Reflective material with protective plate

Abstract

Provided is a reflective member with a protective plate, wherein the reflective member can satisfactorily reflect or re-radiate radio waves incident over a wide range of angles from narrow angles to wide angles. The reflective member with a protective plate has: a reflective member that reflects or re-radiates incident radio waves; and the protective plate installed on the radio-wave-incident side of the reflective member, wherein, when the wavelength specified for the operation center frequency f0 [Hz] is λ0 [mm], the thickness of the protective plate is d [mm], the relative permittivity of the protective plate at the operation center frequency f0 [Hz] is εr, and a constant is α, d=α×λ0 / (1.75×εr 0.555) is satisfied, where 1≦α≦1.25.

Description

[Technical Field]

[0001] The present invention relates to a reflective member with a protective plate. [Background technology]

[0002] Reflective members such as reflectors that reflect or re-radiate incident radio waves are known.

[0003] As such a reflector, for example, Patent Document 1 discloses a configuration including a reflector having a reflecting plate with a reflective surface that reflects incident radio waves, a support body that is a structure having a plurality of legs standing in an approximately vertical direction and supports the reflector, and an adjustment mechanism that is connected to each of the plurality of legs on the support body and has a vertical adjustment mechanism that can move the connection position with the leg up and down.

[0004] Furthermore, Patent Document 2 discloses a reflectarray that has a plurality of elements that are aligned in a first axial direction and a second axial direction that is perpendicular to the first axial direction and that reflect an incident wave, and that reflects the incident wave in a desired direction that is not within a plane that includes the incident wave and the specularly reflected wave.

[0005] Furthermore, Patent Document 3 discloses a configuration in which a reflector of a predetermined radius is installed in a location that is visible from both a first base station antenna and a second base station antenna, thereby reflecting microwave radio waves to perform microwave wireless communication between the first base station and the second base station. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-10304 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-30138 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-32165 Summary of the Invention [Problem to be solved by the invention]

[0007] Reflectors are generally adjusted to face almost directly toward the radio waves from base stations, and traditionally they have often been installed in locations with good visibility from the base station and out of reach of people, such as on top of mountains. However, with communications such as 5G (fifth generation mobile communications systems), it is expected that reflectors will also be installed inside cities, taking advantage of the low diffraction of high-frequency radio waves, i.e., their high directivity and short propagation distance.

[0008] In such a situation, to reduce blind zones, the reflector is required to effectively reflect or re-radiate radio waves incident on the reflector over a wide range of angles, from narrow to wide. Here, re-radiation means that the reflector resonates with the incident radio waves and radiates radio waves with a shifted phase. Furthermore, a narrow angle means that the angle with respect to the normal to the reflector is small. A wide angle means that the angle with respect to the normal to the reflector is large.

[0009] On the other hand, when a reflector is installed near people or their living spaces, a protective plate is required to cover the reflector on the radio wave incident side to protect the reflector from dirt and other issues caused by people touching it.

[0010] It was found that when such a protective plate is installed, conventional technology results in a large transmission loss at the protective plate for radio waves incident at a wide angle, significantly reducing the efficiency of reflection or re-radiation of a reflective member with a protective plate, such as a reflector.

[0011] The present invention has been made in consideration of the above points, and aims to provide a reflective member with a protective plate that can effectively reflect or re-radiate radio waves incident at a wide angle range from narrow angles to wide angles. [Means for solving the problem]

[0012] This protective plate-attached reflective member has a reflective member that reflects or re-radiates incident radio waves, and a protective plate installed on the radio wave incident side of the reflective member, and has a wavelength defined for an operating center frequency f0 [Hz] of λ0 [mm], a thickness of the protective plate of d [mm], and a relative dielectric constant of the protective plate at the operating center frequency f0 [Hz] of ε r , where α is the constant, d=α×λ0 / (1.75×ε r 0.555 ) where 1≦α≦1.25. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a reflective member with a protection plate that can effectively reflect or re-radiate radio waves incident at a wide angle range from a narrow angle to a wide angle. [Brief explanation of the drawings]

