WO2020149407A1 - Leaky waveguide - Google Patents

Abstract

A leaky waveguide is configured by forming metal tubes for propagating electromagnetic waves in such a manner that a cross-section thereof is a flat-circular shape and the metal tubes each have a first opening and a second opening with the distance between the centers of these openings being longer than a half-wave length. The plurality of first openings and second openings are mutually parallel. The plurality of first openings are positioned such that a line connecting the centers thereof is parallel to the axial direction of the metal tubes. The distance between the centers of adjacent ones of the plurality of first openings positioned such that the line connecting the centers thereof is parallel to the axial direction of the metal tubes is approximately equal to the wavelength of the electromagnetic waves. The plurality of second openings are positioned such that a line connecting the centers thereof is parallel to the axial direction of the metal tubes. The distance between the centers of adjacent ones of the plurality of second openings positioned such that the line connecting the centers thereof is parallel to the axial direction of the metal tubes is approximately equal to the wavelength of the electromagnetic waves.

Description

Leaky waveguide

The present invention relates to leaky waveguides.
The present application claims priority based on Japanese Patent Application No. 2019-007323 filed in Japan on January 18, 2019 and Japanese Patent Application No. 2019-007340 filed in Japan on January 18, 2019, and its contents Is used here.

There is known a communication system for performing wireless communication between a moving body such as an automobile or a train and a leaky coaxial cable laid along a moving route of the moving body. Until now, the frequency band of such wireless communication has been 0.7 GHz to 2 GHz, but in recent years, carrier companies have adopted the 3.5 GHz band, or the Wi-Fi service of the 2.4 GHz band or the 5 GHz band. With increasing demand, there is an urgent need to support high frequency bands. However, for example, in a high frequency band such as a 5 GHz band, a loss in a leaky coaxial cable is large. Therefore, it is proposed to use a leaky waveguide (LWG: Leaky Wave Guide) having a smaller loss in place of the leaky coaxial cable. (See FIG. 35).
A leaky waveguide is a hollow tube that has an opening in a conductor that constitutes the waveguide and allows electric waves propagating inside the tube to leak to the outside of the tube through the opening (see Patent Document 1). .. Since the conventional leaky waveguide has never been used for wireless communication between such a moving body and the leaky waveguide, the length of the leaky waveguide is about several meters. .. However, when a leaky waveguide is used for wireless communication between such a moving body and the leaky waveguide, a long leaky guide having a length of several tens to several hundred meters is used from the viewpoint of the efficiency of the laying work. Wave tubes are preferred. Therefore, there is an increasing need for manufacturing a leaky waveguide longer than the conventional leaky waveguide.
However, when such a long leaky waveguide is used, it is difficult to sufficiently realize the above wireless communication simply by manufacturing a leaky waveguide having a structure similar to the conventional one.

In explaining the difficulty of realizing it, first, two characteristics of the conventional leaky waveguide will be described.
The first feature (hereinafter referred to as “feature 1”) is that most of the cross sections of conventional leaky waveguides have an oval shape or an elliptical shape circumscribing a predetermined rectangle, and the opening has a predetermined shape. The feature is that it is located near the center of the long side of the rectangle.
The maximum radiation direction, which is the direction in which the radio wave radiated from the opening propagates with the highest intensity, is the direction in which the opening is viewed from the center of the cross section of the leaky waveguide. The maximum radiation direction is the direction in which the radio wave emitted from the opening propagates with the strongest intensity.
The second feature (hereinafter referred to as "feature 2") is that the conventional leaky waveguide bends in the axial direction without buckling. However, the conventional leaky waveguide has a fixed bending direction. The direction in which the axis of the conventional leaky waveguide bends is the direction of the long side of the predetermined rectangle viewed from the center of the predetermined rectangle.

When installing such a leaky waveguide along the moving path of a moving body, it is desirable from the viewpoint of communication efficiency that the maximum radiation direction be approximately the same as the direction of the moving body seen from the opening. Therefore, the leaky waveguide is installed with the opening facing the moving body. In such a case, the worker who installs the leaky waveguide does not have to simply install the leaky waveguide in a predetermined direction. Such a worker needs to find the position of the opening and install the leaky waveguide according to the installation location of the leaky waveguide so that the opening faces the direction of the moving body. Therefore, the burden on the worker for installing the leaky waveguide may increase.

When installing such a leaky waveguide along the moving path of a moving body, there are problems other than the burden on the worker who installs the opening toward the moving body. If the moving body only travels straight, it suffices to install the leaky waveguide with the opening facing the moving body in advance. However, the moving body may not only go straight, but may curve. In such a case, the leaky waveguide needs to be installed in a bent state. As described above, the leaky waveguide bends only in the direction of the long side of the predetermined rectangle viewed from the center of the predetermined rectangle (Feature 2 above). Therefore, the leaky waveguide needs to be installed so that the long side of a predetermined rectangle faces the direction of the moving body. By installing the leaky waveguide in this way, the leaky waveguide can be installed along the movement path of the moving body. However, due to the characteristic 1, in the conventional leaky waveguide, it is not always possible to make the maximum radiation direction substantially coincide with the direction of the moving body viewed from the opening. There is a problem to be described later due to the situation where the leaky waveguide is laid (hereinafter referred to as the laying destination). For example, it is conceivable to install the leaky waveguide at a laying destination having a curved section that can be installed only at a position diagonally above the moving body. In this case, in order to install the leaky waveguide along the moving path of the moving body, the conventional leaky waveguide is such that the long side of a predetermined rectangle of the leaky waveguide faces the moving body. Need to be installed. The curve section is a section in which the moving body curves. However, in such a case, since the conventional leaky waveguide has the feature 1, the maximum radiation direction is in the direction in which the maximum radiation direction crosses directly above the moving body. Therefore, the communication efficiency may be lower than that when the maximum radiation direction is substantially the same as the direction of the moving body viewed from the opening.

Japanese Patent Laid-Open No. 2003-179415

In view of the above circumstances, the present invention relates to a leaky waveguide installed along a moving path of a moving body, which suppresses a decrease in communication efficiency in wireless communication between the moving body and the leaky waveguide. It is intended to provide a waveguide.

A leaky waveguide according to one aspect of the present invention is a leaky waveguide wound around a drum for storage and transportation, and includes a metal tube that propagates electromagnetic waves, and the metal tube leaks the electromagnetic waves. The shape of the cross section of the metal pipe having a plurality of openings is substantially the same as a flat circular cross section, and the long side of a rectangle circumscribing the flat circular shape is substantially the same. An intersection of the vertical bisector and the surface of the metal tube is a central intersection, and a distance between the center of each of the plurality of openings and the central intersection is greater than 0. The distance between the centers of the first openings, which are a part of the openings, and the second openings, which are the rest of the plurality of openings, is longer than a half wavelength, and the number of the first openings and the The number of two openings is plural, respectively, the plurality of first openings are parallel to each other, the plurality of second openings are parallel to each other, and the plurality of first openings are parallel to each other. The part has a line connecting the centers located parallel to the axial direction of the metal pipe, and a line connecting the centers parallel to the axial direction of the metal pipe, among the plurality of first openings adjacent to each other. The distance between the centers of the first openings is substantially the same as the wavelength of the electromagnetic wave, and the plurality of second openings have a line connecting the centers positioned parallel to the axial direction of the metal tube, The distance between the centers of the adjacent second openings among the plurality of second openings in which the line connecting the centers is parallel to the axial direction of the metal tube is substantially the same as the wavelength of the electromagnetic wave.

In the leaky waveguide according to one aspect of the present invention, the first opening is a coordinate system having an origin at the center of the rectangle, and an axis Q passing through the origin and parallel to the short side of the rectangle is Q. In the Q coordinate system which is the coordinate system of the axis, the Q coordinate value is located in the first space which is 0 or a positive space, and the second opening is a space where the Q coordinate value is a negative space. It may be located in two spaces.

In the leaky waveguide according to one aspect of the present invention, the distance between the center of the first opening and the central intersection is within 19/40 of the long side, and the second opening is formed. The distance between the center and the central intersection may be within 19/40 of the long side.

In the leaky waveguide according to one aspect of the present invention, the distance between the center of the first opening and the central intersection is 7/40 or more of the long side, and the second opening is formed. The distance between the center of and the central intersection may be 7/40 or more of the long side.

In the leaky waveguide according to one aspect of the present invention, the metal tube further has a plurality of third openings for leaking the electromagnetic waves, and each of the plurality of third openings is the first opening. Each of the plurality of third openings is parallel to the first opening and has a shape similar to that of the portion between the center of each of the plurality of third openings and the central intersection point. Is greater than 0, and the distance between the center of the first opening and the center of each of the plurality of third openings may be less than half a wavelength.

In the leaky waveguide according to one aspect of the present invention, the metal tube further has a plurality of fourth openings for leaking the electromagnetic waves, and each of the plurality of fourth openings is the second opening. Each of the plurality of fourth openings is parallel to the second opening and has a shape similar to that of the portion between the center of each of the plurality of fourth openings and the central intersection point. May be greater than 0, and the distance between the center of each of the plurality of fourth openings and the center of the second opening may be less than half a wavelength.

In the leaky waveguide according to one aspect of the present invention, the surface of the metal tube may have wavy unevenness along the axial direction of the metal tube.

In the leaky waveguide according to one aspect of the present invention, the movement path may have a curve, and the metal tube may be bent so that the axial direction is substantially parallel to the movement path.

A leaky waveguide according to one aspect of the present invention is a leaky waveguide wound around a drum for storage and transportation, and includes a metal tube that propagates electromagnetic waves, and the metal tube leaks the electromagnetic waves. The metal tube has a plurality of first openings, and the shape of the cross section of the metal pipe is substantially the same as a flat circular cross section, and the length of a rectangle circumscribing the flat circular shape is substantially the same. The intersection of the vertical bisector of the side and the surface of the metal tube is the center intersection, and the distance between the center of each of the plurality of first openings and the center intersection is greater than 0. And the plurality of first openings are parallel to each other, and the line connecting the centers of the adjacent first openings of the plurality of first openings is parallel to the axial direction of the metal pipe. Therefore, the distance between the centers of the adjacent first openings of the plurality of first openings is substantially the same as the wavelength of the electromagnetic wave.

In the leaky waveguide according to one aspect of the present invention, the distance between the center of each of the plurality of first openings and the central intersection may be within 19/40 of the long side. Good.

In the leaky waveguide according to an aspect of the present invention, the distance between the center of each of the plurality of first openings and the central intersection may be 7/40 or more of the long sides. Good.

In the leaky waveguide according to one aspect of the present invention, the metal tube further has a plurality of second openings for leaking the electromagnetic waves, and each of the plurality of second openings is the first opening. Each of the plurality of second openings is parallel to the first opening, and has a shape similar to that of the portion between the center of each of the plurality of second openings and the central intersection point. May be greater than 0, and the distance between the center of each of the plurality of second openings and the center of the first opening may be less than half a wavelength.

