JP2018026878A - Leakage coaxial cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a leakage coaxial cable that is able to prevent deviation of a radiation angle of an electromagnetic wave and an increase in voltage standing wave ratio (VSWR).SOLUTION: A leakage coaxial cable 20A comprises: an inner conductor 1 extending axially and to which a signal is transmitted; an insulator 2 covering an inner conductor 1; a main outer conductor 3 provided on the outer surface side of the insulator 2; and a sub-outer conductor 5 provided on the outer surface side of the main outer conductor 3. The main outer conductor 3 has a tape-like conductor part, and a tape-like insulation film arranged on the conductive part as a layer. The conductor part has: a plurality of main conductors spaced in the axial direction; and one or more connection parts connecting adjacent main conductors. The main conductor forms a shielding part that shields the signal. A radiation part, from which part of the signal leak, is secured between the adjacent main conductors. The sub-outer conductor 5 is formed by arranging conductor strands in a shielding density for leaking part of the signal outside.SELECTED DRAWING: Figure 11

Description

  The present invention relates to a leaky coaxial cable.

The leaky coaxial cable has a structure in which a plurality of slots are formed as radiating portions on the outer conductor of a normal coaxial cable.
The electromagnetic wave signal supplied to the inner conductor is shielded by the outer conductor, but leaks to the outside through the slot which is the radiating portion. That is, the leaky coaxial cable is a cable-type antenna, and can be said to be a special elongated transmission / reception antenna.
Generally, a metal tape is used for the outer conductor of the leaky coaxial cable. However, since the metal tape is inferior in flexibility, if the leaky coaxial cable is bent, the outer conductor is likely to crack from the slot. In order to realize a leaky coaxial cable excellent in flexibility, it has been proposed to use a laterally wound type or a braided type external conductor in which a metal tape is wound in a spiral shape (see Patent Documents 1 and 2).

However, the leaky coaxial cable having the above structure (1) has a low degree of freedom in design of the pitch of the radiating portion, and (2) the pitch of the radiating portion and the signal wavelength at a frequency that is a radiation angle perpendicular to the axial direction of the leaky coaxial cable. Therefore, there is a problem that a large voltage standing wave ratio (VSWR) is generated in the leaky coaxial cable and it cannot be put into practical use.
In order to solve this problem, a first outer conductor such as a braid and a plurality of second outer conductors spaced apart from each other are provided, and the second outer conductor has an electrical length (the electrical length of the shielding portion) adjacent to the second outer conductor. There has been proposed a leaky coaxial cable having the same electrical length between the outer conductors (the electrical length of the radiating portion) (see Patent Document 3).

JP-A-9-198941 JP 2003-123555 A JP 2013-229772 A

As shown in FIG. 19, when the leaky coaxial cable described in Patent Document 3 is manufactured, the second outer conductor 56 is supplied as a laminated body 53 laminated on a tape-like insulating film 57. When supplied, since tension in the length direction is applied to the laminated body 53, the laminated body 53 has a larger elongation at a portion where the second outer conductor 56 is not present than at a portion where the second outer conductor 56 is present. There is.
In that case, in the leaky coaxial cable manufactured using the multilayer body 53, the length between the adjacent second outer conductors 56, 56 may be larger than the design value. Therefore, problems such as a large voltage standing wave ratio (VSWR) may occur in the leaky coaxial cable at a frequency at which the radiation angle of the electromagnetic wave deviates from the design value and becomes a vertical radiation angle.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the leaky coaxial cable which can prevent the shift | offset | difference of the radiation angle of electromagnetic waves, and the increase in a voltage standing wave ratio (VSWR).

One aspect of the present invention includes an inner conductor that extends in the axial direction and propagates a signal, an insulator that covers the inner conductor, a main outer conductor that is provided on the outer surface side of the insulator, and the main outer conductor. A sub-outer conductor provided on the outer surface side of the main outer conductor, the main outer conductor has a tape-like conductor portion and a tape-like insulating film laminated on the conductor portion, the conductor portion is , Having a plurality of main conductors arranged at intervals in the axial direction, and one or a plurality of connecting portions for connecting adjacent main conductors, wherein the main conductor constitutes a shielding portion for shielding the signal In addition, a radiating portion where a part of the signal leaks to the outside is secured between the adjacent main conductors, and the sub-outer conductor is a conductor element having a shielding density at which a part of the signal leaks to the outside. Provided is a leaky coaxial cable configured by arranging wires.
Preferably, the main outer conductor is formed in a tape shape, and the plurality of connecting portions are formed apart in the width direction of the main conductor.
The plurality of connecting portions preferably include a first connecting portion formed at one side edge of the main conductor and a second connecting portion formed at the other side edge of the main conductor.
It is preferable that the plurality of connecting portions include a third connecting portion formed at an intermediate portion in the width direction of the main conductor.
In the axial direction, it is preferable that the electrical length of the shielding portion is the same as the electrical length of the radiating portion.
The pitch of the main conductor is in the range of {1 / (1 + 0.766ν)} times to {3 / (1 + ν)} times the propagation wavelength, where ν is a wavelength shortening rate of the propagation wavelength of the signal with respect to a free space wavelength. Preferably there is.
The pitch of the main conductor is preferably 0.9 to 1.1 times the propagation wavelength.
The sub external conductor is preferably braided or laterally wound using the conductor wire.

