A semi-omnidirectional resonator for chipless RFID backscattered tag design

Chipless RFID technology with its low-cost printable tags is highly demanded to be used for sensing, identification, and tracking applications. However, many challenges are cooperating with this technology due to the passive nature of the tag. In the conventional backscattered chipless RFID tags, the tag is required to be aligned with the reader antenna to be able to detect the tag ID. Hence, any misalignment causes errors in tag detection. This issue is a barrier for many applications in « hich the directional of the tag is unknown to the reader, or the tag needs to he detected in motion. In this paper, a scmi-Omni directional resonator for chipless RFID tags is proposed, which has a very low sensitivity to its orientation in 3D rotational angles in both co-polar and cross-polar responses. It can be used to design cross-polar orientation insensitive tags which is highly needed for tag detection in a highly reflective environment. The realization of the resonator and a proposed orientation insensitive unit cell are provided in this paper. Also, a 6-bit tag with spiral resonator, printed on adhesive paper, was measured at a reading distance of 20 cm and the promising results are demonstrated.