Digital Beamforming for Spaceborne Reflector - Based Synthetic Aperture Radar, Part 2: Ultra-Wide Swath Imaging Mode

Abstract

Utilizing digital beamforming techniques in conjunction with the feed array of large deployable reflector antennas can boost the performance of synthetic aperture radar (SAR) systems. Multi-channel SAR overcomes the constraints of classical single-channel SAR allowing for wide-swath imaging at fine azimuth resolution. Part 1 of this tutorial provided an introduction to the instrument structure of a digital beamforming (DBF) imaging radar and the particularities/variants of its basic operation mode, known as single-beam scan-on-receive (SCORE), in which a time-variant high-gain receive beam is generated that follows the reflected echo traversing the ground. In its basic implementation, SCORE improves the signal-to-noise ratio and allows for the suppression of range ambiguities, but it does not allow for a substantial increase of the imaged swath width beyond a few tens of kilometers. Part 2 of the tutorial paper addresses the topic of ultra-wide swath imaging in the order of a few hundred kilometers, enabled through DBF. A detailed insight into simultaneous multiple sub-swath imaging is given; gaps (blind ranges) that occur in this operation mode are addressed; and the data streams management at the various on-board processing stages is explained, put in relation to the imaging mode, and expressions for the data rates are provided. A further beamforming topic seized in part 2 of this tutorial trilogy is the feed array excitation (complex weights) and the resulting primary and secondary radiation patterns. This is explained in the context of a reference reflector-feed antenna system providing numerous example cases aiming to foster the understanding of the topic.