Staggered inductive coupling feed ultrahigh frequency tag antenna attached to metal surface

Abstract

The invention discloses a staggered inductive coupling feeding ultrahigh-frequency tag antenna attached to a metal surface, which belongs to the technical field of tag antennas and comprises a dielectric substrate, a conductive layer printed on the dielectric substrate and a tag IC (integrated circuit) chip arranged on the conductive layer. The conductive layer comprises a linear feed unit and a linear coupling unit; the linear feed unit comprises two mutually symmetrical horizontal feed strip lines and first vertical open-circuit stubs respectively arranged on the outer sides of the two horizontal feed strip lines; the tag IC chip is arranged at the central position of the inner side of the two horizontal feed strip lines; the linear coupling unit comprises two mutually symmetrical horizontal coupling strip lines, second vertical open-circuit stubs arranged on the inner sides of the two horizontal coupling strip lines respectively, two coupling broadband lines connected with the two horizontal coupling strip lines, and two rectangular defects etched in the coupling broadband lines respectively. The problems that the scheme is complex and the cost is high when an ultrahigh-frequency tag antenna overcomes a metal structure are solved.

Description

Technical Field

[0001] This invention belongs to the field of tag antenna technology, and particularly relates to an interleaved inductively coupled ultra-high frequency tag antenna attached to a metal surface. Background Technology

[0002] Ultra-high frequency (UHF) radio frequency identification (RFID) technology is widely used in inventory management, asset tracking, electronic payments, and patient monitoring. The basic performance of the tag antenna must be guaranteed to meet different market demands. However, different materials on the tag surface can interfere with the surface current of RFID, especially metal surfaces, which cause more significant interference and affect the tag antenna's input impedance, actual gain, and read distance. Current methods for overcoming metal structures in tag antennas include: (1) attaching tag-type dipoles with spacers to foam to reduce the influence of the backing metal surface, but without spacers, the radiation performance will be significantly degraded; (2) using vertical feeding and short-circuit elements for inverted F antennas of metal-mounted tags, but this increases the complexity and cost of the manufacturing process; (3) using artificial magnetic conductor substrates with metal through-hole offsets to improve the gain and readout range performance of tag antennas, but air gaps or foam are needed to reduce the metal surface effect between the tag antenna and the artificial magnetic conductor substrate, otherwise the antenna gain will be significantly affected; (4) using electrical band gaps to improve the gain of tag antennas while preventing impedance mismatch, but the complexity of the antenna, the thickness of the tag, and the cost of the tag will increase significantly. Summary of the Invention

[0003] To address the aforementioned shortcomings in the prior art, this invention provides an interleaved inductively coupled UHF tag antenna attached to a metal surface, which solves the problems of complex solutions and high costs associated with overcoming the limitations of metal structures in UHF tag antennas.

[0004] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: The present invention provides an interleaved inductively coupled ultra-high frequency tag antenna attached to a metal surface, comprising a dielectric substrate, a conductive layer printed on the dielectric substrate, and a tag IC chip disposed on the conductive layer; the conductive layer includes a linear feeding unit and a linear coupling unit; The linear feed unit includes two mutually symmetrical horizontal feed lines, and N identical first vertical open-circuit stubs respectively set on the outer side of the two horizontal feed lines, where N is a positive integer; The tag IC chip is located at the center of the inner side of the two horizontal power supply lines; The linear coupling unit includes two mutually symmetrical horizontal coupling lines, N-1 identical second vertical open-circuit stubs respectively arranged on the inner side of the two horizontal coupling lines, two coupling broadband lines for connecting the two horizontal coupling lines, and two rectangular defects respectively etched inside the coupling broadband lines.

[0005] Furthermore, the first vertical open-circuit stub and the second vertical open-circuit stub are interleaved.

[0006] Furthermore, the dielectric substrate is a polytetrafluoroethylene dielectric substrate with a thickness of 1.5 mm, a relative permittivity of 2.55, and a loss tangent of 0.0015.

[0007] Furthermore, the tag IC chip uses a UCODE-8 chip.

[0008] Furthermore, the dielectric substrate is mounted on the surface of the metal conductor with a gap thickness of 2 mm.

