Advanced digital beamforming concepts for future SAR systems

Abstract

This paper reviews advanced multi-channel SAR system concepts for the imaging of wide swaths with high resolution. Several novel system architectures employing both direct radiating arrays and reflector antennas fed by a digital array are introduced and compared to each other with regard to their imaging performance. In addition, innovative SAR imaging modes are proposed which enable the mapping of ultra-wide swaths with high azimuth resolution. The new techniques and technologies have the potential to enhance the imaging performance of future SAR systems by one order of magnitude if compared to state of the art SAR sensors like TerraSAR-X, ALOS, Radarsat-2 or Sentinel-1.

A novel ultra-wide swath SAR based on variable PRF and digital beamforming

“…Fig.1-(a)), imaging gaps caused by the coincidence of transmit and receive events disappear by choosing appropriate end-to-end beam positions at slightly different PRFs, as shown in Fig.1-(b). A more advanced concept called MEB ScanSAR based on the reflector antenna is proposed for decreasing the least "Burst" number needed for filling the blind ranges, hence relaxing the impairment of the azimuth resolution [2] (c.f. Fig.1-(c)).…”

“…Another inherent bottleneck for the strip-mapping ultra-wide swath SAR is the blind-range problem [7], which entails the discontinuous mapping. The strategy of variable PRF, firstly proposed in [2], can be adopted to effectively relax the inherent blind-range problem along with the constant PRF by distributing the lost echo-pulses to different slant ranges. On the other hand, the accompanying influences with the continuously variable PRF on the azimuth compression and the SAR system performance caused by the variable PRF are inevitable.…”

Recent Trend and Advance of Synthetic Aperture Radar with Selected Topics

“…A basic design of achieving high resolution in wide swath is DBF on receive with the conventional analogue beam forming on transmit, where a wide swath is illuminated using either a small part of an antenna or a small separate antenna, and the scattered signal is received by multiple independent sub-apertures; these signals are then processed independently to produce images of multiple swaths and to produce a wide-swath image by combining them. Several different approaches have been proposed, including a squinted geometry, a displace phase center antenna technique, both of which use sub-apertures aligned in the azimuth direction, a quad-element rectangular array system, and a high-resolution wide-swath (HRWS) system employing multiple sub-aperture elements split into both the azimuth and range directions [192][193][194][197][198][199], as well as the use of a large reflector antenna with feed arrays [158,200,201]. As mentioned in Section 2.2, Tandem-L will have 10 m resolution covering 350 km swath with repeat cycle of 8 days [22,158].…”

Ambiguity Suppression by Azimuth Phase Coding in Multichannel SAR Systems

“…For instance, a resolution around 1 m could be achieved over a swath width of 10 km; whereas a coverage of 100 km allows for SAR final products with a resolution in the order of 16 m. The importance for many applications of earth observation to overcome this limitation has motivated an intensive research. In particular, since the tradeoff between spatial resolution and swath width is inherent to the system concept and originated by ambiguity constraints, the research has been oriented in two main directions: i) new, more flexible SAR systems [7]- [10]; ii) processing methods for removing the ambiguities from the SAR image [11]- [13].…”