Radar imaging through cinder block walls and other periodic structures

Through-wall radar imaging is a challenging area of research due to the complex multi-layer and inhomogeneous structure of building walls. The wall distorts and attenuates the radar signal in a way that is not easy to predict, except in the most simple of cases. In this paper a general periodic model is developed and applied to the imaging algorithm. Periodic dielectric wall models for microwave transmission and reflection have been investigated by several researchers [1-5]. Floquet mode theory [6] is used to find the discrete plane wave directions that are uniquely determined by the period. Below a certain frequency there are no propagating Floquet modes, so only the specularly transmitted and reflected plane waves are present. In this case it is often possible to use an equivalent 3-layer homogeneous model as described in [4]. This makes it much easier to use a ray tracing code such as the NEC-Basic Scattering Code (NEC-BSC) [7] because the Fresnel plane wave reflection and transmission coefficients may be applied directly. Here we compare the 3-layer model with a volume periodic moment method solution. The goal is to generate model-based images using both approaches to see the effect of the periodicity on the image.