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Wireless power transfer technology has received much attention recently. Although the technology has been existed for a long time, never before has it has received the current level of attention. This can be primarily attributed to social demand related to the increased use of mobile devices, which need frequent recharging, and plugging the device into an outlet is not convenient. It is also due to changes in available technology. The emergence of electromagnetic resonant coupling, which works over a large air gap with high efficiency has until recently not been possible with typical technologies. However, there are limitations to using only a transmitting and a receiving antenna. Repeater antennas have been proposed to extend the length of the air gap. Long distance power transfer is achieved by simply installing a repeater between the transmitting and receiving stations. And by installing repeaters inside walls, below desks, and under the floor, it will be possible to realize a fully wireless house in which it is possible to charge devices anywhere inside its confines. Previous studies have demonstrated that a repeater antenna can extend the distance of the power transfer with the installation of a repeater antenna between a transmitting antenna and a receiving antenna. Detailed studies of mutual inductance, the position of repeater antennas and theoretical studies about equivalent circuits cannot be found in the literature. This paper proposes that theoretical study of equivalent circuits of repeater antennas it includes the problem of sign of mutual inductance which is occurred when the repeater antennas are used.