In the leaky waveguide according to one aspect of the present invention, the surface of the metal tube may have wavy unevenness along the axial direction of the metal tube.

In the leaky waveguide according to one aspect of the present invention, the movement path may have a curve, and the metal tube may be bent so that the axial direction is substantially parallel to the movement path.

According to the above-described aspect of the present invention, a leaky waveguide that is installed along a moving path of a moving body and is capable of suppressing a decrease in communication efficiency in wireless communication with the moving body. Can be provided.

It is a partially broken perspective view which shows the concrete structure of the leaky waveguide 1 which concerns on 1st Embodiment of this invention. It is a figure which shows the specific example of the shape of the cross section of the metal tube 11 which concerns on 1st Embodiment of this invention. It is a top view and a sectional view showing a concrete shape of metal pipe 11 concerning a 1st embodiment of the present invention. It is a figure which shows the outline of the electromagnetic field component of a waveguide, and the distribution of the surface current which flows on the surface of a waveguide. It is a figure which shows the outline of the electromagnetic field component of a waveguide, and the distribution of the surface current which flows on the surface of a waveguide. It is a top view which shows the outline of distribution of the surface current of the metal tube 11 which concerns on 1st Embodiment of this invention. It is a figure which shows the experimental result of the radiation pattern which looked at from the cross section of the electromagnetic wave which the leaky waveguide 1 which concerns on 1st Embodiment of this invention radiates. 5 is an experimental result showing a difference in coupling loss due to a difference in arrangement of the slots 111 according to the first embodiment of the present invention. It is an explanatory view explaining a drum used for storage and transportation of leaky waveguide 1 concerning a 1st embodiment of the present invention. 6 is an experimental result showing the likelihood of buckling due to the difference in the position of the slot 111 according to the first embodiment of the present invention. FIG. 9 is an explanatory diagram illustrating a mechanism in which buckling occurs in a slot 111. FIG. 9 is an explanatory diagram illustrating a mechanism in which buckling occurs in a slot 111. FIG. 7 is a diagram showing a radial position where the center of the slot 111 is preferably located according to the first embodiment of the present invention. FIG. 3 is a top view showing a specific example of the metal tube 11 having an L-shaped slot 111 according to the first embodiment of the present invention. FIG. 3 is a top view showing a specific example of a crank-shaped metal tube 11 having a slot 111 according to the first embodiment of the present invention. FIG. 3 is a top view showing a specific example of the window-shaped metal tube 11 having the slot 111 according to the first embodiment of the present invention. FIG. 3 is a top view showing a specific example of the metal tube 11 having an elliptical slot 111 according to the first embodiment of the present invention. FIG. 6 is a top view showing a specific example of the metal tube 11 in which the slot 111 according to the first embodiment of the present invention is rectangular, and the long sides of the rectangle circumscribing the slot are not parallel to the axial direction. FIG. 6 is a top view showing a specific example of the metal tube 11 including the slot 111-1 and the slot 111-2 according to the first embodiment of the present invention. It is a partially broken perspective view which shows the concrete structure of the leaky waveguide 2 which concerns on 2nd Embodiment of this invention. It is a figure which shows the specific example of the shape of the cross section of the metal tube 21 which concerns on 2nd Embodiment of this invention. It is a top view and a sectional view showing a concrete shape of metal pipe 21 concerning a 2nd embodiment of the present invention. It is a figure which shows the outline of the electromagnetic field component of a waveguide, and the distribution of the surface current which flows on the surface of a waveguide. It is a figure which shows the outline of the electromagnetic field component of a waveguide, and the distribution of the surface current which flows on the surface of a waveguide. It is a top view which shows the outline of distribution of the surface current of the metal tube 21 which concerns on 2nd Embodiment of this invention. It is a figure which shows the experimental result of the radiation pattern which the electromagnetic wave which the leaky waveguide 2 which concerns on 2nd Embodiment of this invention radiates was seen from the cross section. 9 is an experimental result showing a difference in coupling loss due to a difference in arrangement of the slots 211 according to the second embodiment of the present invention. It is explanatory drawing explaining the drum used for storage and conveyance of the leaky waveguide 2 which concerns on 2nd Embodiment of this invention. 9 is an experimental result showing the likelihood of buckling due to the difference in the position of the slot 211 according to the second embodiment of the present invention. FIG. 9 is an explanatory diagram illustrating a mechanism in which buckling occurs in a slot 211. FIG. 9 is an explanatory diagram illustrating a mechanism in which buckling occurs in a slot 211. It is a figure which shows the position of the radial direction with which the center of the slot 211 based on 2nd Embodiment of this invention is located. It is a top view which shows the specific example of the metal tube 21 in which the slot 211 which concerns on 2nd Embodiment of this invention is L-shaped. It is a top view which shows the specific example of the metal tube 21 of the slot 211 which concerns on 2nd Embodiment of this invention. It is a top view which shows the specific example of the window type metal tube 21 with the slot 211 which concerns on 2nd Embodiment of this invention. It is a top view which shows the specific example of the metal tube 21 where the slot 211 which concerns on 2nd Embodiment of this invention is elliptical. It is a top view which shows the specific example of the metal tube 21 which the slot 211 which is 2nd Embodiment of this invention is rectangular, and the long side of a slot circumscribed rectangle is not parallel to an axial direction. It is a top view which shows the specific example of the metal tube 21 provided with the two slots 211 in the radial direction which concerns on 2nd Embodiment of this invention. It is a figure which shows the specific example of the communication system using a leaky waveguide.

(First embodiment)
FIG. 1 is a partially cutaway perspective view showing a specific configuration of a leaky waveguide 1 according to the first embodiment of the present invention. The leaky waveguide 1 is, for example, a long waveguide installed along a moving path of a moving body, and can propagate an electromagnetic wave to a long area and radiate it uniformly. It is a waveguide. The leaky waveguide 1 according to the first embodiment of the present invention can be used in an electromagnetic wave of 4 to 6 GHz, for example. The leaky waveguide 1 includes a metal tube 11 and an outer cover 12. The axial length of the leaky waveguide 1 is, for example, 50 m or more. The direction parallel to the axial direction of the leaky waveguide 1 is a direction substantially parallel to the movement path of the moving body. The movement route may have a curve.

The metal tube 11 is a hollow tube made of a metal material. The metal tube 11 propagates electromagnetic waves. The electromagnetic wave propagates through the hollow portion of the metal tube 11 in the axial direction of the metal tube 11. The shape of the cross section of the metal tube 11 is substantially the same as a flat circular cross section. The cross section is a plane perpendicular to the axial direction of the metal tube 11. The shape of the flat cross-section of the metal tube 11 that is substantially the same as the flat cross-section is circumscribed in a rectangle (hereinafter referred to as a “circumscribed rectangle in cross section”) in which the lengths of the long sides and the short sides satisfy predetermined conditions. The circumscribed rectangle in cross section is, for example, a rectangle in which the ratio of the length of the long side to the length of the short side is approximately equal to 2:1. The rectangle circumscribing the cross section may be, for example, a rectangle having a long side of 50 mm and a short side of 25 mm when the wavelength of the electromagnetic wave propagating through the metal tube 11 is 54 mm.

FIG. 2 is a diagram showing a specific example of the cross-sectional shape of the metal tube 11 according to the first embodiment.
The shape of the cross section of the metal tube 11 may be a rectangle shown in FIG. The shape of the cross section of the metal tube 11 may be a rounded rectangle shown in FIG. The shape of the cross section of the metal tube 11 may be an elliptical shape shown in FIG. The shape of the cross section of the metal tube 11 may be an ellipse as shown in FIG. The shape of the cross section of the metal tube 11 may be a ridge shape as shown in FIG. The shape of the cross section of the metal tube 11 may be a peanut shape shown in FIG.

For simplicity of explanation, it is assumed below that the shape of the cross section of the metal tube 11 is a rectangle or an oval.

Return to the explanation of Figure 1. Since the cross section of the metal pipe 11 is inscribed in the cross-section circumscribed rectangle, the metal pipe 11 is reversibly curved in the direction of the long side of the cross-section circumscribed rectangle viewed from the center of the cross-section circumscribed rectangle along the axial direction. Is possible. The direction of the long side of the rectangle circumscribing the cross section viewed from the center of the rectangle circumscribing the cross section is the direction parallel to the short side of the rectangle circumscribing the cross section. Hereinafter, the direction of the long side of the rectangle circumscribing the section viewed from the center of the rectangle circumscribing the section is referred to as the direction of the short side.

The metal tube 11 has a plurality of slots 111 on its surface. Some of the plurality of slots 111 (first slots) are located on the surface of the metal pipe 11 in the first space, and the rest of the plurality of slots 111 (second slots) are of the metal pipe 11 in the second space. Located on the surface. The first space is a coordinate system whose origin is the center of the rectangle circumscribing the cross section, and whose coordinate axis is the axis parallel to the short side of the rectangle circumscribing the cross section through the origin (hereinafter referred to as "Q coordinate system"). In, the value of the Q coordinate is 0 or a positive space. The second space is a space in which the value of the Q coordinate is negative.

The number of slots 111 located in the first space is plural. The number of slots 111 located in the second space is plural. The slots 111 located in the first space are located on substantially the same plane.
The slots 111 located in the second space are located on substantially the same plane.
The distance between the centers of the slot 111 located in the first space and the slot 111 located in the second space is half a wavelength or more.
For simplicity of description, the slot 111 located on the surface in the first space will be described below, but the description is similarly applied to the slot 111 located on the surface in the second space.

The slots 111 are holes whose centers are located at predetermined intervals S on the surface of the metal tube 11 along the axial direction. “Each interval S” means that the distance between the centers of the adjacent slots 111 (hereinafter referred to as “slot distance”) is S. The predetermined interval S is substantially the same as the wavelength λ.
Each slot 111 is parallel to each other. S is 35 mm, for example, if the frequency of the electromagnetic wave propagating through the metal tube 11 is 6 GHz.

