Slot Resonator Based Novel Orientation Independent Chipless RFID Tag Configurations

The design of two novel orientation-independent slot resonator-based chipless RFID tags is proposed in this paper. These tags make use of multiple L-shaped slots of different lengths on a lossy substrate and are appropriate for item tracking and identifications. The data are encoded in the backscattered signal from the tag after its illumination. The first tag configuration includes multiple L-shaped slot resonators cascaded with each other. It exhibits wideband features and enables the addition of extra resonators for encoding of additional data without an increase in the tag size. The second configuration has alternate resonators on one side of the substrate while the remaining resonators are inverted and are on the other half of the substrate. It leads to reduced mutual coupling between the resonators and hence an improved performance and improved printing flexibility. The proof of concept is demonstrated through the design of tags in CST Microwave Studio and prototype development on the Rogers 5880 substrate. Both the tags are compact, printed on 20 mm $\times$ 20 mm substrate, encode 8-bits in a bandwidth of 3 GHz and thus advance the state of the art significantly. An interesting feature of the proposed tags is the orientation independence and this is a very useful feature for applications, such as tracking of items in a smart retail scenario where the products need to be read by the readers from any orientation.