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

A 2-D near-field uniform diffraction tomographic (UDT) imaging algorithm is formulated to generate images of targets embedded in a layered structure. The conventional diffraction tomography (DT) improperly applies the stationary phase method for stratified environments to reduce the innermost spectral integral. In DT, the large argument is assumed to be the depth, which is not appropriate for near-field imaging. This results in amplitude discontinuities occurring at the interfaces between adjacent layers. The correct large argument is the free space wavenumber as used in high-frequency asymptotic solutions. The UDT therefore yields uniformly continuous images across the interfaces. And like the DT, the UDT retains the fast Fourier transform relation in the algorithm for generating images very efficiently. Numerical and experimental image comparisons between DT and UDT for objects buried in stratified environments are presented to demonstrate the efficacy of the proposed UDT method.