A holographic metamaterial array antenna applied to an RFID reader-writer

Abstract

The application discloses a holographic metamaterial array antenna applied to an RFID reader-writer, which comprises an impedance modulation unit area and a planar monopole area, wherein the impedance modulation unit area is formed by periodically arranging impedance modulation units in a rectangular shape, the impedance modulation unit comprises at least two layers of rectangular metal patch layers and at least two layers of rectangular dielectric layers and is located above a layer of rectangular metal ground plate layers, and the rectangular metal patch layer farthest from the rectangular metal ground plate layer has a slit structure; the planar monopole area is arranged at a central position of the holographic metamaterial array antenna, the planar monopole area comprises a planar monopole, at least one layer of rectangular dielectric layers and a layer of rectangular metal ground plate layers, wherein the planar monopole is located at the same layer as the rectangular metal patch layer; and the thickness of the planar monopole area is less than or equal to the thickness of the impedance modulation unit area. The application has clear working area boundaries, can realize a powerful working area field type and uniform coverage, and further improves reading effect.

Description

Technical Field

[0001] This invention relates to a holographic metamaterial array antenna for use in RFID readers, belonging to the field of RFID reader antenna technology. Background Technology

[0002] Antennas are crucial components in modern wireless communication systems, primarily responsible for converting radio frequency signals into electromagnetic waves for radiation. Antenna performance directly impacts communication distance and quality. Holographic impedance modulation surface antennas with multilayer artificial electromagnetic surfaces offer advantages such as low profile, small size, and simple feeding, making them suitable for various communication scenarios.

[0003] Existing RFID reader antennas generally suffer from the following problems: First, the beam distribution is too loose and the boundary is poor, making the boundary of the antenna's effective area unclear, leading to cross-reading and misreading outside the reading / writing area; second, the antenna field pattern continuity is poor, resulting in reading / writing blind zones, making it impossible to read tags within the reading / writing area; and third, the antenna field pattern uniformity is poor, causing inconsistent tag operation within the working area, affecting reading performance. Therefore, it is necessary to develop more advantageous reader antennas. Summary of the Invention

[0004] The purpose of this invention is to provide a holographic metamaterial array antenna for RFID readers, which has a clear working area boundary, can achieve a strong working area field pattern and uniform coverage, thereby improving the reading effect.

[0005] A holographic metamaterial array antenna for RFID readers includes an impedance modulation unit region and a planar monopole region. The impedance modulation unit region consists of impedance modulation units arranged in a periodic rectangular pattern. Each impedance modulation unit comprises at least two rectangular metal patch layers and at least two rectangular dielectric layers, situated on a rectangular metal ground plane. Each of the rectangular metal patch layers and the rectangular dielectric layers overlaps, and the rectangular metal patch layer furthest from the rectangular metal ground plane has a slotted structure. The planar monopole region is located at the center of the holographic metamaterial array antenna. The planar monopole region includes a planar monopole, at least one rectangular dielectric layer, and one rectangular metal ground plane. The rectangular dielectric layer is located between the planar monopole and the rectangular metal ground plane. The planar monopole and the rectangular metal patch layers are on the same layer, and the thickness of the planar monopole region is less than or equal to the thickness of the impedance modulation unit region.

[0006] Furthermore, the system operating frequency of the array antenna is 300–3000 MHz.

[0007] Furthermore, each rectangular metal patch layer has a slotted structure.

[0008] Furthermore, the long side and the wide side of the rectangular metal floor layer are equal to those of the rectangular dielectric layer.

[0009] Furthermore, the rectangular metal floor layer is made of conductive metals such as gold, silver, and copper, with a thickness of 0.18–0.35 mm and a side length of 10–100 mm.

[0010] Furthermore, the thickness of the rectangular dielectric layer is 2–5 mm, and the dielectric constant is 5–20.

[0011] Furthermore, the metal patch layer is made of conductive metals such as gold, silver, and copper, with a thickness of 0.18–0.35 mm, a side length of 9–99 mm, and a slit width of 0.1–1.5 mm.

[0012] Furthermore, the distance between any side length of the rectangular metal floor layer or any side length of the rectangular dielectric layer and the adjacent side length of the rectangular metal patch layer is 0.5 to 7.5 mm.

