Radio wave reflector

Abstract

Provided is a radio wave reflector that is designed to reflect radio waves in a desired frequency band with little loss. A radio wave reflector 11 comprises first and second electroconductive layers 16, 17 that include a conductor 12, and a dielectric base material layer 13 that supports the first and second electroconductive layers 16, 17. The first electroconductive layer 16, the dielectric base material layer 13, and the second electroconductive layer 17 are layered in the stated order. The radio wave reflector 11 reflects radio waves at a reflection angle α2 that is different from an incident angle α1. A base material design coefficient Db=t･√ε / λ is defined, where λ is the wavelength of the reflected radio waves, t is the thickness of the dielectric base material layer 13, and ε is the relative dielectric constant of the dielectric base material layer 13. The base material design coefficient Db of the radio wave reflector 11 satisfies the relationship 0.02≤Db≤0.9.

Description

Radio wave reflector

[0001] The present invention relates to a radio wave reflector.

[0002] Mobile phones and wireless communications use radio waves in the frequency band of approximately 3 GHz to 300 GHz, known as centimeter waves or millimeter waves. These short-wavelength radio waves tend to travel in a straight line, and if there is an obstacle between the transmitting antenna and the receiving antenna, the radio waves have difficulty circumventing the obstacle and reaching the receiving antenna. For this reason, reflectors are installed on the surfaces of buildings, such as the walls, floors, ceilings, and pillars of buildings (hereinafter referred to as "walls, etc."), to allow radio waves to reach blind spots where they cannot reach.

[0003] When a metal plate such as aluminum is used as a reflector, the incident angle and reflection angle of the metal plate are constant, so in order to deliver radio waves to blind spots, the metal plate must be accurately installed at the optimal position and angle, which makes installation difficult. For this reason, Patent Document 1 proposes a reflector with different incident and reflection angles for radio waves. By designing the reflection angle of the reflector to match the angle and position of the wall on which the reflector is installed, it becomes easier to install the reflector on the wall, etc.

[0004] Japanese Patent Application Laid-Open No. 2015-46821

[0005] Even in such a reflector that performs polarized reflection, it is desired that radio waves of a desired frequency be reflected with as little reflection loss as possible.

[0006] The present invention has been made in light of the above-mentioned problems, and has as its object to provide a radio wave reflector designed to reflect radio waves of a desired frequency with less reflection loss.

[0007] To achieve the above object, the present invention includes the following subject matter.

[0008] Item 1: A radio wave reflector comprising first and second conductive layers each containing a conductor, and a dielectric substrate layer supporting the first and second conductive layers, wherein the first conductive layer, the dielectric substrate layer, and the second conductive layer are laminated in this order, the radio wave reflector reflects radio waves at a reflection angle different from the angle of incidence, and where λ is the wavelength of the reflected radio waves, t is the thickness of the dielectric substrate layer, and ε is the relative dielectric constant of the dielectric substrate layer, a substrate design coefficient Db=t√ε / λ is defined, and the substrate design coefficient Db satisfies 0.02≦Db≦0.9.

[0009] Item 2: The radio wave reflector according to Item 1, wherein the substrate design coefficient Db is 0.02≦Db≦0.03.

[0010] Item 3: The radio wave reflector according to Item 1, wherein the substrate design coefficient Db is 0.09≦Db≦0.9.

[0011] Clause 4: A radio wave reflector comprising first and second conductive layers each containing a conductor, and a dielectric substrate layer supporting the first and second conductive layers, wherein the first conductive layer, the dielectric substrate layer, and the second conductive layer are laminated in this order, the radio wave reflector reflects radio waves at a reflection angle different from the angle of incidence, and wherein, assuming that the wavelength of the reflected radio waves is λ, the thickness of the dielectric substrate layer is t, and the dielectric substrate layer is a layer made of PET, a PET substrate design coefficient Dbp=t / λ is defined, and the PET substrate design coefficient Dbp satisfies 0.01≦Dbp≦0.48.

[0012] Clause 5: A radio wave reflector comprising first and second conductive layers each containing a conductor, and a dielectric substrate layer supporting the first and second conductive layers, wherein the first conductive layer, the dielectric substrate layer, and the second conductive layer are laminated in this order, the radio wave reflector reflects radio waves at a reflection angle different from the angle of incidence, and wherein, assuming that the wavelength of the reflected radio waves is λ, the thickness of the dielectric substrate layer is t, and the dielectric substrate layer is a layer made of FR4, an FR4 substrate design coefficient Dbf=t / λ is defined, and the FR4 substrate design coefficient Dbf satisfies 0.0095≦Dbf≦0.43.

[0013] Clause 6: A radio wave reflector comprising first and second conductive layers each containing a conductor, and a dielectric substrate layer supporting the first and second conductive layers, wherein the first conductive layer, the dielectric substrate layer, and the second conductive layer are laminated in this order, the radio wave reflector reflects radio waves at a reflection angle different from the angle of incidence, and where the wavelength of the reflected radio waves is λ, the thickness of the dielectric substrate layer is t, and the dielectric substrate layer is a layer made of glass, a glass substrate design coefficient Dbg=t / λ is defined, and the glass substrate design coefficient Dbg satisfies 0.0085≦Dbg≦0.39.

[0014] Clause 7: A radio wave reflector comprising first and second conductive layers each containing a conductor, and a dielectric substrate layer supporting the first and second conductive layers, wherein the first conductive layer, the dielectric substrate layer, and the second conductive layer are laminated in this order, the radio wave reflector reflects radio waves at a reflection angle different from the angle of incidence, and where the wavelength of the reflected radio waves is λ, the thickness of the dielectric substrate layer is t, and the dielectric substrate layer is a layer made of silicon, a silicon substrate design coefficient Dbs=t / λ is defined, and the silicon substrate design coefficient Dbs satisfies 0.005≦Dbs≦0.26.

