Radio wave reflector

Abstract

Provided is a radio wave reflector capable of diffuse reflection of radio waves.　The radio wave reflector includes: a dielectric substrate having a first surface located on a radio wave-incident side, and a second surface; a plurality of first frequency selective surface (FSS) elements arranged on the first surface; and a radio wave reflection layer provided on the second surface. The plurality of first FSS elements are divided into a plurality of first groups. Each first group includes two or more first FSS elements arranged along one direction. In each first group, the two or more first FSS elements have different sizes and are arranged in order of size in the one direction. The plurality of first groups include a plurality of types of first groups having different numbers of the first FSS elements in the one direction.

Description

Radio wave reflector

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

[0002] Conventionally, there has been a radio wave absorber having a laminated structure, the radio wave absorber having a visible light transmittance of 50% or more, absorbing radio waves in a certain frequency band, the radio wave absorber having a first main surface which is a surface onto which the radio waves are incident and a second main surface which is a surface opposite to the first main surface, and including, in this order from the first main surface to the second main surface, a first dielectric layer, a conductive layer, a second dielectric layer, a radio wave reflecting layer, and a third dielectric layer, the conductive layer comprising a plurality of conductors and gaps which separate the plurality of conductors from one another, and the plurality of conductors being insulated from one another (for example, see Patent Document 1 listed below).

[0003] International Publication No. 2022 / 044958

[0004] Conventional radio wave absorbers absorb radio waves in a specific frequency band, but do not diffusely reflect them.

[0005] Therefore, an object of the present disclosure is to provide a radio wave reflector that is capable of diffusively reflecting radio waves.

[0006] A radio wave reflector according to an embodiment of the present disclosure includes a dielectric substrate having a first surface located on the radio wave incident side and a second surface, a plurality of first FSS (Frequency Selective Surface) elements arranged on the first surface, and a radio wave reflecting layer provided on the second surface, wherein the plurality of first FSS elements are divided into a plurality of first groups, each of which includes two or more first FSS elements arranged along one direction, and in each first group, the two or more first FSS elements have different sizes and are arranged in order of size in the one direction, and the plurality of first groups include a plurality of types of first groups each having a different number of first FSS elements in the one direction.

[0007] It is possible to provide a radio wave reflector that can diffusely reflect radio waves.

[0008] 3D is a diagram illustrating an example of a configuration of a radio wave reflector 100 according to an embodiment. FIG. 3D is a diagram illustrating an example of a configuration of a radio wave reflector 100 according to an embodiment. FIG. 3D is a diagram illustrating an example of a configuration of a radio wave reflector 100 according to an embodiment. FIG. 3D is a diagram illustrating an example of a configuration of a radio wave reflector 100 according to an embodiment. FIG. 3D is a diagram illustrating an example of a configuration of a radio wave reflector 100 according to an embodiment. FIG. 3D is a diagram illustrating an example of a configuration of a radio wave reflector 100 according to an embodiment. 1 is a diagram illustrating an example of a reflection pattern in a horizontal plane in the radio wave reflector 100. FIG. 2 is a diagram illustrating an example of a reflection pattern in an elevation angle direction in the radio wave reflector 100. FIG. 3 is a diagram illustrating an example of variations in the shapes of the plurality of FSS elements 120A included in the FSS layer 120. FIG. 4 is a diagram illustrating an example of variations in the shapes of the plurality of FSS elements 120A included in the FSS layer 120. FIG. 5 is a diagram illustrating an example of variations in the shapes of the plurality of FSS elements 120A included in the FSS layer 120. FIG. 6 is a diagram illustrating an example of variations in the shapes of the plurality of FSS elements 120A included in the FSS layer 120. FIG. 7 is a diagram illustrating an example of variations in the shapes of the plurality of FSS elements 120A included in the FSS layer 120. 4B and 4C are diagrams illustrating an example of the arrangement of a plurality of FSS elements 120A and a plurality of FSS elements 120B in a radio wave reflector according to a modified example of the embodiment.

[0009] Hereinafter, embodiments to which the radio wave reflector of the present disclosure is applied will be described. In the following, the same elements will be given the same reference numerals, and duplicated explanations may be omitted.

[0010] In the following description, the XYZ coordinate system is defined. The direction parallel to the X axis (X direction), the direction parallel to the Y axis (Y direction), and the direction parallel to the Z axis (Z direction) are perpendicular to one another. For ease of explanation, the -Z direction may be referred to as the lower side or bottom, and the +Z direction may be referred to as the upper side or top. Planar view refers to viewing from the XY plane. In the following description, the length, width, thickness, etc. of each part may be exaggerated to make the configuration easier to understand. Terms such as parallel, right angle, orthogonal, horizontal, vertical, and up and down may be misaligned to the extent that they do not impair the effects of the embodiments.

[0011] In the following description, "radio waves" refers to a type of electromagnetic wave, and generally, electromagnetic waves below 3 THz are referred to as radio waves. Hereinafter, electromagnetic waves emitted from outdoor base stations or relay stations will be referred to as "radio waves," and electromagnetic waves in general will be referred to as "electromagnetic waves." Hereinafter, "millimeter waves" or "millimeter wave band" will include not only the frequency band of 30 GHz to 300 GHz, but also the quasi-millimeter wave band of 24 GHz to 30 GHz.

[0012] The radio waves reflected by the radio wave reflector of the embodiment are preferably in the millimeter wave band of the fifth generation mobile communication system (5G) or the like, or in the frequency band of 1 GHz to 30 GHz including Sub-6. Furthermore, the radio waves reflected by the radio wave reflector of the embodiment may be LTE (Long Term Evolution), LTE-Advanced (LTE-A), or UMB (Ultra Mobile Broadband). Furthermore, the radio waves reflected by the radio wave reflector of the embodiment may be IEEE 802.11 (Wi-Fi (registered trademark)), IEEE 802.16 (WiMAX (registered trademark)), IEEE 802.20, UWB (Ultra-Wideband), Bluetooth (registered trademark), LPWA (Low Power Wide Area), or the like. As the frequency of the radio waves increases, propagation loss due to reflection and diffraction increases, making it more likely that blind zones will occur. Therefore, the radio wave reflector of the embodiment is more suitable for communications using relatively high frequencies. In the following, unless otherwise specified, the millimeter wave band and Sub-6 radio waves will be used as examples.

[0013] 1A and 1B are diagrams illustrating an example of an application of a radio wave reflector 100 according to an embodiment. A base station BS and a terminal UE are shown in 1A and 1B. The base station BS and the terminal UE can communicate with each other at a predetermined frequency. As an example, the predetermined frequency is 4.7 GHz.

[0014] For example, as shown in Figure 1A, when a building BL exists between the base station BS and the terminal UE, radio waves may not be able to reach the terminal UE directly from the base station BS. In reality, there are walls of buildings and structures (not shown) around the base station BS, the terminal UE, and the building BL, so there may be radio waves transmitted from the base station BS that are reflected by buildings (not shown) and reach the terminal UE. However, the radio waves attenuate as they are repeatedly reflected, making it difficult for the terminal UE to obtain good reception conditions.

[0015] In such a case, if the radio wave reflector 100 is placed in a position that avoids the building BL, as shown in Figure 1B, radio waves incident on the radio wave reflector 100 from the base station BS will be reflected and able to reach the terminal UE, improving the radio wave reception conditions at the terminal UE. As an example, the radio wave reflector 100 can reflect radio waves in a desired direction by specular reflection or non-specular reflection (abnormal reflection), so if good communication paths for radio waves can be obtained between the base station BS and the radio wave reflector 100, and between the radio wave reflector 100 and the terminal UE, a good communication environment can be obtained in both directions between the base station BS and the terminal UE.

[0016] <Configuration of radio wave reflector 100> Fig. 2A is a cross-sectional view showing an example of the configuration of the radio wave reflector 100. Fig. 2B is a diagram showing an example of the configuration of a plurality of FSS elements 120A of an FSS (Frequency Selective Surface) layer 120 located on the radio wave incident side of the radio wave reflector 100. The plurality of FSS elements 120A are an example of a plurality of first FSS elements.

[0017] The radio wave reflector 100 includes a dielectric substrate 110, an FSS layer 120, a radio wave reflecting layer 130, an adhesive layer 140, adhesive layers 150A and 150B, and protective plates 160A and 160B. The protective plate 160A is an example of a first protective layer, and the protective plate 160B is an example of a second protective layer.

[0018] 2A , the incident surface of the radio wave reflector 100 is the main surface 161A on the +Z direction side of the protection plate 160A. The radio wave reflector 100 reflects radio waves of a predetermined frequency (4.7 GHz, for example) incident from the main surface 161A in a desired direction.

[0019] As an example, the XZ plane is a horizontal plane. In this embodiment, as an example, a form will be described in which the radio wave reflector 100 is used with the main surface 161A standing perpendicular to the horizontal plane. The incident surface of the radio wave reflector 100 is parallel to the XY plane, and radio waves arrive from the +Z direction. In other words, radio waves arrive from a direction horizontal to the incident surface (main surface 161A) of the radio wave reflector 100.

[0020] Here, unless otherwise specified, an example will be described in which the angle of incidence of radio waves (incident waves) on an incident surface is expressed as an angle in the XZ plane (horizontal plane), and the angle of reflection of reflected radio waves (reflected waves) is expressed as an angle in the XZ plane. The X-axis, which is included in the XZ plane and is included in the XY plane parallel to the plane on which the multiple FSS elements 120A are arranged, is an example of one direction.

[0021] The +Z direction is the direction of 0 degrees for the angle of incidence and the angle of reflection. The angle of incidence and the angle of reflection are expressed as angles with the +Z direction in the XZ plane, and as an example, angles on the +X direction side of the +Z direction are expressed as positive angles (0 degrees to 90 degrees), and angles on the -X direction side of the +Z direction are expressed as negative angles (0 degrees to -90 degrees). Note that the use of the radio wave reflector 100 is not limited to the above-mentioned form in which the main surface 161A is set perpendicular to a horizontal plane.

