Radio wave reflection device

Abstract

This radio wave reflection device includes: a radio wave reflection plate that reflects a radio wave of a target frequency; and a cover that is located on the reflection surface side of the radio wave reflection plate and covers the radio wave reflection plate. The thickness t of the cover satisfies formula (1). In formula (1), n is a natural number, λ is the wavelength of the radio wave, and εr is the relative dielectric constant of the cover. The radio wave reflection plate may include a patch electrode, a ground electrode, and a liquid crystal layer between the patch electrode and the ground electrode.

Description

radio wave reflector

[0001] One embodiment of the present invention relates to a radio wave reflecting device that includes a radio wave reflector that reflects radio waves of a target frequency.

[0002] High-frequency radio waves have high directivity and are easily blocked by obstacles such as buildings. Therefore, in wireless communication using high-frequency radio waves, it is important to eliminate dead zones where radio waves cannot be received, and radio wave reflectors are used as relay devices to change the direction of reflected waves. Radio wave reflectors such as phased array antennas can control the direction of reflected waves by adjusting the amplitude and phase of the incident wave. For example, the radio wave reflector disclosed in Patent Document 1 controls the direction of reflected waves by utilizing the fact that the dielectric constant changes in correspondence with the orientation state of the liquid crystal. Radio wave reflectors are also called IRS (Intelligent Reflecting Surface), etc.

[0003] Japanese Patent Application Publication No. 11-103201

[0004] Since radio wave reflectors are mainly installed outdoors, they are housed in enclosures to improve weather resistance and reliability. However, in radio wave reflecting devices where the reflector is housed in such an enclosure, the incident waves to the reflector and the reflected waves from the reflector pass through the enclosure. In other words, there is a problem in that the reflective characteristics of the radio wave reflecting device are reduced due to the influence of the enclosure.

[0005] One of the objectives of one embodiment of the present invention, in view of the above problems, is to provide a radio wave reflector in which the deterioration of reflective characteristics is suppressed.

[0006] A radio wave reflecting device according to one embodiment of the present invention includes a radio wave reflector that reflects radio waves of a target frequency, and a cover located on the reflective surface side of the radio wave reflector and covering the radio wave reflector, wherein the thickness t of the cover satisfies formula (1).

[0007]

[0008] In equation (1), n ​​is a natural number, λ is the wavelength of the radio wave, and ε ｒ This is the relative permittivity of the cover.

[0009] This is a schematic diagram illustrating the usage of a radio wave reflector according to one embodiment of the present invention. This is a schematic cross-sectional view showing the configuration of a radio wave reflector according to one embodiment of the present invention. This is a schematic plan view showing the configuration of the radio wave reflector plate of a radio wave reflector according to one embodiment of the present invention. This is a schematic cross-sectional view showing the configuration of the reflective antenna cell of the radio wave reflector plate of a radio wave reflector according to one embodiment of the present invention and the direction of radio wave reflection by the reflective antenna cell. This is a schematic cross-sectional view illustrating the effect of the cover thickness on a radio wave reflector according to one embodiment of the present invention. This is a simulation result showing the dependence of the cover thickness when the target frequency is 28 GHz. This is a simulation result showing the dependence of the thickness when the target frequency is 47 GHz.

[0010] Embodiments of the present invention will be described below with reference to the drawings. The following disclosure is merely an example. Configurations that a person skilled in the art could easily conceive by appropriately modifying the configuration of the embodiments while maintaining the spirit of the invention are naturally included within the scope of the present invention. In order to make the explanation clearer, the drawings may schematically represent the width, film thickness, and shape of the components compared to the actual embodiments. However, the illustrated shapes are merely examples and do not limit the interpretation of the present invention. In this specification and drawings, components similar to those described above with respect to previously shown figures are denoted by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0011] In this specification, when a member or region is described as being "above (or below)" another member or region, unless otherwise specified, this includes not only cases where it is directly above (or directly below) the other member or region, but also cases where it is above (or below) the other member or region, that is, cases where another component is included between them above (or below) the other member or region.

