K-Band WPT Link with a DC Output Power of 2.9 Watts and a High Transfer Efficiency of 20.7% from the Transmitter's RF Output Power

In this paper, experimental investigations of K-band wireless power transfer (WPT) link are demonstrated. Four 64-element phased array antenna (PAA) modules (with a total transmitted power P<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tx</inf> of 14 W) and four GaAs 1-Watt rectennas are facing each other in a 150 mm (12.5 wavelengths) spacing. An overall WPT efficiency of 20.7% is achieved, resulting in a DC output power P<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</inf> of 2.9 W from P<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tx</inf> of 14 W. To achieve this high overall WPT efficiency, a GaAs 1-watt rectenna with a 73.9% rectification efficiency is employed, and a focused beam toward the rectennas is formed using the four PAA modules. Furthermore, it is demonstrated that the variation of the input power to each rectifier, due to radiated power distribution and rectennas’ antenna gain variation, has a negligible influence on the WPT link efficiency.