[0022] The radio wave reflector 100 preferably has a visible light transmittance of 50% or more and a haze value of 5% or less. If the visible light transmittance is 50% or more, a user can view a product or scenery through the radio wave reflector 100. The visible light transmittance is preferably 53% or more, and more preferably 55% or more. The visible light transmittance is measured in accordance with Japanese Industrial Standard JIS R 3106:1998 and can be calculated using a formula when a standard D65 light source is used. The haze value is determined in accordance with Japanese Industrial Standard JIS K7136:2000.

[0023] The dielectric substrate 110, FSS layer 120, radio wave reflecting layer 130, adhesive layer 140, adhesive layers 150A and 150B, and protective plates 160A and 160B are arranged in the following order from the +Z direction side to the -Z direction side: protective plate 160A, adhesive layer 150A, FSS layer 120, dielectric substrate 110, adhesive layer 140, radio wave reflecting layer 130, adhesive layer 150B, and protective plate 160B.

[0024] As an example, the radio wave reflector 100 is produced by sandwiching the adhesive layer 150A, the FSS layer 120, the dielectric substrate 110, the adhesive layer 140, the radio wave reflecting layer 130, and the adhesive layer 150B between the protective plate 160A and the protective plate 160B and then thermocompressing them together.

[0025] <Dielectric Substrate 110> The dielectric substrate 110 is a dielectric substrate having a surface 111 located on the radio wave incident side (+Z direction side) and a surface 112 on the opposite side (-Z direction side) from surface 111. Surface 111 is an example of a first surface, and surface 112 is an example of a second surface. An FSS layer 120 is formed on surface 111, and a radio wave reflecting layer 130 is bonded to surface 112 via an adhesive layer 140. By bonding the radio wave reflecting layer 130 to surface 112 of the dielectric substrate 110 via the adhesive layer 140, the radio wave reflecting layer 130 is provided on surface 112 of the dielectric substrate 110.

[0026] The dielectric substrate 110 is formed of any material that is transparent to radio waves emitted from the base station BS or the terminal UE and that can support the FSS layer 120. "Transparent to radio waves" means, for example, that the transmission loss is 10 dB or less. "The dielectric substrate 110 is transparent to radio waves" means that the transmission loss of the dielectric substrate 110 is 10 dB or less, preferably 6 dB or less, more preferably 3 dB or less, and even more preferably 1 dB or less.

[0027] The dielectric substrate 110 may be transparent to visible light. "Transparent" to visible light means that the visible light transmittance is at least 50% or more, preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more.

[0028] As an example, a glass plate is used for the dielectric substrate 110. In this case, as an example, the dielectric substrate 110 is a glass plate provided with a Low-E film as the FSS layer 120. Alternatively, a resin substrate may be used for the dielectric substrate 110. Examples of resin materials that satisfy the above conditions include acrylic resins such as polymethyl methacrylate, cycloolefin resins, polycarbonate resins, and polyethylene terephthalate (PET). When the dielectric substrate 110 is a glass plate or a resin substrate, the thickness of the dielectric substrate 110 is, for example, 2 mm to 6 mm, and preferably 2 mm to 4 mm.

[0029] <FSS Layer 120> The FSS layer 120 has a plurality of FSS elements 120A. The plurality of FSS elements 120A are formed on the surface 111 on the +Z direction side of the dielectric substrate 110. Here, the FSS layer 120 will be described using FIG. 2B in addition to FIG. 2A. FIG. 2B is a diagram showing an example of the configuration of the FSS layer 120 in a plan view. FIG. 2B shows only the surface 111 on the +Z direction side of the dielectric substrate 110 and the FSS layer 120, and omits other components.

[0030] 2B , the multiple FSS elements 120A are, for example, arranged at intervals along the first axis (X-axis) direction and the second axis (Y-axis) direction of the surface 111. As an example, the multiple FSS elements 120A are arranged at equal pitches in the X direction and at equal pitches in the Y direction. The pitch is the distance between the centers of adjacent FSS elements 120A. Here, a configuration in which the multiple FSS elements 120A are arranged at equal pitches in the X direction and the Y direction will be described, but the multiple FSS elements 120A are not limited to a configuration in which they are arranged at equal pitches in the X direction and the Y direction, and the pitches in the X direction or the Y direction do not have to be equal.

[0031] 2B shows, as an example, 36 FSS elements 120A arranged in 4 rows and 9 columns, with 9 in the X direction and 4 in the Y direction. Each row extends in one direction, the X direction, and each column extends in the Y direction, which is perpendicular to the X direction on the surface 111. As an example, the rows are referred to as the first to fourth rows from the +Y direction side to the −Y direction side. As an example, the columns are referred to as the first to ninth columns from the −X direction side to the +X direction side.

[0032] The multiple FSS elements 120A are insulated from one another and are made of, for example, a transparent conductive film such as an ITO (indium tin oxide) film or a Low-E (low emissivity) film. The term "transparent" in a transparent conductive film means that it is transparent to visible light, and "transparent" to visible light means that the visible light transmittance is at least 40% or more, preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more. The multiple FSS elements 120A can be fabricated, for example, by laser cutting a transparent conductive film such as an ITO film or a Low-E film formed on the surface 111 of the dielectric substrate 110.

[0033] The sheet resistance of the plurality of FSS elements 120A is, for example, 30 Ω / sq. or less, preferably 10 Ω / sq. or less, and more preferably 1 Ω / sq. or less.

[0034] The distance in the Z direction between the FSS element 120A and the radio wave reflecting layer 130 is preferably 0.3 mm to 6 mm, more preferably 0.4 mm to 2 mm, and even more preferably 0.5 mm to 1 mm. The thickness of the FSS element 120A is not particularly limited, but if the FSS element 120A is a Low-E film, for example, it is 50 nm to 300 nm.

[0035] <Groups 120G> The multiple FSS elements 120A are divided into multiple groups 120G. More specifically, the 36 FSS elements 120A shown in Fig. 2B are divided into four groups 120G1, four groups 120G2, and four groups 120G3. Hereinafter, when there is no need to distinguish between the groups 120G1 to 120G3, they will simply be referred to as groups 120G.

[0036] FIG. 2B shows a group 120G1 including four FSS elements 120A in the first row and the first to fourth columns, a group 120G2 including three FSS elements 120A in the third row and the fifth to seventh columns, and a group 120G3 including two FSS elements 120A in the first row and the eighth and ninth columns.

[0037] For clarity, FIG. 2B shows only the group 120G1 in the first row, but there is one group 120G1 in each of the first to fourth rows, and each group 120G1 includes four FSS elements 120A in the first to fourth columns in each row.

[0038] Similarly, in FIG. 2B, for clarity, only the group 120G2 in the third row is shown, but there is one group 120G2 in each of the first through fourth rows, and each group 120G2 includes three FSS elements 120A in the fifth through seventh columns in each row.

[0039] Similarly, in FIG. 2B, for ease of viewing, only the group 120G3 in the first row is shown, but there is one group 120G3 in each of the first to fourth rows, and each group 120G3 includes two FSS elements 120A in the eighth and ninth columns in each row.

[0040] Thus, each group 120G includes multiple FSS elements 120A.

[0041] In each group 120G, the FSS elements 120A have different sizes in a plan view in one direction, the X direction, and are arranged in order of size. In Figure 2B, the four FSS elements 120A included in each column have the same size in a plan view, for example.

[0042] The sizes of the nine FSS elements 120A included in each row in plan view are set as follows, for example, in each of the groups 120G1 to 120G3.

[0043] <Arrangement of the Four FSS Elements 120A in Group 120G1> As an example, in group 120G1, the FSS elements 120A in the first column are the largest, and the FSS elements 120A in the fourth column are the smallest. That is, in each group 120G1, the sizes of the four FSS elements 120A in a planar view are, for example, set to decrease in order from the first column to the fourth column. In this way, in group 120G1, the four FSS elements 120A are arranged in order of size in a planar view in the X direction. Note that the order of size in a planar view of the four FSS elements 120A included in group 120G1 may be reversed. That is, as an example, the FSS elements 120A in the first column may be the smallest, and the FSS elements 120A in the fourth column may be the largest.

[0044] <Arrangement of Three FSS Elements 120A in Group 120G2> As an example, in group 120G2, the FSS elements 120A in the fifth column are the largest, and the FSS elements 120A in the seventh column are the smallest. That is, in each group 120G2, the sizes of the three FSS elements 120A in a planar view are, for example, set to decrease in order from the fifth column to the seventh column. In this way, in group 120G2, the three FSS elements 120A are arranged in order of size in a planar view in the X direction. Note that the order of size in a planar view of the three FSS elements 120A included in group 120G2 may be reversed. That is, as an example, the FSS elements 120A in the fifth column may be the smallest, and the FSS elements 120A in the seventh column may be the largest.

[0045] <Arrangement of two FSS elements 120A in group 120G3> As an example, in group 120G3, the FSS elements 120A in the eighth column are the largest, and the FSS elements 120A in the ninth column are the smallest. That is, in each group 120G3, the sizes of the two FSS elements 120A in a planar view are set to decrease in order from the eighth column to the ninth column, as an example. In this way, in group 120G3, the two FSS elements 120A are arranged in order of size in a planar view in the X direction. Note that the order of size in a planar view of the two FSS elements 120A included in group 120G3 may be reversed. That is, as an example, the FSS elements 120A in the eighth column may be the smallest, and the FSS elements 120A in the ninth column may be the largest.

[0046] In each of groups 120G1 to 120G3, as an example, the sizes of the multiple FSS elements 120A in a planar view are all different, but as long as they are arranged in order of size, FSS elements 120A of the same size may be adjacent to each other and arranged in order of size.

[0047] For example, in each group 120G1, four types of FSS elements 120A may be arranged in size order, with two adjacent FSS elements 120A. Alternatively, in each group 120G2, three types of FSS elements 120A may be arranged in size order, with two adjacent FSS elements 120A. Alternatively, in each group 120G3, two types of FSS elements 120A may be arranged in size order, with two adjacent FSS elements 120A.

