An anti-metal broadband RFID tag antenna

Abstract

The application discloses an anti-metal wide-bandwidth RFID tag antenna and belongs to the technical field of radio frequency identification antennas. The antenna comprises a dielectric substrate, a radiation structure arranged on the surface of the dielectric substrate and a feed structure electrically connected with the radiation structure; the radiation structure comprises a perpendicular magnetic ring structure and dipole radiation arms arranged on both sides of the feed structure, wherein the middle part of the feed structure is used for connecting an RFID chip, and the two ends of the feed structure form a vertically closed loop with a metal mounting surface through a short-circuit structure. The perpendicular magnetic ring structure is used for generating a radiation field type mainly in a magnetic dipole mode, so as to reduce the influence of a metal surface on the radiation performance of the antenna; the dipole radiation arms introduce an electric resonance mode through electromagnetic coupling with the feed structure, and form a double-resonance working mechanism with the magnetic ring structure. By adjusting the structural parameters of the dipole radiation arms, the adjustment of the working frequency and impedance characteristics of the antenna can be realized. The antenna has simple structure and small size, is suitable for the application of an ultra-high frequency RFID tag in a metal environment, and can be used for passive Internet of Things application scenarios.

Description

Technical Field

[0001] This invention relates to the field of ultra-high frequency radio frequency identification tag antenna technology, and in particular to an anti-metal wide bandwidth RFID tag antenna. Background Technology

[0002] The large-scale application of passive IoT and the official commercialization of 5G-A technology are driving global commercial and industrial systems into a new stage of digital transformation characterized by "full-element digitalization, full-process automation, and full-lifecycle intelligence." As a key supporting technology for the sensing layer of passive IoT, UHF RFID tags, with their inherent advantages of long reading distance, fast identification speed, passive and maintenance-free operation, and low cost, have become the preferred solution for connecting massive numbers of terminals. They are widely used in core scenarios such as warehouse management, industrial production lines, and power supply chains, and have become the core carrier for the implementation of 5G-A passive IoT capabilities.

[0003] The large-scale deployment of UHF RFID relies on a simple collaborative architecture of "tag-reader-upper-layer system". The high uplink bandwidth, low latency, and wide-area continuous networking characteristics of 5G-A technology provide key support for the full-domain perception of this architecture: the upper-layer system uses the edge computing capabilities of 5G-A to complete the real-time screening and standardization of massive tag data, and seamlessly connects to management systems such as ERP and WMS; the reader achieves multi-node collaboration and full-domain coverage through the 5G-A private network, breaking the limitations of traditional single-point identification, and can flexibly adapt to diverse application scenarios such as fixed deployment in warehouse channels and mobile deployment on drones; the tag, as the core sensing terminal of passive Internet of Things, is composed of a chip and an antenna. After being activated by the radio frequency energy emitted by the reader, it feeds back a unique identifier and associated data, becoming a key terminal component supporting 5G-A connection targets. The entire workflow forms an efficient closed loop: the reader emits radio frequency signals to build an identification area, the tag is activated and feeds back data after entering the area, and the data is uploaded to the upper layer system in real time via the 5G-A network to complete data processing and business response, ultimately achieving a leapfrog upgrade from local identification to full-domain control.

[0004] However, when UHF RFID tags are directly attached to metal surfaces or high-dielectric-constant materials, the mirror effect generated by the metal conductor causes significant cancellation of the antenna radiation field and severe impedance mismatch, leading to problems such as operating frequency drift, a sharp drop in reading distance, or even complete failure. This pain point is particularly prominent in core scenarios such as industrial equipment management, power material storage, and automotive parts traceability enabled by 5G-A. The "blind spot-free, end-to-end" management requirements driven by 5G-A further amplify the performance defects of traditional tags, severely restricting the scenario coverage depth of passive IoT.

[0005] To overcome the technical challenge of anti-metal interference, existing technologies have introduced solutions such as artificial magnetic conductors (AMC), electromagnetic bandgap structures (EBG), and vertical loop structures. Among them, vertical loop antennas, with their unique field distribution characteristics, can reduce metal interference and have a symmetrical structure, making them an important research direction for anti-metal tag design. However, existing related designs still have significant shortcomings: single vertical loop structures have poor impedance matching flexibility and narrow intrinsic bandwidth, making them difficult to be compatible with UHF bands in different countries and regions, and unable to meet the cross-regional application requirements of 5G-A passive IoT; some designs improve performance through fractal geometry and array structures, but suffer from limited bandwidth improvement, structural complexity, and large size, which conflict with the core requirements of passive IoT for "low cost and easy deployment"; other solutions rely on special substrates or precise inter-layer stacking control, leading to increased manufacturing costs and reduced mass production yield, making it difficult to support the massive terminal deployment scenarios enabled by 5G-A.

