| In recent years, there is a lot of research on wireless power transmission (WPT) for various applications, such as mobile devices, electric vehicles, implanted medical devices, sensors, RFID, etc. Compared to wired power transmission, WPT is more convenient and allows the devices to move more freely. Microwave beamforming WPT has been investigated extensively because its fast tracking capability, multiple target tracking capability and so on.;A retro-reflective antenna array based on novel phase-conjugate method is proposed in this dissertation. The phase of the received signal is detected individually and simultaneously at each antenna and the conjugated phase is applied to the corresponding phase shifter of each antenna. Using this method, the antenna element of the array can be placed arbitrarily, which offers high construction flexibility. The single frequency WPT experimental results verify that the proposed retro-reflective antenna array is able to track and focus microwave beam on the receiver. Experiments also show that the transmission efficiency can be improved by increasing the antenna number. A rectenna is also designed to convert received RF energy into DC energy. Measured results show excellent agreement with simulations.;The sidelobe level in the single frequency WPT can be reduced by using ultra-wideband (UWB) retro-reflective beamforming. The system design of the UWB retro-reflective antenna array is improved in this dissertation by using sub-band technique. An impulse receiver is also designed to extract the spectrum of UWB signal. The UWB signal is decomposed into several narrower sub-bands with overlapping regions. An algorithm is developed to seamlessly merge the sub-band spectra into a complete wideband spectrum. Experimental results show that the proposed impulse receiver is able to extract the wideband spectrum with little distortion. |