[0013] Furthermore, the planar monopole includes an annular metal patch and a circular metal patch, wherein the radius of the annular metal patch is larger than that of the circular metal patch, and there is a gap between the annular metal patch and the circular metal patch.

[0014] Furthermore, the planar monopole is made of conductive metals such as gold, silver, and copper, the radius of the annular metal patch is 15–250 mm, the radius of the circular metal patch is 1–100 mm, and the width of the gap is 0.5–20 mm.

[0015] Furthermore, the planar monopole is connected to the active circuit via a coaxial line, with the coaxial line located at the center of the circular metal patch, and the power supply position of the planar monopole located at the bottom of the coaxial line.

[0016] Furthermore, the planar monopole adjusts the resonant frequency by changing the radius of the annular metal patch, and adjusts the impedance bandwidth by changing the radius of the circular metal patch.

[0017] Furthermore, the impedance modulation units of the holographic metamaterial array antenna, which are m rows and n columns in size, are arranged in a periodic rectangular pattern, where m is 11 to 21 and n is 11 to 21.

[0018] Furthermore, the rectangular metal patch layer and the slotted structure form a circularly polarized waveform in the array antenna.

[0019] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0020] (1) This invention uses a holographic metamaterial array antenna to design an RFID reader antenna, which can efficiently edit the field pattern distribution of the RFID reader antenna. Compared with traditional reader antennas, the layered holographic metamaterial array antenna provided by this invention can achieve field pattern editing by changing the phase of the array impedance modulation unit. It can also be combined with application scenarios such as multi-beam and non-diffraction beam generation to achieve the requirements of field pattern boundary and uniformity.

[0021] (2) The impedance adjustment unit of the present invention adopts a rectangular metal patch with a slotted structure. Compared with other types of units, this unit is not only easier to model and process, but also has a larger impedance variation range, which can achieve a larger modulation depth and improve leakage efficiency.

[0022] (3) Compared with conventional holographic metamaterial array antennas composed of single-layer conformal and axial monopoles, the present invention uses multi-layer planar and coaxially fed planar monopoles. The advantage is that it can better meet the space and field of RFID reader applications and can efficiently excite surface waves. Attached Figure Description

[0023] Figure 1 This is a bottom view schematic diagram of the impedance modulation unit with a two-layer structure according to the present invention;

[0024] Figure 2 This is an enlarged schematic diagram of the planar monopole of the present invention;

[0025] Figure 3 This is a bottom view of the two-layer structure of the present invention;

[0026] Figure 4 For the present invention Figure 3 A magnified view of the central area;

[0027] Figure 5 for Figure 4 Enlarged schematic diagram of the L~L' tangent section;

[0028] Figure 6 for Figure 4 Enlarged schematic diagram of the L-L' tangent section of another embodiment;

[0029] Figure 7 for Figure 4 Enlarged schematic diagram of the L-L' tangent section of another embodiment;

[0030] Figure 8 This is a bottom view of the three-layer structure of the present invention;

[0031] Figure 9 For the present invention Figure 3 Near-field contour map of the simulated two-layer structure;

[0032] Figure 10 For invention Figure 8 Near-field contour map of the simulated three-layer structure;

[0033] Figure 11 For the present invention Figure 3 A schematic diagram of the simulation test results of a two-layer holographic metamaterial array antenna reader and tag;

[0034] Figure 12 For the present invention Figure 8 A schematic diagram of the simulation test results of the three-layer holographic metamaterial array antenna reader and tag.

[0035] Specific implementation of the rectangular method

[0036] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0037] This invention establishes a method for a holographic metamaterial array antenna applied to RFID readers, specifically including:

[0038] S1. Establish an impedance modulation unit model, simulate an infinite periodic arrangement using master-slave boundaries, and obtain the eigenfrequency using an eigenmode solver.

[0039] S2. Select the slit angle of the rectangular metal patch layer, and then simultaneously change the side length of the rectangular metal patch layer, the total term difference of the master-slave boundary and the surface wave transmission direction. Obtain the equivalent scalar impedance through the intrinsic frequency calculated in S1.