[0006] Therefore, there is an urgent need for a UHF RFID tag antenna design that is compact, easy to manufacture, cost-controllable, and can effectively solve the problems of impedance matching, broadband coverage, and reading distance stability in metallic environments. This design is intended to meet the massive deployment needs of passive IoT and the all-domain sensing characteristics of 5G-A technology, thereby facilitating the practical implementation of digital transformation in industries such as manufacturing, power, and logistics. Summary of the Invention

[0007] This invention provides a vertical ring dipole coupled anti-metal UHF RFID tag antenna, achieving synergistic optimization of anti-metal characteristics, wide frequency band coverage, good impedance matching, and compact structure.

[0008] Therefore, the tag antenna proposed in this invention includes: a dielectric substrate, a tag chip, and a patch layer disposed on the upper surface of the substrate. The patch layer includes a vertical annular patch and a coupled dipole patch, which work together to achieve the antenna's anti-metallic properties and wide bandwidth.

[0009] The vertical ring patch is arranged perpendicular to the metal surface; the center of the feed line of the vertical ring structure is connected to the tag chip, and the distance from the chip to the two end patches is L1=15mm; the two end patches have slots with a length of a=16mm and a width of b=7mm, which are used to adjust the impedance and reserve installation space for the asymmetric dipole structure; the vertical ring structure is connected to the metal surface through a shorting wire, so that the metal surface is transformed into the artificial ground plane of the antenna system, and its mirror current is in phase with the real current of the radiator and radiates in coordination, suppressing surface wave loss.

[0010] The dipole patch is located on both sides of the feed line and includes two sets of dipole radiating arms of different sizes, namely the first dipole arm (length L2, width W2) and the second dipole arm (length L3, width W3). The spacing between the dipole radiating arms and the feed line is s1=s2=4mm. The dual resonance characteristic is constructed through electromagnetic coupling effect, and the resonant frequencies are located on the upper and lower sides of the target frequency of 915MHz, respectively, to achieve wide frequency band coverage. By adjusting the length, width and spacing of the dipole arms and the feed line, the antenna input impedance can be precisely controlled to achieve conjugate matching with the tag chip.

[0011] The dielectric substrate is made of FR4 epoxy glass fiber material with a dielectric constant of 4.4 and a thickness of 1.6mm. It has good processability, stability and cost advantages, and is suitable for mass production using conventional PCB etching processes.

[0012] The tag chip uses UCODE 8 and is bonded to the narrow gap of the vertical ring structure. The chip has a read sensitivity of -21.85dBm and an impedance of 13-j191Ω at a frequency of 916MHz. Signal coupling and energy harvesting are achieved through the center position of the feeder.

[0013] In summary, the present invention has the following technical advantages: it utilizes a vertical ring structure to transform the metal surface into an artificial ground plane for the antenna system, thereby achieving the antenna's anti-metal properties; it introduces an asymmetric dipole coupling patch to broaden the antenna bandwidth and achieve easy adjustment of the center frequency; and it features an overall planar antenna structure, making it easy to manufacture and producing, and possessing good practicality and engineering feasibility. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of an anti-metal wideband RFID tag antenna in one embodiment; Figure 2 This is a structural diagram of an anti-metal wideband RFID tag antenna in one embodiment; Figure 3 This is a physical diagram of an anti-metal wideband RFID tag antenna in one embodiment; Figure 4 This embodiment illustrates the influence of coupling dipole lengths L2 and L3 on the S11 parameter in an anti-metal wideband RFID tag antenna. Figure 5 The radiation efficiency and gain of an anti-metal wideband RFID tag antenna on different metal surfaces are shown in one embodiment. Figure 6 One embodiment illustrates the effect of an anti-metal wideband RFID tag antenna coupling dipole patch on the center frequency of parameter S11. Figure 7Let be the input impedance of an anti-metal wideband RFID tag antenna in one embodiment, where (a) is the real part of the impedance and (b) is the imaginary part of the impedance; Figure 8 This is an example of surface current distribution for an anti-metal wideband RFID tag antenna; Figure 9 This is a radiation pattern of an anti-metal wideband RFID tag antenna at a frequency of 915MHz in one embodiment. Figure 10 This is a 3D radiation characteristic diagram of an anti-metal wideband RFID tag antenna at a frequency of 915MHz in one embodiment. Detailed Implementation

[0015] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0016] Examples: To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0017] This application provides a metal-mountable UHF RFID tag antenna, such as... Figure 1 As shown, the antenna structure includes: a dielectric substrate, a radiating structure disposed on the surface of the dielectric substrate, and a feeding structure connected to the radiating structure.

