Radio transmission system

Abstract

Provided is a radio transmission system in which both improvement in radio-wave propagation environment and suppression of the leakage of radio waves to the outside of a requisite space are achieved.　This radio transmission system includes: a plurality of electromagnetic wave reflecting devices provided on both sides of a passage along a traveling direction of the passage and reflecting radio waves in a predetermined band selected from 1 MHz to 300 GHz; and a leakage coaxial cable connected to a base station and disposed in a region surrounded by the plurality of electromagnetic wave reflecting devices, which are provided on both sides of the passage, and the floor surface of the passage.

Description

Wireless Transmission System

[0001] The present disclosure relates to wireless transmission systems.

[0002] Conventionally, there has been a wireless transmission system that includes a base station that transmits and receives radio waves in a desired band selected from a frequency band of 1 GHz to 300 GHz, and an electromagnetic wave reflection device that is arranged along at least a part of a production line where production equipment that transmits and receives the radio waves is arranged, and has a reflective surface that reflects the radio waves (see, for example, Patent Document 1).

[0003] International Publication No. 2021 / 199504

[0004] However, depending on the environment in which a wireless transmission system is installed, the location of the base station may be limited, making it difficult to ensure a good positional relationship between the base station and the electromagnetic wave reflector. In such cases, it may be difficult to reduce dead zones, and the radio wave propagation situation may not be improved sufficiently. In addition, there is a need to suppress leakage of radio waves outside the desired area to avoid interference with other commercial radio waves.

[0005] Therefore, an object of the present invention is to provide a wireless transmission system that achieves both an improvement in the radio wave propagation environment and suppression of radio wave leakage outside the required space.

[0006] A wireless transmission system according to an embodiment of the present disclosure includes a plurality of electromagnetic wave reflecting devices provided on both sides of a passageway along the direction of travel of the passageway, and reflecting radio waves in a predetermined band selected from 1 MHz to 300 GHz, and a leaky coaxial cable located within an area surrounded by the plurality of electromagnetic wave reflecting devices provided on both sides of the passageway and the floor of the passageway, and connected to a base station.

[0007] It is possible to provide a wireless transmission system that achieves both an improvement in the radio wave propagation environment and suppression of radio wave leakage outside the required space.

[0008] FIG. 1 is a diagram showing an example of a road 32 on which the wireless transmission system 1 of the embodiment is arranged. FIG. 2 is a diagram showing an example of the configuration of a leaky coaxial cable 80. FIG. 3 is a diagram showing an example of the configuration of an electromagnetic wave reflective fence 100A. FIG. 4 is a diagram showing an example of a manufacturing line 35 of a factory on which the wireless transmission system 1 of the embodiment is arranged. FIG. 5 is a diagram showing an example of the layer structure of a reflective panel 10. FIG. 6 is a diagram showing an example of the configuration of a unit cell 20 of a conductive pattern 15 composed of a hollow pattern 151.

[0009] Hereinafter, an embodiment to which the wireless transmission system of the present disclosure is applied will be described. In the following, the same elements will be denoted by the same reference numerals, and duplicated explanations may be omitted.

[0010] In the following description, the XYZ coordinate system is defined. The direction parallel to the X axis (X direction), the direction parallel to the Y axis (Y direction), and the direction parallel to the Z axis (Z direction) are perpendicular to one another. For ease of explanation, the -Z direction may be referred to as the lower side or bottom, and the +Z direction may be referred to as the upper side or top. Planar view refers to viewing from the XY plane. In the following description, the length, width, thickness, etc. of each part may be exaggerated to make the configuration easier to understand. Terms such as parallel, right angle, orthogonal, horizontal, vertical, and up and down may be misaligned to the extent that they do not impair the effects of the embodiments.

[0011] In an embodiment, a wireless transmission system for indoor and outdoor use uses an electromagnetic wave reflector and a leaky coaxial cable to reduce blind zones. In this specification, a "blind zone" refers to an area where the reception power is reduced by 10 dB or more due to the influence of an obstruction compared to the surrounding reception environment without obstructions. Generally, electromagnetic waves below 3 THz are called radio waves, but in this specification, communication waves transmitted from a base station are called "radio waves," and electromagnetic waves in general are called "electromagnetic waves."

[0012] A dead zone includes not only two-dimensional areas but also three-dimensional space. When production equipment, sensors, or mobile communication terminals equipped with wireless communication functions are located in a dead zone, it becomes difficult to send and receive signals between them and a base station. Therefore, by introducing an electromagnetic wave reflector and a leaky coaxial cable, the dead zone can be reduced and the radio wave environment can be improved.

[0013] <Embodiment> <Wireless transmission system 1 installed outdoors> Fig. 1A is a diagram showing an example of a road 32 on which a wireless transmission system 1 according to an embodiment is installed. Fig. 1A shows, as an example, the wireless transmission system 1 installed outdoors. The road 32 is an example of a passageway, and an example of which is a highway. Here, as an example, a form in which the wireless transmission system 1 is installed on the road 32 will be described. However, in addition to the road 32, the wireless transmission system 1 can also be installed in outdoor facilities such as medical facilities, event venues, and railroad tracks, and indoor facilities such as factories, plants, offices, and commercial facilities.

[0014] The wireless transmission system 1 includes a base station 33, an electromagnetic wave reflecting device 60, and a leaky coaxial cable 80. The base station 33, for example, performs wireless communication at a frequency included in the frequency band of 1 MHz to 300 GHz. The electromagnetic wave reflecting device 60, for example, has a reflective panel that reflects radio waves at the frequency of the base station 33. The leaky coaxial cable 80, for example, is connected to an antenna terminal of the base station 33, is installed along the road 32, and performs wireless communication at a frequency included in the frequency band of 1 MHz to 300 GHz.

[0015] FIG. 1A illustrates a wireless environment in which a road 32 is used as a communication area as an example of an outdoor environment. In the coordinate system of FIG. 1A, the length direction of the road 32 is the X direction, the width direction is the Y direction, and the direction perpendicular to the road surface is the Z direction. A large number of vehicles 31 travel on the road 32. The vehicles 31 may be vehicles with automatic or semi-automatic driving functions, or may not have automatic driving functions. In either case, the vehicles 31 themselves have wireless communication functions installed, not just mobile devices carried by the drivers and passengers, and large amounts of data are transmitted and received between the vehicles 31 and a control and management system.

[0016] In order to realize wireless communication between a mobile object such as a vehicle 31 and a network, a base station 33 and a leaky coaxial cable 80 are placed along a road 32. The leaky coaxial cable 80 is connected to the base station 33 and emits radio waves supplied from the base station 33. Here, a configuration will be described in which the base station 33 directly emits radio waves from an antenna and also supplies radio waves to the leaky coaxial cable 80, which then emits radio waves, but the base station 33 may also be configured to simply output radio waves to the leaky coaxial cable 80 and not emit radio waves.

