ESA´s ground breaking synthetic aperture radar: the ENVISAT-1 ASAR active antenna

The Advanced Synthetic Aperture Radar (ASAR) is a major instrument on board ENVISAT-1. The next Earth observation mission of the European Space Agency. It will represent a sensor of paramount importance for the remote sensing community because of its enhanced flexibility with respect to the existing SARs in the AMI on board ERS-1 and ERS-2. The unique combination of different spatial resolutions, incidence angles, swath width sizes and polarisation diversity will offer an increased number of operational modes tailored for a large set of scientific and operational applications. Among the innovative design features of this radar are the use of an active antenna concept for tailoring the transmit and receive elevation beams to different mode geometries, a digital generation waveform technique for obtaining variable time-bandwidth products and a block adaptive quantization compression scheme. In this paper, the ASAR antenna is described and the development status is presented.