Ultra low-profile metal tag antenna design with an emphasis on radiation efficiency

Ultra low-profile metal tags are highly desired for tagging modern IT assets and metallic cylinders. In contrast to most existing research works, this paper focuses on the radiation efficiency of the ultra low-profile tag antennas. The influence of the substrate thickness on the radiation efficiency is studied with both theoretical calculation and full-wave simulation. It is found that the conductor loss takes over from the dielectric loss as the dominant loss mechanism when the substrate thickness becomes extremely small. Furthermore, the influence of the substrate thickness on the radiation efficiency bandwidth is studied based on an ultra low-profile metal tag antenna. The tag antenna takes the form of an inset-fed patch integrated with a short-circuited transmission line, and is implemented at three substrate thicknesses, i.e. 0.855, 0.513, and 0.171 mm. Measurement and simulation results of the proposed tag antenna demonstrate that the feeding structure has a great impact on the radiation efficiency bandwidth. In particular, when the tag antenna is implemented at extremely small thicknesses, the radiation efficiency bandwidth is found to be a more demanding specification than the impedance bandwidth.