Radio wave reflectors and reflector antennas

Abstract

We provide technology to reduce the weight of reflector antennas. [Solution] The radio wave reflector 11 is provided on the curved reflective surface 31 of the reflecting mirror antenna 30, and has a conductive thin film layer 16 that reflects radio waves by having a structure in which conductors 12 are arranged periodically, and reflects radio waves in a frequency-specific manner.

Description

Technical Field

[0006] , ,

[0005] , , ,

[0001] The present invention relates to a radio wave reflector for reflecting radio waves and a reflector antenna provided with the radio wave reflector on a reflecting mirror surface.

Background Art

[0002] Generally, for antennas installed on the ground, the efficiency of transmission and reception is enhanced by using a large-area metal reflector to collect radio waves at the focal position of the reflecting mirror surface. For this type of antenna using such a reflector, various techniques for enhancing the transmission and reception efficiency have been accumulated so far.

[0003] Antennas are used not only on the ground but also in space. For example, Patent Document 1 below discloses an antenna reflector mounted on a general artificial satellite.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Regarding antennas installed in space as well as those installed on the ground, it is required to produce an antenna with high transmission and reception efficiency. However, a metal reflector has a large mass and a large load when launched into orbit. Therefore, it has been difficult to apply various techniques accumulated so far for the type of antenna using a reflector to antennas installed in space.

[0006] An antenna that uses a reflector to collect radio waves at the focal position of the reflecting mirror surface, and a lightweight antenna suitable for installation in space is required. The present invention provides a technique for reducing the weight of a reflector antenna. [Means for solving the problem]

[0007] To achieve the above objectives, the present invention encompasses the subject matter described in the following sections.

[0008] (Section 1) It is a radio wave reflector that is attached to the curved reflective surface of a reflecting antenna. A radio wave reflector having a conductive thin film layer with a structure in which conductors are periodically arranged to reflect radio waves, thereby reflecting radio waves in a frequency-specific manner. (Section 2) The radio wave reflector according to item 1, wherein the thickness of the conductive thin film layer is 0.02 μm or more and 10 μm or less, and the proportion of the area covered by the conductive thin film layer in a plan view is 36% or more and 46% or less. (Section 3) The radio wave reflector according to claim 1 or 2, further comprising a substrate layer including a substrate that holds the conductive thin film layer. (Section 4) A dielectric layer with a dielectric constant of 2.0 or more and 9 or less is laminated on the surface of the conductive thin film layer, A protective layer laminated on the surface of the dielectric layer, A radio wave reflector as described in any one of items 1 to 3, further comprising the above. (Section 5) A radio wave reflector as described in any one of items 1 to 4, having a bending modulus of 0.05 GPa or more and 4 GPa or less. (Section 6) A reflector antenna having a radio wave reflector described in any one of items 1 to 5 on its reflective surface. [Effects of the Invention]

[0009] According to the present invention, a technology for reducing the weight of a reflector antenna can be provided. [Brief explanation of the drawing]

[0010] [Figure 1] This figure illustrates the angular range of reflected waves reflected by a radio wave reflector according to one embodiment of the present invention. [Figure 2]It shows the overall schematic configuration of the radio wave reflector according to an embodiment of the present invention, and is a cross-sectional view taken along the line B-B of FIG. 3(B). [Figure 3] It shows the overall schematic configuration of the radio wave reflector shown in FIG. 2, where (A) is a plan view and (B) is an enlarged view of part A of (A). [Figure 4] (A) to (E) are plan views of the conductor showing other examples of the conductor arrangement pattern. [Figure 5] It is a plan view of the conductor showing other examples of the conductor arrangement pattern. [Figure 6] It is a plan view of the radio wave reflector showing other examples of the conductor arrangement pattern. [Figure 7] It is a cross-sectional view showing the schematic configuration of the radio wave reflector according to another embodiment. [Figure 8] It is a cross-sectional view showing the schematic configuration of the radio wave reflector according to another embodiment. [Figure 9] It is a diagram for explaining the state where the radio wave reflector according to an embodiment is applied to the curved reflecting surface of a reflector antenna.

Embodiments for Carrying Out the Invention

[0011] (Overall Configuration) Embodiments of the present invention will be described with reference to the drawings. The radio wave reflector 11 of this embodiment is a radio wave reflector provided on the curved reflecting surface of a reflector antenna, and has a structure in which conductors 12 are periodically arranged and includes a conductive thin film layer 16 that reflects radio waves, and is a radio wave reflector 11 that reflects radio waves frequency-specifically. Reflecting radio waves frequency-specifically means reflecting radio waves having a specific frequency band, which is realized by the conductive thin film layer 16.

[0012] As shown in Figure 1, the radio wave reflector 11 of this embodiment reflects radio waves output from the radio wave source 20. The reflected waves are received by the receiving unit 21. The radio wave source 20 is a communication device or the like that has a transmitting antenna capable of transmitting radio waves. The receiving unit 21 is a device capable of receiving radio waves. In this embodiment, the receiving unit 21 is a communication device that has a receiving antenna. Examples of communication devices include smartphones, mobile phones, tablet terminals, notebook PCs, portable game consoles, repeaters, radios, televisions, etc.