[0048] That is, in each of the groups 120G1 to 120G3, a plurality of FSS elements 120A of different sizes may be arranged adjacent to each other in order of size. This type of configuration will be described later with reference to FIG. 3D. In this case, the number of adjacent FSS elements 120A may differ depending on the size of the FSS elements 120A.

[0049] When the radio waves reach the FSS element 120A, the free electrons in the FSS element 120A move in the direction opposite to the electric field direction of the radio waves, causing a current to flow through the FSS element 120A. At this time, energy is periodically accumulated and released in the gaps between the multiple FSS elements 120A due to the electric field generated. As a result, a propagation delay occurs in the radio waves passing through the FSS element 120A. A delay time occurs between the time the radio waves enter the FSS element 120A and the time they are re-radiated. In other words, the phase of the radio waves passing through the FSS layer 120 and the phase of the radio waves reflected by the FSS layer 120 both change relative to the phase of the radio waves entering the FSS layer 120. The radio waves that pass through the FSS layer 120 are reflected in the +Z direction by the radio wave reflecting layer 130.

[0050] As described above, the multiple FSS elements 120A are divided into multiple groups 120G, and each group 120G includes two or more FSS elements 120A arranged along the X direction (one direction). The two or more FSS elements 120A included in each group 120G are different in size and arranged in order of size in one direction. The multiple groups 120G include multiple types of groups 120G1 to 120G3, each of which has a different number of FSS elements 120A in one direction.

[0051] In each group 120G, the multiple FSS elements 120A are arranged in order of size in the X direction, and therefore, in the XZ plane, when the multiple FSS elements 120A reflect an incident wave, the phases they impart to the reflected wave are different. The reflected wave reflected by the multiple FSS elements 120A is reflected in a direction at a predetermined angle determined by the sizes of the multiple FSS elements 120A. The direction of the predetermined angle corresponds to a desired reflection angle selected by the designer of the radio wave reflector 100.

[0052] Furthermore, since the number of FSS elements 120A included in the groups 120G1 to 120G3 differs in the X direction, the desired reflection angle obtained by each of the groups 120G1 to 120G3 differs. In the case of non-specular reflection, the reflection angle at which an incident wave incident from the normal direction (+Z direction) of the surface 111 is reflected differs, for example, 50 degrees for the group 120G1, 40 degrees for the group 120G2, and 30 degrees for the group 120G3. Therefore, the radio wave reflector 100 is capable of diffuse reflection, which reflects the incident wave while diffusing it in directions ranging from 30 degrees to 50 degrees. Note that the radio wave reflector 100 is also capable of diffuse reflection even when configured to perform specular reflection.

[0053] Furthermore, since the number of FSS elements 120A included in the groups 120G1 to 120G3 differs in the X direction, the desired reflection angles obtained by the groups 120G1 to 120G3 differ, and therefore the X direction as one direction is a direction that defines the direction in which radio waves incident on the radio wave reflector 100 are reflected by the radio wave reflector 100. In an XZ plane that includes a straight line (first straight line) extending in the X direction and a normal line (a straight line extending in the Z direction) to the surface 111, the angle that the incident path of the radio wave incident on the radio wave reflector 100 makes with the normal line is the angle of incidence, and the angle that the reflection path along which the incident radio wave is reflected by the radio wave reflector 100 makes with the normal line is the angle of reflection.

[0054] <Radio Wave Reflecting Layer 130 > The radio wave reflecting layer 130 is provided on the surface 112 of the dielectric substrate 110 by being adhered to the surface 112 of the dielectric substrate 110 by an adhesive layer 140 .

[0055] The radio wave reflecting layer 130 reflects radio waves that have passed through the multiple FSS elements 120A. The radio wave reflecting layer 130 is conductive. The sheet resistance of the radio wave reflecting layer 130 is, for example, 3 Ω / sq. or less, preferably 1 Ω / sq. or less, and more preferably 0.1 Ω / sq. or less.

[0056] The radio wave reflecting layer 130 is, for example, made of a metal mesh. The metal mesh has openings, and therefore can achieve a higher visible light transmittance than a metal film. From the viewpoint of suppressing reflection of visible light, the metal mesh is preferably one that has been subjected to an oxidation treatment and a blackening treatment. Stainless steel is generally used as the metal mesh. If the mesh wire diameter is 0.01 mm or more, the radio wave reflector 100 is easy to handle when manufactured. If the mesh wire diameter is 0.1 mm or less, the radio wave reflection characteristics are good. From the viewpoint of ensuring both the transparency and reflection characteristics of the radio wave reflector 100, the mesh wire diameter is particularly preferably 0.01 mm to 0.08 mm, and more preferably 0.02 mm to 0.06 mm.

[0057] The radio wave reflecting layer 130 may also be made of a transparent conductive film. The meaning of "transparency" in a transparent conductive film is the same as in the FSS element 120A. Examples of transparent conductive films include an ITO film and a Low-E film. There are no particular limitations on the thickness of the radio wave reflecting layer 130, but when a transparent conductive film such as a Low-E film is used for the radio wave reflecting layer 130, the thickness is, for example, 100 nm to 500 nm.

[0058] The radio waves that have passed through the FSS layer 120 are reflected by the radio wave reflecting layer 130. The radio waves reflected by the multiple FSS elements 120A of the FSS layer 120 and the radio waves reflected by the radio wave reflecting layer 130 interfere with each other and are combined, resulting in the radio waves being reflected with a phase different from that of the specular reflection. As a result, the radio waves are reflected by the radio wave reflector 100.

[0059] In a radio wave reflector 100 configured to perform specular reflection, the direction in which the radio waves reflected by the plurality of FSS elements 120A and the radio waves reflected by the radio wave reflecting layer 130 constructively interfere with each other is a direction at an angle equal to the angle of incidence of the incident wave on the radio wave reflector 100. In addition, in a radio wave reflector 100 configured to perform non-specular reflection, the direction in which the radio waves reflected by the plurality of FSS elements 120A and the radio waves reflected by the radio wave reflecting layer 130 constructively interfere with each other is a direction at an angle unequal to the angle of incidence of the incident wave on the radio wave reflector 100.

[0060] The radio wave reflecting layer 130 may have an insulating substrate that supports the transparent conductive film. The insulating substrate is, for example, a resin film. For example, the transparent conductive film may be formed on the surface of the insulating substrate by a vapor deposition method, a sputtering method, or the like. The transparent conductive film may also be formed by printing using a conductive ink.

[0061] <Adhesive Layers 140, 150A, and 150B> The adhesive layer 140 bonds the dielectric substrate 110 and the radio wave reflecting layer 130 together. The adhesive layer 150A bonds the dielectric substrate 110 and the protective plate 160A together with the FSS layer 120 sandwiched between them. The adhesive layer 150B bonds the radio wave reflecting layer 130 and the protective plate 160B together. As an example, the adhesive layers 140, 150A, and 150B may be transparent to visible light. The meaning of being transparent to visible light is the same as that of the FSS element 120A and the radio wave reflecting layer 130.

[0062] The adhesive layer 140 is an adhesive layer formed of a thermoplastic adhesive. An adhesive layer formed of a thermoplastic adhesive has high moisture resistance and durability. The adhesive layer 140 is made of, for example, polyvinyl butyral (PVB) resin, ethylene vinyl acetate (EVA) resin, cycloolefin polymer (COP) resin, or thermoplastic polyurethane (TPU) resin. The same applies to the adhesive layers 150A and 150B.

[0063] The water absorption rate of the adhesive layer 140 is, for example, 3% by mass or less. The water absorption rate of the adhesive layer 140 is measured in accordance with Japanese Industrial Standard JIS K 7209:2000. If the water absorption rate of the adhesive layer 140 is 3% by mass or less, it is less likely to deteriorate even in a high-temperature, high-humidity environment. The water absorption rate of the PVB resin, EVA resin, COP resin, and TPU resin may all be 3% by mass or less. The water absorption rate of the adhesive layer 140 is preferably 1% by mass or less. The water absorption rate of the adhesive layer 140 is also preferably 0.01% by mass or more. The same water absorption rates apply to the adhesive layers 150A and 150B.

[0064] Furthermore, when the relative dielectric constant of the adhesive layer 140 is εr, the thickness of the adhesive layer 140 is equal to or less than 1 / (10√εr) of the wavelength at a predetermined frequency of the radio waves reflected by the radio wave reflector 100. The predetermined frequency is 4.7 GHz, for example. The same thickness applies to the adhesive layers 150A and 150B.

[0065] <Protective Plate 160A> The protective plate 160A has principal surfaces 161A and 162A. The principal surface 161A is located on the radio wave incident side. The principal surface 161A is the radio wave incident surface of the radio wave reflector 100. The principal surface 162A is located on the opposite side to the principal surface 161A. As an example, the protective plate 160A may be transparent to visible light. The meaning of being transparent to visible light is the same as that of the FSS element 120A and the radio wave reflecting layer 130.

[0066] The protective plate 160A protects the FSS layer 120. The protective plate 160A can be made of glass, ceramics, resin, or the like. From the viewpoint of weight reduction, resin is preferable. Specific examples of resin include polyethylene terephthalate (PET) resin, polycarbonate (PC) resin, and acrylic resin. On the other hand, from the viewpoint of scratch resistance, glass or ceramics are preferable.

[0067] When the protective plate 160A is made of glass or resin, the thickness is, for example, 2 mm to 6 mm, preferably 2 mm to 4 mm. When the protective plate 160A is made of ceramic, the thickness is, for example, 0.2 mm to 4.0 mm, preferably 0.3 mm to 2.5 mm, and more preferably 0.3 mm to 1.0 mm.

[0068] A resin film may be provided on the surface of the protective plate 160A on the +Z direction side to prevent cracking.

[0069] <Protective Plate 160B> The protective plate 160B has principal surfaces 161B and 162B. The principal surface 161B is located on the radio wave reflecting layer 130 side. The principal surface 162B is located on the opposite side of the principal surface 161B. An adhesive layer 150B is adhered to the principal surface 161B. As an example, the protective plate 160B may be transparent to visible light. The meaning of being transparent to visible light is the same as that of the FSS element 120A and the radio wave reflecting layer 130. However, since the protective plate 160B is located on the -Z direction side of the radio wave reflecting layer 130, it does not have to be transparent to visible light.

