星载 SAR 在轨成像高效处理系统硬件实现设计

On-board Synthetic Aperture Radar（SAR）imaging technology is a key tool for time-sensitive remote sensing applications such as disaster monitoring and military reconnaissance. The typical construction of an on-board SAR imaging system using a Field-Programmable Gate Array（FPGA）coupled with a Digital Signal Processor（DSP）as the processing core is well-regarded for its heterogeneous computing power，energy efficiency，and flexibility. However，current FPGA+DSP systems are still under-researched in terms of algorithm support，large-grain processing，on-chip parallel acceleration，and complex matrix transposition，with significant room for performance enhancement. This paper analyses the Nonlinear Chirp Scaling（NCS）algorithm，suitable for large squint，high-resolution imaging，and partitions the algorithm into main and auxiliary paths based on computational complexity and type. A heterogeneous mapping scheme for the NCS algorithm within the FPGA+DSP system is subsequently proposed. To address the transformation of data storage formats post multi-channel Fast Fourier Transform（FFT）processing，which complicates pipelined processing，this work introduces a multi-channel FFT collaborative method based on time-frequency extraction switching to ensure efficient parallel FFT operations. Additionally，to handle the complexity of transpose requirements across various granularities and parallelisms，a universal cross transpose solution using X-Direct Memory Access（XDMA）and on-chip segmented transposition is developed. Employing two VX690T FPGAs and two FT 6678 DSPs as core processors，this paper presents the development of an on-board SAR imaging card that implements the proposed system design. Moreover，a validation environment using simulated sources plus ground testing is established，processing simulation array data for strip/scan/spotlight/sliding spotlight/TOPS modes and actual data for strip/sliding spotlight modes. The array data demonstrates a two-dimensional peak sidelobe ratio of about −13.2 dB and an integrated sidelobe ratio of around −10.1 dB，indicative of good imaging quality. For instance，in strip mode with an image size of 32K×16K，the average imaging time using the NCS algorithm is 7.81 seconds，markedly accelerating imaging speed compared to existing approaches.