One aspect of the present invention includes an inner conductor that extends in the axial direction and propagates a signal, an insulator that covers the inner conductor, and a main outer conductor that is provided on the outer surface side of the insulator, The main outer conductor has a plurality of main conductors arranged at intervals in the axial direction and one or a plurality of connecting portions that connect adjacent main conductors, and the main conductor shields the signal. A leaky coaxial cable is provided in which a radiating portion is provided between the adjacent main conductors and a part of the signal leaks to the outside.
Preferably, the main outer conductor is formed in a tape shape, and the plurality of connecting portions are formed apart in the width direction of the main conductor.
The plurality of connecting portions preferably include a first connecting portion formed at one side edge of the main conductor and a second connecting portion formed at the other side edge of the main conductor.
It is preferable that the plurality of connecting portions include a third connecting portion formed at an intermediate portion in the width direction of the main conductor.
In the axial direction, it is preferable that the electrical length of the shielding portion is the same as the electrical length of the radiating portion.
The pitch of the main conductor is in the range of {1 / (1 + 0.766ν)} times to {3 / (1 + ν)} times the propagation wavelength, where ν is a wavelength shortening rate of the propagation wavelength of the signal with respect to a free space wavelength. Preferably there is.
The pitch of the main conductor is preferably 0.9 to 1.1 times the propagation wavelength.
One aspect of the present invention preferably includes a sub-outer conductor in which conductor wires are arranged at a shielding density at which a part of the signal leaks to the outside.
The sub external conductor is preferably braided or laterally wound using the conductor wire.

According to one aspect of the present invention, since the main outer conductor has a connecting portion that connects the main conductors, the main conductor is not affected even when a longitudinal tension is applied to the main outer conductor in manufacturing a leaky coaxial cable. Elongation deformation of the main outer conductor in the separating direction is unlikely to occur. Therefore, it is possible to prevent the length between adjacent main conductors from greatly deviating from the design value.
Therefore, problems such as a large voltage standing wave ratio (VSWR) occur in the leaky coaxial cable at a frequency where the radiation angle of the electromagnetic wave deviates from the design value and becomes a vertical radiation angle, and it is excellent as a leaky coaxial cable. Characteristics are obtained.

It is a top view of the leaky coaxial cable of a 1st embodiment. It is a figure which shows the structure of the cross section of the shielding part of the leaky coaxial cable of FIG. It is a figure which shows the structure of the cross section of the radiation | emission part of the leaky coaxial cable of FIG. It is a perspective view of the partially broken state of the leaky coaxial cable of FIG. It is a perspective view of the outer conductor used for the leaky coaxial cable of FIG. It is sectional drawing which shows typically the 1st modification of the leaky coaxial cable of 1st Embodiment. It is sectional drawing which shows typically the 2nd modification of the leaky coaxial cable of 1st Embodiment. It is a figure which shows the structure of the cross section of the shielding part of the leaky coaxial cable of 2nd Embodiment. It is a figure which shows the structure of the cross section of the radiation | emission part of the leaky coaxial cable of a previous figure. It is a perspective view of the partially broken state of the leaky coaxial cable of FIG. It is sectional drawing which shows typically the 1st modification of the leaky coaxial cable of 2nd Embodiment. It is sectional drawing which shows typically the 2nd modification of the leaky coaxial cable of 2nd Embodiment. It is sectional drawing which shows typically the 3rd modification of the leaky coaxial cable of 2nd Embodiment. It is a perspective view of the partially broken state of the leaky coaxial cable using the 1st modification of an external conductor. It is a perspective view of the outer conductor used for the leaky coaxial cable of the previous figure. It is a perspective view of the 2nd modification of an external conductor. It is a perspective view of the 3rd modification of an external conductor. It is a perspective view of the outer conductor used for the leaky coaxial cable of FIG. It is a perspective view of the outer conductor used for an example of the conventional leaky coaxial cable. It is a graph which shows a test result. It is a graph which shows a test result.

  Hereinafter, the leaky coaxial cable of the embodiment will be described with reference to the drawings.