[0070] The protective plate 160B protects the radio wave reflection layer 130. The protective plate 160B may be made of glass, ceramics, resin, or the like. The material of the protective plate 160B can be selected from the same materials as those described above for the protective plate 160A. The thickness of the protective plate 160B can be selected within the thickness range described above for the protective plate 160A. The material and thickness of the protective plate 160B may be the same as or different from the material and thickness of the protective plate 160A.

[0071] <Details of Unit Area 111A and Multiple FSS Elements 120A> Fig. 3A is a diagram showing an example of an arrangement of multiple FSS elements 120A. Similar to Fig. 2B, Fig. 3A shows 36 FSS elements 120A arranged in 4 rows and 9 columns. Furthermore, the surface 111 of the dielectric substrate 110 has multiple unit areas 111A. The multiple unit areas 111A are an example of multiple first unit areas.

[0072] As an example, the plurality of FSS elements 120A are arranged in each of the plurality of unit areas 111A. In other words, the plurality of FSS elements 120A are arranged one inside each of the plurality of unit areas 111A.

[0073] Here, in addition to Fig. 3A, Fig. 3B and Fig. 3C will be used to explain the FSS elements 120A and unit area 111A. Fig. 3B shows an enlarged view of eight FSS elements 120A arranged in two rows and four columns and included in two adjacent groups 120G1 of the four groups 120G1 shown in Fig. 3A. In Fig. 3B, the difference in size of the FSS elements 120A is exaggerated more than in Fig. 3A. Fig. 3C shows an example of the configuration of one unit area 111A and one FSS element 120A.

[0074] 3A and 3B, the unit areas 111A are arranged adjacent to each other on the surface 111 and have the same size in a plan view. 3A and 3B show the unit areas 111A as squares in a plan view as an example, but the shape of the unit areas 111A is not limited to squares and may be any polygon that is adjacent to each other without gaps, such as a rectangle, a triangle, or a regular hexagon.

[0075] As shown in FIG. 3B, for example, in each unit area 111A, the center 111A1 of the unit area 111A and the center of the FSS element 120A are arranged to coincide with each other.

[0076] As an example, the multiple FSS elements 120A include multiple types of FSS elements 120A that have similar shapes but different sizes in a plan view. The multiple FSS elements 120A shown in Figures 3A and 3B are all square, and their sizes decrease in order from the first column to the fourth column in the X direction (one direction). In this way, the multiple FSS elements 120A are arranged in order of size with similar shapes in the X direction, and the four columns of FSS elements 120A shown in Figure 3B are further exaggerated to make the differences in size easier to understand.

[0077] As shown in FIG. 3C , the lengths of the unit area 111A in the X and Y directions are, for example, 5 mm, assuming that the unit area 111A reflects 4.7 GHz radio waves. The lengths of the FSS element 120A in the X and Y directions are, for example, 3 mm. Therefore, the ratio of the area of ​​the FSS element 120A to the area of ​​the unit area 111A (area ratio of the FSS element 120A) shown in FIG. 3C is 36%. When the area ratio of the FSS element 120A is 100%, the outer edge of the FSS element 120A coincides with the outer edge of the unit area 111A. When two FSS elements 120A with an area ratio of 100% are adjacent to each other in the X or Y direction, there is no gap between the FSS elements 120A, and they are integrated.

[0078] When the effective wavelength at the operating frequency of the plurality of FSS elements 120A is λg, the distance between the centers of adjacent unit areas 111A is preferably 0.05λg or more and 0.65λg or less. If the distance between the centers of adjacent unit areas 111A is 0.05λg or more and 0.65λg or less, the resolution of the phase distribution can be improved, and the reflection efficiency for a desired reflection angle can be increased. Furthermore, reflection at angles other than the desired reflection angle can be reduced.

[0079] The effective wavelength λg at the operating frequency of the plurality of FSS elements 120A is the wavelength λ in the air of the radio wave in the frequency band incident on the plurality of FSS elements 120A. ０ and the relative permittivity (effective relative permittivity ε ｅ ) and λg = (1 / √ε ｅ ) λ ０ The following relational expression A holds: Effective relative dielectric constant ε ｅ is the relative dielectric constant ε of the protective plate 160A (or air when the protective plate 160A is not included). ｒＵ and the relative dielectric constant ε of the dielectric substrate 110 ｒＬ Using and, ε ｅ =(ε ｒＵ +ε ｒＬ ) / 2.

[0080] The relative dielectric constant ε of the protective plate 160A (or air when the protective plate 160A is not included) ｒＵis 6.9, and the relative dielectric constant ε of the dielectric substrate 110 is ｒＬ When the effective relative permittivity ε is set to 2.77, ｅ is calculated to be 4.835 from the formula (1) described later. ０ is 63.8 mm, and therefore the effective wavelength λg is 29.0 mm based on the above relational expression A.

[0081] <Modification of Group 120G> Fig. 3D is a diagram showing an example of the configuration of a modification of the group 120G. In the group 120G shown in Fig. 3D, FSS elements 120A of four different sizes are arranged adjacent to each other in groups of three, in order of size.

[0082] In Fig. 3D, 12 FSS elements 120A are arranged in 1 row and 12 columns in each of 12 unit areas 111A adjacent to each other in the X direction. A group 120G shown in Fig. 3D includes 12 unit areas 111A. As an example, the unit area 111A shown in Fig. 3D is rectangular and is longer in the Y direction than in the X direction.

[0083] In the group 120G shown in FIG. 3D , FSS elements 120A of four different sizes are arranged in groups of three adjacent to each other in order of size. The three FSS elements 120A in the first to third columns are equal in size and are the largest of the 12 FSS elements 120A. The three FSS elements 120A in the fourth to sixth columns are equal in size and are the second largest of the 12 FSS elements 120A. The three FSS elements 120A in the seventh to ninth columns are equal in size and are the third largest of the 12 FSS elements 120A. The three FSS elements 120A in the tenth to twelfth columns are equal in size and are the smallest of the 12 FSS elements 120A.

[0084] The four different sizes of FSS elements 120A included in group 120G shown in FIG. 3D are similar in shape but different in size. The area ratio of the three FSS elements 120A in the first to third columns is, for example, 100%, meaning that there are no gaps between the three FSS elements 120A in the first to third columns and they are integrated. The area ratio of the three FSS elements 120A in the fourth to sixth columns is, for example, 90%. The area ratio of the three FSS elements 120A in the seventh to ninth columns is, for example, 80%. The area ratio of the three FSS elements 120A in the tenth to twelfth columns is, for example, 70%.

[0085] 3E is a diagram showing an example of a configuration in which the groups 120G shown in FIG. 3D are arranged in eight columns in the Y direction. When the groups 120G shown in FIG. 3D are arranged in eight columns in the Y direction, the FSS elements 120A in the first to third columns, where the area ratio of the FSS elements 120A is 100%, are integrated in the X and Y directions. The FSS elements 120A in the fourth to twelfth columns have an area ratio smaller than 100%, so there are gaps between adjacent FSS elements 120A in the X and Y directions.

[0086] <Planar configuration of radio wave reflector 100> Fig. 4A is a diagram showing an example of the planar configuration of the radio wave reflector 100. Fig. 4A shows an example of the configuration of the radio wave reflector 100 viewed from the +Z direction side. In Fig. 4A, a striped pattern formed by a plurality of rectangular FSS elements 120A formed on the surface 111 of the dielectric substrate 110 is visible through the transparent adhesive layer 150A and the protective plate 160A. Reference numerals other than 100 are omitted in Fig. 4A.

[0087] As an example, in the radio wave reflector 100 shown in Fig. 4A, 60 FSS elements 120A are arranged in the X direction and 60 FSS elements 120A in the Y direction. The 3,600 FSS elements 120A are divided into four types of groups 120G arranged in the X direction. The lengths of the four types of groups 120G in the X direction are L1, L2, L3, and L4, which are different from one another. As an example, the lengths L2 and L4 are equal, with L3 being the longest, L2 and L4 being the second longest, and L1 being the shortest. In each column, 60 FSS elements 120A of equal size in a plan view are arranged in the Y direction.

[0088] The 60 groups 120G each having an X-direction length of L1 are all positioned at the same position in the X direction, and the same is true for the groups 120G each having an X-direction length of L2, L3, and L4.

[0089] Within each group 120G, for example, the size of the FSS elements 120A in plan view decreases in order from the −X direction side to the +X direction side. Since the 3600 unit areas 111A in which the 3600 FSS elements 120A are arranged all have the same size in plan view, different lengths of the groups 120G in the X direction correspond to different numbers of FSS elements 120A in the X direction included in the groups 120G.

[0090] The group 120G having a length L1 in the X direction has 10 FSS elements 120A arranged in 1 row and 10 columns. The group 120G having a length L2 in the X direction has 15 FSS elements 120A arranged in 1 row and 15 columns. The group 120G having a length L3 in the X direction has 20 FSS elements 120A arranged in 1 row and 20 columns. The group 120G having a length L4 in the X direction has 15 FSS elements 120A arranged in 1 row and 15 columns.

[0091] 4A includes four groups 120G in each row, and therefore includes 240 groups 120G. The 240 groups 120G include four types of groups 120G (lengths L1 to L4) that differ in the number of FSS elements 120A in the X direction, and in each group 120G, the multiple FSS elements 120A have different sizes and are arranged in order of size in the X direction.

[0092] Therefore, the radio wave reflector 100 can diffusely reflect incident waves. In Fig. 4A, the positions in the X direction of the groups 120G having lengths L1, L2, L3, and L4 in the X direction are all equal, but they may be shifted. Figs. 4B and 4C are diagrams showing examples of the planar configurations of radio wave reflectors 100A and 100B according to modified examples of the embodiment.