The slot 111 has a shape having two-fold symmetry, is a line segment parallel to two symmetry axes orthogonal to the two-fold rotation axis, and has an end point that is an intersection of the slot circumscribed rectangle and the symmetry axis. Any shape may be used as long as one of the portions is longer than the other. The slot circumscribed rectangle is a rectangle that is larger than the slot 111 and includes the slot 111, and that minimizes the gap between the slot 111 and the slot 111. The shape of the slot 111 may be rectangular or oval, for example. Hereinafter, for simplicity of explanation, it is assumed that the shape of the slot 111 is rectangular.
The length of the long side and the length of the short side of the slot circumscribed rectangle may be any length depending on the frequency of the electromagnetic wave. For example, when the frequency of the electromagnetic wave is 6 GHz, the length of the long side is It may be 10 mm and the length of the short side may be 2 mm.
The direction of the rectangle circumscribing the slot may be any direction as long as it obstructs the current flowing in the circumferential direction on the surface of the leaky waveguide 1.
For simplicity of description below, it is assumed that the long sides of the slot circumscribed rectangle are parallel to the axial direction.
One of the line segments parallel to the axis of symmetry (first line segment) is parallel to the long side of the slot circumscribing rectangle and has the same length as the long side. The other (second line segment) parallel to the axis of symmetry is parallel to the short side of the slot circumscribing rectangle and has the same length as the short side.
The center of the slot 111 is the intersection of the plane or curved surface including the slot 111 and the two-fold rotation axis.

The metal tube 11 may be made of any substance as long as it has a high electric conductivity, and may be made of copper, for example. Although the metal tube 11 may have any thickness, it is preferably about 0.5 mm in consideration of mechanical strength. The metal tube 11 may be laminated. The size of the cross section of the metal tube 11 corresponds to the cutoff frequency for the electromagnetic wave to be propagated. The cutoff frequency is expressed by the following equation (1).

In Expression (1), f _c represents the cutoff frequency. In Expression (1), D represents the length of the long side of the rectangle circumscribing the section. The specific value of D is D=50 mm, for example, when the frequency of the electromagnetic wave to be propagated by the metal tube 11 is 6 GHz. Further, in this case, for example, the length of the short side of the rectangle circumscribing the cross section is, for example, 25 mm. When the length of the long side of the rectangle circumscribing the cross section is 50 mm and the length of the short side is 25 mm, the metal tube 11 blocks electromagnetic waves having a frequency of 3 GHz or less.
The electromagnetic wave propagating through the metal tube 11 is radiated to the outside from the slot 111.

FIG. 3 is a top view and a cross-sectional view showing a specific shape of the metal tube 11 according to the first embodiment.
FIG. 3A shows a top view of the metal tube 11. FIG. 3B shows a sectional view of the metal tube 11.
The shape of the slot 111 is a rectangle whose major axis direction is parallel to the axial direction. The slot 111 is located not at the center of the surface of the metal tube 11 but at the end thereof. The central portion of the surface of the metal tube 11 passes through the point where the long bisector of the long side of the rectangular circumscribed in section crosses the metal tube 11 and is parallel to the axial direction (hereinafter referred to as “surface central axis”). Is a region near. The end portion is an area other than the central portion of the surface of the metal tube 11. Hereinafter, the point where the long bisector of the long side of the circumscribed rectangle and the metal tube 11 intersect is referred to as the central intersection point.
Specifically, the central portion is an area within a range of (−5/40)×length D to (+5/40)×length D in the radial direction centering on the surface center axis.

The outer skin 12 is a polymer material such as polyethylene and covers the metal tube 11.

Effects obtained by the leaky waveguide 1 according to the first embodiment will be described with reference to FIGS. 4A, 4B, and 5.
FIG. 4A is a diagram schematically showing the distribution of surface current flowing on the surface of the waveguide. FIG. 4B is a diagram showing an outline of the electromagnetic field distribution of the waveguide. 4A and 4B, for simplification, description will be made assuming that the waveguide is a rectangular waveguide.

According to the Maxwell equation of electromagnetic field, since the boundary condition in the rectangular waveguide is satisfied, the magnetic field lines representing the direction of the magnetic field form a closed ring in the waveguide. According to the Maxwell equation of the electromagnetic field, the boundary condition in the rectangular waveguide is satisfied, so that the electric force line representing the electric field is oriented in the direction perpendicular to the magnetic field. According to the Maxwell equation of the electromagnetic field, the boundary condition in the rectangular waveguide is satisfied, so that a part of the surface current flows in the direction in which the electromagnetic wave propagates at a position near the center. Further, according to the Maxwell equation of the electromagnetic field, since the boundary condition in the rectangular waveguide is satisfied, a part of the surface current flows on the surface of the waveguide in a direction perpendicular to the propagation direction of the electromagnetic wave.

FIG. 5 is a top view showing the outline of the distribution of the surface current of the metal tube 11 according to the first embodiment. In FIG. 5, for the sake of simplicity, description will be made assuming that the metal tube 11 is a rectangular waveguide.

A part of the surface current flowing on the surface of the metal tube 11 flows into the slot 111. The surface current flowing into the slot 111 forms an electric field in the hole of the slot 111 that oscillates in a direction parallel to the short side of the slot 111 and that oscillates at the same frequency as the surface current. This means that the slot 111 can be regarded as a virtual dipole moment that oscillates in the direction perpendicular to the axial direction.
Therefore, the slot 111 radiates an electromagnetic wave polarized in a direction perpendicular to the axial direction.
Further, since the inter-slot distance S is approximately the same as the wavelength λ, the dipole moment vibration phases of the respective slots 111 are approximately the same. This means that the phases of the electromagnetic waves emitted from the adjacent slots 111 are substantially the same. Therefore, the electromagnetic waves radiated from each slot 111 of the metal tube 11 reinforce each other and become a highly coherent electromagnetic wave, which is radiated from the metal tube 11.

FIG. 6 is a diagram showing an experimental result of a radiation pattern of an electromagnetic wave emitted by the leaky waveguide 1 according to the first embodiment as seen from a cross-sectional direction. The cross-sectional direction is a direction in which the cross-sectional circumscribed rectangle is viewed from the axial position of the metal tube 11. The frequency of the electromagnetic wave in FIG. 6 is 5.6 GHz. In FIG. 6, the long side of the rectangle circumscribing the cross section is 50 mm, and the short side is 25 mm. The slot is located at a position of 15 mm in the radial direction of the metal tube 11 from the central intersection.
Since the central point of the slot 111 is not located at the central intersection, it can be seen that the direction of maximum radiation intensity (hereinafter referred to as “maximum radiation direction”) is not 0°. Note that the direction of 0° is a direction in which the central intersection is viewed from the center of the rectangle circumscribing the cross section.

FIG. 7 is an experimental result showing a difference in coupling loss of vertically polarized waves due to a difference in arrangement of the slots 111 according to the first embodiment. In FIG. 7, vertical polarization means vertical polarization with respect to the axial direction. The coupling loss is expressed by the following equation (2).

In Expression (2), L _c represents a coupling loss. In Equation (2), P _in represents the input power to the leaky waveguide 1. In Expression (2), P _out represents the output power received by the receiving antenna. The receiving antenna is an antenna installed at a predetermined position with respect to the leaky waveguide 1 in order to measure the coupling loss. The receiving antenna is, for example, a half-wavelength dipole antenna.

In FIG. 7, the leaky waveguide A is a leaky waveguide in which the centers of the slots 111 are at the central intersections, the distances between the centers are approximately equal to a half wavelength, and the adjacent slots 111 are arranged alternately. It is a tube. The adjacent slots 111 being staggered means that the adjacent slots 111 are opposite to each other. The leaky waveguide A is a leaky waveguide whose slot shape and slot arrangement are the same as those of the conventional leaky waveguide. In FIG. 7, the long side of the slot 111 of the leaky waveguide A has a length of 10 mm, and the short side has a length of 2 mm.

7, in the leaky waveguide B, the center of the slot 111 is located at a position of 15 mm in the radial direction of the metal tube 11 from the central intersection, the distance between the centers is substantially equal to a half wavelength, and the leaky waveguides B are adjacent to each other. It is a leaky waveguide in which slots 111 are alternately arranged. In FIG. 7, the long side of the slot 111 of the leaky waveguide B has a length of 10 mm, and the short side has a length of 2 mm.

In FIG. 7, the leaky waveguide C has a slot 111 whose center is located at a position of 15 mm in the radial direction of the metal tube 11 from the center intersection point, a distance between the centers is substantially the same as the wavelength, and adjacent slots are adjacent to each other. 111 is a leaky waveguide arranged parallel to each other. That is, the leaky waveguide C is the leaky waveguide 1. In FIG. 7, the long side of the slot 111 of the leaky waveguide C has a length of 13 mm, and the short side has a length of 2 mm.

In FIG. 7, the leaky waveguide A, the leaky waveguide B, and the leaky waveguide C are located at 0.1 m to 0.7 m in the length direction of the cable.
FIG. 7 shows that the leaky waveguide B has a larger coupling loss than the leaky waveguide A by about 5 dB.
Further, FIG. 7 shows that the leakage waveguide C has a smaller coupling loss than the leakage waveguide B and is closer to the coupling loss of the leakage waveguide A. From this, it is understood that in the conventional leaky waveguide, the coupling efficiency is lowered by merely shifting the position of the slot 111 in the radial direction. Even when the position of the slot 111 is displaced from the central intersection in the radial direction, as long as the central tube distance of the slot 111 is substantially the same as the wavelength and the slots 111 are parallel to each other, it is a conventional practice. It is shown that a coupling efficiency equivalent to that of the leaky waveguide of 1 is realized.
As described above, when the slots 111 are located at positions radially displaced from the central intersection, if the slots 111 are parallel to each other, an increase in coupling loss is suppressed.
Since the center-to-center distance of the slots 111 of the leaky waveguide C is approximately twice the center-to-center distance of the slots 111 of the leaky waveguide B, the number of slots 111 of the leaky waveguide C is This is half the number of slots 111 of the wave tube B. Further, the energy of the electromagnetic wave leaking from the slot of the leaky waveguide increases or decreases in proportion to the length of the long side of the slot. Therefore, if the length of the long side of the slot 111 of the leaky waveguide C is twice the length of the long side of the slot 111 of the leaky waveguide B, the energy of the electromagnetic wave leaking from the leaky waveguide C is The amount should be the same as the amount of energy of the electromagnetic wave leaking from the leaky waveguide B, and the coupling loss should be almost the same. However, the experimental result of FIG. 7 shows that the length of the long side of the slot 111 of the leaky waveguide C is 1.3 times the length of the long side of the slot 111 of the leaky waveguide B, which is 2 times or less. If so, the coupling loss of the leaky waveguide C is smaller than that of the leaky waveguide B. This means that the slots 111 are parallel to each other when the positions of the slots 111 are displaced from the central intersection in the radial direction and the central tube distance of the slots 111 is substantially equal to the wavelength. This means that the effect of suppressing an increase in coupling loss is exerted.

In the leaky waveguide 1, the distance between the centers of the slots 111 is the wavelength length, unlike the conventional leaky waveguide in which the distance between the centers of the slots is half the wavelength. Therefore, the distance between the centers of the slots is longer than that of the conventional leaky waveguide. Therefore, the leaky waveguide 1 can be provided with the slot 111 longer than the conventional one while maintaining the strength of resistance to buckling of the metal tube 11.

