Wearable Ungrounded Tag Antenna for UHF RFID Applications

A single-layer ungrounded tag antenna is designed for on-body radio frequency identification (RFID) applications in the ultrahigh frequency (UHF) band. The ungrounded tag antenna is designed based on a broadside radiating Huygens source. The electric dipole is generated by the center part of an original dipole, while two orthogonal magnetic dipoles are created by stacking another two metallic strips at the edge of the original dipole. The tag antenna shows good robustness of input matching and radiation efficiency with respect to the human-body effect. Furthermore, the designed tag antenna is also able to work with metallic objects and its resonant frequency is stable around 920 MHz. Finally, three tag prototypes, including the proposed tag antenna, are fabricated and tested. The measured reading range confirms the numerical simulations and demonstrates the robustness of the proposed design with respect to different distances between human-body and tag antenna. The proposed tag provides a reading range of 5.0 m (near-body), 8.0 m (free space), and 16.5 m (200 x 200 mm metallic plate), respectively.