Radio wave reflection device

Abstract

This radio wave reflection device includes: a radio wave reflection plate that reflects radio waves of a target frequency and includes a patch electrode, a ground electrode, and a liquid crystal layer between the patch electrode and the ground electrode; and a cover that covers the radio wave reflection plate on the reflection surface side of the radio wave reflection plate so as to be separated from the radio wave reflection plate. When the relative permittivity of the liquid crystal layer changes from a minimum value to a maximum value, the amount of change in the phase of the reflected waves of the radio waves is 250-350 degrees. The target frequency may be 28 GHz or 47 GHz.

Description

Radio wave reflector

[0001] One embodiment of the present invention relates to a radio wave reflector including a radio wave reflection plate that reflects radio waves of a target frequency.

[0002] High-frequency radio waves have high straightness, 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 reflection plates are used as relay devices that change the direction of reflected waves. A radio wave reflection plate such as a phased array antenna can control the direction of reflected waves by adjusting the amplitude and phase of incident waves. For example, the radio wave reflection plate disclosed in Patent Document 1 controls the direction of reflected waves by utilizing the fact that the dielectric constant changes in accordance with the alignment state of liquid crystal. Note that the radio wave reflection plate is also referred to as IRS (Intelligent Reflecting Surface) or the like.

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

[0004] Since the radio wave reflection plate is mainly installed outdoors, the radio wave reflection plate is housed and installed in a housing in order to improve weather resistance and reliability. However, in such a radio wave reflector in which the radio wave reflection plate is housed in the housing, the incident wave to the radio wave reflection plate and the reflected wave from the radio wave reflection plate transmit through the housing. That is, there is a problem that the reflection characteristic of the radio wave reflector is degraded under the influence of the housing.

[0005] In view of the above problem, one embodiment of the present invention has an object of providing a radio wave reflector in which a decrease in reflection characteristics is suppressed.

[0006] A radio wave reflector according to one embodiment of the present invention includes: a radio wave reflection plate that reflects radio waves of a target frequency, the radio wave reflection plate including a patch electrode, a ground electrode, and a liquid crystal layer between the patch electrode and the ground electrode; and a cover that is spaced apart from the radio wave reflection plate on a reflection surface side of the radio wave reflection plate and covers the radio wave reflection plate, wherein a phase change amount of a reflected radio wave when a relative dielectric constant of the liquid crystal layer changes from a minimum value to a maximum value is not less than 250 degrees and not more than 350 degrees.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] Referring to Figures 1 to 4, a radio wave reflector 1 according to one embodiment of the present invention will be described.

[0012] [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.

[0013] 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.

[0014] 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.

[0015] [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.

[0016] 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.

[0017] 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.

[0018] For the sake of clarity, in the following explanation, the direction from the radio wave reflector 10 toward the cover 22 will be referred to as the z-axis direction, and the directions forming a plane substantially perpendicular to the z-axis direction will be referred to as the x-axis direction and the y-axis direction.

[0019] [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.

[0020] 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.

[0021] Now, with reference to Figure 4, the configuration and function of the reflective antenna cell 100 will be described.

[0022] 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.

[0023] 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.

[0024] Glass, quartz, or resin can be used as the first substrate 110-1 and the second substrate 110-2, respectively.

[0025] 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.

[0026] Polyimide resin or the like can be used as the first orientation film 140-1 and the second orientation film 140-2, respectively. The first orientation film 140-1 and the second orientation film 140-2 are subjected to orientation treatment using methods such as rubbing or photo-alignment.

[0027] The liquid crystal layer 150 contains a liquid crystal material having dielectric anisotropy. For example, as the liquid crystal material of the liquid crystal layer 150, a nematic liquid crystal or cholesteric liquid crystal containing liquid crystal molecules capable of twist orientation can be used.

[0028] The orientation treatment of the first alignment film 140-1 and the second alignment film 140-2 controls the initial orientation state (orientation state when no voltage is applied) of the liquid crystal molecules in the liquid crystal layer 150. 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 orientation 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. As will be described in detail later, the radio wave reflector 10 uses the change in the dielectric constant of the liquid crystal layer 150 to control the phase of the reflected radio waves.

[0029] When liquid crystal molecules have positive dielectric anisotropy, the dielectric constant is higher when a voltage is applied than when no voltage is applied. Conversely, when 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 from liquid crystal having dielectric anisotropy can also be considered a variable dielectric layer. The reflective antenna cell 100 can control the phase of scattered waves R1 and R2 to be delayed (or not delayed) by utilizing the dielectric anisotropy of the liquid crystal layer 150.

