Suppression of range and azimuth ambiguities in spaceborne SAR with antenna pattern optimization

Abstract

The synthetic aperture radar (SAR) mounted on mounted on low orbit satellites has been widely used in re-mote sensing because it can acquire high resolution images day and night regardless of weather conditions. To obtain SAR images of the area of interest, a modern SAR uses an active phased array antenna to electronically generate various beams. The main lobe beam pattern generated by the SAR antenna is related to the noise equivalent sigma zero (NESZ) and the swath width, whereas the sidelobe beam pattern is related to the azimuth ambiguity-to-signal ratio (AASR) and the range ambiguity-to-signal ratio (RASR). If the SAR antenna beam can be illuminated only in the AOI, both range and azimuth ambiguities can be well suppressed. However, it is difficult to generate a beam pattern with low sidelobe levels at all angles, because lowering the sidelobes at cer-tain angles tends to increase the sidelobes at other angles. For this reason, beam patterns with low sidelobes only in the direction of large ambiguous echoes are more suitable for suppressing range and azimuth ambigui-ties than those with equiripple sidelobes. In this study, we propose a beam pattern mask design and beam pat-tern synthesis method that can effectively suppress range and azimuth ambiguities in spaceborne SAR.