[0015] Item 8: The radio wave reflector according to any one of Items 1 to 7, wherein the first conductive layer includes a plurality of reflecting elements of two or more different types, and the different types of reflecting elements have different differences in the phase of the radio wave incident on the reflecting element and the phase of the radio wave reflected from the reflecting element.

[0016] According to the present invention, it is possible to provide a radio wave reflector designed to reflect radio waves in a desired frequency band with little loss.

[0017] It is a cross-sectional view showing a part of a radio wave reflector according to one embodiment of the present invention. It is a plan view showing a part of a radio wave reflector. It is a flowchart showing a design method of a dielectric substrate layer. It is an explanatory diagram of the incident angle and reflection angle of a radio wave incident on and reflected from a radio wave reflector.

[0018] (Overall Configuration of Radio Wave Reflector 11) An embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a partial cross-sectional view of a radio wave reflector 11 according to an embodiment of the present invention, and Fig. 2 is a partial plan view of the radio wave reflector 11.

[0019] In this specification, the incident angle α1 is the angle between the incident direction of the incident wave when it enters the radio wave reflector 11 (for example, as shown by arrow A1 in FIG. 4) and the direction in which the normal to the reflecting surface of the radio wave reflector 11 extends (for example, as shown by arrow A2 in FIG. 4). The reflection angle α2 is the angle between the reflection direction of the reflected wave (for example, as shown by arrow A3 in FIG. 4) and the normal to the reflecting surface. The normal refers to a straight line that is perpendicular to the tangent (or tangent plane) at the reflection point.

[0020] The incident wave is reflected by the radio wave reflector 11 as a reflected wave at a reflection angle α2. Reflection at a reflection angle α2 that is the same as the incident angle α1 is called "specular reflection." The direction in which the specularly reflected reflected wave travels is called the "specular reflection direction." Reflection at a reflection angle α2 that is a desired angle different from the incident angle α1 is called "polarized reflection." The direction in which the reflected wave that is polarized reflected at the desired reflection angle α2 travels is called the "polarized reflection direction."

[0021] In the example of Fig. 4, the incident angle α1 of the incident wave is 60 degrees. In the case of specular reflection, the reflected wave is reflected at a reflection angle α2 that is the same as the incident angle α1, i.e., in Fig. 4, in the direction of arrow A3 where the reflection angle α2 is 60 degrees. In the case of polarized reflection, the reflected wave is reflected at a desired reflection angle α2 that is different from the incident angle α1, i.e., in Fig. 4, in the direction of arrow A2 where the desired reflection angle α2 is 0 degrees.

[0022] The radio wave reflector 11 of this embodiment polarizes and reflects incident radio waves at a desired reflection angle α2.

[0023] The radio wave reflector 11 of this embodiment reflects radio waves output from a radio wave generating source 100. The reflected waves are received by a receiving unit 101. The radio wave generating source 100 is a communication device or the like having a transmitting antenna capable of transmitting radio waves. The receiving unit 101 is a device capable of receiving radio waves. The receiving unit 101 of this embodiment is a communication device having a receiving antenna. Examples of communication devices include smartphones, mobile phones, tablet terminals, laptop computers, portable game consoles, repeaters, radios, and televisions.

[0024] The shape of the radio wave reflector 11 in a planar view is not limited, but is preferably, for example, a square with a side length of 20 cm or more and 400 cm or less. Radio waves with frequencies of 3 GHz or more and 300 GHz or less attenuate with distance, but in order to reflect the waves with sufficient strength at all points within a practical distance from the radio wave source, the side length is preferably 20 cm or more. The upper limit of the side length is not particularly limited, but from a manufacturing perspective, 400 cm or less is preferable. The overall shape of the radio wave reflector 11 is not limited to a square and may be a rectangle or a polygon such as a triangle, pentagon, or hexagon. In this 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. When the overall shape of the radio wave reflector 11 is elliptical, the minor axis is set to 20 cm or more and 400 cm or less. When the overall shape of the radio wave reflector 11 is fan-shaped, the length of the shorter side of the arc or radius is set to 20 cm or more and 400 cm or less. Furthermore, the overall shape of the radio wave reflector 11 may be a three-dimensional shape such as a cylindrical or conical shape. The shape and size of the radio wave reflector 11 are selected appropriately depending on the manner in which the radio wave reflector 11 is used.

[0025] It is preferable that the thickness L1 of the radio wave reflector 11 is set to 1 mm or less. The thickness L1 of the radio wave reflector 11 is set to a thickness that allows the radio wave reflector 11 to be flexible and that prevents force from concentrating on the conductor 12 when an external force is applied to the radio wave reflector 11 to bend it.

[0026] (Structure of Radio Wave Reflector 11) The radio wave reflector 11 includes a first conductive layer 16 including a conductor 12, a dielectric substrate layer 13 supporting the first conductive layer 16, and a second conductive layer 17 including a conductor, on the surface of the dielectric substrate layer 13 opposite the surface on which the first conductive layer 16 is provided. In the embodiment shown in FIG. 1 , the first conductive layer 16, the dielectric substrate layer 13, and the second conductive layer 17 are stacked in this order. Radio waves are incident on the first conductive layer 16 side and are reflected. Although not shown, a protective layer for protecting the first conductive layer 16 may be provided on the surface of the first conductive layer 16 opposite the dielectric substrate layer 13 (the upper side of FIG. 1 ) and on the surface of the second conductive layer 17 opposite the dielectric substrate layer 13 (the lower side of FIG. 1 ). Furthermore, an adhesive layer made of an adhesive may be provided between the protective layer and the first conductive layer 16 and the second conductive layer 17 to bond the protective layer to the first conductive layer 16 and the second conductive layer 17.