Here, consider the situation in which the leaky waveguide 1 is laid. The leaky waveguide 1 has a length of 50 m or more. Therefore, when storing and transporting the leaky waveguide 1 to be laid, it is practical to store and transport the leaky waveguide 1 by winding it around a drum having a predetermined radius of curvature. In such a case, since stress is applied to the leaky waveguide 1, buckling may occur in the slot 111. Therefore, the buckling of the leaky waveguide 1 will be considered below.

FIG. 8 is an explanatory diagram illustrating a drum used for storage and transportation of the leaky waveguide 1 according to the first embodiment.
The leaky waveguide 1 is stored or transported while being wound around a drum having a diameter of 1400 mm. In FIG. 8, the diameter of the winding body of the drum around which the leaky waveguide 1 is wound is 1400 mm, but the diameter does not necessarily have to be 1400 mm. The diameter of the winding body of the drum may be, for example, in the range of 1000 to 2000 mm.

FIG. 9 is an experimental result showing the likelihood of buckling due to the difference in the position of the slot 111 according to the first embodiment.
FIG. 9 shows a case where the leakage waveguide 1 in which the slot 111 is located at a position 21 mm in the radial direction from the central intersection is bent so as to have a predetermined radius of curvature, and when the slot 111 is 24 mm in the radial direction from the central intersection. The values of VSWR (voltage standing wave ratio) when the leaky waveguide 1 located at a position is bent to have a predetermined radius of curvature are shown.
As shown in FIG. 9, when the leaky waveguide 1 in which the slot 111 is located at a position of 24 mm in the radial direction from the central intersection is bent so as to have a predetermined curvature radius, the slot 111 is radially moved from the central intersection. The value of VSWR is smaller than that when the leaky waveguide 1 located at the position of 21 mm is bent to have a predetermined radius of curvature. This means that when the leaky waveguide 1 in which the slot 111 is located at a position 24 mm in the radial direction from the central intersection is bent so as to have a predetermined radius of curvature, buckling occurs, and the slot 111 is separated from the central intersection. It shows that no buckling occurs when the leaky waveguide 1 located at a position of 21 mm in the radial direction is bent so as to have a predetermined radius of curvature.
As described above, the difference in the radial position of the slot 111 affects the likelihood of buckling.

10A and 10B are explanatory views for explaining the mechanism of buckling in the slot 111. In FIG. 10, for simplicity of explanation, it is assumed that the cross section has an oval shape.
FIG. 10A is an explanatory diagram illustrating a pressure applied to the slot 111 located in the central portion. FIG. 10B is an explanatory diagram illustrating the pressure applied to the slot 111 located at the end. 10A and 10B are side views of the metal tube 11. 10A and 10B, the metal tube 11 is curved in the short side direction (that is, the Z-axis direction).
Due to the bending of the metal tube 11, compressive stress and tensile stress are applied to the slot 111.
Buckling is caused by the difference between compressive stress and tensile stress. The greater the difference between the compressive stress and the tensile stress, the more likely buckling will occur at the position near the slot 111. The difference in force is proportional to the difference in bending radius due to bending between the location where compressive stress is applied and the location where tensile stress is applied.

In FIG. 10A, since the slot 111 is located at the center of the metal tube 11, the difference between the compressive stress and the tensile stress in FIG. 10A is proportional to the thickness of the surface of the metal tube 11.
When the thickness of the surface of the metal tube 11 is substantially the same as 0, the difference in force between the compressive stress and the tensile stress is substantially the same as 0.
Further, in FIG. 10B, since the slot 111 is located at the end of the metal tube 11, the difference between the compressive stress and the tensile stress in FIG. 10B is proportional to the length of the short side of the slot 111. The length of the short side of the slot 111 is thicker than the thickness of the surface of the metal tube 11.
For example, the length of the short side of the slot 111 is 25 mm, and the thickness of the surface of the metal tube 11 is 0.5 mm.
Therefore, when the slot 111 is located at the end of the metal tube 11 as shown in FIG. 10B, the compressive stress and tensile force are higher than when the slot 111 is located at the center of the metal tube 11 as shown in FIG. 10A. The difference with the stress is large.

As described above, the closer the radial position of the slot 111 is to the end portion, the more easily buckling occurs. Therefore, in the leaky waveguide 1, the radial position of the slot 111 needs to be positioned at an appropriate position according to the diameter of the drum during transportation. The diameter of the drum during transportation is 1400 mm in consideration of actual operation.
According to the experimental results, when the diameter of the drum is 1400 mm, the radial position of the slot 111 is preferably within the range shown in FIG. The desirable radial position shown in FIG. 11 is the position of the slot 111 having the maximum radiation direction in a direction other than the direction of 0°, and the position of the slot 111 whose resistance to buckling is a predetermined strength or more. The predetermined strength is the strength that does not buckle against bending such that the radius of curvature is 700 mm.

FIG. 11 is a diagram showing a radial position where the center of the slot 111 according to the first embodiment is preferably located.
In order for the slot 111 to have the maximum radiation direction in a direction other than the direction of 0°, the slot 111 may be located anywhere as long as the center is located at a position radially separated from the central intersection by a finite length.
However, since there is a limitation due to the manufacturing technique of the slot 111, it is desirable that the center of the slot 111 is located at a position distant from the central intersection in the radial direction by 7/40 or more of the length of the long side of the rectangle circumscribing the section.
Further, it is desirable that the slot 111 is located at a position where buckling does not occur with bending such that the radius of curvature is 700 mm. According to the experimental results, such a position is a position where the distance from the central intersection is within 19/40 of the length of the long side of the rectangle circumscribing the cross section.
Due to such factors, the radial position where the center of the slot 111 is preferably located is the position shown in FIG. That is, the radial position where the center of the slot 111 is preferably located is a position where the distance from the central intersection is 7/40 or more and 19/40 or less of the length of the long side of the rectangle circumscribing the section.

Up to this point, the description has been made assuming that the shape of the slot 111 is an ellipse or a rectangle. However, the shape of the slot 111 does not necessarily have to be oval or rectangular. The shape of the slot 111 may be L-shaped, crank-shaped, window-shaped, or elliptical.
FIG. 12 is a top view showing a specific example of the metal tube 11 having the L-shaped slot 111 according to the first embodiment.
The L-shape is a shape similar to the letter "L" in the alphabet, as shown in FIG.
Such an L-shaped slot 111 produces a dipole moment in the radial and axial directions. Therefore, the metal tube 11 having the L-shaped slot 111 can generate not only the polarized wave in the radial direction (vertical polarized wave) but also the polarized wave in the axial direction (horizontal polarized wave). Therefore, the metal tube 11 having the L-shaped slot 111 has an effect of transmitting information without depending on the polarization direction of the antenna on the reception side of electromagnetic waves.
FIG. 13 is a top view showing a specific example of the crank-shaped metal tube 11 having the slots 111 according to the first embodiment.
The crank-shaped slot 111 has a structure that is bent in a step shape on the surface of the metal tube 11 along the axial direction.
Such a crank type slot 111 produces a dipole moment in the radial and axial directions. Therefore, the metal tube 11 having the crank type slots 111 can generate not only the polarized wave in the radial direction (vertical polarized wave) but also the polarized wave in the axial direction (horizontal polarized wave). Therefore, the metal tube 11 having the crank-shaped slot 111 has an effect of transmitting information without depending on the polarization direction of the antenna on the reception side of electromagnetic waves.

FIG. 14 is a top view showing a specific example of the window-shaped metal tube 11 having the slot 111 according to the first embodiment.
The window-shaped slot 111 has a longer short side than the rectangular slot 111. Therefore, the effect of hindering the surface current along the axial direction is greater than that of the rectangular slot 111. Therefore, the window-shaped slot 111 produces a dipole moment in the radial direction and the axial direction. Since the dipole moment is generated in the radial direction and the axial direction, the metal tube 11 having the window-shaped slot 111 also generates the axial polarization (horizontal polarization) in addition to the radial polarization (vertical polarization). Can be made. Therefore, the metal tube 11 having the window-shaped slot 111 has an effect of transmitting information without depending on the polarization direction of the antenna on the electromagnetic wave receiving side. Further, since such a window type has a long length in the radial direction, it has an effect that the manufacturer can easily process it.

FIG. 15 is a top view showing a specific example of the metal tube 11 having an elliptical slot 111 according to the first embodiment.
Since the elliptical slot 111 has a shorter side length than the rectangular slot 111, a dipole moment is generated in the radial direction and the axial direction like the window slot 111. Therefore, the metal tube 11 having the elliptical slot 111 can generate polarization in the axial direction (horizontal polarization) in addition to polarization in the radial direction (vertical polarization). Therefore, the metal tube 11 having the elliptical slot 111 has an effect of transmitting information without depending on the polarization direction of the antenna on the reception side of electromagnetic waves. Further, such an elliptic shape has a long radial length, like the window shape, and therefore has the effect of being easily processed by the manufacturer. Further, such an elliptical shape is more rounded than the window type. Therefore, the oval-shaped slot 111 has an effect that cracks are less likely to occur from the corners of the slot 111 than the window-shaped slot 111.

Up to this point, for simplicity of explanation, it has been assumed that the long sides of the slot circumscribed rectangle are parallel to the axial direction. However, the slot circumscribed rectangle does not necessarily need to have its long sides parallel to the axial direction. The slot circumscribed rectangle may be formed such that the long side is inclined at an angle with the axial direction.

FIG. 16 is a top view showing a specific example of the metal tube 11 in which the slot 111 according to the first embodiment is rectangular and the long sides of the rectangle circumscribing the slot are not parallel to the axial direction.
The rectangular slot 111 in which the long sides of such a slot-circumscribing rectangle are not parallel to the axial direction produces a dipole moment in the radial direction and the axial direction. Therefore, the metal tube 11 having the rectangular slot 111 in which the long sides of the slot-circumscribing rectangle are not parallel to the axial direction has the axial polarization (horizontal polarization) in addition to the radial polarization (vertical polarization). Can also be generated. Therefore, the metal tube 11 having the rectangular slot 111 whose long side of the slot circumscribed rectangle is not parallel to the axial direction has an effect that information can be transmitted without depending on the polarization direction of the antenna on the electromagnetic wave reception side. The shape of the slot 111 does not necessarily have to be rectangular, and may be oval, L-shaped, crank-shaped, or window-shaped. It may be oval.

