Thales Alenia Space (TAS) has started the “COMPACT-SAR” internal programme to develop a SAR satellite characterized by low cost and reduced mass while providing, at the same time, high image quality in terms of resolution, swath size, and radiometric performance. COMPACT-SAR is a satellite embarking an X-band SAR based on a new technology for the Antenna Subsystem. It consists of an innovative deployable reflector antenna fed by a small active phased array, capable of electronic beam steering in both azimuth and elevation planes. Thanks to this design, the instrument can be operated in both STRIPMAP, DI2S (i.e. enhanced resolution STRIPMAP) and SPOTLIGHT modes. Due to the very high gain provided by the large reflector, the system can also provide a real maritime surveillance mode based on the TAS patented LowPRF mode. The flexibility of the design, based on the large (5m) on-set reflector is also exploited to define a version of the product operating at L-band just by changing the feed array and the RF back-end of the radar. TAS already has a product line on T/R modules at L (and C) band, allowing this new development with minimum risk.