Compact Planar Integrated Rectenna for Batteryless IoT Applications

This paper addresses a new topology of compact rectennas in which the rectifier is integrated directly on the radiating surface. The rectenna is designed for wireless power transmission or microwave energy harvesting application in ISM 900 MHz band and exhibits a very good measured conversion efficiency $(>\mathbf{25}\%)$ on a non-optimal load $(\mathbf{10k}\Omega)$ for very low microwave power densities $(> \mathbf{0.18}\mu \mathbf{W}/\mathbf{cm}^{\mathbf{2}})$ . The measured DC voltage $(> \mathbf{330 mV}$ for microwave power density of at least 0.22 $\mu \mathbf{W}/\mathbf{cm}^{\mathbf{2}})$ obtained from this planar rectenna is in the range of the cold turn-on/start-up voltage of modern commercial off-the-shelf DC-to-DC boost converters and power management units. The proposed rectenna is also very compact: its physical surface $(\mathbf{10.5} \mathbf{x\ 6\ cm}^{\mathbf{2}})$ is only 5% of the square wavelength at the operating frequency (860 MHz).