Radio wave scattered particles

Abstract

The present invention provides a radio wave scatterer that scatters and reflects radio waves over a wide angular range, thereby enhancing interference countermeasures. [Solution] A radio wave scatterer comprising a base layer, a plurality of reflective elements provided on the surface of the base layer, and a conductive layer provided on the back surface of the base layer, which scatters and reflects vertically irradiated radio waves in a desired plurality of directions, The reflective elements are arranged in a grid pattern in a plan view, and the reflection phase of the reflective elements has a direction in which it increases or decreases with a constant period. With the direction in which the reflection phase increases or decreases being the Y direction, and the direction perpendicular to the Y direction being the X direction, the reflection peaks are present in at least three different directions. The reflection peaks include at least one reflection peak in the positive direction of the Y-axis and at least one reflection peak in the negative direction of the Y-axis. A radio wave scatterer characterized by the following features.

Description

Technical Field

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[0001] The present invention relates to a radio wave scatterer for scattering radio waves.

Background Art

[0002] In mobile phones and wireless communications, radio waves in a frequency band of about 2 GHz or more and 300 GHz or less, called centimeter waves and millimeter waves, are used. In particular, high-frequency radio waves are used for high-speed communication and high-sensitivity radar.

[0003] In an environment where a plurality of transmitters and receivers are arranged, the radio waves of each other interfere with each other as noise in the above-mentioned high-frequency radio waves, so countermeasures against interference are required.

[0004] As a countermeasure against interference, it is conceivable to scatter and reflect the radio waves that become noise and weaken them to an intensity that does not affect radio wave utilization. For example, in Patent Document 1, a reflectarray that reflects at a plurality of incident angles or reflection angles has been proposed.

[0005] However, the reflectarray described in Patent Document 1 has a problem that the reflection direction is limited to the same positive and negative directions, and the interference countermeasure effect by reducing the intensity of the reflected radio wave is insufficient.

[0006] Therefore, it is desired to develop a radio wave scatterer that can scatter and reflect radio waves in a wide angle range, has a high radio wave scattering effect, and can exhibit a high interference suppression effect.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention aims to provide a radio wave scatterer that can scatter and reflect incident radio waves over a wide angular range, exhibiting a high radio wave scattering effect and a high interference suppression effect. [Means for solving the problem]

[0009] To achieve the above objectives, the present invention encompasses the following subject matter. 1. A radio wave scatterer comprising a base layer, a plurality of reflective elements provided on the surface of the base layer, and a conductive layer provided on the back surface of the base layer, which scatters and reflects vertically irradiated radio waves in a desired plurality of directions, The reflective elements are arranged in a grid pattern in a plan view, and the reflection phase of the reflective elements has a direction in which it increases or decreases with a constant period. With the direction in which the reflection phase increases or decreases being the Y direction, and the direction perpendicular to the Y direction being the X direction, the reflection peaks are present in at least three different directions. The reflection peaks include at least one reflection peak in the positive direction of the Y-axis and at least one reflection peak in the negative direction of the Y-axis. A radio wave scatterer characterized by the following features. 2. The radio wave scatterer according to item 1, wherein the reflection peaks are equal in number in the positive and negative directions of the Y-axis. 3. The radio wave scatterer according to item 1 or 2, having m reflective elements in the X direction and n(x) (1≦x≦m) reflective elements in the Y direction, wherein the reflection phase of the reflective element located at the x-th coordinate in the X direction (1≦x≦m) and the y-th coordinate in the Y direction (1≦y≦n(x)) is P(x,y), the reflection phase difference between adjacent reflective elements arranged in the Y direction is D(x,y)=P(x,y+1)-P(x,y)(1≦x≦m, 1≦y≦n(x)-1), and Dmax(x) is the value of D(x,y) when |D(x,y)| is maximized when the value of x is fixed and only y is changed, such that for all values ​​of y there exists a value of x that satisfies the following equation 1, and there exists at least one value of x that satisfies equation 2 and at least one value of x that satisfies equation 3. Formula 1: P(x,y)=P(x+1,y)(1≦x≦m-1, 1≦y≦n(x)) Equation 2:|Dmax(x)|=Dmax(x) Equation 3:|Dmax(x)|=-Dmax(x) 4. The radio wave scatterer described in item 3, wherein there are an equal number of x values ​​that satisfy equation 1 and x values ​​that satisfy equation 2. 5. The radio wave scatterer according to item 3 or 4, wherein the value of x that satisfies equation 2 and the value of x that satisfies equation 3 are both consecutive natural numbers. [Effects of the Invention]

