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

Technical Field

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

Background Art

[0002] When high-frequency radio waves such as microwaves, millimeter waves, and terahertz waves are used for wireless communication, high-speed and high-capacity communication becomes possible. On the other hand, high-frequency radio waves from 1 GHz to 10 THz have strong directivity, and there is a drawback that due to the presence of obstacles between the transmitting antenna and the receiving antenna, the radio waves cannot reach and communication becomes impossible. In order to improve the communication environment and communication area of mobile communication using high frequencies, reflectors are used. Since a normal reflector has a specular reflection surface where the incident angle and the reflection angle are equal, there is a limit to the reflection range. In order to expand the communication range, metareflectors having a metasurface that reflects incident waves in a desired direction have been actively developed.

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Because reflect arrays with metasurfaces utilize resonance phenomena, when reflecting at a predetermined frequency in a desired direction (hereinafter also referred to as the "target direction"), the reflection distance to the target and the beam diameter are inversely proportional. As a result, as the reflection distance increases, the beam diameter of the main lobe of the reflected wave in the target direction narrows. When the beam diameter of the main lobe narrows, the coverage area within the radio wave's range is limited, which can lead to communication failure.

[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 direction is increased. [Means for solving the problem]

[0007] In one embodiment, the reflector includes 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 to the first surface, wherein a plurality of 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 along the predetermined direction and the ideal distance is 0.5 mm or more and 1.5 mm or less. [Effects of the Invention]

[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. [Brief explanation of the drawing]

[0009] [Figure 1] This diagram shows the basic configuration of the reflector according to the first embodiment. [Figure 2] This figure shows an example of a conductor pattern design method. [Figure 3A] This figure shows an example of a reflector design according to the first embodiment. [Figure 3B] This figure shows an example of a reflector design according to the first embodiment. [Figure 4] It is a diagram showing the reflection characteristics of a reflector according to the designs of FIGS. 3A and 3B. [Figure 5] It is a diagram showing the composition of the standard deviation of the examples and comparative examples. [Figure 6] It is a diagram showing the reflection characteristics of a reflector according to the design of FIG. 5. [Figure 7] It is a diagram showing the reflection characteristics of a reflector according to the design of FIG. 5. [Figure 8A] It is a diagram showing the reflection characteristics of a low dielectric constant reflector. [Figure 8B] It is a diagram showing the reflection characteristics of a low dielectric constant reflector. [Figure 8C] It is a diagram showing the reflection characteristics of a low dielectric constant reflector. [Figure 9A] It is a diagram showing the reflection characteristics of a high dielectric constant reflector. [Figure 9B] It is a diagram showing the reflection characteristics of a high dielectric constant reflector. [Figure 9C] It is a diagram showing the reflection characteristics of a high dielectric constant reflector. [Figure 10A] It is a diagram showing the reflection range of a low dielectric constant reflector with respect to frequency. [Figure 10B] It is a diagram showing the reflection range of a high dielectric constant reflector with respect to frequency. [Figure 11] It is a diagram showing the relationship between the thickness of dielectric layers with different dielectric constants and the reflection bandwidth. [Figure 12] It is a diagram showing the relationship between the thickness of dielectric layers with different dielectric constants and the reflection intensity. [Figure 13] It is a diagram showing the composition and characteristics of the examples and comparative examples. [Figure 14] It is a schematic diagram of a reflector of the second embodiment. [Figure 15] It is a diagram showing the simulation results with the thickness and dielectric constant of the protective layer changed. [Figure 16A] It is a diagram showing an example of use of a reflector of an embodiment. [Figure 16B] It is a diagram showing an example of use of a normal reflector.

Best Mode for Carrying Out the Invention

[0010] FIG. 1 is a basic configuration diagram of a reflector 10 according to the 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 to the first surface 111 of the dielectric layer 11. The conductive layer 13 includes an arrangement of a plurality of conductor patterns 131 and functions as a 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 a capacitance between the ground layer 12 and each conductor pattern 131, and the magnitude of the phase delay can be controlled for each conductor pattern 131. The conductive layer 13 and the ground layer 12 are not particularly limited as long as they are materials having electrical conductivity, but for example, copper foil is suitable in terms of electrical conductivity, manufacturability, processability, material price, etc.