[0093] <Radio wave reflector 100A shown in Fig. 4B> In Fig. 4B, a concentric elliptical stripe pattern formed by a plurality of rectangular FSS elements 120A formed on the surface 111 of the dielectric substrate 110 can be seen through the transparent adhesive layer 150A and the protective plate 160A. In Fig. 4B, reference numerals other than 100A are omitted.

[0094] 4B includes multiple types of groups 120G each having a different number of FSS elements 120A in the X direction, and in each group 120G, the multiple FSS elements 120A are different in size and are arranged in order of size in the X direction. Because the unit areas 111A in which the FSS elements 120A are arranged have the same size in a planar view, different numbers of FSS elements 120A included in different types of groups 120G correspond to different lengths in the X direction of the different types of groups 120G.

[0095] 4B can be divided into sections A1, A2, and A3 in the Y direction. Section A2, which is located in the center, is a section that includes the ellipse located at the center of the concentric elliptical striped pattern in the Y direction. Section A1 is a section on the +Y direction side of section A2, and section A3 is a section on the −Y direction side of section A2.

[0096] In section A1, four groups 120G of lengths L1, L2, L3, and L4 are arranged from the -X direction side to the +X direction side. As an example, lengths L1 and L4 are equal, and lengths L2 and L3 are also equal. Furthermore, lengths L1 and L4 are different from lengths L2 and L3. Because the striped pattern is a concentric ellipse, lengths L1 and L4 and lengths L2 and L3 vary depending on the row position (position in the Y direction), but lengths L2 and L3 are longer than lengths L1 and L4.

[0097] The boundary between the group 120G of length L2 and the group 120G of length L3 coincides with the center of the length in the X direction of the radio wave reflector 100A. Within each of the two groups 120G of lengths L1 and L2, the FSS elements 120A of the same size are adjacent to each other in the X direction, and the sizes decrease in order from the −X direction side to the +X direction side. Within each of the two groups 120G of lengths L3 and L4, the FSS elements 120A of the same size are adjacent to each other in the X direction, and the sizes increase in order from the −X direction side to the +X direction side.

[0098] In each row, the two groups 120G with lengths L1 and L2 and the two groups 120G with lengths L3 and L4 are symmetrical in the X direction with respect to the center of the X-direction length of the radio wave reflector 100A. In other words, the configuration of the two groups 120G with lengths L3 and L4 is the inverse of the configuration of the two groups 120G with lengths L1 and L2 with respect to a line that passes through the center of the X-direction length of the radio wave reflector 100A and is parallel to the Y-axis.

[0099] Note that due to symmetry in the Y direction, section A3 includes four groups 120G of lengths L1, L2, L3, and L4, similar to section A1. The configuration of the four groups 120G of lengths L1, L2, L3, and L4 in section A3 is the inverse of the configuration of the four groups 120G of lengths L1, L2, L3, and L4 in section A1 with respect to a line that passes through the center of the length of the radio wave reflector 100A in the Y direction and is parallel to the X axis.

[0100] Additionally, in section A2, six groups 120G, each with lengths L1, L2, L2A, L2B, L3, and L4, are arranged from the -X direction side to the +X direction side. As an example, lengths L1 and L4 are equal, lengths L2 and L3 are equal, and lengths L2A and L2B are equal. Furthermore, lengths L1 and L4, lengths L2 and L3, and lengths L2A and L2B are different. Because the striped pattern is a concentric ellipse, lengths L1 and L4, lengths L2 and L3, and lengths L2A and L2B vary depending on the row position (position in the Y direction), but lengths L2 and L3 are longer than lengths L1 and L4 and also longer than lengths L2A and L2B. Furthermore, lengths L2A and L2B are longer than lengths L1 and L4.

[0101] The boundary between the group 120G of length L2A and the group 120G of length L2B coincides with the center of the length in the X direction of the radio wave reflector 100A. Within the group 120G of length L1, FSS elements 120A of the same size are adjacent to each other in the X direction, and the sizes decrease in order from the -X direction side to the +X direction side. Note that within the group 120G of length L1, there is a group 120G in which only the outermost FSS element 120A in the X direction has a size different from the sizes of the other FSS elements 120A.

[0102] In the group 120G of length L2, the FSS elements 120A are adjacent to each other with the same size in the X direction, and the sizes decrease from the −X direction to the +X direction. In the group 120G of length L2A, the FSS elements 120A are adjacent to each other with the same size in the X direction, and the sizes increase from the −X direction to the +X direction. In the group 120G of length L2B, the FSS elements 120A are adjacent to each other with the same size in the X direction, and the sizes decrease from the −X direction to the +X direction. In the group 120G of length L3, the FSS elements 120A are adjacent to each other with the same size in the X direction, and the sizes increase from the −X direction to the +X direction.

[0103] In the group 120G of length L4, the FSS elements 120A of the same size are adjacent to each other in the X direction, and the size increases in order from the −X direction side to the +X direction side. Note that, among the group 120G of length L4, there is a group 120G in which only the outermost FSS element 120A in the X direction has a size different from the sizes of the other FSS elements 120A.

[0104] In each row, the two groups 120G with lengths L1 and L2, the two groups 120G with lengths L2A and L2B, and the two groups 120G with lengths L3 and L4 are symmetrical in the X direction with respect to the center of the X-direction length of the radio wave reflector 100A. In other words, the configuration of the three groups 120G with lengths L2B, L3, and L4 is the inverse of the configuration of the three groups 120G with lengths L1, L2, and L2A with respect to a line that passes through the center of the X-direction length of the radio wave reflector 100A and is parallel to the Y-axis.

[0105] As described above, the radio wave reflector 100A includes multiple types of groups 120G with different numbers of FSS elements 120A in the X direction, and in each group 120G, the multiple FSS elements 120A are different in size and are arranged in order of size in the X direction. Therefore, the radio wave reflector 100A is capable of diffuse reflection in a plane including the X direction and the normal when reflecting an incident wave. In other words, the radio wave reflector 100A is capable of diffuse reflection in the azimuth direction in the XZ plane.

[0106] 4B, 3,600 FSS elements 120A form a concentric elliptical stripe pattern, and therefore, in the Y direction, elements of the same size are adjacent to each other and there are portions where the relationship of being arranged in order of size holds true. Therefore, when reflecting an incident wave, the radio wave reflector 100A is capable of diffuse reflection within a plane including the Y direction and the normal. In other words, the radio wave reflector 100A is capable of diffuse reflection in the elevation angle direction within the YZ plane.

[0107] 4B , the 3,600 FSS elements 120A form a striped pattern of concentric ellipses, and thus, along the radial direction from the center of the concentric ellipses, elements of the same size are adjacent to each other and are arranged in order of size. "The FSS elements 120A are adjacent to each other in the radial direction" means that, in directions parallel to the X or Y directions, the FSS elements 120A are adjacent to each other in the X or Y direction. In directions not parallel to the X or Y directions, this means that the FSS elements 120A located on a line extending radially from the center of the ellipse at any angle are arranged in a continuous order. Therefore, the radio wave reflector 100A is capable of diffuse reflection in the azimuth direction in the XZ plane, diffuse reflection in the elevation direction in the YZ plane, and diffuse reflection in a plane including a normal and a direction in which the FSS elements 120A are arranged in a continuous order on a line extending radially from the center of the ellipse at any angle. That is, the radio wave reflector 100A is capable of diffuse reflection in various planes including the radial direction and the normal, in which the FSS elements 120A of the same size are adjacent to each other and arranged in order of size.

[0108] <Radio wave reflector 100B shown in Fig. 4C> The radio wave reflector 100B shown in Fig. 4C has a striped pattern corresponding to the lower half of the concentric semicircles. The radio wave reflector 100B has a configuration in which the lower half of the concentric elliptical radio wave reflector 100A shown in Fig. 4B is made concentric elliptical.

[0109] The radio wave reflector 100B includes a plurality of groups 120G, each of which has a different number of FSS elements 120A in the X direction. In each group 120G, the plurality of FSS elements 120A are of different sizes and are arranged in order of size in the X direction.

[0110] Therefore, the radio wave reflector 100B can diffusely reflect incident waves, similar to the radio wave reflector 100A shown in Fig. 4B. Note that some of the groups 120G included in the radio wave reflector 100B may have multiple FSS elements 120A of the same size.

[0111] The patterns shown in Figures 4B and 4C are examples designed to satisfy the following formula (1). The principle of diffuse reflection is based on the following formula (1). A concave lens can scatter electromagnetic waves. Referring to Figure 8, the x-coordinate of the focal point F of the concave lens is f ｘ , z coordinate is f ｚ Then, it is expressed as in equation (1). The phase distribution for realizing a concave lens as a plane is given by equation (2).

[0112] In other words, the case of designing a metasurface reflector 100C that diffuses and reflects radio waves in a specific angular range will be described. A concave lens is considered as one method of diffusing electromagnetic waves. Therefore, the metasurface reflector 100C is used to flatten the concave lens. As shown in Figure 8, the metasurface reflector 100C is designed to diffuse and reflect radio waves in a specific angular range θ １ ~θ ２ The focal point F(f ｘ , 0, f ｚ ) is the x direction of the metasurface reflector 100C on the z=0 plane. １ 〜x ２ When the coordinates of each unit element in the plane of the metasurface reflector 100C are in the range of x, the equation (1) is obtained. ｎ , y ｍ ) design phase φ ｎｍ is calculated as in equation (2), where k is the wavelength and φ ｉ is the phase of the incident electric field. The same can be applied to diffuse reflection in different planes, and the light can be diffused in both azimuth and elevation.

[0113]

[0114] 5A to 5C are diagrams illustrating an example of a reflection pattern in a horizontal plane in the radio wave reflector 100. 5A to 5C show the radio wave reflector 100 as viewed from above (the +Y direction side). Furthermore, a dashed line C passing through the radio wave reflector 100 passes through the center of the surface 111 of the dielectric substrate 110 in the Z direction and is parallel to the normal to the surface 111.

