First results from measurements with an experimental

Down-looking 3-Dimensional Synthetic Aperture Radar (3D-SAR) enhances imaging capability of objects in environments where large height variations are present, e.g. urban areas. For a conventional side-looking sensor a large number of objects are normally concealed by radar shadowing in these environments. Using down-looking 3D-SAR the image resolution is obtained by SAR processing in the flight direction and the radar range resolution in the height direction. In the cross flight direction it is a function of flight altitude and the antenna beam width. To reduce the complexity of the antenna architecture and the number of antenna elements, a sparse antenna architecture configured with separated transmitter and receiver elements has been proposed. By using multiple transmitter positions the performance can still match a fully deployed antenna array. The total number of receiver elements can in theory be reduced in the order of N1/2, where N is the number of antenna elements in a fully deployed antenna array. Furthermore, if we apply transmitter elements on both sides of the array, twice the resolution can be achieved. We have developed a test equipment based on a scanner system with travel ranges of 2 m x 1 m and have started off with preliminary radar measurements using different antenna geometries. The registered radar data has been matched to physical ranges and a few different targets and target geometries have been tested, which in all cases have given reasonable and expected imaging results. We have conducted registration using a sparse antenna configuration, corresponding to a 85% decrease in the number of antenna elements, and achieved good results. The obtained 3D resolution is of high quality but the grating lobe attenuation is not ideal. This calls for further development of the experimental system for future measurements.