Novel Topologies of Resonators for Orientation-Insensitive Chipless Radiofrequency Identification Tags

In this paper, three resonators are proposed for the frequency-coded chipless radiofrequency identification (RFID) tags. In real-world implementations, the tag may have an orientation angles as compared to the polarization of an incident wave. This leads to frequency detuning and false detection. To overcome this limitation, we first propose the design rules of the tag to reduce the sensitivity of orientation. Based on these design rules, three topologies are proposed and analyzed, including octagonal slots, Union-Flag strips, and spiral strips. The radar cross section (RCS) characteristics are analyzed. When these resonators are designed at 3 GHz, the results show that the Union-Flag strip and the spiral achieve frequency shifts of 40 MHz and 80 MHz, respectively, which are significantly smaller than the detuning of nonsymmetrical resonators. In particular, these resonators are tested under polarization-mismatch scenarios, and they show very robust performance. Finally, to enhance the data capacity, we arrange multiple resonators on a substrate, showing design guidance to reduce interaction of resonant frequencies.