A retro-directive UHF RFID tag on paper substrate

In this paper, a retro-directive RFID topology is proposed, in order to improve the range of passive RFID tags. The use of a paper substrate permits to obtain low-cost, flexible and easy-to-fabricate circuits. First, the single element of the retro-directive array is proposed, consisting of a dipole with an inductive loop that guarantees the desired impedance matching between the antenna and the RFID chip; then, an array of two dipoles in a Van Atta configuration is presented. The two designs were evaluated by measuring the power received by a reader, for different incidence angles of the signal; the two-element approach showed a 7 dB improvement in the radar cross section at broadside, and less degradation of the received signal level as the angle of incidence moves from the broadside direction.