[0012] In this specification, expressions such as "α includes A, B, or C," "α includes any one of A, B, and C," and "α includes one selected from the group consisting of A, B, and C" do not exclude cases where α includes multiple combinations of A through C, unless otherwise explicitly stated. Furthermore, these expressions do not exclude cases where α includes other components.

[0013] Referring to Figures 1 to 5, a radio wave reflector 1 according to one embodiment of the present invention will be described.

[0014] [1. Usage of the Radio Wave Reflector 1] Figure 1 is a schematic diagram illustrating a usage of the radio wave reflector 1 according to one embodiment of the present invention.

[0015] Base station 1001 is equipped with an omnidirectional antenna and transmits radio waves in all directions. However, in areas 1002 and 1003, the radio waves transmitted from base station 1001 are blocked by building 1004, making it difficult for the radio waves to reach them (or reducing their sensitivity). Therefore, a radio wave reflector 1 is used to transmit radio waves to area 1002 or area 1003 via a route that bypasses building 1004. As shown in Figure 1, if the radio wave reflector 1 is installed in a location where the radio waves are not blocked by building 1004, the radio waves transmitted from base station 1001 are reflected by the radio wave reflector 1 and can reach area 1002 or area 1003.

[0016] As described above, the radio wave reflector 1 can reflect incoming radio waves. In particular, the radio wave reflector 1 can reflect radio waves directionally in a specific direction. For example, the radio wave reflector 1 can selectively reflect radio waves transmitted from the base station 1001 toward either area 1002 or area 1003.

[0017] [2. Configuration of the Radio Wave Reflector 1] Figure 2 is a schematic cross-sectional view showing the configuration of the radio wave reflector 1 according to one embodiment of the present invention.

[0018] As shown in Figure 2, the radio wave reflector 1 includes a radio wave reflector 10 and a housing 20. The housing 20 includes a main body 21 and a cover 22. The radio wave reflector 10 is placed inside the main body 21 of the housing 20 and is covered by the cover 22. That is, the radio wave reflector 10 is housed inside the housing 20. There is a gap between the radio wave reflector 10 and the cover 22. Therefore, although the radio wave reflector 10 is fixedly placed in the main body 21, the radio wave reflector 10 and the cover 22 are spaced apart. In Figure 2, the housing 20 is separated into the main body 21 and the cover 22, but the main body 21 and the cover 22 may be integrally formed using the same material. In this case, a part of the housing 20 located on the side where radio waves are incident on the radio wave reflector 10 corresponds to the cover 22.

[0019] In a radio wave reflector 1 in which the radio wave reflector 10 is housed within a casing 20, the radio wave reflector 10 is less susceptible to external environmental influences such as weather. Therefore, the weather resistance and reliability of the radio wave reflector 10 can be improved in the radio wave reflector 1.

[0020] [2-1. Configuration of the radio wave reflector 10] Figure 3 is a schematic plan view showing the configuration of the radio wave reflector 10 of the radio wave reflecting device 1 according to one embodiment of the present invention.

[0021] As shown in Figure 3, the radio wave reflector 10 includes a reflection antenna region 11 and a peripheral region 12. The reflection antenna region 11 is located in the center of the radio wave reflector 10, and the peripheral region 12 surrounds the reflection antenna region 11 and is located in the peripheral region of the radio wave reflector 10. The reflection antenna region 11 is provided with a plurality of reflection antenna cells 100. The plurality of reflection antenna cells 100 are arranged in a matrix in the x-axis and y-axis directions. However, the arrangement configuration of the plurality of reflection antenna cells 100 is not limited to this. The peripheral region is provided with a drive circuit 200 that generates control signals to control each of the plurality of reflection antenna cells 100. Wiring is also provided to electrically connect the reflection antenna cells 100 and the drive circuit 200. Although not shown, the peripheral region 12 may be provided with terminals for supplying signals or power from the outside.

[0022] Now, with reference to Figure 4, the configuration and function of the reflective antenna cell 100 will be described.

