Backscattering improvement of UHF RFID tag efficiency

In this work, a tag-load selection methodology is proposed for optimized tag-to-reader backscatter communication. Derivation of the method is based on antenna/communication theory and applies to any tag-antenna, including minimum scattering antennas as a special case. In contrast to what is commonly believed, it is shown that amplitude maximization of complex reflection coefficient difference between the two states is not a sufficient condition for optimized tag´s design. Maximization of backscatter carrier power per bit must be sought as well. Optimum load-selection for passive and semi-passive tags is linked to the tag-antenna´s structural mode. A method that allows for the closed-form calculation of this parameter is put forward.