[0018] The radiating structure is disposed on the surface of the dielectric substrate and includes a vertical magnetic ring structure and a dipole radiating arm structure electromagnetically coupled to the feeding structure; the feeding structure includes a feeding wire, and a mounting area for connecting the RFID chip is provided at its center.

[0019] Specifically, such as Figure 2 As shown, the dielectric substrate serves as the support layer for the antenna, supporting the radiating and feeding structures and providing them with stable mechanical support and planar layout space. The RFID chip used is UCODE 8, with a read sensitivity of -21.85dBm and an impedance of 13-j191Ω at a frequency of 916MHz.

[0020] Figure 2Both ends of the feed line are electrically connected to the metal mounting surface via short-circuit structures, forming a vertically closed loop structure, i.e., a vertical magnetic ring structure, together with the metal mounting surface. This vertical magnetic ring structure primarily operates in magnetic dipole radiation mode, with its radiated magnetic field direction perpendicular to the metal mounting surface, thereby reducing the impact of the metal surface on the antenna's radiation performance. Through this structural design, the metal mounting surface is transformed from a traditional interference element into part of the antenna radiation system, ensuring that the mirror current generated on the metal surface is in the same direction as the actual current. This facilitates the release of radiated energy into free space, improving the antenna's stability in metallic environments.

[0021] Furthermore, such as Figure 2 As shown, dipole radiating arm structures are respectively provided on both sides of the feed line. The dipole radiating arms are excited by near-field electromagnetic coupling with the feed line and are not directly electrically connected to the feed line.

[0022] The dipole radiating arms are asymmetrical, meaning the first and second dipole radiating arms located on either side of the feed line are not identical in length or shape parameters. This asymmetrical design allows the two dipole radiating arms to generate different electrical resonant frequencies, thus introducing an auxiliary electrical resonant mode on top of the vertical magnetic ring resonant mode, forming a dual-resonance working mechanism together with the magnetic resonance. By adjusting the length, width, and spacing between the dipole radiating arms and the feed line, the antenna's operating frequency position and input impedance characteristics can be flexibly adjusted to achieve conjugate matching of the RFID chip impedance and wideband coverage.

[0023] Figure 2 The feed line is an inductive feed structure, with its center electrically connected to the RFID chip via a narrow slit. Structurally, this feed line is a slender conductor, providing inductive input characteristics to match the high capacitive impedance of the RFID chip. Slotted structures for impedance adjustment can be further incorporated at both ends of the feed line near the shorting structure, allowing for precise control of the antenna input impedance and resonant frequency by altering the length of the local current path.

[0024] The dielectric substrate is made of FR4 epoxy glass fiber material with a thickness of 1.6 mm and a dielectric constant of approximately 4.4. This material has good mechanical strength, processing stability, and cost advantages, making it suitable for large-scale manufacturing of printed circuit boards. The radiating and feeding structures are formed on the surface of the dielectric substrate using conventional PCB etching processes. The overall structure is a single-layer planar structure, requiring no stack-up, vias, or additional lumped components, resulting in a simple structure and high reliability.

[0025] In one specific embodiment, electromagnetic full-wave simulation software is used to simulate and analyze the input impedance, reflection characteristics, radiation efficiency, gain, and radiation pattern of the metal RFID tag-mountable antenna, and a corresponding physical sample is fabricated, such as... Figure 3 As shown in the figure, the simulation results are basically consistent with the measured results, indicating that the antenna can still maintain stable resonance characteristics and radiation performance under metal mounting conditions.

[0026] Figures 4 to 10 The key performance indicators, such as the impact of critical structural parameters on antenna performance, simulated S11 curves, radiation efficiency and gain variation curves, simulated and measured input impedance, surface current distribution, and radiation pattern at the design frequency, are presented respectively.

[0027] like Figure 4 As shown, after performing parameter sweep analysis on the lengths L2 and L3 of the coupled dipole, it was found that as the length increases, the reflection coefficient curve S11 shifts towards lower frequencies, indicating that the resonant frequency gradually decreases. This is due to the influence of the coupling patch on the current path, further proving the effectiveness of the coupling patch in frequency tuning.

[0028] Figure 5 The figure shows the radiation efficiency and gain of the tag antenna when it is placed on different material surfaces. The results show that the radiation efficiency and gain of the tag antenna are not significantly affected after being placed on a metal surface, thus confirming that the tag antenna has effective anti-metal performance.