[0009] Furthermore, the dimensional parameters of the interleaved inductively coupled UHF tag antenna attached to the metal surface are as follows: The lateral length G of the etched slots on the inner sides of the two horizontal feed lines is 1.0 mm; the lateral length H of the horizontal feed lines is 2.3 mm; the longitudinal width W of the first vertical open-circuit stub is 3.0 mm; the lateral length L of the first vertical open-circuit stub is 21.6 mm; the longitudinal width S of the etched slot between the first and second vertical open-circuit stubs is 0.8 mm; the longitudinal width T of the second vertical open-circuit stub is 3.0 mm; the lateral length A of the horizontal coupling line is 1.0 mm; the longitudinal width B of the coupling broadband line is 4.8 mm; the lateral length D of the rectangular defect... L The longitudinal width D of the rectangular defect is 40.0 mm. W The diameter is 40.0 mm; the projected length E between the edge of the conductive layer and the edge of the dielectric substrate is 0.4 mm, and the lateral length of the dielectric substrate is... The longitudinal width of the dielectric substrate .

[0010] The beneficial effects of this invention are as follows: This invention provides an interleaved inductively coupled UHF tag antenna attached to a metal surface. By setting multiple first and second vertical open-circuit stubs on the linear feeding unit and the linear coupling unit respectively for mutual coupling, the miniaturization of the interleaved inductively coupled UHF tag antenna attached to the metal surface is effectively achieved. This invention can adjust the resonant frequency of the tag antenna over a wide range by adjusting the length, width, and spacing of the first and second vertical open-circuit stubs. This invention can precisely and finely adjust the impedance coefficient of the tag antenna by adjusting the size of the rectangular defect structure, thereby achieving perfect impedance matching with any type of IC chip and adjusting the operating frequency band to any frequency band in the UHF region. This invention is applied to a metal conductor surface, and the resonant frequency of the tag antenna remains stable regardless of changes in the size of the metal conductor surface. The antenna structure of this invention does not require any complex manufacturing processes, does not require metal vias and / or short arms, has a simple structure, and is suitable for mass production and application.

[0011] Other advantages of the present invention will be analyzed in more detail in the following embodiments. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1(a) is a side view of an interleaved inductively coupled ultra-high frequency tag antenna attached to a metal surface in an embodiment of the present invention.

[0014] Figure 1(b) is a top view of an interleaved inductively coupled ultra-high frequency tag antenna attached to a metal surface in an embodiment of the present invention.

[0015] Figure 2(a) is a schematic diagram of the region of the linear power supply unit in an embodiment of the present invention.

[0016] Figure 2(b) is a schematic diagram of the area of ​​the horizontal feed line and the first vertical open circuit stub in an embodiment of the present invention.

[0017] Figure 3(a) is a schematic diagram of the region of the linear coupling unit in an embodiment of the present invention.

[0018] Figure 3(b) is a schematic diagram of the area of ​​the horizontal coupling strip, the second vertical open circuit stub, the coupling broadband line, and the rectangular defect in an embodiment of the present invention.

[0019] Figure 4This is a schematic diagram showing the dimensions of an interleaved inductively coupled ultra-high frequency tag antenna attached to a metal surface, according to an embodiment of the present invention.

[0020] Figure 5 This is an input impedance diagram of an interleaved inductively coupled UHF tag antenna attached to a metal surface at various design stages according to an embodiment of the present invention.

[0021] Figure 6 This is a current distribution diagram of an interleaved inductively coupled ultra-high frequency tag antenna attached to a metal surface at various design stages according to an embodiment of the present invention.

[0022] Figure 7(a) is a graph showing the change in input impedance of an interleaved inductively coupled ultra-high frequency tag antenna attached to a metal surface in an embodiment of the present invention after adjusting the lateral length of the first vertical open circuit stub.

[0023] Figure 7(b) is a graph showing the change in input impedance of an interleaved inductively coupled ultra-high frequency tag antenna attached to a metal surface in an embodiment of the present invention after adjusting the longitudinal width of the first vertical open circuit stub.

[0024] Figure 8(a) is a power reflection coefficient diagram of the lateral length of the rectangular defect of an interleaved inductively coupled ultra-high frequency tag antenna attached to a metal surface in an embodiment of the present invention.

[0025] Figure 8(b) is a power reflection coefficient diagram of the longitudinal width of the rectangular defect of an interleaved inductively coupled ultra-high frequency tag antenna attached to a metal surface in an embodiment of the present invention.

[0026] Figure 9(a) shows the detection distance when the lateral length x of the metal conductor is adjusted to 20cm in an embodiment of the present invention.

[0027] Figure 9(b) shows the detection distance when the longitudinal width y of the metal conductor is adjusted to 20cm in an embodiment of the present invention.

