WO2022019190A1

WO2022019190A1 - Leaky coaxial cable

Info

Publication number: WO2022019190A1
Application number: PCT/JP2021/026448
Authority: WO
Inventors: 邦明公賀; 一平田中
Original assignee: 株式会社フジクラ・ダイヤケーブル
Priority date: 2020-07-20
Filing date: 2021-07-14
Publication date: 2022-01-27
Also published as: JP2022020462A

Abstract

In the present invention, a leaky coaxial cable comprises an internal conductor, an insulator, and an external conductor. The insulator covers the internal conductor. The external conductor covers the insulator. At least one slot is formed in the external conductor. The total length in the length direction of the internal conductor is 10m or less. The length-direction dimension of each slot is at least 10mm. The dimension of the slots in the circumferential direction of the external conductor is within 35–95% of the total circumferential-direction length of the external conductor. The outer diameter of the insulator is at least 5mm.

Description

Leaky coaxial cable

The present invention relates to a leaky coaxial cable.
The present application claims priority based on Japanese Patent Application No. 2020-123971 filed in Japan on July 20, 2020, the contents of which are incorporated herein by reference.

Patent Document 1 discloses a leaky coaxial cable including an inner conductor, an insulator, and an outer conductor in which a slot is formed. The leaky coaxial cable is used as a transmitting / receiving antenna for wireless communication.

Japanese Patent No. 5162713

For example, in order to effectively communicate with a passive RFID tag, it is required to sufficiently reduce the coupling loss of the leaky coaxial cable.

The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a leaky coaxial cable that suppresses coupling loss.

In order to solve the above problems, the leaky coaxial cable according to one aspect of the present invention includes an inner conductor, an insulator that covers the inner conductor, and an outer conductor that covers the insulator and has at least one slot formed therein. , The total length of the inner conductor in the longitudinal direction is 10 m or less, the dimension of the slot in the longitudinal direction is 10 mm or more, and the dimension of the slot in the circumferential direction of the outer conductor is the outer. It is within the range of 35 to 95% with respect to the total length of the conductor in the circumferential direction, and the outer diameter of the insulator is 5 mm or more.

According to the above aspect, the coupling loss can be 40 dB or less in at least a part of the leakage coaxial cable in the longitudinal direction. This makes it possible to provide a leaky coaxial cable that can be used as an antenna for wireless communication in the UHF band with a passive RFID tag.

Here, a plurality of slots including the slot are formed in the outer conductor at intervals in the longitudinal direction, and the dimension of each of the plurality of slots in the circumferential direction is the propagation direction in which the signal propagates. It may be gradually increased.

In this case, the coupling loss of the leaky coaxial cable can be made more even in the longitudinal direction.

Further, in the outer conductor, a plurality of slots including the slot are formed at intervals in the longitudinal direction, and the plurality of slots are repeatedly arranged in the longitudinal direction to determine the repeating dimension of the plurality of slots. When P is set, the dimension of the plurality of slots in the longitudinal direction is W1, the wavelength of the signal transmitted by the leaky coaxial cable is λ, and the wavelength shortening rate is ν, 0.97 × λν ≦ P ≦ 1. .03 × λν and 0.97 × P / 2 ≦ W1 ≦ 1.03 × P / 2 may be satisfied.

In this case, the -1st order radiation from the leaky coaxial cable can be made perpendicular to the longitudinal direction, and an electric field with little fluctuation in the longitudinal direction can be obtained.

According to the above aspect of the present invention, it is possible to provide a leaky coaxial cable that suppresses coupling loss.

It is a perspective view which shows the leakage coaxial cable which concerns on this embodiment. It is a perspective view which shows the leakage coaxial cable which concerns on the modification of this Embodiment. It is a perspective view which shows the leakage coaxial cable which concerns on other modification of this Embodiment. It is a graph which shows the result of Test Example 1-1, 1-2. It is a graph which shows the result of Test Example 2. It is a graph which shows the result of Test Example 3-1, 3-2, 3-3. It is a graph which shows the result of Test Example 4-1 and 4-2.

(First Embodiment)
Hereinafter, the leaky coaxial cable of the first embodiment will be described with reference to the drawings.
As shown in FIG. 1, the leaky coaxial cable 1 includes an inner conductor 2, an insulator 3, and an outer conductor 4. The leaky coaxial cable 1 has a first end portion 1a and a second end portion 1b. The insulator 3 covers the inner conductor 2. The outer conductor 4 covers the insulator 3. A plurality of slots 4a are formed in the outer conductor 4. Each of the plurality of slots 4a is a hole that penetrates the outer conductor 4 in the radial direction. The number of slots 4a formed in the outer conductor 4 may be one. In order to protect the outer conductor 4 and the like, the leaky coaxial cable 1 may include a sheath (rubber, resin, etc.) (not shown) that covers the outer conductor 4.

