Reflective polarization unit based on metasurface and polarization converter

Abstract

The invention discloses a reflective polarization unit based on a metasurface and a polarization converter, the reflective polarization unit based on the metasurface comprises a metal unit structure on the surface layer, a dielectric substrate on the middle layer and a metal bottom plate on the bottom layer, and the metal unit structure, the dielectric substrate and the metal bottom plate are tightly attached; each metal unit structure is of an axial symmetry graph, the whole graph is in a turtle shell shape with a crack in the middle, namely, the exterior of the graph is annular, a hollow regular hexagon is arranged in the annular shape, each vertex of the regular hexagon is connected with the annular shape, and the whole graph is divided into two parts which are symmetrical left and right with the center line of the regular hexagon as the axis. A gap is formed in the middle. The ultra-wideband ultra-wideband antenna is small in size and wide in working frequency band, the working frequency band of the ultra-wideband ultra-wideband antenna can accurately cover the most common X wave band and Ku wave band in the military field by adjusting manufacturing parameters, and the ultra-wideband ultra-wideband antenna is excellent in performance.

Description

Technical Field

[0001] The present invention relates to the field of microwave communication technology, and in particular to a reflective polarization unit and a polarization converter based on a metasurface. Background Art

[0002] Artificial electromagnetic metasurface is a new type of artificial electromagnetic material composed of two-dimensional planar unit structures. Artificial electromagnetic metamaterials refer to artificial composite materials with special physical properties. Artificial electromagnetic metasurface is regarded as a periodic metal unit structure designed on the interface of two media, which cooperates with the medium to make the incident electromagnetic wave undergo a phase mutation on the metasurface to produce abnormal refraction or reflection, so as to achieve the purpose of controlling the refracted or reflected electromagnetic wave. It has the advantages of small size, light weight and lower loss, and can control the phase, polarization mode, propagation direction, etc. of the incident electromagnetic wave. Moreover, it is easier to attach to the surface of large equipment or integrate with small equipment, so it has great advantages over traditional materials in the fields of absorbers, filters, RCS reduction, polarization converters, etc. Polarization is one of the basic properties of electromagnetic waves. This property has very important and wide applications in the fields of antenna covers, communication coding, sensors, imaging, radar stealth, etc. It is very necessary to efficiently control and change the polarization of electromagnetic waves according to human needs, so the polarization converter is a very important device in the regulation of electromagnetic waves.

[0003] Traditional polarization units use gratings, dichroic crystals, birefringence control, etc., but if you want to get a large enough phase difference, these materials must be thick enough, which will inevitably lead to problems such as large losses and low polarization conversion efficiency, and the operating frequency band is also narrow. With the emergence of artificial electromagnetic metasurfaces, the use of artificial electromagnetic metasurfaces to design polarization converters has become a trend and has developed rapidly. However, the polarization converters currently designed using artificial electromagnetic metasurfaces have a large coverage limit and cannot accurately cover the X-band and Ku-band. They are also large in size and have a narrow operating frequency band, making them unsuitable for precision equipment. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a reflective polarization unit and a polarization converter based on a metasurface, which have a small size and a wide operating frequency band. By adjusting the manufacturing parameters, the operating frequency band can accurately cover the X-band and Ku-band most commonly used in the military field, and the performance is excellent.

[0005] In order to achieve the above-mentioned purpose, an embodiment of the present invention provides a reflective polarization unit based on a metasurface, including a metal unit structure of a surface layer, a dielectric substrate of a middle layer and a metal bottom plate of a bottom layer, and the metal unit structure, the dielectric substrate and the metal bottom plate are tightly fitted; the metal unit structure is an axially symmetrical figure, and the overall figure is in the shape of a tortoise shell with a crack in the middle, that is, the outside is a ring, and there is a hollow regular hexagon inside the ring, each vertex of the regular hexagon is connected to the ring, and the overall figure is divided into two left-right symmetrical parts with the midline of the regular hexagon as the axis, forming a gap in the middle.