[0027] (First conductive layer 16) The first conductive layer 16 includes a plurality of reflective elements 20A-20C of two or more different types. Each of the reflective elements 20A-20C includes a thin-film conductor 12 formed in a predetermined shape in plan view on the upper surface of the dielectric base layer 13. The first conductive layer 16 is formed by periodically arranging these different types of reflective elements 20A-20C in a line on the dielectric base layer 13, which is formed in a sheet shape.

[0028] The difference between the phase of the radio wave incident on the reflective elements 20A to 20C and the phase of the radio wave reflected from the reflective elements 20A to 20C (hereinafter also referred to as the "phase difference" or "phase difference of the reflective elements 20A to 20C") is determined according to the shapes and the like of the reflective elements 20A to 20C. Different types of reflective elements 20A to 20C refer to reflective elements 20A to 20C that are designed to have different phase differences for each type. In the example shown in Figures 1 and 2, the first conductive layer 16 includes three types of reflective elements 20A to 20C.

[0029] The radio waves incident on (or reflected from) the reflecting elements 20A to 20C refer to the radio waves incident on (or reflected from) the areas of the radio wave reflector 11 that include each of the reflecting elements 20A to 20C in a planar view.

[0030] As a result, the radio wave reflector 11 polarizedly reflects an incident wave incident at an incident angle α1, i.e., reflects a reflected wave at a desired reflection angle α2 different from the incident angle α1. Note that, for the sake of explanation, only three types of reflecting elements 20A to 20C that constitute one unit are shown in Figures 1 and 2. Also, the two-dot chain lines in Figures 1 and 2 are virtual lines that define the boundary of the reflecting element 20A. The conductors 12 of adjacent reflecting elements 20A may be continuous and integral.

[0031] 2, each of the reflective elements 20A to 20C is made up of a conductor 12 and an area 12a surrounded by the conductor 12 and not containing the conductor 12. When viewed from above, the reflective elements 20A to 20C are different in the shapes of the conductor 12 and the area 12a not containing the conductor 12.

[0032] The configuration of the multiple reflective elements 20A to 20C of the first conductive layer 16 is not limited to the example in Fig. 2, and any configuration may be used as long as it can differentiate the phases of the reflected waves reflected by each of the reflective elements 20A to 20C. For example, the phase differences of the reflected waves of different types of reflective elements 20A to 20C may be differentiated by varying the material, thickness, shape, and size of the conductors 12 constituting each of the reflective elements 20A to 20C, and the shape and size of the regions 12a without the conductors 12.

[0033] Each unit of the reflective elements 20A to 20C may contain two or more types of reflective elements 20A to 20C, and may contain a plurality of the same type of reflective elements 20A to 20C. Also, each unit of the reflective elements 20A to 20C may be of a plurality of types, and each unit may contain different types of reflective elements 20A to 20C.

[0034] The shape, size, and arrangement of the conductors 12 and the regions 12a without conductors 12 may be arbitrary. For example, conductors 12 of any shape, such as rectangular, circular, elliptical, triangular, or polygonal, and regions 12a without conductors 12 between the conductors 12 may be periodically arranged. Furthermore, for example, multiple linear conductors 12 may be arranged vertically and horizontally in a lattice pattern, or may be arranged to form a rectangular, circular, elliptical, triangular, polygonal, or other contour. In this case, the linear conductors 12 surround regions 12a without conductors 12 of any shape, such as square, rectangular, circular, elliptical, triangular, or polygonal. The term "linear" means that the longitudinal length is 3000 times or more the length in the direction perpendicular to the longitudinal direction.

[0035] The reflecting elements 20A to 20C are appropriately selected depending on the frequency and intensity of the radio waves to be absorbed. For example, the planar shape may be any shape such as a rectangle, a circle, an ellipse, a triangle, or a polygon.

[0036] Furthermore, the thickness L3 of the first conductive layer 16, i.e., the thickness (film thickness) L3 of the reflective elements 20A to 20C, is preferably thick enough to transmit visible light. The thickness L3 of the reflective elements 20A to 20C is preferably 0.05 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 conductor 12 is preferably made of, for example, silver. However, the conductor 12 of the first conductive layer 16 may be made of any metal, metal compound, or alloy having free electrons, and is not limited to silver. For example, gold, copper, platinum, aluminum, titanium, silicone, indium tin oxide, and alloys (e.g., alloys containing nickel, chromium, and molybdenum) may also be used. Examples of alloys containing nickel, chromium, and molybdenum include various grades of Hastelloy B-2, B-3, C-4, C-2000, C-22, C-276, G-30, N, W, and X.

[0038] The first conductive layer 16 can be fabricated, for example, by forming a conductive film, etching it to form a pattern, and then extracting a conductive thin film having the pattern. Another example is a method in which a photosensitive resist is applied to a base film having a lift-off layer, a pattern is formed by photolithography, the patterned portion is filled with a conductor 12, and then the conductive thin film having the pattern is extracted. The fabrication method is not limited to the above, and examples of methods for forming the first conductive layer 16 include a method of adhering a metal thin film and a method of vapor-depositing a metal.

[0039] (Dielectric substrate layer 13) The dielectric substrate layer 13 is a sheet-like member on whose upper surface the first conductive layer 16 is formed. The term "sheet" refers to a shape in which the thickness of the object is 10% or less of the maximum length between the outer edges in a planar view. When the shape in a planar view is rectangular, the "maximum length between the outer edges in a planar view" refers to the length of the diagonal. When the shape in a planar view is circular, the "maximum length between the outer edges in a planar view" refers to the length of the diameter. In this specification, the term "sheet" also includes membranes, foils, films, etc.

[0040] The dielectric substrate layer 13 is made of materials such as PET (polyethylene terephthalate), FR4 (glass fiber cloth impregnated with epoxy resin and heat-cured to form a plate), glass, silicon, etc. Alternatively, synthetic resins may be used, examples of which include one or more selected from the group consisting of 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.