[0017] The base station 33 and the leaky coaxial cable 80 transmit and receive signals or data to and from the vehicles 31 at a predetermined frequency within a frequency band of, for example, 1 MHz to 300 GHz. Furthermore, in order to ensure that high-frequency radio waves, which have poor linearity due to the topography and surrounding environment of the road 32 and the presence of many vehicles 31, can reach each vehicle 31 more reliably, a plurality of electromagnetic wave reflecting devices 60 are disposed on both sides of the road 32 (on both sides in the width direction of the road 32) along the traveling direction of the vehicles 31 on the road 32. A plurality of electromagnetic wave reflecting devices 60 may be connected together to form an electromagnetic wave reflecting fence, which is installed on the shoulder of the road 32. The electromagnetic wave reflecting fence will be described later with reference to FIG. 2A .

[0018] The radio waves transmitted and received by the base station 33 and the leaky coaxial cable 80 are preferably, for example, radio waves in the 1 GHz to 300 GHz frequency band, including the Sub-6 frequency band and millimeter wave band of fifth-generation mobile communication systems (5G). Currently, the Sub-6 frequency band and the 28 GHz band, which is included in the millimeter wave band, are used, and the next-generation 6G mobile communication standard is expected to expand to the sub-terahertz band. Using such high-frequency bands significantly expands the communication bandwidth, enabling large-volume data communication with low latency.

[0019] The radio waves transmitted and received by the base station 33 and the leaky coaxial cable 80 may be Long Term Evolution (LTE), LTE-Advanced (LTE-A), Ultra Mobile Broadband (UMB), or Citizens Broadband Radio Service (CBRS). The radio waves transmitted and received by the base station 33 and the leaky coaxial cable 80 may be IEEE 802.11 (Wi-Fi (registered trademark)), IEEE 802.16 (WiMAX (registered trademark)), IEEE 802.20, Ultra Wideband (UWB), Bluetooth (registered trademark), Low Power Wide Area (LPWA), or the like.

[0020] For example, the top (upper end) of the electromagnetic wave reflecting device 60 is installed at a position higher than the base station 33. The base station 33 is preferably located between the electromagnetic wave reflecting devices 60 on both sides of the road 32 and has a directional antenna that forms a beam toward the inside of the road 32. In addition, the leaky coaxial cable 80, together with the electromagnetic wave reflecting devices 60, is arranged on both sides of the road 32 along the traveling direction of the vehicle 31 on the road 32.

[0021] Compared to normal coaxial cables, leaky coaxial cables 80 have a lower degree of freedom in bending and winding. For this reason, it is not practical to route the leaky coaxial cable 80 while bending it along the floor or under the floor, for example. For this reason, it is advantageous in terms of routing to arrange the leaky coaxial cable 80 along an electromagnetic wave reflecting device 60 that is arranged linearly. Furthermore, if the leaky coaxial cable 80 is arranged too high, it becomes difficult to obtain sufficient strength of the radio waves radiated downward. For this reason, it is advantageous from the perspective of building a wireless communication area to attach the leaky coaxial cable 80 to an electromagnetic wave reflecting device 60 that is 2 to 3 meters high or less.

[0022] The leaky coaxial cable 80 is arranged closer to the center of the width of the road 32 than the electromagnetic wave reflecting devices 60 on both sides of the road 32. That is, the leaky coaxial cable 80 is arranged in an area surrounded by the road surface (floor) of the road 32 and the multiple electromagnetic wave reflecting devices 60 arranged on both sides of the road 32, and is connected to an antenna terminal of the base station 33. Furthermore, the leaky coaxial cable 80 is arranged in this area at a position lower than the top (upper end) of the electromagnetic wave reflecting devices 60, for example.

[0023] The area surrounded by the multiple electromagnetic wave reflection devices 60 provided on both sides of the road 32 and the road surface (floor surface) of the road 32 includes a position in the height direction that is higher than the top (upper end) of the electromagnetic wave reflection devices 60. The leaky coaxial cable 80 only needs to be disposed within this area, and therefore may be provided at a position higher than the top (upper end) of the electromagnetic wave reflection devices 60.

[0024] Furthermore, the area surrounded by the multiple electromagnetic wave reflecting devices 60 provided on both sides of the road 32 and the road surface (floor surface) of the road 32 also includes the area directly above the electromagnetic wave reflecting devices 60. That is, the leaky coaxial cable 80 may be located directly above the electromagnetic wave reflecting devices 60. For example, the leaky coaxial cable 80 may be provided along the top (upper end) of the electromagnetic wave reflecting device 60, or may be located directly above the electromagnetic wave reflecting device 60 via a fixing member or the like attached to the top (upper end) of the electromagnetic wave reflecting device 60. The leaky coaxial cable 80 being located directly above the electromagnetic wave reflecting device 60 means that there is a portion where the leaky coaxial cable 80 and the electromagnetic wave reflecting device 60 overlap in the width direction of the road 32 when viewed from directly above. Furthermore, when the leaky coaxial cable 80 is located directly above the electromagnetic wave reflecting device 60, it is preferable that the slot 83A faces toward the center of the road 32 in the width direction. This is because the radio waves emitted from the slot 83A can be emitted toward the road 32.

[0025] In addition to the directional antenna of the base station 33, the electromagnetic wave reflecting devices 60 and the leaky coaxial cables 80 are arranged on both sides of the road 32, so that the radio waves emitted from the base station 33 and the leaky coaxial cables 80 are efficiently concentrated on the road 32 and radio waves leaking outside the road 32 are suppressed. As a result, the received power outside the electromagnetic wave reflecting devices 60 on both sides of the road 32 becomes lower than the average or median value of the received power on the road 32 sandwiched between the electromagnetic wave reflecting devices 60 on both sides.

[0026] Even if the beam shape is controlled by the base station 33, other vehicles 31 may obstruct the LOS (Line of Sight). In such cases, radio waves are emitted from the leaky coaxial cables 80 installed on both sides of the road 32, allowing them to reach the vehicles 31. Furthermore, the radio waves emitted from the base station 33 and the leaky coaxial cables 80 can be reflected by the electromagnetic wave reflecting devices 60 and delivered to the vehicles 31.

[0027] The size of the reflecting surface of the electromagnetic wave reflecting device 60 needs to be large enough to cover at least the area determined by the radius R of the first Fresnel zone. The radius R of the first Fresnel zone when radio waves radiated from the antenna of the base station 33 and reflected by the electromagnetic wave reflecting device 60 reach the vehicle 31 in phase is defined by the following equation:

[0028] R=[λd1d2 / (d1+d2)] １ / ２ Here, λ is the wavelength used, d1 is the distance from the antenna of the base station 33 to the electromagnetic wave reflecting device 60, and d2 is the distance from the electromagnetic wave reflecting device 60 to the antenna of the vehicle 31.