[0115] 5A , light is incident from the −X direction side on the +Z direction side at an incident angle θi1, and the radio wave reflector 100 shown in Fig. 5A can diffusely reflect light within an angle range φr1 that includes a reflection angle θr1. The reflection angle θr1 is, for example, the center angle of the angle range φr1.

[0116] The radio wave reflector 100 includes a plurality of groups 120G, each of which has a different number of FSS elements 120A in the X direction. Such diffuse reflection is possible by setting the sizes of the FSS elements 120A in each group 120G, the number of FSS elements 120A of each size, and the size order of the FSS elements 120A.

[0117] In addition, by setting the multiple sizes of the multiple FSS elements 120A in each group 120G, the number of FSS elements 120A of each size, and the order of the sizes of the FSS elements 120A, it is possible to set either specular reflection in which the reflection angle θr1 is equal to the incident angle θi1, or non-specular reflection in which the reflection angle θr1 is not equal to the incident angle θi1.

[0118] As an example, by arranging three types of groups 120G with different numbers of FSS elements 120A in the +X direction and setting the reflection angles θr1 obtained by the three types of groups 120G to 40 degrees, 50 degrees, and 60 degrees, it is possible to achieve diffuse reflection in the angle range φr1 from 40 degrees to 60 degrees.

[0119] <Reflection pattern of the radio wave reflector 100 shown in Fig. 5B> The radio wave reflector 100 shown in Fig. 5B is capable of diffusively reflecting an incident wave that is incident from the -X direction at any angle included in the angle range φi2 that includes the incident angle θi2, into an angle range φr2 that includes the reflection angle θr2. As an example, the incident angle θi2 is the angle at the center of the angle range φi2, and the reflection angle θr2 is the angle at the center of the angle range φr2.

[0120] The multiple groups 120G included in the radio wave reflector 100 include multiple types of groups 120G with different numbers of FSS elements 120A in the X direction, and by setting multiple sizes of the multiple FSS elements 120A in each group 120G, the number of FSS elements 120A of each size, and the order of sizes of the FSS elements 120A, it is possible to diffusely reflect, within the angle range φr2, an incident wave incident at any angle included in the angle range φi2.

[0121] In addition, by setting the multiple sizes of the multiple FSS elements 120A in each group 120G, the number of FSS elements 120A of each size, and the order of sizes of the FSS elements 120A, it is possible to set either specular reflection in which the reflection angle θr2 is equal to the incident angle θi2, or non-specular reflection in which the reflection angle θr2 is not equal to the incident angle θi2.

[0122] <Reflection Pattern of the Radio Wave Reflector 100 Shown in Fig. 5C> The radio wave reflector 100 shown in Fig. 5C is the same as the radio wave reflector 100 shown in Fig. 5A. Fig. 5C shows reflection patterns obtained when radio waves are incident on the radio wave reflector 100 shown in Fig. 5A from the -X direction at various angles included in the angle range φi3 including the incident angle θi3. As shown in Fig. 5C, this radio wave reflector 100 is capable of reflecting, at a reflection angle θr3, an incident wave that is incident from the -X direction at any angle included in the angle range φi3 including the incident angle θi3. The incident angle θi3 is, for example, the center angle of the angle range φi3.

[0123] The multiple groups 120G included in the radio wave reflector 100 include multiple types of groups 120G with different numbers of FSS elements 120A in the X direction, and by setting multiple sizes of the multiple FSS elements 120A in each group 120G, the number of FSS elements 120A of each size, and the order of sizes of the FSS elements 120A, it is possible to reflect an incident wave incident at any angle included in the angle range φi3 at a reflection angle θr3.

[0124] In addition, by setting the multiple sizes of the multiple FSS elements 120A in each group 120G, the number of FSS elements 120A of each size, and the order of sizes of the FSS elements 120A, it is possible to set either specular reflection in which the reflection angle θr3 is equal to the incident angle θi3, or non-specular reflection in which the reflection angle θr3 is not equal to the incident angle θi3.

[0125] <Explanation of Reflection Pattern in Elevation Angle Direction> Fig. 5D is a diagram illustrating an example of a reflection pattern in the elevation angle direction of the radio wave reflector 100. Fig. 5D shows the radio wave reflector 100 as viewed from the side (+X direction side). In addition, a dashed line C passing through the radio wave reflector 100 passes through the center of the surface 111 of the dielectric substrate 110 in the Z direction and is parallel to the normal to the surface 111.

[0126] As an example, the radio wave reflector 100 shown in FIG. 5D has a configuration in which the radio wave reflector 100 shown in FIG. 5A is rotated by 90 degrees in the clockwise or counterclockwise direction within the XY plane when viewed from the +Z direction side.

[0127] 5D is capable of diffusively reflecting light in an angle range φr4 that includes a reflection angle θr4 when the incident angle is 0 degrees from the +Z direction side. The reflection angle θr4 is, for example, the angle at the center of the angle range φr4.

[0128] The radio wave reflector 100 includes a plurality of groups 120G, each of which has a different number of FSS elements 120A in the Y direction. Such diffuse reflection is possible by setting the sizes of the FSS elements 120A in each group 120G, the number of FSS elements 120A of each size, and the size order of the FSS elements 120A.

[0129] In addition, by setting the multiple sizes of the multiple FSS elements 120A in each group 120G, the number of FSS elements 120A of each size, and the size order of the FSS elements 120A, it is possible to set either specular reflection or non-specular reflection.

[0130] <Variations in Shape of Unit Area 111A and FSS Element 120A> FIGS. 6A to 6G are diagrams showing examples of variations in shape of the plurality of FSS elements 120A included in the FSS layer 120. FIG.

[0131] <Variation shown in FIG. 6A> As an example, the unit area 111A and the FSS element 120A shown in FIG. 6A are regular hexagons in plan view. The center of each FSS element 120A coincides with the center of the unit area 111A. As an example, FIG. 6A shows seven unit areas 111A and FSS elements 120A. The number of unit areas 111A and FSS elements 120A may be more or less than seven, but FIG. 6A shows seven unit areas 111A and FSS elements 120A. The seven unit areas 111A are arranged in a honeycomb pattern.

[0132] As an example, in group 120G including the two FSS elements 120A located furthest to the +Y direction side among the seven FSS elements 120A, the two FSS elements 120A, which are regular hexagons of different sizes, are arranged in order of size in the X direction.

[0133] Of the seven FSS elements 120A, three FSS elements 120A located in the center in the Y direction also constitute a group 120G. In this group 120G, three regular hexagonal FSS elements 120A of different sizes are arranged in order of size in the X direction. Of the seven FSS elements 120A, two FSS elements 120A located furthest from the -Y direction also constitute a group 120G. In group 120G including the two FSS elements 120A located furthest from the -Y direction of the seven FSS elements 120A, two regular hexagonal FSS elements 120A of different sizes are arranged in order of size in the X direction.

[0134] The radio wave reflector 100 may be configured using regular hexagonal FSS elements 120A as shown in Fig. 6A. In the radio wave reflector 100 shown in Fig. 6A, seven FSS elements 120A are divided into three groups 120G, and the sizes of the multiple FSS elements 120A in each group 120G are different and they are arranged in order of size in the X direction. This allows for diffuse reflection in the azimuth angle direction in the XZ plane that includes the X direction and the normal line.

[0135] 6B to 6G As an example, the unit area 111A shown in Fig. 6B has an equilateral triangle shape in plan view, and the FSS element 120A also has an equilateral triangle shape in plan view. As an example, the equilateral triangular FSS element 120A is arranged so that its center coincides with that of the unit area 111A.

[0136] The radio wave reflector 100 may be configured using an FSS layer 120 in which a plurality of FSS elements 120A having different sizes and an equilateral triangle shape are arranged in order of size in the X direction as shown in FIG. 6B, for example.

[0137] As an example, as shown in FIG. 6C , the unit area 111A may be square in plan view, and the FSS element 120A may be rectangular and annular in plan view. The center of each FSS element 120A coincides with the center of the unit area 111A. As an example, as shown in FIG. 6D , the unit area 111A may be regular hexagonal in plan view, and the FSS element 120A may be circular in plan view. The center of each FSS element 120A coincides with the center of the unit area 111A. The radio wave reflector 100 may be configured using an FSS layer 120 in which a plurality of rectangular and annular or circular FSS elements 120A of different sizes are arranged in order of size in the X direction, as shown in FIG. 6C or 6D .

[0138] 6E is, for example, a square in plan view, and the FSS element 120A is, for example, a cross in plan view. The cross-shaped FSS element 120A is, for example, arranged so that its center coincides with that of the unit area 111A.

[0139] The radio wave reflector 100 may be configured using an FSS layer 120 in which a plurality of FSS elements 120A of different sizes are arranged in a cross shape in order of size in the X direction as shown in FIG. 6E.

[0140] Alternatively, the FSS element 120A may have a Jerusalem cross shape as shown in Fig. 6F, or may have a shape obtained by reducing the Jerusalem cross shown in Fig. 6F to three strands spaced 120 degrees apart as shown in Fig. 6G.

[0141] Additionally, the FSS element 120A may have shapes other than those shown in FIGS. 6A to 6G.

[0142] <Second unit area and second FSS element> Figure 7 is a diagram showing an example of the arrangement of a plurality of FSS elements 120A and a plurality of FSS elements 120B in a radio wave reflector according to a modified example of the embodiment. The plurality of FSS elements 120B are arranged one per each of a plurality of unit areas 111B provided on the surface 111. The plurality of unit areas 111B are an example of a plurality of second unit areas. The plurality of FSS elements 120B are an example of a plurality of second FSS elements.

[0143] 7 shows 36 FSS elements 120A arranged on the surface 111 of the dielectric substrate 110, as in FIG. 3A, and 28 FSS elements 120B arranged in 4 rows and 7 columns. The unit area 111A in which the FSS elements 120A are arranged is provided in a section A11 on the +Y direction side of the surface 111, and the unit area 111B in which the FSS elements 120B are arranged is provided in a section A12 on the −Y direction side of the surface 111. Section A12 is adjacent to the −Y direction side of section A11. As an example, the seven unit areas 111B located furthest to the +Y direction side of the 28 unit areas 111B are in contact with the nine unit areas 111A in the fourth column.