[0041] The dielectric substrate layer 13 has an outer shape that is square in plan view, but is not limited to this and may have a rectangular, circular, elliptical, sectorial, polygonal, three-dimensional, or other shape that matches the overall shape of the radio wave reflector 11.

[0042] (Second Conductive Layer 17) The second conductive layer 17 is composed of a single thin film conductor having a size corresponding to the dielectric substrate layer 13, and the conductor is, for example, a thin film of a metal such as aluminum or copper. The second conductive layer 17 reflects radio waves that have passed through the first conductive layer 16 and the dielectric substrate layer 13. The second conductive layer 17 is fabricated on the surface of the dielectric substrate layer 13 opposite to the surface on which the first conductive layer 16 is provided, using the same fabrication method as the first conductive layer. The thickness L11 of the second conductive layer 17 is preferably 0.05 μm or more and 10 μm or less. From the viewpoint of ensuring appropriate radio wave intensity, the thickness L11 is preferably 0.5 nm or more.

[0043] The second conductive layer 17 is not limited to the above configuration, and may be made of a metal plate having a size corresponding to that of the dielectric substrate layer 13 .

[0044] (Substrate Design Coefficient) When the wavelength of the reflected radio wave is λ (mm), the thickness of the dielectric substrate layer 13 is t (mm), and the relative permittivity of the dielectric substrate layer 13 is ε, Equation 1-1 is defined as the substrate design coefficient Db: Db=t·√ε / λ (Equation 1-1) where √ε represents the square root of ε. In this case, the substrate design coefficient Db of the radio wave reflector 11 satisfies the following: 0.02≦Db≦0.9 (Equation 1-2)

[0045] The method for designing the dielectric substrate layer 13 of the radio wave reflector 11 is as follows. First, a step of determining the wavelength λ is performed (Step S1). Since the wavelength λ is determined by the frequency of the radio wave, the frequency of the desired radio wave to be reflected by the radio wave reflector 11 is determined. This determined frequency is also referred to as the "corresponding frequency f." Next, a step of determining the material of the dielectric substrate layer 13 is performed (Step S2). This determines the relative permittivity ε. Then, a step of determining the thickness t of the dielectric substrate layer 13 is performed (Step S3). The thickness t of the dielectric substrate layer 13 is set within a range in which the substrate design coefficient Db satisfies Equation 1-2. Typically, a thinner radio wave reflector 11 is easier to handle during installation and also increases the reflection intensity, so the thickness t of the dielectric substrate layer 13 is set as thin as possible. The shape and size of the radio wave reflector 11 in a planar view are arbitrary.

[0046] The steps of determining the wavelength λ, determining the material of the dielectric substrate layer 13, and determining the thickness t of the dielectric substrate layer 13 may be performed in any order. For example, depending on the installation location of the radio wave reflector 11, it may be difficult to install the radio wave reflector 11 if the thickness L1 of the radio wave reflector 11 is large. In such a case, in order to make the dielectric substrate layer 13 as thin as possible, the step of determining the thickness t of the dielectric substrate layer 13 may be performed first, then the wavelength λ may be determined, and finally a material for the dielectric substrate layer 13 having a relative permittivity ε that satisfies Expression 1-2 may be determined.

[0047] In order for the radio wave reflector 11 to have sufficient reflection strength, the substrate design coefficient Db is preferably 0.19 or more and 0.76 or less, and more preferably 0.19 or more and 0.57 or less.

[0048] In this way, by designing the radio wave reflector 11 so that the base material design coefficient Db shown in Equation 1-1 falls within the range of Equation 1-2, it is possible to easily design a radio wave reflector 11 that reflects radio waves of the corresponding frequency f with sufficient reflection intensity. At this time, it is assumed that the reflection angle α2 of the reflected wave from the radio wave reflector 11 is designed to be a desired angle.

[0049] Furthermore, the range of radio wave frequencies that the radio wave reflector 11 can reflect with sufficient reflection intensity varies depending on the substrate design coefficient Db.

[0050] The substrate design coefficient Db may be designed to satisfy the following relationship: 0.02≦Db≦0.03 (Formula 1-3). In this case, the radio wave reflector 11 is designed to reflect radio waves of the corresponding frequency f in the direction of the reflection angle α2, and to avoid reflecting radio waves of frequencies other than the corresponding frequency f in the direction of the reflection angle α2 as much as possible. The radio wave reflector 11 can reflect radio waves with sufficient reflection strength in the frequency range of 0.994×f (GHz) or more and 1.006×f (GHz).

[0051] The substrate design coefficient Db may be designed to satisfy the following formula: 0.09≦Db≦0.9 (Formula 1-4). In this case, the radio wave reflector 11 is designed to reflect radio waves of a predetermined range of frequencies including the corresponding frequency f in the direction of the reflection angle α2. Radio waves can be reflected with sufficient reflection intensity in the frequency range of 0.9×f (GHz) or more to 1.1×f (GHz), with the corresponding frequency f (GHz) of the radio waves as the center.

[0052] As described above, PET, FR4, glass, and silicon are preferably used as the material for the dielectric substrate layer 13. The relative dielectric constant ε of PET, FR4, glass, and silicon are 3.6, 4.4, 5.5, and 11.9, respectively, and therefore, in Equation 1, the relative dielectric constant ε is determined once the material of the dielectric substrate layer 13 is determined.