[0040] S3. By changing only the side length of the rectangular metal patch layer each time, the tensor impedance corresponding to the side length of each set of rectangular metal patch layers is obtained, and then the relationship between the maximum value of the equivalent scalar impedance corresponding to the tensor impedance and the side length of the rectangular metal patch layer is fitted.

[0041] S4. Calculate the values ​​of each component of the tensor impedance;

[0042] S5. Using the fitting relationship obtained in S3 and the tensor impedance component values ​​obtained in S4, the actual side length and actual slot angle of the rectangular metal patch layer of each impedance modulation unit are obtained, and the impedance modulation unit area of ​​the array antenna is established.

[0043] S6. A planar monopole is added at the center of the array antenna to construct a holographic metamaterial array antenna for use in RFID readers.

[0044] The equivalent scalar impedance in S2 above is obtained based on the following formula:

[0045]

[0046] Among them, Z e Z0 is the equivalent scalar impedance, j is the imaginary unit, and Z0 is the free-space wave impedance. The horizontal rectangular phase difference of the surface wave on the cross section. Let ω be the surface wave phase difference in the vertical rectangular direction on the cross section, c be the speed of light in free space, a be the side length of the rectangular metal floor, and ω be the eigenfrequency.

[0047] The equivalent scalar impedance is obtained by combining different tensor impedances using the following formula:

[0048] make

[0049]

[0050] Where, α z η is the attenuation constant of the surface wave in the direction normal to the impedance surface, k0 is the wave number of the electromagnetic wave in free space, j is the imaginary unit, η0 is the wave impedance of the electromagnetic wave in free space, and θ is the wave impedance of the electromagnetic wave in free space. t Z represents the direction of surface wave propagation. xx For, Z yy Z xy These are three independent tensor impedance components.

[0051] The relationship between the maximum value of the equivalent scalar impedance corresponding to the fitted tensor impedance in S3 above and the side length of the rectangular metal patch layer is shown in the following fitted formula:

[0052] Z max =0.0012*g 6 -0.0078*g 5 +1.789*g 4 -22.1*g 3 +148.7*g 2 -519.9*g 1 +851.7 where Z max is the maximum value of the equivalent scalar impedance, and g is the distance between any side length of the rectangular metal ground plane or any side length of the rectangular dielectric layer and the adjacent side length of the rectangular metal patch layer.

[0053] The method for establishing microwave holography is similar to that of optical methods. A fed planar monopole generates a reference wave, which can also be a surface wave, while the target wave is an object wave. The microwave hologram is a collection of scattered scatterings produced by the interference of the reference wave and the object wave. The object wave can be formed by scattering the reference wave using the microwave hologram. Therefore, the components of the tensor impedance in S4 above can be obtained from the following formulas:

[0054] Reference wave:

[0055] Target wave:

[0056]

[0057] α=α0 / 2+α0 / 2*(1-r i,j / max(r i,j ))

[0058] Among them, J surf To simulate the cylindrical surface wave generated by a monopole, r is the radius vector of the impedance modulation element on the antenna plane, j is the imaginary unit, e is the natural constant, and k t E is the wave number of the surface wave propagating on the antenna surface. rad Let θ be the target beam to be generated, and θ be the elevation angle pointing towards the target beam. Let α be the azimuth angle of the target beam, k be the wavenumber of the target beam propagating in free space, x and y be the planar coordinates of the impedance modulation unit, α0 represent the cone angle of the designed conventional Bessel beam, and r be the azimuth angle of the target beam. i,j Let max(r) be the distance from each element of the antenna array to the center of the array. i,j ) is r i,j The maximum value is then used to modulate the reference wave and the target wave into a tensor surface impedance distribution according to the following moment formula:

[0059]

[0060] This invention establishes a holographic metamaterial array antenna for use in RFID readers through the methods described in S1 to S6 above. The array antenna system of this invention mainly operates at a frequency of 300–3000 MHz, with a preferred operating frequency of 750–1300 MHz.

