Frequency selective reflection member

Abstract

To provide a technique for effectively controlling a radiation direction of a radio wave so as to asymmetrically reflect the radio wave in a target region and for regularly reflecting the radio wave in a non-target region.SOLUTION: In a frequency selective reflection member 4, a frequency selection plate 1 consisting of a laminate which includes two or more pattern layers and one or more dielectric layers and is configured by alternately laminating the pattern layers and the dielectric layers, and a radio wave reflection member 3 are combined while interposing a functional gap 2 therebetween. A functional gap size is equal to or more than Gmin which is determined by the formula (1): Gmin=0.09×λ (mm) that is a target wavelength arbitrarily selected from the inside of a target band.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a frequency selective reflector. [Background technology]

[0002] With the advancement of digitalization in society, data communication speeds in wireless communications have increased dramatically, and the accompanying higher frequencies of electromagnetic waves (hereinafter also referred to as "radio waves") are also increasing. However, as the frequency of electromagnetic waves increases, they tend to travel in a more directional manner, meaning that they cannot bend around shadows of buildings, etc., and this can easily result in blind zones where communication is impossible. For these reasons, in order to realize 5G and 6G communications over a wide area, it is necessary to increase the number of base stations. However, increasing the number of base stations requires a large amount of cost, making it difficult to increase the number of base stations quickly. In recent years, technology that controls the reflection direction of electromagnetic waves has been attracting attention as a solution to these issues.

[0003] Patent Document 1 discloses a reflectarray composed of a combination of one or more reflection control areas, which are the smallest areas capable of controlling the phase of incident electromagnetic waves and reflecting them in a predetermined direction. By using a reflectarray to achieve asymmetric reflection of electromagnetic waves, where the angle of incidence and the angle of reflection differ, it becomes possible to deliver electromagnetic waves to blind areas that were previously difficult for electromagnetic waves to reach. Radio wave reflecting components that control the reflection direction of radio waves include static ones, such as those in Patent Document 1, in which multiple element patterns are arranged and designed to achieve a predetermined phase difference in advance, and dynamic ones in which the phase difference of radio waves is electrically adjusted variably. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7384308 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional radio wave reflecting materials have focused primarily on controlling the reflection direction of radio waves in a target band, without addressing the issue of simultaneously changing the reflection direction of radio waves in surrounding bands. This makes it difficult to precisely address the needs and specifications of each band for communications, antenna installation, etc. For example, controlling the reflection direction of radio waves from carrier A can affect the reflection direction of radio waves from carrier B, which is assigned to a nearby band, making it difficult to address the need for individual reflection control. As a specific example, in the 28 GHz band (27.0-29.5 GHz), there are bands allocated to each carrier and local 5G (Rakuten Mobile: 27.0-27.4 GHz, NTT Docomo: 27.4-27.8 GHz, KDDI: 27.8-28.2 GHz, local 5G: 28.2-29.1 GHz, SoftBank: 29.1-29.5 GHz), and there is expected to be a need to control the reflection direction for each allocated band. In contrast, Patent Document 1 does not disclose any awareness of the issues involved in controlling the reflection direction only for a predetermined band.

[0006] Therefore, an object of the present invention is to provide a technology that effectively controls the reflection direction of radio waves so as to cause asymmetric reflection in a target band, and causes specular reflection of radio waves in a non-target band. [Means for solving the problem]

[0007] In order to solve the above problems, one representative frequency selective reflection member of the present invention is characterized in that a frequency selective plate having two or more pattern layers and one or more dielectric layers, and consisting of a laminate in which the pattern layers and the dielectric layers are alternately stacked, and a radio wave reflection member are combined across a functional gap, and the functional gap size is equal to or greater than Gmin determined by equation (1).

number

[0008] According to the present invention, it is possible to effectively control the reflection direction of radio waves to cause asymmetric reflection in a target band, and to specularly reflect radio waves in non-target bands. For example, it is possible to control the reflection direction of radio waves in one of the bands allocated in the millimeter wave band, while specularly reflecting radio waves in other bands within the millimeter wave band. Alternatively, it is possible to control the reflection direction of radio waves in the entire millimeter wave band, while specularly reflecting radio waves in other bands such as Sub6. Problems, configurations, and effects other than those described above will become apparent from the following description of the preferred embodiments. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing the definitions of angles and coordinate axes. [Figure 2] FIG. 2 is a cross-sectional view schematically showing the configuration of the frequency selective reflecting member. [Figure 3] FIG. 3 is a schematic diagram showing the progression of radio waves incident on and reflected from a frequency selective reflecting member. [Figure 4] FIG. 4 is a cross-sectional view showing the basic structure of a frequency selective surface. [Figure 5] FIG. 5 is a cross-sectional view showing an example of the configuration of a frequency selective surface provided with a functional layer. [Figure 6] FIG. 6 is a plan view showing an example of a pattern shape. [Figure 7] FIG. 7 is a graph showing the ideal transmission characteristics of a frequency selective surface that transmits the entire 28 GHz band and a frequency selective surface that transmits only a specific carrier frequency. [Figure 8] FIG. 8 is a diagram showing an example of the shape of the conductive pattern of the independent pattern structure after etching. [Figure 9]FIG. 9 is a diagram showing the action of the frequency selective reflection member on the incident radio wave when the functional gap size is equal to or smaller than Gmax. [Figure 10] FIG. 10 is a diagram showing the effect of the frequency selective reflection member on the incident radio wave when the functional gap size is larger than Gmax. [Figure 11] FIG. 11 is a cross-sectional view of an example of a frequency selective reflecting member that uses a frequency selective surface as a radome. [Figure 12] FIG. 12 is a cross-sectional view of an example of a frequency selective reflecting member in which a radio wave absorber is provided on the side surface of a radome. [Figure 13] FIG. 13 is a plan view of the pattern shape of the pattern layer in the unit cell of the frequency selective surface in the first embodiment. [Figure 14] FIG. 14 is a graph showing the transmission characteristics of the frequency selective surface in Example 1. As shown in FIG. [Figure 15] FIG. 15 is a partial cross-sectional view of the radio wave reflecting member in the first embodiment. [Figure 16] FIG. 16 is a plan view of the radio wave reflecting member in the first embodiment. [Figure 17] FIG. 17 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the radio wave reflecting member of Example 1 at θix=0° and θiy=0°. [Figure 18] FIG. 18 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency selective reflecting member of Example 1 at θix=0° and θiy=0°. [Figure 19] FIG. 19 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency selective reflecting member of Example 2 at θix=0° and θiy=0°. [Figure 20] FIG. 20 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency selective reflecting member of Example 3 at θix=0° and θiy=0°. [Figure 21] FIG. 21 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency selective reflecting member of Example 4 at θix=0° and θiy=0°. [Figure 22]FIG. 22 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the radio wave reflecting member of Example 5 at θix=0° and θiy=0°. [Figure 23] FIG. 23 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency selective reflecting member of Example 5 at θix=0° and θiy=0°. [Figure 24] FIG. 24 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency selective reflecting member of Comparative Example 1 at θix=0° and θiy=0°. [Figure 25] FIG. 25 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency selective reflecting member of Comparative Example 2 at θix=0° and θiy=0°. [Figure 26] FIG. 26 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency selective reflecting member of Comparative Example 3 at θix=0° and θiy=0°. [Figure 27] FIG. 27 is a graph showing the reflection characteristics when a y-axis polarized wave is irradiated onto the frequency selective reflecting member of Comparative Example 4 at θix=0° and θiy=0°. [Figure 28] FIG. 28 is a graph showing the reflection characteristics when a y-axis polarized wave is irradiated onto the frequency selective reflecting member of Comparative Example 5 at θix=0° and θiy=0°. [Figure 29] FIG. 29 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency selective reflecting member of Comparative Example 6 at θix=0° and θiy=0°. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, in the description of the drawings, the same parts are designated by the same reference numerals.

[0011] (Terminology explanation) In the disclosure of this embodiment, a "frequency selective surface" is a member that can transmit or reflect a predetermined frequency band, and may have a flat or curved shape. In the disclosure of this embodiment, the term "radio wave reflecting material" refers to any material that can control the reflection direction of radio waves, such as a reflecting plate that statically / dynamically controls the reflection direction of radio waves, or a scattering plate that widens the reflection direction of radio waves.