[0029] In the 28 GHz band (wavelength approximately 10.7 mm), assuming that the distance d1 from the antenna of the base station 33 to the electromagnetic wave reflecting device 60 is 20.0 mm and the distance d2 from the electromagnetic wave reflecting device 60 to the vehicle 31 is 10.0 m, the size of the reflecting surface of the electromagnetic wave reflecting device 60 only needs to be several tens of centimeters on one side. On the other hand, from the viewpoint of forming an electromagnetic wave reflecting fence that covers a wide reflection area with a small number of electromagnetic wave reflecting devices 60, the width and length of the reflecting surface of the electromagnetic wave reflecting device 60 may be approximately 2.0 m x 4.0 m. In the embodiment, the electromagnetic wave reflecting device 60 is arranged along the road 32 so that the received power on the back side of the reflecting surface of the electromagnetic wave reflecting device 60, i.e., in the area outside the road 32, is lower than the average or median of the received power on the road 32.

[0030] 1B is a diagram showing an example of the configuration of the leaky coaxial cable 80. The leaky coaxial cable 80 has an inner conductor 81, an insulating layer 82, an outer conductor 83, and an insulating coating 84. The inner conductor 81 is a core wire and is made of a metal such as copper or aluminum. The insulating layer 82 is made of an insulator such as foamed polyethylene, and covers the inner conductor 81 to insulate the inner conductor 81 from the outer conductor 83.

[0031] The outer conductor 83 is a cylindrical conductor provided along the outer surface of the insulating layer 82. For example, the outer conductor 83 is made by winding a tape made of a metal such as copper or aluminum around the outer surface of the insulating layer 82. The outer conductor 83 has a plurality of slots 83A provided along the extension direction (X direction) of the leaky coaxial cable 80. While FIG. 1B shows a configuration in which linear slots 83A are arranged in a wave pattern along the extension direction of the leaky coaxial cable 80, the slots 83A are not limited to being linear and may have various shapes. Furthermore, the arrangement of the multiple slots is not limited to being wave-shaped. The insulating coating 84 covers the outer surface of the outer conductor 83 and is made of, for example, a heat-resistant and flame-retardant resin such as polyethylene.

[0032] When one end of the inner conductor 81 of such a leaky coaxial cable 80 is connected to a signal terminal (feed terminal) among the antenna terminals of the base station 33 and one end of the outer conductor 83 is connected to a ground terminal among the antenna terminals of the base station 33, when the base station 33 transmits radio waves, a signal is supplied from the antenna terminal of the base station 33 to the leaky coaxial cable 80, and the radio waves are transmitted from the slots 83A to the periphery of the leaky coaxial cable 80. When the base station 33 receives radio waves, the radio waves surrounding the leaky coaxial cable 80 are received by the slots 83A, transmitted by the leaky coaxial cable 80, and reach the base station 33.

[0033] Therefore, by connecting the leaky coaxial cable 80 to the antenna terminal of the base station 33, a wireless communication area can be established around the leaky coaxial cable 80 along the road 32. The leaky coaxial cable 80 functions as both a transmission path and an antenna.

[0034] <Attachment Structure of Electromagnetic Wave Reflecting Device 60, Electromagnetic Wave Reflecting Fence 100A, and Leaky Coaxial Cable 80> Figure 2A is a diagram showing an example of the configuration of the electromagnetic wave reflecting fence 100A. The electromagnetic wave reflecting fence 100A is formed by connecting electromagnetic wave reflecting devices 60-1, 60-2, and 60-3 (hereinafter, sometimes collectively referred to as "electromagnetic wave reflecting device 60"), each having reflective panels 10-1, 10-2, and 10-3 (hereinafter, sometimes collectively referred to as "reflective panel 10"), via a frame 50A. In other words, the electromagnetic wave reflecting fence 100A includes multiple electromagnetic wave reflecting devices 60. The configuration of each electromagnetic wave reflecting device 60 is the same as the configuration of each electromagnetic wave reflecting device 60 shown in Figure 1A.

[0035] The coordinate system in Fig. 2A is consistent with the coordinate system in Fig. 1A, with the width or lateral direction of the reflective panel 10 being the X direction, the thickness direction being the Y direction, and the height direction being the Z direction. In Fig. 2A, three electromagnetic wave reflecting devices 60 are connected to form the electromagnetic wave reflective fence 100A, but the number of multiple electromagnetic wave reflecting devices 60 to be connected is determined appropriately depending on the conditions of the road 32.

[0036] 2A has a reflective surface on the +Y direction side, and is disposed on the right side of the road 32 in the traveling direction (+X direction). The leaky coaxial cable 80 is disposed on the reflective surface of the electromagnetic wave reflective fence 100A. The reflective surface of the electromagnetic wave reflective fence 100A disposed on the left side of the road 32 in the traveling direction (+X direction) is located on the -Y direction side, and therefore the leaky coaxial cable 80 is disposed on the -Y direction side of the electromagnetic wave reflective fence 100A. In this way, by providing the leaky coaxial cable 80 on the reflective surfaces of the electromagnetic wave reflective fences 100A on both sides of the road 32, it is possible to establish a wireless communication area along the road 32, even at a position far from the base station 33 in the traveling direction of the road 32.

[0037] The reflective panel 10 used in the electromagnetic wave reflecting device 60 reflects electromagnetic waves in the range of 1 MHz to 300 GHz, preferably 1 GHz to 100 GHz, and more preferably 1 GHz to 80 GHz. The reflective panel 10 has a layer containing a conductive film as a reflective film. The conductive film has a predetermined conductive pattern designed according to the desired reflection angle, frequency band, etc. The conductive pattern may include a periodic pattern, a mesh pattern, a geometric pattern, etc., and may be formed from a transparent conductive film. The reflective panel 10 has a protective layer with ultraviolet protection function as its outermost layer.

[0038] At least a portion of the reflective panel 10 may be a non-specular reflective surface in which the angle of incidence and the angle of reflection of electromagnetic waves differ. Non-specular reflective surfaces include diffusive and scattering surfaces, as well as metasurfaces, which are artificial reflective surfaces designed to reflect radio waves in a desired direction. It may be desirable for the reflective panels 10-1, 10-2, and 10-3 to be electrically connected to each other in order to maintain the continuity of the reflected potential. However, if a metasurface is included, electrical connection between adjacent reflective panels 10 is not necessary. By holding adjacent reflective panels 10 together with a frame 50A, an electromagnetic wave reflective fence 100A connected in the X direction is obtained.

[0039] In addition to the reflective panel 10 and the frame 50A, the electromagnetic wave reflecting device 60 may have legs 56 supporting the frame 50A. The legs 56 may allow the electromagnetic wave reflecting device 60 or the electromagnetic wave reflecting fence 100A to stand on the road surface. The legs 56 may be configured to be fixed to the road surface with screws, bolts, or the like. Conversely, the electromagnetic wave reflecting device 60 or the electromagnetic wave reflecting fence 100A may stand on the road surface and further include casters or other components to make it movable. In addition to the frame 50A, a top frame 57 that holds the upper end of the reflective panel 10 and a bottom frame 58 that holds the lower end may be used. In this case, the frame 50A, the top frame 57, and the bottom frame 58 form a frame that holds the entire periphery of the reflective panel 10. The frame 50A may be referred to as a "side frame" based on its position relative to the top frame 57 and the bottom frame 58. The provision of the top frame 57 and the bottom frame 58 ensures mechanical strength and safety during transportation and assembly of the reflective panel 10. The top frame 57 may be configured so that another reflective panel or a separate member such as an electromagnetic wave absorbing panel can be connected to the upper end of the reflective panel 10. This increases the flexibility in the size and function of the electromagnetic wave reflective fence 100A.

