Reflector

Abstract

An objective of the present invention is to provide a reflector that achieves an increased beam diameter of the main lobe of reflected waves in a target direction. The reflector comprises: a dielectric layer; a conductive layer including a plurality of conductor patterns that are formed on a first surface of the dielectric layer and reflect incident waves; and a ground layer formed on a second surface of the dielectric layer on the opposite side from the first surface. The plurality of conductor patterns are arranged in a prescribed direction. The standard deviation σ of the difference between an ideal distance and the center-to-center distance in the prescribed direction between a reference conductor pattern and an arbitrary conductor pattern from among the plurality of conductor patterns is 0.5-1.5 mm.

Description

Reflector

[0001] The present invention relates to a reflector, and more particularly to a reflector having a metasurface.

[0002] The use of high-frequency radio waves, such as microwaves, millimeter waves, and terahertz waves, in wireless communications enables high-speed, high-capacity communications. However, high-frequency radio waves, such as those in the 1 GHz to 10 THz range, have the disadvantage of being highly directional, meaning that the presence of an obstacle between the transmitting and receiving antennas can prevent the radio waves from reaching the receiving antenna, resulting in communication failure. Reflectors are used to improve the communication environment and coverage area of ​​high-frequency mobile communications. Conventional reflectors have a specular reflective surface with an equal angle of incidence and reflection, limiting their reflection range. To expand communication range, metareflectors, which have a metasurface that reflects incident waves in a desired direction, are being actively developed.

[0003] "Metasurface" refers to an artificial surface that controls the transmission and reflection characteristics of incident electromagnetic waves. Metal patterns of approximately half the wavelength are periodically arranged to control the reflection characteristics and reflect the incident wave in the desired direction. A reflectarray has been proposed in which array elements are formed in divided regions on a substrate, and the gaps between the multiple patches that make up the array element are different for each region (see, for example, Patent Document 1).

[0004] Patent No. 5177708

[0005] Because reflectarrays with metasurfaces utilize the resonance phenomenon, when reflecting radio waves in a desired direction (hereinafter referred to as the "target direction") at a specified frequency, the reflection distance to the target and the beam diameter are inversely proportional. Therefore, as the reflection distance increases, the beam diameter of the main lobe of the reflected wave in the target direction narrows. When the main lobe beam diameter narrows, the coverage area within the reach of the radio waves is limited, and communication may become impossible.

[0006] In one aspect, the present invention aims to provide a reflector in which the beam diameter of the main lobe of the reflected wave toward the target is increased.

[0007] In one embodiment, the reflector has a dielectric layer, a conductive layer formed on a first surface of the dielectric layer and including a plurality of conductor patterns that reflect an incident wave, and a ground layer formed on a second surface of the dielectric layer opposite the first surface, wherein the conductor patterns are arranged in a predetermined direction, and among the plurality of conductor patterns, a standard deviation σ of the difference between the center-to-center distance between a reference conductor pattern and an arbitrary conductor pattern and the ideal distance along the predetermined direction is 0.5 mm or more and 1.5 mm or less.

[0008] The above configuration realizes a reflector in which the beam diameter of the main lobe of the reflected wave toward the target is increased.

[0009] 1 is a diagram showing a basic configuration of a reflector according to a first embodiment; FIG. 2 is a diagram showing an example of a design method for a conductor pattern; FIG. 3 is a diagram showing a design example of a reflector according to the first embodiment; FIG. 4 is a diagram showing the reflection characteristics of a reflector according to the designs of FIGS. 3A and 3B; FIG. 5 is a diagram showing the configuration of standard deviations of an example and a comparative example; FIG. 6 is a diagram showing the reflection characteristics of a reflector according to the design of FIG. 5; FIG. 7 is a diagram showing the reflection characteristics of a reflector according to the design of FIG. 6; FIG. 8 is a diagram showing the reflection characteristics of a low dielectric constant reflector; FIG. 9 is a diagram showing the reflection characteristics of a low dielectric constant reflector; FIG. 10 is a diagram showing the reflection characteristics of a low dielectric constant reflector; FIG. 11 is a diagram showing the reflection characteristics of a high dielectric constant reflector; FIG. 12 is a diagram showing the reflection characteristics of a high dielectric constant reflector; FIG. 13 is a diagram showing the reflection range of a low dielectric constant reflector versus frequency; FIG. 14 is a diagram showing the reflection range of a high dielectric constant reflector versus frequency; FIG. 15 is a diagram showing the relationship between the thickness of dielectric layers with different dielectric constants and the reflection bandwidth; FIG. 16 is a diagram showing the relationship between the thickness of dielectric layers with different dielectric constants and the reflection intensity; FIG. 17 is a diagram showing the configurations and characteristics of an example and a comparative example; FIG. 18 is a schematic diagram of a reflector according to a second embodiment; It is a figure which shows the simulation result which changes the thickness and the dielectric constant of the protective layer. It is a figure which shows the example of using the reflector of the embodiment. It is a figure which shows the example of using a normal reflector.

[0010] FIG. 1 is a diagram illustrating the basic configuration of a reflector 10 according to a first embodiment. The reflector 10 includes a dielectric layer 11, a conductive layer 13 provided on a first surface 111 of the dielectric layer 11, and a ground layer 12 provided on a second surface 112 opposite the first surface 111 of the dielectric layer 11. The conductive layer 13 includes an array of multiple conductor patterns 131 and functions as the reflecting surface of the reflector 10. This reflecting surface is a metasurface that reflects an incident wave at an angle (absolute value) different from the incident angle. The ground layer 12 forms capacitance between the ground layer 12 and each conductor pattern 131, allowing the magnitude of the phase delay to be controlled for each conductor pattern 131. The conductive layer 13 and the ground layer 12 may be made of any electrically conductive material. However, copper foil is preferred in terms of electrical conductivity, manufacturability, processability, and material cost.

