Since its invention 60 years ago the synthetic aperture radar (SAR) principle has been continuously pushed further in terms of information density. Future SAR systems are required to collect data in different frequency bands and polarizations with finer spatio-temporal resolution and higher quality. These requirements drive technology developments with a trend towards digital radars. This type of radar is highly flexible and configurable compared to its analogous counterpart and allows a relatively easy implementation of digital beamforming (DBF) as well as multiple input multiple output (MIMO) techniques. The demand of highly sensitive SAR sensors enforces antenna concepts with large aperture. A promising candidate are large deployable mesh reflector antennas fed by an array of feed elements. Each feed element, or a subset of feed elements, defines a digital channel to be further processed on board the spacecraft or on ground. These innovative class of high-information content SAR sensors are the result of a carefully optimized design in both, the hardware and the signal processing domain. Here, an advanced SAR sensor concept based on array-fed reflector antennas shall be presented. Space, time and frequency adaptive beamforming techniques which complement the antenna design are introduced and demonstrated by means of numerical simulations.