reflector

Abstract

The present invention aims to provide a reflector having reflection characteristics over a wide frequency band. [Solution] A reflector having reflection characteristics over a wide frequency band is provided. The reflector comprises 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, wherein the conductive layer reflects the incident wave at an angle different from the angle of incidence, the dielectric layer is formed of a composite of a fluorine resin and an inorganic porous aggregate, and the porosity of the dielectric layer is 20% or more.

Description

Technical Field

[0005] , , ,

[0001] The present invention relates to a reflector, and 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 due to the presence of obstacles between the transmitting antenna and the receiving antenna, there is a drawback that 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, metamirrors having a metasurface for reflecting 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 a 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] <m

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Because reflector arrays with metasurfaces utilize resonance phenomena, they have a narrow frequency band in which they can reflect in the desired direction. A narrow reflection band can cause the reflection peak to shift due to changes in the operating environment, potentially preventing the desired reflection characteristics from being obtained at the target frequency. In 5G standards, frequency bands of 24 GHz and above are used 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 metareflectors to have reflection characteristics across a wide frequency band covering 24 GHz to 30 GHz.

[0006] In one aspect, the present invention aims to provide a reflector having reflection 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 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. [Effects of the Invention]

[0008] The above configuration realizes a reflector with reflection characteristics across a wide frequency band. [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 3] This figure shows an example of a reflector design according to the first embodiment. [Figure 4]This figure shows the reflective properties of the reflector designed in Figure 3. [Figure 5] This figure shows the reflection characteristics of a low dielectric constant reflector at different frequencies. [Figure 6] This figure shows the reflection characteristics of a high dielectric constant reflector at different frequencies. [Figure 7A] This figure shows the reflection range of a low dielectric constant reflector with respect to frequency. [Figure 7B] This figure shows the reflection range of a high dielectric constant reflector with respect to frequency. [Figure 8] This figure shows the relationship between the thickness of dielectric layers with different dielectric constants and the reflection bandwidth. [Figure 9] This figure shows the relationship between the thickness of dielectric layers with different dielectric constants and their reflectivity. [Figure 10] This figure shows the configuration and characteristics of the examples and comparative examples. [Figure 11] This is a schematic diagram of the reflector according to the second embodiment. [Figure 12] This figure shows the simulation results when the thickness and dielectric constant of the protective layer are changed. [Figure 13] This figure shows an example of using the reflector according to the embodiment, compared to the use of a normal reflector. [Modes for carrying out the invention]

[0010] Figure 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 a periodic arrangement of a plurality of conductor patterns 131 and functions as a reflective surface of the reflector 10. This reflective surface is a metasurface that reflects the incident wave at an angle (absolute value) different from the angle of incidence. The ground layer 12 creates 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] In the conductive layer 13, conductor patterns 131 of different sizes are arranged at a predetermined pitch. 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 used, 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). δ1 - δ2 = (2π / λ)d·sinθ + 2nπ (1) Here, n is an integer.

[0013] In order to reflect radio waves in a desired direction by the reflector 10, δ1, δ2, and d may be designed so as to obtain the required reflection angle θ. The reflection angle θ is set to a desired angle excluding 0° and 90° between the normal direction (0°) and the horizontal direction (90°) of the reflection surface of the reflector 10. The values of δ1 and δ2 representing 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, the thickness and relative permittivity of the reflector 10. For example, when designing the length L of the conductor pattern 131 that can obtain a desired phase difference, a graph of length / phase characteristics shown in FIG. 2 may be prepared to design the conductor pattern 131. The length / phase characteristics in FIG. 2 are obtained by measuring the radio wave reflection pattern while changing the length L of the conductor pattern with other design parameters except the length L (mm) fixed, and analyzing using three-dimensional electromagnetic field simulation software. The length L is the length of the conductor pattern 131 corresponding to the vibration direction of the radio wave. As shown in (A) of FIG. 3, when the conductor patterns 131a to 131g are cross patterns, the vertical and horizontal lengths are equal. As a design parameter other than the length, for example, the relative permittivity ε of the dielectric layer 11 is fixed at ε = 1.88.

[0014] The dielectric layer 11 is formed of a combination of a fluororesin and an inorganic porous aggregate, and the porosity of the dielectric layer is 20% or more. By the dielectric layer 11 satisfying the above conditions, the frequency band of radio waves reflected in a predetermined direction can be expanded. Details of the expansion of the reflection frequency band will be described later with reference to FIG. 5 and subsequent figures. As the fluororesin material constituting the dielectric layer 11, polytetrafluoroethylene or the like is used.