[0012] In the following explanation, an xyz coordinate system is applied, and the frequency selective reflection member is formed on the xy plane, with its components, the frequency selective plate, functional gap, and radio wave reflection member, stacked along the z-axis. A view of the xy plane viewed from above the z-axis (planar view) is called a plan view, and a view of a plane cut by a plane parallel to the z-axis viewed from a direction perpendicular to that (cross-section view) is called a cross-sectional view. Figure 1 is a diagram showing the definitions of angles and coordinate axes. θi represents the angle of incidence of the incident wave. The angle of incidence in the x-axis direction is θix, and the angle of incidence in the y-axis direction is θiy. θr represents the angle of reflection of the main beam of the reflected wave. The angle of reflection in the x-axis direction is θrx, and the angle of reflection in the y-axis direction is θry. Figure 1(a) shows how a radio wave incident at an angle of incidence θix in the x-axis direction is reflected at an angle of reflection θrx in the x-axis direction, and Figure 1(b) shows how a radio wave incident at an angle of incidence θiy in the y-axis direction is reflected at an angle of reflection θry in the y-axis direction. Furthermore, the angle θx in the x-axis direction is expressed as a positive angle (0° to 180°) when it extends from the positive z-axis direction toward the positive x-axis direction, and as a negative angle (0° to -180°) when it extends from the positive z-axis direction toward the negative x-axis direction. Similarly, the angle θy in the y-axis direction is expressed as a positive angle (0° to 180°) when it extends from the positive z-axis direction toward the positive y-axis direction, and as a negative angle (0° to -180°) when it extends from the positive z-axis direction toward the negative y-axis direction. Unless otherwise specified, θix = θiy = 0°.

[0013] (frequency selective reflector) FIG. 2 is a cross-sectional view showing a schematic configuration of a frequency selective reflecting member. The frequency selective reflecting member 4 is configured by laminating a frequency selective plate 1, a functional gap 2, and a radio wave reflecting member 3. Basically, the frequency selective plate 1 and the radio wave reflecting member 3 are laminated so that their centers of gravity in the xy plane are the same, but the centers of gravity may be shifted as long as the characteristics are not changed. Furthermore, if the size of the radio wave reflecting member 3 in the xy plane is smaller than the size of the frequency selective plate 1 in the xy plane, it is preferable to install a radio wave absorber on the same plane as the radio wave reflecting member 3 to correspond to the difference in size.

[0014] Figure 3 is a schematic diagram showing the progression of radio waves incident on and reflected from a frequency selective reflecting member. Only radio waves in the target band (solid arrow) pass through the frequency selective plate 1, and the reflection direction is changed by the radio wave reflecting member 3. They then pass through the frequency selective plate 1 again and are emitted to the outside. On the other hand, radio waves in other bands (dashed arrow) do not pass through the frequency selective plate 1, and are specularly reflected in the same way as a metal body. Here, specular reflection means that θi = -θr is generally satisfied, with the difference between both sides being within ±10°.

[0015] (Configuration of frequency selective surface) FIG. 4 is a cross-sectional view showing the basic structure of a frequency selective surface. The frequency selective surface 1 includes at least two or more pattern layers 5 (5-1, 5-2, ..., 5-n+1 in the case of n+1 layers) and one or more dielectric layers 6 (6-1, 6-2, ..., 6-n in the case of n layers), forming a laminate (basic structure) in which the pattern layers 5 and the dielectric layers 6 are alternately stacked. Essentially, as the number of layers increases, the number of parameters contributing to the electrical effect increases, allowing for more precise control of the transmission characteristics. The voids in the pattern layers 5 may be filled with the dielectric layers 6, or the voids may be left as they are. The characteristics of the frequency selective surface 1 can be changed by changing the specifications of the basic structure.

[0016] If necessary, a layer for improving the adhesion between the pattern layer 5 and the dielectric layer 6 may be formed between them. Also, a layer used for purposes other than improving the adhesion may be formed. Note that intermediate products generated in the manufacturing process of the frequency selective board 1 may be formed in layers and remain on the frequency selective board.

[0017] Depending on the application, the frequency selective board 1 preferably has one or more layers having various functions (hereinafter also referred to as "functional layers") laminated on one or both sides of the basic structure. Examples of functional layers include a design layer that is designed to complement the scenery of the location where the frequency selective board 1 is installed, an installation layer that allows the frequency selective board to be easily installed on a support such as a wall, ceiling, window, or radome, a protective layer that protects the basic structure, and an adhesive or pressure-sensitive adhesive layer that is used to laminate the basic structure and functional layers, or functional layers together, or to attach the basic structure or functional layers to an adherend. As for the lamination method when laminating the functional layers to the basic configuration, the voids in the pattern layer 5 may be filled with the functional layers, or the voids may be left as they are. It is also possible to change the characteristics of the frequency selective surface 1 by changing the lamination method.

[0018] Figure 5 is a cross-sectional view showing an example of the configuration of a frequency selective board with functional layers. Figure 5(a) shows a frequency selective board 1 whose basic configuration includes three pattern layers 5, two dielectric layers 6, protective layers 7 laminated on both sides, and an installation layer 9 on one outer surface via an adhesive layer 8. Figure 5(b) shows a frequency selective board 1 whose basic configuration comprises two pattern layers 5 and one dielectric layer 6, with protective layers 7 laminated on both sides, and further comprising a design layer 10 on one outer side via an adhesive layer 8, and an installation layer 9 on the other outer side via the adhesive layer 8.

[0019] (Patterned layer of frequency selective surface) The pattern layer 5 is composed of conductive patterns and voids, and is classified into two types: a continuous pattern structure, which is a structure in which specific shapes are removed from a uniform conductor, and an independent pattern structure, which is a structure in which conductors showing specific shapes are arranged independently like islands.

[0020] Hereinafter, the term "pattern" refers to the void portion when the pattern layer 5 has a continuous pattern structure, and to the conductive pattern portion when the pattern layer 5 has an independent pattern structure. Therefore, when the pattern shapes are the same, the continuous pattern structure and the independent pattern structure are complementary. The pattern layer 5 is assumed to include one or more patterns of a specific shape and size.

[0021] The two or more pattern layers 5 included in the frequency selective surface 1 may have only a continuous pattern structure, only an independent pattern structure, or a combination of a continuous pattern and an independent pattern structure. In each case, the pattern shape of each pattern layer 5 may be the same or different. Stacking layers with different pattern structures is preferable because it makes it possible to narrow the target band that the frequency selective surface transmits.

[0022] FIG. 6 is a plan view showing examples of pattern shapes. However, the pattern shapes are not limited to these. Various patterns are applicable (see FIGS. 6(a) to 6(h)), and the radio wave transmission characteristics change depending on the shape and size. For example, to obtain similar transmission characteristics for radio waves whose electric field direction is parallel to the x-axis (x-axis polarized waves) and radio waves whose electric field direction is parallel to the y-axis (y-axis polarized waves), the pattern shape needs to be symmetrical with respect to the x-axis and y-axis so that the pattern shape is the same for each polarization. In this way, a shape with higher symmetry can accommodate a wider range of polarizations. The frequency selective surface 1 includes two or more pattern layers 5, and it is preferable to adopt a pattern shape with high symmetry in more pattern layers 5.

[0023] A plurality of patterns of the same shape and size may be included in the same pattern layer 5, or patterns of different shapes and sizes may be mixed together. As for the arrangement of the patterns, the pattern layer 5 may be divided into unit cells and a pattern may be formed for each unit cell, and the patterns may be arranged at equal intervals or with some intervals that vary.

[0024] When there is a large difference in the occupancy rate of the conductive patterns among two or more pattern layers 5, the difference in the stress that the conductive patterns impart to the dielectric layer 6 increases, which may cause warping of the frequency selective board 1. This phenomenon becomes more pronounced when the dielectric layer 6 is thin and highly flexible, but is not desirable in applications where the frequency selective board 1 is used in a flat state. In light of the above, the difference in the occupancy rate of the conductive patterns among the pattern layers 5 is preferably 75 points or less, more preferably 50 points or less, and even more preferably 25 points or less. Here, the proportion of the area of ​​the conductive patterns to the total area of ​​the frequency selective board 1 when viewed from the z-axis direction is referred to as the occupancy rate (%), and the difference in occupancy rate (%) is referred to as the point (which may also be referred to as percentage points (%pt), etc.). Methods for adjusting the area occupied by the conductive patterns include changing the pattern shape and size, forming the conductive patterns into a mesh shape with specific intervals as long as it does not affect the radio wave characteristics of the frequency selective surface 1, or providing specific shaped voids as dummy patterns among the conductive patterns in a continuous pattern structure.