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

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

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

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

[0015] (distance between centers) In the conductive layer 13, multiple conductor patterns 131 of different sizes are arranged at predetermined distances apart. As shown in Figure 3A, in the reflector 10 of the first embodiment, the conductor patterns 131 are arranged in a line along a straight line l. The center point of each conductor pattern 131 is located on an arbitrary straight line. Note that the conductor patterns 131 do not have to be arranged in a straight line; they may be arranged in a staggered pattern or other arrangement pattern in the direction of arrangement. In this specification, "center point of a conductor pattern" means the center point of the circle that inscribes the contour of each conductor pattern when the conductor pattern is viewed in plan. The distance between the center point of a reference conductor pattern and the center point of any conductor pattern is called the "center-to-center distance". Furthermore, when multiple conductor patterns are arranged, for the sake of explanation, the center-to-center distance from the center point of the reference conductor pattern to the center point of the mth conductor pattern counting from the reference conductor pattern may be expressed as "dm" or "dm'", using any integer m of 1 or more. For example, in Figure 3A, the first conductor pattern from the left, 131a, is the reference conductor pattern. The center-to-center distance of the first conductor pattern from the reference conductor pattern in the direction of arrangement (the second conductor pattern from the left in Figure 3A, 131b) is expressed as d1 for the ideal distance and d1' for the actual distance. The ideal distance of the seventh conductor pattern (the eighth pattern from the left in Figure 3A, 131h) is expressed as d7, and the actual distance is expressed as d7'.

[0016] (ideal distance) In designing a conductor layer 13 in which multiple conductor patterns 131 are arranged, the "ideal distance" of the m-th conductor pattern is defined as 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 when an incident wave with the same phase is incident on the reference conductor pattern and the m-th conductor pattern (counting from the reference conductor pattern). In this specification, the ideal distance is denoted as dm. By arranging the conductor patterns 131 of the conductor layer 13 at the ideal distance dm, a reflector with a large reflected wave propagation distance can be obtained. From the viewpoint of robustness when designing the reflection characteristics of the reflector, the ideal distance dm is preferably 0.5λ or more and 0.7λ or less with respect to the wavelength λ of the incident wave.

[0017] (Actual distance) With respect to an ideal distance dm, the distance between the centers of the first conductor pattern and the mth conductor pattern formed on the first surface of the dielectric layer is defined as the "actual distance" of the mth conductor pattern. In this specification, the actual distance is denoted as dm'.

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

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

[0020] Inorganic porous aggregates are produced, for example, by the method described in Japanese Patent Publication No. 2017-171898. By adjusting the material and aggregation density of the porous inorganic fine particles, the porosity of the aggregate can be controlled to 50% or more. By controlling the dielectric constant through adjustment of the porosity, a dielectric constant of 2.0 or less can be achieved.

[0021] Figures 3A and 3B show design examples of the reflector 10 according to the first embodiment. Figure 3A shows the arrangement of conductor patterns 131a to 131h that constitute the conductive layer 13. Figure 3B shows the size of each conductor pattern. Conductor patterns 131a to 131h are cross patterns with equal vertical and horizontal lengths. The size of each conductor pattern 131 is indicated by the vertical or horizontal length L1 to L8. The incident wave is in the 28 GHz band with a wavelength λ = 10.8 mm, and the pitch of conductor patterns 131a to 131h, i.e., the ideal distance dm between centers, is 5.35 mm in all cases.

[0022] The arrangement of 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 to the reflector 10, i.e., the reflection angle relative to the normal. Based on equation (1) above, the phase difference "δ1-δ2" when θ is -42° is found to be 120°. The size of conductor patterns 131a to 131h, i.e., the lengths of L1 to L8, are determined so that this phase difference is obtained.

[0023] The shape of the conductor pattern 131 is not limited to a cross pattern; different sizes of circles, ellipses, polygons, etc., may be provided at a predetermined period. When targeting the 28GHz band, the conductor pattern 131 preferably has a length of 2.0 to 5.0 mm, but the size of the conductor pattern 131 is appropriately designed according to the frequency band. Radio waves of frequencies determined by the size and period 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 extended to a bandwidth of 4GHz or more, more preferably 6GHz 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 of over 6.5GHz / mm per unit thickness (1mm) of the reflector 10 can be realized.

