Space/time/frequency methods in adaptive radar - New Jersey ...

92.1 An Overview of Synthetic Aperture RadarSynthetic aperture radar (SAR) is an airborne/spaceborne radar mapping techniquethat generates high resolution maps of surface terrain and target areas. Thefirst demonstration of SAR mapping was performed in 1953 by a group from theUniversity of Illinois when they mapped a section of Key West, Florida. A fewof the many overview references on the subject of SAR are Brown [25], Kirk [26],and Munson [27]. Fine azimuth resolution may be obtained by using a small radarantenna, storing returns received over time, and integrating the returns so as tosynthesize the equivalent of a long antenna array. SAR may be used to obtain fineresolution in both the slant and cross ranges. Slant range refers to the range in theradar's line of sight. Resolution in this range is typically obtained by coding thetransmitted pulse with an FM chirp. Cross range is the resolution transverse to theradar's line of sight and resolution in this range is obtained by coherently integratingecho energy reflected from the area illuminated by the radar. Synthetic aperturerefers to the distance that the radar travels during the time that reflectivity data iscollected from a point to be resolved which remains illuminated by the radar beam.The length of the synthetic aperture of a side-looking SAR is the ground-trackdistance over which coherent integration occurs. In SAR, ideal processing producesconstant cross-range resolution verses range. A side-looking SAR configuration isshown in Figure 2.1.Echo energy from each range-resolved scatterer in the mapping area is made toarrive in phase at the output of the radar processor to produce the narrow beamwidthassociated with the synthetically generated long aperture. This is achieved bycorrecting for all moving of the radar platform that deviates from straight line motion.Focused SAR, instead of unfocused SAR, has the quadratic phase error of the radarreturn corrected after the signal integration.