[0010] The radio wave scatterer of the present invention can scatter and reflect incident radio waves over a wide angular range by scattering and reflecting them in both positive and negative angular directions, resulting in a high radio wave scattering effect and a high interference suppression effect. [Brief explanation of the drawing]

[0011] [Figure 1] This is a plan view showing the overall schematic configuration of the first embodiment of the radio wave scatterer of the present invention. [Figure 2] This figure shows the reflectance intensity of the radio wave scatterers of Example 1, Comparative Example 1, and Comparative Example 2 in each reflection direction. [Figure 3] This figure shows the reflectance intensity of the radio wave scatterers of Example 2, Comparative Example 3, and Comparative Example 4 in each reflection direction. [Figure 4] This is a plan view showing the arrangement of the reflecting elements of the radio wave scatterer in Example 1. [Figure 5] This is a plan view showing the arrangement of the reflecting elements of the radio wave scatterer in Example 2. [Figure 6] This is a plan view showing the arrangement of the reflecting elements of the radio wave scatterer in Comparative Example 1. [Figure 7] This is a plan view showing the arrangement of the reflecting elements of the radio wave scatterer in Comparative Example 2. [Figure 8] This is a plan view showing the arrangement of the reflecting elements of the radio wave scatterer in Comparative Example 3. [Figure 9] This is a plan view showing the arrangement of the reflecting elements of the radio wave scatterer in Comparative Example 4. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described with reference to the drawings. Note that the drawings are used for explaining the present invention and do not indicate actual scales. Also, the two-dot chain lines in the drawings are virtual lines for indicating regions and sections in the following description, and are not lines drawn on actual radio wave scatterers.

[0013] Also, in this specification, the arrangement in the left-right direction with respect to the paper surface may be described as "row", and the arrangement in the up-down direction may be described as "column".

[0014] (First Embodiment) FIG. 1 is a plan view showing a schematic configuration of a first embodiment of a radio wave scatterer of the present invention. In FIG. 1, a radio wave scatterer 11 of this embodiment includes a base material layer 13 and a plurality of reflection elements 20, and by having this configuration, vertically irradiated radio waves are scattered and reflected in a plurality of desired directions. The base material layer 13 is rectangular in a plan view. The reflection elements 20 are provided on the surface of the base material layer 13, and each reflection element 20 is a conductor having a square shape in a plan view in the example shown in FIG. 1. The reflection elements 20 are arranged along a direction in which the reflection phase increases or decreases on the surface of the base material layer 13 (hereinafter, also referred to as the "Y direction"), and a direction perpendicular to the Y direction (hereinafter, also referred to as the "X direction"). The reflection elements 20 are arranged side by side in a grid pattern in a plan view, that is, arranged in a grid pattern. Although not shown in FIG. 1, the back surface of the base material layer 13 (the surface opposite to the surface on which the reflection elements 20 are formed) has a conductive layer.

[0015] In Figure 1, in the region consisting of rows x1 and x2, the size of the reflective elements 20 decreases in the Y direction, i.e., from left to right relative to the plane of the paper, at a constant period of three reflective elements 20 at a time. As a result, in the region consisting of rows x1 and x2, the reflection phase of the reflective elements 20 decreases at a constant period from left to right relative to the plane of the paper. Similarly, in the region consisting of rows x3 and x4, the size of the reflective elements 20 decreases in the Y direction, i.e., from left to right relative to the plane of the paper, at a constant period of four reflective elements 20 at a time. As a result, in the region consisting of rows x3 and x4, the reflection phase of the reflective elements 20 decreases at a constant period from left to right relative to the plane of the paper.

