Device for improving radar resolution

• US 5,119,100 A
• Filed: 03/21/1991
• Issued: 06/02/1992
• Est. Priority Date: 04/21/1989
• Status: Expired due to Fees

• Current Assignee: Selenia-Industrie Elettroniche Associate SPA (Leonardo S.p.A.)
• Original Assignee: Selenia-Industrie Elettroniche Associate SPA (Leonardo S.p.A.)
• Inventors: Prodi, Francesco, Marini, Stefano
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US07/672,731
• Time in Patent Office: 439 Days
• Field of Search: 342/25, 342/195, 342/196, 342/161
• US Class Current: 342/195
• CPC Class Codes: G01S 13/723 by using numerical data
• CPC Class Codes: G01S 13/9064 Inverse SAR [ISAR]
• CPC Class Codes: G01S 7/02 of systems according to group G01S13/00

Abstract

A device for processing radar signals has the capability of obtaining single or multiple target information as well as target length by utilizing relative radar-target movement. The device includes a radar receiver; an Inverse Synthetic Aperture Radar processor; a list sensor for supplying listing data to the Inverse Synthetic Aperture Radar (ISAR); an element for determining the presence of one or more targets as well as target length; a radar tracking loop for estimating parameters of target motion; and a display unit for displaying the processed information.

Claims

1. A device for processing radar signals for improved target discrimination and resolution when the radar is mounted on a platform which may be moving and which target may be moving relative to the radar comprises:

an Inverse Synthetic Aperture Radar (ISAR) processor;

means for receiving radar signals reflected from a target, said signal receiving means having an output for outputting radar target data samples related to said reflected radar signals to said ISAR processor;

means for detecting motion of the platform on which the radar is mounted, said platform motion detecting means outputting to said ISAR processor platform motion data related to said platform motion;

a radar tracking loop connected to said ISAR processor for providing kinematic target data to said ISAR processor;

said ISAR processor processing the radar target data samples, the platform motion data and the kinematic target data and outputting processed data resulting from said processing, said processed data comprising an ISAR projected high resolution image profile of the target, an estimated value of the radial velocity of the target, and an estimated value of the tangential velocity of the target, each of said estimated values and said image being corrected by said ISAR processor to compensate for the motion of the platform and the motion of the target relative to the radar;

means for determining target characteristics from said ISAR projected high resolution image profile of the target, said target characteristic determining means determining whether the reflected radar signals are from a single target or from multiple targets and for determining a length of the target from said image profile, said determining means outputting target characteristic data relating to the presence of single or multiple targets and target length data relating to target length; and

means for visually displaying data, said visual display means visually displaying the processed data from said ISAR processor, said target characteristic data and said target length data for visual observation and interpretation.

2. The device according to claim 1, wherein said ISAR processor comprises, in series:

means for compensating for the motion of the platform detected by said motion detecting means, said platform motion compensating means subtracting said platform motion from said radar target data samples so that said radar target data samples remain undistorted by said platform motion;

means for estimating target motion parameters based upon said kinematic target data supplied from said radar tracking loop and said radar target data samples which have been compensated by said platform motion compensating means so as to provide an estimate of target range, an estimated radial velocity of the target and an estimated tangential velocity of the target;

means for compensating for the motion of the target relative to the radar based upon the estimate of target range and the radial and tangential velocity estimates from said target motion parameter estimating means, said target motion compensating means subtracting the target motion from said radar target data samples so that said radar target data samples remain undistorted by target motion relative to the radar; and

means for forming an ISAR high resolution target profile image, said ISAR high resolution target profile image being formed by Inverse Fast Fourier Transformation of said radar target data samples after said radar target data samples have been serially processed by said platform motion compensating means, said target motion parameter estimating means and said target motion compensating means.

3. The apparatus according to claim 1, wherein said target motion parameter estimating means comprises, in series:

means for multiplying said radar target data samples by a quadratic phase correction exponent, said multiplying means receiving said radar target data samples to be multiplied from said platform motion compensating means and outputting multiplied radar target data samples;

means for linear phase correction of said multiplied radar target data samples by Inverse Fast Fourier Transform of said multiplied radar target data samples, said linear phase correction means outputting linear phase corrected target data samples;

means for computing a modulus of said linear phase corrected target data samples, said modulus computing means outputting a target data sample modulus;

means for selecting a maximum value of said target data sample modulus;

means for storing said target data sample modulus and said maximum value of said target data sample modulus;

means for extracting a target data sample modulus from said storage means, said extracted target data sample modulus being that modulus which results in the highest maximum value being obtained from said maximum value selection means during a variability interval, said extracting means outputting said extracted target data sample modulus to said target motion compensation means; and

means for determining an estimate of target motion based upon the target data sample modulus extracted by said extracting means and the kinematic target data from said radar tracking loop, said determining means outputting an estimate of target range, an estimated radial velocity of the target and an estimated tangential velocity of the target.

4. The device according to claim 3, wherein said target motion parameter estimating means further comprises means for generating a coefficient, said coefficient generating means generating said quadratic phase correction exponent.

5. The apparatus according to claim 1, wherein said target characteristic determining means determines whether the reflected radar signals are from a single target or from multiple targets by determining differences in the movement of the target relative to the radar based upon said ISAR projected high resolution image profile, such that a difference in the movement of said high resolution image profile denotes the presence of more than one target.