Luneberg lens antenna and preparation method and application thereof

Abstract

The invention provides a Luneberg lens antenna and a preparation method and application thereof, the Luneberg lens antenna comprises a plurality of stacked material layers, holes with specific apertures are distributed in each material layer, the material layers are in direct contact, the relative dielectric constant in the Luneberg lens antenna continuously changes, the dielectric loss of the Luneberg lens antenna can be effectively reduced, and the service life of the Luneberg lens antenna is prolonged. Receiving of full-band electromagnetic waves can be covered, and the azimuth of the radiation direction is wide.

Description

Technical Field

[0001] The technical solution of the embodiment of the present application relates to the field of Luneburg lens antennas, and specifically relates to Luneburg lens antennas, their preparation methods, and applications. Background Art

[0002] In recent years, with the development of communication technology towards high frequency and high speed, the requirements for the accuracy and speed of signal transmission have become increasingly high. If traditional base stations are still used, in the face of the requirements for receiving and transmitting electromagnetic waves in different directions, strip antennas with different frequency bands and different directions need to be installed on a base station tower, resulting in a complex and crowded structure of the base station tower, and the construction and maintenance costs have increased sharply.

[0003] In order to simplify the structure of the base station, the industry has gradually begun to use Luneburg lens antennas to replace strip antennas. In theory, a single Luneburg lens antenna can cover electromagnetic waves in the full frequency band of 6 GHz - 86 GHz, and by installing a feed antenna on its outer surface, electromagnetic waves in multiple directions can be received and transmitted. However, most of the current Luneburg lens antennas are prepared by 3D printing or the cladding method, resulting in discontinuous intra-layer structures of the Luneburg lens antennas, or jumps in the inter-layer dielectric constants, leading to relatively large dielectric losses and poor directivity of the Luneburg lens antennas, and unable to meet the application requirements of high-frequency electromagnetic waves. Summary of the Invention

[0004] In view of this, the embodiment of the present application provides a Luneburg lens antenna, its preparation method, and application. The Luneburg lens antenna has low dielectric loss and can be used to receive and transmit high-frequency electromagnetic waves in multiple directions.

[0005] The first aspect of the embodiment of the present application provides a Luneburg lens antenna, including a plurality of material layers arranged radially from the inside to the outside; each material layer includes a base material and a plurality of holes distributed in the base material, and the aperture of the holes ≤ 500 μm; along the radial direction from the inside to the outside, the volume density of the plurality of material layers decreases layer by layer; and two adjacent material layers are in direct contact.

[0006] The above Luneburg lens antenna adjusts the volume density of the material layer by setting holes in the material layer, and controls the density to gradually decrease layer by layer from the inside to the outside along its radial direction, so as to achieve a gradual decrease in the dielectric constant of each material layer from the inside to the outside along its radial direction. At the same time, two adjacent material layers are in direct contact. Therefore, along the radial direction of the Luneburg lens antenna from the inside to the outside, its dielectric constant changes in a gradient manner, avoiding the dielectric constant jump caused by the adhesive layer or air layer between material layers in the related art, and effectively reducing the dielectric loss of the Luneburg lens antenna. Further, controlling the aperture of the holes in each material layer ≤ 500 μm can effectively reduce the risk of dielectric loss generated in the holes when electromagnetic waves of each band are transmitted inside the Luneburg lens antenna, thereby further reducing the dielectric loss of the Luneburg lens antenna, and further improving the gain and aperture efficiency of the Luneburg lens antenna in the embodiments of the present application. It can also make the azimuth that the Luneburg lens antenna can radiate wider.

[0007] In some embodiments of the present application, the aperture of the hole is 10 μm - 300 μm. In this way, the gain and aperture efficiency of the Luneburg lens antenna under high-frequency electromagnetic waves are improved, and it is easy to manufacture.

[0008] In some embodiments of the present application, the aperture distribution of the holes in the Luneburg lens antenna is uniform. In this way, the structural uniformity of the Luneburg lens antenna can be improved, which is beneficial to avoiding the phenomenon that the dielectric loss increases in some areas due to the difference in aperture when electromagnetic waves are transmitted between different material layers and within the same material layer, and further ensuring that the dielectric loss of the Luneburg lens antenna can be controlled at a relatively low level.

[0009] In some embodiments of the present application, along the radial direction from the inside to the outside of the Luneburg lens antenna, the distribution density of the holes in the multiple material layers increases layer by layer.

[0010] In some embodiments of the present application, any one of the material layers satisfies: where ε c is the relative dielectric constant at room temperature of the material layer, ε m is the relative dielectric constant at room temperature of the base material, ε f is the relative dielectric constant at room temperature of air, V f is the volume fraction of air in the material layer.

[0011] In some embodiments of the present application, the volume density of the material layer is 0.05 g / cm 3 -1 g / cm 3 . In this way, the total weight of the Luneburg lens can be controlled within a suitable range, and it is easy to be stably assembled at a high place.

[0012] In some embodiments of the present application, the material layer further includes inorganic filler particles dispersed in the substrate; the relative permittivity of the inorganic filler particles at room temperature is greater than that of the substrate at room temperature. Thus, the lightweight degree of the Luneburg lens antenna can be effectively improved, which is more conducive to the assembly and application of the Luneburg lens antenna.

[0013] In some embodiments of the present application, the material of the inorganic filler particles includes at least one of titanium dioxide, strontium titanate, barium titanate, and calcium titanate. The above-mentioned inorganic filler particles have a relatively large relative permittivity at room temperature and a wide source.

[0014] In some embodiments of the present application, the D50 of the inorganic filler particles is 2 μm - 3 μm. Thus, it does not affect the propagation of electromagnetic waves inside the Luneburg lens antenna, and can make the inorganic filler particles evenly distributed in the substrate, thereby reducing the risk of increasing the dielectric loss of the material layer due to the agglomeration of the inorganic filler particles.

[0015] In some embodiments of the present application, the material layer satisfies: where ε c is the relative permittivity of the material layer at room temperature, ε c0 is the relative permittivity of the substrate dispersed with the inorganic filler particles at room temperature, ε f is the relative permittivity of air at room temperature, V f is the volume fraction of air in the material layer; where the ε c0 satisfies: ε m is the relative permittivity of the substrate at room temperature, ε a is the relative permittivity of the inorganic filler particles at room temperature, V a is the sum of the volume fractions of the inorganic filler particles in the material layer.

[0016] In some embodiments of the present application, the volume density of the material layer is 0.05 g / cm 3 -0.8 g / cm 3 . Thus, the total weight of the Luneburg lens can be controlled within a suitable range, which is easy to be stably assembled at a high place.

[0017] In some embodiments of the present application, the multiple material layers include a central material layer located in the innermost layer and multiple sleeve material layers sequentially stacked on the surface of the central material layer; the thickness of any one of the sleeve material layers ≤ 8 mm. Thus, the preparation difficulty of the Luneburg lens antenna can be reduced, and it is easy to control the dielectric constant gradient of the multiple material layers in the Luneburg lens antenna to be relatively gentle, making it closer to the ideal state.

[0018] In some embodiments of the present application, the thicknesses of the multiple jacket material layers are equal. In this way, it is beneficial to simplify the design and preparation of the Luneburg lens antenna.

[0019] In some embodiments of the present application, the size of the central material layer is 15 mm - 60 mm. In this way, it is easy to prepare, and the influence on the gain and aperture efficiency of the Luneburg lens is small and can be ignored.