[0023] Figure 4 is a schematic cross-sectional view showing the configuration of the reflective antenna cell 100 of the radio wave reflector 10 of a radio wave reflector 1 according to one embodiment of the present invention, and the direction of radio wave reflection by the reflective antenna cell 100. In Figure 4, two adjacent reflective antenna cells 100 are shown as the first reflective antenna cell 100-1 and the second reflective antenna cell 100-2.

[0024] Each of the first reflective antenna cell 100-1 and the second reflective antenna cell 100-2 includes a patch electrode 120 provided on the first substrate 110-1 and a ground electrode 130 provided on the second substrate 110-2. The patch electrode 120 of the first reflective antenna cell 100-1 and the patch electrode 120 of the second reflective antenna cell 100-2 are not electrically connected. On the other hand, the ground electrode 130 is provided in common to both the first reflective antenna cell 100-1 and the second reflective antenna cell 100-2. A first alignment film 140-1 is provided on the patch electrode 120. A second alignment film 140-2 is provided on the ground electrode 130. The first substrate 110-1 and the second substrate 110-2 are arranged so that the patch electrode 120 and the ground electrode 130 face each other, and a liquid crystal layer 150 is provided between the first alignment film 140-1 and the second alignment film 140-2.

[0025] Glass, quartz, or resin can be used as the first substrate 110-1 and the second substrate 110-2, respectively.

[0026] Metallic materials can be used for both the patch electrode 120 and the ground electrode 130. For example, the metallic materials may be molybdenum (Mo), tungsten (W), titanium (Ti), aluminum (Al), copper (Cu), or alloys thereof. The patch electrode 120 and the ground electrode 130 may each have a single-layer structure or a multilayer structure.

[0027] A polyimide resin or the like can be used for each of the first alignment film 140-1 and the second alignment film 140-2. Alignment treatment is performed on the first alignment film 140-1 and the second alignment film 140-2 by using a rubbing method, a photo-alignment method, or the like.

[0028] The liquid crystal layer 150 includes a liquid crystal material having dielectric anisotropy. For example, as the liquid crystal material of the liquid crystal layer 150, nematic liquid crystal or cholesteric liquid crystal containing liquid crystal molecules capable of twisted alignment can be used.

[0029] Through the alignment treatment of the first alignment film 140-1 and the second alignment film 140-2, the initial alignment state (alignment state when no voltage is applied) of the liquid crystal molecules in the liquid crystal layer 150 is controlled. When a voltage is applied to the patch electrode 120 and a potential difference is formed between the patch electrode 120 and the ground electrode 130, the alignment state of the liquid crystal molecules in the liquid crystal layer 150 changes, and the dielectric constant of the liquid crystal layer 150 also changes. Although details will be described later, in the radio wave reflector 10, the change in the dielectric constant of the liquid crystal layer 150 is utilized to control the phase of reflected radio waves.

[0030] When the liquid crystal molecules have positive dielectric anisotropy, the dielectric constant is higher when a voltage is applied than when no voltage is applied. Further, when the liquid crystal molecules have negative dielectric anisotropy, the dielectric constant is lower when a voltage is applied than when no voltage is applied. The liquid crystal layer 150 formed of liquid crystal having dielectric anisotropy can also be regarded as a variable dielectric layer. The reflective antenna cell 100 can be controlled to delay (or not to delay) the phases of scattered waves R1 and R2 by utilizing the dielectric anisotropy of the liquid crystal layer 150.

[0031] As described above, the basic configurations of the first reflective antenna cell 100-1 and the second reflective antenna cell 100-2 are the same. That is, each of the plurality of reflective antenna cells 100 has the basic configuration described above. On the other hand, each of the plurality of reflective antenna cells 100 is electrically connected to a switching element 160. Specifically, the switching element 160 is electrically connected to the patch electrode 120, and the voltage applied to the patch electrode 120 is changed by controlling the switching element 160.