[0013] The radio wave reflector 11 includes a conductor 12 that reflects radio waves. With the radio wave reflector 11 in a flat position, the radio wave reflects the incident wave at at least one predetermined angle, preferably 45 degrees, and more preferably in the entire range of angles from 15 degrees to 75 degrees, with frequencies of 3 GHz to 5 GHz, 25 GHz to 30 GHz, or 150 GHz to 300 GHz, where the incident angle of the incident wave is 15 degrees to 75 degrees. At this time, there is one frequency at which the intensity of the reflected wave when the incident wave is normally reflected by the radio wave reflector 11 is between -30 dB and 0 dB relative to the incident wave. Preferably, at a frequency of 28.5 GHz, the normal reflection intensity is between -30 dB and 0 dB relative to the incident wave. More preferably, in the entire frequency band from 20 GHz to 60 GHz, the normal reflection intensity is between -30 dB and 0 dB relative to the incident wave. More preferably, in the entire frequency band from 3 GHz to 300 GHz, the normal reflection intensity is -30 dB or more and 0 dB or less relative to the incident wave. "Normal reflection intensity" refers to the reflection intensity, which is the intensity of the reflected wave when the incident wave is reflected normally. "Flat" refers to a state without irregularities or curves.

[0014] The normal reflection intensity is preferably -25 dB or more and 0 dB or less, more preferably -22 dB or more and 0 dB or less, still more preferably -20 dB or more and 0 dB or less, and even more preferably -15 dB or more and 0 dB or less with respect to the incident wave. When the normal reflection intensity is -30 dB or more with respect to the incident wave, the radio wave reflector 11 can reflect radio waves while maintaining a large reflection intensity, and the receiving unit 21 can receive radio waves at a practically useful intensity. In this embodiment, the normal reflection intensity and the reflection intensity are values when the distance between the reflection point 11a of the radio wave reflector 11 and the radio wave source 20 and the distance between the reflection point 11a of the radio wave reflector 11 and the receiving unit 21 are 1 m.

[0015] Referring to FIG. 1 for explanation, normal reflection means that when radio waves emitted from the radio wave source 20 (transmission antenna) are reflected by the radio wave reflector 11, the incident angle θ1 of the incident wave and the reflection angle θ2 of the reflected wave are equal. The reflection direction of the reflected wave when the radio wave is normally reflected is also referred to as the "normal reflection direction". The incident angle θ1 is the angle formed by the incident wave traveling in the incident direction (shown by arrow A1 in FIG. 1) when the radio wave is incident on the radio wave reflector 11 and the normal line 22 of the reflection surface of the radio wave reflector 11. The reflection angle θ2 is the angle formed by the reflected wave traveling in the reflection direction (shown by arrow A2 in FIG. 1) of the reflected wave and the normal line 22 of the reflection surface. The normal line 22 refers to a straight line perpendicular to the tangent (or tangent plane) at the reflection point 11a.

[0016] The surface resistance value of the radio wave reflector 11 in a flat state is 0.003 Ω / square or more and 10 Ω / square or less. The surface resistance value is measured as the surface resistance value of the conductor 12. The surface resistance value of the radio wave reflector 11 in a flat state refers to the surface resistance value of the radio wave reflector 11 when the radio wave reflector 11 is placed on a flat mounting surface. The "plane" refers to a surface such that for any two points on the surface, the straight line connecting them is always on it.

[0017] The radio wave reflector 11 has a surface resistance change rate R of -10% or more and 10% or less. The surface resistance change rate R is the ratio of the change in surface resistance R2 when the radio wave reflector 11 is curved along the surface of a member having a curved surface with a radius of curvature of 200 mm, compared to the surface resistance R1 of the radio wave reflector 11 when it is flat. The surface resistance change rate R(%) is calculated as (R2-R1) / R1×100.

[0018] The reflection intensity of radio waves changes depending on the surface resistance. However, since the rate of change R of the surface resistance of the radio wave reflector 11 is between -10% and 10%, sufficient radio wave reflection intensity can be achieved even when the radio wave reflector 11 is curved, just as it is when it is flat.

[0019] The radio wave reflector 11 preferably has a flexural modulus of 0.05 GPa or more and 4 GPa or less. The flexural modulus is a value that indicates how much bending stress it can withstand and is defined in JIS K7171. By keeping the flexural modulus within the above range, the radio wave reflector 11 is flexible and can be bent without breaking, allowing it to be attached to a curved surface with a radius of curvature of 200 mm or more. The flexural modulus is measured in accordance with JIS K7171. Flexibility refers to the property of being flexible under normal temperature and pressure, and being able to deform by bending, flexing, or folding even when force is applied, without shearing or breaking.