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

[0025] <Beam diameter expansion due to standard deviation σ> For Examples 1-3 and Comparative Examples 1-6, the standard deviation σ of the absolute difference |dm'-dm| between the actual distance dm' and the ideal distance dm was designed by varying the actual distance d1-d7 as shown in Figure 5, such that σ = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5, 2.0, and 2.5. The reflection spectrum for an incident plane wave at 28 GHz was calculated using a dielectric layer 11 with a relative permittivity ε of 1.88. For the analysis of the reflection intensity, Dassault Systèmes CST Studio Suite, a general-purpose 3D electromagnetic field simulation software, was used to analyze the reflection intensity for each angle. The angle at which the peak of the reflection intensity appears was defined as the "reflection peak angle".

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

[0027] Figures 6 and 7 show the simulation results of the reflectivity characteristics of the reflector designed in Figure 5. In Figure 6, the vertical axis represents the reflectivity (unit: dB), and the horizontal axis represents the reflection angle (unit: °).

[0028] As shown in Figures 6 and 7, Examples 1-3 and Comparative Examples 5 and 6, where the standard deviation σ is 0.5 mm or more, show a larger beam diameter than REF. On the other hand, Comparative Examples 5 and 6, where the standard deviation σ is 2.0 or more, show a deviation of 3° or more from the design value in the reflection peak angle, indicating that the desired reflection characteristics cannot be obtained. Conversely, Comparative Examples 1-4, where the standard deviation σ is less than 0.5 mm, show a smaller beam diameter than REF. From the above, it was found that when the standard deviation σ is between 0.5 mm and 1.5 mm, the beam diameter can be increased while maintaining the desired reflection angle.

[0029] (A more preferred configuration) <Expansion of the reflection frequency band by reducing the dielectric constant> By using a material with a low relative permittivity in the dielectric layer 11 of the reflector 10, the reflection frequency band can be extended. The reflection frequency band refers to the frequency range in which the peak intensity of the main lobe of the reflected wave toward the target direction is attenuated by 3 dB for 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] Figures 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, and is a reflector 10 using a dielectric layer 11 with a relative permittivity of 2.0 or less. In this example, a dielectric layer with a relative permittivity ε of 1.88 is used. For comparison, Figures 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 permittivity greater than 2.0.

[0031] Figures 8A to 8C show the calculation of reflection spectra at 26 GHz, 28 GHz, and 31 GHz using a dielectric layer 11 with a relative permittivity ε of 1.88. The reflection intensity on the vertical axis is shown as the radar cross section (RCS), which is an indicator of reflectivity. Plane waves at the 26 GHz, 28 GHz, and 31 GHz frequency bands are incident from the normal direction of the reflector, and the scattering cross section is analyzed at each angle using Dassault Systèmes CST Studio Suite, a general-purpose 3D electromagnetic field simulation software.

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

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

[0034] In the comparison example from Figure 9A to Figure 9C, the relative permittivity ε is changed to 3.62, while other conditions such as the conductor pattern are kept the same as those of the reflector in Figures 8A to 8C. Materials with a relative permittivity of 3.62 include polyphenylene ether (PPE) and acrylic resin. With a relative permittivity of 3.62, reflection peaks appear at 35° to the target at 28 GHz and 31 GHz, but the spectral shape of the main lobe at 31 GHz is degraded. At 26 GHz, no reflection is obtained in the targeted 35° direction.

[0035] The configurations in Figures 9A to 9C directly illustrate the fact that in a metasurface utilizing resonance, the reflection characteristics deteriorate as the frequency changes. By using the low-dielectric-constant reflector of the embodiment shown in Figures 8A to 8C, the frequency characteristics can be greatly improved. Based on Figures 8A to 8C and 9A to 9C, it can be seen that the reflection frequency band can be extended 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 the dielectric layer. The relative permittivity ε of the low-dielectric constant reflector in Figure 10A is set to 1.88, and the relative permittivity ε of the high-dielectric constant reflector in Figure 10B is set to 3.62.

