High gain isotropic rectenna

Abstract

This paper introduces an original strategy to step up the capacity of ambient RF energy harvesters. The low rectification efficiency that comes from weak input power is enhanced through high gain antenna arrays that push the circuit to operate in a more efficient state. The prototype uses beam forming networks to build up a wide coverage since ambient energy can come from any direction, or the orientation of the rectenna may be unknown. By extending the operating range of rectifiers to higher input powers, the system operates as a very efficient narrow beam rectenna or as a synthetic high gain isotropic rectenna. The rectification efficiency pattern of one multi-beam rectenna, functioning in the 2.4 GHz band, is plotted and compared to a dipole rectenna's pattern. For a low incident power density of 4.10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> mW.cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , the rectification efficiency is largely improved in any direction : from 2.6% with a dipole rectenna up to 14%.