Precise calibration techniques for complex SAR systems based on active phased array antennas

In recent years, the antenna technology for spaceborne synthetic aperture radar (SAR) systems has developed from passive slotted waveguide arrays (e.g. ERS-1/2 or X-SAR) to active phased arrays (e.g. ASAR/ENVISAT or TerraSAR-X), offering electronic beam steering capabilities required for acquisitions in different swath geometries and for operation in ScanSAR and Spotlight modes. Furthermore, with an increasing number of operational applications and services, the requirements on radiometric and geometric calibration become increasingly demanding. Hence, product quality is of crucial importance and the success or failure of a mission depends essentially on the method of calibrating the SAR system in an efficient way. In example of TerraSAR-X the paper describes a precise and efficient calibration method applicable for complex spaceborne SAR systems based on an active phased array antenna.