In recent years, single-frequency and wideband
synthetic aperture imaging algorithms have been
used in radar imaging for microwave and
millimeter wave nondestructive testing (NDT) of a
wide range of materials and structures. Synthetic
aperture radar (SAR) techniques are robust and
therefore offer great utility when incorporated with
NDT applications. Unlike most radar applications,
however, NDT applications are often concerned
with layered composite structures in which an
anomalous indication may exist. Therefore, any
such SAR algorithm must be able to account for the
influences of each layer according to its dielectric
properties and thickness (that is, account for the
influence of reflected and transmitted waves at
each boundary). In such applications where small
thicknesses are of interest, if the layered nature of
the structure is not properly taken into account,
then the image of a target may correspond to a
wrong location within the structure, or may be
masked or otherwise significantly altered. In this
paper, an effective one-way SAR algorithm is
presented that is capable of correctly imaging and
determining the location of a target in an arbitrary
multilayered structure. This algorithm employs
spectral-domain Green’s function for a multilayered
structure, which accounts for all reflected and
transmitted signals at each boundary.
Subsequently, a Wiener filter-based deconvolution
process was employed to reconstruct an image.
Reconstructed images produced in this way are
devoid of unfocused and/or misplaced targets,
which usually happens if standard SAR imaging
techniques developed for free-space applications
with homogeneous backgrounds are used for
imaging a multilayered structure. This paper
presents the results of simulations, as well as a
representative measurement, to show the efficacy
of the proposed technique.
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