Reflector

Abstract

Provided is a reflector having a reflection characteristic of a wide frequency band. The reflector comprises: a dielectric layer; an electrically conductive layer provided on a first surface of the dielectric layer and including a periodic array of a plurality of conductor patterns; and a ground layer provided on a second surface opposite the first surface. The electrically conductive layer reflects an incident wave at an angle different from an incident angle thereof. The dielectric layer has a relative permittivity of less than or equal to 2.0.

Description

[Technical Field]

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

[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 frequency range, have the disadvantage that they tend to travel in a very directional direction, and the presence of obstacles between the transmitting and receiving antennas can prevent the radio waves from reaching their destination, 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 extend the communication range, metareflectors, which have metasurfaces that reflect incident waves in the 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). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5177708 Summary of the Invention [Problem to be solved by the invention]

[0005] Reflector arrays with metasurfaces utilize the resonance phenomenon, so the frequency band they can reflect in the desired direction is narrow. A narrow reflection band can cause the reflection peak to shift due to changes in the operating environment, making it difficult to obtain the desired reflection characteristics at the desired frequency. The 5G standard uses frequency bands above 24 GHz in many countries, and in Japan, the 28 GHz band covers 27 to 29.5 GHz. In Europe, the United States, China, and other countries, the frequency bands used each include bandwidths of approximately 1 GHz to 3.5 GHz. It is desirable for a metareflector to have reflection characteristics over a wide frequency band, covering 24 GHz to 30 GHz.

[0006] In one aspect, the present invention aims to provide a reflector having reflective characteristics over a wide frequency band. [Means for solving the problem]

[0007] In one embodiment, the reflector includes a dielectric layer, a conductive layer provided on a first surface of the dielectric layer and including a periodic arrangement of a plurality of conductor patterns, and a ground layer provided on a second surface opposite to the first surface, the conductive layer reflects the incident wave at an angle different from the angle of incidence; The dielectric layer has a relative dielectric constant of 2.0 or less. [Effects of the Invention]

[0008] The above configuration realizes a reflector having reflection characteristics over a wide frequency band. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram showing the basic configuration of a reflector according to the first embodiment. [Figure 2] FIG. 10 is a diagram illustrating an example of a method for designing a conductor pattern. [Figure 3] 3A to 3C are diagrams illustrating a design example of a reflector according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing the reflection characteristics of the reflector designed in FIG. 3. [Figure 5]FIG. 10 shows the reflection characteristics of a low dielectric constant reflector at different frequencies. [Figure 6] FIG. 10 shows the reflection characteristics of a high dielectric constant reflector at different frequencies. [Figure 7A] FIG. 10 is a diagram showing the reflection range of a low dielectric constant reflector versus frequency. [Figure 7B] FIG. 10 is a diagram showing the reflection range of a high dielectric constant reflector versus frequency. [Figure 8] FIG. 10 is a diagram showing the relationship between the thickness of a dielectric layer having different dielectric constants and the reflection bandwidth. [Figure 9] FIG. 10 is a diagram showing the relationship between the thickness of dielectric layers having different dielectric constants and the reflection intensity. [Figure 10] FIG. 1 is a diagram showing the configurations and characteristics of an example and a comparative example. [Figure 11] FIG. 10 is a schematic diagram of a reflector according to a second embodiment. [Figure 12] FIG. 10 is a diagram showing the results of a simulation in which the thickness and dielectric constant of the protective layer are changed. [Figure 13] 10A and 10B are diagrams illustrating an example of use of the reflector of the embodiment in comparison with use of a normal reflector. DETAILED DESCRIPTION OF THE INVENTION

[0010] FIG. 1 is a diagram showing 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 a periodic arrangement 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 a 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.