[0020] In some embodiments of the present application, the relative permittivities of the multiple material layers at room temperature change in an arithmetic progression.

[0021] In some embodiments of the present application, the Luneburg lens antenna is a sphere or a hemisphere, and the multiple material layers are concentrically arranged; alternatively, the Luneburg lens antenna is a cylinder or a semi-cylinder, and the multiple material layers are coaxially arranged.

[0022] In some embodiments of the present application, the substrate includes a polymer, and the polymer includes at least one of polyolefins, polyacrylates, and olefin-acrylate copolymers. The above polymers have appropriate relative permittivities and true densities, which can ensure better comprehensive performance of the Luneburg lens antenna.

[0023] In some embodiments of the present application, the Luneburg lens antenna has a gain ≥ 37 dB and an aperture efficiency ≥ 47% at an electromagnetic wave frequency of 6 GHz - 86 GHz.

[0024] The second aspect of the embodiments of the present application provides a method for preparing a Luneburg lens antenna, including:

[0025] Preparing n material layers by using the emulsion polymerization soft template method to obtain a Luneburg lens antenna; wherein, from the first material layer to the nth material layer, they are arranged from the inside to the outside along the radial direction of the Luneburg lens antenna, and the volume densities of the first to the nth material layers decrease layer by layer, and two adjacent material layers are in direct contact, and n is a positive integer greater than 1;

[0026] The material layer includes a substrate and multiple pores distributed in the substrate, and the aperture of the pores ≤ 500 μm.

[0027] The above preparation method has simple process, high flexibility, and high forming freedom, can be used to prepare Luneburg lens antennas of various shapes, has high production efficiency, and can realize large-scale industrial production.

[0028] In some embodiments of the present application, the preparing n material layers by using the emulsion polymerization soft template method includes:

[0029] Designing a mold, the mold includes a cover plate and n bodies with different sizes, and any one of the bodies and the cover plate can form a closed receiving space;

[0030] Prepare n portions of emulsion, where the emulsion includes water and an oily monomer, and the water content of the 1st to the nth portion of emulsion increases in sequence;

[0031] Pour the i-th portion of emulsion into the i-th main body, cover the cover plate, and perform curing, drying, and detachment from the i-th main body in sequence to obtain the i-th cured product. The i-th cured product includes i layers of the material, where i is any integer from 1 to (n - 1); the i-th cured product and the (i + 1)-th main body can form a cavity for preparing the (i + 1)-th material layer;

[0032] Pour the (i + 1)-th emulsion into the (i + 1)-th main body, immerse the i-th cured product in the (i + 1)-th emulsion, cure, and dry to obtain the (i + 1)-th cured product.

[0033] In some embodiments of the present application, the emulsion is a water-in-oil emulsion; the normal temperature viscosity of the emulsion is 50 cP - 500 cP. In this way, a more ideal pore structure can be obtained, and the molding degree of the material layer can be ensured.

[0034] The third aspect of the embodiments of the present application provides an antenna module, including the Luneburg lens antenna and the feed antenna provided in the first aspect of the embodiments of the present application; or, including the Luneburg lens antenna and the feed antenna prepared by the preparation method provided in the embodiments of the present application.

[0035] Due to the adoption of the Luneburg lens antenna provided in the embodiments of the present application, this antenna module can receive and transmit electromagnetic waves in the full frequency band (6 GHz - 86 GHz) from multiple directions. And, compared with a traditional antenna module with the same performance, the antenna module of the embodiments of the present application has a simple structure and is easy to construct and maintain.

[0036] The fourth aspect of the embodiments of the present application provides a communication system, including the antenna module provided in the third aspect of the embodiments of the present application. Since this communication system adopts the antenna module of the embodiments of the present application, it has strong market competitiveness.

[0037] The fifth aspect of the embodiments of the present application provides a navigation system, including the antenna module of the third aspect of the embodiments of the present application. Since this navigation system adopts the antenna module provided in the embodiments of the present application, it has good application prospects. Description of the Drawings

[0038] Figure 1 It is a schematic structural diagram of the cross-section of the Luneburg lens antenna provided by an embodiment of the present application;

[0039] Figure 2 It is a structural diagram of the cross-section of the Luneburg lens antenna provided by another embodiment of the present application;

[0040] Figure 3Dot plot of "relative permittivity - distance from the center" provided by an embodiment of the present application;

[0041] Figure 4 Process schematic diagram of the preparation method provided by an embodiment of the present application;

[0042] Figure 5 Schematic diagram of a plurality of stacked spherical segment-shaped bodies.

[0043] Explanation of the reference numerals in the drawings: 1 - Luneburg lens antenna; 10 - material layer; 101 - base material; 102 - hole. Detailed implementation manners

[0044] With the rapid development of the information society, communication technologies are developing towards high frequency and high speed. To meet the above trends, the antennas of base stations also need to be adjusted accordingly. The base station antennas need to receive and transmit electromagnetic waves in the full frequency band (6 GHz - 86 GHz), and need to receive and transmit electromagnetic waves in different directions. Thus, the Luneburg lens antenna, a classic electromagnetic lens, is applicable to electromagnetic waves in the full frequency band and has a very wide scanning angle. The Luneburg lens antenna used for antenna functions generally refers to a structure in which the relative permittivity changes continuously from the inside to the outside along the radial direction according to ε r (r) = 2 - (r / R) 2 where r is the distance between any position inside the Luneburg lens antenna and the center of the sphere, and R is the radius of the Luneburg lens antenna. In recent years, with the application of the Luneburg lens antenna in the communication field, hemispherical, cylindrical, and semi-cylindrical Luneburg lens antennas have gradually been produced and applied. Similarly, for the above-shaped Luneburg lens antennas, the dielectric constant gradually decreases from the inside to the outside along the radial direction, and the characteristics of high gain and wide scanning can be retained to a certain extent; and the processing difficulty is slightly reduced.

[0045] However, whether it is a spherical or other-shaped Luneburg lens antenna mentioned above, it is difficult to fabricate a rotationally symmetric structure with a gradually changing dielectric constant. The layered Luneburg lens antenna is still the mainstream product; however, at present, whether using 3D printing or the sleeve layer preparation method, there is a problem of sudden jumps in the dielectric constant between layers, resulting in discontinuous dielectric properties of the Luneburg lens antenna. As a result, the current Luneburg lens antenna is only applicable to the reception and transmission of low-frequency electromagnetic waves. For high-frequency electromagnetic waves, its dielectric loss is too large to be applied; in addition, when receiving and transmitting low-frequency electromagnetic waves, the radiation directions are few and the directivity is poor.

[0046] To solve the above technical problems, an embodiment of the present application provides a Luneburg lens antenna. Please refer to Figure 1, the Luneburg lens antenna 1 includes a plurality of material layers 10 arranged radially from the inside outwards; each material layer 10 includes a base material 101 and a plurality of holes 102 distributed in the base material 101, and the aperture of the holes 102 ≤ 500 μm; along the radial direction from the inside outwards, the volume density of the plurality of material layers 10 decreases layer by layer; two adjacent material layers 10 are in direct contact. It should be noted that Figure 1 the number of material layers, the number of holes, and the quantity in

[0047] In the embodiments of the present application, each hole 102 in each material layer 10 is an empty hole 102, and the inside of the hole 102 is air.

