High resolution millimeterwave SAR

The millimeterwave radar MEMPHIS of FGAN FHR is an experimental pulse-dnppler-radar that simultaneously operates at 35 GHz and 94 GHz. High range resolution is obtained using an LFM chirp with either 100 MHz or 200 MHz bandwidth. In order to increase the range resolution beyond the value of d2B given by the chirp bandwidth, a stepped-frequency mode was implemented using 8 steps with a spacing of 100 MHz leading to a total bandwidth of 800 MHz. The subsequent processing of the radar data avoids the usual "stretch" processing in order to he able to use measured instead of synthetic reference chirps, thus accommodating and compensating all kinds of hardware induced amplitude and phase errors. Due to "spatial concatenation" the method is applicable to scenarios with a range extent much larger than the range related to a single chirp length. A problem area for high resolution SAR imaging is the proper compensation of platform movements, which lead especially to disturbances during the doppler cross-range processing. The specialties for the millimeterwave SAR are discussed and solutions are highlighted.