[0040] As an example, the leaky coaxial cable 80 is fixed to the frame 50A by a fixture 85. The fixture 85 may be any member capable of fixing the leaky coaxial cable 80 to the electromagnetic wave reflecting fence 100A. As an example, the fixture 85 may be a member formed in a mounting hole in the frame 50A, inserted into the mounting hole while holding the leaky coaxial cable 80, and fixed with a bolt or the like. Such a fixture 85 may be made of metal or resin.

[0041] As an example, the leaky coaxial cable 80 may be fixed to the electromagnetic wave reflecting fence 100A as follows. The height position of the leaky coaxial cable 80 from the floor surface may be equal to or lower than the height position of the upper ends of the plurality of electromagnetic wave reflecting devices 60 from the floor surface. By setting the height position of the leaky coaxial cable 80 from the floor surface equal to or lower than the height position of the upper ends of the plurality of electromagnetic wave reflecting devices 60 from the floor surface, the electromagnetic wave radiated from the slot 83A can be reflected by the electromagnetic wave reflecting devices 60 toward the center of the width direction of the road 32, and leakage of the radio waves to the outside of the electromagnetic wave reflecting devices 60 on both sides of the road 32 can be suppressed. Note that the height position of the leaky coaxial cable 80 from the floor surface may be higher than the height position of the upper ends of the plurality of electromagnetic wave reflecting devices 60 from the floor surface.

[0042] Furthermore, the multiple slots 83A of the leaky coaxial cable 80 may face toward the center in the width direction of the road 32. When the slots 83A face toward the center in the width direction of the road 32, radio waves emitted from the slots 83A can more easily reach the vehicle 31. Note that the multiple slots 83A of the leaky coaxial cable 80 may face in a direction other than the center in the width direction of the road 32, but facing only upward is not preferable from the viewpoint of communication efficiency.

[0043] Furthermore, the distance D in the width direction (Y direction) of the road 32 between the plurality of electromagnetic wave reflecting devices 60 and the leaky coaxial cable 80 may be set to a distance that satisfies D≠(¼+N)×λ, where λ is the wavelength of radio waves in free space and N is any natural number. Although not shown in Fig. 2A , the distance D is specifically the distance in the Y direction between the reflecting surface of the electromagnetic wave reflecting device 60 and the slot 83A located on the center side of the leaky coaxial cable 80 in the width direction of the road 32.

[0044] By the distance D satisfying this relationship, it is possible to prevent the radio waves emitted from the slot 83A of the leaky coaxial cable 80 toward the center of the width of the road 32 and the radio waves reflected by the electromagnetic wave reflecting device 60 toward the center of the width of the road 32 from being in opposite phase, thereby preventing the radio waves from canceling each other out.

[0045] Furthermore, the distance D between the plurality of electromagnetic wave reflecting devices 60 and the leaky coaxial cable 80 may be 0.3 m or less. If the distance D is long, the strength of the reflected wave that is reflected by the electromagnetic wave reflecting device 60 from the leaky coaxial cable 80 and propagates toward the center of the width direction of the road 32 will be low, so it is preferable that the leaky coaxial cable 80 is suitably close to the electromagnetic wave reflecting device 60.

[0046] The width of the road 32 may be 5 m to 20 m. Although it depends on the strength of the radio waves, when the strength is, for example, approximately 10 dBi to 30 dBi at most, this is a realistic distance at which the vehicle 31 can receive the radio waves radiated from the slots 83A of the leaky coaxial cables 80 arranged on both sides of the road 32 and acquire the data.

[0047] <Wireless Transmission System 1 Installed Indoors> Fig. 2B is a diagram showing an example of a factory production line 35 in which the wireless transmission system 1 of the embodiment is installed. In Fig. 2B, the wireless transmission system 1 is installed indoors. The production line 35 is a belt-shaped production site in which equipment and devices for assembly and production are arranged in a continuous flow. In the Industrial IoT (Internet of Things), industrial devices, equipment, management systems, etc. used in the production line 35 are connected to a network to improve production efficiency and ensure safety on site.

[0048] In order to connect the equipment on the production line 35 to the network, a base station 33, an electromagnetic wave reflecting device 60, and a leaky coaxial cable 80 are arranged, similar to the road 32 shown in Fig. 1A. In Fig. 2B, as an example, a plurality of AGVs (Automatic Guided Vehicles) are arranged as equipment used on the production line 35, and each AGV communicates with the base station 33 and the leaky coaxial cable 80 to be connected to the network. In the production line 35 shown in Fig. 2B, automobiles are manufactured, as an example.

[0049] To achieve wireless connection between the equipment on the production line 35 and the network, the base station 33, the electromagnetic wave reflector 60, and the leaky coaxial cable 80 provide a long horizontal wireless communication area. The technical specification (TS22.104) of the 3GPP (3rd Generation Partnership Project) (registered trademark), a mobile communications standardization organization, specifies a wireless communication area with a rectangular aspect ratio of 3 to 5 times in the horizontal plane as a system requirement. For example, the area size for a use case called "Motion Control" is specified as 50 m x 10 m x 10 m (length x width x height).

[0050] In order to cover the production line 35 with the wireless communication area provided by the base station 33, the electromagnetic wave reflecting devices 60, and the leaky coaxial cables 80 and realize network connection of the devices present in the production line 35, it is effective in terms of coverage to place multiple electromagnetic wave reflecting devices 60 on both sides of the production line 35 along the direction of travel of the production line 35 (+X direction) and to place the leaky coaxial cables 80 along the electromagnetic wave reflecting devices 60. This is similar to the road 32 shown in FIG. 1A.

[0051] In the coordinate system of Figure 2B, the length direction (travel direction) of the production line 35 is the X direction, the width direction is the Y direction, and the direction perpendicular to the floor surface is the Z direction. A large number of car bodies are transported on the production line 35. Figure 2B shows the production line 35 for car bodies as an example, but it may also be a production line for products other than vehicles. The AGVs and other equipment arranged around the production line 35 have wireless communication capabilities, and large amounts of data are transmitted and received between the AGVs and other equipment and the control and management system.