[0032] As shown in Figure 4, radio waves are incident on the radio wave reflector 10 parallel to the normal direction of the surface of the first substrate 110-1 (see "Direction of Incident Wave Propagation" in Figure 4). Now, consider the case where a first voltage V1 is applied to the patch electrode 120 of the first reflective antenna cell 100-1, and a second voltage V2, which is different from the first voltage V1, is applied to the patch electrode 120 of the second reflective antenna cell 100-2. When radio waves with the same phase are incident on the first reflective antenna cell 100-1 and the second reflective antenna cell 100-2, scattered waves with different phases are generated in the first reflective antenna cell 100-1 and the second reflective antenna cell 100-2 because the dielectric constants of the liquid crystal layer 150 are different in the first reflective antenna cell 100-1 and the second reflective antenna cell 100-2. For example, as shown in Figure 4, the phase of the scattered wave R2 scattered by the second reflective antenna cell 100-2 leads the phase of the scattered wave R1 scattered by the first reflective antenna cell 100-1. In this case, the radio waves reflected in the reflective antenna region 11 propagate in a direction different from the normal direction of the surface of the first substrate 110-1 (see "Direction of reflected wave propagation" in Figure 4). Although Figure 4 shows two adjacent reflective antenna cells 100, the radio wave reflector 10 can control multiple reflective antenna cells 100 arranged in a matrix independently. Therefore, the radio wave reflector 10 can control the direction of radio wave reflection to any desired direction.

[0033] The frequency bands to which the radio wave reflector 10 is applicable include very high frequency (VHF) bands, ultra-high frequency (UHF) bands, super high frequency (SHF, microwave) bands, tremendously high frequency (THF, submillimeter wave) bands, and extra high frequency (EHF, millimeter wave) bands. As described above, in the liquid crystal layer 150, the alignment state of liquid crystal molecules changes according to the voltage applied to the patch electrode 120, but this change hardly follows the frequency of the radio wave incident on the ground electrode 130. Due to such characteristics of liquid crystal molecules, while the dielectric constant of the liquid crystal layer 150 is changed by the patch electrode 120, radio waves can be scattered by the ground electrode 130, and the phase of the scattered radio waves (the reflection phase of the radio waves) can be controlled.

[0034] Note that the method for controlling the reflection phase of radio waves in the radio wave reflector 10 is not limited to the method using liquid crystal. Although a detailed description is omitted, in the radio wave reflector 10, it is also possible to control the reflection phase of radio waves by driving reflective antenna cells using PIN diodes or varactor diodes.

[0035] [2-2. Configuration of housing 20] As materials for the main body 21 and the cover 22, resins such as glass fiber reinforced plastic (FRP), acrylic, and polycarbonate can be used, but there is no particular limitation. The material of the main body 21 and the material of the cover 22 may be the same or different. For example, the material of the cover 22 may be glass. When transparent glass is used as the cover 22, the state of the radio wave reflector 10 housed in the housing 20 can be confirmed from the outside without removing the cover 22.

[0036] Further, a coating may be applied to the surface of the main body 21 or the cover 22. By applying the coating to the surface, the weather resistance and reliability of the radio wave reflector 10 can be further improved.

[0037] The cover 22 is located on the reflecting surface side of the radio wave reflector 10. Therefore, radio waves (incident waves and reflected waves) transmit through the cover 22. The thickness of the main body 21 is not particularly limited. Meanwhile, in the radio wave reflection device 1 according to the present embodiment, the thickness t of the cover 22 satisfies formula (1).

[0038]

[0039] In formula (1), n is a natural number, λ is the wavelength of the radio wave, and ε ｒ is the relative permittivity of the cover 22.

[0040] Here, with reference to FIG. 5, formula (1) will be described in further detail.

[0041] FIG. 5 is a schematic cross-sectional view illustrating the influence exerted by the thickness t of the cover 22 in the radio wave reflection device 1 according to one embodiment of the present invention.

[0042] In FIG. 5, the reflected wave W reflected by the radio wave reflector 10 ｒ besides the first reflected wave wr reflected on the front surface and back surface of the cover 22 １ and the second reflected wave w ｒ２ are shown. The reflected wave W transmitting through the cover 22 ｒ interferes with the first reflected wave w ｒ１ and the second reflected wave w ｒ２ If the first reflected wave w ｒ１ and the second reflected wave w ｒ２ weaken each other, the reflected wave W ｒ no longer interferes with the first reflected wave w ｒ１ and the second reflected wave w ｒ２ Therefore, the thickness t of the cover 22 is determined such that the first reflected wave w ｒ１ and the second reflected wave w ｒ２ weaken each other. When a radio wave having a wavelength λ in vacuum propagates through a medium having a relative permittivity ε ｒ , the wavelength λ in the cover 22 ｇ is expressed as shown in formula (2). Further, the distance l between the first reflected wave w ｒ１ and the second reflected wave w ｒ２ is expressed as shown in formula (3).

