This paper presents a passive cavity type Ultra High Frequency (UHF) Radio Frequency Identification (RFID) tag antenna having the longest read-range, and compares it with existing long-range UHF RFID tag antenna. The study also demonstrates mathematically and experimentally that our proposed longest-range UHF RFID cavity type tag antenna has a longer read-range than existing passive tag antennas. Our tag antenna was designed with 140 × 60 × 10 mm 3 size, and reached 26 m measured read-range and 36.3 m mathematically calculated read-range. This UHF tag antenna can be applied to metal and non-metal objects. By adding a further sensing capability, it can have a great benefit for the Internet of Things (IoT) and wireless sensor networks (WSN).Keywords: RFID tag antenna; long range RFID tag; cavity antenna; RFID metal tag; RFID sensors; Internet of things; wireless sensor network; RFID-based IoT; RFID based WSN; smart RFID IntroductionRFID uses electromagnetic fields to identify automatically and to track tags attached on any object. It's used for applications like animal tagging, asset tracking, electronic passports, smartcards, store security, logistic and etc. [1]. The tags store object information electronically. There are passive and active RFID tags. There are LF (low frequency), HF (high frequency) and UHF RFID tag antennas [2] based on the frequency bands. Passive tags have no battery and collect energy from nearby RFID readers by interrogating radio waves, whereas active tags have a battery and can be detected over 100 m.According to applications and design technology, there are many articles published about UHF active tags. The read-range of the active tag is above 1 km with tag sensitivity under −80 dBm in 5.8 GHz and 433MHz bands [3][4][5]. On the other hand, a general passive UHF tags have about 10-20 m read-range based on the sensitivity of the tag chip and the types of antennas.Our passive UHF RFID tags have longer read-range than other designs. There will be benefits of tag with longer read-range since it can be incorporate with the sensing and communicating capabilities.Article [6] describes many novel applications of RFID sensors, novel antennas for metallic surface, 3D antennas, multi-band antennas, omnidirectional, and directional antennas in UHF, HF, or microwaves (MW) frequency bands. The sizes and read-range are also compared with different RFID Chips, and the longest read-range in the article is 14.6 m for the metal mountable antenna. Our passive UHF RFID tag had 26 m read-range using Higgs 4 RFID Chip manufactured by Alien Tech. Higgs 4 has sensitivity of −20.5 dBm.The more sensitivity of RFID tag chip has longer read-range with the same antenna. Different manufactures and different RFID chips have different level of sensitivities. The chip with the better sensitivity allows the tag to be read from farther range. If tag with longer read-range is integrated with sensors, it can have the following advantages: wireless powered identification in non-line-of-sight way, wide coverage and mobility RF...

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In this paper, various locations of an Ultra High Frequency (UHF) Radio Frequency Identification (RFID) tag on automotive license plates have been considered based on the radiation pattern of the tag antenna. A small, 130 × 50 mm, passive loop antenna type UHF RFID tag for an automotive license plate was simulated with an EM simulation CST program. It was designed to have a larger back-lobe radiation pattern since the front side of the tag faces the back side of the plate holder to protect the tag antenna from bugs and dust when the automobile runs. The tag was attached to the side of a license plate holder with a dimension of 520 × 110 mm, the typical size of the standard license plate. The reflection coefficient of the tag antenna is −21 dB at 920 MHz, and the gain of the tag antenna is 6.29 dBi at the back-lobe. The reading range of the tag antenna with the plate holder, which was measured in an open field, is about 10.3 m, and the reading range of the tag installed on the bumper from the front of the vehicle is 9.4 m. The tag antenna is small enough to apply to a real automobile, and it is applicable because it uses the back-lobe pattern, so it does not require an extra device for protection from damage.

