  Conventional wireless power transfer systems consist of a microwave power
generator and transmitter located at one place and a microwave power receiver
located at a distance. Here we show that wireless power transfer can be
realized as a single distributed microwave generator with an over-the-air
feedback, so that the microwave power is generated directly at the place where
the energy needs to be delivered. We demonstrate that the use of this paradigm
increases efficiency and dramatically reduces sensitivity to misalignments,
variations in load and power, and possible presence of obstacles between the
source and receiver.