[0016] Furthermore, in Figure 1, in the region consisting of rows x5 and x6, the size of the reflective elements 20 increases in the Y direction, that is, from left to right relative to the plane of the paper, at a constant period of 4 elements at a time. As a result, in the region consisting of rows x5 and x6, the reflection phase of the reflective elements 20 increases at a constant period from left to right relative to the plane of the paper. Also, in the region consisting of rows x7 and x8, the size of the reflective elements 20 increases in the Y direction, that is, from left to right relative to the plane of the paper, at a constant period of 3 elements at a time. As a result, in the region consisting of rows x7 and x8, the reflection phase of the reflective elements 20 increases at a constant period from left to right relative to the plane of the paper.

[0017] Based on the above, in Figure 1, in the radio wave scatterer 11 of the present invention, the direction in which the reflection phase increases or decreases is the left-right direction with respect to the plane of the paper, and this direction is the Y direction. Furthermore, the direction perpendicular to the Y direction is the X direction.

[0018] In the example in Figure 1, the reflecting elements 20 are of different sizes, but their shapes may also be different, or both their shape and size may be different. The shape and size of the conductor constituting each reflecting element 20 are appropriately selected according to the frequency and intensity of the radio waves to be reflected. For example, the planar shape may be rectangular, circular, elliptical, triangular, polygonal, etc., or it may be annular, that is, composed of a conductor and a region without a conductor surrounded by the conductor. Also, in the example in Figure 1, the reflecting elements 20 are shown arranged in 8 rows in the x direction and 9 rows in the y direction, but the number of rows and columns in the arrangement can be changed as appropriate.

[0019] The radio wave scatterer of the present invention has reflection peaks in at least three different directions, with the direction in which the reflection phase increases or decreases being the Y direction and the direction perpendicular to the Y direction being the X direction. Of these reflection peaks, it has at least one reflection peak in the positive direction of the Y axis and at least one reflection peak in the negative direction. The following will be explained with reference to the figures.

[0020] Figure 2 shows the reflection intensity of the radio wave scatterers of Example 1, Comparative Example 1, and Comparative Example 2, which will be described later, in each reflection direction. In Figure 2, Example 1, which has the configuration of the radio wave scatterer of the present invention, has reflection peaks in the three directions indicated by arrows: -48deg, 46deg, and 71deg. Of these reflection peaks, one is at -48deg, so it is a reflection peak in the negative direction of the Y axis, and the peaks at 46deg and 71deg are reflection peaks in the positive direction of the Y axis, so it has at least one reflection peak in the positive direction of the Y axis and at least one reflection peak in the negative direction of the Y axis.

[0021] Furthermore, Figure 3 shows the reflection intensity in each reflection direction for the radio wave scatterers of Example 2, Comparative Example 3, and Comparative Example 4, which will be described later. In Figure 3, Example 2, which has the configuration of the radio wave scatterer of the present invention, has reflection peaks in the eight directions indicated by the arrows. In addition, these reflection peaks are present in equal numbers of four in the positive direction and four in the negative direction of the Y axis, with 0 degrees in between. It is preferable that the radio wave scatterer of the present invention has equal numbers of reflection peaks in the positive direction and two in the negative direction of the Y axis, as described above. By having this configuration, reflected radio waves cancel each other out, and radio wave interference can be further suppressed.

[0022] In the radio wave scatterer of the present invention, the determination of reflection peaks is performed according to the following criteria. Specifically, using an electromagnetic field simulator, the reflection profile in the Y direction is analyzed at a far-field level when a 79 GHz Y-polarized radio wave is perpendicularly irradiated onto each radio wave scatterer. In this far-field analysis, the specular reflection intensity of the Al plate is set to 0 dB. The reflection intensity in the front (0 deg) direction and the maximum reflection intensity in the Y direction from -90 to 90 deg are evaluated. Since the front reflection wave has the greatest impact on interference, -25 dB is used as the standard, while the lateral reflection wave, where the reflection intensity takes its maximum, is less affected and therefore -10 dB is used as the standard. The determination of reflection peaks (counting the number of reflection peaks) is performed by counting the maximum values ​​in the reflection profile graph that have an intensity of -5 dB or more relative to the maximum reflection intensity as reflection peaks.

