Abstract
Radio-frequency identification (RFID) is becoming important with emerging applications for smart cities. RFID Tags are required to be small in size, low in cost and must exhibit as long read range as possible. There is a direct tradeoff between Tag antenna size and its read range. In this work, we study this tradeoff through the use of a relatively higher dielectric constant substrate, volumetric folding, and slow-wave structures (SWS). A 3D antenna design is chosen due to two reasons, 1) it can be folded on a 3D structure, 2), the 3D structure can be used as a package for electronics (in case of active RFID implementation). To enable a low-cost realization, the antenna substrate (package) has been 3D printed with filaments of {\varepsilon }_{r}={5}.{3} . A dipole antenna has been folded on this 3D substrate, in a way that the electromagnetic fields radiating from various segments of the antenna do not cancel with each other. Finally, the antenna is loaded with specially designed SWS, whose values have been estimated using artificial transmission line theory. The final antenna design, operating at 866.9 MHz, has a {ka} of 0.26 and demonstrates a radiation efficiency of 32%. The antenna is integrated with a commercial RFID chip (Monza R6) through a silver paste and the measured read range is 2.73 m, while the corrected read range is 4.05 m when the impedance mismatch is considered. Despite being one of the smallest and the lowest cost design (involving 3D printing), the Tag demonstrates one of the highest read range.