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Reader Antennas Requirements in Chipless RFID Systems with Linear and Circular Polarization

Two efficient reading approaches for chipless RFID are compared. The first approach uses a linear polarization interrogation with depolarizing tags able to reflect an electromagnetic signal with orthogonal polarization state with respect to the impinging one. In the second approach a circular polarization interrogation is sent to the tag which scatters it back with opposite rotation sense. The two methods are described in terms of both conversion efficiency and performance at a system level. It is underlined that one of the main requirements for obtaining good performance of the chipless RFID system relies on the design of the reader transmitting and receiving antennas which should be wideband and guarantee a low level of radiated cross-polarization, together with a low-mutual coupling.