Abstract
This paper proposed a novel antenna for ultra-high frequency (UHF) radio frequency identification (RFID) near-field applications with uniform distribution of the electric field along the x-axis (Ex), and the y-axis (Ey). The proposed antenna adopted a spiral structure to achieve broadband and multi-polarization. The novel antenna achieved good impedance matching within 860–960 MHz. Using a ground plate, the proposed antenna achieved low far-field gain and a maximum gain of less than −11 dBi. The component of the excited electric field Ex and Ey parallel to the antenna surface was uniformly distributed, and there was no zero point. The proposed antenna achieved a 100% read rate of tags parallel to its surface in the reading area of 150 mm × 150 mm × 220 mm. Simulation results were consistent with the results of real-world measurements, and the proposed antenna was suitable as a reader antenna in near-field applications. The polarization mode of RFID tags is mostly linear polarization, and the placement of tags in practical applications is diversified. Compared with the traditional RFID reader antenna, the proposed antenna achieves uniform electric field distribution parallel to the antenna surface, but the single-direction electric field has zero-reading points, which is easy to cause the misread of tags. The RFID tags can be read more accurately. To verify the scalability of the reading area of the spiral antenna unit, it was used for array design, and simulations were conducted using 1 × 2, 2 × 2, 1 × 4, and 2 × 4 arrays. The component distribution of the electric field excited by the four array antennas in the x and y directions was uniform and the reading area was controllable. Therefore, the proposed spiral antenna has the expandability of the reading area and can meet the needs of different application scenarios by changing the number of array units. With the array extension, the matching network also extends, and the impedance characteristics of the array antenna are somewhat different, but they also meet the application requirements.
Highlights
Radio frequency identification (RFID) uses radio signals to identify specific targets.RFID operates using a reader antenna to remotely track objects through an RFID tag attached to the object, as well as recognize and store relevant information about objects in order to realize item tracking and real-time monitoring
Depending on electromagnetic field coupling, reader antennas for RFID near-field applications can be based on magnetic field coupling and electric field coupling
The electric to the x-axis (Ex) andtothat to the used, respectively, and these variables were measured in v/m
Summary
Radio frequency identification (RFID) uses radio signals to identify specific targets.RFID operates using a reader antenna to remotely track objects through an RFID tag attached to the object, as well as recognize and store relevant information about objects in order to realize item tracking and real-time monitoring. RFID has been widely adopted because of its no-contact, reliable communication; automatic recognition of moving targets; and quick reading and writing capabilities. It is widely used in freight, retail, indoor positioning, access control management, identity identification, etc. RFID used in far-field applications can identify RFID tags at long distance, but it is easy to misread other tags in near-field. RFID used in near-field applications can accurately and stably identify RFID tags and not miss reading other tags at a long distance. The research on RFID near-field applications with uniform distribution of the electric field along the x-axis (Ex) and the y-axis (Ey) is important. Common antennas for magnetic field coupling are loop structure antennas [4,5,6,7,8,9,10,11,12,13], reconfigurable modular antennas [14,15], and array antennas [16,17,18]
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