||In this thesis Passive UHF RFID Tag Performance characterization and prediction is investigated. To perform tag characterization, we carry out various path loss measurements. Our path loss measurements with varying distance reveals that received power at the reader is not proportional to d to the 4th power as expected from the radar equation. It is deduced that the radar cross section of the RFID Tag is not constant and varies nonlinearly with incident power. Therefore, a power transfer function is investigated to characterize tag backscatter power as a function of incident power. The measurement results show that this function is nonlinear and it is brand dependent. The power transfer function can be used as one parameter in tag characterization. Additionally, we use individual RF parameters of the round-trip path loss, such as transmitting power, distance, orientation, backing material and performance with multiple tags to provide us with more characterization parameters. Comparing these parameters between brands allows us to characterize the performance of individual brands of tags. We also attempt to predict RFID tag performance by using our power transfer function, a coverage area model and a normalized read rate model. The coverage area model predicts operating region of an RFID system and it is found that the operating region is dominated by the downlink turn-on region which is mainly controlled by minimum turn on power of a tag. In the normalized read rate model that predicts the expected read rate versus distance, it suggests increasing transmitting power can improve the read time under challenging fading conditions although it cannot increase the received power at the reader linearly.