[0048] In the embodiments of the present application, no specific limitation is imposed on the shape of the Luneburg lens antenna 1. The Luneburg lens antenna 1 can be spherical, hemispherical, cylindrical, semi-cylindrical, etc. When the function can be realized, the Luneburg lens antenna 1 can also be an irregular shape. Specifically, when the Luneburg lens antenna 1 is spherical or hemispherical, the plurality of material layers 10 are concentrically arranged; when the Luneburg lens antenna 1 is cylindrical or semi-cylindrical, the plurality of material layers 10 are coaxially arranged. Similarly, when the Luneburg lens antenna 1 is of other shapes, the plurality of material layers 10 can form a rotationally symmetric structure.

[0049] In some specific embodiments of the present application, the Luneburg perspective antenna is spherical. In some specific embodiments, the spherical Luneburg lens antenna 1 includes two bonded hemispherical Luneburg lens antennas 1. Specifically, any binder known in the art can be used to bond between the two hemispherical Luneburg lens antennas 1, or the material of any material layer 10 can be used for bonding, or the interface of the hemispherical Luneburg lens antenna 1 can be heated to cause bonding between the materials of the material layers 10 at the interface. Similarly, the cylindrical Luneburg lens antenna 1 can also include two bonded semi-cylindrical Luneburg lens antennas 1, and the bonding method is similar to that of the spherical Luneburg lens antenna 1, which will not be elaborated here.

[0050] In the embodiment of the present application, the Luneburg lens antenna 1 adjusts the volume density of the material layer 10 by setting holes 102 in the material layer 10, and controls the volume density to gradually decrease from the inside to the outside along its radial direction, so as to achieve the gradual decrease of the dielectric constant of each material layer 10 from the inside to the outside along its radial direction. At the same time, two adjacent material layers 10 are in direct contact, so along the radial direction of the Luneburg lens antenna 1 from the inside to the outside, its dielectric constant changes in a gradient manner, avoiding the dielectric constant jump caused by the adhesive layer or air layer between the material layers 10 in the related art, and effectively reducing the dielectric loss of the Luneburg lens antenna 1. Further, by controlling the aperture of the holes 102 in each material layer 10 ≤ 500 μm, the risk of dielectric loss generated in the holes 102 when electromagnetic waves of each band are transmitted inside the Luneburg lens antenna 1 can be effectively reduced, thereby further reducing the dielectric loss of the Luneburg lens antenna 1, and further improving the gain and aperture efficiency of the Luneburg lens antenna 1 in the embodiment of the present application, and also enabling the Luneburg lens antenna to have a wider radiation azimuth.

[0051] Among them, the gain refers to the ratio of the power density of the signal generated by the Luneburg lens antenna 1 and the ideal point source antenna (isotropic radiation with loss from the center point in all directions) at the same point in space under the condition of equal input power. The aperture efficiency refers to the ratio of the maximum gain of the Luneburg lens antenna 1 to its directivity coefficient, aperture efficiency = maximum gain / (4πA / λ 2 ), where the maximum gain refers to the gain in the direction of the maximum gain radiation of the antenna, λ is the wavelength of the electromagnetic wave, unit mm; A is the aperture area of the Luneburg lens antenna, unit mm 2 ; taking the spherical Luneburg lens as an example, aperture efficiency = (maximum gain * λ 2 ) / [4π(πR 2 )], where R is the radius of the spherical Luneburg lens antenna 1.

[0052] In the embodiment of the present application, the direct contact between two adjacent material layers specifically means that "the substrates of two adjacent material layers are in direct contact". Specifically, the Luneburg lens antenna 1 is pretreated to obtain a specimen with the interfaces of two adjacent material layers 10 exposed, and the morphology of the above interfaces is observed under a scanning electron microscope (SEM) or an optical microscope. The substrates of two adjacent material layers 10 are in direct contact, including no separation between adjacent material layers and no other dielectric layers (other dielectric layers generally show a dense structure without holes, for example, an adhesive layer).

[0053] In some embodiments of the present application, the cross-sectional shape of the hole 102 is circular or quasi-circular.

[0054] In the embodiments of the present application, the Luneburg lens antenna 1 is preprocessed to prepare test samples of each material layer 10, and the morphology and aperture of the holes 102 are tested under an optical microscope or SEM. Among them, the aperture of the hole 102 refers to the distance between the two points with the largest cross-section of the hole 102. Specifically, the hollow aperture of each material layer 10 can be, but is not limited to, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 105μm, 110μm, 115μm, 120μm, 120μm, 130μm, 135μm, 140μm, 145μm, 150μm, 155μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 250μm, 240μm, 250μm, 260μm, 270μm, 280μm, 290μm, 300μm, 310μm, 320μm, 350μm, 380μm, 400μm, 420μm, 450μm, 480μm, 500μm, etc. If the aperture of the above-mentioned hole 102 is too large, it will cause dielectric loss of electromagnetic waves (especially those with a frequency ≥ 71GHz) in the hole 102, thereby increasing the dielectric loss of the Luneburg lens antenna 1 and making the Luneburg lens antenna 1 unable to meet the application requirements of high-frequency electromagnetic waves.

[0055] In the embodiments of the present application, the Luneburg lens antenna 1 can be peeled layer by layer to obtain the test samples of each material layer 10, and the bulk density of the test samples of each material layer 10 is tested by the boiling water method or the wax sealing method.

[0056] In current practical applications, the frequency of high-frequency electromagnetic waves generally does not exceed 86GHz (specifically 71GHz - 86GHz). In order to reduce the dielectric loss of 86GHz electromagnetic waves during transmission in the Luneburg lens antenna 1 and improve the gain and aperture efficiency of the Luneburg lens antenna 1 in this frequency band. In some embodiments of the present application, the aperture of the hole 102 in any material layer 10 ≤ 300μm. In addition, in order to reduce the preparation difficulty, in some specific embodiments, the aperture of the hole 102 in any material layer 10 is 10μm - 300μm.

[0057] In some embodiments of the present application, the Luneburg lens antenna 1 has a gain ≥ 37 dB at an electromagnetic wave frequency of 6 GHz - 86 GHz. Specifically, at a high-frequency electromagnetic wave frequency band of 71 - 86 GHz, the gain of the Luneburg lens antenna 1 can reach 37 dB - 45.2 dB. For example, 37 dB, 38 dB, 39 dB, 40 dB, 40.5 dB, 41 dB, 41.5 dB, 42 dB, 42.5 dB, 43 dB, 43.5 dB, 44 dB, 44.5 dB, 45 dB, 45.2 dB, etc.; when used for receiving or transmitting electromagnetic waves with a lower frequency, the gain of the Luneburg lens antenna 1 is higher, for example, ≥ 44.3 dB.

[0058] In some embodiments of the present application, the aperture efficiency of the Luneburg lens antenna 1 is ≥ 47% at an electromagnetic wave frequency of 6 GHz - 86 GHz. Specifically, at a high-frequency electromagnetic wave frequency band of 71 GHz - 86 GHz, the aperture efficiency of the Luneburg lens antenna 1 can reach 47% - 86.2%. For example, 47%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 73%, 74%, 74.5%, 75%, 75.5%, 76%, 76.5%, 77%, 77.5%, 78%, 78.5%, 79%, 79.5%, 80%, 80.5%, 81%, 81.5%, 82%, 82.5%, 83%, 83.5%, 84%, 84.5%, 85%, 86%, 86.5%, etc. Similarly, when used for receiving and transmitting electromagnetic waves with a lower frequency, the aperture efficiency of the Luneburg lens antenna 1 is higher, for example, ≥ 73.3%.