Up to this point, the case where the metal tube 11 has only one slot 111 in the radial direction has been described. However, the metal tube 11 does not necessarily need to include only one slot 111 in the radial direction. The metal tube 11 may include a plurality of slots 111 in the radial direction. Hereinafter, a case where the metal tube 11 includes a plurality of slots 111 in the radial direction will be described. Further, hereinafter, for simplicity of explanation, it is assumed that the metal tube 11 includes two slots 111 in the radial direction. Further, of the two slots 111 provided in the radial direction, the slot 111 close to the surface central axis will be referred to as a slot 111-1, and the slot 111 far from the surface central axis will be referred to as a slot 111-2. Further, hereinafter, when the slot 111-1 and the slot 111-2 are not distinguished, they are referred to as the slot 111.

FIG. 17 is a top view showing a specific example of the metal tube 11 including the slot 111-1 and the slot 111-2 according to the first embodiment. The distance h between the centers of the adjacent slots 111-1 and 111-2 in the radial direction is equal to or less than a half wavelength. Therefore, the phases of the vibrations of the dipole moments excited in the slots 111-1 and 111-2 adjacent to each other in the radial direction are substantially the same. The intermediate distance S between the slots 111-1 and 111-2 adjacent to each other in the axial direction is substantially the same as the wavelength. Therefore, all the slots 111 included in the metal tube 11 vibrate in substantially the same phase. Therefore, the electromagnetic waves radiated from each slot 111 of the metal tube 11 reinforce each other and become a highly coherent electromagnetic wave, which is radiated from the metal tube 11.

The metal tube 11 does not need to have only two slots 111 in the radial direction, and may have three or more slots 111. In such a case, the distance between the centers of the plurality of slots 111 provided in the radial direction is equal to or less than half the wavelength between the center of the slot 111 closest to the central intersection and the center of the slot 111 farthest from the central intersection. It is located at a position that satisfies the condition.
The shape of the slot 111 in FIG. 17 does not necessarily have to be rectangular, and may be oval, L-shaped, crank-shaped, or window-shaped. The shape may be oval or elliptical.

Moreover, it is desirable that the centers of the plurality of slots 111 in the radial direction are located at a position where the distance from the central intersection is 7/40 or more and 19/40 or more of the length of the long side of the rectangle circumscribing the section.

The leaky waveguide 1 having a plurality of slots 111 thus configured in the radial direction has an effect of reducing the coupling loss as compared with the case where one slot 111 is provided in the radial direction.

The leaky waveguide 1 according to the first embodiment configured as described above includes the plurality of slots 111 arranged at the ends at wavelength intervals, and thus can radiate radio waves in directions other than the direction of 0°. it can. Therefore, for example, it is possible to suppress a decrease in communication efficiency in wireless communication with a moving body using the leaky waveguide 1 having a length of 50 m or more. Further, the leaky waveguide 1 configured as described above has an effect that it does not buckle during transportation even though it has a length of, for example, 50 m or more.

The inside of the metal tube 11 does not necessarily have to be hollow. In the leaky waveguide 1, the inside of the metal tube 11 may be a dielectric that transmits electromagnetic waves.

Note that the surface of the metal tube 11 may have wavy unevenness along the axial direction. When the metal tube 11 has wavy unevenness along the axial direction, it becomes possible to increase the angle of reversible bending in the direction of the long side of the circumscribed rectangle of the cross section when viewed from the center of the circumscribed rectangle of the cross section. In addition, the metal tube 11 does not necessarily need to have wavy unevenness in the propagation direction in the metal tube.

(How to make)
Hereinafter, a method of making the leaky waveguide 1 according to the first embodiment will be described. First, a flat copper laminate strip is produced. After that, the flat copper-laminated strip-shaped body wound around the drum of the delivery machine is continuously delivered to the forming part. This forming unit forms a circular forming machine for forming the copper laminate strip into a circular shape from the upstream side (feeding side of the copper laminate strip), and a flattened circular shape for the circular copper laminate strip. It has a flat forming machine. The copper laminate strip sent out to the forming part is curved by the circular forming part into a C shape, and one end edge and the other end edge in the width direction are overlapped to form a circular shape. At this time, the other end edge and one end edge of the copper laminate strip are overlapped to form a joint. Next, in the forming part, the copper laminate strip is heated by a heater to heat-bond the joint part. The method of heat fusion may be any method, for example, arc welding may be used. Next, the copper laminate strip is formed into an elliptical cross section by the flat forming part. In this way, the flat pipe body is formed.
In addition, the copper laminate strip may have an adhesive layer laminated on one surface of a copper tape (thin copper plate).

The flat pipe body having a flat circular cross section is then sent to a slot forming machine that forms a slot 111. The slot forming machine forms the slots 111 by laser, punching, cutting or the like.
The flat pipe body in which the slot 111 is formed is sent to the corrugating machine. The flat pipe body in which the slots 111 are formed has irregularities formed on its surface by a corrugating machine. The corrugating machine eccentrically fits the corrugating die onto the flat pipe body, externally fits the corrugated die, rotates the corrugating die, and sends the corrugating die in the longitudinal direction in synchronization with the rotation, thereby forming a (spiral) uneven wave. To form.
The corrugated flat pipe body is sent to a sinking die. The corrugated flat pipe body is formed into a predetermined cross section by a sinking die. The predetermined shape formed by the sinking die is a shape circumscribing a circumscribing rectangle in cross section, and is substantially the same as a flat circular cross section. The flat pipe body formed by the sinking die is the metal pipe 11.
After being formed by the sinking die, the metal tube 11 is sent to the sheath extruder. The sheath extruder coats the outside of the metal tube 11 with a polymer material such as polyethylene. The polymer material that covers the metal tube 11 is the outer cover 12.

It should be noted that the slot 111 located in the first space and the slot 111 located in the second space may be located in any of the respective spaces. For the slot 111 located in the first space and the slot 111 located in the second space, for example, the center position of the slot 111 passes through the origin of the Q coordinate system and is parallel to the long side of the circumscribed rectangle. It may be located at symmetrical positions with a plane including the axis and the axis parallel to the axial direction passing through the origin of the Q coordinate system. The slot 111 located in the first space and the slot 111 located in the second space are, for example, the center of the slot 111 located in the first space and the center of the slot 111 located in the second space. The position may be such that the minimum value of the axial distance between them is a half wavelength.
The slot 111 located in the first space and the slot 111 located in the second space may have different shapes.
Further, the number of radial slots 111 may be different between the first space and the second space. For example, a plurality of slots 111 may be located in the first space in the radial direction, and one slot 111 may be located in the second space in the radial direction.

The slot 111 is an example of the first opening, the second opening, the third opening, and the fourth opening. The slot 111 located in the first space is an example of the first opening and the third opening. The slot 111 located in the second space is an example of the second opening and the fourth opening. The slot 111-1 is an example of the first opening and the second opening. The slot 111-2 is an example of the third opening and the fourth opening.

(Second embodiment)
FIG. 18 is a partially cutaway perspective view showing a specific configuration of the leaky waveguide 2 according to the second embodiment of the present invention. The leaky waveguide 2 is, for example, a long waveguide installed along a moving path of a moving body, and can propagate an electromagnetic wave to a long area and radiate it uniformly. It is a waveguide. The leaky waveguide 2 according to the second embodiment of the present invention can be used in an electromagnetic wave of 4 to 6 GHz, for example. The leaky waveguide 2 includes a metal tube 21 and an outer cover 22. The axial length of the leaky waveguide 2 is, for example, 50 m or more. The direction parallel to the axial direction of the leaky waveguide 2 is substantially parallel to the moving path of the moving body. The movement route may have a curve.

The metal tube 21 is a hollow tube made of a metal material. The metal tube 21 propagates electromagnetic waves. The electromagnetic wave propagates through the hollow portion of the metal tube 21 in the axial direction of the metal tube 21. The shape of the cross section of the metal tube 21 is substantially the same as the flat circular cross section. The cross section is a plane perpendicular to the axial direction of the metal tube 21. A shape substantially identical to the flat circular cross section of the metal tube 21 is circumscribed into a rectangle (hereinafter referred to as a “circumscribed rectangle in cross section”) whose long sides and short sides satisfy predetermined conditions. The circumscribed rectangle in cross section is, for example, a rectangle in which the ratio of the length of the long side to the length of the short side is approximately equal to 2:1. The rectangle circumscribing the cross section may be, for example, a rectangle having a long side of 50 mm and a short side of 25 mm when the wavelength of the electromagnetic wave propagating through the metal tube 21 is 54 mm.

FIG. 19 is a diagram showing a specific example of the cross-sectional shape of the metal tube 21 according to the second embodiment.
The shape of the cross section of the metal tube 21 may be a rectangle shown in FIG. The shape of the cross section of the metal tube 21 may be a rounded rectangle as shown in FIG. The shape of the cross section of the metal tube 21 may be an elliptical shape shown in FIG. The shape of the cross section of the metal tube 21 may be an elliptical shape as shown in FIG. The shape of the cross section of the metal tube 21 may be a ridge shape as shown in FIG. The shape of the cross section of the metal tube 21 may be a peanut shape shown in FIG.

For simplicity of explanation, it is assumed below that the shape of the cross section of the metal tube 21 is rectangular or oval.

Return to the explanation of FIG. Since the cross-section of the metal tube 21 is inscribed in the cross-section circumscribed rectangle, the metal tube 21 is reversibly curved in the direction of the long side of the cross-section circumscribed rectangle viewed from the center of the cross-section circumscribed rectangle along the axial direction. Is possible. The direction of the long side of the rectangle circumscribing the cross section viewed from the center of the rectangle circumscribing the cross section is the direction parallel to the short side of the rectangle circumscribing the cross section. Hereinafter, the direction of the long side of the rectangle circumscribing the section viewed from the center of the rectangle circumscribing the section is referred to as the direction of the short side.

The metal tube 21 has a plurality of slots 211 on the surface. The plurality of slots 211 are located on substantially the same plane. The slots 211 are holes whose centers are located at predetermined intervals S on the surface of the metal tube 21 along the axial direction. “Each interval S” means that the center-to-center distance between adjacent slots 211 (hereinafter referred to as “slot distance”) is S. The predetermined interval S is substantially the same as the wavelength λ. Each slot 211 is parallel to each other. For example, S is 35 mm when the frequency of the electromagnetic wave propagating through the metal tube 21 is 6 GHz.

