Design and Implementation of External Calibration System for GF-3 Polarimetric Transponder

Transponders play an important role in Chinese first spaceborne SAR GF-3 in-orbit calibration and performance assessment. The accuracy of GF-3 transponder is guaranteed by the external transponder calibration. In this paper, based on traditional radiometric external transponder calibration methods (RETC), two additional error sources of alignment and bi-static RCS of the standard reference are considered. Besides, the polarimetric external transponder calibration (PETC) of channel imbalance is also realized with a simple method with a pair of tilted standard horns and VNA (vector network analyzer).