[0006] As an improvement of the above solution, a line connecting the centers of the three layers of the metal unit structure, the dielectric substrate and the metal bottom plate is perpendicular to the metal unit structure, the dielectric substrate and the metal bottom plate at the same time.

[0007] As an improvement of the above solution, the metal unit structure is rotated 45 degrees counterclockwise relative to the vertical direction and then tightly attached to the dielectric substrate.

[0008] As an improvement of the above solution, the material of the metal unit structure and the metal base plate is any one of gold, silver, copper and aluminum.

[0009] As an improvement of the above scheme, the outer diameter of the ring in the metal unit structure is 6.64mm~9.5mm, the inner diameter of the ring is 5.32mm~7.68mm, the side length of the regular hexagon is 1.56mm~2.26mm, the line width of the regular hexagon is 0.68mm~0.97mm, the line width of the connecting line between the regular hexagon and the ring is 0.59mm~0.85mm, the width of the gap is 0.49mm~0.71mm, and the thickness of the metal unit structure is 0.035mm.

[0010] As an improvement of the above solution, the metal bottom plate is square, the side length of the metal bottom plate is 7.8 mm to 11.28 mm, and the thickness of the metal bottom plate is 0.035 mm.

[0011] As an improvement of the above solution, the dielectric substrate is a polytetrafluoroethylene high-frequency board or a FR-4 substrate.

[0012] As an improvement of the above solution, the dielectric substrate is square, the side length of the dielectric substrate is 7.8 mm to 11.28 mm, and the thickness of the dielectric substrate is 1.6 mm to 2.48 mm.

[0013] An embodiment of the present invention further provides a metasurface-based reflective polarization converter, comprising a plurality of the above-mentioned metasurface-based reflective polarization units, and the plurality of polarization units are periodically arranged in the same plane.

[0014] Furthermore, the polarization units are repeatedly arranged in both horizontal and vertical directions to form a square array.

[0015] Compared with the prior art, the beneficial effect of a reflective polarization unit and polarization converter based on a metasurface provided by an embodiment of the present invention is that by adjusting the geometric parameters of the polarization unit during manufacturing, the operating frequency band can accurately cover the X-band and Ku-band, the two most commonly used bands in the military field, and the operating frequency band can be adjusted to cover 100% of the X-band and only exceed 9.75%, and can also be adjusted to cover 100% of the Ku-band and only exceed 11.7%, which is very suitable for the manufacture of precise polarization controllers and the reduction of RCS in radar stealth. At the same time, the relative bandwidth of the present invention can reach 43.9% and 45.2%, and the center frequencies are 9.99GHz and 14.82GHz respectively, which far exceeds the standard defined by ultra-wideband (relative bandwidth greater than 25%, and center frequency greater than 500MHz is called ultra-wideband), and the performance is excellent. In addition, the side length of the metasurface square unit structure of the present invention is only 7.8 to 11.28 mm, the thickness is only 1.67 to 2.55 mm, the metal resonance unit is only a single layer, the structure is simple, compact, novel, and small in size. It can be realized using the currently mature standard printed circuit board process and photolithography process, which is conducive to integration into other equipment, such as radar. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a front view of a preferred embodiment of a reflective polarization unit based on a metasurface provided by the present invention;

[0017] Figure 2 It is a principle diagram of the generalized Snell's law in a reflective polarization unit based on a metasurface provided by the present invention;

[0018] Figure 3 is a front view of another preferred embodiment of a reflective polarization unit based on a metasurface provided by the present invention;

[0019] Figure 4 It is a side view of a preferred embodiment of a reflective polarization unit based on a metasurface provided by the present invention;

[0020] Figure 5 It is a theoretical analysis diagram of a preferred embodiment of a reflective polarization unit based on a metasurface provided by the present invention;

[0021] Figure 6 is the cross-polarization reflectivity of a preferred embodiment of a reflective polarization unit based on a metasurface provided by the present invention;