[0061] Figure 1 This is a bottom view schematic diagram of the impedance modulation unit with a two-layer structure according to the present invention. Please refer to it. Figure 1The two-layer impedance modulation unit 1 comprises two rectangular metal patch layers 3, two rectangular dielectric layers 5, and a rectangular metal ground layer 6. Each of the rectangular metal patch layers 3 and the rectangular dielectric layers 5 is overlapped. Each rectangular metal patch layer 3 has a slotted structure 3-1. The long side and the wide side of the rectangular metal ground layer 6 are equal to those of the rectangular dielectric layer 5. The distance between any side length of the rectangular metal ground layer 6 or any side length of the rectangular dielectric layer 5 and the adjacent side length of the rectangular metal patch layer 3 is g. In other embodiments, only the rectangular metal patch layer 3 furthest from the rectangular metal ground layer 6 may have the slotted structure 3-1, while the other rectangular metal patch layers 3 may not have the slotted structure 3-1. The rectangular metal patch layer 3 is made of conductive metals such as gold, silver, and copper, with a thickness of 0.18–0.35 mm and a side length of 9–99 mm, preferably 8.1–39 mm. The width of the slot structure 3-1 is 0.1–1.5 mm, and the angle of the slot structure 3-1 can be arbitrarily varied. The rectangular dielectric layer 5 is made of PCB substrate, with a thickness of 2–5 mm and a dielectric constant of 5–20. The rectangular metal ground layer 6 is made of conductive metals such as gold, silver, and copper, with a thickness of 0.18–0.35 mm and a side length of 10–100 mm, preferably 23.1–40 mm. The long side and wide side of the rectangular dielectric layer 5 corresponding to the rectangular metal ground layer 6 are equal; the distance g between any side length of the rectangular metal ground layer 6 or any side length of the rectangular dielectric layer 5 and the adjacent side length of the rectangular metal patch layer 3 is 0.5–7.5 mm.

[0062] Figure 2 This is an enlarged schematic diagram of the planar monopole of the present invention. Please refer to... Figure 2 The planar monopole 4 of this invention includes an annular metal patch 4-1 and a circular metal patch 4-2, wherein the radius D of the annular metal patch 4-1 is larger than the radius d of the circular metal patch 4-2, and a gap 4-3 is formed between the annular metal patch 4-1 and the circular metal patch 4-2. The materials of the annular metal patch 4-1 and the circular metal patch 4-2 are conductive metals such as gold, silver, and copper. The radius D of the annular metal patch 4-1 is approximately 1.5 to 2.5 periods of impedance modulation unit 1, ranging from 15 to 250 mm, preferably 34.65 to 100 mm. The radius d of the circular metal patch 4-2 is approximately 0.1 to 1 period of impedance modulation unit 1, ranging from 1 to 100 mm, preferably 2.31 to 40 mm. The width w of the gap 4-3 is approximately 0.05 to 0.2 periods of impedance modulation unit 1, ranging from 0.5 to 20 mm, preferably 1.16 to 8 mm.

[0063] In detail, the planar monopole 4 adjusts the resonant frequency by changing the radius D of the annular metal patch 4-1, and adjusts the impedance bandwidth by changing the radius d of the circular metal patch 4-2. In other words, by adjusting the dimensions of the planar monopole 4, it can be matched to the input port, further reducing the system profile and efficiently exciting surface waves to meet bandwidth requirements. In this invention, the shape of the planar monopole 4 can be circular, rectangular, or polygonal, etc.

[0064] In this embodiment, the center frequency is selected as 922MHz. The period of impedance modulation unit 1 is generally about 1 / 10 of the working wavelength, while in this embodiment, the working wavelength is set to 36.9 mm. The total phase difference between the master and slave boundaries is 30° to 180°, the propagation direction of the surface wave is 0° to 170°, the width of the slot structure 3-1 of each rectangular metal patch layer 3 is 1 mm, the thickness of the rectangular dielectric layer 5 is 3 mm, the dielectric constant of the rectangular dielectric layer 5 is 6.15, the side length of both the rectangular dielectric layer 5 and the rectangular metal ground layer 6 is 36.9 mm, and the distance g between any side length of the rectangular metal ground layer 6 or any side length of the rectangular dielectric layer 5 and the adjacent side length of the rectangular metal patch layer 3 is 0.5 mm. Based on the above basic parameters and formulas, an infinite periodic array is simulated using the master-slave boundary, and the refractive index error caused by size changes is ignored to establish the impedance modulation unit 1 model. The actual side length and actual slot angle of the rectangular metal patch layer 3 of each impedance modulation unit 1 are then calculated using the above formula, and the impedance modulation unit area of ​​the array antenna is established by periodic rectangular arrangement.