[0011] Conductive patterns 131 of different sizes are arranged at a predetermined pitch on the conductive layer 13. The size and pitch of the conductive patterns 131 are set according to the desired reflection characteristics. Each of the conductive patterns 131 has a size sufficiently smaller than the wavelength used, and selectively reflects radio waves in the target frequency band. The phase of the reflection is controlled by the conductive patterns 131, 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 pattern 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 relative 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 can be designed using the length / phase characteristic graph shown in Figure 2. The length / phase characteristic shown in Figure 2 can be obtained by measuring the radio wave reflection pattern while changing the length L of the conductor pattern with all design parameters other than the length L (mm) fixed, and then analyzing the results using 3D electromagnetic field simulation software. 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] The dielectric layer 11 has a relative permittivity of 2.0 or less. By setting the relative permittivity to 2.0 or less, it is possible to expand the frequency band of radio waves that are reflected in a predetermined direction. Details of expanding the frequency band of reflection will be described later with reference to FIG. 5 and subsequent figures. As a dielectric material having a relative permittivity of 2.0 or less, a fluorinated resin such as polytetrafluoroethylene, a combination of a fluorinated resin and an inorganic porous aggregate, other transparent porous resins, etc. can be used. As a resin that can be combined with an inorganic porous aggregate, polytetrafluoroethylene, polystyrene, etc. can be used. etc. is used.

[0016] The inorganic porous aggregate can be 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.

[0017] FIG. 3 shows a design example of the reflector 10 of the first embodiment. (A) of FIG. 3 shows the arrangement of the conductor patterns 131a to 131g that make up the conductive layer 13. (B) of FIG. 3 shows the size and phase of each conductor pattern. The conductor patterns 131a to 131g are cross patterns with equal vertical and horizontal lengths. The size of each conductor pattern 131 is indicated by the vertical or horizontal lengths L1 to L7. The pitch of the conductor patterns 131a to 131g, i.e., the center-to-center distance d, is set to half the wavelength used. Since the wavelength λ of the 28 GHz band is 10.8 mm, the pitch of the conductor patterns 131a to 131g is 5.4 mm.

[0018] The arrangement of the conductor patterns 131a to 131g aims for a reflection angle of 35°. In this case, the reflection angle is the reflection angle when radio waves are incident perpendicularly on the reflector 10, i.e., 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 35°, the phase difference is 103°. The size of the conductor patterns 131a to 131g, i.e., the lengths L1 to L7, is determined so that this phase difference is obtained.

[0019] 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 2 to 5 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. However, 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, as described below. The selected frequency bandwidth can vary depending on the thickness of the dielectric layer 11 of the reflector 10, so a wideband reflector with a bandwidth per unit thickness (1 mm) of the reflector 10 exceeding 6.5 GHz / mm can be realized.

[0020] FIG. 4 shows the reflection characteristics of the reflector 10 designed as shown in FIG. 3. The horizontal axis represents the angle, and the vertical axis represents the reflection intensity (dB). A main peak is observed at 35°, confirming that the reflector 10 is able to control the reflection direction of radio waves almost exactly as designed. Furthermore, the bandwidth of the 35° main lobe, i.e., the frequency range where the frequency drops by 3 dB from the peak, is 4 GHz or higher, and more preferably 6 GHz or higher. The reflection characteristics of the reflector 10 in oblique directions, which cover a wide frequency bandwidth, are apparent in the frequency band from 24 GHz to 60 GHz.

[0021] <Expansion of the reflection frequency band by reducing the dielectric constant> The reflection frequency band can be expanded by using a material with a low relative dielectric constant for the dielectric layer 11 of the reflector 10. The reflection frequency band is the ratio of the reflected wave in the target direction to the incident wave of the wavelength used. hmm The frequency range attenuated by 3 dB from the peak intensity of the lobe.

[0022] FIG. 5 shows 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, FIG. 6 shows 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.

[0023] In Figure 5, the 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 shown as the radar cross section (RCS), 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 3D electromagnetic field simulation software.

[0024] 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 band.

[0025] 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 to the target 35°, and depending on the environment in which the reflector is used, this can either result in a loss or be beneficial in that it delivers radio waves in two directions at once.

