A Fourier model of ISAR imaging of approaching targets

The authors develop a theory for high-resolution, microwave imaging of approaching targets, using concepts from synthetic aperture radar. Assuming a stepped-frequency waveform, it is shown that the demodulated returned signals provide approximate samples of the two-dimensional Fourier transform of the target reflectivity, on a nearly Cartesian grid. The Fourier model is only an approximation, however, and it is shown that the effect of the true non-Fourier nature of the problem is to shift point targets in the cross-range direction from their actual locations. The importance of autofocus techniques is illustrated, and directions for future research are suggested