[0043]

[0044]

[0045] First reflected wave wr １ and the second reflected wave wr ２ The condition for destructive interference between these two elements can be expressed as shown in equation (4). In equation (4), n is a natural number.

[0046]

[0047] Equation (1) can be derived from equations (2) to (4). Therefore, equation (1) is a conditional equation that reduces the effect of reflection in the cover 22 by utilizing the interference effect. Consequently, by satisfying equation (1) with a thickness t of the cover 22, radio waves passing through the cover 22 can be prevented from being affected by the cover 22.

[0048] Note that the actual thickness t of the manufactured cover 22 will vary. Therefore, although the thickness t of the cover 22 is calculated using equation (1), it can be defined as satisfying equation (1) as long as the thickness t of the cover 22 is within a predetermined range. For example, if the thickness t of the cover 22 is the value calculated using equation (1), then the center value t ０ Let the central value be t. ０ If it is within ±25% of the range, it can be considered to satisfy equation (1). However, it goes without saying that it is preferable for the variation in the thickness t of the cover 22 to be small. Therefore, the thickness t of the cover is preferably the center value t ０ Within ±15% of t, more preferably t ０ Within a range of ±10%, we can consider it to satisfy equation (1).

[0049] Alternatively, when the thickness t of the cover 22 satisfies equation (5), based on a predetermined range (±25%) for n=1, we can consider that the thickness t of the cover 22 satisfies equation (1).

[0050]

[0051] As an example, a simulation was performed on a radio wave reflector 1 comprising a radio wave reflector 10 including a liquid crystal layer 150 and a cover 22. CST Studio (manufactured by Dassault Systèmes K.K.) was used as the simulation software. The relative permittivity ε of the cover 22 was also determined. ｒ I set it to 5.4.

[0052] [1. When the target frequency is 28 GHz] When the target frequency of the radio wave is 28 GHz, the wavelength λ of the radio wave is approximately 10.7 mm. Also, the thickness t of the cover 22 calculated from equation (1) ２８ＧＨｚ This is expressed by equation (6).

[0053]

[0054] Figure 6 shows the simulation results illustrating the dependence of the cover thickness t when the target frequency of the radio waves is 28 GHz. Figure 6 shows a graph in which the distance d between the radio wave reflector 10 and the cover 22 is represented on the horizontal axis, and the phase change amount Δθ is represented on the vertical axis. Here, the phase change amount Δθ is the difference in the reflected phase of the radio waves obtained when the relative permittivity of the liquid crystal layer 150 changes from its minimum value to its maximum value.

[0055] As can be seen from the graph in Figure 6, when the thickness t of the cover 22 is 2.3 mm and 4.6 mm, the phase change amount Δθ becomes almost independent of the distance d (see Figure 5). This means that if the thickness t of the cover 22 is 2.3 mm or 4.6 mm, the reflection characteristics of the radio wave reflector 1 do not depend on the distance d. In other words, the stabilization of the phase change amount Δθ means that a reflected wave with high directivity and low loss can be obtained. Furthermore, the robustness of the radio wave reflector 1 against variations in distance d during the assembly process is also improved. Here, thickness t = 2.3 mm and 4.6 mm correspond to n = 1 and 2 in equation (6). Therefore, when the target frequency of the radio wave is 28 GHz, the deterioration of the reflection characteristics of the radio wave reflector 1 can be suppressed by satisfying equation (1) with a thickness t of the cover 22.

[0056] [2. When the target frequency is 47 GHz] When the target frequency of the radio wave is 47 GHz, the wavelength λ of the radio wave is approximately 6.4 mm. Also, the thickness t of the cover 22 is calculated from equation (2). ４７ＧＨｚ This is expressed by equation (7).