(Direction definition)
In the present embodiment, the direction along the central axis O of the inner conductor 2 or the outer conductor 4 is referred to as a longitudinal direction. The longitudinal direction is represented by the Z axis. The direction that intersects the central axis O when viewed from the longitudinal direction is referred to as a radial direction. When viewed from the longitudinal direction, the direction that orbits around the central axis O is referred to as the circumferential direction. The longitudinal direction is parallel to the propagation direction in which the signal propagates in the leaky coaxial cable 1. In the leaky coaxial cable 1, the signal propagates from the first end 1a to the second end 1b. The direction in which the signal propagates along the longitudinal direction is referred to as the + Z direction or the terminal side. The direction opposite to the + Z direction is referred to as the −Z direction or the signal source side.

The inner conductor 2 is made of a metal such as copper. The inner conductor 2 extends along the longitudinal direction. The inner conductor 2 may be a stranded wire formed by twisting fine wires of a plurality of conductors. The insulator 3 covers the inner conductor 2 from the outside in the radial direction. As the insulator 3, a resin having an insulating property such as foamed polyethylene is used.

The internal conductor 2 is electrically connected to an external signal source and propagates a high frequency signal supplied from the signal source. With the propagation of the high frequency signal, the electromagnetic wave leaks to the outside of the leaky coaxial cable 1 through the slot 4a formed in the outer conductor 4.

The outer conductor 4 covers the insulator 3 from the outside in the radial direction. The outer conductor 4 is formed, for example, by winding a metal (copper or the like) tape around the insulator 3. Therefore, the inner diameter of the outer conductor 4 is substantially the same as the outer diameter of the insulator 3, or slightly larger than the outer diameter of the insulator 3. There may be a layer of air between the insulator 3 and the outer conductor 4. By preliminarily forming through holes to be the plurality of slots 4a in the tape to be the outer conductor 4, a plurality of slots 4a having an arbitrary arrangement and shape can be easily formed. The thickness (dimension in the radial direction) of the outer conductor 4 is, for example, 0.01 to 0.02 mm.

The inner peripheral surface of the outer conductor 4 may be provided with an insulating base material and an adhesive layer for adhering the insulating base material to the outer conductor 4. As the material of the insulating base material, for example, a polyester resin such as polyethylene terephthalate (PET) or a polyolefin resin such as polypropylene or polyethylene can be adopted. As the material of the adhesive layer, for example, an ethylene-based ionomer resin can be adopted. The insulating base material and the adhesive layer may not have an opening corresponding to the slot 4a.

The plurality of slots 4a are formed at intervals in the longitudinal direction. Each slot 4a extends along the longitudinal and circumferential directions. The shape of each slot 4a is rectangular when viewed from the outside in the radial direction. Alternatively, the shape of each slot 4a may be an oval shape or a parallel quadrilateral shape. Further, even when the tape is flat before the tape serving as the outer conductor 4 is wound around the insulator 3, the shape of each slot 4a is rectangular. As shown in FIG. 1, in the present specification, the dimension of the slot 4a in the longitudinal direction is simply referred to as the longitudinal dimension W1. The dimension of the slot 4a in the circumferential direction is simply referred to as the circumferential dimension W2.

In the present embodiment, the peripheral dimension W2 is larger in the slot 4a closer to the second end 1b of the leaky coaxial cable 1. In other words, the peripheral dimension W2 of each of the plurality of slots 4a gradually increases in the propagation direction in which the signal propagates. Although the details will be described later, by forming the plurality of slots 4a in this way, the coupling loss of the leaky coaxial cable 1 can be made more uniform in the longitudinal direction. As a configuration in which the peripheral dimension W2 becomes larger as the slot 4a closer to the second end portion 1b, the configuration as shown in FIG. 2 can be adopted. In the leaky coaxial cable 1 of FIG. 2, two slots 4a having substantially the same peripheral dimension W2 are formed adjacent to each other in the longitudinal direction, and two slots 4a having a larger peripheral dimension W2 are arranged on the terminal side thereof. In addition, "substantially equal" includes the case where the peripheral dimension W2 can be regarded as equal if the manufacturing error is removed.