[0052] In the production line 35 shown in Figure 2B, a leaky coaxial cable 80 is fixed to the electromagnetic wave reflection device 60 on the +Y direction side. For example, the leaky coaxial cable 80 can be fixed to the electromagnetic wave reflection device 60 using a fixture 85 as shown in Figure 2A. For example, the height position of the electromagnetic wave reflection device 60 on the +Y direction side is lower than the height position of the upper end of the electromagnetic wave reflection device 60. Furthermore, for example, the height position of the base station 33 connected to the leaky coaxial cable 80 on the +Y direction side is lower than the height position of the top (upper end) of the electromagnetic wave reflection device 60 on the +Y direction side.

[0053] Furthermore, the leaky coaxial cable 80 on the -Y direction side is suspended from the ceiling by a stay 90. As an example, the height position of the leaky coaxial cable 80 on the -Y direction side is higher than the height position of the upper end of the electromagnetic wave reflection device 60 on the -Y direction side. As an example, the leaky coaxial cable 80 on the -Y direction side is located on the +Y direction side of the electromagnetic wave reflection device 60 on the -Y direction side in the Y direction. This is to propagate the reflected wave in the +Y direction side and to suppress leakage of radio waves in the -Y direction side of the electromagnetic wave reflection device 60 on the -Y direction side.

[0054] Also, as an example, the height position of the base station 33 connected to the leaky coaxial cable 80 on the −Y direction side is higher than the height position of the top (upper end) of the electromagnetic wave reflecting device 60. However, for example, by further lengthening the stay 90 that suspends the leaky coaxial cable 80 and lowering the position of a holder (not shown) that holds the base station 33, the height positions of the leaky coaxial cable 80 on the −Y direction side and the base station 33 may be lower than the height position of the top (upper end) of the electromagnetic wave reflecting device 60. This is advantageous for irradiating a beam from the directional antenna of the base station 33 toward the production line 35.

[0055] As shown in FIG. 2B, the wireless transmission system 1 can be installed indoors, and a leaky coaxial cable 80 can be used to realize a long wireless communication area in the direction in which the production line 35 travels.

[0056] <Layer structure of reflective panel 10> Fig. 3 is a diagram showing an example of the layer structure of the reflective panel 10. The layer structure shown in Fig. 3 is a layer structure in the XY cross section of the reflective panel 10, and the stacking direction is the thickness direction (Y direction) of the reflective panel 10. Fig. 3 shows, as an example, a cross section of the reflective panel 10 of an electromagnetic wave reflection device 60 arranged on the -Y direction side of a road 32 or a production line 35, as viewed from above (the +Z direction side).

[0057] The reflective panel 10 has a dielectric layer 11, a periodic conductive pattern 15 provided on one surface 111 of the dielectric layer 11, and a ground layer 12 provided on the other surface 112 of the dielectric layer 11. The conductive pattern 15 forms the reflective surface of the reflective panel 10 and reflects electromagnetic waves of 1 MHz or more and 300 GHz or less in a predetermined direction.

[0058] The conductive pattern 15 includes a periodic arrangement of a plurality of hollow patterns 151. The specific shape of the hollow patterns 151 will be described later with reference to FIG. 4 . The hollow patterns are formed of, for example, a good conductor such as Ag, Cu, Ni, or Al, and have a thickness of, for example, 0.01 mm or more and 0.05 mm or less. If the thickness is less than 0.01 mm, the surface resistivity becomes high, making it difficult to maintain high reflection efficiency. If the thickness is greater than 0.05 mm, it becomes difficult to maintain the flatness of the reflection surface. The surface of the conductive pattern 15 may be protected with a transparent film having a dielectric constant and dielectric loss tangent equivalent to those of the dielectric layer 11.

[0059] The hollow pattern 151 is bonded to the dielectric layer 11 by, for example, an adhesive layer 13. The adhesive layer 13 is not applied to the entire surface of the dielectric layer 11, but is applied in an amount necessary to stably support the hollow pattern 151. This is to minimize the effect of the adhesive layer 13 on the dielectric constant of the dielectric layer 11. The area occupied by the adhesive layer 13 does not need to be exactly the same as the area occupied by the conductive pattern 15, and may vary slightly as long as the hollow pattern 151 can be stably bonded to the dielectric layer 11. For example, if the area occupancy of the conductive pattern 15 with respect to the dielectric layer 11 is 10.0% or more and 45.0% or less, the area occupancy of the adhesive layer 13 with respect to the dielectric layer 11 is 9.0% or more and 50.0% or less.

[0060] If the area occupation ratio of the conductive pattern 15 is less than 10.0%, it becomes difficult to achieve the desired reflection characteristics and reflection efficiency. If the area occupation ratio of the conductive pattern 15 exceeds 45.0%, it becomes difficult to maintain the transparency of the reflective panel 10. However, in applications that do not require transparency, the area occupation ratio of the conductive pattern 15 may be set to more than 45.0% to prioritize reflection efficiency.

[0061] The adhesive layer 13 is made of a material capable of bonding the conductive pattern 15 to the dielectric layer 11, and may be made of a thermoplastic resin such as vinyl acetate resin, acrylic resin, cellulose resin, or silicone resin. The thickness of the adhesive layer 13 is such that the conductive pattern 15 can be stably bonded to the dielectric layer 11, and is, for example, 0.002 mm or more and 0.050 mm or less. From the viewpoint of ensuring adhesive strength, the thickness is desirably 0.010 mm or more and 0.050 mm or less.

[0062] The dielectric layer 11 is an insulating polymer film made of polycarbonate, cycloolefin polymer (COP), polyethylene terephthalate (PET), fluororesin, or the like, and has a thickness of approximately 0.3 mm to 1.0 mm. The dielectric layer 11 may be made of any material having a relative permittivity and dielectric loss tangent suitable for achieving the target reflection characteristics.

[0063] The ground layer 12 may be made of the same material as the conductive pattern 15, or may be made of a different conductive material. The ground layer 12 forms a predetermined parasitic capacitance between the conductive pattern 15 and the ground layer 12. The amount of phase delay is determined by the parasitic capacitance formed between the conductive pattern 15 and the ground layer 12.

[0064] As an example, the reflective panel 10 may be sandwiched between two dielectric substrates. Such dielectric substrates may be transparent to electromagnetic waves in the gigahertz to terahertz bands, specifically, electromagnetic waves in the range of 1 MHz to 3 THz, for example, 1 MHz to 300 GHz. The dielectric substrate is preferably formed as the outermost layer of the reflective panel 10 from a material with excellent impact resistance, durability, and transparency. Examples of materials that can be used as the dielectric substrate include polycarbonate, acrylic resin, and PET. The thickness of each dielectric substrate can be selected appropriately depending on the installation location, for example, between 1.0 mm and 10.0 mm. The thicknesses of the two dielectric substrates may be the same or different.

[0065] <Configuration Example of Hollow Pattern> Fig. 4 is a diagram showing an example of the configuration of a unit cell 20 of a conductive pattern 15 configured with a hollow pattern 151. Fig. 4 shows, as an example, the configuration of a reflection panel 10 of an electromagnetic wave reflection device 60 arranged on the -Y direction side of a road 32 or a production line 35, as viewed from the +Y direction side.

