Analytical Formulation of Rectenna System Performance and Fully Integrated Design for Polarization Insensitive Wireless Power Transmission

In wireless power transfer (WPT), rectennas are used as RF-to-dc power converter to recharge the batteries of small Internet-of-Things (IoT) nodes. However, the harvested power of the rectenna is affected by the polarization mismatch between the transmitter antenna and the rectenna. The existing rectenna solutions use matching networks (MNs) and hybrid couplers having bulky and lossy elements resulting in degraded power conversion efficiency (PCE). It is unclear which solution is better suited for small IoT nodes. Thus, a mathematical framework is developed for the rectenna performance comparison of the polarization-dependent efficiencies. The efficiency performance for various rectenna designs is formulated and compared. This reveals that the conventional designs are either polarization-sensitive or compromise efficiency. Therefore, a fully integrated and compact linearly polarized multiport rectenna system ( $N$ -LPR) is proposed to address the issues. The proposed design does not use MNs and hybrid couplers thus improving the efficiency. Moreover, the performance of the $N$ -LPR is analytically formulated to achieve polarization insensitivity; furthermore, the impact of dc pick location on the rectenna patch is also analyzed. The proposed framework is validated experimentally, and the results demonstrate the feasibility of the proposed rectenna design to accomplish a polarization-insensitive WPT system suitable for recharging small IoT nodes.