It is not essential to make the circumference dimension W2 of each slot 4a different as described above. That is, as shown in FIG. 3, the peripheral dimensions W2 of the slots 4a formed in the outer conductor 4 may be the same as each other. Further, the longitudinal dimension W1 of each slot 4a may be the same as or different from each other.

Here, the leaky coaxial cable 1 of the present embodiment is used as an antenna for communicating with, for example, a passive RFID tag. In the passive RFID tag, a high frequency signal in the UHF band (for example, about 920 MHz) is generally used. In order to maintain a good communication state with such a high-frequency signal used and the distance between the leaky coaxial cable 1 and the passive RFID tag is, for example, about 1 m, it is required that the coupling loss be 40 dB or less. Be done. In order to reduce the coupling loss, it is required to increase the energy of the electromagnetic wave emitted from the leaky coaxial cable 1. Further, as described above, since the leaky coaxial cable 1 of the present embodiment is used in a state where the energy of the emitted electromagnetic wave is increased, it is not suitable for long-distance transmission exceeding 100 m, for example. Considering the use of communicating with the passive RFID tag, the total length of the leaky coaxial cable 1 may be, for example, 10 m or less.

The leaky coaxial cable 1 propagates energy by an electric field called TEM mode. In the outer conductor 4, a current flows along the longitudinal direction. By forming the slot 4a extending in the circumferential direction and the longitudinal direction in the outer conductor 4, the current flowing through the outer conductor 4 is partially cut off. As a result, a potential difference is generated between the signal source side and the terminal side of the slot 4a, an electric field is generated around the leaky coaxial cable, and energy is released to the outside of the leaky coaxial cable 1. Increasing this energy can be realized by increasing the longitudinal dimension W1 and the peripheral dimension W2 of the slot 4a. According to the results of diligent studies by the inventors of the present application, it is preferable that the longitudinal dimension W1 is 10 mm or more and the peripheral dimension W2 is 35% or more of the entire circumference of the outer conductor 4 (total length in the circumferential direction of the outer conductor 4). .. Hereinafter, a more detailed description will be given.

FIG. 4 shows the relationship between the longitudinal dimension W1 and the coupling loss. The conditions of Test Examples 1-1 and 1-2 are as shown in Table 1 below. The “perimeter of the outer conductor” in Table 1 indicates the total length in the circumferential direction of the portion of the outer conductor 4 in which the slot 4a is not formed. The "peripheral aperture ratio R" is the ratio of the peripheral dimension W2 to the peripheral length of the outer conductor 4.

As shown in FIG. 4, in each of Test Examples 1-1 and 1-2, the longitudinal dimension W1 of the slot 4a was different, and the coupling loss was measured. In any of Test Examples 1-1 and 1-2, in the region where the longitudinal dimension W1 is 50 mm or less, the larger the longitudinal dimension W1, the smaller the coupling loss. This is because the larger the longitudinal dimension W1, the larger the amount of electromagnetic waves leaked from the slot 4a. Further, the binding loss in Test Example 1-1 tended to be smaller than the binding loss in Test Example 1-2. This is because the peripheral dimension W2 and the peripheral aperture ratio R in Test Example 1-1 are larger than the peripheral dimension W2 and the peripheral aperture ratio R in Test Example 1-2.

Under the conditions of Test Example 1-1 (R = 83%), the coupling loss could be 40 dB or less by setting the longitudinal dimension W1 to 10 mm or more. Under the conditions of Test Example 1-2 (R = 70%), the coupling loss could be 40 dB or less by setting the longitudinal dimension W1 to 30 mm or more. The upper limit of the longitudinal dimension W1 is arbitrary. For example, when forming a plurality of slots 4a, it is preferable to set the slots 4a so that they are formed at intervals in the longitudinal direction.

FIG. 5 shows the relationship between the peripheral aperture ratio R and the coupling loss. In Test Example 2, the outer diameter of the outer conductor 4 is 10 mm, the number of slots 4a is one, and the longitudinal dimension W1 is 100 mm. Then, the peripheral dimension W2 (peripheral aperture ratio R) was made different, and the coupling loss was measured. As shown in FIG. 5, the larger the peripheral aperture ratio R, the smaller the coupling loss. Under the conditions of Test Example 2, the coupling loss could be 40 dB or less by setting the peripheral aperture ratio R to 35% or more.