[0023] The radio wave scatterer of the present invention preferably has m reflective elements in the X direction and n(x) (1≦x≦m) reflective elements in the Y direction, and the reflection phase of the reflective element located at the x-th coordinate in the X direction (1≦x≦m) and the y-th coordinate in the Y direction (1≦y≦n(x)) is P(x,y), the reflection phase difference between adjacent reflective elements arranged in the Y direction is D(x,y)=P(x,y+1)-P(x,y)(1≦x≦m, 1≦y≦n(x)-1), and Dmax(x) is the value of D(x,y) when |D(x,y)| is maximized when the value of x is fixed and only y is changed, and for all values ​​of y there exists an x ​​value that satisfies the following equation 1, and preferably there is at least one x value that satisfies equation 2 and at least one x value that satisfies equation 3. Formula 1: P(x,y)=P(x+1,y)(1≦x≦m-1, 1≦y≦n(x)) Equation 2:|Dmax(x)|=Dmax(x) Equation 3:|Dmax(x)|=-Dmax(x)

[0024] The above equations 1 to 3 will be explained using diagrams and tables.

[0025] (Formula 1) Figure 4 is a plan view showing the arrangement of reflective elements in the radio wave scatterer of Example 1, which will be described later. In Figure 4, in the first row in the X direction and the second row in the X direction, reflective elements of the same shape are arranged adjacent to each other toward the Y direction. That is, in the radio wave scatterer of the present invention shown in Figure 4, since reflective elements of the same shape are arranged adjacent to each other for all y values ​​in the first row in the X direction and the second row in the X direction, P(1,y)=P(2,y) is satisfied, and there exists an x1 that satisfies P(x,y)=P(x+1,y), so there exists an x ​​value that satisfies the above equation 1 for all y values. In addition, in the radio wave scatterer of the present invention shown in Figure 4, similarly, reflective elements of the same shape are arranged adjacent to each other in the third row in the X direction and the fourth row in the X direction. The same applies to the fifth row and beyond in the X direction.

[0026] (Formula 2) Table 2 shows the reflection phase difference D(x,y) of the reflection phase in Example 1, which will be described later. In Table 2, for example, at D(9,4), the reflection phase difference Dmax(x) is 238, and since Dmax(x) is a positive value, it satisfies |Dmax(x)|=Dmax(x) (Equation 2).

[0027] (Formula 3) Table 2 shows the reflection phase difference D(x,y) of the reflection phase in Example 1, which will be described later. In Table 2, for example, at D(5,4), the reflection phase difference Dmax(x) is -238, and since Dmax(x) is a negative value, it satisfies |Dmax(x)|=-Dmax(x) (Equation 3).

[0028] Preferably, the radio wave scatterer of the present invention has an equal number of x values ​​that satisfy Equation 1 and x values ​​that satisfy Equation 2. By having this configuration, the reflected radio waves cancel each other out, and radio wave interference can be further suppressed.

[0029] Preferably, in the radio wave scatterer of the present invention, the value of x that satisfies formula 2 and the value of x that satisfies formula 3 are both consecutive natural numbers. By having this configuration, the reflected radio waves cancel each other out, and radio wave interference can be further suppressed.

[0030] The thickness (film thickness) of the reflective element 20 is preferably 5 nm or more, and preferably 0.05 μm or more and 10 μm or less. The thickness is set appropriately from the viewpoint of ensuring appropriate radio wave intensity and visible light transmittance.

[0031] The reflective element 20 is preferably made of silver, for example. The reflective element 20 may be made of a metal, metal compound, or alloy having free electrons, and is not limited to silver. For example, one or more selected from the group consisting of gold, copper, platinum, aluminum, titanium, silicon, indium tin oxide, and alloys (for example, alloys containing nickel, chromium, and molybdenum). Examples of alloys containing nickel, chromium, and molybdenum include various grades such as Hastelloy B-2, B-3, C-4, C-2000, C-22, C-276, G-30, N, W, and X.

[0032] One method for manufacturing the reflective element 20 is to form a conductive film, then create a pattern by etching, and then remove the conductive thin film having the pattern. Another method involves coating a base film with a lift-off layer with a photosensitive resist, forming a pattern by photolithography, filling the patterned area with a conductor, and then removing the conductive thin film having the pattern. The manufacturing method is not limited to the above, and other methods for forming the reflective element 20 include bonding a metal thin film and depositing metal.