[0028] Among them: 1. dielectric substrate; 2. tag IC chip; 3. linear power supply unit; (31) horizontal power supply strip; (32) first vertical open circuit stub; 4. linear coupling unit; (41) horizontal coupling strip; (42) second vertical open circuit stub; (43) coupling broadband line; (44) rectangular defect. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0030] As shown in Figures 1(a) and 1(b), in one embodiment of the present invention, the present invention provides an interleaved inductively coupled ultra-high frequency tag antenna attached to a metal surface, including a dielectric substrate 1, a conductive layer printed on the dielectric substrate 1, and a tag IC chip 2 disposed on the conductive layer; the conductive layer includes a linear feeding unit 3 and a linear coupling unit 4. As shown in Figures 2(a) and 2(b), the linear power supply unit 3 includes two mutually symmetrical horizontal power supply strips 31, and N identical first vertical open-circuit stubs 32 respectively arranged on the outer side of the two horizontal power supply strips 31, where N is a positive integer; in this embodiment, N is 5, that is, the number of first vertical open-circuit stubs 32 is 5 on one side. The tag IC chip 2 is located at the center of the inner side of the two horizontal power supply lines 31; As shown in Figures 3(a) and 3(b), the linear coupling unit 4 includes two mutually symmetrical horizontal coupling strips 41, N-1 identical second vertical open-circuit stubs 42 respectively disposed on the inner side of the two horizontal coupling strips 41, two coupling broadband lines 43 for connecting the two horizontal coupling strips 41, and two rectangular defects 44 respectively etched inside the coupling broadband lines 43; since in this embodiment, N is 5, that is, the number of second vertical open-circuit stubs 42 is 4 on one side; In this solution, by adjusting the length and width of the rectangular defect 44, the impedance coefficient of the interleaved inductively coupled UHF tag antenna attached to the metal surface can be precisely adjusted, thereby achieving perfect impedance matching with any type of IC chip and adjusting the operating frequency band to any frequency band in the UHF (Ultra High Frequency) region.

[0031] The first vertical open-circuit stub 32 and the second vertical open-circuit stub 42 are interleaved.

[0032] In this scheme, by setting the first vertical open-circuit stub 32 and the second vertical open-circuit stub 42 to be interleaved, coupling power can be achieved through inductance. Specifically, by adjusting the dimensions of the first vertical open-circuit stub 32 and the second vertical open-circuit stub 42 to adjust the circuit length and antenna inductance, the current distribution is changed, effectively improving the gain of the tag antenna and ensuring that the resonant frequency can be flexibly controlled.

[0033] The dielectric substrate 1 is a polytetrafluoroethylene dielectric substrate with a thickness of 1.5 mm, a relative permittivity of 2.55, and a loss tangent of 0.0015.

[0034] The overall length of the interleaved inductively coupled fed UHF tag antenna attached to a metal surface provided by this solution is [not specified]. Width The physical dimensions of the height are 53.2mm × 45.4mm × 1.535mm, and the corresponding relative dimensions are... ,in, The wavelength is in free space.

[0035] Free space wavelength formula ,in, At the speed of light, The frequency is given. In this scheme, the height dimension, which has the most accurate relative size among the three dimensions of the conductive layer, is used for calculation based on the free space wavelength formula, resulting in a free space wavelength of [value missing]. The corresponding frequency is It belongs to the UHF RFID frequency band: 860-960MHz, which is consistent with the typical operating frequency of tag antennas.

[0036] The dielectric substrate 1 is mounted on the surface of the metal conductor with a gap thickness of 2 mm.

[0037] In this scheme, by mounting the dielectric substrate 1 on the surface of a metal conductor, the performance of the interleaved inductively coupled UHF tag antenna attached to the metal surface in terms of reflection coefficient, gain, readout mode, actual gain, directivity, or readout range is not affected by the thickness of the substrate metal surface. In this embodiment, it is preferable to mount the interleaved inductively coupled UHF tag antenna attached to the metal surface on a 20cm×20cm metal conductor surface, with a gap thickness of 2mm, wherein the mounted metal conductor surface is preferably a copper surface.

[0038] In this embodiment, the interleaved inductively coupled UHF tag antenna attached to the metal surface operates at a North American frequency band of 902-928MHz, with an actual gain of 2.55dB and a detection distance of 17.15m at a resonant frequency of 915MHz.

[0039] The interleaved inductively coupled UHF tag antenna provided by this solution, which is attached to a metal surface, does not require any complex manufacturing process, such as using metal through-holes and / or short arms. It has a simple structure and is easy to mass-produce.

