Microwave to mmWave Wireless Power Transfer: An Overview of the Design Challenges with a Focus on UK-Based R&D

Microwave and mmWave wireless power transfer (WPT) continues to attract significant interest. This paper presents an overview of selected UK-based activities in WPT and energy harvesting, and highlights the emerging research trends and future directions, with focus on mmWave power transfer. The justification for mmWave power transfer, fueled by beyond-5G hardware, is first introduced. Rectenna and WPT-specific innovations such as beam-forming, bandwidth enhancement, and frequency scanning are then highlighted. The developments are then reviewed from an application perspective, highlighting the novel material and implementations of rectennas, along with the outstanding research challenges. Quantitative performance comparisons are presented summarizing state-of-the-art rectifiers, rectennas, and antennas.