[0037] Figure 10A shows that high reflection intensity (above -30dB and below -20dB) is obtained in the 35° direction of the target, from 24GHz to 33GHz. This reflection intensity is distributed within a range of ±10° centered on 35°, and in particular, in the range from 23° to 35°, reflection intensity of above -30dB and below -20dB is obtained over a frequency band of 10GHz or more. This wide range of reflection frequency characteristics enables high resistance to environmental changes.

[0038] In Figure 10B, when the relative permittivity is 3.62, a high reflection intensity (above -30dB and below -20dB) is obtained in the 35° direction of the target over the range of 21GHz to 28.5GHz. However, considering the frequency bands actually used in various countries, the practical frequency band for the reflector in Figure 10B is in the range of 24GHz to 28.5GHz. Considering the frequency bands used in various countries and the possibility of peak shift, a reflector with a frequency band of 6GHz or more in the frequency band between 24GHz and 60GHz is desirable.

[0039] Figures 10A and 10B show that a lower dielectric constant of the dielectric layer 11 of the reflector results in a wider reflection range (angle range) with respect to frequency, and a wider practical reflection frequency band.

[0040] <Thickness of the dielectric layer> Refer to Figures 11 and 12 to examine the thickness of the dielectric layer 11. Figure 11 shows the relationship between the thickness of dielectric layers with different dielectric constants and the reflection frequency band. Figure 12 shows the relationship between the thickness of dielectric layers with different dielectric constants and the reflection intensity. In Figure 11, the thickness of the dielectric layer 11 is varied 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 in Figure 3A. The conductor pattern configuration is the same, but the relative permittivity ε of the dielectric layer 11 is different. A 28 GHz plane wave is incident from the normal direction of the reflector, and the reflection frequency band 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 the reflection.

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

[0042] As mentioned above, considering the frequency bands and peak shifts used in various countries, it is desirable that the reflection frequency band exceeds 6 GHz in the frequency band between 24 GHz and 30 GHz. Interpolating the data points in Figure 11, it may be possible to achieve a reflection frequency band of 6 GHz by increasing the thickness of the dielectric layer 11 with ε = 3.62 to about 1.2 mm. However, in that case, the reflector becomes thicker, its flexibility decreases, and its range of application is limited.

[0043] In contrast, when ε is 1.88, a dielectric layer 11 with a thickness of 0.75 mm achieves a reflection frequency band of 6.5 GHz, realizing a sheet-like flexible reflector. The sheet-like reflector is easy to handle and can be attached to desired locations like wallpaper. The ability to achieve a wide bandwidth with a thin and flexible dielectric layer 11 is a major advantage.

[0044] In Figure 12, the peak intensity of the reflected wave is calculated by changing the thickness of the dielectric layer 11 to 0.25 mm, 0.30 mm, 0.50 mm, and 0.80 mm. When the relative permittivity ε is 1.88, a peak intensity of over -24 dB can be obtained by setting the thickness of the dielectric layer 11 to 0.30 mm or more. When ε is 3.62, a similar peak intensity cannot be obtained unless the thickness of the dielectric layer 11 is set to 0.5 mm.

[0045] As shown in Figure 12, the low dielectric constant reflector of the embodiment is also advantageous from the viewpoint of thinning and lightening the device.

[0046] Figure 13 shows the configuration and characteristics of the examples and comparative examples. The configuration parameters are the type, thickness, relative permittivity, and porosity of the substrate constituting 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 examples and comparative examples, the conductor pattern 131 is the same as the conductor patterns 131a to 131h in Figure 3A, but the type and parameters of the dielectric layer 11 are changed.

[0047] Simulations were performed under the following conditions, and the frequency bandwidth of the reflections for the examples and comparative examples was determined from the far-field radiation, intensity, and angle of the reflection spectrum relative to the incident wave.