[0053] When the material of the dielectric substrate layer 13 is PET, the substrate design coefficient is particularly defined as a PET substrate design coefficient Dbp, and Equation 2-1 is defined. PET substrate design coefficient Dbp=Db / √ε=t / λ (Equation 2-1) In this case, the PET substrate design coefficient Dbp of the radio wave reflector 11 satisfies the following: 0.01≦Dbp≦0.48 (Equation 2-2)

[0054] When the material of the dielectric substrate layer 13 is FR4, the substrate design coefficient is particularly defined as the FR4 substrate design coefficient Dbf, and Equation 3-1 is defined. FR4 substrate design coefficient Dbf=Db / √ε=t / λ (Equation 3-1) In this case, the FR4 substrate design coefficient Dbf of the radio wave reflector 11 satisfies the following: 0.0095≦Dbf≦0.43 (Equation 3-2)

[0055] When the material of the dielectric substrate layer 13 is glass, the substrate design coefficient is particularly defined as a glass substrate design coefficient Dbg, and Equation 4-1 is defined as follows: Glass substrate design coefficient Dbg=Db / √ε=t / λ (Equation 4-1) In this case, the glass substrate design coefficient Dbg of the radio wave reflector 11 satisfies the following: 0.0085≦Dbg≦0.39 (Equation 4-2)

[0056] When the material of the dielectric substrate layer 13 is silicon, the substrate design coefficient is particularly defined as a silicon substrate design coefficient Dbs, and Equation 5-1 is defined. Silicon substrate design coefficient Dbs=Db / √ε=t / λ (Equation 5-1) In this case, the silicon substrate design coefficient Dbs of the radio wave reflector 11 satisfies the following: 0.005≦Dbs≦0.26 (Equation 5-2)

[0057] In the radio wave reflector 11 of this embodiment, radio waves are incident from the first conductive layer 16 side, pass through the first conductive layer 16 and the dielectric substrate layer 13, and reach the second conductive layer 17. The radio waves then pass through the dielectric substrate layer 13 and the first conductive layer 16 and exit as reflected waves. The phases of the incident and reflected waves of the radio waves that reach the second conductive layer 17 are determined depending on the thickness t of the dielectric substrate layer 13, i.e., the propagation distance of the radio waves, and the relative dielectric constant ε of the dielectric substrate layer 13. In other words, the phases of the incident and reflected waves of the radio wave change depending on the setting of the substrate design coefficient Db, which includes the thickness t and the relative dielectric constant ε, and the reflection direction of the radio waves from the radio wave reflector 11 changes.

[0058] The direction in which the radio wave reflector 11 of this embodiment polarizes and reflects the radio wave is determined appropriately by setting the reflecting elements 20A to 20C having different types of first conductive layers 16, the substrate design coefficient Db, the PET substrate design coefficient Dbp, etc. Note that the "PET substrate design coefficient Dbp, etc." refers to the PET substrate design coefficient Dbp, the FR4 substrate design coefficient Dbf, the glass substrate design coefficient Dbg, and the silicon substrate design coefficient Dbs.

[0059] According to the above configuration, the substrate design coefficient Db is defined by parameters such as the wavelength λ corresponding to the desired corresponding frequency f, the thickness t of the dielectric substrate layer 13, and the relative permittivity ε determined by the material of the dielectric substrate layer 13. These parameters are then determined so that the substrate design coefficient Db falls within a predetermined range. The radio wave reflector 11 designed in this manner polarizes and reflects radio waves of the desired corresponding frequency f so as to minimize reflection loss, that is, it is possible to increase the reflection intensity in the direction of the polarized reflection.

[0060] Furthermore, the range of radio wave frequencies that the radio wave reflector 11 can reflect with sufficient reflection intensity varies depending on the substrate design coefficient Db, with the corresponding frequency f at the center. When the substrate design coefficient Db is set within the range of Equation 1-3, the range of radio wave frequencies that can be reflected with sufficient reflection intensity can be narrowed. When the substrate design coefficient Db is set within the range of Equation 1-4, the range of radio wave frequencies that can be reflected with sufficient reflection intensity is wider than when the substrate design coefficient Db is set within the range of Equation 1-3. In this way, by setting the substrate design coefficient Db to an appropriate value, the range of radio wave frequencies that the radio wave reflector 11 can reflect with sufficient reflection intensity can be adjusted.

[0061] Furthermore, by determining the wavelength λ corresponding to the desired corresponding frequency f and the thickness t of the dielectric substrate layer 13 so that the PET substrate design coefficient Dbp, which is determined depending on the material of the dielectric substrate layer 13, and the like, fall within this predetermined range, the radio wave reflector 11 can reflect radio waves of the desired corresponding frequency f with as little reflection loss as possible.

[0062] (Evaluation Test) Examples 1 to 27 were prepared as the radio wave reflector 11, and evaluation tests were conducted on the radio wave reflection characteristics of Examples 1 to 27 and Comparative Examples 1 to 24. However, the radio wave reflector 11 of the present invention is not limited to Examples 1 to 27.

[0063] (Explanation of Examples and Comparative Examples) (Overall Configuration) The radio wave reflectors 11 produced in Examples 1 to 27 and Comparative Examples 1 to 24 are formed by laminating a second conductive layer 17, a dielectric substrate layer 13, and a first conductive layer 16 in this order. The radio wave reflectors 11 are squares with sides of 36 mm in plan view. The radio wave reflectors 11 produced in Examples 1 to 27 and Comparative Examples 1 to 24 have different configurations of the dielectric substrate layer 13, but the configurations of the first conductive layer 16 and the second conductive layer 17 are the same. The radio wave reflectors 11 in Examples 1 to 27 and Comparative Examples 1 to 24 have a phase or impedance distribution in the sheet-like surface direction, and are designed so that when the incident angle α1 of the radio wave is 60 degrees, the reflection angle α2 of the polarized reflected radio wave is a desired angle (0 degrees).