[0059] In some embodiments of the present application, the aperture distribution of the holes 102 in the Luneburg lens antenna 1 is uniform. Herein, the uniform aperture distribution means that: under an optical microscope or SEM, there is no obvious difference in the aperture distribution of the holes 102 in each material layer 10 of the Luneburg lens, and there is no obvious difference in the aperture distribution of the holes 102 in multiple material layers 10. Specifically, any two material layers are taken, and for the convenience of description, they are named material layer A and material layer B: 10 holes are randomly taken in material layer A, and the average aperture of these 10 holes is a μm; 10 holes are randomly taken in material layer B, and the average aperture of these 10 holes is b μm, and |a - b| ≤ 50 μm. Specifically, the above |a - b| can be, but is not limited to, 0, 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, 35 μm, 38 μm, 40 μm, 42 μm, 45 μm, 48 μm, 50 μm. In this way, the structural uniformity of the Luneburg lens antenna 1 can be improved, which is beneficial to avoiding the phenomenon that the dielectric loss increases in some areas due to the aperture difference when electromagnetic waves are transmitted in different material layers 10 and in the same material layer 10, thereby ensuring that the dielectric loss of the Luneburg lens antenna 1 can be controlled at a relatively low level.

[0060] When the materials of the substrates 101 of multiple material layers 10 are the same, in order to achieve a gradually decreasing volume density of multiple material layers 10, in some embodiments of the present application, in the direction from the inside to the outside along the radial direction of the Luneburg lens antenna 1, the distribution density of the holes 102 in multiple material layers 10 gradually increases. Specifically, the apertures of the holes 102 in multiple material layers 10 are evenly distributed and have the same shape, and the number of the holes 102 in multiple material layers 10 gradually increases. Of course, when the materials of the substrates of multiple material layers 10 are different, the Luneburg lens antenna 1 can also meet the above situation.

[0061] Of course, the materials of the substrates 101 of multiple material layers 10 can also be different, as long as the volume density of multiple material layers 10 gradually decreases. Regardless of whether the materials of the substrates 101 of multiple material layers 10 are the same, in some embodiments of the present application, the Maxwell - Garnett model can be used to regulate the total volume of the holes 102 in each material layer 10: any material layer 10 satisfies where ε c is the relative permittivity at room temperature of the material layer 10, ε m is the relative permittivity at room temperature of the substrate 101, ε f is the relative permittivity at room temperature of air, and V f is the volume fraction of air in the material layer 10. In the embodiments of the present application, since the holes 102 in the Luneburg lens antenna 1 contain air and the holes 102 are filled with air, so V fIt is equal to the total pore volume of the corresponding material layer 10. The relative dielectric constant value of each material layer can be determined by those skilled in the art according to actual needs, and this application does not limit it. In some embodiments of this application, due to the preparation method, the pores 102 are all open pores 102. Therefore, V f can be measured by the gas adsorption and desorption method. In the embodiments of this application, the dielectric constant ε of air at room temperature f takes the value of 1. In the embodiments of this application, room temperature includes 25±2°C.

[0062] In some embodiments of this application, in the above Luneburg lens antenna 1, the volume density of the material layer 10 is 0.05 g / cm 3 -1.0 g / cm 3 . In other words, the volume density of the multiple material layers 10 decreases layer by layer from the inside to the outside along the radial direction of the Luneburg lens antenna 1 within the range of 0.05 g / cm 3 -1.0 g / cm 3 . Specifically, the volume density of the material layer 10 can be, but is not limited to, 0.05 g / cm 3 , 0.1 g / cm 3 , 0.15 g / cm 3 , 0.2 g / cm 3 , 0.25 g / cm 3 , 0.3 g / cm 3 , 0.35 g / cm 3 , 0.4 g / cm 3 , 0.45 g / cm 3 , 0.5 g / cm 3 , 0.55 g / cm 3 , 0.6 g / cm 3 , 0.65 g / cm 3 , 0.7 g / cm 3 , 0.75 g / cm 3 , 0.8 g / cm 3 , 0.85 g / cm 3 , 0.9 g / cm 3 , 0.95 g / cm 3 , 1.0 g / cm 3 and so on. In this way, the total weight of the Luneburg lens can be controlled within a suitable range, which is easy to be stably assembled at a high place.

[0063] In some embodiments of the present application, the material layer 10 further includes inorganic filler particles dispersed in the base material 101; the relative dielectric constant of the inorganic filler particles at room temperature is greater than that of the base material 101 at room temperature. Thus, the lightweight degree of the Luneburg lens antenna 1 can be effectively improved, which is more conducive to the assembly and application of the Luneburg lens antenna 1. Specifically, when adding inorganic filler particles with a relatively large dielectric constant to the base material 101, in order to keep the dielectric constant of the overall material layer 10 unchanged, it is necessary to reduce the amount of the base material 101 and increase the total pore 102 volume of the material layer 10. Therefore, the volume density of the Luneburg lens antenna 1 can be effectively reduced, thereby improving its lightweight degree. In this case, the volume density of the material layer 10 is 0.05 g / cm 3 -0.8 g / cm 3 . In other words, the volume density of multiple material layers 10 decreases layer by layer from the inside to the outside along the radial direction of the Luneburg lens antenna 1 within the range of 0.05 g / cm 3 -0.8 g / cm 3 .

[0064] In some specific embodiments, more preferably, the true density of the inorganic filler particles is less than that of the base material 101; thus, the true density of the material layer 10 can be reduced, thereby further reducing the volume density of the Luneburg lens antenna 1.

[0065] In some embodiments of the present application, the particle size of the inorganic filler particles is 2 μm - 3 μm. The inorganic filler particles with the above particle size do not affect the propagation of electromagnetic waves inside the Luneburg lens antenna 1, and can make the inorganic filler particles evenly distributed in the base material 101, thereby reducing the risk of increasing the dielectric loss of the material layer 10 caused by the agglomeration of the inorganic filler particles, and also making the structure of the material layer 10 relatively uniform. Specifically, the particle size of the inorganic filler particles can be, but is not limited to, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, etc. In the embodiments of the present application, the particle size of the inorganic filler particles can be measured by SEM.

[0066] When inorganic filler particles are dispersed in the base material 101, the total pore 102 volume of the pores 102 in each material layer 10 can also be regulated according to the Maxwell - Garnett model; specifically, the material layer 10 satisfies: where ε c is the relative dielectric constant of the material layer 10 at room temperature, ε c0 is the relative dielectric constant of the base material 101 with dispersed inorganic filler particles at room temperature, ε f is the relative dielectric constant of air at room temperature, V f is the volume fraction of air in the material layer 10; among them, ε c0 satisfies: ε m is the relative permittivity at room temperature of the base material 101, ε a is the relative permittivity at room temperature of the inorganic filler particles, V a is the sum of the volume fractions of the inorganic filler particles in the material layer 10. Similarly, the above V f is the total pore 102 volume of the corresponding material layer 10, which can be measured by the gas adsorption - desorption method.

[0067] In some embodiments of the present application, the material of the above - mentioned inorganic filler particles includes, but is not limited to, at least one of titanium dioxide, strontium titanate, barium titanate, and calcium titanate. The relative permittivity at room temperature of the above - mentioned inorganic filler particles is relatively large, which can effectively increase the above ε c0 .