  FIG. 1 is a plan view of a leaky coaxial cable 10 according to the first embodiment. FIG. 2 is a view showing a cross-sectional structure of the shielding portion 11 of the leaky coaxial cable 10 and is a cross-sectional view taken along the line II of FIG. FIG. 3 is a diagram showing a cross-sectional structure of the radiating portion 12 of the leaky coaxial cable 10, and is a cross-sectional view taken along the line II-II in FIG. FIG. 4 is a perspective view of the leaky coaxial cable 10 in a partially broken state. FIG. 5 is a perspective view of the outer conductor 3 used in the leaky coaxial cable 10.

As shown in FIGS. 1 to 4, the leaky coaxial cable 10 includes an inner conductor 1, an insulator 2, an outer conductor 3 (main outer conductor), and a sheath 4 from the inner circumference side toward the outer circumference side. Have.
The internal conductor 1 is a linear body made of a conductor such as a metal such as copper. C 1 is the central axis of the inner conductor 1.
The insulator 2 is provided so as to cover the outer peripheral surface of the inner conductor 1. For the insulator 2, an insulating resin such as foamed polyethylene is used.

  As shown in FIG. 5, the outer conductor 3 is configured by laminating a tape-shaped conductor portion 6 and a tape-shaped insulating film 7 with the length direction aligned. In FIG. 5, the length direction of the outer conductor 3 is referred to as an X direction, and a direction (width direction) orthogonal to the X direction in a plane along the outer conductor 3 is referred to as a Y direction.

The conductor portion 6 includes a plurality of main conductors 8 formed at intervals in the length direction (X direction) of the outer conductor 3 and a connecting portion 9 that connects adjacent main conductors 8.
The main conductors 8 have a rectangular shape, and are preferably arranged in the length direction at a constant pitch P.

The connecting portions 9 and 9 are formed by connecting adjacent main conductors 8 and 8 at one and the other side edges in the width direction of the main conductor 8. The connecting portions 9 and 9 are side edge connecting portions formed on the side edge of the main conductor 8. The connecting portion 9 formed on one side edge in the width direction of the main conductor 8 is referred to as a first connecting portion 9A, and the connecting portion 9 formed on the other side edge is referred to as a second connecting portion 9B.
The connecting portion 9 is, for example, a band shape having a certain width, and extends in the length direction (X direction). The connecting portion 9 is preferably formed integrally with the main conductor 8.
Since the connecting portions 9 and 9 are formed with a distance in the width direction of the main conductor 8, a change in length between the main conductors 8 and 8 can be prevented over a wide range in the width direction.

An opening between the adjacent main conductors 8 and 8 and between the connecting portions 9 and 9 is referred to as a slot 13.
In FIG. 5, the slot 13 is, for example, an opening having a rectangular shape in plan view defined by inner edges 8 a and 8 a of adjacent main conductors 8 and 8 and inner edges 9 a and 9 a of the connecting portions 9 and 9. Inner edges 8a, 8a of the main conductors 8, 8 are formed in a straight line along the width direction (Y direction) and are parallel to each other. Inner edges 9a, 9a of the connecting portions 9, 9 are formed in a straight line along the length direction (X direction) and are parallel to each other.
The conductor part 6 consists of conductors, such as a metal (copper etc.). The conductor portion 6 may be a metal foil such as a copper foil, a metal layer such as a plating film, or a conductive resin film.

If the width W _S of the slot 13 is too large, when placed on the outer circumferential surface of the insulator 2, a portion of the slot 13 is covered by the connecting portion 9, that the radiation amount of the radio wave at the radiating portion 12 is not appropriate is there. Therefore, the width W _S of the slot 13, and the outer diameter when placing the outer conductor 3 on the outer peripheral surface of the insulator 2 is D, when the width of the conductor portion 6 and a W _T, "0 <W _S ≦ 2πD It is preferable to satisfy “−W _T ”. As a result, the amount of radio waves emitted from the radiation unit 12 can be increased.

Width W _S of the slot 13, the range to be reserved as an opening in the circumferential direction of the insulator 2 (range insulator 2 is exposed) is 50% or more relative to the total circumference of the insulator 2 (preferably 70% It is preferable to be determined so as to satisfy the above. Thereby, the radiation amount of the radio wave in the radiation part 12 can be sufficiently increased.

For the insulating film 7, a polyester resin such as polyethylene terephthalate (PET); a polyolefin resin such as polypropylene or polyethylene can be used.
The sheath 4 is made of a resin such as flame retardant polyethylene or polyvinyl chloride, and is provided so as to cover the outer conductor 3.

As shown in FIGS. 1, 2, and 4, the shielding portion 11 is a region having a length Lw in which the main conductor 8 is disposed. In the shielding part 11, the main conductor 8 covers the entire circumference of the insulator 2.
As shown in FIGS. 1, 3, and 4, the radiating portion 12 is a region having a length Ls between adjacent main conductors 8 and 8. The radiating portion 12 is an area where the range in the length direction coincides with the slot 13. As shown in FIG. 3, the connecting portion 9 is preferably arranged so as not to cover the slot 13. The two connecting portions 9 may be in positions where part or all of them overlap.
The lengths Lw and Ls of the shielding part 11 and the radiation part 12 are made substantially equal.

