A technique based on the Green's function theory is used in the present research in order to study theoretically the focusing properties of a constructed 3D non-invasive microwave imaging system, consisting of an ellipsoidal conductive cavity and a radiometric receiver. A double layered spherical human head model is placed on one focal point of the elliptical reflector, while the receiving antenna is placed on the other focus. Making use of the reciprocity theorem, the equivalent problem of the coupling between an elementary dipole and the double layered lossy dielectric human spherical model is solved. Numerical results concerning the electric field distribution inside the head model and in the rest of the cavity, at two operating frequencies (1.5 GHz and 3.5 GHz), are presented and compared to the results of an electromagnetic simulator. Finally, phantom experimental results validate the proof of concept and determine the temperature and spatial attributes of the system.
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