**Abstract**

Synthetic aperture radar (SAR) based on satellites and or space vehicles as motion platform has the capability to work under all weather conditions, day and nights, and has become an indispensable mean for earth observation. At present, the large-scale phased array antenna, such as the active microstrip-phased array antenna of SIR-C imaging radar and the waveguide slot-phased array antenna of Radarsat-1 imaging radar, is one of the core components of spaceborne SAR and determines the system performance to a large extent. Although the traditional antenna array scheme has been widely used in existing spaceborne SAR systems due to strong beam control ability, sufficient failure redundancy backup, mature design method and so on, it still has drawbacks, for example, large volume, high weight and manufacturing cost, and low energy utilization rate, which restrict the further improvement of performance and are burdens on the research of next-generation high-performance spaceborne SAR system. With the development of electric and electronic techniques, forthcoming SAR array-phased array antennas will make breakthroughs in antenna architectures, concepts, technologies and modes, for instance, periodic reflector array antennas and metamaterial array antennas. This chapter focuses on the present and forthcoming development of spaceborne SAR antenna arrays.

**Keywords:** spaceborne synthetic aperture radar, antenna arrays, beamforming, metamaterials, high-resolution wide-swath
