A Low-Profile Symmetric Dipole UHF RFID Tag Design With Wide Tuning Range for Metallic Platforms

Abstract

A low-profile, compact symmetric dipole planar tag antenna with a single-layer structure is developed for UHF RFID applications on metal surfaces. It incorporates a patch-loaded interconnected arm configuration to enable a wide frequency tuning range. The antenna can be fabricated on a cost-effective FR4 substrate without shorting stubs or metallic vias. It has dimensions of 40 mm $\times $ 38 mm $\times 1$ .57 mm ( $0.122\lambda \times 0.116\lambda \times 0.004{\lambda }$ ). The design features four interconnected arms with individual loading patches, which contribute to maintaining a broader bandwidth while enabling wide-range frequency tuning from 860 MHz to 960 MHz, the entire UHF RFID passband. By adjusting the width of the shorting patches between the arms and the loading patches, the antenna’s capacitive coupling is modified, which in turn alters the input reactance and enables precise tuning of the tag’s resonant frequency. This tuning approach enables resonance adjustment across the UHF range without additional lumped components. The antenna is designed to maintain an optimal impedance matching with the microchip throughout the entire wideband tuning range. When operating at an effective isotropic radiated power (EIRP) of 4 W, the proposed tag antenna achieves a maximum reading distance of approximately 9 meters. Moreover, this design offers a compact, tunable, and cost-effective solution to improve RFID reliability in metal-mount environments.