[0033] The base layer 13 has a reflective element 20 formed on its upper surface and is a sheet-like component. "Sheet" refers to a shape in which the thickness of the object is 10% or less of the maximum length between the outer edges in a plan view. In this specification, films, foils, etc. are also included in "sheet".

[0034] The base layer 13 is made from materials such as PET (polyethylene terephthalate), FR4 (glass fiber cloth impregnated with epoxy resin and heat-cured to form a sheet), glass, or silicone. Other synthetic resins may also be used as materials. Examples of synthetic resins include one or more selected from the group consisting of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polymethyl methacrylate, polyester, polyformaldehyde, polyamide, polyphenylene ether, vinylidene chloride, polyvinyl acetate, polyvinyl acetal, AS resin, ABS resin, acrylic resin, fluororesin, nylon resin, polyacetal resin, polycarbonate resin, polyamide resin, and polyurethane resin.

[0035] The base layer 13 is formed in a rectangular shape when viewed from above. However, it is not limited to this, and may be rectangular, circular, elliptical, sector-shaped, polygonal, three-dimensional, etc., and is appropriately set according to the conditions of the building or wall on which the radio wave scatterer 11 is installed. The thickness of the base layer 13 is set to, for example, 0.1 mm to 1 mm.

[0036] The conductive layer is formed on the back surface of the base layer 13 (the surface opposite to the surface on which the reflective element 20 is formed) and is laminated with the base layer 13. The shape of the conductive layer is not particularly limited, but for example, it can be a layer with the same shape as the base layer 13.

[0037] The conductive layer may contain a conductor made of a metal with free electrons, such as copper, silver, gold, platinum, aluminum, titanium, or silicon. The conductive layer may also contain any synthetic resin or other material in addition to the conductor. The thickness (film thickness) of the conductive layer is not particularly limited and may be 50 nm or more, 100 nm or more, 200 nm or more, 500 nm or more, or 700 nm or more. The thickness (film thickness) of the conductive layer may also be 10 μm or less, 5 μm or less, 3 μm or less, or 2 μm or less.

[0038] Furthermore, in order to protect the reflective element 20, the reflective element 20 may have a protective layer for protecting the reflective element 20 and an adhesive layer for bonding the reflective element 20 and the protective layer. In this case, the radio wave scatterer 11 is laminated in the order of base layer 13, reflective element 20, adhesive layer, and protective layer. The material of the protective layer may be the same as that of the base layer 13.

[0039] The above-mentioned radio wave scatterer 11 is in the form of a sheet, and it is preferable that its thickness be set to 1 mm or less. The thickness of the radio wave scatterer 11 is set such that the radio wave scatterer 11 can be flexible and that when an external force is applied to the radio wave scatterer 11 and the radio wave scatterer 11 is bent, the force does not concentrate on the conductor. Note that since the thickness of the reflective element 20 is very thin compared to the base material layer 13, the thickness of the reflective element 20 may be ignored when setting the thickness of the radio wave scatterer 11.

[0040] The shape of the radio wave scatterer 11 in a plan view is the same as the shape of the base material layer 13. Radio waves with frequencies between 2 GHz and 300 GHz are attenuated with distance, but it is preferable that the size be such that it can reflect with sufficient intensity at all points within a practical distance from the radio wave source. [Examples]

[0041] The present invention will be described in more detail below with reference to examples and comparative examples, but these examples are for illustrative purposes only and do not limit the present invention in any way.

[0042] (Manufacturing of radio wave scatterers) The radio wave scatterers of the examples and comparative examples were manufactured by laminating reflective elements onto the substrate layers shown below. The substrate layers and reflective elements used in the examples and comparative examples are as follows.

[0043] The following points apply to Examples 1 and 2 and Comparative Examples 1 to 4. • Total thickness of radio wave scatterer 11: 202 μm • Thickness of reflective element 20: 1 μm • Material of reflective element 20: Copper • Thickness of substrate layer 13: 200 μm • Material of base layer 13: PET • Material of conductive layer: copper • Thickness of conductive layer: 1 μm • Arrangement of reflective elements: Multiple reflective elements of different shapes or sizes are arranged along the Y direction with a period of 3.4 to 5.1 mm.

[0044] (Evaluation method) The following evaluations were performed on the radio wave scatterers of each example and comparative example.