[0057]

[0058] Figure 7 shows the simulation results illustrating the dependence of the cover thickness t when the target frequency of the radio waves is 47 GHz. Figure 7 also shows a graph where the horizontal axis represents the distance d between the radio wave reflector 10 and the cover 22, and the vertical axis represents the phase change amount Δθ.

[0059] As can be seen from the graph in Figure 7, when the thickness t of the cover 22 is 1.37 mm and 2.74 mm, the phase change amount Δθ becomes almost independent of the distance d. This means that if the thickness t of the cover 22 is 1.37 mm and 2.74 mm, the reflection characteristics of the radio wave reflector 1 do not depend on the distance d. In other words, the stabilization of the phase change amount Δθ means that a reflected wave with high directivity and low loss can be obtained. Furthermore, the robustness of the radio wave reflector 1 against variations in distance d during the assembly process is also improved. Here, thickness t = 1.37 mm and 2.74 mm correspond to n = 1 and 2 in equation (7). Therefore, even when the target frequency of the radio wave is 47 GHz, the deterioration of the reflection characteristics of the radio wave reflector 1 can be suppressed by satisfying equation (1) with a thickness t of the cover 22.

[0060] As described above, in the radio wave reflector 1 according to one embodiment of the present invention, the radio wave reflector 10 is housed in the housing 20, which improves the weather resistance and reliability of the radio wave reflector 10. Furthermore, by satisfying formula (1) with the thickness t of the cover 22 of the housing 20, the influence of the cover 22 can be eliminated, and a decrease in the reflection characteristics of the radio wave reflector 1 can be suppressed. In addition, by satisfying formula (1) with the thickness t of the cover 22 of the housing 20, the dependence on the distance between the radio wave reflector 10 and the cover 22 can be eliminated. As a result, it is possible to manufacture a radio wave reflector 1 with small variations in reflection characteristics, and the manufacturing yield of the radio wave reflector 1 can be improved.

[0061] The embodiments and modifications described above as embodiments of the present invention can be combined and implemented as appropriate, insofar as they do not contradict each other. Furthermore, any additions, deletions, or design changes to components, or additions, omissions, or changes to processes based on each embodiment, made by those skilled in the art, are also included within the scope of the present invention, as long as they retain the essence of the present invention.

[0062] Any effects or benefits other than those brought about by the embodiments and modifications described above, if they are clear from the description herein or easily predictable to those skilled in the art, are naturally considered to be brought about by the present invention.

[0063] 1: Radio wave reflector, 10: Radio wave reflector, 11: Reflection antenna area, 12: Peripheral area, 20: Housing, 21: Main body, 22: Cover, 100: Reflection antenna cell, 100-1: First reflection antenna cell, 100-2: Second reflection antenna cell, 110-1: First substrate, 110-2: Second substrate, 120: Patch electrode, 130: Ground electrode, 140-1: First alignment layer, 140-2: Second alignment layer, 150: Liquid crystal layer, 160: Switching element, 200: Drive circuit, 1001: Base station, 1002, 1003: Area, 1004: Building

Claims

1. A radio wave reflecting device comprising: a radio wave reflector that reflects radio waves of a target frequency; and a cover located on the reflective surface side of the radio wave reflector and covering the radio wave reflector, wherein the thickness t of the cover satisfies formula (1). (Here, n is a natural number, λ is the wavelength of the radio wave, and ε ｒ (This is the relative permittivity of the cover.) 2. The radio wave reflecting device according to claim 1, wherein the radio wave reflector includes a patch electrode, a ground electrode, and a liquid crystal layer between the patch electrode and the ground electrode.

3. The radio wave reflecting device according to claim 1, wherein the radio wave reflector and the cover are spaced apart.

4. The radio wave reflector according to claim 1, wherein the material of the cover is glass.

5. The radio wave reflector according to claim 1, wherein the target frequency is 28 GHz.

6. The radio wave reflector according to claim 1, wherein the target frequency is 47 GHz.

Images