Optimization of passive RFID tag antennas

In this paper, the overall optimization of the antenna impedance of an RFID tag has been considered, under both the power delivery and the backscattering viewpoints. Based on the reciprocity principle, the formulation used does not make any free space nor far field approximation. Consequently, the results obtained can be applied more widely than the usual differential RCS approaches. Explicit formulas have been derived to support the optimization process, depending on whether the power delivery or the backscattered power are more important. In particular, the effects of losses and of the change of the input impedance of the IC as a function of power delivery can easily be accounted for.