[0026] In the comparison example in Figure 6, the relative dielectric constant ε is changed to 3.62, while other conditions such as the conductor pattern are maintained the same as for the reflector in Figure 5. Materials with a relative dielectric constant of 3.62 include polyphenylene ether (PPE) and acrylic resin. With a relative 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, no reflection is obtained in the desired 35° direction.

[0027] The configuration in Figure 6 directly demonstrates the fact that the reflection characteristics of a metasurface that utilizes resonance deteriorate as the frequency changes. The frequency characteristics are significantly improved by using the low-dielectric-constant reflector of the embodiment shown in Figure 5. Figures 5 and 6 show 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.

[0028] Figure 7A shows the reflection range of the low-dielectric reflector, and Figure 7B shows the reflection range of the high-dielectric reflector. In Figures 7A and 7B, the horizontal axis represents the reflection direction, and the vertical axis represents the frequency. The reflector model used has the same conductor pattern as Figure 3(A) formed on the surface of a dielectric layer. The relative dielectric constant ε of the low-dielectric reflector in Figure 7A is set to 1.88, and the relative dielectric constant ε of the high-dielectric reflector in Figure 7B is set to 3.62.

[0029] In Figure 7A, 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 in particular, 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.

[0030] In Figure 7B, when the relative dielectric constant is 3.62, high reflection intensity (greater than -30 dB and less than -20 dB) is obtained from 21 GHz to 28.5 GHz at a 35° angle from the target. However, considering the frequency bands actually used in each country, the practical frequency band for the reflector in Figure 7B is in the range from 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 bandwidth of 6 GHz or more in the frequency band from 24 GHz to 60 GHz is desirable.

[0031] It can be seen from FIGS. 7A and 7B 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.

[0032] <Thickness of dielectric layer> The thickness of the dielectric layer 11 is examined with reference to Figures 8 and 9. Figure 8 shows the relationship between the thickness and bandwidth of dielectric layers with different dielectric constants. Figure 9 shows the relationship between the thickness and reflection intensity of dielectric layers with different dielectric constants. In Figure 8, 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 Figure 3(A). 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 bandwidth of the reflected wave 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 reflection main lobe.

[0033] For a given thickness of the dielectric layer 11, a material with a lower relative dielectric constant ε has a wider reflection bandwidth. Conversely, when achieving the same bandwidth, a reflector with a lower dielectric constant can be made thinner. In the example of Figure 8, when the thickness of the dielectric layer 11 is 0.75 mm, a reflector with an ε of 1.88 achieves a bandwidth of over 6.5 GHz, but a reflector with an ε of 3.62 can only cover a bandwidth of 4.5 GHz.

[0034] As mentioned above, considering the frequency bands used in each country and the peak shift, it is desirable that the reflection frequency bandwidth exceeds 6 GHz in the frequency band between 24 GHz and 30 GHz. Interpolating the data points in Figure 8, the thickness of the dielectric layer 11 with ε of 3.62 is 1.2 m. m Increasing the reflector thickness to around 1000m may enable a 6GHz bandwidth, but this would result in a thicker reflector, reducing flexibility and limiting the range of applications.

[0035] In contrast, when ε is 1.88, a bandwidth of 6.5 GHz is achieved with a dielectric layer 11 thickness of 0.75 mm, resulting in a flexible sheet-like reflector. A sheet-like reflector is easy to handle and can be attached to a desired location like wallpaper. The fact that a wide bandwidth can be achieved with a thin and flexible dielectric layer 11 is a major advantage.

[0036] In Figure 9, 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.

[0037] From the results of FIG. 9, the reflector with a low dielectric constant according to the embodiment is advantageous from the viewpoint of thinning and lightening the device.

[0038] Figure 10 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 base material that constitutes the dielectric layer 11. The values ​​of these parameters are varied. The reflector characteristics are the frequency band of the reflected wave and the bandwidth per unit thickness. Throughout the example and comparative example, the conductor pattern 131 is the conductor patterns 131a to 131g in Figure 3(A), and the type and parameters of the dielectric layer 11 are varied.