[0011] The size and pitch of the conductor patterns 131 are set according to the desired reflection characteristics. Each conductor pattern 131 has a size sufficiently smaller than the wavelength used, and selectively reflects radio waves in the target frequency band. The conductor patterns 131 control the phase of the reflection, and the reflected waves are superimposed to form a reflected beam BM in the desired direction.

[0012] The wavelength of the incident radio wave is λ, the pitch of the conductor patterns 131, i.e., the distance between the centers of adjacent conductor patterns 131, is d, the phases of the radio waves reflected by two adjacent conductor patterns 131 are δ1 and δ2, respectively, and the reflection angle is θ. The phase difference δ1-δ2 is expressed by equation (1).

[0013] δ1-δ2=(2π / λ)d·sinθ+2nπ (1) where n is an integer.

[0014] To reflect radio waves in a desired direction using the reflector 10, δ1, δ2, and d can be designed to obtain the desired reflection angle θ. The reflection angle θ is set to any desired angle between the normal direction (0°) of the reflecting surface of the reflector 10 and the horizontal direction (90°), excluding 0° and 90°. The values ​​of δ1 and δ2, which represent the reflection phase, can be controlled and changed using design parameters such as the wavelength λ of the incident radio waves, the size (length × width) and pitch of the conductor pattern 131, and the thickness and dielectric constant of the reflector 10. For example, when designing the length L of the conductor pattern 131 to obtain a desired phase difference, the conductor pattern 131 may be designed using the length / phase characteristic graph shown in FIG. 2. The length / phase characteristic shown in FIG. 2 can be obtained by measuring the reflection pattern of radio waves while changing the length L of the conductor pattern with design parameters other than the length L (mm) fixed, and analyzing the pattern using three-dimensional electromagnetic field simulation software. The length L is the length of the conductor pattern 131 corresponding to the vibration direction of the radio wave, and when the conductor patterns 131a to 131g are cross patterns as shown in Figure 3A, the vertical and horizontal lengths of each conductor pattern are equal. As a design parameter other than the length, for example, the relative dielectric constant ε of the dielectric layer 11 is fixed at ε = 1.88.

[0015] (Center-to-Center Distance) On the conductive layer 13, multiple conductor patterns 131 of different sizes are arranged at a predetermined distance apart. As shown in FIG. 3A , in the reflector 10 of the first embodiment, the conductor patterns 131 are arranged in a line on a straight line l. The center points of each conductor pattern 131 are located on an arbitrary straight line. Note that the conductor patterns 131 do not have to be arranged in a straight line, and may be arranged in a staggered pattern or other arrangement pattern along the arrangement direction. In this specification, the "center point of a conductor pattern" refers to the center point of a circle that inscribes the outline of each conductor pattern when the conductor patterns are viewed in a plan view. The distance between the center point of a reference conductor pattern and the center point of an arbitrary conductor pattern is referred to as the "center-to-center distance." Furthermore, when multiple conductor patterns are arranged, for convenience of explanation, the center-to-center distance from the center point of the reference conductor pattern to the center point of the m-th conductor pattern counting from the reference conductor pattern may be expressed as "dm" or "dm'" using an arbitrary integer m of 1 or greater. For example, in FIG. 3A, the first conductor pattern 131a from the left is set as the reference conductor pattern, and with regard to the center-to-center distance of the first conductor pattern in the arrangement direction from the reference conductor pattern (the second conductor pattern 131b from the left in FIG. 3A), the ideal distance described below is denoted as d1 and the actual distance is denoted as d1', and the ideal distance of the seventh conductor pattern (the eighth pattern 131h from the left in FIG. 3A) is denoted as d7 and the actual distance is denoted as d7'.

[0016] (Ideal Distance) When designing an arrangement of a plurality of conductor patterns 131 on the conductor layer 13, when an incident wave of the same phase is incident on a reference conductor pattern among the plurality of conductor patterns 131 and an m-th conductor pattern counting from the reference conductor pattern, the center-to-center distance between the reference conductor pattern and the m-th conductor pattern at which the intensity of the reflected wave is strongest is defined as the "ideal distance" of the m-th conductor pattern. In this specification, the ideal distance is represented as dm. By arranging the conductor patterns 131 on the conductor layer 13 at the ideal distance dm, a reflector with a long range of reflected waves can be obtained. From the viewpoint of robustness when designing the reflection characteristics of a reflector, the ideal distance dm is preferably 0.5λ or more and 0.7λ or less, where λ is the wavelength of the incident wave.

[0017] (Actual Distance) The center-to-center distance between the first conductor pattern and the m-th conductor pattern formed on the first surface of the dielectric layer relative to the ideal distance dm is defined as the "actual distance" of the m-th conductor pattern. In this specification, the actual distance is represented as dm'.

[0018] (Increasing Beam Diameter) In the reflector according to the first embodiment of the present invention, the absolute value of the difference between the actual distance dm' and the ideal distance dm is |dm' - dm|, where m is an integer greater than or equal to 1. The standard deviation σ of the group consisting of |dm' - dm| of each conductor pattern other than the reference conductor pattern is 0.5 mm or greater and 1.5 mm or less. As a result of extensive research, the inventors of the present invention have found that by designing the reflector in this manner, the beam diameter of the main lobe of the reflected wave can be increased when the radio wave is incident on the reflector at an arbitrary phase. In this specification, the term "beam diameter" is defined as the reflection angle range in which the difference in intensity Δ from the peak intensity is 10 dB when the intensity distribution of the main lobe of the reflected wave is graphed with the reflection angle on the horizontal axis and the reflected wave intensity on the vertical axis.

