Pure metal anisotropic holographic impedance metasurface antenna and design method

Abstract

The application discloses a pure metal anisotropic holographic impedance metasurface antenna and a design method. Since the pure metal structure and the patch structure with a dielectric substrate have complementary characteristics in structure, according to the Babinet principle, only the angle corresponding to the long axis is increased by 90 degrees to the angle corresponding to the short axis as a rotation angle, and the pure metal structure unit can be used for design. Combined with the holographic principle, the leaky wave theory and the Babinet principle, the mapping relationship between the tensor impedance of the pure metal structure unit and the geometric parameters of the unit is directly calculated, and a pure metal anisotropic impedance holographic metasurface model is established. Compared with the non-flat pure metal modulation tensor impedance metasurface realized by the additive manufacturing process and the pure metal space wave modulation transmitting array and reflecting array, the pure metal anisotropic impedance holographic metasurface has unique advantages of simple manufacturing, super-small appearance and easy integration.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metasurface antennas, and particularly relates to a pure metal anisotropic holographic impedance metasurface antenna and a design method. BACKGROUND

[0002] A metasurface composed of periodic and non-periodic sub-wavelength units is a two-dimensional planar structure derived from three-dimensional spatial structure electromagnetic materials, i.e., metamaterials. These metamaterials realize extraordinary electromagnetic medium parameters that do not exist in nature, expanding the degrees of freedom of electromagnetic modulation. In addition, from the perspective of modulation function, metamaterials can be divided into polarization modulation, frequency modulation, amplitude modulation and phase modulation, and are successfully applied in the fields of electromagnetic wave absorption, frequency selective surface radiators, stealth materials and the like, overcoming the problem of limited function due to structural design limitations of traditional antennas. According to the different electromagnetic wave modulation mechanisms, the metasurface can be divided into surface wave modulation metasurfaces and spatial wave modulation metasurfaces. In the spatial wave modulation metasurface, the most commonly used is the gradient phase surface, which can produce sudden phase changes through the generalized Snell law. Then, the spatial wave modulation metasurface composed of gradient phase surfaces can develop a transmission array and a reflection array using the ray tracing method. Compared with the transmission array, the reflection array increases the shielding of the outgoing wave because its feed and reflected wave are in the same space, which limits its application occasions.

[0003] The patent with the patent number CN117199822A and the invention name of "Circularly polarized non-diffractive electromagnetic wave antenna based on anisotropic holographic impedance metasurface" discloses a circularly polarized non-diffractive electromagnetic wave antenna based on anisotropic holographic impedance metasurface, which solves the problem that the existing antenna cannot generate electromagnetic waves with circular polarization and high beamforming characteristics. However, the presence of a single-layer dielectric plate can create vulnerabilities in other harsh environments (such as extreme cold and extreme heat), thereby destroying the stability of the substrate dielectric constant and changing the strength of the medium, leading to array deformation and affecting the overall performance of the antenna. In addition, the transmission array without a dielectric layer not only reduces dielectric loss, but also can withstand high-power microwave irradiation as a lens. This dual function has broad application prospects in the military field. People have proposed pure metal reflection arrays and transmission arrays, which include four layers of cascaded planar metal layers, three layers of cascaded planar metal layers, two layers of cascaded planar metal layers and a single layer of metal, greatly improving the environmental adaptability and performance stability of the system.

[0004] The feeding structure in the surface wave modulation super surface can be integrated with the surface, greatly improving the integration performance of the system. In the surface wave modulation super surface, the most representative structure is the holographic impedance surface. According to the structural characteristics of the unit, it can be divided into isotropic holographic impedance and anisotropic holographic impedance surface. Similarly, in order to overcome the adverse effects of harsh environment and maintain the performance index of the antenna, a holographic impedance surface based on additive manufacturing of pure metal modulation element surface antenna is proposed, which to some extent expands the adaptability and adjustment ability of the antenna. However, the longitudinal non-uniform growth structure of the unit increases the processing complexity, and at the same time reduces the planar integration performance of the system.