[0014] [Figure 1] 1A and 1B are diagrams illustrating a reflector with a protective plate according to a first embodiment. [Figure 2] FIG. 10 is a diagram illustrating the relationship between f / f0, the constant α, and the angle of incidence. [Figure 3] 3A and 3B are diagrams showing the relationship between the angle of incidence and the normalized transmission loss in Example 1, where FIG. 3A is a diagram for the TE wave and FIG. 3B is a diagram for the TM wave. [Figure 4] 4A and 4B are diagrams showing the relationship between the angle of incidence and the normalized transmission loss in Example 2, where FIG. 4A is a diagram for the TE wave and FIG. 4B is a diagram for the TM wave. [Figure 5] 5A and 5B are diagrams showing the relationship between the angle of incidence and the normalized transmission loss in Example 3, where FIG. 5A is a diagram for the TE wave and FIG. 5B is a diagram for the TM wave. [Figure 6] 6A and 6B are diagrams showing the relationship between the angle of incidence and the normalized transmission loss in Example 4, where FIG. 6A is a diagram for the TE wave and FIG. 6B is a diagram for the TM wave. [Figure 7] 10A and 10B are diagrams illustrating the configuration of a reflector with a protective plate according to a second embodiment. [Figure 8] 10 is a diagram illustrating the relative dielectric constant and layer thickness of a protection plate according to a second embodiment. FIG. [Figure 9]FIG. 10 is a diagram showing conditions for f / f0 and a constant α in an example of the second embodiment. [Figure 10] 10A and 10B are diagrams showing the relationship between the angle of incidence and the normalized transmission loss in Example 5, where FIG. 10A is a diagram for the TE wave and FIG. 10B is a diagram for the TM wave. [Figure 11] 11A and 11B are diagrams showing the relationship between the incident angle and the normalized transmission loss in Example 6, where FIG. 11A is a diagram for the TE wave and FIG. 11B is a diagram for the TM wave. [Figure 12] 12A and 12B are diagrams showing the relationship between the angle of incidence and the normalized transmission loss in Example 7, where FIG. 12A is a diagram for the TE wave and FIG. 12B is a diagram for the TM wave. [Figure 13] 13A and 13B are diagrams showing the relationship between the angle of incidence and the normalized transmission loss in Example 8, where FIG. 13A is a diagram for the TE wave and FIG. 13B is a diagram for the TM wave. [Figure 14] 14A and 14B are diagrams showing the relationship between the angle of incidence and the normalized transmission loss in Example 9, where FIG. 14A is a diagram for the TE wave and FIG. 14B is a diagram for the TM wave. [Figure 15] 15A and 15B are diagrams showing the relationship between the angle of incidence and the normalized transmission loss in Example 10, where FIG. 15A is a diagram for the TE wave and FIG. 15B is a diagram for the TM wave. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations will be omitted where appropriate.

[0016] First Embodiment Fig. 1 is a diagram illustrating a reflector with a protective plate according to the first embodiment. The reflector with a protective plate 1 is a reflective member with a protective plate that reflects incident radio waves. Fig. 1 shows how radio waves incident along an incident direction 21 are reflected by the reflector with a protective plate 1 along a reflection direction 22. As shown in Fig. 1, the reflector with a protective plate 1 has a protective plate 11 and a reflector 12.

[0017] The protective plate 11 is a flat plate-like member that is transparent to radio waves incident on the protective plate-equipped reflector 1. The protective plate 11 is installed on the radio wave incident side of the reflector 12 via an air layer 13, and by covering the reflector 12, it protects the reflector 12 from dirt and the like caused by human contact.

[0018] The material of the protective plate 11 can be resin or glass. When resin is used, fluororesin is preferable from the viewpoint of antifouling, and polytetrafluoroethylene (PTFE) is more preferable. n2 shown in FIG. 1 represents the refractive index of the protective plate 11, and ε r represents the relative dielectric constant of the protection plate 11. r is equal to the square of the refractive index n2, and d represents the thickness of the protection plate 11.

[0019] The reflector 12 includes a reflecting surface 121, and is a reflecting member that reflects, from the reflecting surface 121, radio waves that are incident on the reflector 1 with a protective plate and that have passed through the protective plate 11 and then entered the reflecting surface 121. There are no particular restrictions on the material of the reflector 12, and any material suitable for reflecting radio waves can be selected as appropriate.

[0020] In this embodiment, the reflecting surface 121 is a flat surface. The normal to the reflector 1 with a protection plate is equal to the normal to the reflecting surface 121. In addition, since the reflecting surface 121 and the protection plate 11 are parallel, the normal to the reflector 1 with a protection plate is also equal to the normal to the protection plate 11.