[0020] The radio wave reflector 11 preferably has a Young's modulus of 0.01 GPa or more and 80 GPa or less. Young's modulus is the elastic modulus of a solid when tension is applied in one direction and stretched, and is also called the tensile modulus, as defined in JIS K7161-2014. By keeping the Young's modulus within the above range, the radio wave reflector 11 becomes more easily deformable, and can be curved without breaking the radio wave reflector 11, allowing it to be attached to a curved surface with a radius of curvature of 200 mm or more. The Young's modulus is measured in accordance with JIS K7127-1999.

[0021] Furthermore, it is preferable that the radio wave reflector 11 has a kurtosis of -0.4 or less when the receiving angular position of the reflected wave is changed within an angular range α of -15 degrees or more and +15 degrees or less with respect to the normal reflection direction of the radio wave, in a virtual plane that includes the incident direction of the incident wave and the reflection direction of the reflected wave. The kurtosis is more preferably -1.0 or less, even more preferably -1.1 or less, and even more preferably -1.2 or less. The lower limit of the above kurtosis is not particularly limited, but is usually around -0.5. The virtual plane can also be said to be a plane that includes the reflection point 11a on the reflective surface of the reflector, the radio wave source 20, and the reflected wave receiving section 21. The kurtosis is determined with the radio wave reflector 11 in a flat state.

[0022] Kurtosis is a statistic that represents how much a distribution deviates from a normal distribution, indicating the sharpness of the peak and the breadth of the tail. As shown in Figure 1, assume that radio waves emitted from the radio wave source 20 are incident on the radio wave reflector 11 at a predetermined incident angle θ1. The receiving angular position i of the receiving unit 21 is moved by predetermined angles (for example, 5 degrees each) from the normal reflection direction of the radio waves, centered on the reflection point 11a, within an angular range α of -15 degrees or more and +15 degrees or less relative to the normal reflection direction of the radio waves, and the reflection intensity x is measured. The receiving angular position i of the receiving unit 21 is located on a circular arc centered on the reflection point 11a. Values ​​of the reflection intensity at each receiving angular position i The average value of TIFF2026054790000002.tif1274 In TIFF2026054790000003.tif1010, if the standard deviation is s, the kurtosis can be calculated using the following formula.

[0023] TIFF2026054790000004.tif18139 (Formula 1)

[0024] When kurtosis is a negative value, it indicates that the intensity data at each angular position is flatter than a normal distribution; that is, the data is scattered from around the mean and the tails of the distribution are wide. The smaller the kurtosis value, the flatter the distribution. In this embodiment, by setting the kurtosis to -0.4 or less, the difference in reflection intensity depending on the receiving angular position is reduced within the angular range α of ±15 degrees relative to the normal reflection direction of radio waves.

[0025] The radio wave reflector 11 may be transparent as a whole, i.e., transparent. As will be described in detail later, the radio wave reflector 11 comprises a conductive thin film layer 16 made of a conductor 12. Preferably, the radio wave reflector 11 further comprises a substrate layer 13 including a substrate for holding the conductive thin film layer 16, and more preferably further comprises an adhesive layer 14 (also called a dielectric layer 14) and a protective layer 15. The substrate layer 13, adhesive layer 14 and protective layer 15 may each be formed of a resin that is transparent to visible light, and the conductor 12 of the conductive thin film layer 16 may be formed to a thickness that is transparent to visible light. Here, "transparent" means that the other side of the radio wave reflector 11 is visible when viewed from one side, and includes translucency, and is not limited to complete transparency with a total light transmittance of 100%. The radio wave reflector 11 may also be colored. The radio wave reflector 11 has a total light transmittance of 65% or more in a D65 standard light source, preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. Total light transmittance refers to the ratio of the total transmitted light flux to the parallel incident light flux of a test specimen, and is measured in accordance with JIS K 7375:2008.

[0026] As shown in Figure 3, in this embodiment, the radio wave reflector 11 is preferably square in plan view, with a side length L10 of 20 cm or more and 400 cm or less. Although radio waves with frequencies of 3 GHz or more and 300 GHz or less are attenuated with distance, it is preferable that the side length L10 be 20 cm or more in order to reflect with sufficient intensity at all points within a practical distance from the radio wave source 20. There is no particular upper limit to the side length L10, but from a manufacturing standpoint, 400 cm or less is preferable. The overall shape of the radio wave reflector 11 is not limited to a square, but may be a rectangle, triangle, pentagon, hexagon, or other polygon, in which case the length of the shortest side is set to 20 cm or more and 400 cm or less. Alternatively, the shortest distance between a vertex and the opposite side, or the shortest distance between a side and the opposite side, may be set to 20 cm or more and 400 cm or less. Furthermore, if the overall shape of the radio wave reflector 11 is circular, the diameter is set to 20 cm or more and 400 cm or less. If the overall shape of the radio wave reflector 11 is elliptical, the minor axis is set to be between 20 cm and 400 cm. If the overall shape of the radio wave reflector 11 is sector-shaped, the length of the shorter arc or radius is set to be between 20 cm and 400 cm. Furthermore, the overall shape of the radio wave reflector 11 may be a three-dimensional shape such as cylindrical or conical. The overall shape of the radio wave reflector 11 has a shape and size that can reflect radio waves with a reflection intensity of -30 dB or more relative to the incident wave, and the shape and size are appropriately selected according to the manner in which the radio wave reflector 11 is used.

