OVERVIEW

In the RCS measurement community, radar imagery is generally understood to mean the resolution of target scattering centers in both the range and cross-range dimensions. The formation of radar images demands the collection of coherent RCS data and the subsequent off-line processing of those data with specialized software. The discrete Fourier transform (DFT) is the primary tool used in the processing, and in examples presented in this chapter we rely on the fast Fourier transform version (FFT) of the DFT, based on powers of 2. Two such transformations are involved.

One is in the range dimension and the other in the cross-range dimension. The first is derived from coherently swept- or stepped-frequency waveforms and the second from collections of such sweeps or steps as the target is rotated in angle. Even when the target is stationary, the coherent echo signals can be transformed to the time (range) domain with the ubiquitous FFT, generating range profiles of the distribution of scattering centers. The resolution of the transformed data in the range dimension increases (becomes finer) as the bandwidth of the waveform increases, and scatterers as close as a centimeter or two have been resolved with very wide-band systems.

Scattering centers are resolved in the cross-range dimension by means of target rotation and the collection of several dozen frequency sweeps distributed over a given sector. The resolution in cross-range becomes finer as the angular data collection sector becomes wider. The successful collection of radar image data therefore depends on the resolutions...