Power and Phase Variation of Backscattered RFID Signal with Respect to the Incident Power at the Tag

In this paper, we investigate how the incident power at the tag affects the backscattered signal that reaches the reader. It is shown experimentally and theoretically that the backscattered complex signal, i.e. magnitude and phase, changes significantly with respect to the incident power at the tag’s antenna. This effect is neglected in prior art and is due to the change of the input impedance of the tag’s front end, due to the presence of non-linear components, like the rectifier’s diodes. Measured deviation of 14dBs and phase shift of 100 degrees is reported herein. These variations might lead to large localization errors, depending on the method and the measured quantity, unless the localization algorithm accounts for the expected variability.