[0065] Finally, a planar monopole 4 is added to the center of the holographic metamaterial array antenna. In this embodiment, the radius D of the annular metal patch 4-1 of the planar monopole 4 is 74.8 mm, the radius d of the circular metal patch 4-2 is 6 mm, and the width w of the gap 4-3 is 4 mm. This constructs a holographic metamaterial array antenna for RFID readers with a two-layer impedance modulation unit 1, as shown in the bottom view diagram below. Figure 3 As shown.

[0066] In detail, Figure 3Based on the established impedance distribution and extracted impedance modulation unit 1 database, the impedance modulation units 1 can be arranged periodically in a certain order to simulate the impedance modulation unit region 2 of the tensor impedance distribution. All the impedance modulation units 1 are arranged in a certain rectangular pattern to form different rectangular metal patch layers 3 and slit angles 3-1 to form different fringes to simulate interference fringes. Based on the holographic principle, the interference fringes and impedance distribution correspond to a cylindrical surface wave generated by a plane monopole 4 as the reference wave, and a left-hand circularly polarized plane wave with significant boundaries as the target wave. The holographic metamaterial array antenna for an RFID reader constructed in this invention is based on the rectangular arrangement of the impedance modulation units 1. That is, the holographic metamaterial array antenna is composed of m rows and n columns of impedance modulation units 1 arranged in a periodic rectangular pattern, where m is 11 to 21 and n is 11 to 21. In the holographic metamaterial array antenna for an RFID reader constructed in this invention, the rectangular metal patch layer 3 and the slit structure 3-1 form a circularly polarized waveform in the array antenna.

[0067] To illustrate the detailed structure of the holographic metamaterial array antenna for an RFID reader of the present invention, please also refer to... Figure 3 , Figure 4 and Figure 5 . Figure 4 For the present invention Figure 3 A magnified view of the center area of ​​the two-story structure from below. Figure 5 For the present invention Figure 4 Enlarged schematic diagram of the L~L' tangent cross-section. Figure 5The enlarged cross-sectional schematic diagram shows a planar monopole region 2 and an impedance modulation unit 1 on each of the left and right sides. Each impedance modulation unit 1 comprises at least two rectangular metal patch layers 3 and at least two rectangular dielectric layers 5 located on a rectangular metal ground plane layer 6. Each of the rectangular metal patch layers 3 and the rectangular dielectric layers 5 overlaps. The rectangular metal patch layer 3 furthest from the rectangular metal ground plane layer 6 has a slotted structure 3-1, and the other rectangular metal patch layer 3 also has a slotted structure 3-1. The length of any side of the rectangular metal ground plane layer 6 or any side of the rectangular dielectric layer 5 and the rectangular metal patch layer 6 are... The distance between adjacent sides of layer 3 is g; the planar monopole region 2 is located at the center of the surface layer of the holographic metamaterial array antenna. The planar monopole region 2 includes a planar monopole 4, two rectangular dielectric layers 5, and a rectangular metal ground layer 6. The rectangular dielectric layer 5 is located between the planar monopole 4 and the rectangular metal ground layer 6. The planar monopole 4 and the rectangular metal patch layer 3 farthest from the rectangular metal ground layer 6 are located on the same layer. The thickness of the planar monopole 4 is the same as the thickness of the rectangular metal patch layer 3 of the impedance modulation unit 1, while the thickness of the planar monopole region 2 is equal to the thickness of the impedance modulation unit region 1. In this embodiment, the planar monopole 4 is connected to the active circuit via a coaxial line 7. The coaxial line 7 is located at the center of the circular metal patch 4-2, and the feed position of the planar monopole 4 is located at the bottom of the coaxial line 7.