[0064] (Configuration of first conductive layer 16) The first conductive layer 16 includes different types of reflective elements 20A to 20C. FIG. 2 is a plan view of the radio wave reflectors 11 of Examples 1 to 27 and Comparative Examples 1 to 24 created for this evaluation test, which include three types of reflective elements 20A to 20C. Each of the reflective elements 20A to 20C is a square region with a side length L20 of 4 mm in plan view. The first conductive layer 16 is formed by arranging these aligned reflective elements 20A to 20C as one unit on the dielectric substrate layer 13. Adjacent units of the reflective elements 20A to 20C are arranged without any gaps.

[0065] Each of the reflecting elements 20A to 20C is made of a thin film conductor 12 having a thickness L3 of 2 μm formed on the upper surface of the dielectric substrate layer 13, and a region 12a surrounded by the conductor 12 and free of the conductor 12. The conductor 12 is made of copper.

[0066] The conductor 12 of the reflective element 20A includes upper, lower, left, and right side edge portions 21a-21d extending along the four edges of the square, and a central portion 22 located at the center in the vertical direction in FIG. 2 and extending from the right side edge portion 21a toward the left. The central portion 22 extends to the left for a length approximately 5 / 6 of the length L20 of one side of the reflective element 20A. The central portion 22 includes a first central portion 22a located on the right side edge portion 21a side and having a vertical length approximately 2 / 3 of the length L20 of one side of the reflective element 20A. The central portion 22 also includes a second central portion 22b that is continuous with the first central portion 22a and slightly shorter in the vertical direction than the first central portion 22a. The horizontal length of the first central portion 22a is approximately 1 / 2 of the length L20 of one side of the reflective element 20A. The region 12a without the conductor 12 is a region surrounded by the upper, lower, left, and right side edge portions 21a to 21d, the first central portion 22a, and the second central portion 22b. The dielectric substrate layer 13 is exposed through the region 12a without the conductor 12.

[0067] The reflective element 20B includes upper, lower, left, and right side edge portions 21a-21d extending along the four edges of the square, and a central portion 22 located at the center in the vertical direction in FIG. 2 and extending from the right side edge portion 21a to the left. The central portion 22 extends to the left a length approximately 5 / 6 of the length L20 of one side of the reflective element 20B. The central portion 22 includes a first central portion 22a located on the right side edge portion 21a side and having a vertical length approximately 2 / 3 of the length L20 of one side. The central portion 22 also includes a second central portion 22b that is continuous with the first central portion 22a and slightly longer in the vertical direction than the first central portion 22a. The horizontal length of the first central portion 22a is approximately 1 / 6 of the length L20 of one side. The region 12a without the conductor 12 is a region surrounded by the upper, lower, left, and right side edge portions 21a to 21d, the first central portion 22a, and the second central portion 22b. The dielectric substrate layer 13 is exposed through the region 12a without the conductor 12 surrounded by the conductors 12.

[0068] The reflective element 20C includes side edge portions 21a-21d extending along the four edges of the square, and a central portion 22. The right side edge portion 21a has a length in the left-right direction that is approximately 1 / 2 of the side length L20. The central portion 22 is located in the center in the up-down direction and extends continuously from the right side edge portion 21a toward the left for a length that is approximately 5 / 6 of the side length L20 of the reflective element 20C. The central portion 22 includes a region 12a without conductors 12, whose length in the up-down direction is approximately 2 / 3 of the side length L20, surrounded by the top, bottom, left, and right side edge portions 21 and the central portion 22. The dielectric substrate layer 13 is exposed through the region 12a without conductors 12.

[0069] The phase difference of reflecting element 20A is −34 degrees, the phase difference of reflecting element 20B is 60 degrees, and the phase difference of reflecting element 20C is 155 degrees. Furthermore, due to these phase differences of each of reflecting elements 20A to 20C, when the incident angle α1 of the radio wave is 60 degrees, the reflection angle α2 of the radio wave from radio wave absorber 11 is 0 degrees.

[0070] (Configuration of second conductive layer 17) The second conductive layer 17 is a thin-film conductor made of copper and has a thickness L11 of 2 μm. The second conductive layer 17 is formed on the surface of the dielectric substrate layer 13 opposite to the surface on which the first conductive layer 16 is provided.

[0071] (Dielectric substrate layer 13) The configurations of the dielectric substrate layer 13 of Examples 1 to 9 are shown in Table 1, and the configurations of the dielectric substrate layer 13 of Comparative Examples 1 to 8 are shown in Table 2. Examples 1 to 9 and Comparative Examples 1 to 8 were designed with a corresponding frequency f of 30 GHz, i.e., a wavelength λ of 10 mm. The configurations of the dielectric substrate layer 13 of Examples 10 to 18 are shown in Table 4, and the configurations of the dielectric substrate layer 13 of Comparative Examples 9 to 16 are shown in Table 5. Examples 10 to 18 and Comparative Examples 9 to 16 were designed with a corresponding frequency f of 3 GHz, i.e., a wavelength λ of 100 mm. The configurations of the dielectric substrate layer 13 of Examples 19 to 27 are shown in Table 7, and the configurations of the dielectric substrate layer 13 of Comparative Examples 17 to 24 are shown in Table 8. Examples 19 to 27 and Comparative Examples 17 to 24 were designed with a corresponding frequency f of 300 GHz, i.e., a wavelength λ of 1 mm.

[0072] (Evaluation Method) A radio wave reflection characteristic test (simulation) was conducted for Examples 1 to 27 and Comparative Examples 1 to 24 (hereinafter also referred to as "samples"). When radio waves of a predetermined frequency and intensity were incident on each sample, the reflection intensity RI at a desired reflection angle α2 (0 degrees) was determined for each sample. Furthermore, when radio waves of a predetermined frequency and intensity were incident on an aluminum plate prepared as a reference sample, the reflection intensity RIr in the specular reflection direction was determined. The reflection intensities RI and RIr of each sample and the reference sample were calculated by far-field analysis using the full-wave finite element simulation software ANSYS HFSS. At each radio wave frequency, the reflection loss was calculated from the formula "Reflection loss = Reflection intensity RIr of reference sample - Reflection intensity RI of each sample." The samples were set to have a square shape in a plan view, with the length of one side being 3λ or more.