[0048] Wavelength of incident wave: 10.7 mm (frequency 28 GHz) Frequency variation range of the incident wave: 20 GHz to 35 GHz Incident angle of the incident wave relative to the normal direction of the reflector: 0 degrees The first desired reflection angle θ of the reflection spectrum with respect to the normal direction of the reflector is 35 degrees. Number of conductor patterns: 8 (arranged in series) Conductor pattern pitch: 5.35mm Standard deviation σ: 0.5 mm (Designed with the same pitch as Example 1.)

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

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

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

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

[0053] <Example 8> In Example 8, a fluorine porous substrate is used as the substrate for the dielectric layer 11. The thickness of this dielectric substrate is 0.75 mm, the porosity is 22.5%, and the relative permittivity is 2.00. Different porosity and relative permittivity are designed by controlling the aggregation density of the porous inorganic fine particles used in the fluorine porous substrate. The reflection frequency band of the reflector obtained in Example 8 is 5.5 GHz, and the bandwidth per unit thickness (1 mm) is 7.3 GHz / mm.

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

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

[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 permittivity is 5.00. The relative permittivity is even higher than that of Comparative Example 7. The frequency bandwidth of the reflector obtained in Comparative Example 8 is 3.7 GHz, and the bandwidth per unit thickness (1 mm) is 4.9 GHz / mm.

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

[0058] The results in Figure 13 show that when the relative permittivity of the dielectric layer 11 is 2.0 or less, a broadband reflection characteristic of over 6.5 GHz per unit thickness of the reflector, preferably over 7.0 GHz, and more preferably over 8.0 GHz, can be obtained. When the dielectric layer is thin and the relative permittivity is 1.88 or less, a frequency band of 8.8 GHz or more per unit thickness of the reflector can be achieved. In Examples 8 and 9, by using a material with a low relative permittivity for the fluorine resin combined with the inorganic porous aggregate, a relative permittivity of 2.0 or less can be achieved with a porosity of about 20% for the dielectric layer 11. The thickness of the dielectric layer 11 can be appropriately designed depending on the application. When the reflector 10 is used in a flexible manner, the thickness of the dielectric layer 11 may be 0.3 mm or more and 1.0 mm or less. By making the thickness of the dielectric layer 11 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 large reflectors with sides of approximately 1 m, and offers superior workability and construction costs. Note that when the thickness is 0.3 mm, 1.0 mm, etc., it includes acceptable manufacturing tolerances.

[0059] Figure 14 is a schematic diagram of the reflector 20 of the second embodiment. The main part of the reflector 20 is the same as that of the reflector 10 of the first embodiment, and a dielectric layer 21 with a relative permittivity of 2.0 or less is used. A conductive layer 23 including a predetermined conductor pattern 231 is formed on the first surface 211 of the dielectric layer 21, and a ground layer 22 is provided on the 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, and an example of this is the pattern shown in Figure 3A. 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 covering the conductive layer 23. An adhesive layer 26 is provided on the side of the ground layer 22. 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 in the 24 GHz to 30 GHz range. 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, with respect to incident waves. The protective layer 24 may also be transparent to visible light. By providing the protective layer 24, the reflector 20 can be attached to outdoor bulletin boards or building walls. The board with the reflector 20 attached may also be suspended at a desired location.

[0061] The protective layer 24 protects the conductor pattern 231 of the reflector 20 from deterioration and damage due to external factors, resulting in excellent durability. The conductor pattern 231 of the reflector 20 is susceptible to oxidative deterioration over time due to contact with oxygen and moisture in the atmosphere, but the formation of the protective layer 24 is preferable from the viewpoint of weather resistance, especially when used outdoors. Even indoors, the formation of the protective layer 24 is preferable if the installation environment is prone to condensation. The protective layer 24 preferably has a thickness of 0.1 mm or more and 1.0 mm or less and a relative permittivity of 2.0 or less. By configuring the protective layer 24 in this way, a reflector 20 can be obtained that achieves both high durability and high transparency to incident waves in the 24 GHz to 30 GHz range.

