Retrodirective Energy Harvesting UHF RFID Tag Design with a Rat-Race Coupler

Enhancing the operational capabilities and read range of passive ultra-high-frequency radio-frequency identification (UHF RFID) tags remains a critical challenge. A tag that is passive has to be able to harvest energy from an interrogating signal in the environment in order to operate its internal circuitry and be able to communicate with a RFID reader. Meanwhile, the message the tag backscatters to the reader will be reduced in signal strength due to path loss. This paper proposes a novel design of a full passive RFID tag that integrates energy harvesters alongside a rat-race coupler to simultaneously achieve energy harvesting and retrodirectivity for extended backscatter communications, respectively. To evaluate the components of this proposed design, a retrodirective rat-race coupler was designed, fabricated, and characterized for its retrodirectivity performance, and an energy harvester was designed and analyzed through simulation. An amplitude-based switching mechanism that is dependent on the tag’s backscatter message enables the tag to switch between energy harvesting and retrodirective backscatter for communications, utilizing the same antennas for both functions without dedicating antennas for each. This hybrid approach offers a simple solution for future RFID tag designs to extend their read range in passive systems.