Spaceborne SAR Systems with Digital Beamforming and Reflector Antenna

Abstract

Contactless information retrieval using electromagnetic waves plays an increasingly important role for scientific and industrial progress. In particular the synthetic aperture radar (SAR) principle, numbered among the imaging techniques, nowadays belongs to the standard-repertoire of civil and military Earth observation. Future SAR systems, whose performance significantly depends on the employed hardware as well as the data processing, shall map increasingly large areas in shorter and shorter time intervals. The work at hand deals with sensor systems, whose two main parts encompass antenna techniques, as well as the subsequent analog and digital signal processing. Here, the focus lies on digital beamforming techniques, enabling an efficient operation of the SAR sensor. For this, space-time adaptive algorithms are derived, which are suitable to minimize the system noise of the sensor and to suppress spatial interference. These algorithms are simulated using the example of a spaceborne SAR system, where the innovative concept of a large unfoldable reflector in combination with a digital feed array is employed. The purpose of such a radar type is to digitize the electromagnetic signal almost immediately after the receiver, in order to ensure the maximal flexibility of the SAR system and to save costs for expensive analog electronics at the same time. The second emphasis of this work deals with optimization aspects, where amongst others a new method is proposed, which allows to mitigate an inherent problematic of such reflector-feed-array constellations. Since in the event of a failure of a single or multiple elements of the feed array a blind spot in the field of view is generated, as solution a defocused reflector antenna concept is proposed. Such an antenna concept combines the merit of planar array antennas, namely the preservation of the functionality in case of an antenna element failure, with the advantage of unfurlable reflector antennas, which is the realization of large apertures.