A 3-D Uniform Diffraction Tomographic Algorithm for Near-Field Microwave Imaging Through Stratified Media

The uniform diffraction tomographic (UDT) algorithm corrects discontinuities associated with conventional DT algorithms when applied to imaging of objects buried in layered media. The cause of the discontinuities in DT is in the implementation of the stationary phase solution for evaluating the spectral integral. The usual approach is to make a far-field approximation assuming that the depth is large. However, this is not appropriate for near-field imaging. UDT overcomes this issue by choosing the correct large asymptotic parameter in the exponent of the spectral integrand. In this paper, the original 2-D scalar UDT algorithm is extended to a fully vector 3-D solution involving the dyadic Green's function for the layered media, the polarization of the gain pattern of the probe antenna, and the stationary phase evaluation of a 2-D spectral integral. The 3-D UDT is demonstrated to provide smoothly continuous images, and like the conventional DT, the fast Fourier transform is implemented to generate images in real time. 3-D numerical simulations and experimental results are presented to verify the accuracy and efficacy of the 3-D UDT algorithm.