[0025] (Transmission characteristics of frequency selective surfaces) Radio waves in the operating band (hereinafter also referred to as the "target band") pass through the frequency selective plate 1 and have their reflection direction changed by the radio wave reflecting member 3. They then pass through the frequency selective plate 1 again and are emitted to the outside. In other words, it is assumed that radio waves in the operating band pass through the frequency selective plate 1 twice, with the angle of incidence on the frequency selective plate 1 changing each time. If the transmittance is low in the transmission band, the radio wave intensity will be significantly reduced after two passes. Furthermore, if the characteristics change significantly with changes in the angle of incidence, it is conceivable that the transmittance will be reduced at either the angle of incidence when entering the frequency selective plate 1 from the outside or when entering the frequency selective plate 1 from the radio wave reflecting member 3.

[0026] The transmittance of the frequency selective surface 1 will be described below. In this embodiment, the band whose transmittance difference from the maximum transmittance is within 3 dB is defined as the first transmission band, and the band whose transmittance difference from the maximum transmittance is within 6 dB is defined as the second transmission band. The maximum transmittance is preferably high, at least -10 dB, preferably at least -6 dB, more preferably at least -3 dB, and even more preferably at least -1 dB. It is also preferable that the difference between the first and second transmission bands is small, which is equivalent to a steep decrease in transmittance outside the transmission band. In addition, it is preferable that the transmittance is low outside the second transmission band, at most -6 dB, preferably at most -10 dB, and more preferably at most -20 dB. In practice, it is desirable that the target band be included in at least the second transmission band of the frequency selective surface 1, and more desirably, in the first transmission band.

[0027] Figure 7 is a graph showing the ideal transmission characteristics of a frequency selective surface that transmits the entire 28 GHz band and a frequency selective surface that transmits only a specific carrier frequency. Figure 7 shows the characteristics at θix = θiy = 0°, but it is preferable that the characteristics do not change even when the angle changes. The rectangular transmission characteristics shown in Figure 7 are ideal, but in reality, the transmission characteristics are mountain-shaped. In this case, a steeper mountain means higher frequency selectivity. Therefore, to specify the steepness of the mountain, two points on the mountainside are defined as the first and second transmission bands, as described above.

[0028] In Figure 7(a), the first and second transmission bands are roughly equal, ranging from 27.0 GHz to 29.5 GHz. Converting this to wavelength yields 10.16 mm to 11.10 mm, which translates to a transmission bandwidth of ±4.42% relative to the center wavelength. Furthermore, the transmittance in the first and second transmission bands is near 0 dB, and outside the second transmission band, the transmittance is -20 dB or less. Since physical phenomena can occur on a wavelength basis, if the transmission bandwidth were specified on a frequency basis, the transmission bandwidth for radio waves would differ between the low-frequency and high-frequency bands. For this reason, it was specified on a wavelength basis.

[0029] In Figure 7(b), the first and second transmission bands are roughly equal, ranging from 27.0 GHz to 27.4 GHz. This corresponds to a wavelength of 10.94 mm to 11.10 mm, which corresponds to a transmission bandwidth of ±0.74% relative to the center wavelength. The transmittance in the first and second transmission bands is near 0 dB, and outside the second transmission band, the transmittance is -20 dB or less.

[0030] The frequency selective surface 1 can be designed to transmit the entire millimeter wave band, or it can be designed to transmit individual or multiple bands in the 28 GHz band allocated to each telecommunications carrier and local 5G (Rakuten Mobile: 27.0-27.4 GHz, NTT Docomo: 27.4-27.8 GHz, KDDI: 27.8-28.2 GHz, local 5G: 28.2-29.1 GHz, Softbank: 29.1-29.5 GHz).

[0031] In addition to the 28 GHz band, it can also be applied to the Sub6 band (3.6 to 4.9 GHz) used in 5G and 6G, the millimeter wave band (20 to 300 GHz), and the terahertz band (0.1 to 10 THz).

[0032] For example, if the entire 28 GHz band (27.0 to 29.5 GHz) is the target band, the first transmission band is preferably 27.0 GHz to 29.5 GHz, which corresponds to a wavelength of 10.16 mm to 11.10 mm, with a transmission bandwidth of ±4.42% relative to the center wavelength (10.63 mm). In this case, the second transmission band should be 26.8 GHz to 29.7 GHz, which corresponds to a wavelength of 10.09 mm to 11.19 mm, with a transmission bandwidth of ±5.13% relative to the center wavelength (10.64 mm). From the above, in this case, a frequency selective surface 1 should be used in which the width of the first transmission band is ±4.5% or less relative to the center wavelength and the width of the second transmission band is ±5.2% or less relative to the center wavelength.

[0033] Similarly, if the target band is the lower limit frequency of the 28 GHz band (27.0 GHz to 27.4 GHz), the first transmission band is preferably 27.0 GHz to 27.4 GHz, which corresponds to a wavelength of 10.94 mm to 11.10 mm, with a transmission bandwidth of ±0.74% relative to the center wavelength (11.02 mm). In this case, the second transmission band should be 26.8 GHz to 27.6 GHz, which corresponds to a wavelength of 10.86 mm to 11.19 mm, with a transmission bandwidth of ±1.47% relative to the center wavelength (11.02 mm). From the above, in this case, a frequency selective surface 1 should be used in which the width of the first transmission band is ±0.8% or less relative to the center wavelength and the width of the second transmission band is ±1.5% or less relative to the center wavelength.

[0034] The transmission characteristics of the frequency selective surface 1 described above can be adjusted by adjusting the size of the patterns on the pattern layer 5, the spacing between the patterns, and the physical properties of the dielectric layer 6 (such as thickness and dielectric constant). Generally, a frequency selective surface has multiple transmission bands, for example, bands that roughly correspond to integer multiples of the wavelength of the transmission band. In other words, it may have transmission bands other than the target band. However, these bands other than the target band are not considered to be a problem because they are outside the range of bands whose reflection direction is normally controlled by radio wave reflecting materials.

[0035] The angle of incidence on the frequency selective surface 1 is described below. Radio waves can be incident on the frequency selective surface 1 not only along the negative direction of the z-axis, but also at an oblique angle. Furthermore, even at the same oblique incidence angle, characteristics differ depending on the polarization, so polarization must also be taken into consideration. For example, it is possible that a polarized wave whose electric field direction is parallel to the x-axis is incident from an oblique direction on the xz plane, or a polarized wave whose electric field direction is parallel to the y-axis is incident. Even when radio waves are incident at an oblique angle as described above, it is preferable that the transmission characteristics do not change significantly compared to when radio waves are incident along the negative direction of the z-axis. Specifically, it is preferable that the shift amount of the center wavelength in the first transmission band is within 10% and the change range of the maximum transmittance is within 6 dB for incident angles of 0° to 60° (here, the shift amount is the ratio obtained by dividing the difference in center wavelength before and after the shift in the incident angle of the radio wave by the center wavelength before the shift).It is also preferable that the transmission characteristics do not change when radio waves are incident on the frequency selective surface 1 along the positive direction of the z axis and when radio waves are incident along the negative direction of the z axis.

[0036] (Design method of frequency selective surfaces) We will now explain how to design the frequency selective surface 1. In step 4, by using an optimization method, it is possible to reduce manpower and time required. (Step 1) First, determine the bands to be targeted and the bands to be not targeted. (Step 2) Determine the layer structure. Specifically, determine the number of pattern layers and dielectric layers included in the basic structure, as well as the thickness and material properties of each layer. If functional layers are to be stacked, also determine the thickness and material properties of the functional layers. (Step 3) The structure of the pattern layer (continuous pattern structure or independent pattern structure) and the pattern shape are determined. (Step 4) Any parameters relating to the pattern shape are set as design parameters. (Step 5) Adjust the design parameters so that the desired transmission characteristics are achieved.

[0037] (Manufacturing method of frequency selective surface) The main manufacturing method for the basic structure of the frequency selective board 1 is to form a conductive pattern by cutting or etching (dry etching, wet etching) a copper-clad laminate used in printed circuit boards, etc., or a dielectric layer on one or both sides of which a metal film has been formed by dry coating using a vapor deposition method or sputtering method, plating process, wet coating, etc.