[0039] Simulations were performed under the following conditions, and the frequency bands of the example and comparative example were determined from the far radiation field, intensity, and angle of the reflection spectrum for the incident wave.

[0040] Wavelength of incident wave: 10.7 mm (frequency 28 GHz) Incident wave frequency change range: 20GHz to 35GHz Incident angle of the incident wave relative to the normal direction of the reflector: 0 degrees First desired reflection angle θ of the reflection spectrum relative to the normal direction of the reflector: 35 degrees Number of conductor patterns: 7 (arranged in series) Conductor pattern pitch: 5.4 mm (0.5 λ) [Example]

[0041] In Example 1, a fluorine porous substrate is used as the base material for 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 obtained in Example 1 is 6.6 GHz, and the band per unit thickness (1 mm) is 8.8 GHz / mm. [Example]

[0042] In Example 2, a porous fluorine substrate is used as the base material of 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. The aggregation density of the porous inorganic fine particles used in the porous fluorine substrate is degree By changing the above, the dielectric layer 11 is designed to have different porosities and relative dielectric constants. The reflection frequency band obtained in Example 2 is 7.1 GHz, and the band per unit thickness (1 mm) is 9.5 GHz / mm. [Example]

[0043] In Example 3, a porous fluorine substrate is used as the base material of 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. The aggregation density of the porous inorganic fine particles used in the porous fluorine substrate is degree By changing the thickness of the dielectric layer 11, the dielectric layer 11 is designed to have different porosity and relative dielectric constant. In addition, the dielectric layer 11 is made thinner than in Examples 1 and 2. The reflection frequency band obtained in Example 3 is 4.55 GHz, and the band per unit thickness (1 mm) is 9.1 GHz / mm. [Example]

[0044] In Example 4, 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 1 and 2. The reflection frequency band obtained in Example 4 is 6.5 GHz, and the band per unit thickness (1 mm) is 6.5 GHz / mm. [Example]

[0045] In Example 5, a porous fluorine substrate is used as the base material of the dielectric layer 11. The thickness of this dielectric substrate is 0.75 mm, the porosity is 22.5%, and the relative dielectric constant is 2.00. The aggregation density of the porous inorganic fine particles used in the porous fluorine substrate is degree The reflection frequency band obtained in Example 5 is 5.5 GHz, and the band per unit thickness (1 mm) is 7.3 GHz / mm. [Example]

[0046] In Example 6, a fluorine porous 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 5. The reflection frequency band obtained in Example 6 is 4.1 GHz, and the band per unit thickness (1 mm) is 13.7 GHz.

[0047] <Comparative Example 1>

[0048] In Comparative Example 1, PPE is used as the base material of the dielectric layer 11. The thickness of the PPE base material is 0.75 mm, the porosity is 0.0%, and the relative dielectric constant is 3.62. The reflection frequency band obtained in Comparative Example 1 is 4.5 GHz, and the band per unit thickness (1 mm) is 6.0 GHz / mm. Compared to Examples 1 to 5, although a base material of the same thickness is used, the reflection frequency band is narrower due to the higher relative dielectric constant.

[0049] <Comparative Example 2>

[0050] In Comparative Example 2, 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 higher than that of Comparative Example 1. The reflection frequency band obtained in Comparative Example 2 is 3.7 GHz, and the band per unit thickness (1 mm) is 4.9 GHz / mm.

[0051] <Comparative Example 3>

[0052] In Comparative Example 3, PPE is used as the base material for the dielectric layer 11. The thickness of this dielectric base material is 0.50 mm, the porosity is 0.0%, and the relative dielectric constant is 3.62. The reflection frequency band obtained in Comparative Example 3 is 3.0 GHz, and the band per unit thickness (1 mm) is 6.0 GHz. Although the same PPE base material as in Comparative Example 1 is used, the reflection frequency band is further narrowed by reducing the thickness of the base material.

