Two-Dimensional Autofocus Combined With the TSA for Spotlight SAR

Abstract

For high-resolution spotlight synthetic aperture radar, Doppler aliasing is always introduced in the long synthetic aperture observation time. The existence of signal Doppler aliasing will greatly affect the accuracy of motion compensation. To avoid Doppler aliasing, it is an effective strategy to use the subaperture (SA) approach. However, it will introduce the long synthetic aperture time stitching problem of signal and phase error. Compared with the SA approach, the two-step approach (TSA) based on the full aperture not only eliminates the Doppler aliasing but also avoids the signal splicing problem. Therefore, a two-dimensional (2-D) frequency-domain autofocus combined with the TSA is adopted in this article. First, TSA is used to perform dealiasing and coarse focusing imaging on full-aperture (FA) data. Second, the phase error history and the phase error form in the TSA process are analyzed and deduced, and an accurate prior structure of the phase errors is established. Then, the accurate inversion of the common 2-D phase errors is realized based on this prior structure. Finally, the autofocus process of the FA signal combined with the TSA is realized in the nonaliasing 2-D frequency domain. The validity of the recommended algorithm is verified by simulation and experimental results.

Keywords

• 2-D autofocus process
• motion compensation (MoCo)
• synthetic aperture radar (SAR)
• two-step approach (TSA)