[0027] The radio wave reflector 11 is preferably set to a thickness L11 of 0.01 mm or more and 0.5 mm or less. The thicknesses of the base layer 13, conductive thin film layer 16, adhesive layer 14, and protective layer 15 are set so that the thickness L11 of the radio wave reflector 11 is 0.5 mm or less. The thickness L11 of the radio wave reflector 11 is set to a thickness that allows the radio wave reflector 11 to be flexible and, when an external force is applied to the radio wave reflector 11 and the radio wave reflector 11 is bent, does not concentrate the force on the conductor 12 of the conductive thin film layer 16, but rather distributes the force to the base layer 13, adhesive layer 14, and protective layer 15.

[0028] The radio wave reflector 11 has at least enough flexibility to be attached along a curved surface with a radius of curvature of 200 mm or more, and preferably enough flexibility to be attached along a curved surface with a radius of curvature of 100 mm or more. The thickness L11 of the radio wave reflector 11 is the sum of the thickness L3 of the conductive thin film layer 16 and the thickness L8 of the base layer 13, or the sum of the thickness L3 of the conductive thin film layer 16, the thickness L8 of the base layer 13, the thickness L4 of the adhesive layer 14, and the thickness L5 of the protective layer 15. However, since the thickness L3 of the conductive thin film layer 16 is very thin compared to the thicknesses L8, L4, and L5 of the base layer 13, adhesive layer 14, and protective layer 15, the thickness L3 of the conductive thin film layer 16 may be ignored when calculating the thickness L11 of the radio wave reflector 11.

[0029] The thickness L11 of the radio wave reflector 11, the thickness L3 of the conductive thin film layer 16, the thickness L8 of the substrate layer 13, the thickness L4 of the adhesive layer 14, and the thickness L5 of the protective layer 15 are determined by measuring multiple arbitrary locations and calculating the average value of the obtained measurements. For measuring thicknesses L11, L3, L8, L4, and L5, for example, a reflectance spectroscopic film thickness analyzer (e.g., F3-CS-NIR, manufactured by Filmetrics Co., Ltd.) is used as a measuring instrument.

[0030] The radio wave reflector 11 may be plastic. Plasticity refers to the property of being able to be deformed by applying external pressure, and retaining the deformed shape even after the force is removed when deformation exceeding the elastic limit is applied by pressurization. All of the synthetic resins constituting the base layer 13, adhesive layer 14, and protective layer 15 may be plastic, or at least one of the base layer 13, adhesive layer 14, and protective layer 15 may be plastic.

[0031] (Structure of the radio wave reflector 11) One embodiment of the radio wave reflector 11 will be described with reference to Figures 2 and 3. The radio wave reflector 11 comprises a conductive thin film layer 16 containing a conductor 12 and a resin that maintains the conductor 12 in a sheet shape. The resin may have a base layer 13 containing a substrate, a protective layer 15 containing a protective material for protecting the conductive thin film layer 16, and an adhesive layer 14 containing an adhesive for bonding the conductive thin film layer 16 and the protective layer 15. In the embodiment shown in Figure 2, the radio wave reflector 11 has the conductive thin film layer 16 laminated on the base layer 13, and the adhesive layer 14 and the protective layer 15 laminated thereon in order.

[0032] In the following explanation, the vertical direction is defined based on Figure 2, and the vertical and horizontal directions are defined based on Figure 3. However, the vertical and vertical directions and vertical and horizontal directions are used for explanatory purposes only and do not define the vertical and vertical directions when the radio wave reflector 11 is in use. Also, Figures 1 to 9 do not represent the actual scale. Furthermore, in Figure 3(A), the adhesive layer 14 and protective layer 15 are omitted from the illustration for a portion of the radio wave reflector 11.

[0033] (Base material layer 13) In this embodiment, the base layer 13 is formed in a square shape when viewed from above. However, it is not limited to this, and may be rectangular, circular, elliptical, sector-shaped, polygonal, three-dimensional, etc., to match the overall shape of the radio wave reflector 11. A sheet made of synthetic resin is used as the base material for the base layer 13. Examples of synthetic resins include one or more selected from the group consisting of PET (polyethylene terephthalate), polyethylene, polypropylene, polyvinyl chloride, polystyrene, polymethyl methacrylate, polyester, polyformaldehyde, polyamide, polyphenylene ether, vinylidene chloride, polyvinyl acetate, polyvinyl acetal, AS resin, ABS resin, acrylic resin, fluororesin, nylon resin, polyacetal resin, polycarbonate resin, polyamide resin, and polyurethane resin. In addition, the thickness L8 of the base layer 13 (length in the vertical direction in Figure 2) is set to 0.13 mm in this embodiment, but it is not limited to this, and can be set appropriately depending on the manner in which the radio wave reflector 11 is used. The base layer 13 may also contain any synthetic resin or other material or any other component in addition to the base material.