[0021] Of the radio waves incident on the reflector 1 with protective plate at an incident angle θ1, a first radio wave 211 passes through a first boundary surface 111, which is the surface of the protective plate 11 on the radio wave incident side, and a second radio wave 212 is reflected by the first boundary surface 111. The incident angle θ1 is the angle with respect to the normal to the protective plate 11.

[0022] The first radio wave 211 is refracted at the first boundary surface 111, propagates inside the protection plate 11 in the direction indicated by the refraction angle θ2, and then reaches the second boundary surface 112, which is the surface of the protection plate 11 opposite to the first boundary surface 111. A portion of the arriving first radio wave 211 passes through the second boundary surface 112, and the rest is reflected by the second boundary surface 112. The passing radio wave 211′ that has passed through the second boundary surface 112 passes through the air layer 13, then reaches the reflecting surface 121, and is reflected by the reflecting surface 121.

[0023] On the other hand, the first radio wave 211 reflected by the second boundary surface 112 propagates inside the protective plate 11 toward the first boundary surface 111, is refracted at the first boundary surface 111, and then is emitted from the protective plate 11 to the outside along the reflection direction 22.

[0024] During the propagation of the first radio wave 211, an optical path difference occurs between the second radio wave 212 reflected by the first boundary surface 111 and the second radio wave 212, according to the optical path that passes through the inside of the protection plate 11. ΔL, shown by a bold line in FIG. 1, represents this optical path difference.

[0025] (Method for determining thickness of protective plate) Here, the reflection efficiency of radio waves by the protective plate-equipped reflector 1 is maximized when the transmission loss of radio waves passing through the protective plate 11 is minimized. The condition for minimizing the transmission loss in the protective plate 11 is, for example, a condition for no reflection in the protective plate 11. In this embodiment, by optimizing the plate thickness d of the protective plate 11, the reflection in the protective plate 11 approaches the no-reflection condition, thereby reducing the transmission loss in the protective plate 11.

[0026] The relationship between the incident angle θ1 and the refraction angle θ2 in the protection plate 11 is expressed by the following equation (1).

[0027]

number

[0028] Moreover, the optical path difference ΔL is expressed by the following equation (2).

[0029]

number

[0030] Because the reflection at the first boundary surface 111 is a fixed-end reflection, the phase of the second radio wave 212 changes by π due to the reflection at the first boundary surface 111. On the other hand, because the reflection at the second boundary surface 112 is a free-end reflection, the phase of the first radio wave 211 does not change due to the reflection at the second boundary surface 112. Note that the fixed-end reflection is the reflection occurring when a radio wave is incident from a medium with a small refractive index to a medium with a large refractive index, and the free-end reflection is the reflection occurring when a radio wave is incident from a medium with a large refractive index to a medium with a small refractive index.

[0031] When the amplitude peak of the first radio wave 211 and the amplitude anti-peak of the second radio wave 212 are in phase, they cancel each other out, resulting in no reflection from the protection plate 11. An amplitude peak refers to a maximum or minimum amplitude. An amplitude anti-peak refers to a maximum or minimum amplitude on the opposite side of the peak. For example, if the amplitude peak is a maximum amplitude, i.e., a crest, the amplitude anti-peak is a minimum amplitude, i.e., a valley. If the amplitude peak is a minimum amplitude, the amplitude anti-peak is a maximum amplitude.

[0032] Conventionally, the incident angle of the radio wave was assumed to be approximately 0 degrees, so the thickness of the protection plate 11 was usually determined so that the phases of the peak amplitude of the radio wave reflected by the first boundary surface 111 and the anti-peak amplitude of the radio wave reflected by the second boundary surface 112 were aligned among the radio waves incident on the protection plate 11 at an incident angle of 0 degrees. In other words, the thickness d of the protection plate is d=λ0 / {2×√(ε r )} ···(3) However, with such a thickness, it was difficult to obtain a protective plate with good transmission characteristics over a wide angle.

