Bio-inspired circular polarized UHF RFID tag design using characteristic mode analysis

This article presents a bio-inspired circularly polarized ultrahigh-frequency (UHF) radio frequency identification (RFID) tag antenna for metallic and low-permittivity substances. This tag design is based on a leaf-shaped radiator, two shorting stubs, and slots etched on F4B substrate. Initially, the tag antenna is designed using a characteristics mode analysis (CMA) by analyzing the first six characteristic modes (CM) and characteristic angles. The width of orthogonal slots is varied to get the resonance of CM modes in the required US RFID band. Moreover, the edges are blended to get orthogonal current distribution, which is necessary for circular polarization. In addition, the proposed tag design is optimized further using CST Microwave studio and an RFID chip is exploited as a capacitive coupling element (CCE) to run CM modes with the orthogonal current pattern. This tag can also be tunable to European RFID (EU) band (866-868 MHz) by changing the length of shorter diagonal slot. The tag design offers a read range of 7-4.5 m on 100×100 mm2 metals plate and low-permittivity substrates (for the 902-928-MHz band). In the EU band, the corresponding read ranges are 5.7 and 3.5 m above metal and low-permittivity objects, respectively. This circularly polarized tag antenna is advantageous in terms of cost, circular polarization feature, and ease of fabrication due to the absence of vias, shorting pins, and matching circuits. Therefore, this tag design is suitable for labeling various low-permittivity objects, industrial conveyer belt applications, baggage handling systems, and Internet of Things (IoT) applications.