[0068] Please refer to Figure 2 , in some embodiments of the present application, the multiple material layers 10 include a central material layer located in the innermost layer and a plurality of sheath material layers sequentially stacked on the surface of the central material layer. Taking the spherical Luneburg lens antenna 1 as an example, it may include a spherical central material layer and a plurality of spherical shell - shaped sheath material layers sequentially stacked on the surface of the spherical central material layer. The above - mentioned spherical central material layer is a material layer 10, and a spherical shell - shaped sheath material layer is a material layer 10. In this way, the preparation difficulty of the Luneburg lens antenna 1 can be reduced.

[0069] In some embodiments of the present application, the Luneburg lens antenna 1 includes 5 - 150 material layers 10. Specifically, the number of the material layers 10 can be, but is not limited to, 5, 8, 10, 12, 15, 20, 22, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150. Further, in some specific embodiments, the 5 - 150 material layers 10 include 1 central material layer and 4 - 149 sheath material layers, and the thickness of any sheath material layer ≤ 8 mm. When the thickness of the material layer 10 is kept constant, those skilled in the art can choose to increase the number of the material layers 10 to obtain a larger - sized Luneburg lens antenna 1; when the size of the Luneburg lens antenna 1 is fixed, those skilled in the art can choose to reduce the size of the material layer 10 by increasing the number of the material layers 10, so that the change of the relative permittivity in the Luneburg lens antenna 1 is closer to the ideal state.

[0070] In some embodiments of the present application, the thicknesses of the multiple sheath material layers are equal. In this way, the Luneburg lens is easy to design and manufacture.

[0071] In some embodiments of the present application, the size of the central material layer is 15 mm - 60 mm. In this way, it is easy to prepare, and the influence on the gain and aperture efficiency of the Luneburg lens is small and can be ignored. Specifically, the size of the central material layer can be, but is not limited to, 15 mm, 16 mm, 18 mm, 20 mm, 22 mm, 25 mm, 26 mm, 28 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm. In the embodiments of the present application, for the columnar or spherical Luneburg lens antenna 1, the size of the Luneburg lens antenna 1 is the diameter of the sphere or the diameter of the bottom surface, and the size of its central material layer is the diameter of the spherical central material layer or the diameter of the bottom surface of the columnar central material layer; for the hemispherical or semi-cylindrical Luneburg lens antenna 1, the size of the Luneburg lens antenna 1 is the radius of the hemisphere or the radius of the semi-circular bottom surface, and the size of its central material layer is the radius of the hemispherical central material layer or the radius of the semi-circular bottom surface. For other shaped Luneburg lens antennas 1, the size of the central material layer can be determined according to the above principles.

[0072] In some specific embodiments, the thicknesses of multiple sheath material layers are equal, and the size of the central material layer is the sum of the thicknesses of 3 - 5 sheath material layers. In this way, the Luneburg lens is easy to design and manufacture, and has almost no impact on its performance.

[0073] In some embodiments of the present application, the thickness of any sheath material layer ≤ 8 mm. In this way, it is easy to control the dielectric constant gradient of the multiple material layers 10 in the Luneburg lens antenna 1 to be relatively gentle. In the direction from the inside to the outside along the radial direction of the Luneburg lens antenna 1, the curve of its relative dielectric constant with respect to the radius (or the distance from the center point) is smoother and closer to the ideal state (as Figure 3 shown), which is more conducive to improving the gain and aperture efficiency of the Luneburg lens antenna 1; among them, taking the spherical Luneburg lens antenna 1 as an example, Figure 3 the "distance from the center" in it is the "distance from the center of the sphere"; for the columnar Luneburg lens antenna 1, the "distance from the center" is the "distance from the axis". Specifically, the thickness of the sheath material layer can be, but is not limited to, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, etc. In some specific embodiments, the thickness of any sheath material layer is 1 mm - 8 mm. In this way, it is easy to manufacture and can ensure better performance of the Luneburg lens antenna 1.

[0074] The following further illustrates the performance of the Luneburg lens antenna 1 with the simulation results of multiple material layers 10 of different numbers of spherical Luneburg lens antennas in the COMSOL simulation software. The No. 1 Luneburg lens antenna includes 50 material layers 10 with a thickness of 3 mm. The base materials 101 of the material layers 10 are all PS (the relative dielectric constant of PS at room temperature is 2.5), and the feed position is 1 mm. Here, the feed position refers to the distance from the transmitting signal feed to the Luneburg lens antenna 1. Under electromagnetic waves with frequencies of 71 GHz, 78.5 GHz, and 86 GHz, the aperture efficiencies are 86.2%, 85.3%, and 82.1% respectively, and the gains are 44.38 dB, 44.99 dB, and 45.35 dB respectively.

[0075] The No. 2 Luneburg lens antenna includes 30 material layers 10 with a thickness of 5 mm. The base materials 101 of the material layers 10 are all PS, and the feed position is 1.5 mm. The No. 2 Luneburg lens antenna 1 under electromagnetic waves with frequencies of 71 GHz, 78.5 GHz, and 86 GHz has aperture efficiencies of 84.1%, 82.3%, and 79.2% respectively, and gains of 44.34 dB, 44.80 dB, and 45.14 dB respectively.

[0076] The No. 3 Luneburg lens antenna includes 25 material layers 10 with a thickness of 6 mm. The base materials 101 of the material layers 10 are all PS, and the feed position is 2 mm. The No. 3 Luneburg lens antenna 1 under electromagnetic waves with frequencies of 71 GHz, 78.5 GHz, and 86 GHz has aperture efficiencies of 82.9%, 80.7%, and 78.1% respectively, and gains of 44.18 dB, 44.72 dB, and 45.14 dB respectively.

[0077] The No. 4 Luneburg lens antenna includes 19 material layers 10 with a thickness of 8 mm. The base materials 101 of the material layers 10 are all PS, and the feed position is 2.5 mm. The No. 4 Luneburg lens antenna 1 under electromagnetic waves with frequencies of 71 GHz, 78.5 GHz, and 86 GHz has aperture efficiencies of 75.5%, 73.3%, and 73.0% respectively, and gains of 43.98 dB, 44.43 dB, and 44.94 dB respectively.

[0078] The No. 5 Luneburg lens antenna includes 15 material layers 10 with a thickness of 10 mm. The base materials 101 of the material layers 10 are all PS, and the feed position is 3 mm. The No. 5 Luneburg lens antenna 1 under electromagnetic waves with frequencies of 71 GHz, 78.5 GHz, and 86 GHz has aperture efficiencies of 71.0%, 66.5%, and 61.5% respectively, and gains of 43.59 dB, 43.89 dB, and 44.17 dB respectively.

[0079] In some embodiments of the present application, the relative permittivity of the plurality of material layers 10 at room temperature changes in an arithmetic progression from the inside to the outside in the radial direction of the Luneburg lens antenna 1. It can be understood that, based on the basic principle of the Luneburg lens antenna 1, the common difference of the above arithmetic progression <0. At this time, the thickness of the material layer 10 can be adjusted so that the "relative permittivity - distance from the center point" curve of the Luneburg lens antenna 1 tends to a smooth parabola.

[0080] In some embodiments of the present application, the above substrate 101 includes, but is not limited to, polymers. Considering that in some embodiments, the above plurality of material layers 10 need to be prepared by template polymerization, in order to save process time and reduce production costs, the above polymer is preferably a polymer that can be polymerized by free radical polymerization reaction. Preferably, the polymer includes, but is not limited to, at least one of polyolefins, polyacrylates, and olefin-acrylate copolymers. The above polymer has a suitable relative permittivity and true density, which can ensure better comprehensive performance of the Luneburg lens antenna 1.