[0073] In the above tests, radio waves of frequencies of 27 GHz, 29.8 GHz, 30 GHz, 30.2 GHz, and 33 GHz were reflected for Examples 1 to 9 and Comparative Examples 1 to 8. Radio waves of frequencies of 2.7 GHz, 2.98 GHz, 3.0 GHz, 3.02 GHz, and 3.3 GHz were reflected for Examples 10 to 18 and Comparative Examples 9 to 16. Radio waves of frequencies of 270 GHz, 298 GHz, 300 GHz, 302 GHz, and 330 GHz were reflected for Examples 19 to 27 and Comparative Examples 17 to 24.

[0074] A case where the reflection intensity was sufficient for practical use and the reflection loss was 3 dB or less was evaluated as "◎". A case where the reflection intensity was sufficient for practical use and the reflection loss was more than 3 dB and less than 5 dB was evaluated as "◯". A case where at least one of the reflection intensity was not sufficient for practical use and the reflection loss was more than 5 dB was evaluated as "×".

[0075] (Evaluation Results) The evaluation results of Examples 1 to 9 and Comparative Examples 1 to 8 are shown in Table 3. Examples 1 to 9 were designed to reflect radio waves with a corresponding frequency f of 30 GHz, and the substrate design coefficient Db of the dielectric substrate layer of Examples 1 to 9 was within the range of 0.02≦Db≦0.9 (Equation 1-2). The PET substrate design coefficient Dbp, FR4 substrate design coefficient Dbf, glass substrate design coefficient Dbg, and silicon substrate design coefficient Dbs, which are determined according to the material of each dielectric substrate layer of Examples 1 to 9, were within the ranges of Equation 2-2, Equation 3-2, Equation 4-2, and Equation 5-2, respectively. Examples 1 to 9 reflected radio waves with sufficient strength and had sufficiently small reflection loss. On the other hand, in Comparative Examples 1 to 8, the substrate design coefficient Db was outside the range of 0.02≦Db≦0.9 (Equation 1-2), resulting in large reflection loss and insufficient reflection intensity.

[0076] Furthermore, Examples 1, 4, 6, and 8 are designed so that the substrate design coefficient Db is in the range of 0.02≦Db≦0.03 (Equation 1-3), and are designed to reflect radio waves of the corresponding frequency f of 30 GHz in the direction of the reflection angle α2, while other frequencies are designed to be reflected as little as possible in the direction of the reflection angle α2. Therefore, when the corresponding frequency f deviates in the positive or negative direction, the reflection loss increases and the evaluation is "x". On the other hand, Examples 2, 3, 5, 7, and 9 are designed so that the substrate design coefficient Db is in the range of 0.09≦Db≦0.9 (Equation 1-4). Therefore, even when the frequency of the incident radio waves deviates in the positive or negative direction from the corresponding frequency f of 30 GHz by 5% to 10%, the radio waves are reflected with sufficient reflection intensity and little reflection loss.

[0077] The evaluation results for Examples 10 to 18 and Comparative Examples 9 to 16 are shown in Table 6. Examples 10 to 18 were designed to reflect radio waves with a corresponding frequency f of 3 GHz, and the substrate design coefficient Db of the dielectric substrate layer of Examples 10 to 18 was within the range of 0.02≦Db≦0.9 (Equation 1-2). The PET substrate design coefficient Dbp, FR4 substrate design coefficient Dbf, glass substrate design coefficient Dbg, and silicon substrate design coefficient Dbs, which are determined according to the material of each dielectric substrate layer of Examples 10 to 18, were within the ranges of Equation 2-2, Equation 3-2, Equation 4-2, and Equation 5-2, respectively. Examples 10 to 18 reflected radio waves with sufficient strength and had sufficiently small reflection loss. On the other hand, in Comparative Examples 9 to 16, the substrate design coefficient Db was outside the range of 0.02≦Db≦0.9 (Equation 1-2), resulting in large reflection loss and insufficient reflection intensity.

[0078] Furthermore, in Examples 10, 13, 15, and 17, the substrate design coefficient Db was designed to be in the range of 0.02≦Db≦0.03 (Equation 1-3). Therefore, when the frequency of the incident radio waves deviated positively or negatively from the corresponding frequency f of 3 GHz, the reflection loss increased and the evaluation was "x." On the other hand, in Examples 11, 12, 14, 16, and 18, the substrate design coefficient Db was designed to be in the range of 0.09≦Db≦0.9 (Equation 1-4). Therefore, even when the frequency of the incident radio waves deviated positively or negatively from the corresponding frequency f of 3 GHz by 5% to 10%, the radio waves were reflected with sufficient reflection intensity and little reflection loss.

[0079] The evaluation results of Examples 19 to 27 and Comparative Examples 17 to 24 are shown in Table 9. Examples 19 to 27 were designed to reflect radio waves with a corresponding frequency f of 300 GHz, and the substrate design coefficient Db of the dielectric substrate layer 13 of Examples 19 to 27 was within the range of 0.02≦Db≦0.9 (Equation 1-2). The PET substrate design coefficient Dbp, FR4 substrate design coefficient Dbf, glass substrate design coefficient Dbg, and silicon substrate design coefficient Dbs, which are determined according to the material of each dielectric substrate layer of Examples 19 to 27, were within the ranges of Equation 2-2, Equation 3-2, Equation 4-2, and Equation 5-2, respectively. Examples 19 to 27 reflected radio waves with sufficient strength and had sufficiently small reflection loss. On the other hand, in Comparative Examples 17 to 24, the substrate design coefficient Db was outside the range of 0.02≦Db≦0.9 (Equation 1-2), resulting in large reflection loss and insufficient reflection intensity.