[0029] Figure 6 The diagrams show the return loss of single-resonant patches placed on the upper and lower layers of the feed line, as well as a dual-resonant patch. Dual resonance occurs when both patches are simultaneously coupled to the loop. Results confirm that by appropriately modifying the dual-resonant patch, the bandwidth and impedance can be effectively improved, maintaining a loss below -10dB in the 905MHz-920MHz band, achieving a bandwidth of 15MHz, covering most of the UHF band, and meeting the bandwidth requirements of UHF RFID communication systems.

[0030] Figure 7 The figure shows the simulated and measured values ​​of the input impedance of the tag antenna. As can be seen from the figure, although the impedance curve deviates at some frequencies, the simulated and measured values ​​do not change much in the range of 905MHz-920MHz.

[0031] Figure 8 The surface current distribution of the tag antenna is shown in the figure. The current in the loop exhibits a uniform and in-phase distribution on the ring conductor, indicating that the antenna's radiation mode is dominated by an effective magnetic dipole. The ring current path parallel to the metal surface generates a magnetic field that can effectively penetrate the metal in the near-field region, avoiding the performance degradation caused by short-circuiting of the electric field in traditional electric dipoles.

[0032] Figure 9 and Figure 10 The images show the E-plane radiation pattern and 3D radiation characteristics of the tag antenna, respectively. Due to its unique anti-metal properties, the radiation directionality is concentrated above the metal. The gain at 915MHz is -2.93dB, which meets the RFID tag antenna application standard. This indicates that the antenna design not only achieves broadband performance but also has good gain performance.

[0033] In summary, this invention addresses the problems of interference from metal surfaces and insufficient bandwidth inherent in traditional tag antennas by proposing a miniaturized UHF RFID tag antenna design based on a vertical ring structure and an asymmetric coupled dipole patch. The design employs a short-wire connection between the feed line and the ground plane. The portion of the antenna in contact with the metal surface effectively isolates the patch at the top of the antenna from the metal surface, allowing the antenna patch to exhibit radiation characteristics similar to a magnetic dipole, achieving a crucial step towards good anti-metal properties. Simultaneously, the addition of asymmetric coupled bent dipole patches on both sides of the tag antenna feed line achieves good conjugate matching with the microchip and increases bandwidth.

[0034] The experimental results demonstrate that even with errors caused by the shorted solder wires on both sides and its small size, it still exhibits good radiation on metal surfaces, with an effective reading distance of 7.32 meters. This work addresses the challenges of achieving RFID detection in metallic environments, meeting the size and performance requirements of applications such as logistics management.

[0035] This invention features a novel structure and superior performance, providing an effective technical path for achieving anti-metal properties and broadband coverage for RFID tag antennas. It is particularly suitable for scenarios such as warehouse management, metal asset management, and logistics tracking, and has promising engineering application prospects and promotional value.

Claims

1. A metal-resistant wideband RFID tag antenna, characterized in that, The antenna includes a dielectric substrate and a patch layer disposed on the upper surface of the substrate. The patch layer includes a vertical magnetic ring structure, a dipole radiating arm structure, and a feeding structure. The vertical magnetic ring structure is formed by electrically connecting the two ends of the feed wire to the metal mounting surface through a short-circuit structure, so that the feed wire and the metal mounting surface together form a vertical closed loop. The dipole radiating arm structure is disposed on both sides of the feed wire and operates through electromagnetic coupling with the feed wire. It is used to introduce an electric resonant mode on the basis of the vertical magnetic ring structure, so that the antenna can form a dual resonant operating state in which magnetic resonance and electric resonance coexist.

2. The antenna according to claim 1, characterized in that, The vertical magnetic ring structure is dominated by magnetic dipole radiation mode, and its radiating magnetic field is perpendicular to the metal mounting surface.

3. The antenna according to claim 1, characterized in that, The dipole radiating arm structure includes a first dipole radiating arm and a second dipole radiating arm located on both sides of the feed line, and the first dipole radiating arm and the second dipole radiating arm are asymmetrical in length or shape. By adjusting the length parameters of the first dipole radiating arm and the second dipole radiating arm, the dipole radiating arm generates two electrical resonant points located above and below the target operating frequency.

4. The antenna according to claim 1, characterized in that, The feeder cable is an inductive feeder structure used to achieve impedance conjugate matching with the high-capacitive RFID chip. Both ends of the feeder cable are connected to metal short-circuit conductors to electrically connect the feeder cable to the metal mounting surface.

5. The antenna according to claim 1, characterized in that, The dielectric substrate is an FR4 epoxy fiberglass board with a thickness of 1.6 mm and a dielectric constant of 4.

3. The radiating patch is set on the upper surface of the FR4 dielectric substrate by an etching process.

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