The inner conductor 1 propagates a high frequency signal supplied from an external signal source or the like. In the shielding part 11, since the main conductor 8 shields the high frequency signal, the high frequency signal is not radiated to the outside of the leaky coaxial cable 10.
Since there is no conductor in the radiation part 12, electromagnetic waves are radiated to the outside of the leaky coaxial cable 10. The pitch P of the main conductor 8 is determined according to the frequency of the supplied high frequency signal.

In general, the radiation angle θn of the electromagnetic wave from the leaky coaxial cable is expressed by the following equation, assuming that the radiation angle perpendicular to the axial direction of the leaky coaxial cable is 0 and the radiation direction tilted toward the terminal side is positive. θn = sin ⁻¹ (nλ / P + 1 / ν) (1)

Here, n is a negative integer in the radiation wave mode, λ is the wavelength in free space, and ν is the wavelength shortening rate of the leaky coaxial cable. The wavelength shortening rate ν is expressed by the following formula from the effective relative dielectric constant εs obtained from the volume ratio of the insulator between the inner conductor and the outer conductor and the hollow portion.
ν = 1 / (εs) ^1/2 (2)

  Usually, only the so-called −1st order mode with n = −1 is often used. Since the electromagnetic waves radiated from a plurality of angles including the −1st order mode interfere with each other at the frequency at which the higher order mode after the −2nd order mode occurs, a standing wave is generated. This is because it becomes difficult to achieve the above.

  In the leaky coaxial cable 10, the axial lengths of the radiating portion 12 and the shielding portion 11 are matched to prevent the −2nd order mode from occurring. Here, the electrical length is the product of the physical length and the wavelength shortening rate ν. The effective relative permittivity of the radiating portion 12 and the shielding portion 11 is not the same, but is substantially equal. Therefore, the electrical lengths are matched by making the physical lengths of the radiation part 12 and the shielding part 11 substantially the same. Thus, in the leaky coaxial cable 10, it is possible to prevent radiation of the -second order mode with a simple structure, and it is possible to increase the bandwidth.

Specifically, the frequency band in which only the −1st order mode is emitted is expressed by the following equation.
(1 + 1 / ν) / 2 <λ / P <(1 + 1 / ν) (3)

In the leaky coaxial cable 10, since there is no radiation in the −2nd order mode, the conventional frequency region in which the −1st order mode and the −2nd order mode are emitted can also be used. Therefore, the frequency band is expanded as follows:
(1 + 1 / ν) / 3 <λ / P <(1 + 1 / ν) (4)
In other words, a range from the radiation angle of −90 ° to + 30 ° in which the −3 order mode occurs can be used.

From equation (4), the pitch P may be set so as to satisfy the condition of the following equation.
λg / (1 + ν) <P <3λg / (1 + ν) (5)
Here, λg is a propagation wavelength in the leaky coaxial cable 10, and λg = νλ. Empirically, -50 ° is a practical limit angle for the radiation angle of the −1st order mode. Accordingly, the pitch P is preferably in the following range.
λg / (1 + 0.776ν) <P <3λg / (1 + ν) (6)

Further, at the frequency at which the radiation angle of the −1st order mode is 0 °, the slot pitch and the wavelength match. Therefore, in the general leaky coaxial cable 10, the VSWR in the leaky coaxial cable 10 becomes large and cannot be practically used.
On the other hand, in the leaky coaxial cable 10, the lengths Ls and Lw that are the physical lengths of the radiation portion 12 and the shielding portion 11 are made substantially equal. The impedance Z1 of the radiating part 12 is larger than the impedance Z2 of the shielding part 11. Therefore, the propagation signal is slightly reflected at the boundary surface between the radiating portion 12 and the shielding portion 11. For example, the reflected voltage V1 of the propagation signal from the radiating unit 12 to the shielding unit 11 is (Z2−Z1) / (Z2 + Z1), and the reflected voltage V2 of the propagation signal from the shielding unit 11 to the radiating unit 12 is (Z1−Z1). Z2) / (Z2 + Z1). The reflected voltage V1 and the reflected voltage V2 are opposite in phase.
Accordingly, the reflected wave does not strictly become 0 in consideration of the attenuation amount of the leaky coaxial cable 10 and the influence of multiple reflection, but can be almost 0. As a result, VSWR can be suppressed, and it can be used even at a frequency at which the radiation angle in the −1st order mode is 0 °. Specifically, in the leaky coaxial cable 10, the pitch P may be in the range of 0.9 to 1.1 times the propagation wavelength in the leaky coaxial cable 10.

