Patent ID: 8446257

Claim:
A radio frequency (RF) charging system, for charging an RF device that generates a response signal upon receiving an RF signal, the RF charging system comprising: an antenna set, comprising a plurality of antennas; a switch unit, coupled to the antenna set; an RF module, coupled to the switch unit, for generating the RF signal; a microcontroller unit (MCU), coupled to the switch unit and the RF module, for controlling the switch unit to select from the antenna set an antenna that receives the response signal and has a highest transmit/receive efficiency among the plurality of antennas, and transmitting the RF signal through the selected antenna to charge the RF device; and a display panel, coupled to the MCU, wherein the MCU estimates a distance between the RF device and the antenna set according to whether the antennas receive the response signal, and controls the display panel to display a predetermined area when the estimated distance indicates that the RF device is not within the predetermined area of the display panel, and wherein the antenna comprises concentric ring antennas in different sizes having a same center, and the MCU estimates the distance between the RF device and the center according to a smallest ring antenna capable of receiving the response signal.