Next generation of multi beam rotating antenna on SWIM scatterometer

In the frame of the development of the instrument SWIM (Surface Waves Investigation and Monitoring) on the CFOSAT program (Chinese French Oceanographic Satellite) funded by CNES, Thales Alenia Space is currently developing a new multi beam rotating antenna in Ku Band. This single reflector offset antenna includes a rotating feed comprising 6 beams. The SWIM instrument is the first ever space radar concept that is mainly dedicated to the measurement of ocean waves directional spectra and surface wind velocities through multi-azimuth and multi-incidence observations. Orbiting on a 500 km sun-synchronous orbit, its multiple Ku-band (13,575 GHz) beams illuminating from nadir to 10° incidence and scanning the whole azimuth angles (0-360°) provide with a 180 km wide swath and a quasi global coverage of the planet between the latitude of -80 and 80°. Such a wide range of observations requiring high range resolution (about 20 m on the ground) have led to design an instrument whose architecture and technology goes beyond what has been done on altimeter and scatterometer systems. At antenna subsystem level, multi-azimuth and multi-incidence observations requirements have led to design an ambitious antenna subsystem that rotates at 6 rotations per minute while transmitting RF signals towards 6 differents beams in Transmit and Receive Modes. Thales Alenia Space started in January 2009 under CNES contract phase B studies on the design of this multi beam rotating antenna in order to contribute to the System Preliminary Design Review held successfully in January 2010. B Phase complementary activities are currently under progress to prepare the C/D Phase planned to start beginning of 2011. This paper aims at giving an overview of the SWIM antenna preliminary design and performances.