[0038] FIG. 8 shows an example of the shape of a conductive pattern with an independent pattern structure after etching. FIG. 8(a) shows a plan view of the conductive pattern, and FIGS. 8(b) to 8(d) show cross-sectional views of the conductive pattern. When etching is used, corner rounding (FIG. 8(a)) or pinholes may occur in the conductive pattern 11. It is also expected that the cross-sectional view of the conductive pattern 11 will have a forward taper (FIG. 8(b)), a reverse taper (FIG. 8(c)), or rounding (FIG. 8(d)). When etching is used, the cross-sectional shape of the conductive pattern 11 is preferably a forward taper shape that widens in the negative direction of the z-axis. The forward taper shape makes it difficult for air to enter when the functional layer is laminated, making it possible to suppress changes in transmission characteristics and a decrease in adhesion. When the above-mentioned shape change occurs, the transmission characteristics may deviate from the design, but this can be resolved by redesigning the optical fiber taking the shape change into consideration. Generally, when cutting, the dimensional error of the conductive pattern 11 is about ±100 μm, and when etching, the dimensional error of the conductive pattern 11 is about ±50 μm.

[0039] Other manufacturing methods include a method of directly forming the conductive pattern 11 on the dielectric layer 6. It is also possible to form the conductive pattern 11 by printing using letterpress printing, lithographic printing, intaglio printing, stencil printing, transfer printing, or the like, or by masking the dielectric layer 6 except for the conductive pattern 11 portion with masking tape or a masking agent, and then dry coating, plating, painting, or spraying the conductive pattern 11.

[0040] Examples of methods for laminating functional layers onto the basic structure include lamination, printing / coating, and extrusion molding. Examples of lamination include, but are not limited to, dry lamination, wet lamination, thermal lamination, and extrusion lamination.

[0041] (Conductive pattern on frequency selective surface) The conductive pattern 11 is made of a conductive material such as an inorganic oxide material, a metal material, or a conductive organic material. Examples of inorganic oxide and metal materials include indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), gallium zinc oxide (GZO), antimony tin oxide, Ag, Al, Au, Pt, Pd, Cu, Co, Cr, In, Ag-Cu, Cu-Au, and Ni. Nanoparticles or nanowires containing at least one of these materials may also be used. Conductive organic materials include polythiophene derivatives, polyacetylene derivatives, polyaniline derivatives, polypyrrole derivatives, carbon nanotubes, and graphene. Cu and Al are particularly preferred from the perspectives of material cost, conductivity, and film formation. To reflect electromagnetic waves, a ground layer with a surface resistance of 100 Ω / □ or less is desirable. If this requirement can be met, transparent frequency selective surfaces can be fabricated using ITO or a mixture of polyethylenedioxythiophene (PEDOT) and polystyrene sulfonate (PSS) (PEDOT / PSS). When a transparent conductive material is used for the conductive pattern 11, the frequency selective surface exhibits visible light transparency, making it possible to maintain the appearance after installation.

[0042] When a metal material is used, the method for forming the conductive pattern 11 can be selected from dry coating such as sputtering or vapor deposition, wet coating such as gravure coating or die coating by turning the metal material into ink, and surface treatment such as plating. Alternatively, a rolled metal plate can be used as the conductive pattern 11. When an inorganic oxide material is used, dry coating can be selected as the method for forming the conductive pattern 11. When an organic material is used, wet coating can be selected as the method for forming the conductive pattern 11. Alternatively, the conductive pattern 11 can be formed by painting or spraying.

[0043] When the conductive pattern 11 is in the form of a thin film formed by plating or vapor deposition, the flexibility of the frequency selective board 1 can be improved, which makes it possible to use it on curved surfaces or to implement a roll-to-roll production process.

[0044] When the conductive pattern 11 is formed using a thin film, it is preferable that the thickness is greater than the skin depth calculated from equation (4), where d is the skin depth, ω is the angular frequency, μ is the magnetic permeability of the material, and σ is the electrical conductivity of the material.

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[0045] (Dielectrics in Frequency Selective Surfaces) The dielectric 6 may be made of a simple resin or glass, or a composite material in which paper, glass fiber, carbon fiber, or the like is impregnated with resin. Examples of simple resins include polyethylene (εr = 2.2 to 2.4), polypropylene (εr = 2.0 to 2.6), polystyrene (εr = 2.4 to 2.6), polyvinyl chloride (εr = 2.8 to 8.0), AS resin (εr = 2.6 to 3.1), ABS resin (εr = 2.4 to 4.1), polyethylene terephthalate (εr = 2.9 to 3.0), acrylic resin (εr = 2.7 to 4.5), urethane resin (εr = 4.0 to 7.1), epoxy resin (εr = 2.5 to 6.0), and nylon (εr Examples of suitable dielectric materials include polyimide (εr = 3.0 to 5.0), polyimide (εr = 2.4 to 2.7), fluororesin (εr = 2.0 to 2.6), polycarbonate (εr = 2.9 to 8.9), polyphenylene ether (εr = 2.8 to 8.2), polyphenylene sulfide (εr = 3.2 to 4.6), polyvinylidene fluoride (εr = 6.4 to 10.0), polyethylene naphthalate (εr = 2.9), phenolic resin (εr = 3.0 to 12.0), and cycloolefin polymer (εr = 2.3 to 2.5). Here, εr indicates the relative dielectric constant. In particular, polyethylene terephthalate (PET) is preferred because of its low cost and versatility. The dielectric layer 6 can be a single layer or multiple layers. The dielectric layer 6 may be made of a foamed material obtained by foaming the above materials. A highly flexible foam is preferably used as the foam. Examples of composite materials include paper / phenolic resin, paper / epoxy resin, glass / epoxy resin, and glass / fluororesin composite materials.

[0046] Another example is the use of a mixture containing resin components or a dielectric compound and a resin component, from the viewpoint of adjusting the dielectric constant. The relative dielectric constant of the mixture can be adjusted by selecting the dielectric compound and its content. The relative dielectric constant of a mixture can be predicted, for example, by using the Maxwell-Garnett law. In a mixture of dielectric A with a relative dielectric constant εa and dielectric B with a relative dielectric constant εb, when the volume fraction of A is δa, the relative dielectric constant εm of the mixture is expressed by the relational expression (5).

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[0047] Examples of the dielectric compound include barium titanate (εr=250 to 20000), titanium oxide (εr=83 to 183), lead zirconate titanate, strontium tantalate bismuthate, and bismuth ferrite.

[0048] When a transparent dielectric is used, the frequency selective surface exhibits visible light transparency, making it possible to maintain the appearance after installation.

[0049] The dielectric loss tangent of the dielectric layer 6 is preferably in the range of 0.00005 to 0.01, more preferably in the range of 0.00005 to 0.001. If it is in the above range, the transmittance in the transmission band can be increased.

[0050] The dielectric layer 6 can be formed by, for example, wet coating such as die coating, comma coating, or gravure coating, melt extrusion such as the T-die method or inflation method, calendar film formation, solution casting, or heat pressing. Alternatively, a co-extrusion method in which multiple resins are extruded in multiple layers to form a film may be used.

[0051] If the thickness of the dielectric layer 6 is small, the flexibility of the frequency selective surface 1 can be improved, which makes it possible to use it on a curved surface or to carry out a roll-to-roll production process. The thickness of the dielectric layer is 5 mm or less, preferably 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.1 mm or less. The frequency selective plate 1 preferably has a flexural modulus (JIS K7171) of 20 GPa or less, more preferably 10 GPa or less, and even more preferably 5 GPa or less. By setting the flexural modulus within the above range, the frequency selective plate 1 is flexible. When the frequency selective plate 1 is flexible, for example, even when the frequency selective plate 1 is wound around a core with an inner diameter of 6 inches and a thickness of 8 mm and held for 1 minute, appearance abnormalities such as wrinkles and creases are unlikely to occur. This makes it easy to use the frequency selective plate 1 on curved surfaces.

[0052] (Radio wave reflective material) The configuration of the radio wave reflecting member 3 is not particularly limited as long as it is a member that has the function of controlling the reflection direction of radio waves. In the case of static control, for example, a configuration in which a ground layer, a dielectric layer, and an element pattern are laminated, and the phase of the reflected radio waves is controlled for each element pattern with slightly different shapes, thereby realizing reflection in a predetermined direction is conceivable. In the case of dynamic control, for example, a configuration in which a ground layer, a liquid crystal layer, and an element pattern are laminated, and the orientation of the liquid crystal is electrically controlled to control the phase of the reflected radio waves for each element pattern, thereby realizing reflection in a predetermined direction is conceivable.

