Method and apparatus for calibrating an electronically scanned reflector

• US 6,320,538 B1
• Filed: 04/07/2000
• Issued: 11/20/2001
• Est. Priority Date: 04/07/2000
• Status: Expired due to Term

• Current Assignee: BAE Systems Space & Mission Systems Incorporated (BAE Systems Plc)
• Original Assignee: Ball Aerospace & Technologies Corporation (Ball Corporation)
• Inventors: Lalezari, Farzin, Kelly, P. Keith
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/545,226
• Time in Patent Office: 592 Days
• Field of Search: 342/368, 342/371, 342/174, 342/5
• US Class Current: 342/371
• CPC Class Codes: H01Q 25/007 using two or more primary active elements in the focal region of a focusing device for operation on different wavebands H01Q5/22
• CPC Class Codes: H01Q 3/267 Phased-array testing or checking devices

Abstract

A method an apparatus for calibrating an electronically scanned reflector (ESR) antenna to compensate for mechanical distortions in a reflector and feed thereof first determines displacement values for a multitude of points on the reflector and the feed. The displacement values are then analyzed to determine the types of distortion, if any, that are present within the ESR antenna system. Compensation values are then determined for each of a plurality of beam positions based on the type(s) of distortion identified. The compensation values are stored in a lookup table for later use in generating antenna beams in the corresponding beam position.

Claims

1. A method for calibrating an electronically scanned reflector (ESR) antenna including a reflector and a phased array feed having a plurality of antenna elements, comprising the steps of:

measuring a mechanical displacement associated with a plurality of points on the reflector and a plurality of points on the phased array feed, said measuring step resulting in a plurality of displacement values;

analyzing said plurality of displacement values to ascertain a type of distortion, if any, within the reflector and a type of distortion, if any, within the phased array feed; and

determining compensation values for use in connection with said plurality of antenna elements for compensating for mechanical distortions within said ESR antenna system based on the types of distortion ascertained in said step of analyzing, said step of determining compensation values includes determining a set of compensation values for each of a plurality of antenna beam positions to be supported by said ESR antenna system and storing said compensation values in memory in association with corresponding antenna beam positions for later use in generating antenna beams in said antenna beam positions.

2. The method claimed in claim 1, wherein:

said step of analyzing includes ascertaining whether one or more of the following distortion types are present;

reflector curvature, reflector ripple, reflector offset, reflector twist, feed curvature, feed ripple, feed offset, and feed tilt.

3. The method claimed in claim 1, wherein:

said step of determining compensation values includes determining said compensation values by mathematical manipulation of said plurality of displacement values.

4. The method claimed in claim 1, wherein:

said step of determining compensation values includes determining a phase compensation value for each of a subset of said plurality of antenna elements corresponding to a first beam position when at least one of the following distortion types are present;

reflector curvature distortion, reflector ripple distortion, reflector offset distortion, feed curvature distortion, feed ripple distortion, and feed offset distortion.

5. The method claimed in claim 4, wherein:

said step of determining a phase compensation value includes determining, for a first antenna element associated with said first beam position, an error distance between a point where the reflector is and a point where the reflector should be along a line that intersects said first antenna element and is in a direction related to a direction of said first beam position when at least one of the following distortion types are present;

reflector curvature distortion, reflector ripple distortion, and reflector offset distortion.

6. The method claimed in claim 5, wherein:

said step of determining a phase compensation value includes doubling said error distance.

7. The method claimed in claim 1, wherein:

said plurality of antenna elements are arranged in columns and rows.

8. The method claimed in claim 7, wherein:

said step of determining compensation values includes determining, when reflector twist distortion or feed tilt distortion is present, whether a different row of antenna elements should be used to generate a first beam position than a row previously designated to generate said first beam position.

9. The method claimed in claim 7, wherein:

said step of determining compensation values includes determining a plurality of amplitude weighting coefficients for use by a row of elements associated with a first beam position when reflector twist or feed tilt is present.

10. A method for calibrating an electronically scanned reflector (ESR) antenna including a reflector and a phased array feed having a plurality of antenna elements, comprising the steps of:

measuring a mechanical displacement associated with each of a plurality of points on said reflector and each of a plurality of points on said phased array feed, said measuring step resulting in a plurality of displacement values;

for a first beam position of the ESR antenna, determining a phase compensation value for each antenna element within a subset of said plurality of antenna elements associated with said first beam position using said plurality of displacement values; and

storing said phase compensation values in a memory for later use in generating an antenna beam in said first beam position.

11. The method claimed in claim 10, further comprising:

repeating said steps of determining and storing for a second beam position of the ESR antenna.