[0068] Please refer to Figure 6 . Figure 6 for Figure 4 An enlarged schematic diagram of the L-L' tangent section of another embodiment. Figure 6 and Figure 5 The difference in the enlarged cross-sectional view lies in the structure of the planar monopole region 2, in which... Figure 6 The planar monopole region 2 includes a planar monopole 4, a rectangular dielectric layer 5, and a rectangular metal ground layer 6. The rectangular dielectric layer 5 is located between the planar monopole 4 and the rectangular metal ground layer 6. The thickness of the planar monopole 4 is the same as the sum of the thickness of the two rectangular metal patch layers 3 and the rectangular dielectric layer 5 in the impedance modulation unit 1. In other words, the thickness of the planar monopole region 2 is equal to the thickness of the impedance modulation unit region 1.

[0069] Figure 7 for Figure 4 An enlarged schematic diagram of the L-L' tangent section of another embodiment. Figure 7 and Figure 5 The difference in the enlarged cross-sectional view lies in the structure of the planar monopole region 2, in which... Figure 7The planar monopole region 2 includes a planar monopole 4, a rectangular dielectric layer 5, and a rectangular metal ground layer 6. The rectangular dielectric layer 5 is located between the planar monopole 4 and the rectangular metal ground layer 6. The thickness of the planar monopole 4 is the same as the thickness of the rectangular metal patch layer 3 in the impedance modulation unit 1. That is to say, the thickness of the planar monopole region 2 is less than the thickness of the impedance modulation unit region 1.

[0070] Based on the above method and considering changes in the usage environment and conditions, a holographic metamaterial array antenna for RFID readers with two or more layers can also be constructed. Figure 8 This is a bottom view of the three-layer structure of the present invention. In detail, the holographic metamaterial array antenna of the RFID reader of the present invention, regardless of the number of layers, allows the rectangular metal patch layer 3 and the slotted structure 3-1 to form a circularly polarized waveform within the array antenna.

[0071] To verify the performance of the holographic metamaterial array antenna designed for RFID readers, full-wave simulation is required to analyze its standing wave characteristics and matrix pattern features.

[0072] After simulation of the reflection coefficient test, the results show that within the set frequency band, regardless of whether the impedance modulation unit 1 is a two-layer holographic metamaterial array antenna or a three-layer holographic metamaterial array antenna, its reflection coefficient is lower than -15dB, which shows that the matching effect of the present invention is good.

[0073] Please refer to Figure 9 and Figure 10 The simulated near-field contour distribution diagrams of the two-layer and three-layer holographic metamaterial array antennas show that, regardless of whether it is a two-layer or three-layer holographic metamaterial array antenna, the field pattern uniformity is good, the boundaries are clear and there are no discontinuities, which meets the design requirements.

[0074] Next, a joint simulation test of signal reception was conducted between the reader / writer equipped with the holographic metamaterial array antenna of this invention and the tag. First, the reader / writer sends a signal to the test tag through the holographic metamaterial array antenna to activate the tag. Then, the tag feeds back a signal to the holographic metamaterial array antenna. The reader / writer then analyzes the content and strength of this signal. The signal strength is represented by the RSSI value; that is, the RSSI value represents the relative quality of the signal received by the reader / writer. The higher the RSSI value, the stronger the signal. Please refer to [reference needed]. Figure 11 and Figure 12 of Figure 3 The two-layer structure and Figure 8 A schematic diagram illustrating the simulation test results of the three-layer holographic metamaterial array antenna reader and tag based on this invention. After joint simulation testing of the holographic metamaterial array antenna reader and tag according to this invention, [the results are shown in the diagram]. Figure 11 Simulation results of the two-layer holographic metamaterial array antenna reader show that for tags 1-9, the signal reading effect with an RSSI value greater than -60dB on the X-axis can reach a distance of 1.2 meters, while the signal reading effect with an RSSI value greater than -60dB on the Z-axis can reach a distance of 3 meters. This indicates that the two-layer holographic metamaterial array antenna of this invention has strong coverage and excellent reading performance. Figure 12 Simulation test results of the three-layer holographic metamaterial array antenna reader show that the signal reading effect of the X-axis RSSI value greater than -60dB for tags 1 to 9 can reach a distance of 2 meters, while the signal reading effect of the Z-axis RSSI value greater than -60dB can also reach a distance of 3 meters. It can be seen that the three-layer holographic metamaterial array antenna of the present invention also has strong coverage and excellent reading effect.