[0019] In a second embodiment of the present invention, in addition to the configuration of the first embodiment, the reflector has a dielectric layer 11 with a relative dielectric constant of 2.0 or less. By setting the relative dielectric constant to 2.0 or less, the frequency band of radio waves that are reflected in a predetermined direction can be expanded. Details of expanding the reflection frequency band will be described later with reference to FIG. 5 and subsequent figures. As a dielectric material with a relative dielectric constant of 2.0 or less, a fluorinated resin such as polytetrafluoroethylene, a combination of a fluorinated resin and an inorganic porous aggregate, or other transparent porous resin can be used. As a resin that is combined with the inorganic porous aggregate, polytetrafluoroethylene, polystyrene, etc. can be used.

[0020] The inorganic porous aggregate is produced, for example, by the method described in JP 2017-171898 A. By adjusting the material, aggregation density, etc. of the porous inorganic fine particles, the porosity of the aggregate can be controlled to 50% or more. By adjusting the porosity and controlling the relative dielectric constant, a dielectric constant of 2.0 or less can be achieved.

[0021] 3A and 3B show a design example of the reflector 10 of the first embodiment. FIG. 3A shows the arrangement of the conductor patterns 131a to 131h that make up the conductive layer 13. FIG. 3B shows the size of each conductor pattern. The conductor patterns 131a to 131h are cross patterns with equal vertical and horizontal lengths. The size of each conductor pattern 131 is indicated by its vertical or horizontal length L1 to L8. The incident wave has a wavelength λ of 10.8 mm in the 28 GHz band, and the pitch of the conductor patterns 131a to 131h, i.e., the ideal center-to-center distance dm, is 5.35 mm for all of them.

[0022] The arrangement of the conductor patterns 131a to 131h aims for a reflection angle of -42°. In this case, the reflection angle is the reflection angle when radio waves are incident perpendicularly on the reflector 10, that is, the reflection angle with respect to the normal. When the phase difference "δ1 - δ2" is calculated based on the above formula (1) when θ is -42°, the phase difference is 120°. The size of the conductor patterns 131a to 131h, that is, the lengths L1 to L8, are determined so that this phase difference can be obtained.

[0023] The shape of the conductor pattern 131 is not limited to a cross pattern, and may be a circle, ellipse, polygon, or other shape of different sizes arranged at a predetermined interval. The size of the conductor pattern 131 is preferably 2.0 to 5.0 mm when targeting the 28 GHz band, but the size of the conductor pattern 131 is appropriately designed depending on the frequency band. Radio waves of a frequency determined by the size and interval of the conductor pattern 131 are selectively reflected. Generally, the frequency band selected by resonance is narrow, but by setting the relative permittivity of the dielectric layer 11 to 2.0 or less, the selected frequency band can be expanded to a bandwidth of 4 GHz or more, more preferably 6 GHz or more. Since the selected frequency bandwidth can vary depending on the thickness of the dielectric layer 11 of the reflector 10, a wideband reflector with a bandwidth per unit thickness (1 mm) of the reflector 10 exceeding 6.5 GHz / mm can be realized.

[0024] 4 shows the reflection characteristics of the reflector 10 using Ref, which was designed so that the standard deviation σ of the absolute value |dm' - dm| of the difference between the actual distance dm' and the ideal distance dm is 0 in the conductor pattern design of FIGS. 3A and 3B. The horizontal axis represents the reflection angle, and the vertical axis represents the reflection intensity (dB). A main peak was observed in the -42° direction, confirming that the reflector 10 was able to control the reflection direction of the radio waves almost as designed. In addition, the beam diameter of the main lobe at -42°, i.e., the reflection angle range 10 dB lower than the peak, was 36.4°.

[0025] <Expansion of Beam Diameter Due to Standard Deviation σ> For Examples 1 to 3 and Comparative Examples 1 to 6, the standard deviation σ of the absolute value |dm' - dm| of the difference between the actual distance dm' and the ideal distance dm was determined. The actual distance was varied from d1 to d7 as shown in FIG. 5 so that σ = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5, 2.0, and 2.5. A dielectric layer 11 with a relative permittivity ε of 1.88 was used to calculate the reflection spectrum of an incident 28 GHz plane wave. The reflection intensity was analyzed using Dassault Systèmes' CST Studio Suite, a general-purpose three-dimensional electromagnetic field simulation software. The angle at which the reflection intensity peak appears was defined as the "reflection peak angle."

[0026] The reflection peak angle and beam diameter were evaluated as follows: ◯: The beam diameter was wider than the REF, and the difference in the reflection peak angle with respect to the reflection peak angle of the REF was within ±2°. △: The beam diameter was wider than the REF, but the reflection peak angle was shifted. ×: The beam diameter was narrower than the REF.

[0027] The simulation results of the reflection characteristics of the reflector designed in Figure 5 are shown in Figures 6 and 7. The vertical axis of Figure 6 represents the reflection intensity (unit: dB) and the horizontal axis represents the reflection angle (unit: °).

[0028] As shown in Figures 6 and 7, it can be seen that Examples 1 to 3 and Comparative Examples 5 and 6, in which the standard deviation σ is 0.5 mm or more, have a larger beam diameter than REF. On the other hand, it was found that Comparative Examples 5 and 6, in which the standard deviation σ is 2.0 or more, have a deviation in the reflection peak angle of 3° or more from the design value, and therefore do not achieve the desired reflection characteristics. On the other hand, it was found that Comparative Examples 1 to 4, in which the standard deviation σ is less than 0.5 mm, have a smaller beam diameter than REF. From the above, it can be seen that when the standard deviation σ is 0.5 mm or more and 1.5 mm or less, the beam diameter can be increased while maintaining the desired reflection angle.

