In-Flight Performance Monitoring of TerraSAR-X Active Phased Array Antenna

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Abstract
TerraSAR-X is a high resolution synthetic aperture radar (SAR) satellite launched in 2007. Its active phased array X-band antenna hosts 384 transmit/receive modules (TRMs) controlling the beam shape and steering in azimuth and elevation. A mathematical antenna model approach is used for pattern optimisation and calculation of all possible operation beams. For keeping the excellent radiometric performance of the SAR system the front-end antenna must be monitored throughout mission life time and calibrated if necessary. A calibration network provides monitoring of the instrument behaviour by evaluating internal calibration pulses. Evaluation of these calibration pulses for every image acquisition guarantees high radiometric stability of all SAR products. This paper shows the latest in-orbit results of the antenna performance and TRM stability complementary to the traditional approach of external antenna measurements over calibration targets. For this purpose, the novel PN Gating method is applied in a spaceborne environment for the first time ever.