Retrodirective Chipless RFID With Cross-Polarized Frequency Encoding

This letter presents a new configuration of fully passive frequency-encoded chipless RFIDs with improved detectability at oblique angles of incidence and in the presence of clutter. The proposed architecture is comprised of a wideband Van Atta retrodirective array that rotates the polarization of the retransmitted signal by 90°. The presence or absence of stopbands, generated by resonators along the feed lines, form a unique binary ID across frequency in the retrodirected signal. By using an array to point a cross-polarized beam toward the source, power transfer (and thus, range) is increased while reflections from surrounding objects are minimized. As a result, robust and affordable RFID tags may be designed for operation in cluttered environments with an optimal range of distances and angles. A prototype operating from 2.5 to 3.0 GHz is fabricated, and the monostatic radar cross section (RCS) is measured across frequency to demonstrate the retrodirective frequency-encoded chipless RFID concept.