[0053] From the results in Figure 10, it can be seen that when the dielectric constant of the dielectric layer 11 is 2.0 or less, a wideband reflection characteristic exceeding 6.5 GHz per unit thickness, preferably exceeding 7.0 GHz, and more preferably exceeding 8.0 GHz, can be obtained. When the thickness of the dielectric layer is thin and the dielectric constant is 1.88 or less, a frequency band exceeding 8.8 GHz per unit thickness is realized. In Examples 5 and 6, the inorganic porous sexBy using a fluorinated resin with a low relative dielectric constant for the aggregate, a relative dielectric constant 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 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 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, this is advantageous for reducing the weight when designing a large reflector with a side length of about 1 m, and is excellent in terms of ease of construction and construction costs. Note that thicknesses of 0.3 mm, 1.0 mm, etc. are intended to include allowable manufacturing errors.

[0054] 11 is a schematic diagram of a reflector 20 according to the second embodiment. The main part of the reflector 20 is the same as the reflector 10 according to the first embodiment. and The dielectric layer 21 has the same dielectric constant as the conductor pattern 23 and a dielectric constant of 2.0 or less. A conductive layer 23 including a predetermined conductive 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 conductive pattern 231 is designed so that the reflection direction of the main lobe of an incident wave in the 28 GHz band is tilted at a predetermined angle from the normal direction, and an example of this pattern is shown in Fig. 3(A).

[0055] A protective layer 24 is provided to cover 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 position, 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 for use. The board to which the reflector 20 is attached may be hung at a desired position for use.

[0056] The protective layer 24 protects the conductor pattern 231 of the reflector 20 from deterioration or damage due to external factors, and provides 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, but the formation of the protective layer 24 is preferable from the viewpoint of weather resistance, especially when used outdoors. Even indoors, if the installation environment is prone to condensation, etc., the formation of the protective layer 24 is also preferable. protection It is preferable to form the protective layer 24. 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 way, it is possible to obtain a reflector 20 that has both high durability and high transparency to incident waves of 24 GHz to 30 GHz.

[0057] Using a model of the configuration shown in Figure 11 excluding the adhesive layer 26, a simulation was performed under the following conditions, and the reflection angle deviation (%) and reflection intensity loss (%) of the example and comparative example were calculated 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) Incident wave frequency range: 20GHz-35GHz Incident angle of the incident wave relative to the normal direction of the reflector: 0 degrees First desired reflection angle θ of the reflection spectrum relative to the normal direction of the reflector: -43 degrees Number of conductor patterns: 5 (arranged in series) Conductor pattern pitch: 5.4 mm (0.5λ) 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 Five cross patterns of different sizes are used as the shape of the conductor pattern, and the reflection angle and reflection intensity are calculated by changing the thickness and relative dielectric constant of the protective layer 24 covering the conductor pattern.

[0058] FIG. 12 shows the results of the simulation. "Ref" in the leftmost column of FIG. 12 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 the reflection intensity of 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 7 to 10, and Comparative Examples 4 to 11, and the reflection angle deviation (unit: %) and reflection intensity loss (unit: %) were calculated. The reflection angle deviation and reflection intensity loss were evaluated as follows. Reflection angle deviation of 10% or less: A Reflection angle deviation exceeds 10%: B Reflection intensity loss of 5% or less: S Reflection intensity loss is 10% or less: A Reflection intensity loss exceeds 10%: B ·comprehensive evaluation Pass: Both the reflection angle deviation and reflection intensity loss were rated "A" Fail: Either the reflection angle deviation or reflection intensity loss rating is "B"

[0059] As shown in FIG. 12, Examples 7 to 10 passed the test. Furthermore, Examples 7 to 9 had small reflection intensity losses, and more preferable results were obtained. As shown in FIG. 12, when the relative dielectric constant Dk is high, the reflection angle deviation and reflection intensity loss are large, and it is desirable that the relative dielectric constant Dk is 2.0 or less. When the relative dielectric constant is 1.5 or less, the reflection intensity loss is 5% or less, which is more desirable (evaluated as "S" in FIG. 12). When the thickness of the protective layer 24 is large, the reflection angle deviation and reflection intensity loss are large, and it is desirable that the thickness of the protective layer 24 be 0.1 mm or more and 1.0 mm or less.

