Experimental investigations of accuracy improvement and limitations of a free space measurement system including thin lenses

In this paper a free space measurement system, including two horn antennas and two lenses, is considered. It has been shown that an experimental investigation of the fabricated lenses is of paramount importance, since fabrication inaccuracies could lead to system performance deterioration. A method to determine the focal length of the fabricated lenses, the operational frequency and the separations between horns and lenses and the lenses themselves, without a priori information about the phase centers of the horn antennas, has been given. It has been shown that for the alignment of such a system the phase centers of the horns are not needed at all. The proposed experimental alignment method in this paper improved the accuracy of the material measurements. Finally limitations on the thickness of the MUT for certain accuracy were discussed.