[0144] The unit area 111B as the second unit area is a unit area having a different size in a planar view from the unit area 111A as the first unit area. For example, the size of the unit area 111B in a planar view is larger than the size of the unit area 111A in a planar view, but it may also be smaller.

[0145] The 36 FSS elements 120A are divided into four groups 120G1, four groups 120G2, and four groups 120G3. Similarly, the 28 FSS elements 120B are divided into four groups 120G4 and four groups 120G5. Groups 120G4 and 120G5 are examples of second groups. When groups 120G4 and 120G5 are not distinguished from groups 120G1 to 120G3, they are simply referred to as groups 120G.

[0146] As an example, in group 120G4, the FSS elements 120B in the first column are the largest, and the FSS elements 120B in the fourth column are the smallest. That is, in each group 120G4, the sizes of the four FSS elements 120B in a planar view are set to decrease in order from the first column to the fourth column, as an example. In this way, in group 120G4, the four FSS elements 120B are arranged in order of size in a planar view in the X direction. Note that the order of size in a planar view of the four FSS elements 120B included in group 120G4 may be reversed.

[0147] As an example, in group 120G5, the FSS elements 120B in the fifth column are the largest, and the FSS elements 120B in the seventh column are the smallest. That is, in each group 120G5, the sizes of the three FSS elements 120B in a planar view are set to decrease in order from the fifth column to the seventh column, as an example. In this way, in group 120G5, the three FSS elements 120B are arranged in order of size in a planar view in the X direction. Note that the order of the sizes of the three FSS elements 120B in group 120G5 in a planar view may be reversed.

[0148] 7 illustrates a configuration in which the FSS elements 120B are arranged in order of size in the X direction within each of the groups 120G4 and 120G5, similar to the FSS elements 120A. However, the FSS elements 120B do not have to be arranged in order of size. Furthermore, the FSS elements 120B may be of equal size within the groups 120G4 and / or 120G5.

[0149] As shown in FIG. 7, FSS elements 120A and 120B arranged in unit regions 111A and 111B of different sizes can be made larger by increasing the area ratio of the FSS element 120B compared to the FSS element 120A.

[0150] Therefore, by using FSS elements 120A and 120B arranged in unit areas 111A and 111B of different sizes, it is possible to increase the frequency band of radio waves that can be reflected and to achieve a wider frequency band than when only FSS element 120A arranged in unit area 111A is used.

[0151] When the effective wavelength at the operating frequency of the plurality of FSS elements 120B is λg, the distance between the centers of adjacent unit regions 111B is preferably 0.05λg or more and 0.65λg or less. If the distance between the centers of adjacent unit regions 111B is 0.05λg or more and 0.65λg or less, the resolution of the phase distribution can be improved, and the reflection efficiency for a desired reflection angle can be increased. Furthermore, reflection at angles other than the desired reflection angle can be reduced.

[0152] <Effects> The radio wave reflector 100 includes a dielectric substrate 110 having a surface 111 (first surface) located on the radio wave incident side and a surface 112 (second surface), a plurality of FSS elements 120A (first FSS elements) arranged on the surface 111 (first surface), and a radio wave reflecting layer 130 provided on the surface 112 (second surface), the plurality of FSS elements 120A are divided into a plurality of first groups, and each first group (groups 120G1 to 120G3) includes two or more FSS elements 120A arranged along one direction, the two or more FSS elements 120A in each first group being different in size and arranged in order of size in the one direction, and the plurality of first groups include a plurality of types of first groups each having a different number of FSS elements 120A in the one direction. In this way, by including a plurality of types of first groups each having a different number of FSS elements 120A in the one direction, diffuse reflection of radio waves is possible. Furthermore, by including a plurality of types of first groups each having a different number of FSS elements 120, the size of the radio wave reflector 100 can be reduced.

[0153] Therefore, it is possible to provide a radio wave reflector 100 that can diffusely reflect radio waves.

[0154] The dielectric substrate 110 may further include a plurality of unit areas 111A that are arranged adjacent to each other on the surface 111 (first surface) and have the same size in a planar view, and the plurality of FSS elements 120A may be arranged one per each of the plurality of unit areas 111A. This allows the plurality of FSS elements 120A to be easily arranged on the surface 111.

[0155] Furthermore, the one direction is a direction that defines the direction in which radio waves incident on the radio wave reflector 100 are reflected by the radio wave reflector 100, and within a plane that includes a first straight line extending in the one direction and a normal to the surface 111 (first surface), the angle that the incident path of the radio waves that are incident on the radio wave reflector 100 makes with the normal may be the angle of incidence, and the angle that the reflection path along which the incident radio waves are reflected by the radio wave reflector 100 makes with the normal may be the angle of reflection. Therefore, the reflection angle of diffuse reflection is obtained within the plane that includes the one direction and the normal.

[0156] In each unit area 111A, the center of the unit area 111A may coincide with the center of the FSS element 120A. By being able to uniformly arrange the FSS elements 120A within each unit area 111A, it becomes easier to set the reflection angle of diffuse reflection. In addition, the size of each FSS element 120A can be easily set.

[0157] When the effective wavelength at the operating frequency of the plurality of FSS elements 120A is λg, the distance between the centers of adjacent unit areas 111A may be 0.05λg or more and 0.65λg or less. This can improve the resolution of the phase distribution and increase the reflection efficiency for a desired reflection angle. Furthermore, it can reduce reflections at angles other than the desired reflection angle.

[0158] Furthermore, the plurality of FSS elements 120A may include a plurality of types of FSS elements 120A that are similar in shape but different in size in a plan view, which makes it easier to set the reflection angle of diffuse reflection.

[0159] Furthermore, multiple types of FSS elements 120A with similar shapes and different sizes may be arranged in order of size in one direction, which makes it easier to equalize the radio wave intensity over the entire reflection angle of diffuse reflection in one direction.

[0160] Furthermore, multiple types of FSS elements 120A with similar shapes and different sizes may be arranged in order of size, with two or more FSS elements 120A of equal size being adjacent to each other in one direction, which makes it easier to equalize the radio wave intensity over the entire reflection angle of diffuse reflection in one direction.

[0161] The radio wave reflecting layer 130 may be made of a conductive film or a metal mesh. It is possible to provide a radio wave reflector 100 that has good visibility by suppressing unevenness due to differences in visible light transmittance while ensuring the function of reflecting radio waves.

[0162] The FSS device may further include a protective plate 160A (first protective layer) located on the opposite side of the dielectric substrate 110 from the plurality of FSS elements 120A. The protective plate 160A can protect the plurality of FSS elements 120A.

[0163] The device may further include a protection plate 160B (second protection layer) located on the opposite side of the radio wave reflection layer 130 from the dielectric substrate 110. The radio wave reflection layer 130 can be protected by the protection plate 160B.

[0164] Furthermore, the protective plate 160A may be a glass or resin substrate. When the protective plate 160A is a glass or resin substrate, the glass or resin protective plate 160A can protect the multiple FSS elements 120A.

[0165] Furthermore, the protective plate 160B may be a glass or resin substrate. When the protective plate 160B is a glass or resin substrate, the radio wave reflecting layer 130 can be protected by the glass or resin protective plate 160B.

[0166] Furthermore, the sheet resistance of the plurality of FSS elements 120A may be 1 Ω / sq. or more and 30 Ω / sq. or less. By setting the sheet resistance of the plurality of FSS elements 120A to an appropriate value, it is possible to provide a radio wave reflector 100 with good radio wave reflection characteristics.

[0167] The thickness of the protection plate 160A may be 2 mm or more and 6 mm or less. By setting the thickness of the protection plate 160A to an appropriate value, it is possible to provide a radio wave reflector 100 with good radio wave reflection characteristics.

[0168] The sheet resistance of the radio wave reflective layer 130 may be 3 Ω / sq. or less. By setting the sheet resistance of the radio wave reflective layer 130 to an appropriate value, it is possible to provide a radio wave reflector 100 with good radio wave reflection characteristics.

[0169] Furthermore, when the relative dielectric constant of the dielectric substrate 110 is εr, the thickness of the dielectric substrate 110 may be equal to or less than 1 / (10√εr) of the wavelength at the frequency of the radio waves reflected by the radio wave reflector 100. By setting the thickness of the dielectric substrate 110 to an appropriate value, it is possible to provide a radio wave reflector 100 with good radio wave reflection characteristics.

[0170] Alternatively, the visible light transmittance may be 50% or more and the haze value may be 5% or less, thereby providing a radio wave reflector 100 with good visibility.

[0171] The dielectric substrate 110 may further include a plurality of FSS elements 120B (second FSS elements), and the dielectric substrate 110 may further include a plurality of second unit areas arranged adjacent to each other on the surface 111 (first surface) and having equal sizes in a planar view, the size of the second unit areas in a planar view being different from the size of the unit area 111A in a planar view, and the plurality of FSS elements 120B may be arranged one per each of the plurality of second unit areas on the surface 111 (first surface). By using a plurality of FSS elements 120B (second FSS elements), it is possible to provide a radio wave reflector 100 that can reflect radio waves in a wider band.

[0172] Furthermore, the multiple FSS elements 120B are divided into multiple second groups (groups 120G4 to 120G5), each of which includes two or more FSS elements 120B arranged in one direction, and the multiple second groups may include multiple types of second groups with different numbers of FSS elements 120B in one direction. It is also possible to diffusely reflect radio waves reflected using the multiple FSS elements 120B (second FSS elements).

[0173] When the effective wavelength at the operating frequency of the plurality of FSS elements 120B is λg, the distance between the centers of adjacent unit regions 111B may be 0.05λg or more and 0.65λg or less. This can improve the resolution of the phase distribution and increase the reflection efficiency for a desired reflection angle. Furthermore, it can reduce reflections at angles other than the desired reflection angle.

[0174] Although exemplary radio wave reflectors according to the present disclosure have been described above, the present disclosure is not limited to the specifically disclosed embodiments, and various modifications and variations are possible without departing from the scope of the claims.