[0081] In the embodiments of the present application, the material of the substrate 101 can be tested by infrared spectrometry (IR) or pyrolysis gas chromatography (PY-GCMS).

[0082] When the above polymer is prepared by emulsion polymerization, the above polymer may also contain a small amount of emulsifier for forming the emulsion, and the influence of the small amount of emulsifier on the polymer (or on the substrate 101) can be ignored.

[0083] Specifically, the monomers of the polymer include, but are not limited to, at least one of styrene, methyl styrene, divinylbenzene, 1,4-cyclohexanedimethanol divinyl ether, cyclohexyl vinyl ether, 2-ethylhexyl vinyl ether, diethylene glycol divinyl ether, benzyl vinyl ether, 1,4-cyclohexanedimethanol divinyl ether, tetrafluoroethylene, trifluorostyrene, perfluoropropyl perfluorovinyl ether, vinyl cyanide, triallyl isocyanurate, diallyl phthalate, and triallyl cyanurate, methyl acrylate, n-butyl acrylate, methyl methacrylate, n-butyl methacrylate, glycidyl methacrylate, benzyl methacrylate, 2-phenoxyethyl methacrylate, tetrahydrofurfuryl methacrylate, trimethylolpropane formal acrylate, 3,3,5-trimethylcyclohexyl acrylate, o-phenylphenoxyethyl acrylate, benzyl acrylate, tetrahydrofurfuryl acrylate, ethylene glycol dimethacrylate, hexanediol diacrylate, triallyl isocyanurate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate.

[0084] In some specific embodiments, the above polymer includes polystyrene (PS). Polystyrene has relatively high strength, and both its true density and relative dielectric constant are appropriate, which is conducive to ensuring better comprehensive performance of the Luneburg lens antenna 1. In some specific embodiments, the mass percentage of styrene monomer residues in the polymer is ≥ 60%, for example, 70% - 99.9%. Specifically, the mass percentage of styrene monomer residues in the polymer can be, but is not limited to, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 99%, etc.

[0085] The embodiment of the present application also provides a preparation method of a Luneburg lens antenna, which can be used to prepare the aforementioned Luneburg lens antenna 1, and includes: preparing n material layers by using an emulsion polymerization soft template method to obtain a Luneburg lens antenna; wherein, from the 1st material layer to the nth material layer, they are arranged from the inside to the outside along the radial direction of the Luneburg lens antenna, and the volume density of the material layers decreases layer by layer from the 1st to the nth material layer, and two adjacent material layers are in direct contact, and n is a positive integer greater than 1; the above material layer includes a substrate and a plurality of holes distributed in the substrate, and the aperture of the holes is ≤ 500 μm.

[0086] By using the emulsion soft template method, the (i + 1)th material layer can be directly grown on the surface of the ith material layer. Therefore, in the obtained Luneburg lens antenna, two adjacent material layers are in direct contact. The above preparation method has simple process, high flexibility and high forming freedom, can be used to prepare Luneburg lens antennas of various shapes, has high production efficiency, and can realize large-scale industrial production.

[0087] In some embodiments of the present application, the preparation of n material layers by using the emulsion polymerization soft template method includes:

[0088] Providing n portions of emulsions, the emulsions include water and oil monomers, and the water content of the 1st portion of emulsion to the nth portion of emulsion increases in sequence; curing and drying the n portions of emulsions in sequence. During the curing process, the monomers polymerize to form a substrate, and water droplets are dispersed in the substrate. In the subsequent drying process, the water in the substrate evaporates and escapes, thereby forming holes in the substrate, and the holes are filled with air.

[0089] In some specific embodiments, the above n portions of emulsions are all water-in-oil emulsions. In this way, the uniformity of the holes in the Luneburg lens antenna can be fully improved, and it is easier to obtain holes with a circular cross-section, thereby ensuring better gain and higher aperture efficiency of the Luneburg lens antenna. In some specific embodiments, the fineness of the n portions of emulsions is the same, that is, the size distribution of the droplets is uniform, and the aperture distribution of the holes in the obtained Luneburg lens antenna is uniform.

[0090] In some embodiments of the present application, the oily monomer includes at least one of vinyl monomers and acrylic monomers. Among them, the vinyl monomers include, but are not limited to, at least one of styrene, methylstyrene, divinylbenzene, 1,4-cyclohexanedimethanol divinyl ether, cyclohexyl vinyl ether, 2-ethylhexyl vinyl ether, diethylene glycol divinyl ether, benzyl vinyl ether, 1,4-cyclohexanedimethanol divinyl ether, tetrafluoroethylene, trifluorostyrene, perfluoropropyl perfluorovinyl ether, vinyl cyanide, triallyl isocyanurate, diallyl phthalate, and triallyl cyanurate. The acrylic monomers include, but are not limited to, at least one of methyl acrylate, n-butyl acrylate, methyl methacrylate, n-butyl methacrylate, glycidyl methacrylate, benzyl methacrylate, 2-phenoxyethyl methacrylate, tetrahydrofurfuryl methacrylate, trimethylolpropane formal acrylate, 3,3,5-trimethylcyclohexyl acrylate, o-phenylphenoxyethyl acrylate, benzyl acrylate, tetrahydrofurfuryl acrylate, ethylene glycol dimethacrylate, hexanediol diacrylate, triallyl isocyanurate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate. In some specific embodiments, the oily monomer includes styrene. When the oily monomer further includes monomers other than styrene, the mass percentage of styrene in the oily monomers in the emulsion is ≥60%.

[0091] Understandably, in order to enable the above monomers to polymerize relatively quickly during the curing process and save process time, in some embodiments of the present application, the emulsion further includes an initiator. Considering the differences in the properties of the monomers, some can undergo thermal-initiated radical polymerization, and some can undergo photo-initiated radical polymerization. Therefore, the initiators in the embodiments of the present application include, but are not limited to, free radical thermal initiators and free radical photo initiators; the above initiators can be selected from any materials well-known in the art as long as they can initiate the radical polymerization reaction of the corresponding monomers.

[0092] Specifically, the free radical thermal initiators include, but are not limited to, at least one of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, azoisobutyronitrile formamide, 2,2-azobis(2,4,4-trimethylpentane), 2,2-azobis(N-butyl-2-methylpropionamide), 1,1'-azobis(cyanocyclohexane), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide), 2,2'-azobis(2-methylpropamidine) dihydrochloride, 2,2'-azobis(2-imidazoline) dihydrochloride, 4,4'-azobis(4-cyanovaleric acid), benzoyl peroxide, diisopropylbenzene peroxide, diisopropyl peroxydicarbonate, tert-butyl peroxybenzoate, and potassium persulfate.

[0093] Specifically, the free radical photoinitiator includes but is not limited to at least one of 2,4,6-(trimethylbenzoyl) diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphosphinate, 2-methyl-1-(4-methylthiophenyl)-2-morpholin-1-propanone, 2-isopropylthioxanthone, 1-hydroxy-cyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, benzoin dimethyl ether, methyl o-benzoylbenzoate, benzophenone, 4-chlorobenzophenone, 4-phenylbenzophenone, 2-benzyl-2-dimethylamino-1-(4-morpholinobenzylphenyl) butanone, phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide, benzoate esters, 2-hydroxy-1-(4-(2-hydroxy-2-methylpropanoyl)phenyl) benzyl)-2-methyl-1-propanone, bis(2,6-difluoro-3-pyrrolylphenyl) titanocene, and ethyl 4-dimethylaminobenzoate.