UHF band (860~960MHz) RFID tag strip-line antennas for non-metallic object and slotted patch RFID antenna for metallic objects have been optimized with a GA. The antennas are optimized for commercially available RFID tag IC chips. Different cell sizes of FDTD have been tried while the GA optimizes the symmetrical shape of RFID antennas. I. IntroductionAn RFID system consists of a reader, a transponder (tag) and a computer connected to the reader. A transponder consists of an antenna and an RFID IC chip. The reader has an antenna. The reader transmits modulated electromagnetic field, which powers up the tag, while the reader sends the data to the tag. The RFID IC microchip is attached to the feeding point of the tag antenna [1-2]. The passive tag receives all the required energy from the RF energy of the carrier signal of the reader. The tag sends a coded signal back to the reader using the tag antenna by backscattering method. References [3-5] introduce a method to power up the tag. The method uses a rectifying Schottky detector diode circuit that converts microwave energy into DC. The rectified or DC part of the energy is used to power up the electronics in a passive tag chip. Various shapes of UHF RFID antennas are introduced in [6]. Reference [7] introduces electromagnetic band gap (EBG) antennas for RFID tag and reader antennas. An EBG antenna is attached to metal objects. When general tag antenna attached to a metallic object, the tag cannot be powered up by the field strength emitted by the reader since the metallic object reflects RF wave. The impedance of the tag antenna, resonant frequency of the antenna and radiation efficiency will be changed due to the parasitic capacitance between the tag antenna and the metallic object. [8]. To minimize effect of the parasitic capacitor between the tag antenna and metallic object, and the effect of the reflection of the RF wave by metallic object, it is better to put a gap between the tag antenna and the metallic object, and to add dielectric material with high dielectric constant between them.A genetic algorithm has been applied to optimize an RFID antenna. The impedance of a tag antenna should be matched to the conjugate of the impedance of an RFID IC Chip. The chip impedance has real and capacitive imaginary parts due to the parasitic capacitance of the RFID chip. The different impedance values of commercially available RFID chips are matched to the impedance of antenna.

This paper presents the design of a 920 MHz Ultra High Frequency (UHF) band radio frequency identification (RFID) conductive fabric tag antenna. The DC (Direct Current) resistance and impedance of the conductive fabric are measured by a DC multimeter and by a network analyzer at a UHF frequency band. The conductivities of the fabrics are calculated with their measured DC resistance and impedance values, respectively. The conductivities of the fabric are inserted into the CST simulation program to simulate the fabric tag antenna designs, and the results of the tag designs with two conductivities are compared. Two fabric UHF RFID tag antennas with a T-Matching structure, one with the name-tag size of 80 × 40 mm, and another with 40 × 23 are simulated and measured the characteristics of tag antennas. The simulated and measured results are compared by reflection coefficient S11, radar cross-section and reading range. The reading range of the 80 × 40 mm fabric tag antenna is about 4 m and 0.5 m for the 40 × 23 size tag. These fabric tags can be easily applied to an entrance control system as they can be attached to other fabrics and clothes.

This paper presents a design of a radio frequency identification (RFID) tag antenna in the ultra-high-frequency (UHF) range, which is applicable to a vehicular license plate attached to a vehicle bumper. The main goals are to first improve the identification ratio by controlling the radiation beam pattern and, second, to control the beam direction. Since every vehicle has a license plate, the available plate structure is used to design the antenna. The shape of the tag is rectangular and has a dimension of 525 mm × 116 mm, which is smaller than the typical size of standard plates, 540 mm × 120 mm, used in Europe and Korea. The fabricated tag antenna, the license plate, and the vehicular bumper are fixed by volt and nut. For vehicle tracking and identification, RFID readers are deployed on the road side. For efficient identification, a long distance passive UHF RFID license plate with a patch antenna is proposed to provide not only line-of-sight identification but also left and right beams. Unlike the general UHF tag antennas, in this paper, the patch antenna is designed to attach to the metal part of the car, the license plate holder. The beam patterns of the RFID tag antenna can be controlled by the patch antenna parameter values. The simulation result demonstrates that the proposed UHF RFID tag antenna has a beam radiation pattern as required at 920 MHz. In addition, the estimated read range of the proposed plate meets the requirement of RFID systems.