[0053] The distribution of reflection phases in the radio wave reflecting member is determined, for example, according to equations (6) and (7). Here, the wavelength of the operating frequency (hereinafter also referred to as the "target wavelength") is λ (mm), the x-axis component of the incident angle of the radio wave incident on the radio wave reflecting member is θix, the y-axis component is θiy, the x-axis component of the reflection angle of the electromagnetic wave reflected from the radio wave reflecting member is θrx, the y-axis component is θry, the reflection phases at arbitrary coordinates x1 and x2 parallel to the x-axis within the radio wave reflecting member are φx1 and φx2, respectively, the distance between coordinates x1 and x2 is Δx, and the reflection phase difference between coordinates Φx1 and Φx2 is ΔΦx. Furthermore, the reflection phases at arbitrary coordinates y1 and y2 parallel to the y-axis are φy1 and φy2, respectively, the distance between coordinates y1 and y2 is Δy, and the reflection phase difference between coordinates Φy1 and Φy2 is ΔΦy. When the radio wave reflecting member is intended to perform asymmetric reflection along the x-axis direction, it is preferable that it satisfies formula (6), and when the radio wave reflecting member is intended to perform asymmetric reflection along the y-axis direction, it is preferable that it satisfies formula (7). Furthermore, when the radio wave reflecting member is intended to perform asymmetric reflection in both the x-axis direction and the y-axis direction, it is preferable that it satisfies both formulas (6) and (7).

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[0054] (functionality gap) The functional gap 2 refers to the space between the conductive pattern 11 of the pattern layer 5 closest to the radio wave reflecting member 3 in the frequency selective surface 1 and the element pattern in the radio wave reflecting member 3, and the functional gap size refers to the closest distance between the two. The functional gap 2 serves to ensure the distance between the two, and an air gap or a dielectric exists therein. If there is no functional gap 2 or if the functional gap size is too small, the electrical interaction between the frequency selective plate 1 and the radio wave reflecting member 3 becomes stronger, causing a shift in the resonant frequency, etc. As a result, the inherent characteristics of each member change. Furthermore, if the functional gap size is too small, the wavefront of the radio wave immediately after passing through the frequency selective plate 1 is disturbed, and the radio wave reflecting member 3 may not exhibit its inherent reflection characteristics for such a wavefront. The inventors have found that the minimum functional gap size (Gmin) required to achieve the effects of this embodiment is given by formula (1).

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[0055] The functional gap size can be any value greater than or equal to Gmin shown in formula (1), but in order to maximize the effect of the frequency selective surface 1, it is preferable that Gmaxx and Gmaxy calculated from formulas (2) and (3) are compared and that the functional gap size is equal to or less than the smaller value (hereinafter referred to as Gmax). However, L fx , L fy are the lengths of the frequency selective surface 1 in the x-axis and y-axis directions, respectively, and L rx , L ry are the lengths in the x-axis direction and the y-axis direction of the radio wave reflecting member 3, respectively. θix and θiy are the x-axis component and the y-axis component of the incident angle θi of the incident wave, respectively.

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[0056] Fig. 9 shows the effect of the frequency selective reflecting member on incident radio waves when the functional gap size is equal to or smaller than Gmax. As shown in Fig. 9(a), incident waves in the target band that pass through the frequency selective plate 1 are reflected by the radio wave reflecting member 3 without any hindrance, whereas as shown in Fig. 9(b), incident waves outside the target band are blocked by the frequency selective plate 1 and cannot reach the radio wave reflecting member 3, so that they are prevented from mixing with radio waves in the target band.

[0057] Fig. 10 is a diagram showing the effect of the frequency selective reflecting member on incident radio waves when the functional gap size is larger than Gmax. As shown in Fig. 10(a), incident waves in the target band are reflected by the radio wave reflecting member 3 without any hindrance, whereas as shown in Fig. 10(b), incident waves outside the target band are partially specularly reflected by the frequency selective plate 1 and do not mix with radio waves in the target band, but the remainder reaches the radio wave reflecting member 3 and undergoes multiple diffuse reflections in the space within the gap, which creates the risk of being emitted as noise outside the frequency selective reflecting member 4, which is undesirable. However, even if the functional gap size is larger than Gmax, it is possible to prevent radio waves from penetrating the radio wave reflecting material directly without passing through the frequency selective plate by installing a material that prevents radio waves from entering, such as a radio wave absorber (described below), on the side of the frequency selective reflecting material.

[0058] The functional gap 2 contains an air gap or a dielectric. The dielectric may be a functional layer provided on the frequency selective surface 1. If the dielectric constant of the dielectric is high, the frequency characteristics of the radio wave reflecting member 3 and the frequency selective surface 1 alone are likely to change. Furthermore, if the dielectric loss tangent is high, the radio wave reflection efficiency decreases. Therefore, it is preferable to use a material with low dielectric constant and low dielectric loss tangent for the dielectric.

[0059] The dielectric may be a simple resin or glass, or a composite material made by impregnating paper, glass fiber, or carbon fiber with resin. Foamed resin may also be used. In the case of foamed materials, the expansion ratio is usually several to a hundred times, but the higher the expansion ratio, the easier it is to achieve low dielectric constant and low dielectric loss tangent. Examples of foamed resins include polystyrene foam, polyurethane foam, polyethylene foam, polypropylene foam, foamed EVA, PET resin foam, phenol foam, silicone foam, polyvinyl chloride foam, urea foam, acrylic foam, polyimide foam, EPDM dome, foamed melamine resin, epoxy foam, melamine foam, foamed ABS, and fluororesin foam.

[0060] (Radome) The weather resistance of the frequency selective reflecting member 4 can be improved by incorporating the whole or part of it into a radome. A radome is a cover for protecting an antenna and radio wave control members. In this case, a frequency selective plate 1 can be used as the radome. Figure 11 is a cross-sectional view of an example of a frequency selective reflecting member that uses a frequency selective plate as a radome. Figure 11(a) shows an example in which the frequency selective plate is incorporated into a radome 12, and Figure 11(b) shows an example in which the frequency selective plate 1 is attached to the inside of the radome 12, and shows the frequency selective reflecting member 4 in which the radio wave reflecting member 3 is covered by the radome 12 equipped with these frequency selective plates 1.

[0061] The radome 12 may have any shape, such as a flat, cylindrical, or spherical shape. Furthermore, the mechanical strength can be increased by employing a honeycomb structure inside the radome 12. When the frequency selective plate 1 is installed in a curved shape, it becomes possible to reduce the angle change when radio waves enter the frequency selective plate 1 from the outside and when the radio waves are reflected from the radio wave reflecting member 3 and enter the frequency selective plate 1 again.

[0062] 12 is a cross-sectional view of an example of a frequency selective reflecting member in which a radio wave absorber is installed on the side surface of a radome. By installing a radio wave absorber 13 on the side surface of a radome 12, it is possible to prevent radio waves from penetrating the frequency selective plate 1 and directly hitting the radio wave reflecting member 3.

[0063] The radome 12 can be made of, for example, a resin alone or a resin containing additives, glass fiber, or carbon fiber. The lower the dielectric tangent of these materials, the more radio wave loss in the radome can be reduced. Examples of the resin include polyamide resin, polyester resin, polypropylene resin, polystyrene resin, polycarbonate resin, modified polyphenylene ether resin, and acrylic resin. The radio wave loss in the radome 12 is 3 dB or less, preferably 2 dB or less, and more preferably 1 dB or less.

[0064] (protective layer) For the protective layer 7, a film or sheet having gas barrier properties, water vapor barrier properties, water resistance, abrasion resistance and scratch resistance is used to prevent oxidation deterioration of the element and base plate, physical damage and peeling. When the frequency selective board 1 is intended for indoor use, it is preferable to use a protective layer that has antibacterial, antiviral, and contamination resistance properties. When the frequency selective board 1 is intended for outdoor use, weather resistance is required, so a layer containing UVA (ultraviolet absorber) or HALS (light stabilizer) may be used. The protective layer may be laminated with an adhesive layer or pressure-sensitive adhesive layer, or, depending on the material, may be directly attached to the basic structure by heat sealing.