[0005] The existing design method can only be applied to the structure of metal patch with dielectric substrate. When the whole adopts pure metal structure, the traditional design method is no longer applicable when calculating the size of the unit, and the connection relationship between the metal structures needs to be considered additionally. SUMMARY

[0006] The unmanned aerial vehicle redundancy steering gear speed reducer provided by the application solves the problem that the traditional design method is no longer applicable when calculating the size of the unit, and the connection relationship between the metal structures needs to be considered additionally.

[0007] To achieve the above object, the application provides the following technical scheme:

[0008] A pure metal anisotropic holographic impedance super surface antenna, comprising a transmission array, a monopole antenna arranged at the center of the transmission array, the transmission array comprising a plurality of array arranged impedance units, the impedance unit comprising a lower metal floor and an upper hollow metal plate, and an air layer arranged between the two metal plates.

[0009] The upper metal plate of each unit is composed of a circular hollow structure and a rectangular metal structure passing through the center of the hollow structure, and the upper metal plate has an angle with the horizontal plane of the transmission array.

[0010] Preferably, the transmission array comprises 49x49 impedance units.

[0011] Preferably, the thickness of the upper metal plate and the thickness of the lower metal plate are the same, and the thickness of the air layer is 2 times the thickness of the upper metal plate.

[0012] A design method of a pure metal anisotropic holographic impedance super surface antenna, comprising:

[0013] Determine the illumination direction of the beam, and obtain the components of the impedance tensor of each impedance unit according to the illumination direction of the beam.

[0014] According to the relationship between the equivalent scalar impedance and the surface wave creeping direction, an elliptical curve is drawn;

[0015] According to the relationship between the equivalent scalar impedance and the surface wave creeping direction, an elliptical curve is drawn;

[0016] According to the elliptical curve, the maximum value of the equivalent scalar impedance and the angle between the upper metal plate and the horizontal plane of the transmission array are obtained;

[0017] According to the maximum value of the equivalent scalar impedance, the radius of the circular hollow is obtained.

[0018] Preferably, the irradiation direction of the beam is determined, and the steps of obtaining the components of the impedance tensor of each impedance unit according to the irradiation direction of the beam are specifically:

[0019]

[0020] wherein k z represents the wave number in the Z-axis direction, k0 represents the wave number in the free space, is the normalized equivalent scalar impedance, Z xx , Z xy , and Z yy are three components of the impedance tensor Z, respectively.

[0021] Preferably, the impedance components are obtained according to the surface current field of the monopole antenna on the impedance unit and the electric field of the monopole antenna.

[0022] Preferably, the components of the impedance tensor Z further include Z yx According to the energy conservation law and the symmetry characteristics of the proposed unit, the impedance tensor Z is a pure imaginary matrix, Z xy = Z yx .

[0023] Preferably, drawing the elliptical curve according to the relationship between the equivalent scalar impedance and the surface wave creeping direction is specifically:

[0024] For impedance units at different positions, the equivalent isotropic impedance value of the anisotropic surface impedance changes with different creeping angles θ k of the surface wave, and the change of the equivalent scalar impedance value of the surface wave in different propagation directions on the tensor impedance surface presents an elliptical curve form.

[0025] Preferably, obtaining the maximum value of the equivalent scalar impedance according to the elliptical curve is specifically:

[0026] The major axis of the elliptical curve corresponds to the maximum value of the equivalent scalar impedance.

[0027] Preferably, the angle between the upper metal plate and the horizontal plane of the transmission array is the angle between the major axis of the elliptical curve and the X-axis plus 90 degrees.

[0028] Compared with the prior art, the present application has the following beneficial effects: the present application provides a pure metal anisotropic holographic impedance metasurface antenna, characterized in that it comprises a transmission array, a monopole antenna is arranged at the center of the transmission array, the transmission array comprises a plurality of array-arranged impedance units, the impedance unit comprises a lower metal floor and an upper hollow metal plate, an air layer is arranged between the two metal plates, the upper metal plate of each unit is composed of a circular hollow part and a rectangular metal structure passing through the center of the hollow part, and there is an included angle between the upper metal plate and the horizontal plane of the transmission array; the surface wave is converted into a leak wave by using a pure metal flat structure; the anisotropic holographic impedance surface has the unique characteristics of simple manufacturing, ultra-thin type and easy integration.