The leaky coaxial cable 10 can be manufactured as follows.
An insulator 2 containing the internal conductor 1 is prepared.
A tape-like outer conductor 3 shown in FIG. 5 is vertically attached to the insulator 2 so as to wrap the insulator 2. Next, the sheath 4 is formed on the outer peripheral side of the outer conductor 3.
Thereby, the leaky coaxial cable 10 shown in FIGS. 1 to 4 is obtained.

In the leaky coaxial cable 10, the outer conductor 3 has a plurality of main conductors 8 and a connecting portion 9 that connects the adjacent main conductors 8. Even if tension is applied, the outer conductor 3 is not easily deformed in the direction in which the main conductors 8 are separated from each other. Therefore, it is possible to prevent the length Ls between the adjacent main conductors 8 from greatly deviating from the design value.
Therefore, problems such as a large voltage standing wave ratio (VSWR) occur in the leaky coaxial cable at a frequency where the radiation angle of the electromagnetic wave deviates from the design value and becomes a vertical radiation angle, and it is excellent as a leaky coaxial cable. Characteristics are obtained.

The leaky coaxial cable 10 is excellent in design flexibility because the pitch P of the radiating portion 12 and the like can be defined by the arrangement of the main conductor 8 of the outer conductor 3.
Further, the leaky coaxial cable 10 is highly flexible and excellent in handling because the main conductor 8 of the outer conductor 3 is spaced apart.

FIG. 6 is a cross-sectional view schematically showing a leaky coaxial cable 10 </ b> A that is a first modification of the leaky coaxial cable 10.
In the leaky coaxial cable 10 </ b> A, an adhesive layer 14 is provided between the outer peripheral surface of the outer conductor 3 (specifically, the outer peripheral surface of the insulating film 7) and the inner peripheral surface of the sheath 4, and the outer conductor 3 is interposed via the adhesive layer 14. The configuration is the same as that of the leaky coaxial cable 10 shown in FIG. The adhesive used for the adhesive layer 14 is not particularly limited, and for example, urethane-based, epoxy-based and the like can be appropriately selected and used.
By adhering the outer conductor 3 and the sheath 4 via the adhesive layer 14, fluctuations in the lengths Ls, Lw or the pitch P of the radiating portion 12 and the shielding portion 11 can be prevented. Therefore, unstable radiation of electromagnetic waves and the like can be suppressed, and the characteristics of the leaky coaxial cable 10A can be obtained stably over a long period of time.

FIG. 7 is a cross-sectional view schematically showing a leaky coaxial cable 10 </ b> B that is a second modification of the leaky coaxial cable 10.
The leaky coaxial cable 10B is provided with an adhesive layer 15 between the inner peripheral surface of the outer conductor 3 (specifically, the inner peripheral surface of the insulating film 7) and the outer peripheral surface of the insulator 2, and the outside via the adhesive layer 15 The conductor 3 and the insulator 2 are bonded.
The outer conductor 3 is provided with the insulating film 7 on the inner peripheral surface side. The adhesive used for the adhesive layer 15 is the same as the adhesive layer 14 in the first modification.
By bonding the outer conductor 3 and the insulator 2 via the adhesive layer 15, fluctuations in the lengths Ls, Lw or the pitch P of the radiating portion 12 and the shielding portion 11 can be prevented. Therefore, it is possible to suppress unstable radiation of electromagnetic waves and the like, and to stably obtain the characteristics of the leaky coaxial cable 10B over a long period of time.

  FIG. 8 is a diagram illustrating a cross-sectional structure of the shielding portion of the leaky coaxial cable 20 according to the second embodiment. FIG. 9 is a diagram illustrating a cross-sectional structure of the radiating portion of the leaky coaxial cable 20. FIG. 10 is a perspective view of the leaky coaxial cable 20 in a partially broken state. Hereinafter, the same components as those of the leaky coaxial cable 10 of the first embodiment may be denoted by the same reference numerals and description thereof may be omitted.

As shown in FIGS. 8 to 10, the leaky coaxial cable 20 includes an inner conductor 1, an insulator 2, a first outer conductor 5 (sub-outer conductor), a second outer conductor from the inner peripheral side toward the outer peripheral side. It has an outer conductor 3 (main outer conductor) and a sheath 4.
The leaky coaxial cable 20 has the same configuration as the leaky coaxial cable 10 of the first embodiment except that the first outer conductor 5 is provided.
The first outer conductor 5 may be, for example, a conductive braid using a conductor wire such as metal (copper or the like), a horizontal winding of a metal tape, or the like. The first outer conductor 5 is provided on the outer peripheral surface of the insulator 2.

The shielding density of the first outer conductor 5 with respect to the outer peripheral surface of the insulator 2 is preferably 70% or less. Thereby, the radiation of the electromagnetic wave from the radiation part 22 can be improved. The shielding density can be 10% or more, for example.
The shielding density is the ratio of the area of the conductor wire arranged on the surface of the insulator 2 to the surface area of the insulator 2.

