Near‐field radio frequency identification leaky‐wave antenna based on artificial transmission line

Abstract

The artificial transmission line (ATL) has a good characteristic of wavelength shortening, which can effectively cut down the size of microwave devices. In this article, the near-field radio frequency identification antenna based on an ATL was proposed. It mainly includes the radiating unit structure on the upper layer and the feeding structure on the lower layer. The two layers are connected by copper pillars for feeding. The height of the copper pillars is 16 mm (h0), which can obtain the maximum bandwidth. The antenna unit based on ATL consists of three curved microstrip lines, two interdigital microstrip lines, and four open microstrip lines. The interdigital structure on the upper layer of the antenna unit mainly affects the resonant frequency of the antenna unit, and the asymmetric interdigital microstrip lines increase the impedance matching bandwidth of the antenna unit. Compared with previous antennas, the proposed antenna features a low profile, and a good miniaturization based on an ATL by bending inductance and interdigital capacitance. The leaky-wave characteristic makes the energy radiate at a certain angle on the surface of the antenna. The leaky-wave characteristic and circular polarization characteristic of the antenna achieve a uniform field distribution. The simulated and measured bandwidth cover from 0.78 to 1.1 GHz for |S11| less than −10 dB. More importantly, the antenna has a large recognition area. The measured results demonstrate that the proposed reader antenna has a 100% read rate in 400 × 350 × 400 mm3 area in the metal shelf.