RFID tag load impedance measurement using backscattered signal

Radio frequency identification is a pervasive technology used for many different purposes. This paper presents a unique technique to evaluate tag´s loads impedance without modifying its electronics. In this in-situ technique, no external measuring equipment such as vector network analyzer was directly connected with the tag. The complex back scattered signal together with simulated tag antenna´s impedance and gain were used to extract its load impedance. The evaluated load impedance showed unified effect of the tag electronics and board parasitics.