From the viewpoint of reducing the coupling loss in a leaky coaxial cable having only one slot 4a, a larger peripheral aperture ratio R is preferable. On the other hand, in a leaky coaxial cable having a plurality of slots 4a, if the peripheral aperture ratio R of the slots 4a is too large, the transmission loss in the portion where the slots 4a is formed becomes large. As a result, the energy of the signal supplied to the slot 4a near the second end 1b is extremely reduced. As a guide, the peripheral aperture ratio R is preferably 95% or less. When the peripheral aperture ratio R is 95% or less, appropriate energy is secured even in the signal supplied to the slot 4a near the second end 1b, and the coupling loss can be reduced for the entire leakage coaxial cable.

FIG. 6 shows the relationship between the inner diameter of the outer conductor 4 (the outer diameter of the insulator 3) and the coupling loss. In Test Examples 3-1 to 3-3, the outer diameters of the inner conductor 2 are 0.6 mm, 1 mm, and 2 mm, respectively. Further, the outer diameter (D) of the insulator 3 is 1.5 mm, 2.5 mm, and 5 mm. The outer diameter of the outer conductor 4 is substantially the same as the value obtained by adding twice the thickness of the outer conductor 4 to the outer diameter of the insulator 3. The following conditions were common to Test Examples 3-1 to 3-3.
Overall length of leaky coaxial cable 1: 5m
Material of insulator 3: Polyethylene foam (wavelength shortening rate 0.8)
Longitudinal dimension W1: 110mm
Peripheral aperture ratio R: 80%
Shape of slot 4a seen from the outside in the radial direction: Number of rectangular slots 4a: 21
Spacing between slots 4a in the longitudinal direction: 128 mm
Signal frequency: 920MHz

The coupling loss was measured by arranging the measuring instrument (dipole antenna) 1.5 m away from each leaky coaxial cable 1 and moving the measuring instrument in the longitudinal direction with respect to the leaky coaxial cable 1. In FIG. 6, the horizontal axis (measurement position) indicates the position of the measuring instrument in the longitudinal direction. Specifically, the point where the horizontal axis is 0 m corresponds to the first end portion 1a of the leaky coaxial cable 1, and the point where the horizontal axis is 5 m corresponds to the second end portion 1b of the leaky coaxial cable 1.

As shown in FIG. 6, the larger the outer diameter D of the insulator 3, the smaller the coupling loss. In particular, in Test Example 3-3 in which the outer diameter D of the insulator 3 is 5 mm, the coupling loss is 40 dB or less in most regions in the longitudinal direction. As in Test Example 3-3, even if the coupling loss exceeds 40 dB in a part of the longitudinal direction, it is possible to communicate with the passive RFID tag. For example, it is sufficient to use only the region of the leakage coaxial cable 1 in which the coupling loss is 40 dB or less (the region where the position in the longitudinal direction is 0 to 4.7 m in Test Example 3-3) as the communication antenna. Alternatively, if the distance between the leaky coaxial cable 1 and the passive RFID tag is made smaller than 1.5 m, the coupling loss can be adjusted to 40 dB or less over the entire length of the leaky coaxial cable 1 in the longitudinal direction.

Here, in general, when the longitudinal dimension W1 is the same, the coupling loss is determined by the ratio between the outer diameter D of the insulator 3 and the length of the edge extending in the circumferential direction of the slot 4a. Therefore, in Test Examples 3-1 to 3-3 in which the peripheral aperture ratios R are equal to each other, it is considered that the coupling loss is also equal. However, such a result was not obtained in Test Examples 3-1 to 3-3, and the larger the outer diameter D of the insulator 3, the smaller the coupling loss. It is conceivable that the reason is that the impedance does not increase due to the edge being coupled to the other portion of the outer conductor 4. For example, in Test Examples 3-1 to 3-3, since the shape of the slot 4a is rectangular, the corners are bent at substantially right angles. Therefore, there is a possibility that the edge extending in the circumferential direction and the edge extending in the longitudinal direction of the slot 4a are capacitively coupled. In this case, the current may travel through the insulator 3 without passing through the outer conductor 4. Alternatively, it is conceivable that the intermediate portion of the edge is coupled to the inner conductor 2. When such a phenomenon occurs, it is considered that the effective edge length is shortened even if the outer diameter D is large, and the coupling loss is not reduced.

Summing up the results of FIGS. 4 to 6, it is preferable to satisfy the following condition A or condition B in order to suppress the binding loss to 40 dB or less.
Condition A: The longitudinal dimension W1 is 10 mm or more, the peripheral aperture ratio R is within the range of 35 to 95%, and the outer diameter D of the insulator 3 is 5 mm or more.
Condition B: The longitudinal dimension W1 is 30 mm or more, the peripheral aperture ratio R is within the range of 70 to 95%, and the outer diameter D of the insulator 3 is 5 mm or more.