[0060] Figure 13 shows an example of use of the reflector 20 of the embodiment in comparison with use of a normal reflector. Figure 13(A) shows a usage mode of the reflector 10 or 20 of the embodiment. The reflector 10 or 20 of the embodiment is thin and flexible, so it can be installed along an L-shaped passage, street, hallway, etc.

[0061] The reflector of this 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 12, 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.

[0062] As shown in Figure 13(B), 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 installed in a corner, as shown in Figure 13(B), 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.

[0063] 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 before use and the reflector may be attached to the desired location. 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.

[0064] The above disclosure may take the following forms. (Section 1) a dielectric layer; a conductive layer provided on a first surface of the dielectric layer and including a periodic arrangement of a plurality of conductor patterns; a ground layer provided on a second surface opposite to the first surface; and the conductive layer reflects the incident wave at an angle different in magnitude from the angle of incidence; The dielectric constant of the dielectric layer is 2.0 or less. Reflector. (Section 2) the conductive layer forms a reflective surface of the reflector; An adhesive layer is provided on the side opposite to the reflective surface. 、 Item 1. The reflector according to item 1. (Section 3) an adhesive layer provided on a surface of the ground layer opposite to the dielectric layer; Item 3. The reflector according to item 1 or 2, (Section 4) a protective layer covering the conductive layer; 4. The reflector according to any one of items 1 to 3, 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 dielectric constant 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. m Below is the Item 6. The reflector according to any one of items 1 to 5. (Section 7) The size of the conductor pattern is 2 mm or more and 5 mm or less. 、 Item 7. The reflector according to any one of items 1 to 6. (Section 8) The reflector has a reflection frequency bandwidth per unit thickness of more than 6.5 GHz / mm; Item 8. The reflector according to any one of items 1 to 7. (Section 9) 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. Item 9. The reflector according to any one of items 1 to 8.

[0065] This application claims priority based on Japanese Patent Application No. 2022-006361, filed on January 19, 2022, and includes the entire contents of this Japanese patent application. [Explanation of symbols]

[0066] 10, 20 reflector 11, 21 Dielectric layer 111, 211 1st surface 112, 212 2nd surface 12, 22 Ground layer 13, 23 Conductive layer 131, 231 Conductor pattern 24 Protective layer 26 Adhesive layer

Claims

1. a dielectric layer; a conductive layer provided on a first surface of the dielectric layer and including a periodic arrangement of a plurality of conductor patterns; a ground layer provided on a second surface opposite to the first surface; and the conductive layer reflects the incident wave at an angle different in magnitude from the angle of incidence; the dielectric layer has a relative dielectric constant of 2.0 or less, 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; Reflector.

2. the conductive layer forms a reflective surface of the reflector; An adhesive layer is provided on the side opposite to the reflective surface. The reflector according to claim 1 .

3. an adhesive layer provided on the surface of the ground layer opposite to the dielectric layer; 2. The reflector of claim 1, wherein

4. a protective layer covering the conductive layer; The reflector of claim 1 further comprising:

5. the frequency of the incident wave is 20 GHz to 35 GHz, the thickness of the protective layer is 0.1 mm or more and 1.0 mm or less, and the relative dielectric constant is 2.0 or less; 5. The reflector according to claim 4.

6. 5. The reflector according to claim 1, wherein the frequency of the incident wave is between 20 GHz and 35 GHz.

7. The thickness of the dielectric layer is 0.3 mm or more and 1.0 mm or less.

7. The reflector according to claim 6.

8. The size of the conductor pattern is 2 mm or more and 5 mm or less.

7. The reflector according to claim 6.

9. The reflector has a reflection frequency bandwidth per unit thickness of more than 6.5 GHz / mm.

7. The reflector according to claim 6.

Images