[0029] The present application also provides a pure metal anisotropic holographic impedance metasurface antenna design method; since the pure metal structure and the patch structure with a dielectric substrate have complementary characteristics in structure, according to the Babinet principle, only the angle corresponding to the long axis is increased by 90 degrees to the angle corresponding to the short axis as the rotation angle, and the pure metal structure unit can be designed. Combined with the holographic principle, the leak wave theory and the Babinet principle, the mapping relationship between the tensor impedance of the pure metal structure unit and the geometric parameters of the unit is directly calculated, and a pure metal anisotropic impedance holographic metasurface model is established. Compared with the non-flat pure metal modulation tensor impedance metasurface realized by the additive manufacturing process and the pure metal spatial wave modulation transmitting array and reflecting array, the pure metal anisotropic impedance holographic metasurface has the unique advantages of simple manufacturing, ultra-small shape and easy integration. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a schematic diagram of the overall structure of the antenna part of the embodiment of the present application, which comprises a monopole antenna and a holographic impedance modulation surface.

[0031] Figure 2 It is a schematic diagram of the tensor impedance unit structure.

[0032] Figure 3 It is a unit with a narrow metal cuboid width g s = 2 mm, a radius R s = 5 mm, and a rotation angle θ s = 60. k The corresponding equivalent scalar impedance.

[0033] Figure 4 It is the relationship between the maximum equivalent scalar impedance and different hollow cylinder radii R s .

[0034] Figure 5 It is the parameter Rs The distribution of .

[0035] Figure 6 The parameter θ of the invented anisotropic holographic impedance surface when operating in a single beam at 7.5 GHz s The distribution of .

[0036] Figure 7 The parameter R of the invented anisotropic holographic impedance surface when operating in dual-beam configuration at 7.5 GHz. s The distribution of .

[0037] Figure 8 The parameter θ of the invented anisotropic holographic impedance surface when operating in dual-beam configuration at 7.5 GHz s The distribution of .

[0038] Figure 9 a is the 3D far-field radiation pattern obtained from a simulation of a single-beam anisotropic holographic impedance surface at 7.5 GHz. Figure 9 b is the 3D far-field radiation pattern obtained from the simulation of a dual-beam anisotropic holographic impedance surface at 7.5 GHz.

[0039] Figure 10 Simulated and measured far-field radiation patterns of the invented single-beam anisotropic holographic impedance surface at 7.5 GHz.

[0040] Figure 11 Simulated and measured far-field radiation patterns of the invented dual-beam anisotropic holographic impedance surface at 7.5 GHz.

[0041] Figure 12 S11 when the invented single-beam anisotropic holographic impedance surface is in operation.

[0042] Figure 13 S11 when the invented dual-beam anisotropic holographic impedance surface is in operation.

[0043] In the diagram, 1-upper perforated metal plate, 2-monopol antenna, 3-metal ground plane Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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.

[0045] Therefore, the following detailed description of embodiments of the application provided in the accompanying drawings is not intended to limit the scope of the application claimed, but merely represents selected embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the application.

[0046] It should be noted that similar reference numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0047] In the description of embodiments of the application, it should be noted that if the terms "upper", "lower", "horizontal", "inner" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship when the product of the application is used, it is only for the convenience of describing the application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the application. In addition, the terms "first", "second" and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0048] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly inclined. For example, "horizontal" only means that its direction is relatively more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0049] In the description of embodiments of the application, it should also be noted that unless otherwise explicitly specified and limited, if the terms "arrangement", "installation", "connection", "connection" appear, they should be understood broadly, for example, they can be fixedly connected, or can be detachably connected, or integrally connected; can be mechanically connected, or can be electrically connected; can be directly connected, or indirectly connected through an intermediate medium; can be connected inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0050] In order for those skilled in the art to better understand the technical solutions of the application, the application will be further described in detail below with reference to the drawings.

