Abstract: An example transmitter comprises a housing with a top surface that allows for placement of a ring device to be wirelessly charged by the transmitter, the ring device is a device that is capable of receiving a power from the transmitter. An antenna, placed inside of the housing and disposed below the top surface, configured to transmit radio frequency (“RF”) waves to the ring device, where a radiator of the antenna has a circular shape that is positioned coplanar with the inner surface of the housing and the radiator has a certain thickness that is defined by an inner radiator diameter and an outer radiator diameter; and the inner radiator diameter of the radiator is substantially equal to the first inner ring diameter of the smallest ring device, and the outer radiator diameter of the radiator is substantially equal to the first outer ring diameter of the largest ring device.