[0022] Figure 7It is a phase difference curve diagram of a preferred embodiment of a reflective polarization unit based on a metasurface provided by the present invention;

[0023] Figure 8 is the cross-polarization reflectivity of another preferred embodiment of a reflective polarization unit based on a metasurface provided by the present invention;

[0024] Fig. 9 is a phase difference curve diagram of another preferred embodiment of a reflective polarization unit based on a metasurface provided by the present invention;

[0025] Fig.10 It is a three-dimensional structural schematic diagram of a preferred embodiment of a reflective polarization converter based on a metasurface provided by the present invention. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] See also Figure 1 , Figure 1 It is a front view of a preferred embodiment of a reflective polarization unit based on a metasurface provided by the present invention. The reflective polarization unit based on a metasurface includes a metal unit structure on the surface layer, a dielectric substrate on the middle layer, and a metal bottom plate on the bottom layer, and the metal unit structure, the dielectric substrate, and the metal bottom plate are tightly fitted; the metal unit structure is an axisymmetric figure, and the figure as a whole is in the shape of a tortoise shell with a crack in the middle, that is, the outside is a ring, and there is a hollow regular hexagon inside the ring, each vertex of the regular hexagon is connected to the ring, and the figure as a whole is divided into two left-right symmetrical parts with the midline of the regular hexagon as the axis, forming a gap in the middle.

[0028] Specifically, the reflective polarization unit based on the metasurface provided in the embodiment of the present invention includes a three-layer structure, wherein the surface layer is a metal unit structure, the middle layer is a dielectric substrate, and the bottom layer is a metal bottom plate, and the metal unit structure, the dielectric substrate and the metal bottom plate are tightly fitted, and there is no gap between each layer. The metal unit structure is an axisymmetric figure, and the figure as a whole is in the shape of a tortoise shell with a crack in the middle, that is, the outside is a ring, and there is a hollow regular hexagon inside the ring, and each vertex of the regular hexagon is connected to the ring, and the figure as a whole is divided into two parts that are symmetrical on the left and right with the midline of the regular hexagon as the axis, and a gap is formed in the middle.

[0029] It should be noted that at any point in the air, the electric field of the electromagnetic wave at that point The direction and size of the electromagnetic wave change with time. This phenomenon is called the polarization of electromagnetic waves. The trajectory formed over time divides the polarization of electromagnetic waves into three polarization forms: linear polarization, circular polarization, and elliptical polarization.

[0030] If the electric field of a linearly polarized electromagnetic wave In the xy vertical coordinate system, it is divided into two components, x and y. Then the phases of these two components must be the same or the phase difference is equal to π, that is, Or ±π, which is the definition of a linearly polarized wave. That is, if When , assuming and The initial phase is equal to 0, then the electric field The size E can be expressed as the following formula:

[0031]

[0032] electric field The angle α with the x-axis can be expressed as the following formula:

[0033]

[0034] From equation (1.1), we can get that the electric field The intensity of will change with the time t, and it can be seen from equation (1.2) that the angle α between it and the x-axis remains a constant, so it is a linearly polarized wave. Assume When The initial phase is equal to 0, The initial phase is equal to π, then the electric field at this time The size E can be expressed as the following formula:

[0035]

[0036] At this time, the electric field The angle α with the x-axis can be expressed as the following formula:

[0037]

[0038] From equations (1.3) and (1.4), we can draw conclusions similar to the previous two equations. At this time, the electromagnetic wave is also a linearly polarized wave. In addition, if the electric field vector of a linearly polarized wave changes only in the horizontal direction, it is called a horizontally polarized wave, and the corresponding electric field vector changes only in the vertical direction and is called a vertically polarized wave. The cross-polarization form is used to describe the polarization form that is perpendicular to the original polarization form of the electromagnetic wave at 90°, so the cross-polarization form of the horizontally polarized wave is a vertically polarized wave, and vice versa, the cross-polarization form of the vertically polarized wave is a horizontally polarized wave.

