Simple Test and Modeling of RFID Tag Backscatter

Abstract

We consider here worst-case analysis of backscatter from passive radio frequency identification (RFID) tags. The basis is a figure of merit “ <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$B$</tex></formula> ” to relate link power at reader ports to tag circuit parameters. A minimum bound for received monostatic backscatter can be determined by inspection from measured <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$B$</tex></formula> . The bound is general for narrowband signals in any causal linear propagation. For an assembled tag, this minimum varies only with reader transmit power, tag antenna tuning, and chip power sensitivity of different commands. To validate this model, we propose a backscatter calibration device to enable measurements with estimated <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pm {\hbox {0.5 dB}}$</tex></formula> uncertainty. We then demonstrate how the minimum bound can inform reader sensitivity specification to help ensure reliable inventory performance.