[0033] The inventors conducted extensive research based on the optical path difference ΔL, taking into consideration the phases of the amplitude peak in first radio wave 211 and the amplitude anti-peak in second radio wave 212. As a result, it was found that determining the plate thickness d of protection plate 11 according to the following equations (4) and (5) effectively suppresses the transmission loss in protection plate 11 and ensures high reflection efficiency of radio waves by reflector 1 with protection plate. d=α×λ0 / (1.75×ε r 0.555 ) (4) 1≦α≦1.25 (5)

[0034] Here, λ0 represents the wavelength [mm] defined for the operating center frequency f0 [Hz], d represents the plate thickness [mm] of the protection plate 11, and ε r represents the relative dielectric constant of the protection plate 11 at the operating center frequency f0 [Hz], and α represents a constant.

[0035] The operating center frequency f0 represents the center frequency of the radio waves incident on the reflector 1 with protective plate. The wavelength λ0 [mm] is defined as 1000 × c / f0, where c represents the speed of light and is approximately 3.0 × 10 8 [m / s].

[0036] Equations (4) and (5) apply to both TE (Transverse Electric) and TM (Transverse Magnetic) waves in radio waves. In other words, this embodiment includes both TE and TM waves.

[0037] Furthermore, the relative dielectric constant of protective plate 11 is preferably 2 or more and 10 or less, and more preferably 2 or more and 5 or less. Within this range, it is possible to more easily design a protective film with good characteristics over a wide band and at a wide angle.

[0038] (Relationship between f / f0, constant α, and normalized transmission loss) 2 is a diagram showing an example of the relationship between the operating center frequency f0, the constant α, and the angle of incidence according to this embodiment. The horizontal axis of Fig. 2 represents the constant α, and the vertical axis represents f / f0, which is the ratio of the operating frequency f [Hz] to the operating center frequency f0.

[0039] The density of the color bar 30 represents the angle of incidence of radio waves at which the normalized transmission loss is 1 dB. The whiter the color bar 30, the lower the density, indicating a larger angle of incidence, and the wider the angle at which the radio waves are incident on the protection plate 11. The blacker the color bar 30, the lower the angle of incidence, and the narrower the angle at which the radio waves are incident on the protection plate 11.

[0040] Here, normalized transmission loss refers to transmission loss normalized so that the smallest transmission loss is 0 [dB] when f / f0 is 1.0. Hereinafter, to simplify the explanation, the angle of incidence of radio waves at which the normalized transmission loss is 1 [dB] will be referred to as the allowable angle of incidence.

[0041] Figure 2 shows the relative permittivity ε r The allowable angle of incidence was calculated by electromagnetic field analysis while changing the constant α and the operating frequency f, with the operating center frequency f and α being determined in advance. The analysis was performed using CST Studio Suite. In the example in Figure 2, f=28[GHz], 20[GHz]≦f≦50[GHz], and 0.714≦f / f0≦1.786.

[0042] Point 33 indicates the point where f / f0 is 1.0 and the constant α is 1.1. Note that the region 40 indicated by horizontal hatching is a region where no calculations were performed.

[0043] In this embodiment, the constant α that maximizes the allowable incident angle is determined according to FIG. 2, and the constant α and the relative dielectric constant ε r The thickness d is determined by substituting the wavelength λ0 defined by the operating center frequency f0 into equation (4).

[0044] Here, in order to improve robustness against fluctuations in the operating frequency f, it is preferable to determine the constant α so that the range of f / f0 is as wide as possible.

[0045] The frequency range around the operating center frequency f0 where the allowable angle of incidence is 60 degrees or more is defined as Δf [Hz]. In this case, if the constant α satisfies equation (5), the frequency range where f / f0 is 0.9 to 1.1 and Δf / f0 is 20% is ensured.

[0046] 2, the region between the lower boundary line 31 and the upper boundary line 32 is the region where the allowable incident angle is 60 degrees or more. The target region 34 enclosed by the dashed rectangle is the region where the constant α satisfies equation (5) and f / f0 is 0.9 or more and 1.1 or less.

[0047] From the viewpoint of ensuring a wide frequency range, it is more preferable that the constant α is 1≦α≦1.23. Also, from the viewpoint of increasing robustness against fluctuations in the operating frequency f, Δf / f0 is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more.

[0048] Examples and Comparative Examples Examples and comparative examples will be described below, but the present invention is not limited to these examples. Example 1 is a comparative example, and Examples 2 to 4 are examples.

