Asymmetric Retrodirective UHF RFID Tags: Design and Measurement Results

In this paper we investigate the use of retrodirective arrays in transponders of ultra high frequency (UHF) radio-frequency identification (RFID) systems and their potential to enhance both the communication range and the energy range of RFID systems. The communication range is increased through the retrodirectivity of the backscatter transponders. An asymmetry in the transponder array is intended to support wireless power transfer (WPT) by focusing the incoming wave onto one rectifier to maximize its efficiency. In this study we use a commercially available integrated circuit (IC) for UHF RFID transponders making the constructed retrodirective transponder compatible with the EPC Gen2 protocol. Theoretical investigations show that through the use of N antennas in the transponder both energy range and communication range can be increased by a factor of √ N, corresponding to an increase of about 41% when using two antennas. The realized EPC Gen2-compatible transponder with two antennas achieved an increase of up to 34% in energy range and 38% in communication range. The presented technique is not limited to two antennas and can help to extend the range of backscatter systems without modifications to the reader. This could especially be interesting for applications within the Ambient Internet of Things (A-IoT) of upcoming 6G networks.