[0051] The application first proposes a low-cost ultrathin pure metal anisotropic impedance holographic super surface, and explores it in the C-band radio frequency range. In order to better adapt to the harsh conditions of extreme cold and extreme heat, and possibly realize the radiation modulation of high-power microwaves, the application discards the substrate-based super surface in the traditional printed circuit board (PCB) process, and uses a pure metal plane structure to convert surface waves into leaky waves.

[0052] As Figure 1 shown, the present application provides a pure metal anisotropic holographic impedance super surface antenna, comprising a transmission array, a monopole antenna is arranged at the center of the transmission array, the transmission array comprises a plurality of array arranged impedance units, the impedance unit comprises a lower metal floor and an upper hollow metal plate, an air layer is arranged between the two metal plates.

[0053] The upper metal plate of each unit is composed of a circular hollow and a long rectangular metal structure passing through the center of the hollow, and there is an included angle between the upper metal plate and the horizontal plane of the transmission array.

[0054] The upper metal plate of each unit is composed of a circular hollow with a radius R s and a long rectangular metal structure passing through the center of the hollow with a rotatable rotation angle of θ s . The size of the circular hollow and the rotation angle of the long rectangular metal structure of different impedance units are different.

[0055] As Figure 2 shown, the geometric structure shows that the period is P = 16 mm, the thickness of the two metal plates is 1 mm, and the height of the air layer in the middle is 2 mm

[0056] In this design, a quarter wavelength monopole antenna with a working frequency of 7.5 GHz is used to excite, and the surface current field of the monopole antenna is given by the following formula:

[0057]

[0058] Where, is the position vector of the center geometric position of the super surface unit in the mth row and nth column on the anisotropic holographic impedance super surface; (x mn ,y mn ,0) represents the position coordinates of the super surface unit in the mth row and nth column on the super surface, n e is the equivalent refractive index of the modulated anisotropic holographic impedance surface.

[0059] When the monopole antenna is placed as a feed source at the origin of the XOY plane, the electric field is given by the following formula:

[0060]

[0061] Where (1, 0, 0) represents that the polarization direction of the radiation wave is along the x axis, is the wave vector of the i spatial beam.

[0062] The tensor impedance expression formula three satisfies the energy conservation law and the reciprocity theorem at the same time:

[0063]

[0064] Where X represents the average modulation impedance, and M represents the average modulation depth, determined by the maximum and minimum equivalent scalar impedances. represents the cross product of vectors, and * represents the conjugate transpose.

[0065] Substituting Equations 1 and 2 into Equation 3, the design beam illumination direction is determined. Then, for the metasurface element in the m-th row and n-th column, the three components Z of the impedance tensor Z are... xx Z xy Z yy It can be given by the following formula:

[0066]

[0067] Considering the law of conservation of energy and the symmetry characteristics of the proposed unit, the non-Hermitian matrix Z must satisfy the reciprocity theory, requiring Z to be a purely imaginary matrix such that the components Z xy =Z yx .

[0068] To simplify the calculation of the relationship between the element impedance tensor and its own geometric parameters, and to further clarify the propagation law of surface waves on symmetric tensor impedance surface elements, for a given tensor impedance Z and surface wave propagation direction θ... k We can then obtain formula four:

[0069]

[0070] Where k z k represents the wave number along the Z-axis, and k0 represents the wave number in free space. This is the normalized equivalent scalar impedance. Therefore, according to Formula 4, we can obtain the impedance through the specific tensor impedance component Z. xx Z xy Z yx Z yy To determine the equivalent scalar impedance and surface wave creep direction θ k The relationship.

[0071] like Figure 3 As shown, for elements at different locations, we can obtain the equivalent isotropic impedance value of the anisotropic surface impedance as a function of different surface wave creep angles θ. k The variation curve of the equivalent scalar impedance value of the surface wave in different propagation directions on the tensor impedance surface is in the form of an elliptic curve.

