Constrained Inverse Near-Field Scattering Using High Resolution Wire Grid Models

The microwave inverse problem is addressed using a wire grid model representation with capacitors loaded in parallel with resistors to respectively replace the permittivity and the conductivity of the device under test. A new approach is presented to embed the properties of isotropy and positiveness of the constitutive parameters without additional penalty terms or weighting parameters. An edge-preserving regularization technique is used to better estimate the discontinuities present in the device under test (DUT) and to decrease the sensitivity to noise during the reconstruction process. The optimization algorithm makes use of the conjugate gradient method to minimize the objective function. Synthetic data are used to assess the reconstruction speed of the new method. Simulation results show a five-fold reduction of the computation time compared to what had been presented previously. Experimental near-field measurements at 2.45 GHz on thin plate DUTs are used to assess the validity of the proposed reconstruction method. Satisfactory results are obtained and a spatial resolution of λ/20 is achieved.