[0094] In order to improve the stability of the emulsion, in some embodiments of the present application, an emulsifier is further included in the above emulsion. In the embodiments of the present application, any emulsifier well-known in the art can be selected as the emulsifier. Specifically, the above emulsifier includes but is not limited to at least one of cholesterol, sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dibutylnaphthalene sulfonate, sodium laurate, tetradecyltrimethylammonium bromide, cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, docosyl dimethyl ammonium bromide, sorbitan monooleate, polyoxyethylene(20)-sorbitan monooleate, dodecyl-β-D-glucoside, silica micro-nano particles, carbon dioxide micro-nano particles, and zinc oxide micro-nano particles.

[0095] In some embodiments of the present application, the normal temperature viscosity of the emulsion is 50 cP - 500 cP. In this way, it is more conducive to the emulsion filling the accommodation space of the template, so that the Luneburg lens antenna can be obtained more smoothly. Specifically, the normal temperature viscosity of the emulsion can be but is not limited to 50 cP, 60 cP, 80 cP, 100 cP, 120 cP, 150 cP, 180 cP, 200 cP, 250 cP, 300 cP, 350 cP, 400 cP, 450 cP, 500 cP, etc.

[0096] In some embodiments of the present application, the above-mentioned inorganic filler particles are further added to the emulsion. In this way, a material layer in which the inorganic filler particles are dispersed can be prepared. In some specific embodiments, the particle size of the inorganic filler particles is 2 μm - 3 μm. At this time, a laser particle size analyzer can be used to measure the particle size of the inorganic filler particles.

[0097] In some embodiments of the present application, preparing n material layers by using the emulsion polymerization soft template method further includes:

[0098] S11. Design a mold, which includes a cover plate and n bodies with different sizes. Any body and the cover plate can form a closed receiving space; the sizes of the first body to the nth body increase in sequence. During specific operations, pour the ith emulsion into the ith body, cover the cover plate, and successively perform curing, drying, and detachment from the ith body to obtain the ith cured product; the ith cured product includes i material layers, where i is any integer from 1 to (n - 1); the ith cured product and the (i + 1)th body can form a cavity for preparing the (i + 1)th material layer.

[0099] S12. Pour the (i + 1)th emulsion into the (i + 1)th body, and immerse the ith cured product into the (i + 1)th emulsion, then cure and dry to obtain the (i + 1)th cured product. It can be understood that when i is (n - 1), after demolding, a Luneburg lens antenna can be obtained.

[0100] Please refer to Figure 4 , and the following takes the preparation of a hemispherical Luneburg lens antenna with 7 material layers as an example for detailed description:

[0101] (1) Determine the dielectric constant of each material layer. The room-temperature relative dielectric constants of the 7 material layers from the inside to the outside along the radial direction are 1.91, 1.82, 1.73, 1.62, 1.49, 1.36, and 1.18 in sequence. Use the Maxwell - Garnett model to calculate the volume density of each material layer. Among them, polystyrene (room-temperature relative dielectric constant is 2.5) is selected as the base material, and the calculated volume densities of the 7 material layers from the inside to the outside along the radial direction are 0.69 g / cm 3 、0.63 g / cm 3 、0.56 g / cm 3 、0.49 g / cm 3 、0.39 g / cm 3 、0.29 g / cm 3 、0.16 g / cm 3 .

[0102] Prepare 7 portions of styrene emulsion according to the above volume densities. From the first styrene emulsion to the seventh styrene emulsion, their water contents increase in sequence.

[0103] (2) Prepare a mold, which includes 7 concentric hemispherical bodies with diameters of 60 mm, 75 mm, 90 mm, 105 mm, 120 mm, 135 mm, and 150 mm respectively and a cover plate ( Figure 4 not shown in the figure). To ensure the concentricity of the final hemispherical Luneburg lens antenna, a plurality of concentric rings are provided on the direction of the cover plate facing the body. The diameters of the concentric rings match the opening sizes of the respective hemispherical bodies, so that the cover plate can form a closed receiving space with each body;

[0104] (3) Pour the first styrene emulsion into the first main body with a diameter of 60 mm, heat and cure for 2 h, take out the first cured product fixed on the cover plate from the first main body, and dry it in an oven to remove moisture, obtaining the first cured product (i.e., the first material layer); the heating temperature can be 70 °C.

[0105] (4) Pour the second styrene emulsion into the second main body with a diameter of 75 mm. Among them, the second main body can form a domed cavity for preparing the second material layer with the first cured product. Immerse the first cured product fixed on the cover plate into the second styrene emulsion, heat and cure for 2 h, take out the second cured product fixed on the cover plate from the second main body, and dry it in an oven to remove moisture, obtaining the second cured product (i.e., the first material layer and the second material layer stacked).

[0106] (5) Operate according to the above method to obtain a hemispherical cured product with 7 material layers arranged concentrically, separate it from the cover plate to obtain a hemispherical Luneburg lens antenna. After slicing the above hemispherical Luneburg lens antenna and testing it under SEM, the aperture diameter of the holes in each material layer is 50 μm - 300 μm.

[0107] Please refer to Figure 5 , in some specific embodiments, in order to ensure the accuracy of the hemispherical Luneburg lens antenna, a spherical segment-shaped main body and a matching cover plate ( Figure 5 not shown in the figure) are used. The height H of each spherical segment main body is greater than its radius. Finally, a spherical segment-shaped cured product with multiple material layers arranged concentrically is obtained, and then it is cut to obtain a hemispherical Luneburg lens antenna. Figure 5 The dimensions of the mold and the number of main bodies in the figure are exemplary drawings and do not limit the present application.

[0108] In some embodiments of the present application, before the above step (1), it further includes designing the thickness of the material layer by using COMSOL simulation software. Further, the designed Luneburg lens antenna can also be simulated and tested to simulate its gain and aperture efficiency at different electromagnetic wave frequencies to determine the optimal design scheme.

[0109] In order to further reduce the influence of the emulsifier on the dielectric constant of the substrate, in some embodiments of the present application, it further includes removing the emulsifier in the cured product obtained after drying. In some specific embodiments, the Soxhlet extraction method can be used to remove the emulsifier in the cured product.

[0110] In some specific embodiments, two identical hemispherical Luneburg lens antennas can be prepared and bonded to obtain a spherical Luneburg lens antenna. Among them, the bonding methods include but are not limited to bonding with adhesives, bulk polymerization bonding, emulsion polymerization bonding, and heating bonding.

[0111] Those skilled in the art can design molds with different shapes and sizes according to the above method to fabricate Luneburg lens antennas of any shape.

[0112] In the embodiments of the present application, the material of the above mold is not limited, as long as the cured product can be smoothly demolded. For the convenience of preparation and cost reduction, in some specific embodiments of the present application, the material of the above mold is aluminum alloy.

[0113] The embodiments of the present application also provide an antenna module, which includes the Luneburg lens antenna provided by the embodiments of the present application and a feed antenna, or includes the Luneburg lens antenna fabricated by the fabrication method provided by the embodiments of the present application.