[0039] Snell's Law, commonly referred to as Snell's Law, means that when an incident electromagnetic wave reaches the interface between two different media, the refracted wave and reflected wave generated at this time can be calculated according to the classical law of refraction and the law of reflection. The law of refraction is:

[0040] sinθ t n t = sinθ i n i , (2.1)

[0041] Law of reflection:

[0042] θ r =θ i (2.2)

[0043] Among them, θi is the incident angle, θt is the refraction angle, θr is the reflection angle, nt and ni are the refractive indices of the two media. However, when the incident wave has a phase mutation at the interface between the two media When θi, θt, and θr are related, the relationship between them should be expressed by the generalized Snell's law. Figure 2 A diagram showing the principle of the generalized Snell's law. Generalized Snell's Law of Refraction:

[0044]

[0045] Generalized Snell's law of reflection:

[0046]

[0047] Where λ 0 It represents the wavelength of the incident electromagnetic wave in a vacuum. The emergence of the generalized Snell's law provides a reasonable explanation and basis for achieving phase change by selecting different materials and designing different structures, making it possible to artificially design materials and surfaces with abnormal reflection and refraction based on this theory and control them.

[0048] Most of the materials naturally formed in nature are basically isotropic. Isotropy is a material or medium whose composition and properties are uniform in every direction. The response of electromagnetic waves acting on them is independent of the polarization form and propagation direction of the electromagnetic waves. The opposite of isotropy is anisotropy. The electromagnetic parameters of anisotropic materials have different values ​​in different directions. For example, natural anisotropic materials in nature have different refractive indices in different directions. Because of this feature, they are widely used in polarization conversion waveguides. However, when using these natural anisotropic materials to design electromagnetic wave polarization converters, the polarization will only change when there is a certain difference in the phase of the electromagnetic wave during refraction or reflection. In order to achieve such a phase difference, these materials usually need to be very thick, and the working bandwidth is often very narrow.

[0049] The emergence and rapid development of artificial metamaterials have enabled people to design and produce materials with special properties according to their own ideas and concepts. It has greatly increased people's research on anisotropic media and accelerated their development. For example, left-handed materials that can adjust the direction of electromagnetic wave transmission and electromagnetic metasurface structures that can also control electromagnetic wave beam propagation or polarization control are both anisotropic materials. The constitutive relations of isotropic and anisotropic materials are different. and For these two formulas, is the electric flux, ε is the dielectric constant, is the electric field strength, is the magnetic induction intensity, μ is the magnetic permeability, is the magnetic field intensity. Isotropic ε and μ are in scalar form, while anisotropic ε and μ are in tensor form, because they are distributed differently in different directions when they are anisotropic. Anisotropy is also divided into electrical anisotropy and magnetic anisotropy. Electrical anisotropy refers to the electric flux of the material. and electric field The direction is not the same; magnetic anisotropy refers to the magnetic induction intensity of the material and The directions of the magnetic fields are not the same.

[0050] Traditionally, the polarization of electromagnetic waves is usually regulated by materials with birefringence effects such as mica, quartz, and liquid crystal. In such materials, electromagnetic waves propagating in different directions will have different refractive indices, and the transmission speed of electromagnetic waves in the medium is determined by the refractive index. After it propagates a certain distance in the medium with birefringence properties, the two components in different directions will produce a phase difference, thereby changing the polarization of the electromagnetic wave. However, these traditional polarization converters have very obvious disadvantages, that is, to obtain a sufficiently large phase difference, these materials must be thick enough, which inevitably leads to problems such as large losses and low polarization conversion efficiency. In addition, they can generally only have this property at a specific single frequency, and it is very complicated to design polarization conversion at a specific frequency. In recent years, the emergence of artificial electromagnetic metasurfaces has effectively solved the shortcomings of traditional polarization converters. Its anisotropy and artificial adjustability of electromagnetic parameters have greatly reduced the design difficulty and equipment size of polarization converters, and can achieve requirements such as broadband working frequency bands and multi-polarization conversion, improving the effectiveness and simplicity of polarization converters. Using artificial electromagnetic metasurfaces to design polarization converters has become a trend and has developed rapidly. However, the polarization converters currently designed using artificial electromagnetic metasurfaces have a large coverage margin and cannot accurately cover the X-band and Ku-band. They are also large in size and have a narrow operating frequency band, making them unsuitable for precision equipment. Based on this, an embodiment of the present invention provides an ultra-wideband reflective polarization unit based on a metasurface that can accurately cover the X-band and Ku-band, and is suitable for converting linearly polarized incident waves into cross-polarized reflected waves at 7.8 to 12.18 GHz and 11.47 to 18.17 GHz. The operating frequency band can accurately cover the X-band and Ku-band, and has an ultra-wideband with a relative bandwidth of 43.9% and 45.2% and a very small and thin volume, making it more suitable for the manufacture of precise polarization controllers and reducing RCS in radar stealth.

