A compact chipless RFID tag using polarization diversity for encoding and sensing

The chipless RFID tag presented exploits the advantage offered by polarization diversity to encode more information within a given surface size. It is based on 3 split ring resonators with variable gap configuration. Depending on the used linear polarization, different resonant modes can be measured for the same resonator so that the coding capacity is increased. Since the used structure is very sensitive to polarization angle, this interesting behavior can be used to detect a rotation angle of an item with 20° of accuracy. On the other hand, contrary to most of chipless tags that need UWB operating frequencies, the proposed tag is based on diversity polarization and only narrow frequency bands are needed. Using only 3 resonant frequencies in the 3.4 GHz to 7.1 GHz band, a capacity of coding of 6 bits is reached within a tag of size 3×3 cm². Measurements done using a bi-static radar configuration in the frequency domain validate this new concept.