[0015] The inorganic porous aggregate is produced, for example, by the method described in JP-A-2017-171898. By adjusting the material, aggregation density, etc. of the porous inorganic fine particles, the porosity of the combination of the fluororesin and the inorganic porous aggregate can be controlled to 20% or more. If it is a combination of a fluororesin and an inorganic porous aggregate, by adjusting the porosity to 20% or more, a dielectric constant of 2.0 or less can be realized.

[0016] 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 constituting 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 length L1 to L7. The pitch of the conductor patterns 131a to 131g, that is, the center-to-center distance d, is set to 1 / 2 of the wavelength used. Since the wavelength λ in the 28 GHz band is 10.8 mm, the pitch of the conductor patterns 131a to 131g is 5.4 mm.

[0017] The arrangement of the conductor patterns 131a to 131g aims at a reflection angle of 35°. The reflection angle in this case is the reflection angle when radio waves are incident perpendicularly to the reflector 10, that is, the reflection angle with respect to the normal. Based on the above formula (1), when θ is 35°, the phase difference "δ1 - δ2", which is the phase difference at this time, is obtained, and the phase difference is 103°. The sizes of the conductor patterns 131a to 131g, that is, the lengths of L1 to L7, are determined so as to obtain this phase difference.

[0018] 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. 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 designed appropriately 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 4 GHz or more, more preferably 6 GHz or more, as described later. The selected frequency bandwidth can change depending on the thickness of the dielectric layer 11 of the reflector 10, so a wideband reflector with a bandwidth of more than 6.5 GHz / mm per unit thickness (1 mm) of the reflector 10 can be realized.

[0019] Figure 4 shows the reflection characteristics of reflector 10 designed in Figure 3. The horizontal axis represents angle, and the vertical axis represents reflection intensity (dB). A main peak is observed in the 35° direction, confirming that reflector 10 is able to control the direction of radio wave reflection almost as designed. Furthermore, the bandwidth of the 35° main lobe, i.e., the frequency range where the intensity drops by 3dB from the peak, is 4GHz or higher, more preferably 6GHz or higher. The oblique reflection characteristics of reflector 10, which cover a wide frequency bandwidth, manifest in the frequency band of 24GHz to 60GHz.

[0020] <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 an incident wave of the operating wavelength.

[0021] Figure 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, 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, Figure 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 permittivity greater than 2.0.

[0022] 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), 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.

[0023] When ε = 1.88, a peak in the reflection spectrum appears at a 35° direction 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 a bandwidth of at least 5 GHz.

[0024] 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.

[0025] In the comparative example in Figure 6, the relative permittivity ε is changed to 3.62, while other conditions such as the conductor pattern are kept the same as in the reflector in Figure 5. 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.

[0026] The configuration in Figure 6 directly illustrates 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 Figure 5, the frequency characteristics can be greatly improved. Based on Figures 5 and 6, 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 some extent.

[0027] Figure 7A shows the reflection range of a low-dielectric-constant reflector, and Figure 7B shows the reflection range of a high-dielectric-constant reflector. In Figures 7A and 7B, the horizontal axis represents the reflection direction, and the vertical axis represents frequency. The reflector model used has the same conductor pattern as in Figure 3(A) formed on the surface of the dielectric layer. The relative permittivity ε of the low-dielectric-constant reflector in Figure 7A is set to 1.88, and the relative permittivity ε of the high-dielectric-constant reflector in Figure 7B is set to 3.62.

[0028] Figure 7A 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.

[0029] In Figure 7B, 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 a 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 7B 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 bandwidth of 6GHz or more in the frequency band between 24GHz and 60GHz is desirable.

[0030] Figures 7A and 7B show that a lower dielectric constant of the reflector's dielectric layer 11 results in a wider reflection range (angle range) with respect to frequency, and a wider practical reflection frequency band.

[0031] <Thickness of the dielectric layer> Refer to Figures 8 and 9 to examine the thickness of the dielectric layer 11. 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 reflectivity of dielectric layers with different dielectric constants. In Figure 8, 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 3 (A). 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 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 main lobe of the reflection.

[0032] When the thickness of the dielectric layer 11 is the same, a lower relative permittivity ε results in a wider reflection bandwidth. Conversely, to achieve the same bandwidth, a material with a lower dielectric constant allows for the formation of a thinner reflector. In the example in Figure 8, when the thickness of the dielectric layer 11 is 0.75 mm, a reflector with ε = 1.88 achieves a bandwidth exceeding 6.5 GHz, but a reflector with ε = 3.62 can only cover a bandwidth of 4.5 GHz.

