Monochromatic nonuniqueness in plane-wave inverse scattering

In this paper we examine the nonuniqueness behavior of the least squares error functional which is iteratively minimized to obtain the material scattering parameters. For monochromatic, plane-wave scattering from a homogeneous, infinite dielectric cylinder and an inhomogeneous dielectric cylinder (2-layered case), the least squares error functional surface has many local minima, creating traps for any gradient-search algorithm. Multi-frequency illumination is shown to reduce significantly the occurrence and depth of these local minima.