[0040] like Figure 4 As shown, the dimensional parameters of the interleaved inductively coupled UHF tag antenna attached to the metal surface are as follows: The lateral length G of the etched slots inside the two horizontal feed lines 31 is 1.0 mm; the lateral length H of the horizontal feed line 31 is 2.3 mm; the longitudinal width W of the first vertical open-circuit stub 32 is 3.0 mm; the lateral length L of the first vertical open-circuit stub 32 is 21.6 mm; the longitudinal width S of the etched slot between the first vertical open-circuit stub 32 and the second vertical open-circuit stub 42 is 0.8 mm; the longitudinal width T of the second vertical open-circuit stub 42 is 3.0 mm; the lateral length A of the horizontal coupling line 41 is 1.0 mm; the longitudinal width B of the coupling broadband line 43 is 4.8 mm; the lateral length D of the rectangular defect 44 is... L The longitudinal width D of the rectangular defect 44 is 40.0 mm. W The diameter is 40.0 mm; the projected length E between the edge of the conductive layer and the edge of the dielectric substrate 1 is 0.4 mm, and the lateral length of the dielectric substrate 1 is... The longitudinal width of dielectric substrate 1 .

[0041] In this scheme, the horizontal length of the second vertical open stub 42 is the same as the horizontal length of the first vertical open stub 32.

[0042] Typically, less than 2500mm 2 The tag antenna has a higher resonant frequency, therefore, designing a miniature tag antenna by lowering the resonant frequency to the ultra-high frequency band is a complex process: like Figure 5As shown, in the first stage of the design, two symmetrical E-type feed units and staggered open-circuit stubs were simulated, resulting in resonance at 1.323 GHz, higher than the desired frequency band. In the second stage, two vertical open-circuit stubs were added to each horizontal feed unit and coupling unit, increasing the coupling inductance and reducing the resonant frequency to 1.069 GHz. In the third stage, a rectangular defect 44 was etched into the patch connection area, specifically the coupling bandwidth line 43, to further reduce the resonant frequency, bringing it closer to the target UHF band. In the fourth stage, by optimizing the size of the vertical open-circuit stubs and the defect area, the tag antenna was made to operate in the North American frequency band of 902-948 MHz. Based on the above design stages, optimal matching with the IC chip at 915 MHz was achieved, along with miniaturization, eliminating the need for any complex structures and significantly reducing the cost of large-scale manufacturing.

[0043] like Figure 6 As shown, in the second stage, by adding two additional open-circuit stubs to each horizontal feed line, the antenna inductance is effectively increased, thereby reducing the operating frequency of the UHF tag antenna band. In this embodiment, the highest surface current density is observed in the gap region between the open-circuit stubs and the horizontal coupling lines. In the patch connection region, i.e., the rectangular defect 44 etched in the coupling bandwidth line 43, the overall surface current direction can be optimized, thereby significantly reducing current interference and increasing the maximum surface current density from 3.8 A / m to 47.9 A / m. It can be seen that the overall structure of the staggered inductively coupled fed UHF tag antenna attached to the metal surface proposed in this scheme can adjust the resonant frequency.

[0044] This solution can achieve impedance matching between the conductive layer and the tag IC chip 2 by adjusting the size of the vertical open-circuit stub. The strength of the inductive coupling is determined by the lateral length L and longitudinal width W of the first vertical open-circuit stub 32, as well as the longitudinal width S of the etch gap between the first vertical open-circuit stub and the second vertical open-circuit stub. As shown in Figure 7(a), as the lateral length L of the first vertical open-circuit stub 32 is adjusted from 18mm to 24mm and the longitudinal width W is fixed at 3mm, it can be observed that the resonant frequency decreases from 1.061 GHz to 0.874 GHz at a rate of approximately 32MHz / 1mm. As shown in Figure 7(b), when the longitudinal width W is adjusted from 2.0 mm to 4.0 mm and the transverse length L is fixed at 23.5 mm, the resonant frequency decreases from 1.026 GHz to 0.829 GHz at a rate of approximately 50 MHz / 0.5 mm.

[0045] In this solution, by adjusting the size of the rectangular defect 44, the impedance matching between the conductive layer and the tag IC chip 2 can be finely adjusted, and this is reflected by the power reflection coefficient. As shown in Figure 8(a), when the lateral length D of the rectangular defect... L Adjusted from 34mm to 40mm, vertical width D W When the diameter is adjusted from 1.0mm to 1.5mm, the resonant frequency of the interleaved inductively coupled UHF tag antenna attached to the metal surface is within the North American band (902-928MHz), and the power transmission coefficient is less than -30dB. As shown in Figure 8(b), when the horizontal length D L =40mm, longitudinal width D W When the thickness is 1.2mm, the resonant frequency of the interleaved inductively coupled UHF tag antenna attached to the metal surface is 915MHz, and the power transfer coefficient is -49.5dB.