The shape of the slot 211 is a shape having a two-fold symmetry, is a line segment parallel to two symmetry axes orthogonal to the two-fold rotation axis, and has an end point that is an intersection of the slot circumscribed rectangle and the symmetry axis. Any shape may be used as long as one of the portions is longer than the other. The slot circumscribing rectangle is a rectangle that is larger than the slot 211 and that includes the slot 211 and that minimizes the gap with the slot 211. The shape of the slot 211 may be rectangular or oval, for example. Hereinafter, for simplicity of explanation, it is assumed that the shape of the slot 211 is rectangular.
The length of the long side and the length of the short side of the slot circumscribed rectangle may be any length depending on the frequency of the electromagnetic wave. For example, when the frequency of the electromagnetic wave is 6 GHz, the length of the long side is It may be 10 mm and the length of the short side may be 2 mm.
The orientation of the rectangle circumscribing the slot may be any orientation as long as it obstructs the current flowing in the circumferential direction on the surface of the leaky waveguide 2.
For simplicity of description below, it is assumed that the long sides of the slot circumscribed rectangle are parallel to the axial direction.
One of the line segments parallel to the axis of symmetry (first line segment) is parallel to the long side of the slot circumscribing rectangle and has the same length as the long side. The other (second line segment) parallel to the axis of symmetry is parallel to the short side of the slot circumscribing rectangle and has the same length as the short side.
The center of the slot 211 is the intersection of the plane or curved surface including the slot 211 and the two-fold rotation axis.

The metal tube 21 may be made of any substance as long as it has a high electric conductivity, and may be made of copper, for example. The metal tube 21 may have any thickness, but in consideration of mechanical strength, it is preferably about 0.5 mm. The metal tube 21 may be laminated. The size of the cross section of the metal tube 21 corresponds to the cutoff frequency for the electromagnetic wave to be propagated. The cutoff frequency is expressed by the following equation (3).

In Expression (3), f _c represents a cutoff frequency. In Expression (3), D represents the length of the long side of the rectangle circumscribing the cross section. The specific value of D is, for example, D=50 mm when the frequency of the electromagnetic wave to be propagated by the metal tube 21 is 6 GHz. Further, in this case, for example, the length of the short side of the rectangle circumscribing the cross section is, for example, 25 mm. When the length of the long side of the rectangle circumscribing the cross section is 50 mm and the length of the short side is 25 mm, the metal tube 21 blocks electromagnetic waves having a frequency of 3 GHz or less.
The electromagnetic wave propagating through the metal tube 21 is radiated to the outside from the slot 211.

20A and 20B are a top view and a cross-sectional view showing a specific shape of the metal tube 21 according to the second embodiment.
FIG. 20A shows a top view of the metal tube 21. FIG. 20B shows a sectional view of the metal tube 21.
The shape of the slot 211 is a rectangle whose major axis direction is parallel to the axial direction. The slot 211 is located not at the center of the surface of the metal tube 21 but at the end thereof. The central portion of the surface of the metal tube 21 passes through the point where the long bisector of the long side of the rectangle circumscribing the cross section intersects with the metal tube 21, and is an axis parallel to the axial direction (hereinafter referred to as "surface central axis"). Is a region near. The end portion is an area other than the central portion of the surface of the metal tube 21. Hereinafter, the point where the long bisector of the long side of the rectangle circumscribing the cross section and the metal tube 21 intersect is referred to as the central intersection point.
Specifically, the central portion is an area within a range of (−5/40)×length D to (+5/40)×length D in the radial direction centering on the surface center axis.

The outer skin 22 is a polymer material such as polyethylene and covers the metal tube 21.

The effect of the leaky waveguide 2 according to the second embodiment will be described with reference to FIGS. 21A, 21B, and 22.
FIG. 21A is a diagram showing an outline of the distribution of the surface current flowing on the surface of the waveguide. FIG. 21B is a diagram showing an outline of the electromagnetic field distribution of the waveguide. 21A and 21B, for simplification, description will be made assuming that the waveguide is a rectangular waveguide.

According to the Maxwell equation of electromagnetic field, since the boundary condition in the rectangular waveguide is satisfied, the magnetic field lines representing the direction of the magnetic field form a closed ring in the waveguide. According to the Maxwell equation of the electromagnetic field, the boundary condition in the rectangular waveguide is satisfied, so that the electric force line representing the electric field is oriented in the direction perpendicular to the magnetic field. According to the Maxwell equation of the electromagnetic field, the boundary condition in the rectangular waveguide is satisfied, so that a part of the surface current flows in the direction in which the electromagnetic wave propagates at a position near the center. Further, according to the Maxwell equation of the electromagnetic field, since the boundary condition in the rectangular waveguide is satisfied, a part of the surface current flows on the surface of the waveguide in a direction perpendicular to the propagation direction of the electromagnetic wave.

FIG. 22 is a top view showing the outline of the distribution of the surface current of the metal tube 21 according to the second embodiment. In FIG. 22, for the sake of simplicity, description will be given assuming that the metal tube 21 is a rectangular waveguide.

A part of the surface current flowing on the surface of the metal tube 21 flows into the slot 211. The surface current flowing into the slot 211 forms an electric field in the hole of the slot 211 that vibrates in the direction parallel to the short side of the slot 211 and that vibrates at the same frequency as the surface current. This means that the slot 211 can be regarded as a virtual dipole moment that oscillates in a direction perpendicular to the axial direction.
Therefore, the slot 211 radiates an electromagnetic wave polarized in a direction perpendicular to the axial direction.
Further, since the inter-slot distance S is approximately the same as the wavelength λ, the dipole moment vibration phases of the respective slots 211 are approximately the same. This means that the phases of electromagnetic waves emitted from the adjacent slots 211 are substantially the same. Therefore, the electromagnetic waves radiated from each slot 211 of the metal tube 21 strengthen each other and become an electromagnetic wave with high coherence, which is radiated from the metal tube 21.

FIG. 23 is a diagram showing an experimental result of a radiation pattern of an electromagnetic wave radiated by the leaky waveguide 2 according to the second embodiment as seen from a cross-sectional direction. The cross-sectional direction is the direction in which the cross-sectional circumscribed rectangle is viewed from the axial position of the metal tube 21. The frequency of the electromagnetic wave in FIG. 23 is 5.6 GHz. In FIG. 23, the long side of the rectangle circumscribing the cross section is 50 mm, and the short side is 25 mm. The slot is located at a position of 15 mm in the radial direction of the metal tube 21 from the central intersection.
Since the center point of the slot 211 is not located at the center intersection point, it can be seen that the direction of maximum radiation intensity (hereinafter referred to as “maximum radiation direction”) is not 0°. Note that the direction of 0° is a direction in which the central intersection is viewed from the center of the rectangle circumscribing the cross section.

FIG. 24 is an experimental result showing a difference in vertical polarization coupling loss due to a difference in arrangement of the slots 211 according to the second embodiment. In FIG. 24, vertical polarization means vertical polarization in the axial direction. The coupling loss is expressed by the following equation (4).

In Expression (4), L _c represents a coupling loss. In Equation (4), P _in represents the input power to the leaky waveguide 2. In Expression (4), P _out represents the output power received by the receiving antenna. The receiving antenna is an antenna installed at a predetermined position with respect to the leaky waveguide 2 in order to measure the coupling loss. The receiving antenna is, for example, a half-wavelength dipole antenna.

In FIG. 24, a leaky waveguide A is a leaky waveguide in which the centers of the slots 211 are at the central intersections, the center-to-center distances are substantially equal to a half wavelength, and the adjacent slots 211 are arranged alternately. Is. The staggering of the adjacent slots 211 means that the adjacent slots 211 are in opposite directions. The leaky waveguide A is a leaky waveguide whose slot shape and slot arrangement are the same as those of the conventional leaky waveguide. In FIG. 24, the long side of the slot 211 of the leaky waveguide A has a length of 10 mm, and the short side has a length of 2 mm.

24, in the leaky waveguide B, the center of the slot 211 is located at a position of 15 mm in the radial direction of the metal tube 21 from the center intersection point, the center-to-center distance is substantially equal to a half wavelength, and the adjacent slots are adjacent to each other. Reference numeral 211 is a leaky waveguide arranged alternately. In addition, in FIG. 24, the length of the long side of the slot 211 of the leaky waveguide B is 10 mm, and the length of the short side is 2 mm.

24, in the leaky waveguide C, the center of the slot 211 is located at a position of 15 mm in the radial direction of the metal tube 21 from the central intersection point, the center-to-center distance is substantially the same as the wavelength, and the adjacent slots 211 are adjacent to each other. Are leaky waveguides arranged in parallel with each other. That is, the leaky waveguide C is the leaky waveguide 2. In addition, in FIG. 24, the length of the long side of the slot 211 of the leaky waveguide C is 13 mm, and the length of the short side is 2 mm.

In FIG. 24, the leaky waveguide A, the leaky waveguide B, and the leaky waveguide C are located at 0.1 m to 0.7 m in the length direction of the cable.
FIG. 24 shows that the leaky waveguide B has a larger coupling loss than the leaky waveguide A by about 5 dB.
Further, FIG. 24 shows that the leakage waveguide C has a smaller coupling loss than the leakage waveguide B and is closer to the coupling loss of the leakage waveguide A. From this, it can be seen that in the conventional leaky waveguide, the coupling efficiency is lowered by merely shifting the position of the slot 211 in the radial direction. Further, even when the position of the slot 211 is located at a position displaced in the radial direction from the central intersection, if the central tube distance of the slot 211 is substantially the same as the wavelength and the slots 211 are parallel to each other, it is conventional. It is shown that a coupling efficiency equivalent to that of the leaky waveguide of 1 is realized.
In this way, when the slots 211 are located at positions displaced from the central intersection in the radial direction, if the slots 211 are parallel to each other, an increase in coupling loss is suppressed.
Since the distance between the centers of the slots 211 of the leaky waveguide C is approximately twice the distance between the centers of the slots 211 of the leaky waveguide B, the number of slots 211 of the leaky waveguide C is equal to This is half the number of slots 211 of the wave tube B. Further, the energy of the electromagnetic wave leaking from the slot of the leaky waveguide increases or decreases in proportion to the length of the long side of the slot. Therefore, if the length of the long side of the slot 211 of the leaky waveguide C is twice the length of the long side of the slot 211 of the leaky waveguide B, the energy of the electromagnetic wave leaking from the leaky waveguide C is The amount should be the same as the amount of energy of the electromagnetic wave leaking from the leaky waveguide B, and the coupling loss should be almost the same. However, the experimental result of FIG. 24 shows that the length of the long side of the slot 211 of the leaky waveguide C is 1.3 times the length of the long side of the slot 211 of the leaky waveguide B, which is 2 times or less. If so, the coupling loss of the leaky waveguide C is smaller than that of the leaky waveguide B. This means that the slots 211 are parallel to each other when the positions of the slots 211 are displaced from the central intersection in the radial direction and the central tube distance of the slots 211 is substantially equal to the wavelength. This means that the effect of suppressing an increase in coupling loss is exerted.

In the leaky waveguide 2, the distance between the centers of the slots 211 is the length of the wavelength, unlike the conventional leaky waveguide in which the distance between the centers of the slots is a half wavelength. Therefore, the distance between the centers of the slots is longer than that of the conventional leaky waveguide. Therefore, the leaky waveguide 2 can be provided with the slot 211 longer than the conventional one while maintaining the strength of the metal tube 21 against buckling.

