Retrieval of equivalent currents by the use of an integral representation and the extinction theorem --- radome applications

The aim of this thesis is to solve an inverse source problem. The approach is based on an integral representation together with the extinction theorem. Both a scalar and a full-wave integral representation are implemented and solved by a Method of Moment procedure. The body of revolution enables usage of a Fourier transform to reduce the dimensions of the problem. A singular value decomposition is utilized to suppress singular values in the inversion process. A nose-cone radome is diagnosed by recreating the equivalent surface currents on its surface from measured near fields. It is shown how the radome interacts with the field, creating beam deflection, pattern distortion, etc. The phase shift of the field due to the transmission through the radome, i.e., the insertion phase delay, is visualized. Disturbances due to defects, not detectable in the measured near field, are correctly localized by the equivalent surface currents. The alteration of side and flash lobes, together with the introduction of scattering due to the defects, are also visualized. Verification is made by comparison between the calculated and measured far field

Sensitivity analysis for antenna near-field imaging

Although imaging and inverse scattering problems have been thoroughly studied during the last century, there is only a partial understanding of these complex problems. Most of the efforts have been placed on the development of efficient inversion algorithms and mathematical uniqueness results. In comparison, there are very few results and a limited knowledge about the information content in the inversion data. In this paper, we provide a mathematical framework for sensitivity analysis of antenna near-field imaging problems, based on the multipole expansion of the electromagnetic field and the Fisher information to quantify the quality of data. By exploiting this framework, a fundamental relation for accuracy and resolution is formulated based on the Cramer-Rao bound (CRB). The sensitivity analysis is illustrated using a relevant example with cylindrical measurement data