[0034] (Conductive thin film layer 16) Preferably, the conductive thin film layer 16 is formed as a thin film on the upper surface of the substrate layer 13, comprising one or more linear conductors 12. Preferably, the conductor 12 is composed of silver (Ag), for example. The conductor 12 may be composed of a metal, metal compound, or alloy having free electrons, and is not limited to silver; for example, it may be gold, copper, platinum, aluminum, titanium, silicon, indium tin oxide, and alloys (for example, alloys containing nickel, chromium, and molybdenum). Examples of alloys containing nickel, chromium, and molybdenum include various grades such as Hastelloy B-2, B-3, C-4, C-2000, C-22, C-276, G-30, N, W, and X.

[0035] In this embodiment, as shown in Figure 3(B), one or more linear conductors 12 are arranged surrounding multiple regions 12a without conductors 12. That is, the conductors 12 and regions 12a without conductors 12 are arranged periodically at predetermined intervals. The interval between adjacent regions 12a without conductors 12 may be equal to the line width L6 of the conductor 12, or it may be greater than the line width L6. Note that "linear" means that the length in the longitudinal direction is 3000 times or more the length in the direction perpendicular to the longitudinal direction. In the example shown in Figure 3(B), the conductors 12 are arranged at equal intervals along the vertical and horizontal directions, and the regions 12a without conductors 12 surrounded by the conductors 12 are square. That is, the regions 12a without conductors 12 are arranged at intervals equal to the line width L6 of the conductors 12. At the intersection where the conductor 12(12A) oriented horizontally and the conductor 12(12B) oriented vertically overlap, the conductors 12A and 12B are electrically conductive. The line width L6 of the conductor 12 is preferably set to 0.05 μm or more and 15 μm or less. The spacing L7 between adjacent conductors 12 along the vertical or horizontal direction (the length of one side of the square area 12a without conductors 12) is set to be greater than the wavelength of visible light and less than the wavelength of radio waves reflected by the radio wave reflector 11, and in this example, it is set to 2 μm or more and 10 cm or less. More preferably 20 μm or more and 1 cm or less, and even more preferably 25 μm or more and 1 mm or less. Even more preferably 30 μm or more and 250 μm or less.

[0036] Furthermore, the thickness (film thickness) L3 of the conductor 12 is preferably such that it is transparent to visible light. The thickness L3 of the conductor 12 is preferably 0.02 μm or more and 10 μm or less. From the viewpoint of ensuring appropriate radio wave intensity, the thickness L3 is preferably 5 nm or more.

[0037] The surface roughness Sa of the conductor 12 is not particularly limited, but is preferably 1 μm or more and 7 μm or less, and more preferably 1.03 μm or more and 6.72 μm or less. A surface roughness Sa within this range makes it easier to diffusely reflect radio waves.

[0038] The surface roughness Sa is determined by the arithmetic mean height according to ISO 25178 and measured in accordance with ISO 25178. The surface roughness Sa of the conductor 12 can be determined by measuring the surface roughness at multiple locations on the surface of the conductor 12 using a laser microscope (product name VK-X1000 / 1050, manufactured by Keyence Corporation, or an equivalent product) and calculating the average value of the obtained measurements. In some cases, the conductor 12 and the substrate layer 13 may be the targets of measurement. In this embodiment, there are multiple conductors 12, and the surface roughness is measured at multiple locations on each conductor 12, and the average value of these measurements is taken as the surface roughness Sa of the conductor 12.

[0039] The conductive thin film layer 16 preferably has a coverage rate of 36% or more and 46% or less. Coverage rate refers to the ratio of the area occupied by the conductor 12 per unit area in a plan view. In the embodiments shown in Figures 2 and 3, it refers to the ratio of the area of ​​the conductor 12 in a plan view to the area of ​​the substrate layer 13 in a plan view. Coverage rate can also be said to be the area of ​​the substrate layer 13 covered by the conductor 12 relative to the area of ​​the substrate layer 13 in a plan view. Coverage rate is measured using a scanning electron microscope (SEM), transmission electron microscope (TEM), optical microscope, etc.

[0040] In the arrangement of conductors 12 shown in Figure 3(B), the shape of the region 12a without conductors 12 is square. However, for example, the spacing between adjacent laterally extending conductors 12A and the spacing between adjacent vertically extending conductors 12B may be different, and the shape of the region 12a without conductors 12 may be rectangular. Furthermore, the conductors 12 may be arranged in the arrangement patterns shown in Figures 4(A) to (E). In Figure 4(A), multiple conductors 12A are arranged laterally and vertically with predetermined spacings, and multiple vertically extending conductors 12B are arranged in a staggered pattern between vertically adjacent conductors 12A. A staggered arrangement refers to a state in which multiple conductors 12B extending in the vertical direction are arranged horizontally at predetermined intervals, and the multiple conductors 12B forming one row are located between the multiple conductors 12B forming the adjacent row in the vertical direction of that row, and the conductors 12B in skipped rows are arranged in a straight line. In Figure 4(B), the conductor 12A extends horizontally, and the conductors 12B and 12C extend along diagonal directions that are symmetrically tilted with respect to the horizontal direction, and the conductors 12B and 12C intersect each other on the conductor 12A. As a result, the shape of the region 12a without conductors 12 is an equilateral triangle. Note that the shape of the region 12a without conductors 12 may not be an equilateral triangle, but an isosceles triangle or a triangle with three sides of different lengths. In Figure 4(C), hexagonal regions 12a without conductors 12, surrounded by linear conductors 12, are periodically arranged. In Figure 4(D), pentagonal regions 12a without conductors 12, surrounded by linear conductors 12, are periodically arranged. In Figure 4(E), circular regions 12a without conductors 12, surrounded by linear conductors 12, are periodically arranged. Note that Figures 4(A) to (E) only show the conductors 12.