[0066] In the example shown in FIG. 4 , the unit cell 20 has six hollow patterns 151 a, 151 b, 151 c, 151 d, 151 e, and 151 f. The width W1 and length L of the hollow patterns 151 a to 151 f correspond to the width (X) and height (Z) directions of the reflective panel 10 in FIG. 2A , respectively. The hollow patterns 151 a to 151 f have the same width W1 and different lengths L, but their central axes are aligned (the Y coordinate position of the central axis is constant). The pitch or spacing G in the X direction is constant. The shape and size of the hollow patterns 151 a to 151 f control the phase of reflection, and the reflected waves are superimposed to form a reflected beam in the desired direction. In this example, the unit cell 20 is designed to reflect the reflected wave beam of electromagnetic waves incident perpendicularly (with an incident angle of 0°) in a direction 50° from the normal.

[0067] Hollow patterns 151a, 151b, 151c, 151d, 151e, and 151f (hereinafter sometimes collectively referred to as "hollow patterns 151") are hollowed out with a width W2. The hollow patterns have a rectangular annular shape when viewed in the XZ plane. The width of the vertical line segments is half the difference between the outer width W1 and the inner width W2 of each hollow pattern 151. Similarly, the thickness of the horizontal line segments of hollow pattern 151 is determined according to the area of ​​the hollowed out portion. The vertical and horizontal line segments of hollow pattern 151 enable reflection of both vertically polarized and horizontally polarized radio waves.

[0068] The corners of the outer edge of the hollow pattern 151 may be right angles without any curvature, or may be curved with a curvature radius R1. In the case of a right angle, the curvature radius R1 = 0.0 mm. The corners of the inner periphery of the hollow pattern 151 are curved with a curvature radius R2. The curvature radius R1 is the same as or smaller than R2. By rounding the corners of the hollow pattern 151, particularly the corners on the inner edge side, with a predetermined curvature radius, current concentration is prevented and reflection efficiency is maintained. Specifically, by rounding the corners on the inner edge side of the hollow pattern 151 with a curvature radius R2 that is between 1 / 10 and 1 / 2 of the width W1, current concentration is suppressed while enabling response to both vertically polarized waves and horizontally polarized waves.

[0069] The conductive pattern 15 is a periodic pattern in which unit cells 20 are repeatedly arranged in the X and Z directions. By providing a reflective surface formed by the conductive pattern 15 on at least a part of the reflective panel 10, it becomes possible to reflect both horizontally polarized and vertically polarized electromagnetic waves that are incident in controlled directions.

[0070] <Experimental Results> An experiment was conducted in an indoor facility measuring 100.0 m in length, 50.0 m in width, and 10.0 m in ceiling height. A production line for assembling automotive parts was located in the center, and multiple structures such as metal racks, self-driving robots such as AGVs, and robot arms were located around the production line. In this indoor facility, a blind zone existed behind the structures when the electromagnetic wave reflecting device 60 and the leaky coaxial cable 80 were not installed. In the following, the width of the electromagnetic wave reflecting device 60 refers to the width in the X direction in FIG. 2B , and the height of the electromagnetic wave reflecting device 60 refers to the height in the Z direction.

[0071] Example 1 Example 1 is Example 1. A base station having an antenna with a maximum output of 20 dBm and a half-width of 15° vertically and 30° horizontally was placed at a position 7.5 m in the X direction from the end in the X direction of the electromagnetic wave reflecting device 60 connected to the base station and at a height of 5.0 m, and radio waves in the frequency band of 28.2 GHz were transmitted and received.

[0072] Thirty electromagnetic wave reflecting devices 60, each 1.0 m wide and 2.0 m high, were provided on both sides of the width direction of the production line, and these were connected along the production line to form a 30.0 m electromagnetic wave reflecting fence 100A. The electromagnetic wave reflecting fences 100A on both sides of the production line were spaced 10.0 m apart and arranged parallel to the production line.

[0073] A leaky coaxial cable 80 was installed on the reflecting surface of the electromagnetic wave reflecting device 60 of the electromagnetic wave reflecting fence 100A and connected to the antenna terminal of a base station. The slot 83A of the leaky coaxial cable 80 was oriented so that radio waves emitted from the slot 83A would propagate toward multiple structures, such as a production line, metal racks, autonomous robots such as AGVs, and robot arms. After installing the electromagnetic wave reflecting device 60 and the leaky coaxial cable 80, the radio wave intensity in the blind zone changed from -110.0 dBm to -85.0 dBm, confirming an improvement of +25.0 dB. Furthermore, the radio wave intensity outside the electromagnetic wave reflecting device 60 (the back side as viewed from the production line) remained unchanged at -125.0 dBm before and after installing the electromagnetic wave reflecting device 60 and the leaky coaxial cable 80.

[0074] Thus, in Example 1, it was confirmed that by installing the electromagnetic wave reflection device 60 and the leaky coaxial cable 80, the blind zones in the production line can be reduced and the leakage of radio waves outside the area where the electromagnetic wave reflection device 60 and the leaky coaxial cable 80 are installed can be suppressed.

[0075] Example 2 is Example 2. A base station having an antenna with a maximum output of 20 dBm and a half-width of 15° in the vertical direction and 30° in the horizontal direction was placed at a position 5.0 m in the X direction from the end in the X direction of electromagnetic wave reflecting device 60 connected to the base station and at a height of 10.0 m, and radio waves in the frequency band of 28.2 GHz were transmitted and received.

[0076] Thirty electromagnetic wave reflecting devices 60, each 1.0 m wide and 2.0 m high, were provided on both sides of the width direction of the production line, and these were connected along the production line to form a 30.0 m electromagnetic wave reflecting fence 100A. The electromagnetic wave reflecting fences 100A on both sides of the production line were spaced 10.0 m apart and arranged parallel to the production line.

[0077] A leaky coaxial cable 80 was suspended from the ceiling, installed 30 cm above the top end of the electromagnetic wave reflecting device 60 of the electromagnetic wave reflecting fence 100A, and connected to the antenna terminal of a base station. The slot 83A of the leaky coaxial cable 80 was oriented so that radio waves emitted from the slot 83A would propagate toward multiple structures, such as a production line, metal racks, autonomous robots such as AGVs, and robot arms. After installing the electromagnetic wave reflecting device 60 and the leaky coaxial cable 80, the radio wave intensity in the blind zone changed from -110.0 dBm to -92.0 dBm, confirming an improvement of +18.0 dB. Furthermore, the radio wave intensity outside the electromagnetic wave reflecting device 60 (the back side as viewed from the production line) remained unchanged at -125.0 dBm before and after installing the electromagnetic wave reflecting device 60 and the leaky coaxial cable 80.