[0114] Due to the adoption of the Luneburg lens antenna provided by the embodiments of the present application, this antenna module can receive and transmit electromagnetic waves in the full frequency band (6 GHz - 86 GHz) from multiple directions. Moreover, compared with traditional antenna modules with the same performance, the antenna module of the embodiments of the present application has a simple structure and is easy to construct and maintain.

[0115] In some embodiments, the feed antenna is mounted on the surface of the Luneburg lens antenna.

[0116] In some embodiments of the present application, the above antenna module includes but is not limited to outdoor base station antenna modules and vehicle radar antenna modules.

[0117] The embodiments of the present application also provide a communication system, which includes the antenna module provided by the embodiments of the present application. Since this communication system adopts the antenna module of the embodiments of the present application, it has strong market competitiveness.

[0118] The embodiments of the present application also provide a navigation system, which includes the antenna module provided by the embodiments of the present application. Since this navigation system adopts the antenna module of the embodiments of the present application, it has good application prospects.

[0119] In the embodiments of the present application, except for professional terms, the range value represented by "a - b" includes the endpoint values a and b. For example, the range represented by "10 - 300" includes the endpoint value 10 and the endpoint value 300.

[0120] The above are the exemplary embodiments of the present application. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present application, several improvements and refinements can still be made, and these improvements and refinements are also regarded as the protection scope of the present application.

Claims

1. A Luneburg lens antenna, characterized in that, it includes a plurality of material layers arranged radially from the inside outwards; each of the material layers includes a substrate and a plurality of holes distributed in the substrate, and the aperture of the holes is ≤500 μm; along the radial direction from the inside outwards, the volume density of the plurality of material layers decreases layer by layer; two adjacent material layers are in direct contact.

2. The Luneburg lens antenna according to claim 1, characterized in that, the aperture of the holes is 10 μm - 300 μm.

3. The Luneburg lens antenna according to claim 1 or 2, characterized in that, the aperture distribution of the holes in the Luneburg lens antenna is uniform.

4. The Luneburg lens antenna according to any one of claims 1 - 3, characterized in that, along the radial direction from the inside outwards of the Luneburg lens antenna, the distribution density of the holes in the plurality of material layers increases layer by layer.

5. The Luneburg lens antenna according to any one of claims 1 - 4, characterized in that, Any one of the said material layers satisfies that: wherein, ε c is the relative permittivity at room temperature of the said material layer, ε m is the relative permittivity at room temperature of the said base material, ε f is the relative permittivity at room temperature of air, and V f is the volume fraction of air in the said material layer.

6. The Luneburg lens antenna according to any one of claims 1 - 5, characterized in that, The bulk density of the material layer is 0.05 g / cm 3 - 1.0 g / cm 3 .

7. The Luneburg lens antenna according to any one of claims 1 - 4, characterized in that, the material layer further includes inorganic filler particles dispersed in the substrate; the relative permittivity at room temperature of the inorganic filler particles is greater than the relative permittivity at room temperature of the substrate.

8. The Luneburg lens antenna according to claim 7, characterized in that, the material of the inorganic filler particles includes at least one of titanium dioxide, strontium titanate, barium titanate, and calcium titanate.

9. The Luneburg lens antenna according to claim 7 or 8, characterized in that, the D50 of the inorganic filler particles is 2 μm - 3 μm.

10. The Luneburg lens antenna according to any one of claims 7 - 9, characterized in that, the material layer satisfies: Among them, ε c is the relative permittivity at room temperature of the material layer, ε c0 is the relative permittivity at room temperature of the substrate in which the inorganic filler particles are dispersed, ε f is the relative permittivity at room temperature of air, V f is the volume fraction of air in the material layer; Among them, the ε c0 satisfies: ε m is the relative permittivity at room temperature of the substrate, and ε a is the relative permittivity at room temperature of the inorganic filler particles, and V a is the sum of the volume fractions of the inorganic filler particles in the material layer.

11. The Luneburg lens antenna according to any one of claims 7 - 10, characterized in that, The bulk density of the material layer is 0.05 g / cm 3 - 0.8 g / cm 3 .

12. The Luneburg lens antenna according to any one of claims 1 - 11, characterized in that, the plurality of material layers include a central material layer located in the innermost layer and a plurality of sleeve material layers sequentially stacked on the surface of the central material layer; the thickness of any one of the sleeve material layers is ≤8 mm.

13. The Luneburg lens antenna according to claim 12, characterized in that, the thicknesses of the plurality of sleeve material layers are equal.

14. The Luneburg lens antenna according to any one of claims 12 - 13, characterized in that, the size of the central material layer is 15 mm - 60 mm.

15. The Luneburg lens antenna according to any one of claims 1 - 12, characterized in that, the relative permittivity at room temperature of the plurality of material layers changes in an arithmetic progression.

16. The Luneburg lens antenna according to any one of claims 1 - 15, characterized in that, the Luneburg lens antenna is a sphere or a hemisphere, and the plurality of material layers are concentrically arranged; or, the Luneburg lens antenna is a cylinder or a semi - cylinder, and the plurality of material layers are coaxially arranged.

17. The Luneburg lens antenna according to any one of claims 1 - 16, characterized in that, The substrate includes a polymer, and the polymer includes at least one of polyolefins, polyacrylates, and olefin-acrylate copolymers.

18. The Luneburg lens antenna according to any one of claims 1-17, characterized in that at an electromagnetic wave frequency of 6 GHz - 86 GHz, the gain of the Luneburg lens antenna is ≥ 37 dB, and the aperture efficiency is ≥ 47%.

19. A method for manufacturing a Luneburg lens antenna, characterized in that it includes: preparing n material layers by using an emulsion polymerization soft template method to obtain a Luneburg lens antenna; wherein, from the 1st material layer to the nth material layer are arranged radially from the inside to the outside of the Luneburg lens antenna, and the volume density of the 1st to the nth material layers decreases layer by layer, and two adjacent material layers are in direct contact, and n is a positive integer greater than 1; the material layer includes a substrate and a plurality of holes distributed in the substrate, and the aperture of the holes is ≤ 500 μm.

20. The manufacturing method according to claim 19, characterized in that the preparing n material layers by using an emulsion polymerization soft template method includes: designing a mold, the mold includes a cover plate and n bodies with different sizes, and any one of the bodies and the cover plate can form a closed receiving space; preparing n portions of emulsion, the emulsion includes water and an oil-based monomer, and the water content of the 1st portion of emulsion to the nth portion of emulsion increases in sequence; pouring the i-th portion of emulsion into the i-th body, covering the cover plate, and sequentially performing curing, drying, and detaching from the i-th body to obtain the i-th cured product, the i-th cured product includes i material layers, and i is any integer from 1 to (n - 1); the i-th cured product and the (i + 1)-th body can form a cavity for preparing the (i + 1)-th material layer; pouring the (i + 1)-th portion of emulsion into the (i + 1)-th body, and immersing the i-th cured product in the (i + 1)-th emulsion, followed by curing and drying to obtain the (i + 1)-th cured product.

21. The manufacturing method according to claim 19 or 20, characterized in that the emulsion is a water-in-oil emulsion; the normal temperature viscosity of the emulsion is 50 cP - 500 cP.

22. An antenna module, characterized in that it includes the Luneburg lens antenna according to any one of claims 1-18 and a feed antenna; or, it includes the Luneburg lens antenna prepared by the manufacturing method according to any one of claims 19-21 and a feed antenna.

23. A communication system, characterized in that it includes the antenna module according to claim 22.

24. A navigation system, characterized in that it includes the antenna module according to claim 22.

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