[0041] Examples of methods for manufacturing the conductive thin film layer 16 having the arrangement patterns shown in Figures 3(B) and 4 include the following: a method in which a conductive film is formed, a pattern is formed by etching, and the conductive thin film having the pattern is removed; a method in which a photosensitive resist is coated onto a base film having a lift-off layer, a pattern is formed by photolithography, a conductor is filled into the patterned area, and then the conductive thin film having the pattern is removed. However, the manufacturing method is not limited to the above, and in forming the conductive thin film layer 16, methods such as bonding a metal thin film or depositing metal can be used.

[0042] (Other embodiments of the conductive thin film layer 16) Figure 5 shows another embodiment of the conductive thin film layer 16. In the embodiment of Figure 5, a plurality of conductors 12 are periodically arranged on the upper surface of the substrate layer 13 in a sheet shape (thin film). In this embodiment, circular conductors 12 are used in a plan view. The diameter L1 and the shortest distance (spacing) L2 between adjacent conductors 12 are set according to the frequency band of the radio waves to be reflected. In this embodiment, in particular, it is set to reflect radio waves in the frequency band of 20 GHz or more and 300 GHz or less, which is related to the fifth-generation mobile communication system (5G). However, it is not limited to this, and the diameter L1 and spacing L2 may be set so that the conductors 12 reflect radio waves with frequencies of 3 GHz or more and 300 GHz or less. The diameter L1 of each conductor 12 may be 0.7 mm or more and 800 mm or less, and the spacing L2 may be 1 μm or more and 1000 μm or less. The number of conductors 12 is set appropriately according to the size (area) of the substrate layer 13. A sheet shape refers to a shape in which the length in the longitudinal direction is approximately the same as, or less than 3000 times, the length in the direction perpendicular to the longitudinal direction.

[0043] The shape of the conductor 12 is not limited to a circle, but may be any shape. Preferably, the shape is such that the sides of one conductor 12 are parallel to the sides of adjacent conductors 12, and the spacing between a given conductor 12 and all adjacent conductors 12 is equal, allowing for periodic arrangement. For example, it may be a square, rectangle, triangle, hexagon, etc. In this case, the length of the shortest side of the conductor 12, the shortest distance between a vertex of the conductor 12 and the opposite side, or the shortest distance between a certain side and the opposite side may be set to 0.005 μm or more and 100 mm or less. More preferably, it may be set to 0.1 μm or more and 1000 μm or less. The other configurations and operations are the same as those of the embodiments shown in Figures 2 and 3, so detailed explanations are omitted by using the same reference numerals for corresponding components.

[0044] (Other embodiments of the conductive thin film layer 16) The conductive thin film layer 16 may have, for example, a metamaterial structure. The metamaterial structure consists of sheet-shaped conductors 12, which are dielectrics, arranged periodically in equal proportions. This periodic arrangement structure gives it a negative dielectric constant and reflects radio waves belonging to a specific frequency band determined based on the periodic interval. The shape of each conductor 12 is not limited and may be as described above, but for example, as shown in Figure 6, each conductor 12 may be square-shaped. The length of one side L12 and the spacing L13 between adjacent conductors 12 may be set so that the conductors 12 reflect radio waves with frequencies of 3 GHz or more and 300 GHz or less. In this case, the length of one side L12 of the conductor 12 may be 0.7 mm or more and 800 mm or less, and the spacing L13 may be 1 μm or more and 1000 μm or less. The thickness L3 of the conductor 12 is preferably 350 nm (0.35 μm) or less, more preferably 100 nm or less, and even more preferably 50 nm or less. The number of conductors 12 is set appropriately according to the size (area) of the substrate layer 13. In one example, four conductors 12 may be formed on the substrate layer 13, two vertically and two horizontally, according to the size of the substrate layer 13. In this case, the length L12 of one side of each conductor 12 is set to 77.460 mm, the spacing L13 between adjacent conductors 12 is set to 100 μm, and the thickness L3 is set to 350 nm (0.35 μm) or less.

