Development of cross-polar orientation-insensitive chipless RFID tags

Chipless RFID is a potential wireless identification technology for tracking and identification applications. However, there are still some unsolved challenges in the implementation of this system in real-world applications. One of the crucial challenges in chipless RFID systems is the effect of the dynamic environment and the effect of the attached item on the tag response, which causes interference in the tag ID measurement process. One approach to solve this problem at the tag design level is to use cross-polar chipless RFID tags, which conventionally are orientation-sensitive. However, even though it is desirable to detect the tag ID in different orientations (in 2-D at least) for practical applications, having both cross-polar RCS and orientation insensitivity in a tag is a challenge. Therefore, in this article, a technique to develop cross-polar resonators and unit cells that display a consistent reflection regardless of tag orientations is proposed. The results of the simulation and measurement of a few samples of the proposed tags are depicted to demonstrate the feasibility of using the proposed tags in a system with reflective items in the background. Five cross-polar structures with low sensitivity to orientation are introduced in this article. Among all structures, the flower-shaped unit cell provides a very consistent cross-polar response at different rotational angles with a maximum of 11 dB peak RCS variation.