[0030] As described above, the basic configuration of the first reflective antenna cell 100-1 and the second reflective antenna cell 100-2 is the same. That is, each of the multiple reflective antenna cells 100 has the basic configuration described above. On the other hand, each of the multiple reflective antenna cells 100 is electrically connected to a switching element 160. Specifically, the switching element 160 is electrically connected to a patch electrode 120, and by controlling the switching element 160, the voltage applied to the patch electrode 120 changes.

[0031] 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.

[0032] The frequency bands to which the radio wave reflector 10 is applicable are the very high frequency (VHF) band, the ultra-high frequency (UHF) band, the super high frequency (SHF) band, the extremely high frequency (THF) band, or the extra high frequency (EHF) band. As described above, in the liquid crystal layer 150, the orientation state of the liquid crystal molecules changes depending on the voltage applied to the patch electrode 120, but it hardly follows the frequency of the radio waves incident on the ground electrode 130. Due to these properties of liquid crystal molecules, the dielectric constant of the liquid crystal layer 150 can be changed by the patch electrode 120, while the radio waves are scattered by the ground electrode 130, thereby controlling the phase of the scattered radio waves (the reflection phase of the radio waves).

[0033] [2-2. Configuration of the Housing 20] The main body 21 and the cover 22 can be made of glass fiber reinforced plastic (FRP), acrylic, polycarbonate, or other resins, but are not particularly limited. The materials of the main body 21 and the cover 22 may be the same or different. For example, the material of the cover 22 may be glass. If transparent glass is used as the cover 22, the state of the radio wave reflector 10 housed inside the housing 20 can be checked from the outside without removing the cover 22.

[0034] Furthermore, the surface of the main body 21 or the cover 22 may be coated with paint. By coating the surface with paint, the weather resistance and reliability of the radio wave reflector 10 can be further improved.

[0035] The cover 22 is located on the reflective surface side of the radio wave reflector 10. Therefore, radio waves (incident waves and reflected waves) pass through the cover 22. The thickness of the main body 21 and the cover 22 is not particularly limited. However, in the radio wave reflector 1 according to this embodiment, even if the radio wave reflector 10 is covered by the cover 22, the phase change amount of the reflected wave satisfies 250 degrees or more and 350 degrees or less. Here, the phase difference change amount refers to the phase difference at the target frequency obtained when the relative permittivity of the liquid crystal layer 150 changes from its minimum value to its maximum value. Therefore, by satisfying the above range for the phase change amount, the phase of the reflected wave is stabilized.

[0036] The amount of phase change can vary depending on the thickness t of the cover 22 and the distance d between the radio wave reflector 10 and the cover 22 (see Figure 2). As will be explained in detail in the embodiments described later, when the distance d between the radio wave reflector 10 and the cover 22 is in the range of 3.21 mm to 4.29 mm when the target frequency of the radio wave is 28 GHz, and when the distance d is in the range of 3.19 mm to 4.47 mm when the target frequency of the radio wave is 47 GHz, the amount of phase change will generally satisfy the above range, regardless of the thickness t of the cover 22.

[0037] Furthermore, it is important that the reflected wave not only stabilizes the phase change but also has low loss (attenuation). Therefore, it is preferable that the loss of the reflected wave relative to the incident wave be 10 dB or less. In this case, the range of the distance d between the radio wave reflector 10 and the cover 22 is further limited, and the distance d between the radio wave reflector 10 and the cover 22 is in the range of 3.21 mm to 3.48 mm when the target frequency of the radio wave is 28 GHz, and in the range of 3.51 mm to 3.83 mm when the target frequency of the radio wave is 47 GHz.

[0038] 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.

[0039] [1. When the target frequency is 28 GHz] Table 1 shows the values of the phase change amount (unit: degree) of the reflected wave when simulation is performed in the case where the target frequency of the radio wave is 28 GHz. Specifically, Table 1 shows the phase change amount of the reflected wave when the thickness t of the cover 22 and the distance d between the radio wave reflector 10 and the cover 22 are changed.

[0040]

[0041] As can be seen from Table 1, when the distance d is not less than 3.21 mm and not more than 4.29 mm, a phase change amount of approximately 250 degrees to 350 degrees can be obtained generally without depending on the thickness t of the cover. Therefore, when the distance d between the radio wave reflector 10 and the cover 22 is not less than 3.21 mm and not more than 4.29 mm, the phase change amount of the reflected wave can be stabilized.

[0042] Further, the calculation result in which the phase change amount of the reflected wave is within the range of 250 degrees to 350 degrees and the loss of the reflected wave with respect to the incident wave is 10 dB or less is evaluated as "○", and other calculation results are evaluated as "×". The evaluation results are shown in Table 2.

