Permittivity Estimates of Dielectric Spheres Using Radar Scattering Measurements

Broadband coherent radar scattering measurements were used to estimate the complex permittivity of homogeneous isotropic spheres. A Nelder-Mead optimization minimized differences between measured coherent scattering data and a corresponding forward solution provided by the dielectric Mie series. The method was applied across a range of dielectric materials to include Teflon, polystyrene foam, alumina oxide, neoprene rubber, and shungite. Dielectric constant estimates were achieved to within 0.1-6.85% of published values using traditional waveguide or cavity approaches. The method could not satisfactorily estimate dielectric loss tangent for low loss materials (e.g., foam and Teflon) but increased in accuracy with increasing dielectric loss.