Design of Continuous Beam Steerable and Scalable Unit Module for Wireless Power Transmission Using Injection-locked Oscillator Array

Long-range wireless power transmission (WPT) is implemented with the beamforming using the phased array transmitter technology, which has been extensively applied in the radar system. The cost of conventional phased array transmitter module scales up in proportion to the number of antenna elements, as the massive number of transmit channels results in the increasing complexity of hardware and feeding antenna elements. Besides, the conventional phase-shifting transmitter architecture has the lower DC to RF power conversion efficiency due to the insertion loss of power combining network at microwave frequency. In this paper, the concept of spatial power combining transmitter is utilized and the upconversion circuit is greatly simplified to an injection locked oscillator. Our WPT system is implemented with the technology of oscillator array antenna at 2.4 GHz, which converts DC power to RF power and radiates into the air directly. The feedback voltage controlled oscillator (VCO) is implemented as the microwave source using a off-the-shelf bandpass filter and the external signal is injected to the oscillator via a microstrip coupler. The oscillator core shows the DC-to-RF conversion efficiency of 45.87% with the injected power of 0 dBm at 2.4 GHz. Then the digital phase shifter is used to phase shifting the injected signal to extend the beam coverage. From the link budget analysis, the overall DC-to-DC efficiency of our highly-integrated system shows the 1.5 times (0.22%) of the conventional phased array (0.15%) when the separation between the transmit array and the receive horn antenna is 1.2 meter. Therefore, as an modularized array, the proposed system demonstrate the promising capability of upscaling to an efficient massive array with greatly reduced bill-of-materials (BOM).