Inverse precision velocity update for monopulse calibration

• US 6,853,330 B1
• Filed: 05/13/2004
• Issued: 02/08/2005
• Est. Priority Date: 05/13/2004
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Rosen, Robert A., Krikorian, Kapriel V.
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US10/845,884
• Time in Patent Office: 271 Days
• Field of Search: 342 25 R- 25 F, 342 61- 65, 342 73- 75, 342/80, 342368-384, 342/147, 342149-154, 342165-176, 342/179, 342190-197
• US Class Current: 342/149
• CPC Class Codes: G01S 13/9092 combined with monopulse techniques
• CPC Class Codes: G01S 7/4026 Antenna boresight
• CPC Class Codes: G01S 7/403 in azimuth, i.e. in the horizontal plane
• CPC Class Codes: G01S 7/4034 in elevation, i.e. in the vertical plane
• CPC Class Codes: G01S 7/4091 during normal radar operation
• CPC Class Codes: G01S 7/52004 Means for monitoring or calibrating short-range imaging G01S7/5205

Abstract

A radar system derives a correction for an actual boresight (311) of a radar monopulse antenna mounted on a moving platform from Σ data and Δ data generated with respect to an a priori known, calibrated boresight (309). The monopulse antenna (602) is coupled to a ground position measuring system (616) while acquiring data. The radar receiver acquires a Σ and Δ synthetic aperture map of the same radar scattering location with respect to the calibrated boresight. Σ SAR data and the Δ SAR data are motion compensated using the position and velocity supplied by the ground positioning system. A computer forms a ratio of the aligned Δ pixels to the aligned Σ pixels for each of a plurality of aligned Σ pixels located near the calibrated boresight. The correction for the location of the actual boresight of the monopulse antenna is computed by an analysis of the ratio of aligned Σ pixels and corresponding aligned Δ pixels over the radar scattering location. Typically, a least square fit analysis is used to plot the Δ/Σ ratio, and ascertain where the zero crossing of the monopulse angle=0 line is found thereby identifying the position of the actual boresight, and the correction from the a priori, calibrated boresight.

Claims

1. A method for estimating an actual boresight of a radar monopulse antenna mounted on a moving platform from Σ

data and Δ

data generated with respect to a calibrated boresight of said monopulse antenna, said Σ

data generated from a Σ

channel, said Δ

data generated from a Δ

channel, said monopulse antenna coupled to a ground position measuring system, said ground positioning measuring system reporting a position of said monopulse antenna with respect to a reference and a velocity with respect to said reference, said method comprising the steps of;

acquiring a Σ

synthetic aperture map of a radar scattering location, using said Σ

channel of said monopulse antenna with respect to said calibrated boresight, said radar scattering location centered about said calibrated boresight, said Σ

synthetic aperture map formed from Σ

data;

acquiring a Δ

synthetic aperture map of said radar scattering location using said Δ

channel of said monopulse antenna with respect to said calibrated boresight, said Δ

synthetic aperture map formed from a data;

is motion compensating said Σ

data with respect to said reference using said position and said velocity to obtain aligned Σ

pixels;

motion compensating said Δ

data with respect to said reference using said position and said velocity to obtain aligned Δ

pixels, each of said aligned Δ

pixels matched to corresponding said aligned Σ

pixels obtained from said radar scattering location;

forming a ratio of said aligned Δ

pixels to said aligned Σ

pixels for each of a plurality of said aligned Σ

pixels located near said calibrated boresight;

identifying the location of said actual boresight of said monopulse antenna by an analysis of said ratio for a plurality of said aligned Σ

pixels and corresponding said aligned Δ

pixels over said radar scattering location.

2. A method as described in claim 1 wherein said analysis of said ratio is a least square fit of said plurality of aligned Σ

pixels around said calibrated boresight.

3. A method as described in claim 2 wherein said plurality of said Σ

data forming said Σ

synthetic aperture map is a 512 by 512 matrix centered with respect to said calibrated boresight, and wherein said analysis of said ratio is computed for 20 by 20 said aligned Σ

pixels around said calibrated boresight to identify said actual boresight.

4. A method as described in claim 3 wherein said ground position measuring system provides said velocity with an accuracy between 1 and 10 millimeters per second, said velocity integrated over time for reporting said position with respect to said reference for motion compensating said Σ

data and said Δ

data.

5. A method as described in claim 4 wherein said monopulse antenna is used in elevation, said elevation mapping said radar scattering location generally aligned with earth'"'"'s gravity.

6. A method as described in claim 4 wherein said monopulse antenna is used in azimuth, said azimuth mapping said radar scattering location generally perpendicular to earth'"'"'s gravity.

7. A radar system deriving a correction for an actual boresight of a radar monopulse antenna mounted on a moving platform from Σ

data and Δ

data generated with respect to a calibrated boresight of said monopulse antenna, said Σ

data generated from a Σ

channel, said Δ

data generated from a Δ

channel, said monopulse antenna coupled to a ground position measuring system, said ground positioning measuring system reporting a position of said monopulse antenna with respect to a reference and a velocity with respect to said reference, said radar system comprising;

a radar receiver for acquiring a Σ

synthetic aperture map of a radar scattering location using said Σ

channel of said monopulse antenna, and a Δ

synthetic aperture map of said radar scattering location using said Δ

channel of said monopulse antenna, said Σ

synthetic aperture map and said Δ

synthetic aperture map acquired with respect to said calibrated boresight, said Σ

synthetic aperture map formed from Σ

data, said Δ

synthetic aperture map formed from Δ

data;

motion compensator using said ground position measuring system for motion compensating said Σ

data with respect to said reference and said Δ

data with respect to said reference using said position and said velocity to obtain aligned Σ

pixels and aligned Δ

pixels;

computer for forming a ratio of said aligned Δ

pixels to said aligned Σ

pixels for each of a plurality of said aligned Σ

pixels located near said calibrated boresight;

said computer also computing said correction for the location of said actual boresight of said monopulse antenna by an analysis of said ratio for a plurality of said aligned Σ

pixels and corresponding said aligned Δ

pixels over said radar scattering location.

8. A radar as described in claim 7 wherein said analysis of said ratio is a least square fit of said plurality of aligned Σ

pixels around said calibrated boresight.

9. A radar as described in claim 8 wherein said plurality of said Σ

data forming said E synthetic aperture map is a 512 by 512 matrix centered with respect to said calibrated boresight, and wherein said analysis of said ratio is computed for 20 by 20 said aligned Σ

pixels around said calibrated boresight to identify said actual boresight and said correction.

10. A radar as described in claim 9 wherein said ground position measuring system provides said velocity with an accuracy between 1 and 10 millimeters per second, said velocity integrated over time for reporting said position with respect to said reference for motion compensating said Σ

data and said Δ

data.

11. A radar as described in claim 10 wherein said monopulse antenna is used in elevation, said elevation mapping said radar scattering location generally aligned with earth'"'"'s gravity.

12. A method as described in claim 10 wherein said monopulse antenna is used in azimuth, said azimuth mapping said radar scattering location generally perpendicular to earth'"'"'s gravity.