[0033] As mentioned above, considering the frequency bands and peak shifts used in various countries, 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, it may be possible to achieve a 6 GHz bandwidth by increasing the thickness of the dielectric layer 11 with ε = 3.62 to about 1.2 m. However, in that case, the reflector becomes thicker, its flexibility decreases, and its range of application is limited.

[0034] In contrast, when ε is 1.88, a dielectric layer 11 with a thickness of 0.75 mm achieves a bandwidth 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.

[0035] In Figure 9, 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.

[0036] As shown in Figure 9, the high porosity reflector of the embodiment is also advantageous from the viewpoint of thinning and lightening the device.

[0037] Figure 10 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 frequency band of the reflected wave and the bandwidth per unit thickness. Throughout the examples and comparative examples, the conductor pattern 131 is the conductor pattern 131a to 131g of Figure 3(A), with the type and parameters of the dielectric layer 11 being varied.

[0038] Simulations were performed under the following conditions, and the frequency bandwidths of the examples and comparative examples were determined from the far-field radiation, intensity, and angle of the reflection spectrum for the incident wave. 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: 7 (arranged in series) Conductor pattern pitch: 5.4 mm (0.5 λ) [Examples]

[0039] <Example 1> In Example 1, 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 frequency bandwidth of the reflection obtained in Example 1 is 6.6 GHz, and the bandwidth per unit thickness (1 mm) is 8.8 GHz / mm.

[0040] <Example 2> In Example 2, 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 bandwidth of the reflection obtained in Example 2 is 7.1 GHz, and the bandwidth per unit thickness (1 mm) is 9.5 GHz / mm.

[0041] <Example 3> In Example 3, 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 1 and 2. The frequency bandwidth of the reflection obtained in Example 3 is 4.55 GHz, and the bandwidth per unit thickness (1 mm) is 9.1 GHz / mm.

[0042] <Example 4> In Example 4, 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 greater than in Examples 1 and 2. The frequency bandwidth of the reflection obtained in Example 4 is 6.5 GHz, and the bandwidth per unit thickness (1 mm) is 6.5 GHz / mm.

[0043] <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 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 frequency bandwidth of the reflection obtained in Example 5 is 5.5 GHz, and the bandwidth per unit thickness (1 mm) is 7.3 GHz / mm.

[0044] <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 0.3 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 5. The frequency bandwidth of the reflection obtained in Example 6 is 4.1 GHz, and the bandwidth per unit thickness (1 mm) is 13.7 GHz.

[0045] <Comparative Example 1> In Comparative Example 1, 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 reflection frequency bandwidth obtained in Comparative Example 1 is 4.5 GHz, and the bandwidth per unit thickness (1 mm) is 6.0 GHz / mm. Compared with Examples 1-2 and 5, although the same substrate thickness is used, the reflection frequency bandwidth is narrower due to the higher relative permittivity.

[0046] <Comparative Example 2> 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 permittivity is 5.00. The relative permittivity is even higher than that of Comparative Example 1. The frequency bandwidth of the reflection obtained in Comparative Example 2 is 3.7 GHz, and the bandwidth per unit thickness (1 mm) is 4.9 GHz / mm.

[0047] <Comparative Example 3> In Comparative Example 3, 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 reflection frequency bandwidth obtained in Comparative Example 3 is 3.0 GHz, and the bandwidth per unit thickness (1 mm) is 6.0 GHz. Although the same PPE substrate as in Comparative Example 1 is used, the reflection frequency bandwidth is further narrowed by reducing the thickness of the substrate.

[0048] The results in Figure 10 show that when the dielectric layer 11 is formed from a composite of fluorinated resin and an inorganic porous aggregate, and the porosity is 20% or more, the relative permittivity becomes 2.0 or less, and a broadband reflection characteristic of over 6.5 GHz per unit thickness, 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 can be achieved. In Examples 5 and 6, by using a material with a low relative permittivity for the fluorinated 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. Increasing the porosity of the dielectric layer 11 further reduces the relative permittivity. The porosity of the dielectric layer 11 is preferably 30% or more, and more preferably 50% or more. 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 about 1 m, and is superior in terms of ease of installation and installation cost. Note that when the thickness is 0.3 mm, 1.0 mm, etc., it includes an acceptable manufacturing tolerance.

[0049] Figure 11 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 uses a dielectric layer 21 formed of a composite of fluorinated resin and inorganic porous aggregate with a porosity of 33.0%. 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 3(A).