[0078] Thus, in Example 2, it was confirmed that the installation of the electromagnetic wave reflecting device 60 and the leaky coaxial cable 80 reduced blind zones in the production line and suppressed leakage of radio waves outside the area where the electromagnetic wave reflecting device 60 and the leaky coaxial cable 80 were installed. Compared to Example 1, the improvement in radio wave intensity was small, and it was found that placing the leaky coaxial cable 80 on the reflecting surface of the electromagnetic wave reflecting device 60 had a greater effect on improving radio wave intensity.

[0079] Example 3 Example 3 is Example 3. A base station having an antenna with a maximum output of 20 dBm and a half-width of 15° in the vertical direction and 30° in the horizontal direction was placed at a position 10.0 m in the X direction from the end in the X direction of electromagnetic wave reflecting device 60 connected to the base station and at a height of 10.0 m, and radio waves in the frequency band of 28.2 GHz were transmitted and received.

[0080] Thirty electromagnetic wave reflecting devices 60, each 1.0 m wide and 2.0 m high, were provided on both sides of the width direction of the production line, and these were connected along the production line to form a 30.0 m electromagnetic wave reflecting fence 100A. The spacing between the electromagnetic wave reflecting fences 100A on both sides of the production line was set to 20.0 m, and they were arranged parallel to the production line.

[0081] A leaky coaxial cable 80 was suspended from the ceiling, installed 50 cm above the top end of the electromagnetic wave reflecting device 60 of the electromagnetic wave reflecting fence 100A, and connected to the antenna terminal of a base station. The slot 83A of the leaky coaxial cable 80 was oriented so that radio waves emitted from the slot 83A would propagate toward multiple structures, such as a production line, metal racks, automated guided vehicle (AGV), and robot arms. After installing the electromagnetic wave reflecting device 60 and the leaky coaxial cable 80, the radio wave intensity in the blind zone changed from -110.0 dBm to -100.0 dBm, confirming an improvement of +10.0 dB. Furthermore, the radio wave intensity outside the electromagnetic wave reflecting device 60 (the back side as viewed from the production line) remained unchanged at -125.0 dBm before and after installing the electromagnetic wave reflecting device 60 and the leaky coaxial cable 80.

[0082] Thus, in Example 3, it was confirmed that by installing the electromagnetic wave reflecting device 60 and the leaky coaxial cable 80, it was possible to reduce blind zones in the production line and suppress leakage of radio waves outside the area where the electromagnetic wave reflecting device 60 and the leaky coaxial cable 80 were installed. Compared to Example 1, the improvement in radio wave intensity was small, and therefore it was found that placing the leaky coaxial cable 80 on the reflecting surface of the electromagnetic wave reflecting device 60 had a greater effect on improving radio wave intensity. Furthermore, compared to Example 2, increasing the height of the leaky coaxial cable 80 had a smaller effect on reducing blind zones.

[0083] Example 4 Example 4 is Comparative Example 1. In Example 4, an experiment was conducted by providing only the electromagnetic wave reflecting device 60 without providing the leaky coaxial cable 80. The experimental conditions for Example 4 were the same as those for Example 2, except that the leaky coaxial cable 80 was omitted.

[0084] The electromagnetic wave reflecting device 60 was placed at a position 5.0 m in the X direction from the end in the X direction of the connected base station having an antenna with a maximum output of 20 dBm and a half-width of 15° in the vertical direction and 30° in the horizontal direction, and at a height of 10.0 m, and radio waves in the frequency band of 28.2 GHz were transmitted and received.

[0085] Thirty electromagnetic wave reflecting devices 60, each 1.0 m wide and 2.0 m high, were provided on both sides of the width direction of the production line, and these were connected along the production line to form a 30.0 m electromagnetic wave reflecting fence 100A. The electromagnetic wave reflecting fences 100A on both sides of the production line were spaced 10.0 m apart and arranged parallel to the production line.

[0086] When radio waves were emitted from the base station antenna, it was confirmed that the radio wave strength in the blind zone changed from -110.0 dBm to -108.0 dBm, an improvement of only +2.0 dB. Furthermore, the radio wave strength outside the electromagnetic wave reflecting device 60 (the back side as seen from the production line) remained unchanged at -85.0 dBm.

[0087] Example 5 Example 5 is Comparative Example 2. In Example 5, an experiment was conducted without providing the electromagnetic wave reflection device 60 and only providing the leaky coaxial cable 80. The experimental conditions for Example 5 were the same as those for Example 2, except that the leaky coaxial cable 80 was omitted.

[0088] The electromagnetic wave reflecting device 60 was placed at a position 25.0 m in the X direction from the end in the X direction of the connected base station having an antenna with a maximum output of 20 dBm and a half-width of 15° in the vertical direction and 30° in the horizontal direction, and at a height of 10.0 m, and radio waves in the 28.2 GHz frequency band were transmitted and received.

[0089] Leaky coaxial cable 80 was placed at the same position as leaky coaxial cable 80 in Example 2 on both sides of the width direction of the production line, and the direction of slot 83A was set so that the radio waves emitted from slot 83A of leaky coaxial cable 80 connected to the antenna terminal of the base station would propagate toward multiple structures such as the production line, metal racks, autonomous traveling robots such as AGVs, and robot arms.

[0090] When radio waves were emitted from the slot 83A of the leaky coaxial cable 80, it was confirmed that the radio wave strength in the blind zone changed from -110.0 dBm to -108.0 dBm, an improvement of only +2.0 dB. Furthermore, the radio wave strength outside the production line remained unchanged at -115.0 dBm. The position outside the production line was the same as the position on the back side of the electromagnetic wave reflecting device 60 in Examples 1 to 4.

[0091] From the experimental results of Examples 1 to 5, it was confirmed that the installation of both the electromagnetic wave reflecting device 60 and the leaky coaxial cable 80 reduces blind zones in the production line and suppresses leakage of radio waves outside the area where the electromagnetic wave reflecting device 60 and the leaky coaxial cable 80 are installed. It was also confirmed that the effect of improving radio wave intensity in blind zones is greater when the leaky coaxial cable 80 is placed on the reflecting surface of the electromagnetic wave reflecting device 60 rather than at a position above the upper end of the electromagnetic wave reflecting device 60.

[0092] <Effects> The wireless transmission system 1 includes a plurality of electromagnetic wave reflecting devices 60 provided on both sides of the passage along the direction of travel of the passage and reflecting radio waves in a predetermined band selected from 1 MHz to 300 GHz, and a leaky coaxial cable 80 disposed in an area surrounded by the plurality of electromagnetic wave reflecting devices 60 provided on both sides of the passage and the floor of the passage and connected to the base station 33. This allows radio waves to be radiated along the passage via the leaky coaxial cable 80. Furthermore, the electromagnetic wave reflecting devices 60 can reflect radio waves within the area surrounded by the plurality of electromagnetic wave reflecting devices 60 provided on both sides of the passage and the floor of the passage, and can suppress leakage of radio waves outside the area.

[0093] Therefore, it is possible to provide a wireless transmission system 1 that achieves both an improvement in the radio wave propagation environment and suppression of radio wave leakage outside the required space.

