Wireless Power Transfer Through Simultaneous Near-Field Focusing and Far-Field Synthesis

A technique for the synthesis of antenna arrays that can account, simultaneously, for near-field (NF) focusing on one or more spots and far-field (FF) specifications is proposed, which deals with wireless power transfer applications. The technique is based on the minimization of a properly defined cost function accounting for both NF and FF requirements at the same time and including a tradeoff parameter to balance each specification in the final result. By synthesizing the weights that have to be applied to the elements of the array fulfilling all the specifications, a wireless link between the antenna array and different devices can be established more efficiently since power radiated at undesired positions or directions can be reduced. Some illustrative examples are presented to show the ability of the method to solve problems with independent specifications for NF and FF distributions. A prototype of a 16 x 16 planar array operating at 16 GHz has been realized and characterized; it is shown that it is able to, simultaneously, focus on two NF spots and at an assigned FF direction.