Proposal of electric far field suppression helical antenna for high efficiency WPT system

Wireless power transfer(WPT) system is very important technology in order to realize a ubiquitous society. This technology is a very effective to provide the energy to a communication device without the power unit. Strongly-coupled WPT system is proposed and experimentally demonstrated in 2007⁽¹⁾. Principle of the system is able to be considered as two-stage bandpass filter using resonant antennas⁽²⁾. High efficiency is obtained in the conditions of high Q value of antenna and appropriate load matching to port impedance⁽³⁾. It is necessary to suppress the far-field radiation even though the antenna is a resonant state. Open type helical antenna, which encourages the magnetic coupling, is used on WPT in many cases^(1-3). This antenna also has a dipole mode which generates a far field radiation and the radiation field is a factor in transmission loss. This paper proposes a double-helical antenna to suppress the far-field radiation caused by dipole mode.