[0051] The embodiment of the present invention does not need to change the shape of the surface metal unit structure, and only adjusts the size parameters of the metal unit structure to achieve accurate coverage of the X-band (8-12GHz) and Ku-band (12-18GHz) in the working frequency band. It is usually stipulated that the polarization conversion rate is above 90% as the usable frequency band. The working frequency band with a polarization conversion rate greater than 90% of the present invention can be adjusted to 7.79-12.18GHz, completely covering the X-band and only exceeding the coverage by 9.75%; it can also be adjusted to 11.47-18.17GHz, completely covering the Ku-band and only exceeding the coverage by 11.7%, so that this feature can be used for the manufacture of precise polarization controllers for the X or Ku band, reducing RCS in radar stealth, etc.

[0052] In another preferred embodiment, a line connecting the centers of the three layers of the metal unit structure, the dielectric substrate and the metal bottom plate is perpendicular to the metal unit structure, the dielectric substrate and the metal bottom plate at the same time.

[0053] Specifically, in the embodiment of the present invention, the center points of the three layers of the metal unit structure, the dielectric substrate and the metal bottom plate are located on the same straight line. If the straight line is perpendicular to a horizontal plane, then the three layers are perpendicular to the horizontal plane, that is, the line connecting the centers of the three layers of the metal unit structure, the dielectric substrate and the metal bottom plate is perpendicular to the metal unit structure, the dielectric substrate and the metal bottom plate at the same time.

[0054] In another preferred embodiment, the metal unit structure is rotated 45 degrees counterclockwise relative to the vertical direction and then tightly attached to the dielectric substrate.

[0055] In another preferred embodiment, the metal unit structure and the metal base plate are made of any one of gold, silver, copper and aluminum.

[0056] Specifically, the metal unit structure and the metal bottom plate in the embodiment of the present invention are made of the same material, which is any one of gold, silver, copper, and aluminum, preferably copper.

[0057] In another preferred embodiment, the outer diameter of the ring in the metal unit structure is 6.64mm~9.5mm, the inner diameter of the ring is 5.32mm~7.68mm, the side length of the regular hexagon is 1.56mm~2.26mm, the line width of the regular hexagon is 0.68mm~0.97mm, the line width of the connecting line between the regular hexagon and the ring is 0.59mm~0.85mm, the width of the gap is 0.49mm~0.71mm, and the thickness of the metal unit structure is 0.035mm.

[0058] For details, please refer to Figure 3 and Figure 4 , Figure 3 is a front view of another preferred embodiment of a reflective polarization unit based on a metasurface provided by the present invention, Figure 4 is a side view of a preferred embodiment of a reflective polarization unit based on a metasurface provided by the present invention, Figure 4 1-1 represents the metal unit structure layer, 1-2 represents the dielectric substrate layer, and 1-3 represents the metal bottom plate layer, wherein the metal unit structure and the metal bottom plate have the same material and thickness. The outer diameter R1 of the ring in the metal unit structure is 6.64mm-9.5mm, the inner diameter R2 of the ring is 5.32mm-7.68mm, the side length a of the regular hexagon is 1.56mm-2.26mm, the line width b of the regular hexagon is 0.68mm-0.97mm, the line width c of the connecting line between the regular hexagon and the ring is 0.59mm-0.85mm, the width of the gap d is 0.49mm-0.71mm, and the thickness T of the metal unit structure is 0.035mm.

