A Nested Multi-Scaling Inexact-Newton Iterative Approach for Microwave Imaging

A microwave imaging technique based on the integration of the Inexact-Newton method within a multi-scaling strategy is proposed in the framework of the contrast field formulation of the electromagnetic inverse scattering. The inversion problem is solved by means of a nested procedure that considers three different logical levels: (a) an outer multi-focusing loop aimed at implementing a synthetic zoom for focusing the scatterer support within the investigation domain; (b) a local linearization of the original full-nonlinear inverse scattering function; and (c) a truncated Landweber inner loop devoted to regularize the arising ill-posed linear problem. Thanks to the features of the integrated approach, a reliable inversion technique able to suitably face the non-linearity and the ill-posedness/ill-conditioning issues of the imaging problem is designed. A numerical validation dealing with different objects, measurement setups, and noise conditions is carried out to assess the features and the potentialities as well as the limitations of the proposed strategy. Comparisons with bare approaches and other multi-resolution formulations are presented, as well.