  The 2nd outer conductor 3 is good also as a structure similar to the outer conductor 3 of the leaky coaxial cable 10 of 1st Embodiment shown in FIGS. The second outer conductor 3 is provided so as to cover the first outer conductor 5. The conductor portion 6 of the second outer conductor 3 abuts on the first outer conductor 5 and can be electrically connected to the first outer conductor 5. When the second outer conductor 3 is electrically connected to the first outer conductor 5, the first outer conductor 5 and the second outer conductor 3 have the same potential.

The shielding part 21 is an area having a length range in which the main conductor 8 of the second outer conductor 3 is disposed. The radiating portion 22 is a region in the length range between the adjacent main conductors 8 and 8, and the region in the length direction coincides with the slot 13.
The lengths of the shielding part 21 and the radiation part 22 are made substantially equal.
In the shielding part 21, since the 2nd outer conductor 3 (main conductor 8) shields a high frequency signal, a high frequency signal is not radiated | emitted outside. In the radiation part 22, a part of high frequency signal leaks outside.

Since the leaky coaxial cable 20 has the connecting portion 9 for connecting the main conductor 8, similarly to the leaky coaxial cable 10 of the first embodiment, in manufacturing the leaky coaxial cable 20, the leaky coaxial cable 20 is connected to the second outer conductor 3 in the length direction. Even if tension is applied, the extension deformation of the second outer conductor 3 in the direction in which the main conductors 8, 8 are separated from each other hardly occurs. Therefore, it is possible to prevent the length Ls between the adjacent main conductors 8 from greatly deviating from the design value.
Therefore, problems such as a large voltage standing wave ratio (VSWR) occur in the leaky coaxial cable at a frequency where the radiation angle of the electromagnetic wave deviates from the design value and becomes a vertical radiation angle, and it is excellent as a leaky coaxial cable. Characteristics are obtained.

The leaky coaxial cable 20 is excellent in design flexibility because the pitch P of the radiating portion 22 and the like can be defined by the arrangement of the main conductor 8 of the outer conductor 3.
The leaky coaxial cable 20 is braided or laterally wound as the first outer conductor 5 and the main conductor 8 of the second outer conductor 3 is spaced apart. Therefore, the leaky coaxial cable 20 is highly flexible and excellent in handling. ing.

  Since the leaky coaxial cable 20 has the first outer conductor 5, mechanical performance (such as durability against bending and tension) can be improved as compared with the leaky coaxial cable 10 of the first embodiment. Further, in the leaky coaxial cable 20, the first outer conductor 5 and the second outer conductor 3 are electrically connected. Therefore, even if the second outer conductor 3 is disconnected, the first outer conductor 5 ensures conduction. The function as a cable type antenna can be maintained.

FIG. 11 is a cross-sectional view schematically showing a leaky coaxial cable 20A that is a first modification of the leaky coaxial cable 20 of the second embodiment.
The leaky coaxial cable 20 </ b> A includes an inner conductor 1, an insulator 2, a second outer conductor 3, a first outer conductor 5 provided on the outer peripheral surface side of the second outer conductor 3, and a sheath 4.
The leaky coaxial cable 20A has the same configuration as the leaky coaxial cable 20 shown in FIG. 8 and the like except that the first outer conductor 5 is provided on the outer peripheral surface side of the second outer conductor 3.
The second outer conductor 3 is provided with the conductor portion 6 on the outer peripheral surface side.
The first outer conductor 5 is provided so as to cover the second outer conductor 3. The first outer conductor 5 can contact the conductor portion 6 of the second outer conductor 3.

FIG. 12 is a cross-sectional view schematically showing a leaky coaxial cable 20 </ b> B that is a second modification of the leaky coaxial cable 20.
The leaky coaxial cable 20 </ b> B is provided with an adhesive layer 16 between the outer peripheral surface of the second outer conductor 3 (specifically, the outer peripheral surface of the insulating film 7) and the inner peripheral surface of the sheath 4. 2 Except that the outer conductor 3 and the sheath 4 are bonded, the configuration is the same as that of the leaky coaxial cable 20 shown in FIG. The adhesive used for the adhesive layer 16 is not particularly limited, and for example, urethane-based, epoxy-based and the like can be appropriately selected and used.
By bonding the second outer conductor 3 and the sheath 4 via the adhesive layer 16, fluctuations in the lengths Ls, Lw or the pitch P of the radiating portion 22 and the shielding portion 21 can be prevented. Therefore, the unstable radiation | emission of electromagnetic waves etc. can be suppressed and the characteristic of the leaky coaxial cable 20B can be obtained stably over a long period of time.

