This paper presents an overview of state-of-the-art waveform engineering, target tracking, synchronization, coherent beamforming, and integrated TX / RX antenna design approaches for far-field wireless power transfer networks that power mobile targets. One example application potentially powers UAVs in flight with advanced elements to accomplish long range power beaming such as distributed arrays of coherent beam-steerable transmitters, and highly efficient receiver rectennas to harvest the power with superior power conversion efficiency (PCE). Metasurface approaches to shorter range power transfer is also discussed. Future research directions are identified to overcome limitations and gaps.