Study of a repeater Tx antenna concept of a portable device wireless battery charging system

A Study of a repeater concept of a transmitting antenna (Tx) for wireless battery charging system of a portable devices is reported in this paper. The objective is to extend the charging area by using the repeater coil concept. The repeater coil is located near the Tx active coil in the same plane of Tx active coil without any direct connection from a source. The operating frequency at 6.78MHz is chosen by following the frequency A4WP wireless battery charging system specification. The proposed Tx antenna is designed for extending a charging distance of the portable devices on xy-plane (such as on table) using a repeater coil (called Rp). The charging area of the proposed antenna is larger than a conventional single Tx antenna. The repeater coil is the same size of the single Tx antenna. The single Tx antenna transfers the magnetic energy to the repeater coil. The receiving antenna (small coil) in a mobile phone picks up the magnetic energy from the repeater coil. The suitable separating distance between the single Tx coil and the repeater coil will be investigated. The study is performed by analyzing the power transfer efficiency of the proposed antennas via scattering parameters [S-parameters] and of the two port network representation. The 50 Ohms system impedance is chosen in this study. The optimum impedance matching at the Tx and Rx sides are considered. It is found that the charging area is increased by using the proposed repeater coil antenna.