Loop-Fed Planar Inverted-L Antennas (PILAs) for Omnidirectional UHF on-Metal Tag Design

• Published in: IEEE transactions on antennas and propagation 2020-08, Vol.68 (8), p.5864-5871
• Main Authors: Lee, Yong-Hong, Lim, Eng-Hock, Bong, Fwee-Leong, Chung, Boon-Kuan
• Format: Article
• Language: English
• Subjects: Antenna radiation patterns; Antennas; Azimuth; Constellations; Dipole antennas; Directive antennas; Impedance matching; Metals; Omnidirectional; on-metal; Reactance; Surface impedance; UHF radio frequency identification (RFID) tag
• ISSN: 0018-926X; 1558-2221
• DOI: 10.1109/TAP.2020.2990287

A new type of tag antenna, which is made by placing four identical planar inverted-L antennas (PILAs) in rotational symmetry constellation, is proposed for designing a miniature on-metal tag antenna. It shows good omnidirectional characteristics in the azimuth plane. In the design, the directive radiation beams of the respective PILAs are tactfully combined to form a stable omnidirectional pattern. The proposed tag is compact with a small size of 40 mm \times40 mm \times1.6 mm ( 0.122\,\,\lambda \times 0.122\,\,\lambda \times 0.005\,\,\lambda ). Here, all the PILAs are inductively excited by a circular loop, which also introduces additional reactance for improving the impedance matching. The proposed tag antenna is able to achieve a stable read distance of 5.9 m on metal in the azimuth plane when it is tested using equivalent isotropic radiated power of 4 W. The operating frequency of the tag is stable and it is not affected much by changes in the backing metal.