Classical RFID Versus Chipless RFID Read Range: Is Linearity a Friend or a Foe?

This article presents a comparison between the read range of classical radio frequency identification (RFID) and chipless RFID in free-space and real environments (REs). From the presented model, read range is derived using analytical formulation over nonisolated channels for both technologies. This article shows that the well-known bounds classically used in free space cannot be achieved in REs, i.e., subjected to leakage, coupling, and/or reflections) and therefore need to be modified. Although the introduced bound for semipassive tags is close to the one corresponding to free space, however, we show that for chipless tags, read range cannot be predicted by the radar equation and presents severe limitations since these tags are linear time-invariant systems. This new bound does not depend on the transmitted power or the reader sensitivity but relies on the concept of residual environment. We show that this quantity is the key parameter to evaluate the read range of a chipless RFID system. Moreover, the residual environment can easily be estimated or measured for any reading system. We show that the proposed bound can accurately predict the read range of a chipless system in different environments from anechoic chamber to nonstationary REs. Results are confirmed in simulation and measurements where the difference between the theoretical read range and the measured one is only 20 cm.