Aim of this study is the improvement of the focusing properties of a microwave radiometry tomography system, used for the imaging of the product of temperature and conductivity in biological tissues via contactless measurements. The operation principle of the device in question is based on an ellipsoidal conductive wall cavity, which provides the required beamforming and focusing. The biological tissue under measurement is placed on one of the two focal points whereas on the other one, a dipole antenna measures the black body type radiation emitted from the head's tissue. In the framework of the present research several approaches are followed in order to improve and optimize the system's focusing properties on the tissue area of interest. Extensive simulations using a commercial FEM tool are performed in a wide range of operation frequencies. Dielectric spheres of various electromagnetic characteristics are placed either around the source (human head model) or the receiver (dipole antenna) in order to improve the matching on the head-air interface. The ability of focusing the electromagnetic energy in specific areas inside the human head is herein investigated in detail and further discussed.