Low frequency imaging of separated objects using the ramp response technique

Abstract

The stealthiness is intended to produce a very weak radar return in usual radar frequency bands. But, this can be countered with lower frequencies studies. These lower frequency bands correspond to the Rayleigh region and the resonance region for object dimensions respectively small and of the same order compared to electromagnetic wavelengths. Contrary to high frequency imaging, low frequency methods cannot provide high resolution but they give information on the overall dimension and the approximate shape of the target. A low frequency method, proposed by Young [1] and known as the ramp response technique, permits to generate a three dimensional (3D) image of the target shape from its ramp response signatures. The ramp response of a target is directly related to the profile function of the target, namely its transverse cross-sectional area along the line-of-sight. Usual 3D image generation uses “approximate limiting surfaces” [1], supposed to enclose the unknown target, and gives an estimate of the target shape by iteratively fitting some geometrical parameters. However, this algorithm can be used only for convex and single objects. That is why we have proposed a new algorithm permitting to reconstruct objects with arbitrary shape, as well as separated objects [2]. In this paper, we determine the limit of separation provided by this new imaging algorithm, using the example of two perfectly electric conducting (PEC) spheres.