Enhancing the Per-Unit-Length Data Density in Near-Field Chipless-RFID Systems With Sequential Bit Reading

In this letter, a novel near-field chipless-Radio Frequency Identification (RFID) system with sequential bit reading is reported. The main novelty concerns the tags, implemented by means of straight half-wavelength resonators separated by a small distance and forming a linear chain in the direction orthogonal to their axis. By this means, the number of resonant elements (or bits) per unit length of the tag is significantly increased, as compared to the previous implementations, with the result of very competitive tags in terms of data density. The active part of the reader is a microstrip line loaded with a shunt stub. Through a proper design, it is possible to achieve a significant excursion of the transmission coefficient when the stub is either loaded or unloaded with a functional resonant element of the tag. Consequently, by tag motion over the reader (stub), it is possible to infer the Identification (ID) code by simply injecting a harmonic signal to the input port of the stub-loaded line (the ID code is contained in the amplitude modulated, signal at the output port). This system has been validated by considering 100 b tags exhibiting a surface data density of 4.9 b/cm
²
. However, the relevant parameter is the data density per unit length, as high as 16.7 b/cm, i.e., much larger than previous values reported in the literature in similar chipless-RFID systems.