[0045] (Method for measuring reflection phase) The reflection phase of the manufactured radio wave scatterer was measured using an electromagnetic field simulator (Ansys HFSS). Specifically, the direction in which the reflection phase increases or decreases was defined as the Y direction, and radio waves were irradiated onto the radio wave scatterer. The reflection peaks in the Y-axis direction from -90deg to 90deg were then measured.

[0046] The following shows the morphology of the reflecting element of the radio wave scatterer and the measurement results such as the reflection phase for each example and comparative example.

[0047] (Example 1) Figure 4 shows a plan view of the radio wave scatterer in Example 1. The reflection phase P(x,y) of the radio wave scatterer, in which the reflectors are arranged as shown in Figure 4, was measured using the method described above. The results are shown in Table 1. In addition, the reflection phase difference D(x,y) between adjacent reflectors in the Y direction was calculated. The results are shown in Table 2.

[0048] [Table 1]

[0049] [Table 2]

[0050] (Example 2) Figure 5 shows a plan view of the radio wave scatterer in Example 2. The reflection phase P(x,y) of the radio wave scatterer, in which the reflectors are arranged as shown in Figure 5, was measured using the method described above. The results are shown in Table 3. In addition, the reflection phase difference D(x,y) between adjacent reflectors in the Y direction was calculated. The results are shown in Table 4.

[0051] [Table 3]

[0052] [Table 4]

[0053] (Comparative Example 1) Figure 6 shows a plan view of the radio wave scatterer of Comparative Example 1. The reflection phase P(x,y) of the radio wave scatterer, in which the reflectors are arranged as shown in Figure 6, was measured using the method described above. The results are shown in Table 5. In addition, the reflection phase difference D(x,y) between adjacent reflectors in the Y direction was calculated. The results are shown in Table 6.

[0054] [Table 5]

[0055] [Table 6]

[0056] (Comparative Example 2) Figure 7 shows a plan view of the radio wave scatterer of Comparative Example 2. The reflection phase P(x,y) of the radio wave scatterer, in which the reflectors are arranged as shown in Figure 7, was measured using the method described above. The results are shown in Table 7. In addition, the reflection phase difference D(x,y) between adjacent reflectors in the Y direction was calculated. The results are shown in Table 8.

[0057] [Table 7]

[0058] [Table 8]

[0059] (Comparative Example 3) Figure 8 shows a plan view of the radio wave scatterer of Comparative Example 3. The reflection phase P(x,y) of the radio wave scatterer, in which the reflectors are arranged as shown in Figure 8, was measured using the method described above. The results are shown in Table 9. In addition, the reflection phase difference D(x,y) between adjacent reflectors in the Y direction was calculated. The results are shown in Table 10.

[0060] [Table 9]

[0061] [Table 10]

[0062] (Comparative Example 4) Figure 9 shows a plan view of the radio wave scatterer of Comparative Example 4. The reflection phase P(x,y) of the radio wave scatterer, in which the reflectors are arranged as shown in Figure 9, was measured using the method described above. The results are shown in Table 11. In addition, the reflection phase difference D(x,y) between adjacent reflectors in the Y direction was calculated. The results are shown in Table 12.

[0063] [Table 11]

[0064] [Table 12]

[0065] Figure 2 shows the reflection intensity of the radio wave scatterers of Example 1, Comparative Example 1, and Comparative Example 2 in each reflection direction. In Figure 2, Example 1, which has the configuration of the radio wave scatterer of the present invention, has reflection peaks in the three directions indicated by the arrows: -48deg, 46deg, and 71deg. Of these reflection peaks, one is at -48deg, which is a reflection peak in the negative direction of the Y-axis, and the peaks at 46deg and 71deg are reflection peaks in the positive direction of the Y-axis, so it has at least one reflection peak in the positive direction of the Y-axis and at least one reflection peak in the negative direction of the Y-axis.

