Digital beamforming interferometry

• US 9,523,768 B1
• Filed: 09/30/2014
• Issued: 12/20/2016
• Est. Priority Date: 09/30/2014
• Status: Active Grant

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Rincon, Rafael F.
• Primary Examiner(s): Brainard, Timothy A
• Application Number:
  US14/501,456
• Time in Patent Office: 812 Days
• Field of Search: 342/156, 342/25
• US Class Current: 1/1
• CPC Class Codes: G01S 13/9023 combined with interferometric techniques
• CPC Class Codes: G01S 13/904 SAR modes

Abstract

A method according to an illustrative embodiment includes generating first, second, third, and fourth signals. The method also includes transmitting from an antenna, the first signal, and transmitting the antenna, the second signal. The first and second signals are configured such that when the signals are transmitted simultaneously the signals constructively interact to form a first beam signal. The first beam signal has a first look angle. The method also includes transmitting from the antenna the third signal and from the antenna the fourth signal. The third and fourth signals are configured such that when the signals are transmitted simultaneously the signals constructively interact to form a second beam signal. The second beam signal has a second look angle. The method also includes receiving a first and second reflected signals and generating an interferogram utilizing information in the first and second reflected signals.

Claims

1. A method comprising:

generating, by a processor of a computing device, a first signal, a second signal, a third signal, and a fourth signal, wherein each of the first signal, the second signal, the third signal, and the fourth signal have a frequency, a phase, and an amplitude;

transmitting, by the processor, from a first sub-array of a plurality of sub-arrays of an antenna, the first signal;

transmitting, by the processor, from a second sub-array of the antenna, the second signal, wherein a first signal amplitude, a first signal frequency, a first signal phase, a second signal amplitude, a second signal frequency, and a second signal phase are configured such that when the first signal and the second signal are transmitted simultaneously the first signal and the second signal constructively interact to form a first beam signal, and further wherein the first beam signal is configured to have a first look angle;

transmitting, by the processor, from a third sub-array of the antenna, the third signal;

transmitting, by the processor, from a fourth sub-array of the antenna, the fourth signal, wherein a third signal amplitude, a third signal frequency, a third signal phase, a fourth signal amplitude, a fourth signal frequency, and a fourth signal phase are configured such that when the third signal and the fourth signal are transmitted simultaneously the third signal and the fourth signal constructively interact to form a second beam signal, and further wherein the second beam signal is configured to have a second look angle;

receiving a first reflected signal by at least one sub-array of the plurality of sub-arrays of the antenna, wherein the first reflected signal comprises a reflected portion of the first beam signal, and wherein the reflected portion of the first beam signal has been reflected off of a first region within the first look angle;

receiving a second reflected signal by at least one sub-array of the plurality of sub-arrays of the antenna, wherein the second reflected signal comprises a reflected portion of the second beam signal, and wherein the reflected portion of the second beam signal has been reflected off of a second region within the second look angle; and

generating, by the processor, an interferogram utilizing information in the first reflected signal and the second reflected signal.

2. The method of claim 1, wherein the first region and the second region are approximately a single region.

3. The method of claim 2, wherein the antenna is aboard an aircraft or spacecraft, and further wherein the single region comprises a portion of a surface of earth and anything located on the portion of the surface of the earth.

4. The method of claim 3, wherein the single region is a function of the first look angle, the second look angle, and a height from the surface of the earth.

5. The method of claim 2, wherein the single region comprises a plant, water, ice, soil, a man-made structure or object, a human being, an animal, a vehicle, or a road.

6. The method of claim 2, wherein the interferogram indicates relative heights of the single region and anything located on the single region.

7. The method of claim 2, wherein the interferogram indicates a relative velocity of an object within the single region.

8. The method of claim 1, wherein the plurality of sub-arrays of the antenna comprise a phased array configuration.

9. The method of claim 1, wherein each of the plurality of sub-arrays of the antenna comprise antenna elements and further wherein the antenna elements are arranged in a phased array configuration.

10. The method of claim 1, further wherein the first signal and the second signal destructively interact at a third look angle and the third signal and the fourth signal destructively interact at a fourth look angle.

11. The method of claim 10, wherein the third look angle and the fourth look angle are approximately the same and further wherein the first look angle and the second look angle are approximately the same.

12. The method of claim 10, wherein a first lobe of the first beam signal is located within the first look angle and not within the third look angle, and further wherein a first lobe of the second beam signal is located within the second look angle and not within the fourth look angle.

13. The method of claim 12, further comprising controlling the first lobe of the first beam signal and the first lobe of the second beam signal by adjusting the first signal, the second signal, the third signal, and the fourth signal according to a desired predefined first look angle, a desired predefined second look angle, a desired predefined ground swath width that corresponds to the first beam signal and the second beam signal, and a predefined desired sidelobe level.

