Summary: An airborne X- and L-band synthetic aperture radar system was developed by the Communications Research Laboratory and the National Space Development Agency of Japan in their joint project from 1993 to 1996. It is installed in the airplane, Gulfstream II. In both the azimuth and range directions, the resolution is 1.5 m for the X-band and 3 m for the L-band. Both SARs can make fully polarimetric observations. The X-band SAR has a cross-track interferometric function. In this paper we describe the SAR system, its ground processing system, and its performance. We also discuss motion compensation and interferogram quality.