[0029] (More Preferred Configuration) <Expansion of Reflection Frequency Band by Reducing Dielectric Constant> By using a material with a low relative dielectric constant for the dielectric layer 11 of the reflector 10, it is possible to expand the reflection frequency band. The reflection frequency band refers to the frequency range in which the peak intensity of the main lobe of the reflected wave in the target direction is attenuated by 3 dB relative to the incident wave of the wavelength used. Below, the target value of the reflection peak angle was changed to "35°" in the design, and analysis and evaluation were performed by simulation.

[0030] 8A to 8C show the reflection characteristics of a low-dielectric-constant reflector for incident waves of different frequencies. The low-dielectric-constant reflector is a reflector of the embodiment, which is a reflector 10 using a dielectric layer 11 with a relative dielectric constant of 2.0 or less. In this example, a dielectric layer with a relative dielectric constant ε of 1.88 is used. For comparison, FIGS. 9A to 9C show the reflection characteristics of a high-dielectric-constant reflector for incident waves of different frequencies. The high-dielectric-constant reflector is a reflector using a dielectric layer with a relative dielectric constant exceeding 2.0.

[0031] 8A to 8C, reflection spectra at 26 GHz, 28 GHz, and 31 GHz are calculated using a dielectric layer 11 with a relative permittivity ε of 1.88. The reflection intensity on the vertical axis is represented by the radar cross section (RCS), which is an index of reflection ability. Plane waves in the frequency bands of 26 GHz, 28 GHz, and 31 GHz are incident from the normal direction of the reflector, and the scattering cross section is analyzed for each angle using Dassault Systèmes' CST Studio Suite, a general-purpose three-dimensional electromagnetic field simulation software.

[0032] When ε = 1.88, a peak appears in the reflection spectrum at a 35° angle at 26 GHz, 28 GHz, and 31 GHz. In all frequency bands, the peak value is within the range of -25 dB ± 2.5 dB, and a stable peak intensity is obtained at a target reflection angle of 35° over at least a 5 GHz frequency band.

[0033] In particular, at 28 GHz and 31 GHz, the main lobe at a reflection angle of 35° is clearly distinguishable from the other side lobes, and it can be seen that the incident wave is reflected with good control in the targeted 35° direction. At 26 GHz, in addition to the 35° peak, other peaks appear at 0° and -65°. The 0° peak is a reflection in the same direction as the incident wave, so it represents a loss. The -65° peak is a reflection in the opposite direction from the target 35°, and depending on the environment in which the reflector is used, this can result in a loss, or it can be beneficial to deliver radio waves in two directions at once.

[0034] In the comparative examples shown in Figures 9A to 9C, the dielectric constant ε is changed to 3.62, while maintaining the same other conditions as the reflectors shown in Figures 8A to 8C, such as the conductor pattern. Materials with a dielectric constant of 3.62 include polyphenylene ether (PPE) and acrylic resin. With a dielectric constant of 3.62, reflection peaks appear at 35° from the target at 28 GHz and 31 GHz, but the spectral shape of the main lobe at 31 GHz is degraded. At 26 GHz, reflection is not achieved in the desired 35° direction.

[0035] The configurations shown in Figures 9A to 9C clearly demonstrate the fact that the reflection characteristics of a metasurface that utilizes resonance deteriorate as the frequency changes. The use of the low-dielectric-constant reflector of the embodiment shown in Figures 8A to 8C significantly improves the frequency characteristics. Based on Figures 8A to 8C and Figures 9A to 9C, it can be seen that the frequency band of reflection can be expanded by lowering the dielectric constant of the dielectric layer 11 used in the reflector 10 to a certain extent.

[0036] Figure 10A shows the reflection range of a low-dielectric-constant reflector, and Figure 10B shows the reflection range of a high-dielectric-constant reflector. In Figures 10A and 10B, the horizontal axis represents the reflection angle, and the vertical axis represents the frequency of the incident wave. The reflector model used has the same conductor pattern as in Figure 3A formed on the surface of a dielectric layer. The relative dielectric constant ε of the low-dielectric-constant reflector in Figure 10A is set to 1.88, and the relative dielectric constant ε of the high-dielectric-constant reflector in Figure 10B is set to 3.62.

[0037] In Figure 10A, a high reflection intensity (greater than -30 dB and less than -20 dB) is obtained from 24 GHz to 33 GHz at an angle of 35 degrees from the target. This reflection intensity is distributed within a range of ±10 degrees from 35 degrees, and particularly in the range of 23 degrees to 35 degrees, a reflection intensity of greater than -30 dB and less than -20 dB is obtained over a frequency band of 10 GHz or more. This wide range of reflection frequency characteristics realizes high resistance to environmental changes.

[0038] In Figure 10B, when the relative dielectric constant is 3.62, a high reflection intensity (greater than -30 dB and less than -20 dB) is obtained from 21 GHz to 28.5 GHz in a direction of 35° from the target. However, considering the frequency bands actually used in each country, the practical frequency band for the reflector in Figure 10B is in the range of 24 GHz to 28.5 GHz. Taking into account the frequency bands used in each country and the possibility of peak shifts, a reflector with a frequency band of 6 GHz or more in the frequency band from 24 GHz to 60 GHz is desirable.

[0039] 10A and 10B, it can be seen that the lower the dielectric constant of the dielectric layer 11 of the reflector, the wider the reflection range (angle range) for frequency and the wider the practical reflection frequency band.

