An Orthogonally Polarized Multibeam Rectenna System to Imitate Isotropic DC Pattern for Orientation-Insensitive Microwave Power Delivery

The Wireless Power Transfer (WPT) rectenna systems suffer from low power conversion efficiency (PCE) due to lower receiver (Rx) gain, polarization mismatch, and angular misalignment that can occur between the transmitter (Tx) and receiver (Rx). This impedes the realization of self-sustaining freely rotating the Internet of Things (IoT) sensor nodes. To address this issue, an orthogonally polarized, multibeam, orientation-insensitive WPT system is proposed to achieve a nearly isotropic dc pattern. The system employs orthogonally polarized endfire rectennas (Rect-I and Rect-II) in each sector and a centrally placed cross-polarized patch rectenna (Rect-III) to attain 3-D dc coverage. Furthermore, the antenna and rectifier circuit are conjugately matched to achieve miniaturization. A fully integrated hybrid dc combining topology and a smart bypassing network is employed to minimize combining losses. The three rectenna elements offer a PCE of 51%, 44.9%, and 58.9%, with an open-circuit harvested dc voltage of 1600 mV. Thus, orthogonally polarized, nearly isotropic dc pattern and polarization insensitivity of the proposed multibeam rectenna system (MBRS) makes it suitable for powering small battery-less IoT sensor nodes.

I. Introduction

The rectenna is an indispensable component of the WPT system [1], designed by integrating a receiving antenna (Rx) and a rectifier circuit [2]. This allows miniaturized the Internet of Things (IoT) sensor nodes to overcome the problem of limited battery capacity in wireless sensor network applications such as agriculture [3], healthcare [4], and smart cities [5]. The significant problem with the WPT systems is low power conversion efficiency (PCE) due to various system design challenges, such as low Rx gain, higher-order harmonics [6], polarization mismatch [7], and angular misalignment [8] between Tx and Rx antennas. The latter problem originates in the freely moving IoT nodes due to relative rotation between Rx and Tx antenna [9], which reduces PCE significantly. Moreover, polarization mismatching reduces the PCE due to loss of RF power, resulting in low power received at the Rx terminal, which affects the impedance matching of the rectenna. The proposed work aims to design a WPT system having high Rx gain and polarization-oblivious nearly isotropic coverage for realizing zero-power IoT sensor node applications.