[0175] The following supplementary notes are further disclosed in relation to the above embodiments. (Supplementary Note 1) A radio wave reflector including: a dielectric substrate having a first surface located on the radio wave incident side and a second surface; a plurality of first FSS (Frequency Selective Surface) elements arranged on the first surface; and a radio wave reflecting layer provided on the second surface, wherein the plurality of first FSS elements are divided into a plurality of first groups, each of which includes two or more first FSS elements arranged along one direction, wherein the two or more first FSS elements in each first group are different in size and arranged in order of size in the one direction, and the plurality of first groups include a plurality of types of first groups with different numbers of first FSS elements in the one direction. (Supplementary Note 2) The radio wave reflector according to Supplementary Note 1, wherein the dielectric substrate further includes a plurality of first unit areas arranged adjacent to each other on the first surface and having equal sizes in a planar view, and wherein the plurality of first FSS elements are arranged one by one in each of the plurality of first unit areas. (Supplementary Note 3) The radio wave reflector according to Supplementary Note 1 or 2, wherein the one direction is a direction that defines a direction in which radio waves incident on the radio wave reflector are reflected by the radio wave reflector, and within a plane including a first straight line extending in the one direction and a normal to the first surface, an angle that an incident path of the radio waves incident on the radio wave reflector makes with the normal is an incident angle, and an angle that a reflection path of the incident radio waves reflected by the radio wave reflector makes with the normal is a reflection angle. (Supplementary Note 4) The radio wave reflector according to Supplementary Note 2, wherein in each first unit area, a center of the first unit area coincides with a center of the first FSS element. (Supplementary Note 5) The radio wave reflector according to any one of Supplementary Notes 1 to 4, wherein the plurality of first FSS elements include a plurality of types of first FSS elements that have similar shapes but different sizes in a planar view. (Supplementary Note 6) The radio wave reflector according to Supplementary Note 5, wherein the plurality of types of first FSS elements that have similar shapes but different sizes are arranged in order of size in the one direction. (Supplementary Note 7) The radio wave reflector according to Supplementary Note 5, wherein the plurality of types of first FSS elements having similar shapes but different sizes are arranged in order of size such that two or more first FSS elements having the same size are adjacent to each other in the one direction.(Supplementary Note 8) The radio wave reflector according to any one of Supplementary Notes 1 to 7, wherein the radio wave reflective layer is made of a conductive film or a metal mesh. (Supplementary Note 9) The radio wave reflector according to any one of Supplementary Notes 1 to 8, further including a first protective layer located on the opposite side of the dielectric substrate to the plurality of first FSS elements. (Supplementary Note 10) The radio wave reflector according to any one of Supplementary Notes 1 to 9, further including a second protective layer located on the opposite side of the dielectric substrate to the radio wave reflective layer. (Supplementary Note 11) The radio wave reflector according to Supplementary Note 9, wherein the first protective layer is a glass or resin substrate. (Supplementary Note 12) The radio wave reflector according to Supplementary Note 10, wherein the second protective layer is a glass or resin substrate. (Supplementary Note 13) The radio wave reflector according to any one of Supplementary Notes 1 to 12, wherein the sheet resistance of the plurality of first FSS elements is 30 Ω / sq. or less. (Supplementary Note 14) The radio wave reflector according to Supplementary Note 9, wherein the thickness of the first protective layer is 2 mm or more and 6 mm or less. (Supplementary Note 15) The radio wave reflector according to any one of Supplementary Notes 1 to 14, wherein the sheet resistance of the radio wave reflecting layer is 3 Ω / sq. or less. (Supplementary Note 16) The radio wave reflector according to any one of Supplementary Notes 1 to 15, wherein the thickness of the dielectric substrate is 1 / (10√εr) or less of the wavelength at the frequency of the radio waves reflected by the radio wave reflector, where εr is the relative permittivity of the dielectric substrate. (Supplementary Note 17) The radio wave reflector according to any one of Supplementary Notes 1 to 16, wherein the visible light transmittance is 50% or more and the haze value is 5% or less. (Supplementary Note 18) The radio wave reflector according to Supplementary Note 2, further including a plurality of second FSS elements, wherein the dielectric substrate further includes a plurality of second unit areas arranged adjacent to each other on the first surface and having equal sizes in a planar view, wherein the size of the second unit areas in a planar view is different from the size of the first unit areas in a planar view, and wherein the plurality of second FSS elements are arranged one by one in each of the plurality of second unit areas on the first surface. (Supplementary Note 19) The radio wave reflector according to Supplementary Note 18, further including a plurality of second groups each including two or more second FSS elements arranged along the one direction, and wherein the plurality of second groups include a plurality of types of second groups each having a different number of second FSS elements in the one direction.The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-217164 filed on December 22, 2023 are hereby incorporated by reference as the disclosure of the specification of the present invention.

[0176] REFERENCE SIGNS LIST 100 Radio wave reflector 110 Dielectric substrate 111 Surface (an example of a first surface) 111A Unit area (an example of a first unit area) 111B Unit area (an example of a second unit area) 112 Surface (an example of a second surface) 120 FSS layer 120A FSS element (an example of a first FSS element) 120B FSS element (an example of a second FSS element) 120G Group 120G1 to 120G3 groups (an example of a first group) 120G4, 120G5 groups (an example of a second group) 130 Radio wave reflecting layer 140 Adhesive layer 150A, 150B Adhesive layer 160A Protective plate (an example of a first protective layer) 160B Protective plate (an example of a second protective layer)

Claims

1. A radio wave reflector comprising: a dielectric substrate having a first surface located on the radio wave incident side and a second surface; a plurality of first FSS (Frequency Selective Surface) elements arranged on the first surface; and a radio wave reflecting layer provided on the second surface, wherein the plurality of first FSS elements are divided into a plurality of first groups, each first group comprising two or more first FSS elements arranged along one direction, wherein in each first group, the two or more first FSS elements have different sizes and are arranged in order of size in the one direction, and the plurality of first groups include a plurality of types of first groups each having a different number of first FSS elements in the one direction.

2. The radio wave reflector according to claim 1, wherein the dielectric substrate further has a plurality of first unit areas arranged adjacent to each other on the first surface and having equal sizes in a planar view, and the plurality of first FSS elements are arranged one by one in each of the plurality of first unit areas.

3. A radio wave reflector as described in claim 1 or 2, wherein the one direction is a direction that defines a direction in which radio waves incident on the radio wave reflector are reflected by the radio wave reflector, and within a plane that includes a first straight line extending in the one direction and a normal to the first surface, an angle that an incident path of the radio waves incident on the radio wave reflector makes with the normal is an incident angle, and an angle that a reflection path along which the incident radio wave is reflected by the radio wave reflector makes with the normal is a reflection angle.

4. A radio wave reflector as described in claim 2 or 3, wherein in each first unit area, the center of said first unit area coincides with the center of said first FSS element.

5. A radio wave reflector as described in any one of claims 2 to 4, wherein when the effective wavelength at the operating frequency of the plurality of first FSS elements is λg, the distance between the centers of adjacent first unit areas is 0.05 λg or more and 0.65 λg or less.

6. A radio wave reflector according to any one of claims 1 to 5, wherein the plurality of first FSS elements include a plurality of types of first FSS elements having similar shapes but different sizes in a plan view.

7. The radio wave reflector according to claim 6, wherein the first FSS elements of a plurality of types having similar shapes but different sizes are arranged in order of size in the one direction.

8. The radio wave reflector according to claim 6, wherein the plurality of types of first FSS elements having similar shapes but different sizes are arranged in order of size in the one direction, with two or more first FSS elements having the same size being adjacent to each other.

9. A radio wave reflector according to any one of claims 1 to 8, wherein the radio wave reflecting layer is made of a conductive film or a metal mesh.

10. A radio wave reflector as claimed in any one of claims 1 to 9, further comprising a first protective layer located on the opposite side of said dielectric substrate to said plurality of first FSS elements.

11. A radio wave reflector according to any one of claims 1 to 10, further comprising a second protective layer located on the opposite side of said radio wave reflecting layer from said dielectric substrate.

12. The radio wave reflector according to claim 10, wherein the first protective layer is a substrate made of glass or resin.

13. The radio wave reflector according to claim 11, wherein the second protective layer is a substrate made of glass or resin.

14. The radio wave reflector according to any one of claims 1 to 13, wherein the sheet resistance of the plurality of first FSS elements is 30 Ω / sq. or less.

15. The radio wave reflector according to claim 10 or 12, wherein the thickness of the first protective layer is 2 mm or more and 6 mm or less.

16. The radio wave reflector according to any one of claims 1 to 15, wherein the sheet resistance of the radio wave reflecting layer is 3 Ω / sq. or less.

17. A radio wave reflector as claimed in any one of claims 1 to 16, wherein the thickness of the dielectric substrate is 1 / (10√εr) or less of the wavelength at the frequency of the radio waves reflected by the radio wave reflector, where εr is the relative dielectric constant of the dielectric substrate.

18. A radio wave reflector according to any one of claims 1 to 17, having a visible light transmittance of 50% or more and a haze value of 5% or less.

19. A radio wave reflector as described in any one of claims 2 to 18, further comprising a plurality of second FSS elements, wherein the dielectric substrate further has a plurality of second unit areas arranged adjacent to each other on the first surface and having equal sizes in a planar view, the size of the second unit areas in a planar view being different from the size of the first unit area in a planar view, and the plurality of second FSS elements are arranged one by one in each of the plurality of second unit areas on the first surface.

20. The radio wave reflector of claim 19, wherein the plurality of second FSS elements are divided into a plurality of second groups, each of the second groups including two or more second FSS elements arranged along the one direction, and the plurality of second groups include a plurality of types of second groups having different numbers of the second FSS elements in the one direction.

21. A radio wave reflector as described in claim 19 or 20, wherein when the effective wavelength at the operating frequency of the plurality of second FSS elements is λg, the distance between the centers of adjacent second unit areas is not less than 0.05 λg and not more than 0.65 λg.

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