Here, consider the situation in which the leaky waveguide 2 is laid. The leaky waveguide 2 has a length of, for example, 50 m or more. Therefore, when storing and transporting the leaky waveguide 2 to be laid, it is practical to store and transport the leaky waveguide 2 by winding it around a drum having a predetermined radius of curvature. In such a case, since stress is applied to the leaky waveguide 2, buckling may occur in the slot 211. Therefore, the buckling of the leaky waveguide 2 will be considered below.

FIG. 25 is an explanatory diagram illustrating a drum used for storage and transportation of the leaky waveguide 2 according to the second embodiment.
The leaky waveguide 2 is stored or transported while being wound around a drum having a diameter of 1400 mm. Note that, in FIG. 25, the diameter of the winding body of the drum around which the leaky waveguide 2 is wound is 1400 mm, but the diameter is not necessarily 1400 mm. The diameter of the winding body of the drum may be, for example, in the range of 1000 to 2000 mm.

FIG. 26 is an experimental result showing the likelihood of buckling due to the difference in the position of the slot 211 according to the second embodiment.
FIG. 26 shows a case where the slot 211 is bent so that the leaky waveguide 2 located at a position of 21 mm in the radial direction from the central intersection has a predetermined radius of curvature and the slot 211 has a radius of 24 mm in the radial direction from the central intersection. The values of VSWR (voltage standing wave ratio) when the leaky waveguide 2 positioned at a position is bent to have a predetermined radius of curvature are shown.
As shown in FIG. 26, when the leaky waveguide 2 in which the slot 211 is located at a position of 24 mm in the radial direction from the central intersection is bent so as to have a predetermined radius of curvature, the slot 211 is radially moved from the central intersection. The value of VSWR is smaller than that when the leaky waveguide 2 located at the position of 21 mm is bent to have a predetermined radius of curvature. This means that when the leaky waveguide 2 located at a position 24 mm in the radial direction from the central intersection point is bent so as to have a predetermined radius of curvature, buckling occurs, and the slot 211 is separated from the central intersection point. It shows that buckling does not occur when the leaky waveguide 2 located at a position of 21 mm in the radial direction is bent to have a predetermined radius of curvature.
As described above, the difference in the radial position of the slot 211 affects the likelihood of buckling.

27A and 27B are explanatory views for explaining a mechanism in which buckling occurs in the slot 211. 27A and 27B, it is assumed that the cross section has an oval shape for the sake of simplicity.
FIG. 27A is an explanatory diagram illustrating a pressure applied to the slot 211 located in the central portion. FIG. 27B is an explanatory diagram illustrating the pressure applied to the slot 211 located at the end. 27A and 27B are side views of the metal tube 21. 27A and 27B, the metal tube 21 is curved in the short side direction (that is, the Z-axis direction).
Due to the bending of the metal tube 21, compressive stress and tensile stress are applied to the slot 211.
Buckling is caused by the difference between compressive stress and tensile stress. The greater the difference between the compressive stress and the tensile stress, the more likely buckling will occur at the position near the slot 211. The difference in force is proportional to the difference in bending radius due to bending between the location where compressive stress is applied and the location where tensile stress is applied.

In FIG. 27A, since the slot 211 is located at the center of the metal tube 21, the difference between the compressive stress and the tensile stress in FIG. 27A is proportional to the thickness of the surface of the metal tube 21.
When the thickness of the surface of the metal tube 21 is substantially the same as 0, the force difference between the compressive stress and the tensile stress is substantially the same as 0.
27B, since the slot 211 is located at the end of the metal tube 21, the difference between the compressive stress and the tensile stress in FIG. 27B is proportional to the length of the short side of the slot 211. The length of the short side of the slot 211 is thicker than the thickness of the surface of the metal tube 21.
For example, the length of the short side of the slot 211 is 25 mm, and the thickness of the surface of the metal tube 21 is 0.5 mm.
Therefore, when the slot 211 is located at the end of the metal tube 21 as shown in FIG. 27B, the compressive stress and tensile force are higher than when the slot 211 is located at the center of the metal tube 21 as shown in FIG. 27A. The difference with the stress is large.

As described above, the closer the radial position of the slot 211 is to the end, the more easily buckling occurs. Therefore, in the leaky waveguide 2, the radial position of the slot 211 needs to be positioned at an appropriate position according to the diameter of the drum during transportation. The diameter of the drum during transportation is 1400 mm in consideration of actual operation.
According to the experimental results, when the diameter of the drum is 1400 mm, the radial position of the slot 211 is preferably in the range shown in FIG. The desirable radial position shown in FIG. 28 is the position of the slot 211 having the maximum radiation direction in a direction other than the direction of 0°, and the position of the slot 211 whose resistance to buckling is a predetermined strength or more. The predetermined strength is the strength that does not buckle against bending such that the radius of curvature is 700 mm.

FIG. 28 is a diagram showing a radial position where the center of the slot 211 is preferably located according to the second embodiment.
In order for the slot 211 to have the maximum radiation direction in a direction other than the direction of 0°, the slot 211 may be located anywhere as long as the center is located at a position finite distance in the radial direction from the central intersection.
However, since there is a limitation due to the manufacturing technology of the slot 211, it is desirable that the center of the slot 211 is located at a position distant from the central intersection in the radial direction by 7/40 or more of the length of the long side of the rectangle circumscribing the section.
Further, it is desirable that the slot 211 is located at a position where buckling does not occur with bending such that the radius of curvature is 700 mm. According to the experimental results, such a position is a position where the distance from the central intersection is within 19/40 of the length of the long side of the rectangle circumscribing the cross section.
Due to such factors, the radial position where the center of the slot 211 is preferably located is the position shown in FIG. That is, the radial position where the center of the slot 211 is preferably located is a position where the distance from the central intersection is 7/40 or more and 19/40 or less of the length of the long side of the rectangle circumscribing the cross section.

Up to this point, the description has been made assuming that the shape of the slot 211 is an ellipse or a rectangle. However, the shape of the slot 211 does not necessarily have to be oval or rectangular. The shape of the slot 211 may be L-shaped, crank-shaped, window-shaped, or elliptical.
FIG. 29 is a top view showing a specific example of the metal tube 21 having an L-shaped slot 211 according to the second embodiment.
As shown in FIG. 29, the L-shape is a shape similar to the letter "L" of the alphabet.
Such an L-shaped slot 211 produces a dipole moment in the radial and axial directions. Therefore, the metal tube 21 having the L-shaped slot 211 can generate polarization in the axial direction (horizontal polarization) in addition to polarization in the radial direction (vertical polarization). Therefore, the metal tube 21 having the L-shaped slot 211 has an effect of transmitting information without depending on the polarization direction of the antenna on the reception side of electromagnetic waves.
FIG. 30 is a top view showing a specific example of the crank-shaped metal tube 21 having the slots 211 according to the second embodiment.
The crank type slot 211 has a structure that is bent in a step shape on the surface of the metal tube 21 along the axial direction.
Such a crank type slot 211 produces a dipole moment in the radial and axial directions. Therefore, the metal tube 21 having the crank type slot 211 can generate not only the polarized wave in the radial direction (vertical polarized wave) but also the polarized wave in the axial direction (horizontal polarized wave). Therefore, the metal tube 21 having the crank type slot 211 has an effect that information can be transmitted without depending on the polarization direction of the antenna on the electromagnetic wave receiving side.

FIG. 31 is a top view showing a specific example of the window-shaped metal tube 21 having the slot 211 according to the second embodiment.
The window-shaped slot 211 has a shorter side length than that of the rectangular slot 211. Therefore, the effect of blocking the surface current along the axial direction is larger than that of the rectangular slot 211. Therefore, the window-shaped slot 211 produces a dipole moment in the radial direction and the axial direction. Since the dipole moment is generated in the radial direction and the axial direction, the metal tube 21 having the window-shaped slot 211 also generates the axial polarization (horizontal polarization) in addition to the radial polarization (vertical polarization). Can be made. Therefore, the metal tube 21 having the window-shaped slot 211 has an effect that information can be transmitted without depending on the polarization direction of the antenna on the reception side of electromagnetic waves. Further, since such a window type has a long length in the radial direction, it has an effect that the manufacturer can easily process it.

FIG. 32 is a top view showing a specific example of the metal tube 21 having an elliptical slot 211 according to the second embodiment.
Since the elliptical slot 211 has a shorter side length than the rectangular slot 211, it produces a dipole moment in the radial direction and the axial direction like the window type slot 211. Therefore, the metal tube 21 having the elliptical slot 211 can generate polarization in the axial direction (horizontal polarization) in addition to polarization in the radial direction (vertical polarization). Therefore, the metal tube 21 having the elliptical slot 211 has an effect of transmitting information without depending on the polarization direction of the antenna on the reception side of electromagnetic waves. Further, such an elliptic shape has a long radial length, like the window shape, and therefore has the effect of being easily processed by the manufacturer. Further, such an elliptical shape is more rounded than the window type. Therefore, the oval-shaped slot 211 has an effect that a crack is less likely to be generated from the corner of the slot 211 than the window-shaped slot 211.

Up to this point, for simplicity of explanation, it has been assumed that the long sides of the slot circumscribed rectangle are parallel to the axial direction. However, the slot circumscribed rectangle does not necessarily need to have its long sides parallel to the axial direction. The slot circumscribed rectangle may be formed such that the long side is inclined at an angle with the axial direction.

FIG. 33 is a top view showing a specific example of the metal tube 21 in which the slots 211 according to the second embodiment are rectangular and the long sides of the rectangle circumscribing the slots are not parallel to the axial direction.
The rectangular slot 211 in which the long sides of such a slot-circumscribing rectangle are not parallel to the axial direction generates a dipole moment in the radial direction and the axial direction. Therefore, the metal tube 21 having the rectangular slot 211 in which the long sides of the slot-circumscribing rectangle are not parallel to the axial direction has the axial polarization (horizontal polarization) in addition to the radial polarization (vertical polarization). Can also be generated. Therefore, the metal tube 21 having the rectangular slot 211 whose long side of the slot circumscribed rectangle is not parallel to the axial direction has an effect that information can be transmitted without depending on the polarization direction of the antenna on the electromagnetic wave receiving side. The shape of the slot 211 does not necessarily have to be rectangular, and may be oval, L-shaped, crank-shaped, or window-shaped. It may be oval.

Up to this point, the case where the metal tube 21 has only one slot 211 in the radial direction has been described. However, the metal tube 21 does not necessarily need to include only one slot 211 in the radial direction. The metal tube 21 may include a plurality of slots 211 in the radial direction. Hereinafter, a case where the metal tube 21 includes a plurality of slots 211 in the radial direction will be described. Further, hereinafter, for simplification of description, it is assumed that the metal tube 21 includes two slots 211 in the radial direction. Further, of the two slots 211 provided in the radial direction, the slot 211 close to the surface central axis is referred to as a slot 211-1 and the slot 211 far from the surface central axis is referred to as a slot 211-2. Further, hereinafter, when the slot 211-1 and the slot 211-2 are not distinguished, they are referred to as the slot 211.