[0065] (installation layer) The mounting layer 9 is a layer for fixing the frequency selective plate 1 to the support. For example, if the support is made of metal, a magnet can be used. When a magnet is used, the position and angle of the frequency selective plate can be easily changed.

[0066] (Design layer) The design layer 10 is a layer for imparting design to the surface of the frequency selective board 1. For example, when used as a building material such as wallpaper, a design layer 10 may be further provided to harmonize with the space. When used as a whiteboard, a functional film may be used as the design layer 10. The function of the protective layer 7 may be imparted to the design layer 10.

[0067] [Example] Examples and comparative examples will be described below. The purpose of the frequency selective reflection member 4 is to cause asymmetric reflection at a target frequency and not cause asymmetric reflection at non-target frequencies, and in this example, this characteristic is evaluated by "frequency selective reflection performance". Specifically, at the target frequency, the angle at which the asymmetric reflection of the radio wave reflecting member 3 alone is maximized is defined as θ, and the reflection intensity is defined as a tgt. (dBsm or dB), and the reflection intensity at the angle θ of the frequency selective reflecting member 4 at the target frequency is b tgt. (dBsm or dB), and the reflection intensity at the angle θ of the frequency selective reflector at a non-target frequency is b off-tgt. When the frequency selective reflection performance is expressed in dBsm or dB, if the formula (8) is satisfied, the frequency selective reflection performance is evaluated as pass (◯), and if not, the frequency selective reflection performance is evaluated as fail (×).

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[0068] Example 1 <Structure and characteristics of frequency selective surfaces> The frequency selective surface 1 was composed of two pattern layers 5 and one dielectric layer 6. The conductive patterns of the pattern layer 5 were made of copper with a thickness of 0.018 mm, and the dielectric layer 6 was made of polystyrene resin with a thickness of 0.110 mm. The conductivity of copper was set to 5.8 x 10^7 siemens / m, and the real part of the relative permittivity of the polystyrene resin was set to 2.428 and tan δ to 0.000667.

[0069] Figure 13 is a plan view of the pattern shape of the pattern layer in the unit cell of the frequency selective surface in Example 1. Figure 13(a) shows the pattern shape of the pattern layer 5-1, and Figure 13(b) shows the pattern shape of the pattern layer 5-2 (see Figures 4 and 5). The pattern layer 5-1 has a continuous pattern structure with cross-shaped gaps. The pattern layer 5-2 has an independent pattern structure with a circular conductive pattern. The detailed parameters were: the unit cell size Ux in the x-axis direction of pattern layers 5-1 and 5-2 was 5.000 mm, and the unit cell size Uy in the y-axis direction was 5.000 mm. In pattern layer 5-1, the length Lx of the cross in the x-axis direction was 2.397 mm, the length Ly of the cross in the y-axis direction was 2.397 mm, the width Wx of the cross in the x-axis direction was 0.291 mm, and the width Wy of the cross in the y-axis direction was 0.291 mm. In pattern layer 5-2, the inner radius R of the ring was 0.686 mm, and the width Wc of the ring was 0.295 mm. When constructing the frequency selective reflection member 4, 32 frequency selective plates 1 were arranged in the x-axis and y-axis directions so that the unit cells of the pattern layers 5-1 and 5-2 were aligned when viewed in a plane, and the size in the xy plane was 160.00 mm x 160.00 mm.

[0070] Fig. 14 is a graph showing the transmission characteristics of the frequency selective surface in Example 1. Fig. 14(a) shows the results when x-axis polarized waves are irradiated from angles of 0° (θix=0°, θiy=0°) and 45° (θix=45°, θiy=0°). Fig. 14(b) shows the results when y-axis polarized waves are irradiated from angles of 0° (θix=0°, θiy=0°) and 45° (θix=45°, θiy=0°). Note that the analysis was performed on a structure in which unit cells are arranged infinitely on the xy plane.

[0071] As shown in Figure 13, the pattern shapes of the pattern layers 5-1 and 5-2 are symmetrical with respect to the x-axis and y-axis, so the results for 0° incidence were the same for both polarization directions. The transmission band was at least in the 28 GHz band, with the first transmission band width being ±1.4% and the second transmission band width being ±3.2%. The maximum transmittance within the transmission band was -1.3 dB. Furthermore, at an incidence angle of 45°, the shift amount of the center wavelength in the first transmission band was 0.2% for x-axis polarized waves and 0.6% for y-axis polarized waves, both of which were low values.

[0072] <Structure and characteristics of radio wave reflective material> The radio wave reflecting member 3 was designed to reflect a target radio wave of 28 GHz (wavelength 10.7 mm) asymmetrically at 0° incidence (θix=0°, θiy=0°) and 45° reflection (θrx=45°, θry=0°). The structure and characteristics are shown below.

[0073] FIG. 15 is a partial cross-sectional view of the radio wave reflecting member of Example 1. The radio wave reflecting member 3 was constructed by laminating a ground layer 14, a dielectric layer 15, and an element pattern 16 along the positive direction of the z-axis. The shape of the radio wave reflecting member 3 in the xy plane was a square with a side length of 60.56 mm, with each side parallel to the x-axis and y-axis, respectively. The ground layer and element pattern were made of copper with a thickness of 0.018 mm, and the dielectric layer was made of polystyrene resin with a thickness of 0.110 mm. The conductivity of copper was 5.8×10^7 siemens / m, and the real part of the relative permittivity of the polystyrene resin was 2.428, with tan δ of 0.000667.

[0074] Fig. 16 is a plan view of the radio wave reflecting member in Example 1. A total of 256 element patterns 16 were arranged along the x-axis and y-axis directions, with the distance between their centers of gravity maintained at 3.785 mm (see Fig. 16(a)). Each element pattern 16 has a cross shape in the xy plane, with two squares crossing at right angles with a common center of gravity, and the shape varies slightly along the x-axis. Specifically, four element patterns adjacent in the x-axis direction constitute one period (see Fig. 16(b)), and these are repeatedly arranged along the x-axis. Elements of the same shape are arranged along the y-axis direction.

[0075] For the nth element pattern within one period, if the long side of the cross in the x-axis direction is lxn, the short side is wxn, and the long side of the cross in the y-axis direction is lyn and the short side is wyn, the shape parameters of each element pattern are lx1 = 3.500 mm, wx1 = 2.158 mm, ly1 = 3.500 mm, wy1 = 2.093 mm, lx2 = 3.500 mm, wx2 = 2.421 mm, ly2 = 3.500 mm, wy2 = 2.419 mm, lx3 = 3.500 mm, wx3 = 2.662 mm, ly3 = 3.500 mm, wy3 = 2.702 mm, lx4 = 3.500 mm, wx4 = 1.404 mm, ly4 = 3.500 mm, wy4 = 1.398 mm.

[0076] 17 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the radio wave reflecting member of Example 1 at θix=0° and θiy=0°. For radio waves of 28 GHz, reflection in the direction of θrx=45° was observed. Similar reflection characteristics were also observed for radio waves of 27 GHz and 29 GHz, which are offset by ±1 GHz from 28 GHz.

[0077] <Structure and characteristics of frequency-selective reflectors> The frequency selective plate 1 and radio wave reflecting member 3 described above were combined across a functional gap 2 to form a frequency selective plate member 4. For the functional gap 2, polystyrene foam with an expansion ratio of 80 and a dielectric constant of 0 for both the real part and tan δ was used. The size of the polystyrene foam in the xy plane was 160.00 mm x 160.00 mm to match the size of the frequency selective plate 1, and the polystyrene foam, frequency selective plate 1, and radio wave reflecting member 3 were layered so that their centers of gravity in the xy plane were the same. The functional gap size was 0.09 λ (0.96 mm) when the target wavelength was λ (10.7 mm).

[0078] FIG. 18 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency-selective reflecting member of Example 1 at θix=0° and θiy=0°. For 28 GHz radio waves, reflection in the θrx=45° direction was observed. However, for 27 GHz and 29 GHz radio waves, which are offset by ±1 GHz from 28 GHz, reflection in the θrx=45° direction was not observed, and reflection at θrx=0° (specular reflection) was dominant. The frequency-selective reflection performance calculated using equation (8) also passed. This result indicates that the operating band of the frequency-selective reflecting member 4 is narrower than that of the radio wave reflecting member 3. Therefore, the use of the frequency-selective reflecting member 4 can reduce the impact on bands surrounding the target band compared to conventional techniques.

