Dual- Band RFID Antenna for 0. GHz Near- Field and 2. GHz Far- Field Applications. School of Electronics and Information, Northwestern Polytechnical University, Xi’an 7. China. Received 2. March 2. 01. 7; Revised 2. ![]() April 2. 01. 7; Accepted 1 June 2. Published 1. 0 July 2. Copyright © 2. 01. Zijian Xing et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A novel antenna used in the near field of a 0. GHz and the far field of a 2. GHz RFID reader system is investigated. The new antenna achieves strong magnetic field distribution over 0. GHz with good performance of detecting tags when applied in FCC RFID systems, as well as a good performance of circular polarization at 2. GHz. Furthermore, the investigation shows the operation principle by circuit models and the advantages of the structure in terms of the operation frequency and field performances. The advantages of these two bands could be achieved by this novel RFID reader antenna. Introduction. Radio frequency identification (RFID), which was developed around World War II, is a technology that provides wireless identification and tracking capability [1, 2]. Reader antennas are an important unit of RFID systems. Reader antennas can be classified into two classes by reading range for different application purposes: near- field (NF) antenna and far- field (FF) antenna. Operation frequencies of reader antennas include 1. KHz, 1. 3. 5. 6 MHz, 4. MHz, UHF (ultrahigh frequency) 0. GHz, 2. 4. 5 GHz, and 5. GHz. Currently, 0. GHz and 2. 4. 5 GHz are more attractive because of their good performances of data speed and antienvironment jam ability [3–6]. Ultrahigh frequency (UHF) near- field RFID technology received a lot of attention due to its good performances in item- level RFID applications such as sensitive products tracking, pharmaceutical logistics, transport and medical products (blood, medicines, and vaccines), and biosensing applications [7–1. The primary concern of UHF near- field RFID is to make the RFID system working in a short distance as reliable as that of the LF/HF near- field RFID. Inductive coupling systems are preferred in most applications of near- field UHF RFID, because most of the reactive energy is stored in the magnetic field. Magnetic coupling is stable in terms of the impact of liquid or metal. In contrast, capacitive coupling is the opposite because the energy is severely affected by high permittivity materials. In the 2. 4. 5 GHz band, far- field circularly polarized RFID antennas receive more attention because of the high data speed and long identification distance. A compact Ultra-WideBand (UWB) slot antenna is presented in this paper. The slot is modified rectangular in shape and asymmetrically cut in the ground plane. A. Related posts: A Tutorial on Decoding NOAA and Meteor M2 Weather Satellite Images in Ubuntu; Building a simple NOAA APT Antenna out of an Umbrella. International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research. IEEE Xplore. Delivering full text access to the world's highest quality technical literature in engineering and technology. Because of these interrogation characters, energy transmission speed and efficiency are very important and have been studied a lot recently [1. In far- field RFID systems, the RFID tags are always located in large range applications and the tags are normally single or dual linearly polarized (LP), and thus circularly polarized (CP) reader antennas are suitable for ensuring the stability of communications between readers and tags. Moreover, under most practical circumstances, other requirements for the reader antenna should be under consideration, such as structure sizes, acceptable gains, impedance bandwidths, multibands, and axial ratio (AR) bandwidths. As advantages of these two standards, it is essential to integrate these two standards into one system. In this situation, a reader antenna covering 0. GHz near field and 2. ![]() GHz far field is a good design, which avoids using two single- band antennas. One challenge in RFID applications is to design such an antenna because the operation mode and frequency differences between 2. GHz far field and 0. GHz near field are too large to operate properly for dual- band structures [4–6]. Even though many dual- band RFID reader antennas are proposed, there are very few antennas that could fulfill this design goal. Most of the dual- band antennas are applied for far- field operation mode whereas most of the dual mode antennas are operated at the same frequency [1. In [2. 1], the dual- band 0. GHz unidirectional CP antenna is presented employing multiloops and a complex power splitter, but the operation modes of these two frequencies are all far field. In [2. 2], the antenna can be operated in both near- field and far- field modes at a UHF band. However, these two operation modes share the same frequency, so that the total power is split into two components and then the efficiency of each mode will be decreased. There are also some papers that focus on the study of dual- band antennas [2. In this paper, a compact 0. GHz near- field and 2. GHz far- field dual- band antenna is proposed to generate strong magnetic field and circularly polarized wave, respectively. The two operation modes of the antenna are operated at different frequencies; the two modes work at different frequencies, so the efficiency of the two modes is high. But in [2. 2], the two modes of operation work at the same frequency, so the energy is divided and the efficiency is reduced. The difficulty of this design is whether the feed network can establish high isolation between the two operation modes. Finally, the designing goal is achieved by the proposed antenna which is also investigated in detail. The methodology to complete impedance matching is addressed with the theory analysis. The structure, theory, and the performances of the antenna are analyzed in detail as follows. This paper is organized as follows. Structure and modeling of the antenna will be introduced in Section 2. In Section 3, analysis and discussions are carried out to investigate the operation principle of the antenna and impedance matching theory. In Section 4, the performances of the antenna will be studied and analyzed. In the last part, conclusion will be given. Modeling and Structure. The structure of the antenna is shown in Figure 1(a), which is composed of four layers which are FR4 layer 1, composite PTFE layer 2 and layer 3, and composite dielectric board layer 4. From the top layer to the bottom layer, these four layers are marked by numbers which are 1, 2, 3, and 4 in Figure 1(b). Layer 1 is mainly composed of two half- rectangle loops which have two folded straight terminals. Layer 2 and layer 3 are strip line feed network with lead printed onto the interface of the two, respectively. Fed at the edge of the bottom layer, 5. The two branches are connected to two metal columns in another end. The other end of each column is connected to one metal half- rectangle loop strip. There is one load on each half- rectangle loop in Figure 1(a). Layer 1 and layer 2 are connected by two metal columns. A rectangle single feed circularly polarized antenna (layer 4) is fed by the main strip line and connected to layer 3. The material of the circularly polarized antenna part is composite dielectric with low loss tangent. Figure 1: Model and structure of the proposed antenna: (a) 3. D view, (b) side view, (c) top transparent view of the middle layer, and (d) bottom view of the circularly polarized antenna. Top layer 1 is the near- field antenna, and layer 2 and layer 3 are the feed network. Figure 1(b) shows the side view of the antenna. The circularly polarized antenna is located under layer 3. All of the sizes are marked in Figure 1(b), where height and square of the antenna is and , respectively. Thicknesses of FR4 PCB board and circularly polarized antenna are denoted by , , and , respectively. The gap between layer 1 and layer 2 is . In Figure 1(c), top view and transparent view of the feed network are shown, where all of the sizes are marked. The widths of 5. 0- ohm transmission line and two branches are marked by and , respectively. The sizes of the loop are marked by , , and . Layer 4 is a circularly polarized antenna, and the edge lengths of the substrate and patch are marked by and , respectively. Analysis and Discussion. The operation energies of the antenna include two parts which are 0. GHz near field and 2. GHz circularly polarized far field. In order to obtain good performances of the two modes, one challenge for designing the antenna is to establish high isolation between the near- field mode and the far- field mode, that is, less energy input to another mode at the operation frequency of one mode. The operation principle of the two modes and the theory analysis of the isolation technology are provided below.
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