Communications Research Laboratory (CRL) and National Space Development Agency of Japan (NASDA) have jointly developed a new airborne synthetic aperture radar system operated at X-band and L-band. Both the X and L-band radar's have polarimetric capability and the X-band one has interferometric capability. The radar system is on board a Gulfstream-2 aircraft whose navigation altitude is 20000 to 40000 feet. Following to system performance test flights in August 1996, a series of calibration flights is ongoing. For calibration of the X-band SAR, we have developed an active radar calibrator (ARC) in CRL. The ARC is designed to return H and V radar signals simultaneously with two transmission antennas for polarimetric calibration. It will be employed, along with several corner reflectors, in calibration experiments planned in May and October 1997 at Tottori dune area in Japan. In this paper, we present plan of the experiments and procedure to calibrate the SAR system, focusing on the X-band SAR.