Investigation on an ultra–wide-swath, multiple-elevation-beam SAR based on sweep-PRI mode

A promising candidate for ultra-wide-swath spaceborne synthetic aperture radar (SAR) imaging with a fine resolution is the multiple-elevation-beam (MEB) SAR. Conventional MEB SAR suffers from deterioration of noise-equivalent sigma zero (NESZ) and range ambiguity-to-signal ratio (RASR) performances in the far end of the imaging swath and disturbances between different subbeam elevations. Another inherent problem of previously proposed MEB SAR systems is the blind range effect, which blocks continuous mapping. In this paper, we introduce a potential modified MEB SAR system based on space-time-frequency waveform encoding on transmit and on digital beamforming (DBF) on receive that provides a much improved performance of NESZ and RASR, a lower requirement for the transmit peak power, and a more flexible signal energy distribution. Furthermore, to overcome the blind range problem, a periodic sweep of pulse repetition interval (PRI) design strategy is employed. In this paper we are developing the idea of sweep-PRI mode into a complete detailed processing scheme. The explicit signal model, the instructive system design guideline, and the corresponding signal processing scheme for this operational mode are described in detail. A recurrent nonuniform reconstruction algorithm is adopted first to cope with the problems of nonuniform sampling and periodic gaps in the azimuth preprocessing. Additionally, an in-depth analysis of system performance for the presented MEB SAR system is carried out. Finally, an example system with a 400-km-wide swath and 3-m resolution is designed based on the proposed strategies. The simulation results demonstrate that the presented SAR system shows satisfactory performance.