Orientation-Insensitive and Normalization-Free Reading Chipless RFID System Based on Circular Polarization Interrogation

A novel normalization-free reading scheme to recover data encoded in chipless radio frequency identification (RFID) tags is presented. The proposed approach exploits the circular polarization to isolate the field scattered by the tag from that of surrounding objects. The desired polarization mismatch is achieved by exploiting the properties of high-impedance surfaces that can suitably manipulate the reflected field. A thorough analysis of the interaction between the circularly polarized (CP) interrogation and the field scattered by the chipless RFID tag as well as the hosting platform is provided. The proposed method does not require any a priori calibration if a reading antenna with a suitable axial ratio is available. More importantly, the CP-based reading approach guarantees the correct tag detection regardless of the tag orientation. The case of the tag mounted on metallic platform is also analyzed and it is demonstrated that the circular polarization reading procedure is robust under the hypothesis of a proper axial ratio of the probing antennas. The minimum requirements of axial ratio are derived by using a theoretical model. Measurements confirmed the speculations obtained through the theoretical analysis both in the case of low-scattering items as well as for metallic platforms.