[0049] [Example 1] In Example 1, the material of the protection plate 11 is PTFE, the operating center frequency f0 is 28 [GHz], the constant α is 0.097, and the plate thickness d is 3.7 [mm]. PTFE has a relative dielectric constant ε r is 2.1 and the loss coefficient tanδ is 0.001.

[0050] The plate thickness d in Example 1 was determined using the above-mentioned equation (3) so that, among the radio waves incident on the protective plate 11 at an incident angle of 0 degrees, the phase of the amplitude peak of the radio waves reflected by the first boundary surface 111 and the phase of the amplitude anti-peak of the radio waves reflected by the second boundary surface 112 are aligned.

[0051] FIG. 3 shows the relationship between the angle of incidence and normalized transmission loss in Example 1. FIG. 3(a) shows the TE wave, and FIG. 3(b) shows the TM wave. FIG. 3 shows the results of electromagnetic field analysis of the normalized transmission loss when the angle of incidence is changed. CST Studio Suite was used for the analysis. The horizontal axis of FIG. 3 represents the angle of incidence of the radio wave on the protection plate 11, and the vertical axis represents the normalized transmission loss. The legend also shows the cases where f / f0 is changed from 0.90 to 1.10 in increments of 0.05. A threshold value of 50 represents a normalized transmission loss of 1 dB. The interpretation and meaning of these figures are the same for Examples 2 to 4 shown below.

[0052] As shown in Figure 3, in Example 1, the normalized transmission loss was smallest when the incident angle was 0 degrees for any f / f0, and the normalized transmission loss gradually increased as the incident angle increased. For TE waves, the allowable incident angle was smallest at 52 degrees when f / f0 was 0.90.

[0053] For TM waves, the difference for each f / f0 value was smaller than for TE waves. The allowable incident angle was smallest at 74 degrees when f / f0 was 0.90.

[0054] [Example 2] In Example 2, the material of the protection plate 11 is PTFE, the operating center frequency f0 is 28 [GHz], and the constant α is 1.1. The plate thickness d is determined by the above-mentioned formula (4). PTFE has a relative dielectric constant ε r is 2.1 and the loss coefficient tanδ is 0.001.

[0055] 4A and 4B are diagrams showing the relationship between the incident angle and the normalized transmission loss in Example 2. Fig. 4A is a diagram of the TE wave, and Fig. 4B is a diagram of the TM wave.

[0056] As shown in Figure 4, in Example 2, for both the TE wave and the TM wave, when the incident angle was 0 degrees, the normalized transmission loss was smallest when f / f0 was 0.90, and the normalized transmission loss increased as f / f0 increased.

[0057] Furthermore, for both TE waves and TM waves, the normalized transmission loss of the protective plate 11 decreased as the incident angle of the radio waves changed from 0 degrees to 50 degrees at the operating center frequency f0 (f / f0 is 1.0), and after reaching a minimum value, increased as the incident angle increased.

[0058] For the TE wave in Example 2, the allowable incident angle was the smallest at 65 degrees when f / f0 was 0.90. Therefore, the minimum allowable incident angle for the TE wave in Example 2 is larger than the 52 degrees in Example 1. The minimum allowable incident angle refers to the smallest of the allowable incident angles.

[0059] For the TM wave in Example 2, the allowable incident angle was the smallest at 77 degrees when f / f0 was 0.90. Therefore, the minimum allowable incident angle for the TE wave in Example 2 is larger than that of Example 1, which is 74 degrees.

[0060] From the above, it was found that the minimum allowable incident angle for both the TE wave and the TM wave in Example 2 was larger and wider than that in Example 1.

[0061] The only difference between Examples 1 and 2 is the method for determining the thickness d of the protection plate 11, and the other conditions are the same. Therefore, it was found that the method for determining the thickness d in Example 2 makes it possible to provide a reflector 1 with a protection plate that can effectively reflect radio waves incident over a wider angle range than the comparative example.

[0062] [Example 3] In Example 3, the material of the protection plate 11 is PTFE, the operating center frequency f0 is 40 [GHz], and the constant α is 1.1. The plate thickness d is determined by the above-mentioned formula (4). PTFE has a relative dielectric constant ε r is 2.1 and the loss coefficient tanδ is 0.001.

[0063] 5A and 5B are diagrams showing the relationship between the incident angle and the normalized transmission loss in Example 3. Fig. 5A is a diagram of the TE wave, and Fig. 5B is a diagram of the TM wave.