FIG. 13 is a cross-sectional view schematically showing a leaky coaxial cable 20 </ b> C that is a third modification of the leaky coaxial cable 20.
The leaky coaxial cable 20 </ b> C is provided with an adhesive layer 17 between the inner peripheral surface of the second outer conductor 3 (specifically, the inner peripheral surface of the insulating film 7) and the outer peripheral surface of the insulator 2. The second outer conductor 3 and the insulator 2 have the same configuration as the leaky coaxial cable 20 shown in FIG. The adhesive used for the adhesive layer 17 is the same as the adhesive layer 16 in the second modification.
By bonding the second outer conductor 3 and the insulator 2 via the adhesive layer 17, fluctuations in the lengths Ls, Lw or the pitch P of the radiating portion 22 and the shielding portion 21 can be prevented. For this reason, it is possible to suppress unstable radiation of electromagnetic waves and the like, and to stably obtain the characteristics of the leaky coaxial cable 20C over a long period of time.

FIG. 14 is a perspective view of a partially broken state of a leaky coaxial cable 10 </ b> C using an outer conductor 3 </ b> A that is a first modification of the outer conductor 3.
The leaky coaxial cable 10 </ b> C has the same configuration as the leaky coaxial cable 10 of the first embodiment shown in FIG. 4 and the like except that it has an outer conductor 3 </ b> A instead of the outer conductor 3.

As shown in FIG. 15, the conductor portion 6A of the outer conductor 3A includes not only the connecting portions 9 and 9 (the first connecting portion 9A and the second connecting portion 9B) between the adjacent main conductors 8 and 8, but also the connecting portion. 19 (third connecting portion 19) (intermediate connecting portion) is different from the conductor portion 6 shown in FIG.
The connecting portion 19 is formed by connecting the main conductors 8 and 8 at an intermediate portion (for example, the center in the width direction) of the adjacent main conductors 8 and 8 in the width direction. The connecting portion 19 is, for example, a band shape having a certain width, and extends in the length direction (X direction).
Since the outer conductor 3 </ b> A has the connecting portion 19, elongation deformation in the direction in which the main conductors 8, 8 are separated from each other is further less likely to occur. Therefore, it is possible to prevent the length between the adjacent main conductors 8 from deviating from the design value.
The outer conductor 3A may be used in place of the second outer conductor 3 of the leaky coaxial cable 20 of the second embodiment shown in FIG.

FIG. 16 is a perspective view of an outer conductor 3 </ b> B that is a second modification of the outer conductor 3. The conductor portion 6B of the outer conductor 3B is different from the conductor portion 6 shown in FIG. 5 and the like in that the connecting portion 9 is provided only at one side edge portion of the main conductors 8 and 8 in the width direction.
FIG. 17 is a perspective view of an outer conductor 3 </ b> C that is a third modification of the outer conductor 3. The conductor portion 6C of the outer conductor 3C is different from the conductor portion 6 shown in FIG. 5 and the like in that a connecting portion 19 shown in FIG. 15 is provided between the main conductors 8 and 8 instead of the connecting portion 9. . The connecting portion 19 is provided at the center in the width direction of the main conductors 8 and 8.
Since the outer conductors 3B and 3C shown in FIGS. 16 and 17 are provided with the connecting portion 9 or the connecting portion 19 that connects the adjacent main conductors 8 and 8, like the outer conductor 3 shown in FIG. It is possible to prevent the length of the radiating portion 12 from greatly deviating from the design value.

Example 1
As shown in FIG. 18, a tape-shaped outer conductor 3 (outer conductor 3 tape) in which the conductor portion 6 and the insulating film 7 were laminated was produced.
A copper foil having a thickness of 10 μm was used for the conductor portion 6. Table 1 shows the length L _S of the radiating portion, the length L _W of the shielding portion, the width W _{T of} the tape, and the width W _{S of the} slot 13 (see FIG. 5). The insulating film 7 was a polyethylene terephthalate (PET) film having a thickness of 12 μm.
The outer conductor 3 was gripped by a jig (not shown) at an interval of 200 mm, and a tensile force was applied in the length direction at a speed of 10 mm / min.

(Comparative Example 1)
As shown in FIG. 19, an outer conductor 53 similar to the outer conductor 3 of Example 1 was produced except that the connecting portion 9 was not provided. A tensile force was applied to the outer conductor 53 in the same manner as in Example 1.

The test results are shown in FIG. The elongation percentage indicates the change in length with respect to the length of 200 mm at the start of the test as a percentage. Since the stress generated when the tensile force is applied is concentrated on the radiating portion where the tensile strength is weak, it can be considered that the elongation rate represents the elongation of the length L _S of the radiating portion.

From FIG. 20, it was confirmed that Example 1 had a smaller elongation rate than Comparative Example 1.
Generally, the tensile force applied to the external conductor tape when producing a leaky coaxial cable is about 200 gf. Assuming cable fabrication, from the test results, the elongation of the length L _S of the radiating portion of Comparative Example 1 is 0.5%, whereas the length of the length of the radiating portion L _S of Example 1 is It is 0.05%, and the effect of suppressing the elongation of the radiation portion by adopting Example 1 is about 1/10.

