A Low-profile UHF-RFID Tag Antenna with Interdigitated Inductive-coupling-fed for Metallic Objects

This study presents a low frequency ultra-high frequency (UHF) radio frequency identification (RFID) tag antenna with staggered inductance coupling feed which can be attached to a metallic surface is proposed. The proposed design consists of two symmetrical horizontal feeders and patches, each strip line loaded with identical vertical open-circuit stubs of multiple interlaced coupled inductors and an integrated circuit (IC) chip installed in the middle of the feeder structure. In this paper, by adjusting the Open-stubs and the defect structure in the patch area to affect the electrical length and antenna inductance, the current distribution is changed to achieve the gain improvement of the metal-mounted tag antenna while ensuring that the resonant frequency can be controlled flexibly. Therefore, by adjusting the size parameters of the structure, the proposed design can achieve perfect impedance with any type of IC chip and operate in any UHF regional band. Molding the antenna’s geometry can be applied to realize conjugated impedance with any sort of IC chip due to the flexibility of the tag structure.The designed label is manufactured on a single Polytetrafluoroethylene (PTFE) substrate. In addition, the constructed structure does not require any complex manufacturing processes such as the use of metal through-holes and/or short walls, which makes it structurally simple and suitable for mass production. The tag’s size is 53.2 mm × 45.4 mm × 1.535 mm (0.16λ0 × 0.14λ0 × 0.0047λ0), and On the 20 cm × 20 cm PEC surface, the actual gain of the label antenna is 2.55dB, and the detection distance is 17.15 m, at the North American band (902–928 MHz).