360°-Beam-Steering Low-Sidelobe Time Reversal Microwave Power Transfer by Superposition of Multiple Weighted Radiation Modes

This letter proposes a 360°-beam-steering low-sidelobe time reversal microwave power transfer (TR-MPT) method. The beam steering is implemented by only one circular patch antenna fabricated with multiple feeding ports. The multiple feeding ports are designed to stimulate different radiation modes and their combinations to steer the beam within 360° in the azimuth plane. To depress the sidelobe levels and enhance the beam gain, a disc-top-loaded monopole antenna is added at the center of the patch antenna, which is used to excite an additional mode out of phase with the maximal sidelobe but in phase with the main lobe. Finally, time reversal (TR) is adopted for optimally weighting the stimulated modes and focusing the power beam adaptively to the desired receiver. A prototype of the TR-MPT system based on the proposed method is established. The experiments demonstrate that the new method can not only adaptively focus the power at the receiver placed at any azimuth angle within 360°, but also achieve a low sidelobe level of smaller than −8.57 dB under a 0.7-wavelength aperture. Additionally, the power transferred to the receiver at different angles has a small fluctuation of less than 0.7 dB.