[0066] Figure 3 shows the reflection intensity of the radio wave scatterers of Example 2, Comparative Example 3, and Comparative Example 4 in each reflection direction. In Figure 3, Example 2, which has the configuration of the radio wave scatterer of the present invention, has reflection peaks in the eight directions indicated by the arrows (-47deg, -36deg, -29deg, -24deg, 24deg, 29deg, 36deg, 47deg). Furthermore, these reflection peaks are present in equal numbers, four in the positive direction and four in the negative direction of the Y axis, with 0deg in between. As described above, the radio wave scatterer of Example 2 has equal numbers of reflection peaks in the positive and negative directions of the Y axis, so the reflected radio waves cancel each other out, and radio wave interference is further suppressed.

[0067] In Figures 2 and 3, the identification of reflection peaks was performed according to the following criteria. Specifically, using an electromagnetic field simulator, the reflection profile in the Y direction was analyzed using a 79 GHz Y-polarized radio wave perpendicularly to each radio wave scatterer. In this far-field analysis, the specular reflection intensity of the Al plate was set to 0 dB. The reflection intensity in the front (0 deg) direction and the maximum reflection intensity in the Y direction from -90 to 90 deg were evaluated. Since the front reflection wave has the greatest impact on interference, -25 dB was used as the baseline, while the lateral reflection wave, where the reflection intensity reaches its maximum, was set to -10 dB as it has relatively less impact. The identification of reflection peaks (counting the number of reflection peaks) was performed by counting reflection peaks among the maximum values ​​in the reflection profile graph that had an intensity of -5 dB or more relative to the maximum reflection intensity.

[0068] For each example and comparative example, the 0-degree reflectance and the maximum reflectance were evaluated. The evaluation criteria for the 0-degree reflectance and the maximum reflectance are shown in Table 13. Furthermore, the overall evaluation criteria based on the evaluation of the 0-degree reflectance and the maximum reflectance are shown in Table 14.

[0069] [Table 13]

[0070] [Table 14]

[0071] The evaluation was conducted according to the above evaluation criteria. The evaluation results are shown in Table 15. The locations and number of identified reflectance peaks are shown in Table 16.

[0072] [Table 15]

[0073] [Table 16] [Explanation of Symbols]

[0074] 11 Radio wave scatterer 13 Base material layer 20 Reflective crawl

Claims

1. A radio wave scatterer comprising a base layer, a plurality of reflective elements provided on the surface of the base layer, and a conductive layer provided on the back surface of the base layer, which scatters and reflects vertically irradiated radio waves in a desired plurality of directions, The reflective elements are arranged in a grid pattern in a plan view, and the reflection phase of the reflective elements has a direction in which it increases or decreases with a constant period. With the direction in which the reflection phase increases or decreases being the Y direction, and the direction perpendicular to the Y direction being the X direction, the reflection peaks are present in at least three different directions. The reflection peaks include at least one reflection peak in the positive direction of the Y-axis and at least one reflection peak in the negative direction of the Y-axis. A radio wave scatterer characterized by the following features.

2. The radio wave scatterer according to claim 1, wherein the reflection peaks are present in equal numbers in the positive and negative directions of the Y-axis.

3. The radio wave scatterer according to claim 1 or 2, wherein there are m reflective elements in the X direction and n(x) (1≦x≦m) reflective elements in the Y direction, and the reflection phase of the reflective element located at the x-th coordinate in the X direction (1≦x≦m) and the y-th coordinate in the Y direction (1≦y≦n(x)) is P(x,y), the reflection phase difference between adjacent reflective elements arranged in the Y direction is D(x,y)=P(x,y+1)-P(x,y) (1≦x≦m, 1≦y≦n(x)-1), and Dmax(x) is the value of D(x,y) when |D(x,y)| is maximized when the value of x is fixed and only y is changed, and for all values ​​of y there exists a value of x that satisfies the following equation 1, and there exists at least one value of x that satisfies equation 2 and at least one value of x that satisfies equation 3. Formula 1: P(x,y)=P(x+1,y) (1≦x≦m-1, 1≦y≦n(x)) Equation 2: |Dmax(x)|=Dmax(x) Equation 3: |Dmax(x)|=-Dmax(x)

4. The radio wave scatterer according to claim 3, wherein there are an equal number of x values ​​that satisfy formula 1 and x values ​​that satisfy formula 2.

5. The radio wave scatterer according to claim 3, wherein both the value of x that satisfies equation 2 and the value of x that satisfies equation 3 are consecutive natural numbers.

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