[0059] In another preferred embodiment, the metal bottom plate is square, the side length of the metal bottom plate is 7.8 mm to 11.28 mm, and the thickness of the metal bottom plate is 0.035 mm.

[0060] In another preferred embodiment, the dielectric substrate is a polytetrafluoroethylene high-frequency board or a FR-4 substrate.

[0061] Specifically, in the embodiment of the present invention, the dielectric substrate is a polytetrafluoroethylene high-frequency board or a FR-4 substrate, preferably a polytetrafluoroethylene high-frequency board, because the dielectric constant of the polytetrafluoroethylene high-frequency board is 2.65 and the loss tangent is 0.0015.

[0062] In another preferred embodiment, the dielectric substrate is square, and the side length of the dielectric substrate is 7.8 mm to 11.28 mm, and the thickness of the dielectric substrate is 1.6 mm to 2.48 mm.

[0063] Specifically, in the embodiment of the present invention, the dielectric substrate is square, and the side length L of the dielectric substrate is 7.8 mm to 11.28 mm, and the thickness h of the dielectric substrate is 1.6 mm to 2.48 mm.

[0064] The thickness of the polarization unit provided in the embodiment of the present invention is only between 1.67 mm and 2.55 mm, and the side length of each square unit structure is between 7.8 mm and 11.28 mm. Compared with the traditional method of using mica, quartz, liquid crystal and other materials with birefringence effect to control the polarization of electromagnetic waves, the present invention has the advantages of simpler and more compact structure, easier integration, and easy processing and manufacturing, and can be realized using the mature standard printed circuit board process and photolithography process.

[0065] See also Figure 5 , Figure 5 This is a theoretical analysis diagram of a preferred embodiment of a reflective polarization unit based on a metasurface provided by the present invention. The working principle of the reflective polarization unit based on the electromagnetic metasurface is as follows: an incident wave with polarization along the x direction is called an x-polarized wave, and the uv coordinate system is a relative coordinate system obtained by rotating the xy coordinate system 45 degrees counterclockwise with the origin as the center. If the x-polarized incident wave is decomposed into the u and v directions for analysis, the expression of the incident wave can be obtained as follows:

[0066]

[0067] Then the expression of the reflected wave is:

[0068]

[0069] In formula (3.1) is the x-polarized incident wave, E iv and E iuare the amplitudes of the incident waves decomposed into the v and u directions of the x-polarized wave, and are the unit vectors in the v and u directions respectively, φ iv and φ iu are the phases of the two incident wave components respectively; in equation (3.2) is the final reflected wave, E rv and E ru They represent the reflected wave amplitude in the v and u directions respectively, r v and r u are the reflection efficiencies in the v and u directions, φ rv and φ ru are the phases of the two reflected wave components. The anisotropy of the electromagnetic metasurface will cause the reflected waves in the u direction and the v direction to have a phase difference. If r u ≈r v And when the phase difference Δφ≈180°, the two reflected wave components are finally synthesized The polarization direction is along the positive or negative direction of the y-axis. Because the unit structure of the metasurface is symmetrical along the v-axis or u-axis, by the same token, when the incident wave is a vertically incident y-polarized wave, the decomposition and analysis of the electromagnetic wave and the final result are exactly the same as when the incident wave is a vertically incident x-polarized wave, and polarization conversion can also occur.