[0046] This solution provides an interleaved inductively coupled UHF tag antenna attached to a metal surface, the maximum detection distance of which varies depending on the size of the metal conductor surface: As shown in Figures 9(a) and 9(b), when the longitudinal width y of the metal conductor is 10cm, 12cm, 14cm, 16cm, 18cm, and 20cm respectively, and the lateral length x of the metal conductor is adjusted to 20cm, or when the lateral length x of the metal conductor is 10cm, 12cm, 14cm, 16cm, 18cm, and 20cm respectively, and the longitudinal width y of the metal conductor is adjusted from 10cm to 20cm, the resonant frequency of the tag antenna is located in the North American frequency band (902-928MHz), and the maximum reading distance is greater than 15m. In particular, when both the lateral length x and the width w of the metal conductor are equal to 20cm, the resonant frequency of the antenna is 915MHz, and the corresponding reading distance is 17.15m. The above results show that the resonant frequency remains stable when the size of the metal surface changes; that is, regardless of the displacement of the metal surface in the x or y direction, the response of the RFID tag to the reader still appears in the same frequency range. This characteristic is more suitable for RFID metal installation implementation.

[0047] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A staggered inductively coupled ultra-high frequency tag antenna attached to a metal surface, characterized in that, It includes a dielectric substrate (1), a conductive layer printed on the dielectric substrate (1), and a tag IC chip (2) disposed on the conductive layer; the conductive layer includes a linear feeding unit (3) and a linear coupling unit (4). The linear feed unit (3) includes two mutually symmetrical horizontal feed lines (31), and N identical first vertical open-circuit stubs (32) respectively set on the outer side of the two horizontal feed lines (31), where N is a positive integer; The tag IC chip (2) is located at the center of the inner side of the two horizontal power supply lines (31); The linear coupling unit (4) includes two mutually symmetrical horizontal coupling strips (41), N-1 identical second vertical open-circuit stubs (42) respectively set on the inner side of the two horizontal coupling strips (41), two coupling broadband lines (43) for connecting the two horizontal coupling strips (41), and two rectangular defects (44) respectively etched inside the coupling broadband lines (43).

2. The interleaved inductively coupled UHF tag antenna attached to a metal surface according to claim 1, characterized in that, The first vertical open-circuit stub (32) and the second vertical open-circuit stub (42) are interleaved.

3. The interleaved inductively coupled UHF tag antenna attached to a metal surface according to claim 1, characterized in that, The dielectric substrate (1) is a polytetrafluoroethylene dielectric substrate with a thickness of 1.5 mm, a relative permittivity of 2.55, and a loss tangent of 0.0015.

4. The interleaved inductively coupled UHF tag antenna attached to a metal surface according to claim 1, characterized in that, The tag IC chip (2) is a UCODE-8 chip.

5. The interleaved inductively coupled UHF tag antenna attached to a metal surface according to claim 1, characterized in that, The dielectric substrate (1) is mounted on the surface of the metal conductor with a gap thickness of 2 mm.

6. The interleaved inductively coupled UHF tag antenna attached to a metal surface according to claim 1, characterized in that, The dimensional parameters of the interleaved inductively coupled fed UHF tag antenna attached to the metal surface are as follows: The transverse length G of the etched gap inside the two horizontal feed lines (31) is 1.0 mm; the transverse length H of the horizontal feed line (31) is 2.3 mm; the longitudinal width W of the first vertical open circuit stub (32) is 3.0 mm; the transverse length L of the first vertical open circuit stub (32) is 21.6 mm; the longitudinal width S of the etched gap between the first vertical open circuit stub (32) and the second vertical open circuit stub (42) is 0.8 mm; the longitudinal width T of the second vertical open circuit stub (42) is 3.0 mm; the transverse length A of the horizontal coupling line (41) is 1.0 mm; the longitudinal width B of the coupling broadband line (43) is 4.8 mm; the transverse length D of the rectangular defect (44) is... L The longitudinal width D of the rectangular defect (44) is 40.0 mm. W The diameter is 40.0 mm; the projected length E between the edge of the conductive layer and the edge of the dielectric substrate (1) is 0.4 mm, and the lateral length of the dielectric substrate (1) is 40.0 mm. The longitudinal width of the dielectric substrate (1) .

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