An UHF-Band Rectenna with Material- and Location-Independent Operation Enabling Long-Range Energy Harvesting for RFID and IoT Nodes

The paper presents the design, simulation, and fabrication of a rectenna operating in the UHF band (868 MHz), optimized for energy harvesting in IoT applications. The system consists of a patch antenna fabricated on an FR4 substrate and excited via a coaxial pin, connected to a distributed impedance matching network implemented on the back side of the structure using a Rogers substrate to maximize power transfer to a nonlinear rectifier. The FR4 and Rogers substrates are separated by a ground plane, which serves as a shield between the antenna and the rectifier, ensuring that the rectenna's operation remains independent of the mounting surface. Measurement results show good impedance matching and an effective RF-to-DC conversion suitable for low-power, long-range (up to 20 meters) applications. An input power of at least <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{- 1 9} \mathbf{~ d B m}$</tex> is required for the cold-start of the DC-DC converter connected to the rectenna, and with this system, the suitability for ultra-low-power energy harvesting scenarios is demonstrated.