High accuracy digitally controlled active radar ground calibrator system for TerraSAR-X

April 2006, the TerraSAR-X satellite was launched. This paper describes the development of a novel and highly integrated, digitally controlled active SAR system calibrator (DARC). It consists of both an active transponder path for absolute radiometric calibration and a calibrated receiver chain for antenna pattern evaluation of the satellite antenna. A total of 16 active transponder and receiver systems and 17 receiver only systems were fabricated for a calibration campaign in 2006.