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Multipath resolving correlation interferometer direction finding

  • US 20070273576A1
  • Filed: 05/27/2006
  • Published: 11/29/2007
  • Est. Priority Date: 05/27/2006
  • Status: Active Grant
First Claim
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1. A method for determining the azimuth and elevation to an aircraft at long range that is transmitting an electromagnetic signal while flying at a low altitude above water, the signal being received using a plurality of vertically polarized antennas and horizontally polarized antennas in an antenna array, the received signal is received directly from the aircraft subject to electromagnetic scattering perturbations and is received via multi-path reflections from the surface of the water, and there is a calibration manifold having stored array steering vectors that is used to correct for the perturbations, the method comprising the steps of:

  • (a) forming a first plurality of covariance matrices from a like plurality of sets of samples of the electromagnetic signal received by the plurality of vertically polarized antennas;

    (b) forming a second plurality of covariance matrices from a like plurality of sets of samples of the electromagnetic signal received by the plurality of horizontally polarized antennas;

    (c) calculating signal eigenvalues and associated eigenvectors for each of the plurality of covariance matrices formed in steps (a) and (b) for the signal received directly from the aircraft and received via multi-path reflections from the surface of the water;

    (d) comparing the signal eigenvalues for the first plurality of covariance matrices with the signal eigenvalues for the second plurality of covariance matrices to determine if the received signal has stronger vertical or horizontal polarization, and selecting the signal eigenvector associated with the signal having the stronger polarization for subsequent processing in steps (e) and (f);

    (e) performing a global correlation maximum search, assuming mirror sea-state reflection conditions using the signal eigenvector selected in step (d) with steering vectors retrieved from the calibration array manifold to determine a first azimuth and elevation; and

    (f) performing a conjugate gradient based correlation search using the selected signal eigenvector and the array manifold in the region of the first azimuth and elevation to determine accurate azimuth and elevation information to the aircraft.

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