[0045] (adhesive layer 14) The adhesive layer 14 adheres the protective layer 15 to the base layer 13 and the conductive thin film layer 16, and is composed of an adhesive. The adhesive layer 14 has a size corresponding to the base layer 13 in a plan view. As the adhesive for the adhesive layer 14, adhesive sheets made of synthetic resin or rubber are used. Examples of synthetic resins include acrylic resin, silicone resin, and polyvinyl alcohol resin. The thickness L4 of the adhesive layer 14 is preferably set to 5 μm or more and 500 μm or less. In addition to the adhesive, the adhesive layer 14 may also contain any synthetic resin or other substance or any component.

[0046] The adhesive layer 14 is preferably made of a synthetic resin material with a dielectric loss tangent (tanδ) of 0.018 or less. A lower dielectric loss tangent is preferable, but it is usually 0.0001 or higher. The dielectric loss tangent represents the degree of electrical energy loss within the dielectric material; materials with a larger dielectric loss tangent result in greater electrical energy loss. By using an adhesive layer 14 with a dielectric loss tangent of 0.018 or less, the loss of electrical energy of radio waves in the radio wave reflector 11 is reduced, and the reflection intensity can be increased.

[0047] Furthermore, it is preferable that the synthetic resin material of the adhesive layer 14 has a relative permittivity that changes depending on the frequency of the electric field. Relative permittivity is the ratio of the permittivity of the medium (synthetic resin material in this embodiment) to the permittivity of vacuum. By changing the relative permittivity in response to the electric field, the intensity of reflected waves at electric fields of specific frequencies can be increased. It is preferable that the relative permittivity changes between 2.0 and 9. The inductive loss tangent and relative permittivity are measured using a measuring device (for example, Toyo Technica, model TTPX tabletop cryogenic prober, material impedance analyzer MIA-5M) by known methods (for example, cavity resonator method, coaxial resonator method).

[0048] Furthermore, not only the adhesive layer 14, but also the synthetic resin materials constituting the base layer 13 and the protective layer 15 may have a dielectric loss tangent of 0.018 or less, and their relative permittivity may change depending on the electric field.

[0049] (Protective layer 15) The protective layer 15 has a size corresponding to the base layer 13 in a plan view and protects the conductor 12, and is composed of a protective material. As the protective material for the protective layer 15, for example, a sheet (film) of multilayer insulation (MLI) can be used. Examples of materials that can be used for multilayer insulation include polyimide, fluoropolymer, and polypropylene, but are not limited to these materials. The use of these materials improves durability in outer space. The thickness L5 of the protective layer 15 is preferably set to 0.02 mm or more and 0.30 mm or less. In addition to the protective material, the protective layer 15 may also contain any synthetic resin or other substance or any component.

[0050] (Other embodiments) Figure 7 shows another embodiment of the present invention. The radio wave reflector 11 shown in Figure 7 is formed by laminating conductive materials 12A and 12B in two layers vertically using resin substrate layers 13A and 13B. Each conductive material 12A formed on the substrate layer 13A and each conductive material 12B formed on the substrate layer 13B are aligned and laminated so as to overlap when viewed from above. Note that the arrangement patterns of the conductive thin film layers 16A and 16B in Figure 7 do not necessarily have to overlap when viewed from above, and the conductive thin film layers 16A and 16B may be formed in different arrangement patterns. The lower surface of the substrate layer 13B is attached to the conductive material 12A by adhesive layer 14A, and a protective layer 15 is attached to the conductive material 12B by adhesive layer 14B. In this embodiment, the Young's modulus is preferably 0.01 GPa or more and 80 GPa or less, and the thickness of the radio wave reflector is preferably 0.01 mm or more and 0.5 mm or less. The total light transmittance of the radio wave reflector 11 is 70%.

[0051] Radio waves incident on the radio wave reflector 11 are reflected by the first layer of conductor 12B, but some pass through the conductor 12B without being reflected. These radio waves that pass through the conductor 12B are reflected by the second layer of conductor 12A. In this way, by stacking multiple layers of conductor 12 in the vertical direction, radio waves that have passed through the upper layer of conductor 12B can be reflected by the lower layer of conductor 12A, and the reflection intensity of the radio wave reflector 11 can be kept higher than when there is only one layer of conductor 12. In addition, the kurtosis of the reflection intensity distribution in the angular range α of ±15 degrees with respect to the normal reflection direction of radio waves can be further reduced, and the difference in reflection intensity depending on the angular position within the angular range α becomes smaller. Furthermore, since two adhesive layers 14A and 14B are used, the dielectric loss tangent value becomes even smaller than in the embodiment shown in Figure 2, and the reflection intensity can be kept even higher. The other configurations and operations are the same as in the embodiments shown in Figures 2 and 3, so detailed explanations are omitted by assigning the same reference numerals to the corresponding components.

[0052] In the embodiment shown in Figure 7, the conductor 12 formed on the base layer 13 is laminated in two layers, but it may be laminated in three or more layers. Increasing the number of laminated conductors 12 increases the reflectivity, but the overall thickness of the radio wave reflector 11 increases, reducing its flexibility and visible light transmittance. For this reason, the number of laminates should be set appropriately according to the intended use, for example, by increasing the number of laminates when the radio wave reflector 11 is to be installed in a location where flexibility or transparency is not particularly required.