[0040] <Thickness of Dielectric Layer> The thickness of the dielectric layer 11 will be examined with reference to FIGS. 11 and 12. FIG. 11 shows the relationship between the thickness of a dielectric layer with different dielectric constants and the frequency band of reflection. FIG. 12 shows the relationship between the thickness of a dielectric layer with different dielectric constants and the reflection intensity. In FIG. 11, the thickness of the dielectric layer 11 is changed to 0.30 mm, 0.50 mm, and 0.75 mm. The conductor pattern 131 formed on the first surface 111 of the dielectric layer 11 is the same as that shown in FIG. 3A. The conductor pattern configuration is the same, but the relative dielectric constant ε of the dielectric layer 11 is changed. A 28 GHz plane wave is incident from the normal direction of the reflector, and the frequency band of reflection is analyzed. As described above, the bandwidth of the reflected wave is the frequency bandwidth attenuated by 3 dB from the peak value of the main lobe of reflection.

[0041] For a given thickness of the dielectric layer 11, a lower relative dielectric constant ε results in a wider reflection frequency band. Conversely, when achieving the same reflection frequency band, a reflector made of a material with a lower dielectric constant can be made thinner. In the example of Figure 11, when the thickness of the dielectric layer 11 is 0.75 mm, a reflector with an ε of 1.88 achieves a reflection frequency band exceeding 6.5 GHz, but a reflector with an ε of 3.62 can only cover a reflection frequency band of 4.5 GHz.

[0042] [Correction under Rule 91 24.01.2025] As mentioned above, considering the frequency bands and peak shifts used in each country, it is desirable for the reflection frequency band to exceed 6 GHz in the frequency band between 24 GHz and 30 GHz. Interpolating the data points in Figure 11, it appears that a 6 GHz reflection frequency band may be achieved by increasing the thickness of the dielectric layer 11 with an ε of 3.62 to about 1.2 mm. However, this would increase the thickness of the reflector, reducing its flexibility and limiting its range of application.

[0043] In contrast, when ε is 1.88, a reflection frequency band of 6.5 GHz is realized with a dielectric layer 11 having a thickness of 0.75 mm, and a flexible sheet-like reflector is realized. A sheet-like reflector is easy to handle and can be attached to a desired location like wallpaper. The fact that a wide band can be achieved with a thin and flexible dielectric layer 11 is a major advantage.

[0044] In Figure 12, the thickness of the dielectric layer 11 is changed to 0.25 mm, 0.30 mm, 0.50 mm, and 0.80 mm, and the peak intensity of the reflected wave is calculated. When the relative dielectric constant ε is 1.88, a peak intensity exceeding -24 dB can be obtained by making the thickness of the dielectric layer 11 0.30 mm or more. When ε is 3.62, the thickness of the dielectric layer 11 must be 0.5 mm to obtain the same level of peak intensity.

[0045] From the results of FIG. 12, the reflector having a low dielectric constant according to the embodiment is advantageous from the viewpoint of thinning and lightening the device.

[0046] Figure 13 shows the configurations and characteristics of the example and comparative example. The configuration parameters are the type, thickness, relative dielectric constant, and porosity of the substrate that constitutes the dielectric layer 11. The values ​​of these parameters are varied. The reflector characteristics are shown as the reflection frequency band and the band per unit thickness. Throughout the example and comparative example, the conductor pattern 131 is the conductor patterns 131a to 131h in Figure 3A, and the type and parameters of the dielectric layer 11 are varied.

[0047] Simulations were performed under the following conditions, and the frequency bands of reflection for the example and comparative example were determined from the far radiation field, intensity, and angle of the reflection spectrum for the incident wave.

[0048] Wavelength of incident wave: 10.7 mm (frequency 28 GHz) Frequency change range of incident wave: 20 GHz to 35 GHz Incident angle of incident wave with respect to the normal direction of the reflector: 0 degrees First desired reflection angle θ of the reflection spectrum with respect to the normal direction of the reflector: 35 degrees Number of conductor patterns: 8 (arranged in series) Pitch of conductor patterns: 5.35 mm Standard deviation σ: 0.5 mm (designed with the same pitch as in Example 1)

[0049] Example 4 In Example 4, a fluorine porous substrate is used as the base material of the dielectric layer 11. The fluorine porous substrate is a combination of a fluorinated resin and an inorganic porous aggregate. Polytetrafluoroethylene is used as the fluorinated resin. The thickness of this dielectric substrate is 0.75 mm, the porosity is 33.2%, and the relative dielectric constant is 1.88. The reflection frequency band of the reflector obtained in Example 1 is 6.6 GHz, and the band per unit thickness (1 mm) is 8.8 GHz / mm.

[0050] Example 5 In Example 5, a porous fluorine substrate is used as the base material for the dielectric layer 11. The thickness of this dielectric substrate is 0.75 mm, the porosity is 67.7%, and the relative dielectric constant is 1.50. By changing the aggregation density of the porous inorganic fine particles used in the porous fluorine substrate, the dielectric layer 11 is designed to have different porosities and relative dielectric constants. The reflection frequency band of the reflector obtained in Example 5 is 7.1 GHz, and the band per unit thickness (1 mm) is 9.5 GHz / mm.

[0051] Example 6 In Example 6, a porous fluorine substrate is used as the base material for the dielectric layer 11. The thickness of this dielectric substrate is 0.50 mm, the porosity is 33.0%, and the relative dielectric constant is 1.88. By changing the aggregation density of the porous inorganic fine particles used in the porous fluorine substrate, the dielectric layer 11 is designed to have a different porosity and relative dielectric constant. In addition, the dielectric layer 11 is thinner than in Examples 4 and 5. The reflection frequency band of the reflector obtained in Example 6 is 4.55 GHz, and the band per unit thickness (1 mm) is 9.1 GHz / mm.

