A Novel Frequency Scanning Variable PRI Imaging Mode for Ultrawide Continuous Swath Spaceborne SAR Imaging

Digital beamforming (DBF) technique in elevation and variable pulse repetition interval (PRI) technique in azimuth are used to achieve ultrawide continuous swath imaging in synthetic aperture radar (SAR). However, the use of DBF technique inevitably increases the complexity of the spaceborne SAR system. To tackle this problem, a novel frequency scanning variable PRI (FS-VPRI) spaceborne SAR imaging mode is proposed in this paper. In this mode, an advanced frequency scanning technique is employed in elevation, which together with the variable PRI technique to achieve ultrawide continuous swath imaging. In view of the opportunities and challenges presented by the use of the above two techniques, the modeling of FS-VPRI SAR is presented, including system model and signal model. Then, fully taking the special echo timing of FS-VPRI SAR into account, a dedicated PRI sequence is designed, where the improved linear PRI design strategy is adopted to take advantage of a relatively large pulse duration. Moreover, a complete signal processing procedure for FS-VPRI SAR is proposed, where an echo separation approach, termed joint time-frequency filtering (JTFF), is developed. Finally, simulations are conducted to verify the advancement of the proposed FS-VPRI SAR, and the results demonstrate that FS-VPRI SAR can obtain superior system performance at a low cost. The work in this paper can be viewed as an important candidate for future spaceborne SAR.