Electromagnetic spectral determination of the material composition of penetrable radar targets

The resonance theory of scattering is applied to radar backscattering from penetrable targets in an attempt to solve the inverse scattering problem, i.e., the extraction of sufficient material-composition information from the returned echoes to permit target identification. For the case of a conducting spherical target coated with a dielectric layer, electromagnetic resonances are identified in the calculated radar cross section of the target by the solution of equations for the target eigenvibrations. The inverse scattering problem is then solved by the use of the expressions obtained for the modal impedances and admittances and the asymptotic forms of the Bessel functions, resulting in an expression for the dielectric constant and the thickness of the coating in terms of the uniform spacings and widths of the resonances in the high frequency region of the resonance spectrum. It is noted that a similar analysis may be carried out for targets of other known shape but unknown material composition, and for applications other than radar backscattering.