams in the respective first frequency channels, the respective ones of the first antenna feeds arranged such that they each have a physical separation that causes the respective first beams to be directed to respective first subswaths of a swath on the Earth separated one from the next by respective subswath gaps;
generating concurrent second radar pulses in respective second frequency channels;
second controlling the subswath switch to couple the T/R switch to the second antenna feeds to perform transmitting, and receiving returns of, respective ones of the concurrent second radar pulses by respective ones of the second antenna feeds configured with respective second feed horns that are fed by RF energy to form respective second beams in the respective second frequency channels, the respective ones of the second antenna feeds arranged such that they each have a physical separation that causes the respective second beams to be directed to respective second subswaths of the swath on the Earth separated one from the next to coincide with the subswath gaps; and
performing SAR processing on the returns of the first radar pulses from the first subswaths and the returns of the second radar pulses from the second subswaths to form a SAR image that is contiguous across the swath.

2. The method of claim 1 , wherein:
the generating the concurrent first radar pulses includes generating a first train of the concurrent first radar pulses at a first pulse repetition frequency (PRF); and
the generating the concurrent second radar pulses includes generating a second train of the concurrent second radar pulses at a second PRF.

3. The method of claim 2 , wherein the first PRF and the second PRF are different and are configured with respect to each other such that the second subswaths coincide with the subswath gaps.

4. The method of claim 3 , further comprising:
during a first time period, performing first controlling and performing the transmitting, and receiving returns of, the concurrent first radar pulses; and
during a second time period that is offset in time from the first time period, performing second controlling and performing the transmitting, and receiving returns of, the concurrent second radar pulses.

5. The method of claim 2 , wherein:
the generating the first train of the concurrent first radar pulses includes generating alternating horizontally polarized (H) and vertically polarized (V) concurrent first radar pulses;
the transmitting, and receiving returns of, the concurrent first radar pulses includes transmitting, and receiving returns of, the alternating H and V concurrent first radar pulses; and
the performing SAR processing includes performing SAR processing on the returns of the alternating H and V concurrent first radar pulses, and the returns of the concurrent second radar pulses to form the SAR image.

6. The method of claim 5 , wherein:
the generating the second train of the concurrent second radar pulses includes generating alternating H and V concurrent second radar pulses;
the transmitting, and receiving returns of, the concurrent second radar pulses includes transmitting, and receiving returns of, the alternating H and V concurrent second radar pulses; and
the performing SAR processing further includes performing SAR processing on the returns of the alternating H and V concurrent first radar pulses, and the returns of the alternating H and V concurrent second radar pulses.

7. The method of claim 1 , wherein the first frequency channels are non-overlapping frequency channels and the second frequency channels are non-overlapping frequency channels.

8. The method of claim 7 , wherein the first frequency channels and the second frequency channels are the same.

9. The method of claim 1 , wherein the concurrent first radar pulses are concurrent chirps and the concurrent second radar pulse are concurrent chirps.

10. The method of claim 1 , further comprising:
forming the respective first beams as a set of first elevation beams that are positionally offset from each other; and
forming the respective second beams as a set of second elevation beams that are positionally offset with respect to each other and with respect to the first elevation beams.

11. A synthetic aperture radar (SAR) for a flight vehicle, comprising:
first antenna feeds and second antenna feeds;
a transmit/receive (T/R) switch and a subswath switch to selectively couple the T/R switch to the first antenna feeds over a first radio frequency (RF) path or to the second antenna feeds over a second RF path; and
a controller coupled to the T/R switch and the subswath switch and configured to generate concurrent first radar pulses in respective first frequency channels, and to generate concurrent second radar pulses in respective second frequency channels;
wherein the controller is configured to control the first subswath switch to couple the T/R switch to the first antenna feeds such that respective first feed horns of the first antenna feeds are fed by RF energy to form respective first beams to transmit, and receive returns of, respective ones of the concurrent first radar pulses by the respective ones of the first beams in the respective first frequency channels, the first antenna feeds arranged such that they each have a physical separation that causes the respective first beams to be directed in elevation to respective first subswaths of a swath on the Earth separated one from the next by respective subswath gaps;
wherein the controller is configured to control the first subswath switch to couple the T/R switch to the second antenna feeds such that respective second feed horns of the second antenna feeds are fed by RF energy to form respective second beams to transmit, and receive returns of, respective ones of the concurrent second radar pulses by the respective second beams in the respective second frequency channels, the second antenna feeds arranged such that they each have a physical separation that causes the respective second beams to be directed in elevation to respective second subswaths of the swath on the Earth separated one from the next to coincide with the subswath gaps; and
wherein the controller is configured to perform SAR processing on the returns of the concurrent first radar pulses from the first subswaths and the returns of the concurrent second radar pulses from the second subswaths to form a SAR image contiguous across the swath.

12. The SAR of claim 11 , wherein the controller is configured to:
generate the concurrent first radar pulses to include a first train of the concurrent first radar pulses at a first pulse repetition frequency (PRF); and

generate the concurrent second radar pulses to include a second train of the concurrent second radar pulses at a second PRF.

13. The SAR of claim 12 , wherein the first PRF and the second PRF are different and configured with respect to each other to ensure

Assignees

• Eagle Tech Llc

Inventors

• Speed Kerry Timothy
• Lieb Donald A
• Durham Timothy Earl
• Taylor Robert M

Classifications

• G01S13/9076 Primary

  Polarimetric features in SAR · CPC title

• G01S13/227

  with repetitive trains of uniform pulse sequences, each sequence having a different pulse repetition frequency · CPC title

• G01S13/9056

  Scan SAR mode · CPC title

• G01S13/90 Primary

  using synthetic aperture techniques {, e.g. synthetic aperture radar [SAR] techniques} · CPC title

• G01S13/26

  wherein the transmitted pulses use a frequency- or phase-modulated carrier wave · CPC title