Short antenna spaceborne SAR concepts

Abstract

This analysis concludes that, for a “swath/azimuth resolution” (SAR) ratio not exceeding 10 4 (as is the case for the missions designed and imagined up until now), it is possible, thanks to new imaging modes based on timing diagram saturation, to reduce the length of the antenna by two (defined along the speed vector) under equivalent performance, antenna area, onboard energy and spectral occupancy conditions. One of the advantages is that the Spotlight mode is not needed except if one wishes to exceed the ratio of 10 4, which gives, in addition to the elimination of the operational limitations of this mode, high cost reduction possibilities with very simplified antenna architectures. These principles are applicable to all types of satellite architectures provided that the rejection of the nadir echo is done other than in the temporal domain, here too saturated. They are especially interesting for the RADAR SAIL case, lowering the costs of the RADAR satellite concept invented by CNES, based on the use of a vertical antenna placed in the orbit plane. On the one hand, they get round the length limitation related to this concept and generalise its utilisation range. On the other hand, the absence of the nadir echo (physically rejected on account of the SAIL concept geometry) enables antenna simplification to be pushed as far as possible without having to preserve a minimum number of control points required for beam nulling toward nadir and, in addition, a single diagram, that of the pencil beam, enables all incidences and modes to be covered, which simplifies the characterisation, calibration and operation of the Radar.