[0052] Example 7 In Example 7, a porous fluorine substrate is used as the base material for the dielectric layer 11. The thickness of this dielectric substrate is 1.00 mm, the porosity is 33.0%, and the relative dielectric constant is 1.88. The thickness of the dielectric layer 11 is greater than in Examples 4 and 5. The reflection frequency band of the reflector obtained in Example 7 is 6.5 GHz, and the band per unit thickness (1 mm) is 6.5 GHz / mm.

[0053] Example 8 In Example 8, a porous fluorine substrate is used as the base material for the dielectric layer 11. This dielectric substrate has a thickness of 0.75 mm, a porosity of 22.5%, and a relative dielectric constant of 2.00. The aggregation density of the porous inorganic fine particles used in the porous fluorine substrate is controlled to design different porosities and relative dielectric constants. The reflection frequency band of the reflector obtained in Example 8 is 5.5 GHz, and the band per unit thickness (1 mm) is 7.3 GHz / mm.

[0054] Example 9 In Example 9, a porous fluorine substrate is used as the base material for the dielectric layer 11. The thickness of this dielectric substrate is 0.3 mm, the porosity is 33.0%, and the relative dielectric constant is 1.88. The thickness of the dielectric layer 11 is thinner than in Example 8. The reflection frequency band of the reflector obtained in Example 9 is 4.1 GHz, and the band per unit thickness (1 mm) is 13.7 GHz.

[0055] Comparative Example 7 In Comparative Example 7, PPE is used as the substrate of the dielectric layer 11. The thickness of the PPE substrate is 0.75 mm, the porosity is 0.0%, and the relative dielectric constant is 3.62. The reflection frequency band of the reflector obtained in Comparative Example 7 is 4.5 GHz, and the band per unit thickness (1 mm) is 6.0 GHz / mm. Compared to Examples 4 to 5 and 8, although a substrate of the same thickness is used, the reflection frequency band is narrower due to the higher relative dielectric constant.

[0056] Comparative Example 8 In Comparative Example 8, a glass epoxy substrate is used as the substrate for the dielectric layer 11. The thickness of this dielectric substrate is 0.75 mm, the porosity is 0.0%, and the relative dielectric constant is 5.00. The relative dielectric constant is even higher than that of Comparative Example 7. The reflection frequency band of the reflector obtained in Comparative Example 8 is 3.7 GHz, and the band per unit thickness (1 mm) is 4.9 GHz / mm.

[0057] Comparative Example 9 In Comparative Example 9, PPE is used as the substrate of the dielectric layer 11. The thickness of this dielectric substrate is 0.50 mm, the porosity is 0.0%, and the relative dielectric constant is 3.62. The reflection frequency band of the reflector obtained in Comparative Example 9 is 3.0 GHz, and the band per unit thickness (1 mm) is 6.0 GHz. Although the same PPE substrate as in Comparative Example 7 is used, the reflection frequency band is further narrowed by reducing the thickness of the substrate.

[0058] The results in Figure 13 show that when the dielectric layer 11 has a dielectric constant of 2.0 or less, a wideband reflection characteristic exceeding 6.5 GHz, preferably exceeding 7.0 GHz, and more preferably exceeding 8.0 GHz per unit thickness of the reflector can be obtained. When the dielectric layer is thin and the dielectric constant is 1.88 or less, a frequency band exceeding 8.8 GHz per unit thickness of the reflector can be achieved. In Examples 8 and 9, by using a fluorinated resin with a low dielectric constant combined with the inorganic porous aggregate, a dielectric constant of 2.0 or less can be achieved with a porosity of approximately 20% for the dielectric layer 11. The thickness of the dielectric layer 11 can be designed appropriately depending on the application. When the reflector 10 is used in a flexible form, the thickness of the dielectric layer 11 may be 0.3 mm or more and 1.0 mm or less. By setting the thickness of the dielectric layer 11 to 0.3 mm or more, a highly robust reflector 10 can be obtained. Furthermore, if the thickness of the dielectric layer 11 is 1.0 mm or less, it is advantageous for weight reduction in the design of a large reflector with a side length of about 1 m, and is excellent in workability and construction cost. Note that when the thickness is 0.3 mm, 1.0 mm, etc., it is assumed that an allowable manufacturing error is included.

[0059] FIG. 14 is a schematic diagram of a reflector 20 of the second embodiment. The main components of the reflector 20 are the same as those of the reflector 10 of the first embodiment, and a dielectric layer 21 with a relative dielectric constant of 2.0 or less is used. A conductive layer 23 including a predetermined conductor pattern 231 is formed on a first surface 211 of the dielectric layer 21, and a ground layer 22 is provided on a second surface 212. The conductor pattern 231 is designed so that the reflection direction of the main lobe for an incident wave in the 28 GHz band is tilted at a predetermined angle from the normal direction, as shown in FIG. 3A as an example. Below, the target value of the reflection peak angle was changed to "-43°" and analysis and evaluation were performed by simulation.

[0060] A protective layer 24 is provided to cover the conductive layer 23. An adhesive layer 26 is provided on the ground layer 22 side. The adhesive layer 26 allows the reflector 20 to be attached to a desired location, such as a wall or ceiling. The protective layer 24 is transparent to incident waves of 24 GHz to 30 GHz. "Transparent to incident waves" means having a transmittance of 60% or more, preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more for the incident waves. The protective layer 24 may be transparent to visible light. By providing the protective layer 24, the reflector 20 can be attached to an outdoor bulletin board or the wall of a building. The board to which the reflector 20 is attached may be hung at a desired location.

