Performance analysis of passive UHF RFID tags with GNU-radio

Performance evaluation of passive Radio Frequency Identification (RFID) tags is a crucial but challenging task. In fact, tag performance depends on multiple factors like the goodness of the conjugate matching between chip and antenna, the chip sensitivity, and the strength and quality of backscattered signal. Moreover, passive RFID tags lack wired connectors and therefore cannot be directly interfaced with conventional measurement instruments. Some solutions for tag testing and performance evaluation are commercially available on the market, but they are expensive and not totally flexible. In this work we propose a novel approach to the problem of tag performance analysis based on Software-Defined Radio (SDR). We show that a SDR tool for UHF RFID reading allows the characterization of tag performance by any metric and for any operating frequency, with a total equipment cost below 1000 USD. We present the methodology to measure tag sensitivity, differential radar cross-section and Signal-to-Noise ratio, and provide numerical results for five different tags.