COSMO-SkyMed: The advanced SAR instrument

This paper describes the COSMO-SkyMed SAR instrument and its active phased array, developed by Thales Alenia Space Italia under contract of Italian Space Agency and Italian Ministry of Defence. Major focus is given to the performance, operation modes, design solutions and description of the antenna with the technological results. COSMO-SkyMed (Constellation of Small Satellites for Mediterranean basin Observation) is a 4-satellite constellation funded by ASI (Agenzia Spaziale Italiana) and Italian Ministry of Defence. The overall objective of this program is the global Earth observation and the relevant data exploitation for the needs of both the military and the civil (institutional, commercial) communities. The first satellite was launched June, 7th 2007, the second was launched on December-2007, the third followed in 2008, and finally the complete deployment of the constellation was achieved with the fourth satellite in October 2010. Each of the four satellites is equipped with a SAR operating in X-band with multimode (spotlight, stripmap, and scansar) and multipolarisation capability. Operational flexibility (multimode, access area, left and right looking) is one of the major system requirements driving the selection of a system based on an active phased array with steering capability on both the elevation and the azimuth planes. In addition to the operational flexibility, the demand on image quality in terms of spatial resolution, swath extension and ambiguity suppression led to some of the system solutions (instantaneous bandwidth, beam shaping capability in the elevation plane, beam setting separately in Tx and Rx on a PRI basis) which constrained the selected architecture and drove the selection of an active phased array for the antenna subsystem.