Dipolar Tag Antenna With a Top-Loading Inductive Channel With Broad Range Frequency Tuning Capability

Abstract

For the first time, the concept of inductive channel is introduced for tuning the resonant frequency of a bowtie dipolar tag antenna, which has a compact physical size of 50 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times50$ </tex-math></inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times3.38$ </tex-math></inline-formula> mm (0.1447 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda \,\,\times0.1447\,\,\lambda \,\,\times 0.0098\,\,\lambda$ </tex-math></inline-formula> ), for applying on metal surfaces. The narrow inductive channel, which is embedded with an external lumped inductor, is loaded on top of the dipolar antenna for achieving arbitrary tuning capability in a broad range. It has been found that the top-loading patch can enhance the fields of the dipole, and the inductive channel can regulate the current flows on the top-loading patch. By adjusting the channel width and the external inductance, the resonant frequency can be effectively adjusted without affecting the read performances of the tag much. Here, an equivalent circuit has also been constructed for analyzing the impedance characteristics of the proposed tag antenna. The proposed tag antenna can achieve a measured maximum reading distance of nearly 19 m at an effective isotropic radiated power of 3.28 W. It can be arbitrarily tuned to operate at any frequency in the UHF band by simply adjusting the lumped inductor’s value, without changing the antenna structure. The proposed antenna is found to be insensitive to the variation in the backing metal plate, and its operating frequency does not fluctuate with the plate size.