電磁最佳化實驗室EM Optimization LabYen-Sheng Research Group, Department of Electronic Engineering

A novel rectenna system having multidirectional receiving capability and scalable antenna gain is presented for radio-frequency (RF) energy harvesting. As the level of ambient energy varies over time and space, the proposed system can scale in array size, antenna gain, direction of reception, and radiation pattern to optimize conversion efficiency and dc outputs. The proposed device comprises five cells of rectenna, each one aiming at an angular sector of 72° in the azimuthal plane. Each cell consists of a quasi-Yagi antenna with variable number of directors and one RF-to-dc energy-harvesting circuit. Thus, the proposed system can achieve either uniform coverage with enhanced antenna gain or highly directional characteristics at one/multiple incidence angle(s). A prototype is designed, fabricated, and tested two-fold. First, the performance of each component is evaluated. The antenna shows robust return loss whatever antenna scale is used. Additionally, antenna gain can be enhanced by scaling in array size, and so is incident power, which leads to improved conversion efficiency. Second, the distinctive characteristics are examined as a system. The experimental results show that the proposed system can be accommodated to various scenarios, and it outputs optimum power as scaling is performed in direction of reception and antenna gain.