Principles of Modern Radar - Volume 2 1891121537

614 CHAPTER 13 Introduction to Radar PolarimetryESPRIT image simply consists of the estimated locations of the principal scatterers. TheFourier image, since these locations are not directly available, is the conventional contourplot of the discrete 2-D Fourier transform of the windowed radar data. The improvementthat ESPRIT processing provides, both in sharpness and spectral splatter, is striking. Itimages accurately all three slots and resolves reliably the two edges of slot 3, the largestin diameter. The phantom scatterer lying behind the base of the cone is the result of thedoubly diffracted ray that crosses the flat base of the target from one edge to the otherand returns to the radar along the line of sight [49]. These doubly diffracted rays causeextended returns in radar target signatures because the corresponding scattering centersare located beyond the target [26].As an example on how polarization-dependent scattering from lossy dielectric materials,such as heat-resistant coatings on reentry vehicles, can be used to discriminatebetween targets of interest and fake targets or decoys, polarimetric behavior of the conicaltest target (Figure 13-8) is considered for the case when it coated with a dielectricmaterial. Figure 13-10 compares the X band (10 GHz) monostatic RCS images of bothbare and coated targets as a function of transmit and receive polarization states. Only theco-polarized states HH and VV are depicted.FIGURE 13-10Radar images(range/cross-range)of co-polarizedreturns for bare andcoated cones.1.510.50−0.5−1−1.5 −1.51.510.50−0.5−1−1.5 −1.5 −1 −0.5 0 0.5 1 1.51.510.50−0.5−11.510.50−0.5−1−1.5 −1.5−1.5−1 −0.5 0 0.5 1 1.5 −1.5 −1 −0.5 0 0.5 1 1.5−60 −55 −50 −45 −40 −35 −30 −25 −20 −15 −10