Abstract-In this paper, measured results for complex permittivity of some commonly used building walls under different hydration (wetness) levels are presented and a simple hybrid measurement and electromagnetic modeling approach for the estimation of power returns from targets located behind walls in various through-the-wall radar imaging (TWRI) scenarios is discussed. The radar cross section (RCS) of some typical targets of interest, such as an AK47 assault rifle and human, are first investigated in free-space using numerical electromagnetic modeling. A modified radar range equation, which analytically accounts for the wall effects, including multiple reflections within a given homogeneous or layered wall, is then employed in conjunction with wideband measured parameters of various common wall types, to estimate the received power versus frequency from modeled targets of interest. The proposed technique, which can be helpful in TWRI dynamic-range system design consideration, is, in principle, applicable to both bistatic and monostatic operations. The results for various wall types, including drywall, brick, solid concrete, and cinder block, the latter two under both wet and dry conditions, are presented.

[1] Development of an imaging algorithm that accurately models the wave propagation physical process has become an important topic in through-the-wall radar imaging (TWRI). In this paper, a full polarimetric beam-forming algorithm for through-the-wall radar imaging for a general multilayer wall case is presented and applied to various 2D and 3D simulated and measured scenarios. Polarimetric TWRI not only enhances the target characterization but also mitigates the wall ringing effect in cross polarizations. The far field layered medium Green's function is incorporated in the proposed TWRI algorithm for the quad-polarization of the target returns, namely, VV, HV, VH and HH. Due to the incorporation of the layered medium Green's function, the imaging algorithm not only takes into account the wall reflection, bending, and delay effects but also accounts for the complex scattering mechanism due to the presence of the wall. Numerical and experimental results show that the proposed full polarimetric beam former can provide high quality focused images in various wall-target scenarios, in particular, when the technique is combined with a wall parameter estimation technique.

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