FIG. 34 is a top view showing a specific example of the metal tube 21 including the slots 211-1 and 211-2 according to the second embodiment. The distance h between the centers of the adjacent slots 211-1 and 211-2 in the radial direction is equal to or less than a half wavelength. Therefore, the phases of vibrations of the dipole moments excited in the slots 211-1 and 211-2 adjacent to each other in the radial direction are substantially the same. In addition, the intermediate distance S between the slots 211-1 and 211-2 that are axially adjacent to each other is substantially the same as the wavelength. Therefore, all the slots 211 provided in the metal tube 21 vibrate in substantially the same phase. Therefore, the electromagnetic waves radiated from each slot 211 of the metal tube 21 strengthen each other and become an electromagnetic wave with high coherence, which is radiated from the metal tube 21.

The metal tube 21 does not need to have only two slots 211 in the radial direction, and may have three or more slots 211. In such a case, the distance between the centers of the plurality of slots 211 provided in the radial direction is equal to or less than half the wavelength between the center of the slot 211 closest to the central intersection and the center of the slot 211 farthest from the central intersection. It is located at a position that satisfies the condition.
The shape of the slot 211 in FIG. 34 does not necessarily have to be rectangular, and may be oval, L-shaped, crank-shaped, or window-shaped. The shape may be oval or elliptical.

Further, it is desirable that the centers of the plurality of slots 211 in the radial direction be located at a position where the distance from the central intersection is 7/40 or more and 19/40 or less of the length of the long side of the rectangle circumscribing the cross section.

The leaky waveguide 2 including the plurality of slots 211 configured in the radial direction in this way has an effect of reducing the coupling loss as compared with the case where one slot 211 is provided in the radial direction.

The leaky waveguide 2 according to the second embodiment configured as described above includes a plurality of slots 211 arranged at the ends at wavelength intervals, and thus can emit radio waves in directions other than 0°. it can. Therefore, for example, it is possible to suppress a decrease in communication efficiency in wireless communication with a moving body using the leaky waveguide 2 having a length of 50 m or more. Further, the leaky waveguide 2 configured as described above has an effect that it does not buckle during transportation even though it has a length of, for example, 50 m or more.

The inside of the metal tube 21 does not necessarily have to be hollow. The inside of the metal tube 21 of the leaky waveguide 2 may be a dielectric that allows electromagnetic waves to pass therethrough.

Note that the surface of the metal tube 21 may have wavy unevenness along the axial direction. When the metal tube 21 has wavy unevenness along the axial direction, it becomes possible to increase the angle of reversible bending in the direction of the long side of the circumscribed rectangle of the section as viewed from the center of the circumscribed rectangle of the section. Note that the metal tube 21 does not necessarily have to have wavy unevenness in the propagation direction in the metal tube.

(How to make)
Hereinafter, a method of making the leaky waveguide 2 according to the second embodiment will be described. First, a flat copper laminate strip is produced. After that, the flat copper-laminated strip-shaped body wound around the drum of the delivery machine is continuously delivered to the forming part. This forming unit forms a circular forming machine for forming the copper laminate strip into a circular shape from the upstream side (feeding side of the copper laminate strip), and a flattened circular shape for the circular copper laminate strip. It has a flat forming machine. The copper laminate strip sent out to the forming part is curved by the circular forming part into a C shape, and one end edge and the other end edge in the width direction are overlapped to form a circular shape. At this time, the other end edge and one end edge of the copper laminate strip are overlapped to form a joint. Next, in the forming part, the copper laminate strip is heated by a heater to heat-bond the joint part. The method of heat fusion may be any method, for example, arc welding may be used. Next, the copper laminate strip is formed into an elliptical cross section by the flat forming part. In this way, the flat pipe body is formed.
In addition, the copper laminate strip may have an adhesive layer laminated on one surface of a copper tape (thin copper plate).

The flat pipe body having a flat circular cross section is then sent to a slot forming machine that forms slots 211. The slot forming machine forms the slots 211 by laser, punching, cutting or the like.
The flat pipe body in which the slots 211 are formed is sent to the corrugating machine. The flat pipe body in which the slots 211 are formed has irregularities formed on its surface by a corrugating machine. The corrugating machine eccentrically fits the corrugating die onto the flat pipe body, externally fits the corrugated die, rotates the corrugating die, and sends the corrugating die in the longitudinal direction in synchronization with the rotation, thereby forming a (spiral) uneven wave. To form.
The corrugated flat pipe body is sent to a sinking die. The corrugated flat pipe body is formed into a predetermined cross section by a sinking die. The predetermined shape formed by the sinking die is a shape circumscribing a circumscribing rectangle in cross section, and is substantially the same as a flat circular cross section. The flat pipe body formed by the sinking die is the metal pipe 21.
After being formed by the sinking die, the metal tube 21 is sent to the sheath extruder. The sheath extruder coats the outside of the metal tube 21 with a polymer material such as polyethylene. The polymer material that covers the metal tube 21 is the outer skin 22.

The slot 211 is an example of the first opening and the second opening. The slot 211-1 is an example of the first opening. The slot 211-2 is an example of the second opening.

Although the embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment and includes a design and the like within a range not departing from the gist of the present invention.

1, 2... Leakage waveguide, 11, 21... Metal tube, 12, 22... Outer skin, 111, 211... Slot

Claims (14)

1. A leaky waveguide that is wound around a drum for storage and transportation.
   Equipped with a metal tube that propagates electromagnetic waves,
   The metal tube has a plurality of openings for leaking the electromagnetic waves,
   The cross-sectional shape of the metal tube is substantially the same as a flat circular cross section,
   The intersection of the vertical bisector of the long side of the rectangle circumscribing in the substantially same shape as the cross-section flat circular shape and the surface of the metal pipe is the central intersection.
   The distance between the center of each of the plurality of openings and the central intersection is greater than 0,
   The distance between the centers of the first openings that are a part of the plurality of openings and the second openings that are the rest of the plurality of openings is longer than a half wavelength,
   The number of the first openings and the number of the second openings are each plural,
   The plurality of first openings are parallel to each other,
   The plurality of second openings are parallel to each other,
   A line connecting the centers of the plurality of first openings is located parallel to the axial direction of the metal pipe,
   The distance between the centers of the adjacent first openings of the plurality of first openings in which the line connecting the centers is parallel to the axial direction of the metal tube is substantially the same as the wavelength of the electromagnetic wave. ,
   A line connecting the centers of the plurality of second openings is positioned parallel to the axial direction of the metal tube,
   The distance between the centers of the adjacent second openings of the plurality of second openings in which the line connecting the centers is parallel to the axial direction of the metal tube is substantially the same as the wavelength of the electromagnetic wave,
   Leaky waveguide.
2. The first opening is a coordinate system having a center of the rectangle as an origin, and a coordinate system having a Q axis as an axis passing through the origin and parallel to the short side of the rectangle. Located in the first space where the value is 0 or positive space,
   The second opening is located in a second space in which the value of the Q coordinate is negative.
   The leaky waveguide according to claim 1.
3. The distance between the center of the first opening and the central intersection is within 19/40 of the long side,
   The distance between the center of the second opening and the central intersection is within 19/40 of the long side,
   The leaky waveguide according to claim 1.
4. The distance between the center of the first opening and the central intersection is 7/40 or more of the long side,
   The distance between the center of the second opening and the central intersection is 7/40 or more of the long side,
   The leaky waveguide according to any one of claims 1 to 3.
5. The metal tube further has a plurality of third openings for leaking the electromagnetic waves,
   Each of the plurality of third openings has the same shape as the first opening,
   Each of the plurality of third openings is parallel to the first opening,
   The distance between the center of each of the plurality of third openings and the central intersection is greater than 0,
   A distance between a center of the first opening and a center of each of the plurality of third openings is shorter than a half wavelength;
   The leaky waveguide according to any one of claims 1 to 4.
6. The metal tube further has a plurality of fourth openings for leaking the electromagnetic waves,
   Each of the plurality of fourth openings has the same shape as the second opening,
   Each of the plurality of fourth openings is parallel to the second opening,
   The distance between the center of each of the plurality of fourth openings and the central intersection is greater than 0,
   A distance between a center of each of the plurality of fourth openings and a center of the second opening is shorter than a half wavelength;
   The leaky waveguide according to any one of claims 1 to 5.
7. The surface of the metal tube has wavy unevenness along the axial direction of the metal tube,
   The leaky waveguide according to any one of claims 1 to 6.
8. The movement path has a curve,
   The metal tube is bent so that the axial direction is substantially parallel to the movement path,
   The leaky waveguide according to any one of claims 1 to 7.
9. A leaky waveguide that is wound around a drum for storage and transportation.
   Equipped with a metal tube that propagates electromagnetic waves,
   The metal tube has a plurality of first openings for leaking the electromagnetic waves,
   The cross-sectional shape of the metal tube is substantially the same as a flat circular cross section,
   The intersection of the vertical bisector of the long side of the rectangle circumscribing in the substantially same shape as the cross-section flat circular shape and the surface of the metal pipe is the central intersection.
   The distance between the center of each of the plurality of first openings and the central intersection is greater than 0,
   The plurality of first openings are parallel to each other,
   A line connecting the centers of the adjacent first openings of the plurality of first openings is parallel to the axial direction of the metal tube,
   The distance between the centers of the adjacent first openings of the plurality of first openings is substantially the same as the wavelength of the electromagnetic wave.
   Leaky waveguide.
10. The distance between the center of each of the plurality of first openings and the central intersection is within 19/40 of the long side,
    The leaky waveguide according to claim 9.
11. The distance between the center of each of the plurality of first openings and the central intersection is 7/40 or more of the long sides,
    The leaky waveguide according to claim 9 or 10.
12. The metal tube further has a plurality of second openings for leaking the electromagnetic waves,
    Each of the plurality of second openings has the same shape as the first opening,
    Each of the plurality of second openings is parallel to the first opening,
    The distance between the center of each of the plurality of second openings and the central intersection is greater than 0,
    A distance between a center of each of the plurality of second openings and a center of the first opening is shorter than a half wavelength;
    The leaky waveguide according to any one of claims 9 to 11.
13. The surface of the metal tube has wavy unevenness along the axial direction of the metal tube,
    The leaky waveguide according to any one of claims 9 to 12.
14. The movement path has a curve,
    The metal tube is bent so that the axial direction is substantially parallel to the movement path,
    The leaky waveguide according to any one of claims 9 to 13.

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