[0064] As shown in FIG. 5, almost the same results as in Example 2 were obtained in Example 3, and it was found that the relationship between the incident angle and the normalized transmission loss remains almost unchanged even when the operating center frequency f0 changes.

[0065] [Example 4] In Example 4, the material of the protection plate 11 is glass, the operating center frequency f0 is 28 [GHz], and the constant α is 1.0. The plate thickness d is determined by the above-mentioned formula (4). Glass has a relative dielectric constant ε r is 6.8 and the loss coefficient tanδ is 0.02.

[0066] Figure 6 shows the relationship between the incident angle and the normalized transmission loss in Example 4. Figure 6(a) shows the TE wave, and Figure 6(b) shows the TM wave. Note that Figure 6 only shows the case where f / f0 is 1.0.

[0067] As shown in Figure 6, the allowable incident angle for TE waves was 68 degrees. For TM waves, the normalized transmission loss was less than 1 dB even at the largest incident angle of 85 degrees.

[0068] Although not shown, when f / f0 was 0.9 or 1.1, the results were slightly inferior to the other examples. This is presumably due to the relatively high dielectric constant of the protection plate, 6.8.

[0069] (Effect of reflector 1 with protective plate) As explained above, the reflector 1 with a protective plate has the reflector 12 that reflects incident radio waves and the protective plate 11 that is placed on the radio wave incident side of the reflector 12. Let λ0 [mm] be the wavelength defined for the operating center frequency f0 [Hz], d [mm] be the thickness of the protective plate 11, and ε be the relative permittivity of the protective plate 11 at the operating center frequency f0 [Hz]. r , where α is the constant, d=α×λ0 / (1.75×ε r 0.555 ) where 1≦α≦1.25.

[0070] This makes it possible to widen the range of incident angles at which the normalized transmission loss at the protective plate 11 is 1 dB, thereby providing a reflector 1 with a protective plate that can effectively reflect radio waves over a wide range of angles from narrow to wide angles.

[0071] Second Embodiment A description will now be given of a reflector with a protective plate according to the second embodiment. Note that the same components as those in the first embodiment are given the same reference numerals, and redundant description will be omitted where appropriate.

[0072] 7 is a diagram illustrating the configuration of a reflector 1a with a protective plate according to the second embodiment. The reflector 1a with a protective plate has a protective plate 11a. The protective plate 11a has a first dielectric layer 51 and a second dielectric layer 52 provided between the first dielectric layer 51 and the reflector 12. The function of the reflector 1a with a protective plate is the same as that of the reflector 1 with a protective plate, and the function of the protective plate 11a is the same as that of the protective plate 11.

[0073] The first dielectric layer 51 can be made of a material such as resin, and the second dielectric layer 52 can be made of a material such as resin or glass. Since the first dielectric layer 51 is exposed to the outside air, it is preferable that the material be excellent in weather resistance, chemical resistance, abrasion resistance, heat resistance, etc. Since the second dielectric layer 52 is not exposed to the outside air, it is preferable that the material be easy to obtain, easy to process, inexpensive, etc.

[0074] The protective plate 11a can be produced, for example, by forming the second dielectric layer 52 and then covering the surface of the second dielectric layer 52 opposite to the surface facing the reflector 12 with the first dielectric layer 51.

[0075] 8 is a diagram illustrating the relative dielectric constant and thickness of the protection plate 11a. The thickness of the first dielectric layer 51 is d1 [mm], and the relative dielectric constant of the first dielectric layer 51 is ε r1 , the thickness of the second dielectric layer 52 is d2 [mm], and the relative dielectric constant of the second dielectric layer 52 is ε r2 , the effective relative dielectric constant ε of the protection plate 11a is raand the plate thickness da are expressed by the following equations (6) and (7). ε ra ={(d1+d2)×ε r1 ×ε r2} / (d1×ε r2 +d2×ε r1 ) ···(6) da = d1 + d2 (7)

[0076] The protection plate 11a satisfies the conditions expressed by the following formulas (8) and (9). da=α×λ0 / (1.75×ε ra 0.555 ) ···(8) 1≦α≦1.25 (9)

[0077] Example Examples of the second embodiment will be described below, but the present invention is not limited to these examples. Examples 5 to 10 are all examples.