[0061] The protective layer 24 protects the conductor pattern 231 of the reflector 20 from deterioration or damage due to external factors, resulting in excellent durability. The conductor pattern 231 of the reflector 20 is subject to oxidation deterioration over time due to contact with oxygen and moisture in the atmosphere, and the formation of the protective layer 24 is preferable from the standpoint of weather resistance, particularly when used outdoors. Even indoors, the formation of the protective layer 24 is preferable in installation environments where condensation and the like are likely to occur. The protective layer 24 preferably has a thickness of 0.1 mm or more and 1.0 mm or less and a relative dielectric constant of 2.0 or less. By configuring the protective layer 24 in this manner, a reflector 20 can be obtained that combines high durability with high transparency to incident waves of 24 GHz to 30 GHz.

[0062] Using a model of the configuration shown in FIG. 14 excluding the adhesive layer 26, simulations were performed under the following conditions for Examples 10 to 13 and Comparative Examples 10 to 17, in which the protective layer thickness (mm) and relative dielectric constant Dk were changed as shown in FIG. 15 , and the reflection angle deviation (%) and reflection intensity loss (%) of the Examples and Comparative Examples were determined from the far radiation field, intensity, and angle of the reflection spectrum for the incident wave. - Wavelength of incident wave: 10.7 mm (frequency 28 GHz) - Frequency change range of incident wave: 20 GHz - 35 GHz - Incident angle of incident wave with respect to the normal direction of the reflector: 0 degrees - First desired reflection angle θ of the reflection spectrum with respect to the normal direction of the reflector: -43 degrees - Number of conductor patterns: 5 (arranged in series) - Pitch of conductor patterns: 5.35 mm - Relative dielectric constant of protective layer 24: 1.0 (Ref), 1.5, 2.0, 3.0, 5.0 - Thickness of protective layer 24: 0.0 mm (Ref), 0.2 mm, 0.5 mm, 1.0 mm Five cross patterns of different sizes were used as the shape of the conductor patterns, and the reflection angle and reflection intensity were calculated by changing the thickness and relative dielectric constant of the protective layer 24 covering the conductor patterns.

[0063] The simulation results are shown in Figure 15. "Ref" in the leftmost column of Figure 15 indicates a reference configuration in which the protective layer 24 is not provided. In the reference configuration, an air layer covers the conductor pattern, so the thickness of the protective layer 24 is set to 0.0 mm and the relative dielectric constant is set to 1.0. The unit of reflection intensity for the reference configuration is (dB). "Reflection angle deviation" indicates the rate of change (%) from the reflection angle of the reference configuration, and "Reflection intensity loss" indicates the rate of decrease (%) from the reflection intensity of the reference configuration. The peak angle and peak intensity of the main lobe relative to the incident wave were compared between the reference configuration (Ref) and Examples 10 to 13 and Comparative Examples 10 to 17, and the reflection angle deviation (unit: %) and reflection intensity loss (unit: %) were determined. The reflection angle deviation and reflection intensity loss were evaluated as follows.・Reflection angle deviation of 10% or less: A ・Reflection angle deviation of more than 10%: B ・Reflection intensity loss of 5% or less: S ・Reflection intensity loss of 10% or less: A ・Reflection intensity loss of more than 10%: B ・Overall evaluation Pass: Both the reflection angle deviation and reflection intensity loss evaluation are "A" Fail: Either the reflection angle deviation or reflection intensity loss evaluation is "B"

[0064] As shown in Figure 15, Examples 10 to 13 passed the test. Furthermore, Examples 10 to 12 had small reflection intensity losses, and more favorable results were obtained. As can be seen from Figure 15, when the relative dielectric constant Dk is high, the reflection angle deviation and reflection intensity loss are large, and it is therefore desirable that the relative dielectric constant Dk be 2.0 or less. When the relative dielectric constant Dk is 1.5 or less, the reflection intensity loss is 5% or less, which is more preferable (evaluated as "S" in Figure 15). When the thickness of the protective layer 24 is large, the reflection angle deviation and reflection intensity loss are large, and it is therefore desirable that the thickness of the protective layer 24 be 0.1 mm or more and 1.0 mm or less.

[0065] Fig. 16A shows an example of use of the reflector 20 of the embodiment. Fig. 16B shows a comparison of an example of use of a normal reflector. Fig. 16A shows how the reflector 10 or 20 of the embodiment is used. The reflector 10 or 20 of the embodiment is thin and flexible, and can be installed along an L-shaped passage, street, corridor, etc.

[0066] The reflector of the embodiment has a metasurface including a periodic array of multiple conductor patterns 131, and reflects incident waves in a direction other than specular reflection. As shown in Figure 16A, when radio waves are perpendicularly incident on reflector 10 or 20 installed on a wall surface at a corner, the incident radio waves are reflected at an oblique angle other than the vertical and horizontal directions of the reflector. This allows radio waves to be sent to smartphones, electronic devices, lighting equipment, etc. located in area A.

[0067] As shown in Figure 16B, a typical reflector RFL with a specular reflective surface reflects perpendicularly incident radio waves back in the direction of incidence. Therefore, the reflector RFL must be installed at an oblique angle to the incident radio waves. If it is placed in a corner, as shown in Figure 16B, the space cannot be used effectively. In contrast, the reflector 10 or 20 of the embodiment can reduce radio wave blind zones without taking up space or compromising the appearance.