[0079] Example 2 In Example 2, only the functional gap size was changed to 0.10λ (1.07 mm) in the frequency selective reflecting member of Example 1. The other configurations are the same as those of Example 1, so a description thereof will be omitted. Figure 19 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency-selective reflector of Example 2 at θix = 0° and θiy = 0°. As with Example 1, reflection in the θrx = 45° direction was observed for 28 GHz radio waves, while no reflection in the θrx = 45° direction was observed for 27 GHz and 29 GHz radio waves, which are offset by ±1 GHz from 28 GHz, and reflection at θrx = 0° (specular reflection) became dominant. The frequency-selective reflection performance calculated using equation (8) also passed. This result indicates that the effect of the frequency-selective reflector 4 is exhibited even when the gap is 0.10λ.

[0080] Example 3 In Example 3, only the functional gap size was changed to 0.93λ (10 mm) in the frequency selective reflecting member of Example 1. The other configurations are the same as those of Example 1, so a description thereof will be omitted. Figure 20 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency-selective reflector of Example 3 at θix = 0° and θiy = 0°. As with Examples 1 and 2, reflection in the θrx = 45° direction was observed for 28 GHz radio waves, while reflection in the θrx = 45° direction was not observed for 27 GHz and 29 GHz radio waves, which are offset by ±1 GHz from 28 GHz, and reflection at θrx = 0° (specular reflection) became dominant. The frequency-selective reflection performance calculated using equation (8) also passed. This result indicates that the effect of the frequency-selective reflector 4 is exhibited even when the gap is 0.93λ.

[0081] Example 4 In Example 4, only the functional gap size was changed to 4.67λ (50 mm) in the frequency selective reflecting member of Example 1. The other configurations are the same as those of Example 1, so a description thereof will be omitted. Fig. 21 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency-selective reflecting member of Example 4 at θix = 0° and θiy = 0°. As in Examples 1 to 3, reflection in the θrx = 45° direction was observed for 28 GHz radio waves, while no reflection in the θrx = 45° direction was observed for 27 GHz and 29 GHz radio waves, which are offset by ±1 GHz from 28 GHz, and reflection at θrx = 0° (specular reflection) became dominant. The frequency-selective reflection performance calculated using equation (8) also passed. This result indicates that the effect of the frequency-selective reflecting member 4 is exhibited even when the gap is 4.67λ.

[0082] Example 5 Next, the actual measurement results of Example 5 will be explained. The structure of the frequency selective surface 1 is the same as that of Example 1, except that the thickness of the dielectric layer 6 is 0.115 mm and the real part of the relative dielectric constant of the polystyrene resin is 2.42. The details of the pattern layers 5-1 and 5-2 of the frequency selective surface 1 are the same as those of Example 1, except that in the pattern layer 5-1 (see Figure 13(a)), the length Lx of the cross in the x-axis direction is 2.551 mm, the length Ly of the cross in the y-axis direction is 2.551 mm, the width Wx of the cross in the x-axis direction is 0.243 mm, and the width Wy of the cross in the y-axis direction is 0.243 mm; and in the pattern layer 5-2 (see Figure 13(b)), the inner diameter R of the ring is 0.610 mm, and the width Wc of the ring is 0.289 mm. When constructing the frequency selective reflection member 4, 20 frequency selective plates 1 were arranged in the x-axis and y-axis directions so that the unit cells of the pattern layers 5-1 and 5-2 were aligned when viewed in a plane, and the size in the xy plane was 100 mm x 100 mm. The structure of the radio wave reflecting member 3 is the same as that of the first embodiment.

[0083] 22 is a graph showing the reflection characteristics when y-axis polarized waves were irradiated onto the radio wave reflecting member of Example 5 at θix=0° and θiy=0°. For radio waves of 28 GHz, reflection in the direction of θrx=45° was observed. Similar reflection characteristics were also observed for radio waves of 27 GHz and 29 GHz, which are offset by ±1 GHz from 28 GHz.

[0084] In Example 5, S21 (dB) was used to measure the reflection intensity. S21 represents the ratio of received power to transmitted power, regardless of whether it is in the far field or near field. Since the reflecting object and the receiving antenna were not far apart in the actual measurements, S21 measured in the near field was used. In contrast, RCS is used as a physical quantity that represents the reflection characteristics of a reflecting object in the far field, where the reflecting object and the receiving antenna are far enough apart. The specific measurement method was to place the reflecting object to be measured inside the compact range system, irradiate it with a plane wave, and measure the reflection intensity by scanning the angle of the receiving antenna on the xz plane at a radius of 0.5 m from the reflecting object.In the compact range system, a reflector is installed inside the anechoic chamber, and the reflector converts the incident wave from a spherical wave to a plane wave.

[0085] The frequency selective plate 1 and radio wave reflecting member 3 described above were combined across a functional gap 2 to form a frequency selective plate member 4. The size of the functional gap 2 in the xy plane was 100 mm x 100 mm, matching the size of the frequency selective plate 1, but was the same as in Example 1. In addition, the functional gap size was 4.67 λ (50 mm) with a target wavelength λ (10.7 mm).

[0086] 23 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency-selective reflector of Example 5 at θix=0° and θiy=0°. As in Examples 1 to 4, reflection in the θrx=45° direction was observed for 28 GHz radio waves, while no reflection in the θrx=45° direction was observed for 27 GHz and 29 GHz radio waves, which are offset by ±1 GHz from 28 GHz. The frequency-selective reflection performance calculated using equation (8) also passed. From these results, it was confirmed by actual measurements that the effect of the frequency-selective reflector 4 is exhibited when the gap is 4.67λ.

[0087] (Comparative Example 1) In Comparative Example 1, only the functional gap size was changed to 0.00λ (0.00 mm) in the frequency selective reflecting member of Example 1. The other configurations were the same as those of Example 1, so a description thereof will be omitted. FIG. 24 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency-selective reflecting member of Comparative Example 1 at θix=0° and θiy=0°. Only reflection at θrx=0° (specular reflection) occurred for all frequencies, and no reflection at θrx=45° (asymmetric reflection) occurred. The frequency-selective reflection performance calculated using equation (8) was unsuccessful. This is thought to be because the absence of functional gap 2 strengthened the electrical interaction between the frequency selective plate 1 and radio wave reflecting member 3, changing the inherent characteristics of the radio wave reflecting member 3. Therefore, it was shown that the effect of the frequency-selective reflecting member 4 would not be achieved if functional gap 2 were not present.

[0088] (Comparative Example 2) In Comparative Example 2, only the functional gap size was changed to 0.01λ (0.11 mm) in the frequency selective reflecting member of Example 1. The other configurations were the same as those of Example 1, so a description thereof will be omitted. FIG. 25 is a graph showing the reflection characteristics when y-axis polarized waves were irradiated onto the frequency-selective reflecting member of Comparative Example 2 at θix=0° and θiy=0°. Only reflection at θrx=0° (specular reflection) occurred for all frequencies, and no reflection at θrx=45° (asymmetric reflection) occurred. The frequency-selective reflection performance calculated using equation (8) failed. This is thought to be because the functional gap size was too small, which strengthened the electrical interaction between the frequency selective plate 1 and the radio wave reflecting member 3, or because the wavefront of the radio waves immediately after passing through the frequency selective plate 1 was disturbed, changing the original characteristics of the radio wave reflecting member 3. Therefore, it was shown that when the functional gap size was so small, the effect of the frequency-selective reflecting member 4 was not exhibited.

[0089] (Comparative Example 3) In Comparative Example 3, only the functional gap size was changed to 0.05λ (0.54 mm) in the frequency selective reflecting member of Example 1. The other configurations were the same as those of Example 1, so a description thereof will be omitted. FIG. 26 is a graph showing the reflection characteristics when y-axis polarized waves were irradiated onto the frequency-selective reflecting member of Comparative Example 3 at θix=0° and θiy=0°. Only reflection at θrx=0° (specular reflection) occurred for all frequencies, and no reflection at θrx=45° (asymmetric reflection) occurred. The frequency-selective reflection performance calculated using equation (8) failed. This is thought to be because the functional gap size was too small, which strengthened the electrical interaction between the frequency selective plate 1 and the radio wave reflecting member 3, or because the wavefront of the radio waves immediately after passing through the frequency selective plate 1 was disturbed, changing the original characteristics of the radio wave reflecting member 3. Therefore, it was shown that when the functional gap size was so small, the effect of the frequency-selective reflecting member 4 was not exhibited.