[0053] (Other embodiments) Figure 8 shows another embodiment of the radio wave reflector 11. In the embodiment of Figure 8, a conductive thin film layer 16 and a substrate layer 13 are provided, which are composed of a plurality of linear conductors 12, similar to the embodiments shown in Figures 2 and 3, but the adhesive layer 14 and protective layer 15 are not provided. In this embodiment, the flexural modulus is preferably 0.05 GPa or more and 4 GPa or less, the Young's modulus is preferably 0.01 GPa or more and 80 GPa or less, and the thickness of the radio wave reflector is preferably 0.01 mm or more and 0.5 mm or less. The total light transmittance of the radio wave reflector 11 is 70%. The other configurations and operations are the same as in the embodiments shown in Figures 2 and 3, so detailed explanations are omitted by assigning the same reference numerals to the corresponding components.

[0054] In the embodiment shown in Figure 8, the conductive thin film layer 16 is composed of a plurality of linear conductors 12. However, the conductive thin film layer 16 is not limited to this embodiment. For example, a single sheet-shaped dielectric conductor 12 may be formed in a square shape over substantially the entire upper surface of the substrate layer 13. In this case, the coverage rate is defined as the ratio of the area occupied by the conductor 12 per unit area in the portion of the substrate layer 13 on which the conductive thin film layer 16 is provided, and the coverage rate is 100%. Note that in a plan view, the size of the conductor 12 is slightly smaller than the size of the substrate layer 13, and the conductor 12 does not have to be formed in a region close to the side edge of the substrate layer 13.

[0055] Furthermore, the conductive thin film layer 16 in the embodiment shown in Figure 8 may be formed by periodically arranging multiple sheet-like conductors 12 in an equal arrangement, similar to the conductive thin film layer 16 in the embodiment shown in Figure 6. In this case, the multiple conductors 12 are arranged at predetermined intervals across substantially the entire upper surface of the substrate layer 13. The shape of the conductors 12 may be square, circular, rectangular, triangular, polygonal, or the like. The conductive thin film layer 16 may also have a metamaterial structure.

[0056] (use) Figure 9 illustrates a state in which a radio wave reflector according to one embodiment is applied to the reflective surface of a reflector antenna.

[0057] The illustrated reflector antenna 30 comprises a primary radiator 32 positioned at the focal point of a curved reflector surface 31, and a waveguide 33 that guides radio waves to the primary radiator 32. In one embodiment, the radio wave reflector 11 is provided on the curved reflector surface 31 of the reflector antenna 30. By configuring the reflector surface 31 of the reflector antenna 30 using the radio wave reflector 11, the reflector antenna 30 can resonate and reflect radio waves in a frequency-specific manner, and the amount of metal used in the material is reduced compared to a reflector antenna of the type that uses a metal reflector. As a result, the reflector antenna 30 is lighter, reducing the weight burden during launch and making it suitable for installation in space.

[0058] In this embodiment, the reflector antenna 30 is a parabolic antenna, but a reflector antenna constructed using the radio wave reflector 11 only needs to have a curved reflector surface, and the reflector antenna may be a Gregorian antenna using a subreflector instead of the parabolic antenna exemplified. [Explanation of symbols]

[0059] 11. Radio wave reflector 11a Reflection point 12, 12A, 12B conductors 13, 13A, 13B base material layer 14, 14A, 14B adhesive layer 15 Protective layer 16 Conductive thin film layer 20 Radio wave sources 21 Receiving unit 30 Reflector Antenna 31. Curved reflective mirror surface 32 Primary radiator 33 Waveguide L1 Diameter of the conductor L2: Distance between adjacent conductors L3 Thickness of the conductor L4 thickness of the adhesive layer L5 Protective layer thickness L6 Conductor line width L7 Distance between adjacent conductors L8 substrate layer thickness L10 Length of one side of the radio wave reflector L11 Thickness of the radio wave reflector

Claims

1. It is a radio wave reflector that is attached to the curved reflective surface of a reflecting antenna. A radio wave reflector having a conductive thin film layer with a structure in which conductors are periodically arranged to reflect radio waves, thereby reflecting radio waves in a frequency-specific manner.

2. The radio wave reflector according to claim 1, wherein the thickness of the conductive thin film layer is 0.02 μm or more and 10 μm or less, and the proportion of the area covered by the conductive thin film layer in a plan view is 36% or more and 46% or less.

3. The radio wave reflector according to claim 1, further comprising a substrate layer including a substrate for holding the conductive thin film layer.

4. A dielectric layer with a dielectric constant of 2.0 or more and 9 or less is laminated on the surface of the conductive thin film layer, A protective layer laminated on the surface of the dielectric layer, The radio wave reflector according to claim 1, further comprising the features described above.

5. The radio wave reflector according to claim 1, wherein the flexural modulus is 0.05 GPa or more and 4 GPa or less.

6. A reflector antenna having a radio wave reflector according to any one of claims 1 to 5 on its reflective surface.

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