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A holographic metamaterial array antenna for use in RFID readers, characterized in that, It includes an impedance modulation unit region and a planar monopole region, wherein: The impedance modulation unit area is formed by periodically arranging impedance modulation units in a rectangular pattern. Each impedance modulation unit includes at least two rectangular metal patch layers and at least two rectangular dielectric layers located on a rectangular metal floor layer. Each of the rectangular metal patch layers and the rectangular dielectric layers overlaps, and only the rectangular metal patch layer furthest from the rectangular metal floor layer has a slot structure. The planar monopole region is located at the center of the holographic metamaterial array antenna. The planar monopole region includes a planar monopole and at least one rectangular dielectric layer and one rectangular metal ground plane layer. The rectangular dielectric layer is located between the planar monopole and the rectangular metal ground plane layer. The planar monopole and the rectangular metal patch layer are located on the same layer. The thickness of the planar monopole region is less than the thickness of the impedance modulation unit region.

2. The holographic metamaterial array antenna for RFID readers according to claim 1, characterized in that, The system operating frequency of the array antenna is 300~3000MHz.

3. A holographic metamaterial array antenna for use in RFID readers according to claim 1, characterized in that, Each rectangular metal patch layer has a slotted structure.

4. A holographic metamaterial array antenna for use in RFID readers according to claim 1, characterized in that, The rectangular metal floor layer has the same long side and the same wide side as the rectangular dielectric layer.

5. A holographic metamaterial array antenna for use in RFID readers according to claim 1, characterized in that, The rectangular metal floor layer is made of conductive metals such as gold, silver, and copper, with a thickness of 0.18 to 0.35 mm and a side length of 10 to 100 mm.

6. A holographic metamaterial array antenna for use in RFID readers according to claim 1, characterized in that, The rectangular dielectric layer has a thickness of 2-5 mm and a dielectric constant of 5-20.

7. A holographic metamaterial array antenna for use in RFID readers according to claim 1 or 3, characterized in that, The rectangular metal patch layer is made of conductive metals such as gold, silver, and copper, with a thickness of 0.18~0.35 mm and a side length of 9~99 mm. The width of the slit structure is 0.1~1.5 mm.

8. A holographic metamaterial array antenna for use in RFID readers according to claim 1 or 3, characterized in that, The distance between any side length of the rectangular metal floor layer or any side length of the rectangular dielectric layer and the adjacent side length of the rectangular metal patch layer is 0.5~7.5 mm.

9. A holographic metamaterial array antenna for use in RFID readers according to claim 1, characterized in that, The planar monopole includes an annular metal patch and a circular metal patch, wherein the radius of the annular metal patch is larger than that of the circular metal patch, and there is a gap between the annular metal patch and the circular metal patch.

10. A holographic metamaterial array antenna for use in RFID readers according to claim 9, characterized in that, The planar monopole is made of gold, silver, or copper conductive metals. The radius of the annular metal patch is 15-250 mm, the radius of the circular metal patch is 1-100 mm, and the width of the gap is 0.5-20 mm.

11. A holographic metamaterial array antenna for use in RFID readers according to claim 9, characterized in that, The planar monopole is connected to the active circuit via a coaxial line, which is located at the center of the circular metal patch, and the power supply position of the planar monopole is located at the bottom of the coaxial line.

12. A holographic metamaterial array antenna for use in RFID readers according to claim 9, characterized in that, The planar monopole adjusts the resonant frequency by changing the radius of the annular metal patch and adjusts the impedance bandwidth by changing the radius of the circular metal patch.

13. A holographic metamaterial array antenna for use in RFID readers according to claim 1, characterized in that, The holographic metamaterial array antenna has an m-row, n-column impedance modulation unit arranged in a periodic rectangular pattern, where m is 11-21 and n is 11-21.

14. A holographic metamaterial array antenna for use in RFID readers according to claim 1 or 3, characterized in that, The rectangular metal patch layer and the slotted structure form a circularly polarized waveform in the array antenna.

Images