Harmonic Reflection Rectenna for Precise Wireless Power Transfer Antenna Alignment

This study introduces a highly efficient harmonic reflection (HR) rectenna designed for precise wireless power transfer (WPT) antenna alignment. The proposed HR rectenna not only converts RF signals to DC power but also transmits a second-harmonic signal to determine the beam alignment between the device and transmitter in diverse environments, including free space and within a medium such as the human body. The proposed rectenna integrates a dual-band slot patch antenna and a HR rectifier. The HR rectifier is configured using a matched voltage doubler and independent second-harmonic impedance control network (ISHICN). To reduce the complexity of the dual-band matching network and mitigate the coupling between the fundamental and harmonic impedances of the HR rectifier, an independent matching technique is applied to a matched voltage doubler and ISHICN, to ensure matching at both the fundamental and harmonic frequencies. Measurement results of the proposed HR rectifier demonstrate impressive performance metrics, including a peak power conversion efficiency (PCE) of 71.6 % at 28 dBm of input power, as well as a peak conversion gain (CG) of -10.4 dB at 8.4 dBm of input power. Notably, the frequency range for PCE >50 % and CG > -22$ dB spans over 0.8 GHz. The antenna adopts a microstrip-fed slot patch design for wide beamwidth at 2.45 GHz and 4.9 GHz, achieving peak gains of 4.9 dBi and 3.8 dBi, respectively. The HR rectenna is integrated with a dual-band microstrip-fed slot patch antenna with sized 60 mm $\times 72.5$ mm. The implemented rectenna is verified to be an efficient WPT receiver through an antenna beam alignment experiment in free space and minced-pork environment.