[0078] In each example, the normalized transmission loss was calculated and evaluated by electromagnetic field analysis using CST Studio Suite when the incident angle was changed under seven conditions, from condition A to condition G, which had different f / f0 and constant α.

[0079] Fig. 9 is a diagram showing f / f0 and constant α for each of conditions A to G. Like Fig. 2, Fig. 9 shows the relationship between f / f0, constant α, and incident angle, and plots f / f0 and constant α for each of conditions A to G.

[0080] The materials used for the first dielectric layer 51 were PTFE, polyvinylidene difluoride (PVDF), perfluoroalkoxy alkane (PFA), and thermoplastic fluoride resin (ethylene tetrafluoroethylene (ETFE)). Table 1 below shows the relative dielectric constant ε of each of these materials. r1 and tan δ1 are shown.

[0081] [Table 1]

[0082] The materials used for the second dielectric layer 52 were polycarbonate (PC), polyvinyl chloride (PVC), ABS (Acrylonitrile, Butadiene, Styrene) resin, polyethylene terephthalate (PET), and glass. Table 2 below shows the relative dielectric constant ε of each of these materials. r2 and tan δ2 are shown.

[0083] [Table 2]

[0084] In the evaluation, if both the TE wave and the TM wave met the criteria of an incident angle of 60 degrees or more and a normalized transmission loss threshold of 1 dB or less, the evaluation was marked "Good", and if the criteria were not met, the evaluation was marked "Poor".

[0085] [Example 5] Table 3 shows details of conditions A to G in Example 5 and the evaluation results under each condition. In Table 3, "1 layer" indicates the material of the first dielectric layer 51, and "2 layer" indicates the material of the second dielectric layer 52. This also applies to Tables 4 to 8 shown below.

[0086] [Table 3]

[0087] Fig. 10 shows the relationship between the angle of incidence and the normalized transmission loss in Example 5. Fig. 10(a) shows the TE wave, and Fig. 10(b) shows the TM wave. Each graph in Fig. 10 shows the results under each condition. This also applies to Figs. 11 to 15 shown below.

[0088] As shown in Table 3 and FIG. 10, in Example 5, the evaluation was "x" under conditions F and G, and the evaluation was "o" under the other conditions.

[0089] [Example 6] Table 4 shows details of conditions A to G in Example 6 and the evaluation results under each condition.

[0090] [Table 4]

[0091] 11A and 11B are diagrams showing the relationship between the incident angle and the normalized transmission loss in Example 6. Fig. 11A is a diagram for the TE wave, and Fig. 11B is a diagram for the TM wave.

[0092] As shown in Table 4 and FIG. 11, in Example 6, the evaluation was "x" under conditions F and G, and the evaluation was "good" under the other conditions.

[0093] [Example 7] Table 5 shows details of conditions A to G in Example 7 and the evaluation results under each condition.

[0094] [Table 5]

[0095] 12A and 12B are diagrams showing the relationship between the incident angle and the normalized transmission loss in Example 7. Fig. 12A is a diagram of the TE wave, and Fig. 12B is a diagram of the TM wave.

[0096] As shown in Table 5 and FIG. 12, in Example 7, the evaluation was "x" under conditions F and G, and the evaluation was "o" under the other conditions.

[0097] [Example 8] Table 6 shows details of conditions A and F in Example 8 and the evaluation results under each condition.

[0098] [Table 6]

[0099] 13A and 13B are diagrams showing the relationship between the incident angle and the normalized transmission loss in Example 8. Fig. 13A is a diagram for the TE wave, and Fig. 13B is a diagram for the TM wave.

[0100] As shown in Table 6 and FIG. 13, in Example 8, the evaluation was "good" under condition A, and "poor" under condition F.

[0101] [Example 9] Table 7 shows details of conditions A to G in Example 9 and the evaluation results under each condition.

[0102] [Table 7]

[0103] 14A and 14B are diagrams showing the relationship between the incident angle and the normalized transmission loss in Example 9. Fig. 14A is a diagram for the TE wave, and Fig. 14B is a diagram for the TM wave.

[0104] As shown in Table 7 and FIG. 14, in Example 9, the evaluation was "x" under conditions F and G, and the evaluation was "o" under the other conditions.

[0105] [Example 10] Table 8 shows details of conditions A and F in Example 10 and the evaluation results under each condition.

