Wide-angle radar imaging using time–frequency distributions

Low-frequency radar systems provide some attractive advantages in a few niche applications, such as foliage penetration and covert operation. In low-frequency imaging systems, data must be collected over a wide range of angles to obtain cross-range resolution comparable to that obtainable from a competing small-angle high-frequency system. The reflectivity of a target varies with aspect angle; although this variation is usually ignored by traditional radar imaging algorithms, it sometimes cannot be neglected in wide-angle scenarios. To account for aspect dependence of reflectivity, time–frequency transforms have been invoked to generate a series of images corresponding to different look angles; these images may be considered individually or synthesised into a single image. A simple theoretical analysis with a point scatter illustrates why the angular dependence needs explicit consideration. The potential of time–frequency methods is illustrated via simulations.