[0070] Example 1, when the working frequency band is fixed at the X-band, as a preferred embodiment, h is the thickness of the dielectric substrate, which is 2.48 mm, L is the side length of the square dielectric substrate and the metal bottom plate, which is 11.28 mm, R1 is the diameter of the large circle in the metal structure pattern, which is 9.5 mm, R2 is the diameter of the small circle in the metal structure pattern, which is 7.68 mm, a is the side length of the hollow regular hexagon, which is 2.26 mm, b is the line width of the metal regular hexagon, which is 0.97 mm, c is the line width of the regular hexagon and the circular connection pattern, which is 0.85 mm, d is the width of the gap in the middle of the pattern, which is 0.71 mm, and T is the thickness of the metal structure pattern, T = 0.035 mm. The cross-polarization reflectivity of this embodiment is calculated using the commercial software HFSS15 for simulation as follows: Figure 6 As shown, the phase difference is Figure 7 As shown, it can be seen that the cross-polarization reflectivity is greater than 90% in the frequency range of 7.8 to 12.18 GHz, the relative bandwidth is 43.9%, and the cross-polarization reflectivity is maximum near 8.4 GHz and 10.95 GHz, with the maximum value close to 100%.

[0071] Example 2, when the working frequency band is fixed at the Ku band, as a preferred embodiment, h is the thickness of the dielectric substrate, which is 1.6 mm, L is the side length of the square dielectric substrate and the metal bottom plate, which is 7.8 mm, R1 is the diameter of the large circle in the metal structure pattern, which is 6.64 mm, R2 is the diameter of the small circle in the metal structure pattern, which is 5.32 mm, a is the side length of the hollow regular hexagon, which is 1.56 mm, b is the line width of the metal regular hexagon, which is 0.68 mm, c is the line width of the regular hexagon and the circular connection pattern, which is 0.59 mm, d is the width of the gap in the middle of the pattern, which is 0.49 mm, and T is the thickness of the metal structure pattern, T = 0.035 mm. The cross-polarization reflectivity of this embodiment is calculated using the commercial software HFSS15 for simulation as follows: Figure 8 As shown, the phase difference is Fig. 9 As shown, it can be seen that the cross-polarization reflectivity is greater than 90% in the frequency range of 11.47 to 18.17 GHz, the relative bandwidth is 45.2%, and the cross-polarization reflectivity is maximum near 12.2 GHz and 16.5 GHz, with the maximum value close to 100%.

[0072] Embodiments 1 and 2 of the present invention provide two different sets of geometric parameters, and it can be inferred that the characteristic of the frequency range for realizing electromagnetic wave polarization regulation can be changed to a certain extent by appropriately adjusting the geometric parameters of the present invention. Therefore, the present invention is not limited to the above embodiments, and ordinary technicians in this field can make relevant changes and deformations to the present invention without departing from the essence of the present invention. If these modifications and deformations based on the present invention still fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and deformations.

[0073] See also Fig.10 , Fig.10 It is a three-dimensional structural schematic diagram of a preferred embodiment of a reflective polarization converter based on a metasurface provided by the present invention.

[0074] Correspondingly, the present invention also provides a metasurface-based reflective polarization converter, comprising a metasurface-based reflective polarization unit in any one of the above embodiments, and a plurality of polarization units are periodically arranged in the same plane.

[0075] The embodiment of the present invention provides a reflective polarization converter based on a metasurface that can accurately cover the X or Ku band, which can convert linearly polarized incident electromagnetic waves into cross-polarized reflected waves in an ultra-wide frequency band, and has good polarization conversion performance in the entire working frequency band. In addition, it has the advantages of simple and thin structure, easy processing and realization, and accurate overlap of the working frequency band with the commonly used frequency band of military radars, and has broad prospects in practical applications.

[0076] Preferably, the polarization units are repeatedly arranged in both horizontal and vertical directions to form a square array.

[0077] Specifically, viewed from a direction perpendicular to the plane of the dielectric substrate, the polarization units are repeatedly arranged in both the horizontal and vertical directions, ie, the x direction and the y direction, and the number is equal to form a square array. Preferably, the number of repeated polarization units is not less than 20×20=400.