14. The method of claim 1, further comprising:

generating, by the processor, a fifth signal;

transmitting, by the processor, the fifth signal from a fifth sub-array of the antenna, wherein the fifth signal is transmitted simultaneously with the first signal and the second signal, wherein the first signal, the second signal, and the fifth signal constructively interact to form the first beam signal; and

performing a null-steering procedure to reduce interference with the fifth signal, wherein the fifth signal is weighted to account for the interference.

15. The method of claim 1, wherein the first signal frequency is approximately the same as the second signal frequency, the second signal frequency is different from the third signal frequency, and wherein the third signal frequency is approximately the same as the second frequency.

16. The method of claim 15, wherein the first signal phase is different from the second signal phase, and further wherein a phase difference between the first signal phase and the second signal phase is a function of a physical distance between the first sub-array and the second sub-array, the first signal frequency, and a desired look angle of the first beam signal.

17. The method of claim 1, wherein the first beam signal and the second beam signal are transmitted simultaneously.

18. The method of claim 1, wherein generating the interferogram comprises:

generating a first image from the first reflected signal, wherein the first image is generated by measuring changes in phase of the first reflected signal;

generating a second image from the second reflected signal, wherein the second image is generated by measuring changes in phase of the second reflected signal;

combining the first image and the second image to form the interferogram;

filtering out noise from the interferogram; and

performing a phase unwrap of the interferogram.

19. An apparatus comprising:

a memory;

a processor coupled to the memory; and

a set of instructions stored on the memory and configured to be executed by a processor, wherein the processor is configured to;

generate a first signal, a second signal, a third signal, and a fourth signal, wherein each of the first signal, the second signal, the third signal, and the fourth signal have a frequency, a phase, and an amplitude;

transmit, from a first sub-array of a plurality of sub-arrays of an antenna, the first signal;

transmit, from a second sub-array of the antenna, the second signal, wherein a first signal amplitude, a first signal frequency, a first signal phase, a second signal amplitude, a second signal frequency, and a second signal phase are configured such that when the first signal and the second signal are transmitted simultaneously the first signal and the second signal constructively interact to form a first beam signal, and further wherein the first beam signal is configured to have a first look angle;

transmit, from a third sub-array of the antenna, the third signal;

transmit, from a fourth sub-array of the antenna, the fourth signal, wherein a third signal amplitude, a third signal frequency, a third signal phase, a fourth signal amplitude, a fourth signal frequency, and a fourth signal phase are configured such that when the third signal and the fourth signal are transmitted simultaneously the third signal and the fourth signal constructively interact to form a second beam signal, and further wherein the second beam signal is configured to have a second look angle;

receive a first reflected signal by at least one sub-array of the plurality of sub-arrays of the antenna, wherein the first reflected signal comprises a reflected portion of the first beam signal, and wherein the reflected portion of the first beam signal has been reflected off of a first region within the first look angle;

receive a second reflected signal by at least one sub-array of the plurality of sub-arrays of the antenna, wherein the second reflected signal comprises a reflected portion of the second beam signal, and wherein the reflected portion of the second beam signal has been reflected off of a second region within the second look angle; and

generate an interferogram utilizing information in the first reflected signal and the second reflected signal.

20. A non-transitory computer readable medium having instructions stored thereon that, upon execution by a computing device, cause the computing device to perform the operations comprising:

generating a first signal, a second signal, a third signal, and a fourth signal, wherein each of the first signal, the second signal, the third signal, and the fourth signal have a frequency, a phase, and an amplitude;

transmitting, from a first sub-array of a plurality of sub-arrays of an antenna, the first signal;

transmitting, from a second sub-array of the antenna, the second signal, wherein a first signal amplitude, a first signal frequency, a first signal phase, a second signal amplitude, a second signal frequency, and a second signal phase are configured such that when the first signal and the second signal are transmitted simultaneously the first signal and the second signal constructively interact to form a first beam signal, and further wherein the first beam signal is configured to have a first look angle;

transmitting, from a third sub-array of the antenna, the third signal;

transmitting, from a fourth sub-array of the antenna, the fourth signal, wherein a third signal amplitude, a third signal frequency, a third signal phase, a fourth signal amplitude, a fourth signal frequency, and a fourth signal phase are configured such that when the third signal and the fourth signal are transmitted simultaneously the third signal and the fourth signal constructively interact to form a second beam signal, and further wherein the second beam signal is configured to have a second look angle;

receiving a first reflected signal by at least one sub-array of the plurality of sub-arrays of the antenna, wherein the first reflected signal comprises a reflected portion of the first beam signal, and wherein the reflected portion of the first beam signal has been reflected off of a first region within the first look angle;

receiving a second reflected signal by at least one sub-array of the plurality of sub-arrays of the antenna, wherein the second reflected signal comprises a reflected portion of the second beam signal, and wherein the reflected portion of the second beam signal has been reflected off of a second region within the second look angle; and

generating an interferogram utilizing information in the first reflected signal and the second reflected signal.