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Synthetic aperture radar system having a third order tuned auto compensator for residual antenna motion and method for its use

  • US 5,012,249 A
  • Filed: 11/28/1989
  • Issued: 04/30/1991
  • Est. Priority Date: 11/28/1989
  • Status: Expired due to Term
First Claim
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1. In a SAR system that receives reflections of radar signals from a target region, wherein such signals are combined with position signals from a motion sensor indicating antenna position, with the reflected signals and the position signals being integrated into range lines that may be combined to form a radar image, and wherein there may be residual motion between the antenna and the motion sensor, a method of correcting the position signals from the motion sensor to compensate for the amplitude and phase of antenna residual motion that may cause phase corruption in the radar image, the method comprising the steps of:

  • a. transforming a received radar signal into a range line having a plurality of azimuth positions,b. transforming said received signal into a frequency spectrum f indicating the reflectivity of point reflectors at said azimuth positions, wherein one point reflector is located at each azimuth position, and wherein each point reflector is represented by a complex number having a certain magnitude and phase angle;

    c. sampling the range line for substantially symmetric sets of point reflectors separated consecutively from each other by a distance corresponding to a frequency θ

    , wherein said frequency corresponds to a mode of residual vibration of the antenna, and wherein said substantially symmetric set includes a main lobe point reflector, a pair of first order point reflectors, and a pair of second order point reflectors, each of said point reflectors being represented by a complex number, with said main lobe point reflector being centrally positioned between said pairs of first and second order point reflectors,d. calculating a product of a predetermined threshold with the greater magnitude of the two complex numbers f(x-θ

    ) and f(x+θ

    ), representing the pair of first order point reflectors,e. comparing the product with the magnitude of the complex number f(x) representing the main lobe point reflector,f. establishing first and second criteria of a symmetry relation, depending upon whether the magnitude of the complex number representing the main lobe point reflector is greater or less than the product of the predetermined threshold with the greater magnitude of the two complex numbers representing the pair of first order point reflectors,g. determining whether the complex numbers representing the main lobe point reflector, the pair of first order point reflectors, and the pair of second order point reflectors meet the first or second symmetry relation, depending upon the result of the comparison of step e,h. calculating estimates of the amplitude and phase of the antenna residual motion, depending upon the result of the comparison of step e,i. generating an antenna residual motion signal therefrom, andj. combining the antenna residual motion signal with the position signals from the motion sensor, to correct for antenna residual motion between the motion sensor and the antenna.

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