12. The method claimed in claim 10, further comprising:

repeating said steps of determining and storing for each of the beam positions supported by the ESR antenna.

13. The method claimed in claim 10, wherein:

said plurality of antenna elements are arranged in columns and rows, wherein said subset of said plurality of antenna elements associated with said first beam position includes a first row of antenna elements.

14. The method claimed in claim 10, wherein:

said step of determining a phase compensation value includes calculating, for a first antenna element within said subset, an error distance between a point where said reflector is and a point where said reflector should be along a direction associated with said first beam position.

15. The method claimed in claim 14, wherein:

said step of determining a phase compensation value includes determining an electrical length of double said error distance.

16. The method claimed in claim 10, wherein:

said step of determining a phase compensation value includes calculating, for a first antenna element within said subset, an error distance between a point where said feed array is and a point where said feed array should be along a direction associated with said first beam position.

17. The method claimed in claim 16, wherein:

said step of determining a phase compensation value includes calculating an electrical length of said error distance.

18. The method claimed in claim 10, wherein:

said step of determining a phase compensation value includes calculating a first error distance associated with said reflector and a second error distance associated with said feed array and combining said first and second error distance into a single distance value.

19. The method claimed in claim 18, wherein:

said step of combining includes calculating a sum of said second error distance and twice said first error distance.

20. The method claimed in claim 10, further comprising:

for said first beam position of said ESR antenna, determining whether a different row of said plurality of antenna elements should be used to generate an antenna beam in said first beam position than a row originally designated to generate an antenna beam in said first beam position when reflector twist distortion or feed tilt distortion is present.

21. A self-calibrating electronically scanned reflector (ESR) antenna system, comprising:

a reflector having a feed array located approximately at a focal point thereof for generating an antenna beam in any of a plurality of predetermined beam positions;

means for determining displacement values for a plurality of points on said reflector and a plurality of points on said feed array, said displacement values indicating a displacement between an actual location of said points and a desired location of said points;

means for ascertaining mechanical distortion types present within said reflector and said feed array, if any, based on said displacement values;

means for generating compensation values for said ESR antenna system based on said distortion types identified by said means for ascertaining; and

a memory that stores said compensation values for each of said plurality of predetermined beam positions being supported by said ESR antenna system, said compensation values being used in generating antenna beams in said predetermined beam positions.

22. The antenna system claimed in claim 21, wherein:

said means for determining displacement values includes a plurality of target scatterers distributed upon said reflector and a plurality of probes distributed upon said feed array.

23. The antenna system claimed in claim 22, wherein:

said plurality of probes includes a plurality of radio frequency (RF) probes and said means for determining displacement values includes means for performing a plurality of RF phase measurements using said plurality of target scatterers and said plurality of RF probes.

24. The antenna system claimed in claim 22, wherein:

said plurality of targets scatterers includes a plurality of mirrors, said plurality of probes includes a plurality of optical sensors, and said means for determining displacement values includes means for performing a plurality of optical angle measurements using a light source, said plurality of mirrors, and said plurality of optical sensors.

25. The antenna system claimed in claim 21, wherein:

said means for determining displacement values includes a plurality of temperature sensors distributed upon said reflector and a plurality of temperature sensors distributed upon said feed array.

26. The antenna system claimed in claim 21, wherein:

said means for determining displacement values includes means for performing optical path length measurements.

27. The antenna system claimed in claim 21, wherein:

said means for ascertaining mechanical distortion types includes means for identifying at least one of the following distortion types;

reflector curvature distortion, reflector ripple distortion, reflector offset distortion, reflector twist distortion, feed curvature distortion, feed ripple distortion, feed offset distortion, and feed tilt distortion.

28. The antenna system claimed in claim 21, wherein:

said means for generating compensation values includes means for generating a compensation value set for each of said plurality of predetermined beam positions.

29. The antenna system claimed in claim 21, wherein:

said means for generating compensation values includes means for generating phase compensation values for antenna elements within said feed array when any of the following distortion types are present;

reflector curvature distortion, reflector ripple distortion, reflector offset distortion, feed curvature distortion, feed ripple distortion, and feed offset distortion.

30. The antenna system claimed in claim 21, wherein:

said feed array includes a plurality of antenna elements, said plurality of antenna elements including a first group of elements for use in generating an antenna beam within a first subgroup of beam positions and a second group of elements for use in generating an antenna beam within a second subgroup of beam positions, wherein said means for generating compensation values includes means for determining whether to change the group of elements associated with a particular beam position when reflector twist or feed tilt is present.