[0072] In traditional substrate-based non-metallic metasurface units, the major axis of the elliptical impedance curve corresponds to the maximum value Z of the equivalent scalar impedance. emax, the angle between the long axis and the x-axis is equal to the slot angle of the designed unit s However, in this design, the angle of the rectangular metal plate s There is an additional 90-degree difference between the long axis angle of the equivalent scalar impedance ellipse curve. This difference is mainly due to the complementary structural characteristics between this pure planar metal tensor unit and the traditional substrate-based rectangular slot design, which can be explained by the principle of Babinet.

[0073] So far, we have obtained the maximum value of the equivalent scalar impedance corresponding to each position unit of the designed metasurface. The maximum value of the equivalent scalar impedance Z emax is determined by the hollow cylindrical radius R s For units with different hollow cylindrical radii R s , their performance can be simulated by CST simulation software, and a simple mapping relationship between the impedance tensor and the geometric parameters of the designed unit is established, as shown in Figure 4 .

[0074] In summary, after determining the feed and the designed beam irradiation direction , the three components Z xx , Z xy , Z yy of the impedance tensor Z at different positions on the array can be obtained. Then we can obtain the relationship between the equivalent scalar impedance and the surface wave creeping direction k , the long axis of the formed image corresponds to the maximum value of the equivalent scalar impedance Z emax , and the angle between the long axis and the x-axis plus 90 degrees is equal to the slot angle of the designed unit s . Finally, by comparing the simulation results of the unit under different hollow cylindrical radii, the hollow cylindrical radius R s corresponding to the maximum equivalent scalar impedance is found. The rotation angle of the rectangular metal structure of the unit at different positions s and the radius of the hollow cylindrical structure R S .

[0075] In this invention, two kinds of anisotropic holographic impedance metasurface antennas are designed: one is a wide-side single-beam The other is a double-beam, where the pencil beam #1 points to The pencil beam #2 points to The entire metasurface is composed of 49x49 units, with an aperture size of 784mmx784mm. It is composed of two metal plates, the lower layer is a pure metal ground plate with a thickness of 1mm, and the upper layer is a patterned metal plate with a thickness of 1mm, and the air gap thickness between the two layers is 2mm. According to the above formula, the E objand J ref , and then the tensor impedance component Z is calculated. In addition, considering the equivalent scalar equation and the mapping relationship between the maximum equivalent scalar impedance and the hollow radius of the cylinder, the geometric parameters R s and θ s are obtained. Figure 5 , 6, 7, 8.

[0076] On the other hand, the specific parameters of the monopole feed antenna are as follows. The monopole feed antenna can adopt a cylindrical metal monopole antenna. The monopole antenna used in the present application has a length of 10 mm and a diameter of 1.8 mm, and the entire antenna is fed through a cylindrical hole with a radius of 5 mm in the middle of the metasurface.

[0077] The above cases are simulated by combining the electromagnetic simulation software HFSS.

[0078] Simulation 1: The 2D far-field pattern of the single-beam pure metal anisotropic impedance holographic metasurface in the embodiment of the present application is simulated, and the result is shown in Figure 10 .

[0079] Simulation 2: The 2D far-field pattern of the single-beam pure metal anisotropic impedance holographic metasurface in the embodiment of the present application is simulated, and the result is shown in Figure 11 .

[0080] Simulation 3: The S11 parameter of the single-beam pure metal anisotropic impedance holographic metasurface in the embodiment of the present application is simulated, and the result is shown in Figure 12 .

[0081] Simulation 4: The S11 parameter of the single-beam pure metal anisotropic impedance holographic metasurface in the embodiment of the present application is simulated, and the result is shown in Figure 13 .

[0082] Simulation and test result analysis

[0083] As shown in Figure 9 a, Figure 9 b, Figure 10 and 11 . From the radiation pattern, it can be seen that when working at 7.5 GHz, the main radiation direction is consistent with the expected radiation angle . In addition, the corresponding pointing directions of the double-beam are and , which are basically consistent with the design.

[0084] Due to the limited conductivity of the conductor, the measured far-field radiation gain is 1.5 dB less than the simulated gain at the frequency of 7.5 GHz.