[0094] Furthermore, the leaky coaxial cable 80 may be fixed to a plurality of electromagnetic wave reflecting devices 60. By using a plurality of electromagnetic wave reflecting devices 60, the leaky coaxial cable 80 can be easily arranged along the passage. Furthermore, since radio waves can be more reliably emitted from the leaky coaxial cable 80 into the passage, blind zones can be effectively reduced.

[0095] Alternatively, the area may have a ceiling, and the leaky coaxial cable 80 may be suspended from the ceiling. Utilizing the ceiling allows the leaky coaxial cable 80 to be easily arranged along the passageway. Furthermore, since the leaky coaxial cable 80 can more reliably radiate radio waves into the passageway, blind zones can be effectively reduced.

[0096] Furthermore, the height position of the leaky coaxial cable 80 may be equal to or lower than the height position of the upper ends of the plurality of electromagnetic wave reflection devices 60. Since a larger amount of radio waves radiated from the leaky coaxial cable 80 is reflected within the area surrounded by the plurality of electromagnetic wave reflection devices 60 provided on both sides of the passage and the floor surface of the passage, it is possible to more effectively reduce blind zones and suppress leakage of radio waves outside the area.

[0097] Furthermore, the leaky coaxial cable 80 may have a plurality of slots 83A that radiate radio waves, and the plurality of slots 83A may face the center of the passage in the width direction. By propagating the radio waves radiated from the slots 83A within an area surrounded by the plurality of electromagnetic wave reflecting devices 60 provided on both sides of the passage and the floor of the passage, it is possible to effectively reduce blind zones.

[0098] Furthermore, the distance D between the plurality of electromagnetic wave reflecting devices 60 and the leaky coaxial cable 80 may be a distance that satisfies D≠(¼+N)×λ, where λ is the wavelength of radio waves in free space and N is any natural number. This makes it possible to prevent radio waves radiated from the slot 83A of the leaky coaxial cable 80 toward the center of the width direction of the road 32 and radio waves reflected by the electromagnetic wave reflecting device 60 toward the center of the width direction of the road 32 from being in opposite phase, thereby making it possible to prevent the radio waves from canceling each other out.

[0099] Furthermore, the distance D between the plurality of electromagnetic wave reflecting devices 60 and the leaky coaxial cable 80 may be 0.3 m or less. If the distance D is long, the strength of the reflected wave that is reflected from the leaky coaxial cable 80 by the electromagnetic wave reflecting device 60 and propagates toward the center of the width of the road 32 will be low. Therefore, by placing the leaky coaxial cable 80 appropriately close to the electromagnetic wave reflecting device 60, the strength of the reflected wave will be increased, and blind zones can be reduced.

[0100] The width of the passage may be 5 m to 20 m. In a passage of such a practical width, it is possible to improve the radio wave propagation environment while suppressing radio wave leakage outside the required space.

[0101] While exemplary wireless transmission systems of the present disclosure have been described above, the present disclosure is not limited to the specifically disclosed embodiments, and various modifications and variations are possible without departing from the scope of the claims.

[0102] The following supplementary notes are further disclosed in relation to the above embodiments. (Supplementary Note 1) A wireless transmission system including: a plurality of electromagnetic wave reflecting devices provided on both sides of a passage along the direction of travel of the passage, the plurality of electromagnetic wave reflecting devices reflecting radio waves in a predetermined band selected from 1 MHz to 300 GHz; and a leaky coaxial cable located in an area surrounded by the plurality of electromagnetic wave reflecting devices provided on both sides of the passage and the floor of the passage, and connected to a base station. (Supplementary Note 2) The wireless transmission system according to Supplementary Note 1, wherein the leaky coaxial cable is fixed to the plurality of electromagnetic wave reflecting devices. (Supplementary Note 3) The wireless transmission system according to Supplementary Note 1, wherein the area has a ceiling, and the leaky coaxial cable is suspended from the ceiling. (Supplementary Note 4) The wireless transmission system according to any one of Supplements 1 to 3, wherein the height position of the leaky coaxial cable is equal to or lower than the height position of upper ends of the plurality of electromagnetic wave reflecting devices. (Supplementary Note 5) The wireless transmission system according to any one of Supplements 1 to 4, wherein the leaky coaxial cable has a plurality of slots that radiate radio waves, and the plurality of slots face the center in the width direction of the passage. (Supplementary Note 6) The wireless transmission system according to any one of Supplements 1 to 5, wherein a distance D between the plurality of electromagnetic wave reflecting devices and the leaky coaxial cable satisfies D≠(1 / 4+N)×λ, where λ is the wavelength of the radio waves in free space and N is an arbitrary natural number. (Supplementary Note 7) The wireless transmission system according to any one of Supplements 1 to 6, wherein the distance D between the plurality of electromagnetic wave reflecting devices and the leaky coaxial cable is 0.3 m or less. (Supplementary Note 8) The wireless transmission system according to any one of Supplements 1 to 7, wherein a width of the passage is 5 m to 20 m.

[0103] This international application claims priority based on Japanese Patent Application No. 2023-194312, filed on November 15, 2023, the entire contents of which are incorporated herein by reference.

[0104] 1 Wireless transmission system 32 Road (an example of a passage) Base station 33 35 Production line (an example of a passage) 60 Electromagnetic wave reflecting device 80 Leaky coaxial cable 83A Slot 85 Fixture 90 Stay

Claims

1. A wireless transmission system comprising: a plurality of electromagnetic wave reflecting devices provided on both sides of a passage along the direction of travel of the passage, which reflect radio waves in a predetermined band selected from 1 MHz to 300 GHz; and a leaky coaxial cable located within an area surrounded by the plurality of electromagnetic wave reflecting devices provided on both sides of the passage and the floor of the passage, and connected to a base station.

2. The wireless transmission system of claim 1, wherein said leaky coaxial cable is fixed to said plurality of electromagnetic wave reflecting devices.

3. The wireless transmission system of claim 1, wherein the area has a ceiling and the leaky coaxial cable is suspended from the ceiling.

4. A wireless transmission system according to any one of claims 1 to 3, wherein the height position of the leaky coaxial cable is lower than the height position of the upper ends of the plurality of electromagnetic wave reflecting devices.

5. The wireless transmission system according to claim 1, wherein the leaky coaxial cable has a plurality of slots for radiating radio waves, the plurality of slots facing toward the center in the width direction of the passage.

6. A wireless transmission system as described in claim 1, wherein the distance D between the plurality of electromagnetic wave reflecting devices and the leaky coaxial cable is a distance that satisfies D ≠ (1 / 4 + N) × λ, where λ is the wavelength of the radio wave in free space and N is any natural number.

7. The wireless transmission system according to claim 1, wherein the distance D between said plurality of electromagnetic wave reflecting devices and said leaky coaxial cable is 0.3 m or less.

8. The wireless transmission system of claim 1, wherein the width of the passage is between 5m and 20m.

Images