[0090] Comparative Example 4 In Comparative Example 4, only the functional gap size was changed to 0.06λ (0.64 mm) in the frequency selective reflecting member of Example 1. The other configurations were the same as those of Example 1, so a description thereof will be omitted. FIG. 27 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency-selective reflector of Comparative Example 4 at θix=0° and θiy=0°. Although asymmetric reflection (θrx=45°) occurred at the target frequency, asymmetric reflection also occurred at non-target frequencies. The frequency-selective reflection performance calculated using equation (8) failed. This is thought to be because the functional gap size was too small, which strengthened the electrical interaction between the frequency selective plate 1 and the radio wave reflecting member 3, or because the wavefront of the radio waves immediately after passing through the frequency selective plate 1 was disturbed, changing the original characteristics of the radio wave reflecting member 3. Therefore, it was shown that the effect of the frequency-selective reflecting member 4 was not exhibited when the functional gap size was so small.

[0091] (Comparative Example 5) In Comparative Example 5, only the functional gap size was changed to 0.07λ (0.75 mm) in the frequency selective reflecting member of Example 1. The other configurations were the same as those of Example 1, so a description thereof will be omitted. FIG. 28 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency-selective reflector of Comparative Example 5 at θix=0° and θiy=0°. Although asymmetric reflection (θrx=45°) occurred at the target frequency, asymmetric reflection also occurred at non-target frequencies. The frequency-selective reflection performance calculated using equation (8) failed. This is thought to be because the functional gap size was too small, which strengthened the electrical interaction between the frequency selective plate 1 and the radio wave reflecting member 3, or because the wavefront of the radio waves immediately after passing through the frequency selective plate 1 was disturbed, changing the original characteristics of the radio wave reflecting member 3. Therefore, it was shown that when the functional gap size was so small, the effect of the frequency-selective reflecting member 4 was not exhibited.

[0092] (Comparative Example 6) In Comparative Example 6, only the functional gap size was changed to 0.08λ (0.86 mm) in the frequency selective reflecting member of Example 1. The other configurations were the same as those of Example 1, so a description thereof will be omitted. FIG. 29 is a graph showing the reflection characteristics when y-axis polarized waves are irradiated onto the frequency-selective reflector of Comparative Example 6 at θix=0° and θiy=0°. Although asymmetric reflection (θrx=45°) occurred at the target frequency, asymmetric reflection also occurred at non-target frequencies. The frequency-selective reflection performance calculated using equation (8) failed. This is thought to be because the functional gap size was too small, which strengthened the electrical interaction between the frequency selective plate 1 and the radio wave reflecting member 3, or because the wavefront of the radio waves immediately after passing through the frequency selective plate 1 was disturbed, changing the original characteristics of the radio wave reflecting member 3. Therefore, it was shown that when the functional gap size was so small, the effect of the frequency-selective reflecting member 4 was not exhibited.

[0093] The results of the examples and comparative examples are summarized in Table 1. [Table 1] a_28GHz and b_28GHz are the a in equation (8), respectively. tgt., b tgt. b_27GHz and b_29GHz are equivalent to b off-tgt. is equivalent to As is clear from Table 1, a significant difference was observed in frequency-selective reflection performance between functional gap sizes of 0.09λ or more and less than 0.09λ. This shows that by providing a functional gap of 0.09λ or more for a frequency-selective reflection member with a target wavelength λ (mm), it is possible to achieve the effect of the frequency-selective reflection member.

[0094] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention. For example, the frequency selective surface is not limited to one that selectively transmits radio waves of a target wavelength, but may be one that selectively reflects them.

[0095] The following are examples of possible embodiments of the present invention, but the present invention is not limited to these. (Aspect 1) A frequency selective reflecting member, characterized in that the frequency selective plate is a laminate comprising two or more pattern layers and one or more dielectric layers, the laminate being formed by alternately stacking the pattern layers and the dielectric layers, and the radio wave reflecting member are combined across a functional gap, and the functional gap size is equal to or larger than Gmin determined by formula (1).

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[0096] 1... frequency selective plate, 2... functional gap, 3... radio wave reflecting member, 4... frequency selective reflecting member 5(5-1, 5-n+1)...Pattern layer 6(6-1, 6-n)...Dielectric layer 7...protective layer, 8...adhesive layer, 9...installation layer, 10...design layer, 11...conductive pattern 12...Radome, 13...Radio wave absorber 14...ground layer, 15...dielectric layer, 16...element pattern

Claims

1. A frequency selective reflecting member, characterized in that the frequency selective plate is a laminate comprising two or more pattern layers and one or more dielectric layers, the laminate being formed by alternately stacking the pattern layers and the dielectric layers, and the radio wave reflecting member are combined across a functional gap, and the functional gap size is equal to or larger than Gmin determined by formula (1). [Equation 1] (λ (mm) is a target wavelength arbitrarily selected within the target band)

2. 2. The frequency selective reflector according to claim 1, wherein the frequency selective plate has a transmission band in at least the millimeter wave band, the width of the first transmission band being ±4.5% or less with respect to the center wavelength, and the width of the second transmission band being ±5.2% or less with respect to the center wavelength.

3. 2. The frequency selective reflector according to claim 1, wherein the frequency selective plate has a transmission band in at least the millimeter wave band, the width of the first transmission band being ±0.8% or less with respect to the center wavelength, and the width of the second transmission band being ±1.5% or less with respect to the center wavelength.

4. 2. The frequency selective reflector according to claim 1, wherein the maximum transmittance in the transmission band of said frequency selective surface is −3 dB or more.

5. 2. The frequency selective reflector according to claim 1, wherein the frequency selective plate has a center wavelength of the first transmission band that is shifted by 10% or less for incident angles of 0 to 60 degrees.

6. 2. The frequency selective reflecting member according to claim 1, wherein the frequency selective plate comprises two of the pattern layers and one of the dielectric layers, and is a laminate in which the pattern layers and the dielectric layers are alternately stacked.

7. 2. The frequency selective reflecting member according to claim 1, wherein the frequency selective plate comprises three layers of the patterned layers and two layers of the dielectric layers, and is formed as a laminate in which the patterned layers and the dielectric layers are alternately stacked.

8. The frequency selective reflecting member of claim 1, characterized in that the pattern layer of the frequency selective plate is composed of a conductive pattern and voids, and has a continuous pattern structure in which a specific shape is removed from a uniform conductor, or an independent pattern structure in which conductors showing specific shapes are each arranged independently like islands.

9. 9. The frequency selective reflector according to claim 8, wherein the frequency selective surface includes a pattern layer having a continuous pattern structure and a pattern layer having an independent pattern structure.

10. 9. The frequency selective reflector according to claim 8, wherein the difference in occupancy rate of the conductive patterns between the pattern layers in the frequency selective surface is 75 points or less.

11. 2. The frequency selective reflector according to claim 1, wherein at least one of the pattern layers of the frequency selective surface is divided into unit cells, and a pattern is formed for each unit cell.

12. 2. The frequency selective reflector according to claim 1, wherein the frequency selective plate has a flexural modulus of elasticity of 20 GPa or less.

13. 2. The frequency selective reflector according to claim 1, wherein the frequency selective plate has a curved surface shape.

14. 2. The frequency selective reflector according to claim 1, wherein the frequency selective plate comprises a protective layer.

15. The frequency selective reflector according to claim 1 , wherein the frequency selective plate has a design layer.

16. 2. The frequency selective reflector according to claim 1, wherein the frequency selective surface comprises a mounting layer.

17. 2. The frequency selective reflector according to claim 1, wherein the functional gap size is equal to or less than the smaller of Gmaxx and Gmaxy calculated from equations (2) and (3). [Equation 2] [Equation 3]

18. A frequency selective reflecting member with a radome, comprising the frequency selective reflecting member according to claim 1 wholly or partly incorporated into a radome.

19. 14. The frequency selective reflector with a radome according to claim 13, further comprising a radio wave absorber on a side surface of the radome.

20. 2. A method for designing a frequency selective plate included in the frequency selective reflecting member of claim 1, which is capable of transmitting or reflecting radio waves of the target wavelength, comprising the steps of setting design parameters related to the pattern shape of the pattern layer and adjusting the design parameters so as to exhibit predetermined transmission characteristics.

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