A Compact Dual-Band Four-Port Ambient RF Energy Harvester With High-Sensitivity, High-Efficiency, and Wide Power Range

The design of an ambient radio frequency (RF) energy harvesting system is introduced to replace the battery of the mass Internet-of-Things devices. This system can achieve high sensitivity with high efficiency over a wide input power range by optimizing the differential-drive cross-coupled (DDCC) rectifier and the load. The impedance of the dual-band four-port loop antenna array is directly conjugated to match with the rectifier, which reduces insertion loss of the matching network to improve efficiency. At 915 and 945 MHz for ISM and GSM bands, the rectenna can achieve high sensitivity of −30 dBm with 22% and 24% efficiency, high efficiency of 65% and 48% with −20-dBm input power, and a wide input power range from −30 to −18 dBm with 22–65% and 24–48% efficiency. The dual-band design explores the frequency diversity to harvest more RF energy from the environment, while the cross-shaped antenna array utilizes the space diversity to harvest RF energy from different directions with a compact size of $0.15\lambda \times 0.15\lambda $ per antenna element (where $\lambda $ is the free space wavelength at 915 MHz). This new harvesting system can provide output dc power of 21.4 and $2.95~\mu \text{W}$ in real-world outdoor and indoor ambient environments, respectively.