[0043]

[0044] As can be seen from Table 2, when the distance d is not less than 3.21 mm and not more than 3.48 mm, not only a phase change amount of approximately 250 degrees to 350 degrees can be obtained generally without depending on the thickness t of the cover, but also the loss can be reduced to approximately 10 dB or less. Therefore, when the distance d between the radio wave reflector 10 and the cover 22 is not less than 3.21 mm and not more than 3.48 mm, the loss of the reflected wave can also be reduced.

[0045] [2. When the target frequency is 47 GHz] Table 3 shows the values of the phase change amount (unit: degree) of the reflected wave when simulation is performed in the case where the target frequency of the radio wave is 47 GHz. Specifically, Table 3 shows the phase change amount of the reflected wave when the thickness t of the cover 22 and the distance d between the radio wave reflector 10 and the cover 22 are changed.

[0046]

[0047] As can be seen from Table 3, when the distance d is between 3.19 mm and 4.47 mm, a phase shift of approximately 250 degrees to 350 degrees can be obtained, regardless of the cover thickness t. Therefore, when the distance d between the radio wave reflector 10 and the cover 22 is between 3.19 mm and 4.47 mm, the phase shift of the reflected wave can be stabilized.

[0048] Furthermore, calculation results where the phase change of the reflected wave was within the range of 250 degrees to 350 degrees, and the loss of the reflected wave relative to the incident wave was 10 dB or less, were evaluated as "○", while all other calculation results were evaluated as "×". The evaluation results are shown in Table 4.

[0049]

[0050] As can be seen from Table 4, when the distance d is between 3.51 mm and 3.83 mm, a phase shift of approximately 250 degrees to 350 degrees can be obtained, regardless of the cover thickness t, and the loss can be reduced to approximately 10 dB or less. Therefore, when the distance d between the radio wave reflector 10 and the cover 22 is between 3.51 mm and 3.83 mm, the loss of reflected waves can also be reduced.

[0051] 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, the radio wave reflector 1 is configured such that the phase change amount of the reflected wave is 250 degrees or more and 350 degrees or less. For example, when the target frequency is 28 GHz, the distance between the radio wave reflector 10 and the cover 22 is configured to be 3.21 mm or more and 4.29 mm or less. When the target frequency is 47 GHz, the distance between the radio wave reflector 10 and the cover 22 is configured to be 3.19 mm or more and 4.47 mm or less. With this configuration, the thickness dependence of the cover 22 can be suppressed. Furthermore, the radio wave reflector 1 is configured such that the loss of the reflected wave relative to the incident wave is 10 dB or less. For example, when the target frequency is 28 GHz, the distance between the radio wave reflector 10 and the cover 22 is configured to be 3.21 mm or more and 3.48 mm or less. Furthermore, when the target frequency is 47 GHz, the distance between the radio wave reflector 10 and the cover 22 is configured to be between 3.51 mm and 3.83 mm. This suppresses a decrease in the reflection characteristics of the radio wave reflector 1. In addition, it is possible to manufacture a radio wave reflector 1 with small variations in reflection characteristics, thereby improving the manufacturing yield of the radio wave reflector 1.

[0052] 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.

[0053] 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.

[0054] 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 includes a patch electrode, a ground electrode, and a liquid crystal layer between the patch electrode and the ground electrode; and a cover that covers the radio wave reflector on the reflective surface side of the radio wave reflector at a distance from the radio wave reflector, wherein the amount of phase change of the reflected radio wave when the relative permittivity of the liquid crystal layer changes from a minimum value to a maximum value is 250 degrees or more and 350 degrees or less.

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

3. The radio wave reflecting device according to claim 2, wherein the distance between the radio wave reflector and the cover is 3.21 mm or more and 4.29 mm or less.

4. The radio wave reflector according to claim 3, wherein the loss of the reflected wave relative to the incident wave of the radio wave at the target frequency is 10 dB or less.

5. The radio wave reflecting device according to claim 4, wherein the distance between the radio wave reflector and the cover is 3.21 mm or more and 3.48 mm or less.

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

7. The radio wave reflecting device according to claim 6, wherein the distance between the radio wave reflector and the cover is 3.19 mm or more and 4.47 mm or less.

8. The radio wave reflector according to claim 7, wherein the loss of the reflected wave relative to the incident wave of the radio wave at the target frequency is 10 dB or less.

9. The radio wave reflecting device according to claim 8, wherein the distance between the radio wave reflector and the cover is 3.51 mm or more and less than 3.83 mm.

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