[0062] Using the configuration model shown in Figure 14, excluding the adhesive layer 26, simulations were performed under the following conditions for Examples 10-13 and Comparative Examples 10-17, in which the protective layer thickness (mm) and relative permittivity Dk were varied as shown in Figure 15. The far-field radiation, intensity, and angle of the reflection spectrum for the incident wave were used to determine the reflection angle shift (%) and reflection intensity loss (%) for the Examples and Comparative Examples. • Wavelength of incident wave: 10.7 mm (frequency 28 GHz) • Frequency range of incident wave: 20GHz-35GHz • Incident angle of the incident wave relative to the normal direction of the reflector: 0 degrees • The 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) • Conductor pattern pitch: 5.35mm • Relative permittivity of protective layer 24: 1.0 (Ref), 1.5, 2.0, 3.0, 5.0 • Thickness of protective layer 24: 0.0mm (Ref), 0.2mm, 0.5mm, 1.0mm Using five cross patterns of different sizes as the shape of the conductor pattern, the reflection angle and reflection intensity are calculated by changing the thickness and relative permittivity of the protective layer 24 covering the conductor pattern.

[0063] Figure 15 shows the simulation results. The leftmost column of Figure 15, "Ref," shows the standard configuration without the protective layer 24. In the standard configuration, the air layer covers the conductor pattern, so the thickness of the protective layer 24 is set to 0.0 mm and the relative permittivity to 1.0. The unit of the reflection intensity of the standard configuration is (dB). "Reflection angle shift" shows the percentage change from the reflection angle of the standard configuration, and "Reflection intensity loss" shows the percentage decrease from the reflection intensity of the standard configuration. The peak angle and peak intensity of the main lobe for the incident wave were compared between the standard configuration (Ref), Examples 10 to 13, and Comparative Examples 10 to 17, and the reflection angle shift (unit: %) and reflection intensity loss (unit: %) were determined. The reflection angle shift and reflection intensity loss were evaluated as follows. • Reflection angle deviation is 10% or less: A • Reflection angle deviation exceeds 10%: B • Reflectance loss of 5% or less: S • Reflectance loss of 10% or less: A • Reflectance loss exceeds 10%: B ·comprehensive evaluation Passing grade: Both the evaluation of reflection angle deviation and reflection intensity loss are "A". Failure: Either the reflection angle deviation or the reflection intensity loss evaluation is "B".

[0064] As shown in Figure 15, Examples 10 to 13 passed the test. Furthermore, Examples 10 to 12 showed smaller reflectance loss, yielding more favorable results. From Figure 15, it can be seen that a high relative permittivity Dk results in large reflection angle shift and reflectance loss, and it is desirable for the relative permittivity Dk to be 2.0 or less. When the relative permittivity Dk is 1.5 or less, the reflectance loss is 5% or less, which is more favorable (rated "S" in Figure 15). A thicker protective layer 24 results in large reflection angle shift and reflectance loss, and it is desirable for the thickness of the protective layer 24 to be between 0.1 mm and 1.0 mm.

[0065] Figure 16A shows an example of use of the reflector 20 of the embodiment. Figure 16B shows a comparison with an example of use of a normal reflector. Figure 16A shows the usage of the reflector 10 or 20 of the embodiment. The thin and flexible reflector 10 or 20 of the embodiment can be installed along L-shaped passages, streets, corridors, etc.

[0066] The reflector of this embodiment has a metasurface including a periodic arrangement of multiple conductor patterns 131, which reflects the incident wave in a direction other than specular reflection. As shown in Figure 16A, when radio waves are incident perpendicularly on a reflector 10 or 20 installed on a corner wall, the incident radio waves are reflected at oblique angles other than the vertical and horizontal directions of the reflector. This makes it possible to transmit radio waves to smartphones, electronic devices, lighting equipment, etc. located in area A.

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

[0068] As described above, the reflector of the embodiment can extend the reflection frequency band and improve environmental resistance by using a dielectric layer with a low relative permittivity. Furthermore, the thickness of the reflector can be reduced while maintaining the same reflection frequency characteristics, thereby broadening the range of applications. When the reflector is formed in the form of wallpaper, the surface of the adhesive layer 26 may be protected with a protective film, and the protective film may be peeled off and attached to the desired location when in use. The reflector of the embodiment may be used in combination with small cells or repeaters. In this case, the number of devices such as small cells and repeaters is not increased, and the dead zone can be further reduced without taking up space for reflector installation.

