Time-varying spectral analysis for radar imaging of manoeuvring targets

Fourier transforms are the basis for conventional radar range-Doppler imaging. Target rotation during the coherent integration time results in a time-varying Doppler frequency shift that produces, after Fourier transform, a smeared Doppler spectrum and a blurred image. Sophisticated motion compensation algorithms must be applied to obtain focused images using Fourier techniques. However, image blurring can be mitigated without resorting to sophisticated focusing algorithms by using time-varying spectral analysis in place of the Fourier analysis for Doppler processing. Various methods of time-varying spectral analysis are described and compared. Range-Doppler images of manoeuvring aircraft produced by conventional Fourier analysis are then compared with those produced by time-varying spectral analysis. A quantitative simulation illustrates the benefit of using the latter.