Asymmetric Retrodirective UHF RFID Tags: Design and Measurement Results

This paper investigates retrodirective UHF RFID transponders and their potential to enhance wireless power transfer (WPT). Retrodirectivity is used to increase the communication range of an RFID system. An asymmetry in the transponder array is intended to support WPT by focusing the incoming power on one rectifier to maximize its efficiency. A commercially available UHF RFID tag IC compatible with EPC C1G2 was used for this study. Theoretical investigations show that both energy and communication range can be increased by a factor of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sqrt{2}$</tex> or about 41% through the use of two antennas in the transponder without reducing the transponder's read angle. Practically, a constructed C1G2-compatible transponder achieved an increase of approximately 15% in energy range and 19% in communication range. The presented technique is not limited to two antennas and can help to extend the range of RFID systems without modifications to the reader. This could especially be interesting for applications within the Ambient IoT (A-IoT) of 6G networks.