Methods for two-dimensional autofocus in high resolution radar systems

#1. Field of the Invention

#The present invention relates to two-dimensional autofocus methods in a Synthetic Aperture Radar (“SAR”) systems. More specifically, the present invention relates to two-dimensional autofocus methods which compensate both on and off-axis distortions in SAR signal history.

#2. Discussion of Background Information

#While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed the same will be better understood from the following description taken in conjunction with the accompanying drawings, which illustrate, in a non-limiting fashion, the best mode presently contemplated for carrying out the present invention, and in which like reference numerals designate like parts throughout the Figures, wherein:

#FIG. 1 illustrates a comparison between the previous one-dimensional autofocus stacking technique and the two-dimensional technique used by the methods of embodiments of the present invention.

#FIG. 2A illustrates the summing operation utilized by the two-dimensional Shear Phase Gradient Autofocus (“shear PGA”) method according to an exemplary embodiment of the present invention.

#The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

#As mentioned above, previous autofocus techniques, based on one-dimensional estimates, are only capable of removing phase errors which appear as distortions of a target in the cardinal directions. However, SAR imagery which is collected with an antenna utilizing a large dwell angle (for example, UltraSAR) may contain phase errors in which the off-axis target distortions are significant. As such, the methods of the exemplary embodiments of the present invention seek to mitigate those phase errors which are not compensated for using the previous one-dimensional techniques.

#It should be realized that the processing steps according to the exemplary embodiments of the present invention may be performed by a processor-based system. In one embodiment, the system may include an input/output (“I/O”) interface, a processor and memory. It is contemplated that more than one interface may be utilized in the system. For example, one interface may be configured to receive inputs and a second interface may be configured to output data to a display. Further, multiple interfaces may be used to receive separate inputs without deviating from the scope and spirit of the exemplary embodiments of the present invention.