[0068] As described above, the reflector of the embodiment can expand the reflection frequency band and improve environmental resistance by using a dielectric layer with a low relative dielectric constant. Furthermore, the thickness of the reflector can be reduced while maintaining the same reflection frequency characteristics, thereby broadening the range of applications. When forming the reflector in a wallpaper-like shape, the surface of the adhesive layer 26 may be protected with a protective film, and the protective film may be peeled off and the reflector attached to the desired location before use. The reflector of the embodiment may also be used in combination with small cells or repeaters. In this case, blind zones can be further reduced without increasing the number of devices such as small cells or repeaters, and without occupying space for the reflector.

[0069] [Correction based on Rule 91 24.01.2025] The above disclosure may take the following forms: (Item 1) A reflector comprising: a dielectric layer; a conductive layer formed on a first surface of the dielectric layer and including a plurality of conductor patterns that reflect incident waves; and a ground layer formed on a second surface of the dielectric layer opposite the first surface, wherein a plurality of the conductor patterns are arranged along a predetermined direction, and among the plurality of conductor patterns, the standard deviation σ of the difference between the center-to-center distance between a reference conductor pattern and an arbitrary conductor pattern and the ideal distance on a straight line along the predetermined direction is 0.5 mm or more and 1.5 mm or less. (Item 2) The reflector according to item 1, wherein, when the incident wave of the same phase is incident on a reference conductor pattern and an m-th conductor pattern in the arrangement direction from the reference conductor pattern among the plurality of conductor patterns, the center-to-center distance between the reference conductor pattern and the m-th conductor pattern at which the intensity of the reflected wave is strongest is defined as an ideal distance dm of the m-th conductor pattern, the center-to-center distance between the reference conductor pattern and the m-th conductor pattern formed on the first surface of the dielectric layer is defined as an actual distance dm' of the m-th conductor pattern, the absolute value of the difference between the actual distance dm' and the ideal distance dm is defined as |dm' - dm|, where m is an integer of 1 or greater, the standard deviation of a group consisting of |dm' - dm| of each conductor pattern other than the reference conductor pattern is 0.5 mm or greater and 1.5 mm or less. (Item 3) The reflector according to item 1, further comprising an adhesive layer provided on a surface of the ground layer opposite to the dielectric layer. (Item 4) The reflector according to item 1, further comprising a protective layer covering the conductive layer. (Item 5) The reflector according to item 4, wherein the protective layer has a thickness of 0.1 mm or more and 1.0 mm or less and a relative dielectric constant of 2.0 or less. (Item 6) The reflector according to item 1, wherein the dielectric layer has a thickness of 0.3 mm or more and 1.0 mm or less. (Item 7) The reflector according to item 1, wherein the conductor pattern has a length of 2.0 mm or more and 5.0 mm or less. (Item 8) The reflector according to item 1, wherein the frequency band of reflection per unit thickness of the reflector exceeds 6.5 GHz / mm.(Item 9) The reflector according to any one of Items 1 to 8, wherein the dielectric layer is formed of a combination of a fluorinated resin and an inorganic porous aggregate, and the porosity of the dielectric layer is 20% or more.

[0070] This application claims priority based on Japanese Patent Application No. 2023-058657 filed with the Japan Patent Office on March 31, 2023, and incorporates all of the contents of the above application by reference.

[0071] 10, 20 Reflector 11, 21 Dielectric layer 111, 211 First surface 112, 212 Second surface 12, 22 Ground layer 13, 23 Conductive layer 131, 231 Conductive pattern 24 Protective layer 26 Adhesive layer

Claims

1. A reflector comprising: a dielectric layer; a conductive layer formed on a first surface of the dielectric layer and including a plurality of conductor patterns that reflect an incident wave; and a ground layer formed on a second surface of the dielectric layer opposite the first surface, wherein a plurality of the conductor patterns are arranged along a predetermined direction, and a standard deviation σ of the difference between the center-to-center distance between a reference conductor pattern and an arbitrary conductor pattern among the plurality of conductor patterns and the ideal distance along the predetermined direction is 0.5 mm or more and 1.5 mm or less.

2. The reflector according to claim 1, wherein, when the incident wave of the same phase is incident on a reference conductor pattern and an mth conductor pattern in an arrangement direction from the reference conductor pattern among the plurality of conductor patterns, the center-to-center distance between the reference conductor pattern and the mth conductor pattern at which the intensity of the reflected wave is strongest is defined as an ideal distance dm of the mth conductor pattern, the center-to-center distance between the reference conductor pattern and the mth conductor pattern formed on the first surface of the dielectric layer is defined as an actual distance dm' of the mth conductor pattern, and an absolute value of a difference between the actual distance dm' and the ideal distance dm is defined as |dm'-dm|, where m is an integer of 1 or more, the standard deviation of a group consisting of |dm'-dm| of each conductor pattern other than the reference conductor pattern is 0.5 mm or more and 1.5 mm or less.

3. The reflector according to claim 1, further comprising: an adhesive layer provided on a surface of the ground layer opposite to the dielectric layer.

4. The reflector according to claim 1, further comprising a protective layer covering said conductive layer.

5. The reflector according to claim 4, wherein the protective layer has a thickness of 0.1 mm or more and 1.0 mm or less, and a relative dielectric constant of 2.0 or less.

6. [Correction under Rule 91 24.01.2025] The reflector according to claim 1, wherein the thickness of the dielectric layer is 0.3 mm or more and 1.0 mm or less.

7. [Correction under Rule 91 24.01.2025] The reflector according to claim 1, wherein the length of the conductor pattern is 2.0 mm or more and 5.0 mm or less.

8. The reflector according to claim 1, wherein the frequency band of reflection per unit thickness of the reflector exceeds 6.5 GHz / mm.

9. The reflector according to any one of claims 1 to 8, wherein the dielectric layer is formed of a combination of a fluorinated resin and an inorganic porous aggregate, and the porosity of the dielectric layer is 20% or more.

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