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The present paper deals with the inversion from experimental data provided by Institut Fresnel, France. The distorted-wave Born iterative approach is applied to the reconstruction of two lossless configurations involving dielectric circular cylinders. The dynamic range and the resolution of this scheme are governed by the operating frequency. For a low frequency, the dynamic range is large and the resolution is limited; raising the frequency improves the resolution at the cost of dynamic range. To obtain a high resolution for a large contrast, scattered-field information at multiple frequencies can be used. This is demonstrated for two cases where a direct inversion does not lead to convergence.

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Abstract-The scattering from a large complex structure comprised of many objects may be efficiently tackled by embedding each object within a bounded domain (brick) which is described through a scattering operator. Upon electromagnetically combining the scattering operators we arrive at an equation which involves the total inverse scattering operator 1 of the structure: We call this procedure linear embedding via Green's operators (LEGO). To solve the relevant equation we then employ the eigencurrent expansion method (EEM)-essentially the method of moments with a set of basis and test functions that are approximations to the eigenfunctions of 1 (termed eigencurrents). We have investigated the convergence of the EEM applied to LEGO in cases when all the bricks are identical. Our findings lead us to formulate a simple and practical criterion for controlling the error of the computed solution a priori.Index Terms-Boundary integral equations, composite structures, domain decomposition method, eigencurrent expansion method, equivalence principle, method of moments (MoM).