Clarification of Why Range-Doppler Algorithm Fails for SFCW Radars: Theoretical Analysis and Experimental Evaluation Using Real GB-SAR Data

In a recent study, we have reported a modified range-Doppler algorithm (RDA) for synthetic aperture radar (SAR) imaging with stepped-frequency continuous wave (SFCW) illumination. In this article, the theory behind this modified RDA, that is, SFCW-RDA, is re-examined in detail to provide a better understanding of the origin of the SFCW-dependent defocusing terms of the conventional RDA. The range-azimuth coupling errors are evaluated, and the modifications to correct these errors are made in an alternative formulation of SFCW-RDA. To determine to what extent the original RDA fails in SFCW processing and to demonstrate the performance of the proposed algorithm, both the simulation and real data results are presented. A hypothetical SAR data composed of perfect point-scatterers are assumed in the simulation. Furthermore, ground-based SAR experimental data from a typical scene with man-made targets is used to evaluate the proposed technique. The corresponding SAR images of the conventional and the proposed RDA visually prove that the modified RDA can trustfully be used for the imaging of SFCW radar echoes.