[0050] 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.

[0051] 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, if the installation environment is prone to condensation, the formation of the protective layer 24 is also preferable. 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.

[0052] Using the model of the configuration shown in Figure 11, excluding the adhesive layer 26, simulations were performed under the following conditions to determine the reflection angle shift (%) and reflection intensity loss (%) for the example and comparative example from the far radiation field, intensity, and angle of the reflection spectrum for the incident wave. • Wavelength of incident wave: 10.7 mm (frequency 28 GHz) • Frequency 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: 5.4mm (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 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.

[0053] Figure 12 shows the simulation results. The leftmost column of Figure 12, "Ref," shows the reference configuration without the protective layer 24. In the reference 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 reference configuration is (dB). "Reflection angle shift" shows the percentage change from the reflection angle of the reference configuration, and "Reflection intensity loss" shows the percentage decrease from the reflection intensity of the reference configuration. The peak angle and peak intensity of the main lobe for the incident wave were compared between the reference configuration (Ref), Examples 7 to 10, and Comparative Examples 4 to 11, 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 exceeding 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".

[0054] As shown in Figure 12, Examples 7 to 10 passed the test. Furthermore, Examples 7 to 9 showed smaller reflectance loss and yielded more favorable results. From Figure 12, 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 is 1.5 or less, the reflectance loss is 5% or less, which is more favorable (rated "S" in Figure 12). 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.

[0055] Figure 13 shows an example of using the reflector 20 of the embodiment, compared to the use of a normal reflector. Figure 13(A) shows how the reflector 10 or 20 of the embodiment is used. The thin and flexible reflector 10 or 20 of the embodiment can be installed along L-shaped passages, streets, corridors, etc.

[0056] 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 12, 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 send radio waves to smartphones, electronic devices, lighting equipment, etc. located in area A.

[0057] As shown in Figure 13(B), a conventional reflector RFL with a specular reflective surface reflects perpendicularly incident radio waves in the direction of incidence. Therefore, the reflector RFL must be installed at an oblique angle to the incident radio waves. When placed in a corner, as shown in Figure 13(B), 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.

[0058] As described above, the reflector of the embodiment is formed from a composite of fluorinated resin and an inorganic porous aggregate, and by using a dielectric layer with a porosity of 20% or more, the frequency band of reflection can be extended and resistance to the environment can be improved. Furthermore, the thickness of the reflector can be reduced while maintaining the same reflection frequency characteristics, thereby broadening the range of application. In addition, since a porosity of 20% or more in the dielectric layer can suppress the weight increase when the sheet size of the reflector is increased, the present invention is particularly suitable for large-format reflectors. 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.

[0059] The above disclosure may take the following forms: (Section 1) Dielectric layer and A conductive layer is provided on the first surface of the dielectric layer and includes a periodic arrangement of a plurality of conductor patterns, A ground layer provided on the second surface opposite to the first surface, It has, The conductive layer reflects the incident wave at an angle different from the angle of incidence. 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. Reflector. (Section 2) The conductive layer forms the reflective surface of the reflector. An adhesive layer is provided on the side opposite to the reflective surface. 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 according to item 1 or 2 having the following characteristics. (Section 4) A protective layer covering the conductive layer, A reflector according to any one of items 1 to 3, further having the following: (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. Reflector as described in item 4 (Section 6) The thickness of the dielectric layer is 0.3 mm or more and 1.0 mm or less. A reflector as described in any of items 1 to 5. (Section 7) The size of the aforementioned conductor pattern is between 2 mm and 5 mm. A reflector as described in any of items 1 through 6. (Section 8) The bandwidth of the reflection frequency per unit thickness of the reflector exceeds 6.5 GHz / mm. A reflector as described in any of items 1 through 7. (Section 9) The relative permittivity of the dielectric layer is 2.0 or less. A reflector as described in any of items 1 through 8. [Explanation of symbols]

[0060] 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 is provided on the first surface of the dielectric layer and includes a periodic arrangement of a plurality of conductor patterns, A ground layer provided on the second surface opposite to the first surface, It has, The conductive layer reflects the incident wave at an angle different from the angle of incidence. 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. Reflector.

2. The conductive layer forms the 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 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 m or less. The reflector according to claim 1.

7. The size of the aforementioned conductor pattern is between 2 mm and 5 mm. The reflector according to claim 1.

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

9. The relative permittivity of the dielectric layer is 2.0 or less. A reflector according to any one of claims 1 to 8.

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