Further, a cable was manufactured using the external conductor tape of Example 1 and Comparative Example 1, and how much the length L _S of the radiating part and the length L _W of the shielding part changed before and after the manufacture. investigated. The results are shown in Table 2.

  From Table 2, the elongation of the radiating portion of Example 1 was about 1/10 of the elongation of the radiating portion of Comparative Example 1.

Using the external conductor tape of Example 1, a leaky coaxial cable 10 shown in FIG. The inner conductor 1 of the leaky coaxial cable is a soft conductor having an outer diameter of about 1.5 mm. The insulator 2 is a foamed polyethylene having an outer diameter of about 7.3 mm. The sheath 4 is made of polyvinyl chloride (PVC) having a thickness of about 1 mm and an outer diameter of about 10 mm.
A leaky coaxial cable was produced in the same manner as in Example 1 except that the external conductor tape of Comparative Example 1 was used.

For the leaky coaxial cable of Example 1 and Comparative Example 1, the VSWR at the resonance frequency was measured. The results are shown in FIG.
In the leaky coaxial cable, resonance occurs at a specific frequency due to the slot of the outer conductor, and the VSWR is increased. The n-th resonance frequency _frn is derived by the following calculation formula. c is the speed of light, n is a natural number, P is a slot pitch, and ε _S is a relative dielectric constant.

The leaky coaxial cable of Example 1 suppresses VSWR at the secondary resonance frequency by matching the electrical length at the radiating portion with the electrical length at the shielding portion. When the speed of light is c = 3.0 × 10 ⁸ m / s, and P = 0.091 m and ε _S = 1.7 are substituted into the formula (7) from the design values of the first embodiment, the secondary resonance frequency f _rn is 2.5 GHz.
From the results shown in FIG. 21, it can be seen that in Comparative Example 1, the VSWR increases at 2.5 GHz, and secondary resonance occurs.
On the other hand, in Example 1, the increase in VSWR at 2.5 GHz was not observed, and it was confirmed that the secondary resonance could be suppressed.

  The preferred embodiments have been described above, but these are exemplifications of the present invention, and additions, omissions, substitutions, and other changes can be made without departing from the scope of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Internal conductor, 2 ... Insulator, 3 ... External conductor (main outer conductor), 5 ... 1st outer conductor (sub-outer conductor), 8 ... Main conductor -Connection part, 9A ... 1st connection part, 9B ... 2nd connection part, 19 ... Connection part (3rd connection part), 11, 21 ... Shielding part, 12, 22 ... Radiation part.

Claims (8)

An inner conductor that extends in the axial direction and propagates the signal;
An insulator covering the inner conductor;
A main outer conductor provided on the outer surface side of the insulator;
A sub-outer conductor provided on the outer surface side of the main outer conductor,
The main outer conductor has a tape-shaped conductor portion and a tape-shaped insulating film laminated on the conductor portion,
The conductor portion has a plurality of main conductors arranged at intervals in the axial direction, and one or a plurality of connecting portions for connecting adjacent main conductors,
The main conductor constitutes a shielding part that shields the signal, and a radiation part from which a part of the signal leaks to the outside is secured between the adjacent main conductors,
The leaky coaxial cable, wherein the sub-outer conductor is configured by arranging conductor wires at a shielding density at which a part of the signal leaks to the outside. The main outer conductor is formed in a tape shape,
The leaky coaxial cable according to claim 1, wherein the plurality of connecting portions are formed apart from each other in the width direction of the main conductor.   The plurality of connecting portions include a first connecting portion formed at one side edge portion of the main conductor and a second connecting portion formed at the other side edge portion of the main conductor. The leaky coaxial cable according to claim 2.   4. The leaky coaxial cable according to claim 3, wherein the plurality of connecting portions include a third connecting portion formed at an intermediate portion in the width direction of the main conductor.   5. The leaky coaxial cable according to claim 1, wherein an electrical length of the shielding portion is the same as an electrical length of the radiating portion in the axial direction.   The pitch of the main conductor is in the range of {1 / (1 + 0.766ν)} times to {3 / (1 + ν)} times the propagation wavelength, where ν is a wavelength shortening rate of the propagation wavelength of the signal with respect to a free space wavelength. The leaky coaxial cable according to claim 1, wherein the leaky coaxial cable is provided.   The leaky coaxial cable according to any one of claims 1 to 6, wherein a pitch of the main conductor is 0.9 to 1.1 times the propagation wavelength.   The leaky coaxial cable according to any one of claims 1 to 7, wherein the sub-outer conductor is a braid or a horizontal winding using the conductor wire.

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