[0078] The embodiment of the present invention provides a reflective polarization unit and a polarization converter based on a metasurface. By adjusting the geometric parameters of the polarization unit during manufacturing, the operating frequency band can accurately cover the X-band and Ku-band, the two most commonly used bands in the military field, and the operating frequency band can be adjusted to cover 100% of the X-band and only exceed 9.75%, and can also be adjusted to cover 100% of the Ku-band and only exceed 11.7%. It is very suitable for the manufacture of precise polarization controllers and the reduction of RCS in radar stealth. At the same time, the relative bandwidth of the present invention can reach 43.9% and 45.2%, and the center frequencies are 9.99GHz and 14.82GHz respectively, which far exceeds the standard defined by ultra-wideband (relative bandwidth greater than 25%, and center frequency greater than 500MHz is called ultra-wideband), and the performance is excellent. In addition, the side length of the metasurface square unit structure of the present invention is only 7.8 to 11.28 mm, the thickness is only 1.67 to 2.55 mm, the metal resonance unit is only a single layer, the structure is simple, compact, novel, and small in size. It can be realized using the currently mature standard printed circuit board process and photolithography process, which is conducive to integration into other equipment, such as radar.

[0079] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A reflective polarization unit based on a metasurface, characterized in that: It includes a metal unit structure of the surface layer, a dielectric substrate of the middle layer and a metal bottom plate of the bottom layer, and the metal unit structure, the dielectric substrate and the metal bottom plate are tightly fitted; the metal unit structure is an axisymmetric figure, and the overall figure is in the shape of a tortoise shell with a crack in the middle, that is, the outer part is a ring, and the interior of the ring has a hollow regular hexagon, each vertex of the regular hexagon is connected to the ring, and the overall figure is divided into two left-right symmetrical parts with the midline of the regular hexagon as the axis, forming a gap in the middle.

2. The reflective polarization unit based on a metasurface according to claim 1, characterized in that: The line connecting the centers of the three layers of the metal unit structure, the dielectric substrate and the metal bottom plate is perpendicular to the metal unit structure, the dielectric substrate and the metal bottom plate.

3. The metasurface-based reflective polarization unit according to claim 2, characterized in that: The metal unit structure is rotated 45 degrees counterclockwise relative to the vertical direction and then tightly attached to the dielectric substrate.

4. The metasurface-based reflective polarization unit according to claim 3, characterized in that: The material of the metal unit structure and the metal base plate is any one of gold, silver, copper and aluminum.

5. The metasurface-based reflective polarization unit according to claim 4, characterized in that: The outer diameter of the ring in the metal unit structure is 6.64mm~9.5mm, the inner diameter of the ring is 5.32mm~7.68mm, the side length of the regular hexagon is 1.56mm~2.26mm, the line width of the regular hexagon is 0.68mm~0.97mm, the line width of the connecting line between the regular hexagon and the ring is 0.59mm~0.85mm, the width of the gap is 0.49mm~0.71mm, and the thickness of the metal unit structure is 0.035mm.

6. The metasurface-based reflective polarization unit according to claim 5, characterized in that: The metal bottom plate is square, and the side length of the metal bottom plate is 7.8 mm to 11.28 mm, and the thickness of the metal bottom plate is 0.035 mm.

7. The metasurface-based reflective polarization unit according to claim 6, characterized in that: The dielectric substrate is a polytetrafluoroethylene high-frequency board or a FR-4 substrate.

8. The metasurface-based reflective polarization unit according to claim 1, characterized in that: The dielectric substrate is square, and the side length of the dielectric substrate is 7.8 mm to 11.28 mm. The thickness of the dielectric substrate is 1.6 mm to 2.48 mm.

9. A reflective polarization converter based on a metasurface, characterized in that: It comprises a plurality of reflective polarization units based on a metasurface as described in any one of claims 1 to 8, and the plurality of polarization units are periodically arranged in the same plane.

10. The reflective polarization converter based on a metasurface according to claim 9, characterized in that: The polarization units are repeatedly arranged in both horizontal and vertical directions to form a square array.

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