A Planar Integrated Rectenna Array With 3-D-Spherical DC Coverage for Orientation-Tolerant Wireless-Power-Transfer-Enabled IoT Sensor Nodes

Multiple IoT sensor nodes with radio frequency (RF) power harvesting are deployed in random positions and orientations with respect to the power transmitter (Tx) generally installed on ceiling and side walls. The IoT sensor nodes with wireless power transfer (WPT) systems employing conventional rectenna designs with complex structures can provide only 2-D coverage, thus, free-positioning and orientation-insensitive WPT is unrealizable. Therefore, a novel, compact, planar-integrated rectenna-array providing 3-D-spherical coverage is proposed for the WPT system in two-layer PCB technology. The proposed design scheme harvests maximum RF power in both, azimuth and elevation planes, by encapsulating endfire and inherent tilted-beam bore-sight rectenna elements within a single sector. The radial integration of six such sectors coordinately achieves 3-D-spherical dc coverage, and the bore-sight 3
$\times1$
patch antenna array (PA) functions as a dc low pass filter (dc-LPF) offering miniaturization and insertion loss reduction. The endfire and bore-sight rectenna components harvest 240 and 255 mV at 1280 and
$1176~\Omega $
output loads with RF-dc conversion efficiency of 69.1% and 65.28% at 5.8 GHz, respectively. Further, the rectenna elements are integrated using a simple and easily realizable low-loss parallel dc combining circuit, making it suitable for IoT sensor nodes.