Physical limits of batteryless HF RFID transponders defined by system properties

This paper motivates the usage of RF system properties of an ISO/IEC 14443 HF RFID communication link to describe defined properties at the air interface. An analytic derivation of the transponder loading effect and an empirical equation to estimate load modulation are presented. Based on this system model a lower bound for the physical limit of the transponder antenna size is proposed. This specifies the smallest antenna size that is capable of ISO/IEC 10373-6 compliant side-band amplitudes with passive load modulation. Measurement data is used to verify the presented system level descriptions and to extract typical quality factor values of batteryless RFID transponders. The outcome of this work can be applied to other HF RFID communication standards like EMVCo or NFC Forum.