[0069] The above disclosure may take the following forms: (Section 1) Dielectric layer and A conductive layer formed on the first surface of the dielectric layer, which includes a plurality of conductor patterns that reflect incident waves, A ground layer formed on the second surface of the dielectric layer opposite to the first surface, It has, The aforementioned conductor patterns are arranged in multiple locations along a predetermined direction, 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 along a straight line in the predetermined direction is 0.5 mm or more and 1.5 mm or less. Reflector. (Section 2) Among the plurality of conductor patterns, when an incident wave with the same phase is incident on a reference conductor pattern and the m-th conductor pattern in the direction of arrangement from the reference conductor pattern, the distance between the centers of 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 dm of the m-th conductor pattern. The distance between the centers of the reference conductor pattern and the mth conductor pattern formed on the first surface of the dielectric layer is defined as the actual distance dm' of the mth conductor pattern. Let |dm'-dm| be the absolute value of the difference between the actual distance dm' and the ideal distance dm. Let m be an integer greater than or equal to 1. The standard deviation of the group consisting of |dm'-dm| for each conductor pattern other than the aforementioned reference conductor pattern is 0.5 mm or more and 1.5 mm or less. The reflector described in item 1. (Section 3) An adhesive layer provided on the side of the ground layer opposite to the dielectric layer, A reflector as described in item 1, having the following characteristics. (Section 4) A protective layer covering the conductive layer, The reflector according to item 1, further comprising: (Section 5) The protective layer has a thickness of 0.1 mm or more and 1.0 mm or less, and a relative permittivity of 2.0 or less. The reflector described in item 4. (Section 6) The thickness of the dielectric layer is 0.3 mm or more and 1.0 mm or less. The reflector described in item 1. (Section 7) The length of the conductor pattern is 2.0 mm or more and 5.0 mm or less. The reflector described in item 1. (Section 8) The frequency bandwidth of the reflection per unit thickness of the reflector exceeds 6.5 GHz / mm. The reflector described in item 1. (Section 9) The dielectric layer is formed from a composite of a fluorinated resin and an inorganic porous aggregate, and the porosity of the dielectric layer is 20% or more. A reflector as described in any of items 1 through 8.

[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 the contents of the said application. [Explanation of Symbols]

[0071] 10, 20 reflectors 11, 21 Dielectric layer 111, 211 1st surface 112, 212 2nd surface 12, 22 Ground Layer 13, 23 Conductive layer 131, 231 Conductor Patterns 24 Protective layer 26 Adhesive layer

Claims

1. Dielectric layer and A conductive layer formed on the first surface of the dielectric layer, which includes a plurality of conductor patterns that reflect incident waves, A ground layer formed on the second surface of the dielectric layer opposite to the first surface, It has, The aforementioned conductor patterns are arranged in multiple locations along a predetermined direction, 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 along the predetermined direction is 0.5 mm or more and 1.5 mm or less. Reflector.

2. Among the plurality of conductor patterns, when an incident wave with the same phase is incident on a reference conductor pattern and the m-th conductor pattern in the direction of arrangement from the reference conductor pattern, the distance between the centers of 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 dm of the m-th conductor pattern. The distance between the centers of the reference conductor pattern and the mth conductor pattern formed on the first surface of the dielectric layer is defined as the actual distance dm' of the mth conductor pattern. Let |dm' - dm| be the absolute value of the difference between the actual distance dm' and the ideal distance dm. If m is an integer greater than or equal to 1, The standard deviation of the group consisting of |dm'-dm| for each conductor pattern other than the aforementioned reference conductor pattern is 0.5 mm or more and 1.5 mm or less. The reflector according to claim 1.

3. An adhesive layer provided on the side of the ground layer opposite to the dielectric layer, A reflector according to claim 1, having the following features.

4. A protective layer covering the conductive layer, The reflector according to claim 1, further comprising:

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

6. The thickness of the dielectric layer is 0.3 mm or more and 1.0 mm or less. The reflector according to claim 1.

7. The length of the conductor pattern is 2.0 mm or more and 5.0 mm or less. The reflector according to claim 1.

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

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

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