Mutual coupling reduction in linearly polarized compact extended C-shaped chipless RFID tag

Compact chipless RFID tags suffer from the mutual coupling between neighboring elements that have close resonant frequencies. In such tags, it is difficult for the words including zero bits to be detected by a reader, leading to false detection. In this paper, two techniques to reduce the mutual coupling effect based on rearrangement of the extended elements with reduced size are proposed. These techniques are applied to a compact chipless RFID tag, which has several nested C-shaped strips placed on both surfaces of the substrate. Top and bottom strips are connected through vias, and slots are placed in the middle of the bottom strips. The resonant frequencies are adjusted by varying the slot lengths in the first technique and variable vias position in the second technique. Through these techniques, the neighboring resonant frequencies can be placed farther apart. In doing so, the stability of the RCS frequency response is improved, which enables a reliable reading where zero bits are coded. For a 9-bit tag, the radius of the substrate is 7.8 mm, equivalent to 0.097λg operating over 2-9 GHz. A prototype is fabricated and measured.