[0106] [Table 8]

[0107] 15A and 15B are diagrams showing the relationship between the incident angle and the normalized transmission loss in Example 10. Fig. 15A is a diagram of the TE wave, and Fig. 15B is a diagram of the TM wave.

[0108] As shown in Table 8 and FIG. 15, in Example 10, the evaluation was "good" under condition A, and "poor" under condition F.

[0109] As described above, the reflector 1a with a protective plate can also achieve the same effects as the reflector 1 with a protective plate according to the first embodiment. From the viewpoint of widening the range that satisfies the criteria of an incident angle of 60 degrees or more and a normalized transmission loss threshold of 1 dB or less, it is preferable to use materials with low dielectric constants for the first dielectric layer 51 and the second dielectric layer 52.

[0110] In this embodiment, a configuration in which the protective plate-equipped reflectors 1 and 1a reflect incident radio waves is exemplified, but the same effect can be obtained in a configuration in which the protective plate-equipped reflectors 1 and 1a re-radiate incident radio waves.

[0111] Although the preferred embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0112] This application claims priority based on Japanese Patent Application No. 2021-031839 filed with the Japan Patent Office on March 1, 2021, and includes the entire contents of this Japanese patent application. [Explanation of symbols]

[0113] 1, 1a Reflector with protective plate 11, 11a Protective plate 111 1st boundary surface 112 Second boundary surface 12 Reflector 121 Reflective surface 13 Air Layer 21 Incident direction 211 1st radio wave 211' passing radio wave 212 2nd radio wave 22 Reflection direction 50 threshold 51 First dielectric layer 52 Second Dielectric Layer θ1 incident angle θ2 refraction angle ΔL Optical path difference d, da, d1, d2 plate thickness ε r , ε r1 , ε r2 relative permittivity ε ra effective relative permittivity n2 refractive index alpha constant f Operating frequency f0 operating center frequency Δf frequency range

Claims

1. A reflecting member that reflects or re-radiates incident radio waves; a protective plate disposed on the radio wave incident side of the reflecting member, Operating center frequency f ０ The wavelength specified for [Hz] is λ ０ [mm], the thickness of the protective plate is d [mm], and the operating center frequency f ０ The relative dielectric constant of the protection plate in [Hz] is ε ｒ , where the constant is α, d = α × λ ０ / (1.75 × ε ｒ ０．５５５ ) A reflective member with a protective plate, wherein 1≦α≦1.

25.

2. The reflective member with a protection plate according to claim 1 , wherein the protection plate has a relative dielectric constant of 2 or more and 10 or less.

3. The operating center frequency f ０ When the frequency range around [Hz] where the incident angle of the radio wave at which the normalized transmission loss of the protection plate is 1 [dB] is 60 [degrees] or more is Δf [Hz], Δf / f ０ The reflective member with a protective plate according to claim 1 or 2, wherein the ratio of the reflection coefficient to the reflection coefficient is 10% or more.

4. 4. The reflector with a protective plate according to claim 1, wherein the protective plate is made of a material selected from the group consisting of fluororesin and glass.

5. 5. The reflector with a protective plate according to claim 1, wherein the protective plate is made of polytetrafluoroethylene.

6. The normalized transmission loss of the protection plate is ０ 6. The reflective member with protection plate according to claim 1, wherein the frequency, in [Hz], decreases as the incident angle of the radio wave changes from 0 degrees to 50 degrees.

7. the protective plate has a first dielectric layer and a second dielectric layer provided between the first dielectric layer and the reflecting member, The thickness of the first dielectric layer is d １ [mm], the relative dielectric constant of the first dielectric layer is ε ｒ１ , the thickness of the second dielectric layer is d ２ [mm], the relative dielectric constant of the second dielectric layer is ε ｒ２ , the effective relative dielectric constant of the protection plate is ε ｒａ , where the thickness of the protective plate is da, ε ｒａ = {(d １ +d ２ ) × ε ｒ１ ×ε ｒ２ } / (d １ ×ε ｒ２ +d ２ ×ε ｒ１ ) where da=d １ +d ２ and da=α×λ ０ / (1.75 × ε ｒａ ０．５５５ 7. The reflective member with protection plate according to claim 1, wherein α satisfies 1≦α≦1.25.

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