[0080] Furthermore, in Examples 19, 22, 24, and 26, the substrate design coefficient Db was designed to be in the range of 0.02≦Db≦0.03 (Equation 1-3). Therefore, when the frequency of the incident radio waves deviated positively or negatively from the corresponding frequency f of 3 GHz, the reflection loss increased and the evaluation was "x". On the other hand, in Examples 20, 21, 23, 25, and 27, the substrate design coefficient Db was designed to be in the range of 0.09≦Db≦0.9 (Equation 1-4). Therefore, even when the frequency of the incident radio waves deviated positively or negatively from the corresponding frequency f of 3 GHz by 5% to 10%, the radio waves were reflected with sufficient reflection intensity and little reflection loss.

[0081]

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[0090] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit and scope of the present invention. The dimensions, materials, shapes, and relative arrangements of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention. For example, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express relative displacements with a tolerance or angle or distance to the extent that the same function is obtained. For example, expressions expressing the equality of things, such as "same," "equal," and "homogeneous," not only express strict equality, but also express tolerance or differences to the extent that the same function is obtained. For example, expressions expressing shapes such as a square or cylindrical shape not only express shapes such as a square or cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is obtained. The expressions "comprise," "include," "have," "includes," or "have" one component are not exclusive expressions that exclude the presence of other components. In addition, expressions that include "approximately," such as "approximately parallel" or "approximately perpendicular," are sometimes used. For example, "approximately parallel" means that the component is essentially "parallel," and does not mean a strictly "parallel" state, but also includes an error of a few degrees. The same applies to other expressions that include "approximately." In addition, expressions that include "... part," such as "end portion," are sometimes used. For example, "end portion" means a portion having a certain range that includes the "end." The same applies to other expressions that include "... part."

[0091] 11 Radio wave reflector 12 Conductor 13 Dielectric substrate layer 16 First conductive layer 20 Reflection element λ Wavelength t Thickness of dielectric substrate layer ε Relative permittivity of dielectric substrate layer

Claims

1. A radio wave reflector comprising first and second conductive layers containing a conductor, and a dielectric substrate layer supporting the first and second conductive layers, wherein the first conductive layer, the dielectric substrate layer, and the second conductive layer are laminated in this order, the radio wave reflector reflects radio waves at a reflection angle different from the angle of incidence, and wherein, where λ is the wavelength of the reflected radio waves, t is the thickness of the dielectric substrate layer, and ε is the relative dielectric constant of the dielectric substrate layer, a substrate design coefficient Db = t √ε / λ is defined, and the substrate design coefficient Db is in the range of 0.02≦Db≦0.

9.

2. The radio wave reflector according to claim 1, wherein the substrate design coefficient Db is in the range of 0.02≦Db≦0.

03.

3. The radio wave reflector according to claim 1, wherein the substrate design coefficient Db is 0.09≦Db≦0.

9.

4. A radio wave reflector comprising first and second conductive layers containing a conductor, and a dielectric substrate layer supporting the first and second conductive layers, wherein the first conductive layer, the dielectric substrate layer, and the second conductive layer are laminated in this order, the radio wave reflector reflects radio waves at a reflection angle different from the angle of incidence, and wherein, assuming that the wavelength of the reflected radio waves is λ, the thickness of the dielectric substrate layer is t, and the dielectric substrate layer is a layer made of PET, a PET substrate design coefficient Dbp=t / λ is defined, and the PET substrate design coefficient Dbp satisfies 0.01≦Dbp≦0.

48.

5. A radio wave reflector comprising first and second conductive layers containing a conductor, and a dielectric substrate layer supporting the first and second conductive layers, wherein the first conductive layer, the dielectric substrate layer, and the second conductive layer are laminated in this order, the radio wave reflector reflects radio waves at a reflection angle different from the angle of incidence, and wherein, assuming that the wavelength of the reflected radio waves is λ, the thickness of the dielectric substrate layer is t, and the dielectric substrate layer is a layer made of FR4, an FR4 substrate design coefficient Dbf = t / λ is defined, and the FR4 substrate design coefficient Dbf satisfies 0.0095≦Dbf≦0.

43.

6. A radio wave reflector comprising first and second conductive layers containing a conductor, and a dielectric substrate layer supporting the first and second conductive layers, wherein the first conductive layer, the dielectric substrate layer, and the second conductive layer are laminated in this order, the radio wave reflector reflects radio waves at a reflection angle different from the angle of incidence, and wherein, assuming that the wavelength of the reflected radio waves is λ, the thickness of the dielectric substrate layer is t, and the dielectric substrate layer is a layer made of glass, a glass substrate design coefficient Dbg = t / λ is defined, and the glass substrate design coefficient Dbg satisfies 0.0085≦Dbg≦0.

39.

7. A radio wave reflector comprising first and second conductive layers containing a conductor and a dielectric substrate layer supporting the first and second conductive layers, wherein the first conductive layer, the dielectric substrate layer and the second conductive layer are laminated in this order, the radio wave reflector reflects radio waves at a reflection angle different from the angle of incidence, and wherein the wavelength of the reflected radio waves is λ, the thickness of the dielectric substrate layer is t and the dielectric substrate layer is a layer made of silicon, a silicon substrate design coefficient Dbs=t / λ is defined, and the silicon substrate design coefficient Dbs satisfies 0.005≦Dbs≦0.

26.

8. A radio wave reflector as described in any one of claims 1 to 7, wherein the first conductive layer comprises a plurality of reflecting elements of two or more different types, and the different types of reflecting elements have different differences in the phase of the radio wave incident on each of the reflecting elements and the phase of the radio wave reflected from each of the reflecting elements.

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