A new synthesis technique for near-field focusing systems

Pattern synthesis techniques have been widely used during the years to define and sculpt the radiation patterns of an antenna system in its far-field region. However, in several applications such as near-field probing and radiometry, medical imaging, etc. it is important to focus the energy in the Fresnel zone or even in the extreme near-field (reactive zone) of an electromagnetic device. In (J. W. Sherman, III, IRE Trans. Antennas Propagat., vol. AP-10, no. 4, pp. 399-408, July 1962), the properties of the electromagnetic fields in the far-field and Fresnel zone of a focusing radiating aperture are examined. The latter are the fields near the axis of a defined focal plane parallel to the aperture. It is shown that the fields in these two zones present the same properties as long as a quadratic phase taper of the tangential field distribution is adjusted on the focusing aperture. Therefore, the optimization/shaping of fields in the Fresnel zone can be achieved by using classical far-field techniques. However, this is not possible within the near-field or reactive zone of a radiating system. © 2013 IEEE.