[0085] Figure 12 and 13The reflection coefficient S11 of the anisotropic holographic impedance super surface varies with different working frequencies. As can be seen from the figure, when the working frequency is in the frequency band of 6.6GHz-8.0GHz, the antenna reflection coefficient is less than-10dB, indicating that the bandwidth is in the frequency band of 6.6GHz-8.0GHz, and good impedance matching is achieved.

[0086] Although the embodiments of the present application are described above with reference to the drawings, the present application is not limited to the above-described specific embodiments and application fields, and the above-described specific embodiments are merely illustrative and instructive, but not restrictive. Those skilled in the art can make many forms under the guidance of the specification without departing from the scope protected by the claims of the present application, and these all belong to the protection of the present application.

Claims

1. A pure metal anisotropic holographic impedance metasurface antenna, characterized in that, The transmission array is centrally provided with a monopole antenna, and the transmission array comprises a plurality of arrayed impedance units, the impedance units comprising a lower metal floor and an upper hollow metal plate, and an air layer is arranged between the two metal plates. The upper metal plate of each unit is composed of a circular hollow with a radius of and a narrow rectangular metal structure with a rotatable rotation angle of passing through the center of the hollow, and the size of the circular hollow and the rotation angle of the narrow rectangular metal structure are different for different impedance units.

2. A pure metal anisotropic holographic impedance metasurface antenna according to claim 1, characterized in that, The transmission array comprises 49x49 impedance units.

3. A pure metal anisotropic holographic impedance metasurface antenna according to claim 1, characterized in that, The thickness of the upper metal plate and the thickness of the lower metal plate are the same, and the thickness of the air layer is 2 times the thickness of the upper metal plate.

4. A method of designing a pure metal anisotropic holographic impedance metasurface antenna, characterized in that, The pure metal anisotropic holographic impedance metasurface antenna based on any one of claims 1-3 comprises: determining the illumination direction of the beam, and obtaining the components of the impedance tensor of each impedance unit according to the illumination direction of the beam; obtaining the relationship between the equivalent scalar impedance and the surface wave creeping direction according to the components of the impedance tensor of each impedance unit; drawing an elliptical curve according to the relationship between the equivalent scalar impedance and the surface wave creeping direction; obtaining the maximum value of the equivalent scalar impedance, the size of the circular hollow on the upper layer of the impedance unit, and the rotation angle of the narrow rectangle according to the elliptical curve; obtaining the radius of the circular hollow according to the maximum value of the equivalent scalar impedance; drawing an elliptical curve according to the relationship between the equivalent scalar impedance and the surface wave creeping direction is specifically: For different position of impedance unit, the equivalent isotropic impedance value of anisotropic surface impedance changes with different creeping angle of surface wave The equivalent scalar impedance value of surface wave in different propagation direction of tensor impedance surface presents elliptical curve form.

5. The method of claim 4, wherein the method is characterized by: determining the illumination direction of the beam, and obtaining the components of the impedance tensor of each impedance unit according to the illumination direction of the beam is specifically: wherein denotes the wave number in the Z-axis direction, denotes the wave number in free space, is the normalized equivalent scalar impedance, , , are the three components of the impedance tensor Z, respectively.

6. The method of claim 5, wherein the method is characterized by: The impedance components are obtained according to the surface current field of the monopole antenna on the impedance unit and the electric field of the monopole antenna.

7. The method of claim 5, wherein the method is characterized by: The components of the impedance tensor Z also include According to the law of conservation of energy and the symmetry characteristics of the proposed unit, the impedance tensor Z is a pure imaginary matrix, = .

8. The method of claim 4, wherein the method is characterized by: obtaining the maximum value of the equivalent scalar impedance according to the elliptical curve is specifically: The major axis of the elliptical curve corresponds to the maximum value of the equivalent scalar impedance.

9. The method of claim 4, wherein, The size of the circular hollow on the upper layer of the impedance unit and the rotation angle of the narrow rectangle are the angle between the major axis of the elliptical curve and the X-axis plus 90 degrees.

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