A Low-Profile Metal-Backed Dipole Loaded With Closely Coupled Arc-Shaped Open Stubs for On-Metal Tag Design With Wide Frequency Tuning Capability

This research has presented a single-layer metal-backed dipole antenna, which consists of a feedline loaded with two pairs of closely coupled arc-shaped open stubs, for designing a metal-mountable tag that features tuning capability over a wide range of frequencies. Here, the stubs can generate sufficient inductive reactance to bring down the tag’s resonant frequency, making it tunable in both the regulated ultrahigh-frequency (UHF) radio frequency identification (RFID) passbands (North American (NA) and Lower European (LEu) standards). Adjusting the stubs’ length can be utilized as a simple and effective tuning mechanism, enabling broadband frequency adjustment between the two major spectra straightforwardly while maintaining a maximum power transmission coefficient (
$\tau =1$
). In addition, the proposed antenna structure is easy to construct. The tuning mechanism has enabled the antenna to match well with any commercial RFID chips, and it does not require the use of any external lumped components or shorting elements (vias or stubs). The proposed tag can be easily fabricated using an inexpensive flexible polytetrafluoroethylene (PTFE) substrate, which is broadly adopted by the RFID industry. Stable read performance is achievable, providing freedom of frequency tuning without the need to modify the radiator structure. The volume of the tag is
$\pi \,\, \times ({28}) ^{2}\,\, \times 1.5$
mm3, which is reasonably small. It has a measured detection distance of 9.75 m (4 W EIRP) on the metal surface in the NA RFID passband, while it is 8.41 m (3.24 W EIRP) in the LEu passband.