An Efficient Algorithm Based on Frequency Scaling for THz Stepped-Frequency SAR Imaging

An efficient algorithm based on the frequency scaling algorithm (FSA) for terahertz (THz) stepped-frequency (SF) synthetic aperture radar (SAR) imaging is proposed in this article. THz SF SAR has an urgent application demand in close-range medical imaging, close-range security check, and near-space military target reconnaissance. In these fields, the real-time performance of the imaging algorithm is of great significance. The back projection algorithm (BPA) is an accurate time-domain imaging algorithm, but it has a huge amount of calculation and cannot meet the requirements of real-time imaging. The frequency-domain SF SAR imaging algorithms are based on interpolation, which will cause Gibb's phenomenon. An efficient THz SF SAR imaging algorithm named SF-FSA is proposed in this article, which uses the frequency scaling operation and phase multiplication to complete precise range cell migration correction (RCMC), thereby avoiding Gibb's phenomenon caused by interpolation while ensuring high efficiency. In particular, compared with other interpolation-based algorithms, SF-FSA only needs the fast Fourier transform (FFT) and complex multiplication, which is easier to implement on FFT-based signal processors and fast parallel signal processors. By the formula derivation of SF-FSA, the problem on how to select parameters in the frequency scaling operation in SF-FSA is solved, the aliasing phenomenon caused by the frequency scaling operation in SF-FSA is explained, and the corresponding method to avoid the aliasing phenomenon is given. Finally, the validity and feasibility of SF-FSA are demonstrated by simulation and experimental results.