Next, with reference to FIG. 7, the effect of increasing the peripheral dimension W2 toward the slot 4a closer to the second end portion 1b will be described. In Test Examples 4-1 and 4-2 shown in FIG. 7, the following conditions are common. In Test Examples 4-1 and 4-2, the foaming rate of the foamed polyethylene, which is the material of the insulator 3, is different from the foaming rate in Test Example 3-1 and the like, so that the wavelength shortening rate is also different.
Leakage coaxial cable 1 length: 1 m
Outer diameter of inner conductor 2: 4.3 mm
Outer diameter D of insulator 3: 10 mm
Material of insulator 3: Polyethylene foam (wavelength shortening rate 0.87)
Longitudinal dimension W1: 100 mm
Shape of slot 4a seen from the outside in the radial direction: Number of rectangular slots 4a: 5
Spacing between slots 4a in the longitudinal direction: 128 mm
Signal frequency: 920MHz

On the other hand, as shown in Table 2, the peripheral dimension W2 is different between Test Example 4-1 and Test Example 4-2. In Test Example 4-1 all the peripheral dimensions W2 of the five slots 4a are common (28 mm). In Test Example 4-2, as shown in FIG. 2, the peripheral dimension W2 is larger in the slot 4a closer to the second end portion 1b. More specifically, the peripheral dimension W2 of the first and second slots 4a counting from the signal source side is 17 mm. The peripheral dimension W2 of the third and fourth slots 4a counting from the signal source side is 20 mm. The peripheral dimension W2 of the fifth slot 4a (closest to the second end 1b) counting from the signal source side is 28 mm.

The coupling loss according to Test Examples 4-1 and 4-2 shown in FIG. 7 is based on a simulation. The horizontal axis of FIG. 7 is a position in the longitudinal direction. As shown in FIG. 7, in any of Test Examples 4-1 and 4-2, the binding loss could be 40 dB or less. However, in Test Example 4-1 the gradual coupling loss decreases in the direction toward the terminal side (+ Z side). This is because the electromagnetic wave leaks as the signal propagates toward the terminal side, and the strength of the signal flowing in the outer conductor 4 is attenuated. On the other hand, in Test Example 4-2, the bond loss could be made more even in the longitudinal direction. This is because the strength of the signal flowing through the outer conductor 4 is attenuated in the direction in which the signal flows by adopting a configuration in which the peripheral dimension W2 is increased toward the slot 4a closer to the second end portion 1b to facilitate leakage of electromagnetic waves. This is because it was canceled. As described above, by adopting a configuration in which the peripheral dimension W2 is increased by the slot 4a closer to the second end portion 1b, the coupling loss can be made more uniform in the longitudinal direction.

Next, a range of preferable slot pitch P when a plurality of slots 4a are provided in the outer conductor 4 will be described. As used herein, the "slot pitch P" is a repeating dimension of the arrangement of slots 4a in the longitudinal direction. More specifically, the slot pitch P is the sum of the longitudinal dimension W1 and the distance between the slots 4a. For example, in Test Example 4-1 described above, since the longitudinal dimension W1 is 100 mm and the distance between the slots 4a is 128 mm, P = 100 + 128 = 228 mm.

Generally, the radial angle θn of the electromagnetic wave from the leaky coaxial cable 1 is expressed by the following equation (1), where the radial angle perpendicular to the central axis O is 0 and the radiation angle inclined toward the terminal side is positive. Will be done.
θn = sin ^-1 (nλ / P + 1 / ν)… (1)
However, n is the radiation mode (negative integer), λ is the wavelength in free space, and ν is the wavelength shortening rate of the leaky coaxial cable 1. The wavelength shortening rate ν is expressed by the following equation (2) based on the effective specific permittivity εs obtained from the volume ratio of the insulator 3 and the hollow portion in the region between the inner conductor 2 and the outer conductor 4. ..
ν = 1 / (εs) ^1/2 ... (2)

Usually, only the so-called -1st order mode of n = -1 is often used. Empirically, -50 ° to + 30 ° is a practical limit range for the direction angle of the -1st mode. Therefore, it is preferable that the slot pitch P satisfies the following equation (3).
λg / (1 + 0.766ν) <P <3λg / (1 + ν)… (3)
Here, λg is the propagation wavelength in the leaky coaxial cable 1, and λg = νλ.
For example, under the condition that the frequency of the signal is 920 MHz (λ≈325.9 mm) and the wavelength shortening rate ν is 0.8, the range of the slot pitch P is preferably 161 mm to 434 mm.

As described above, the leaky coaxial cable 1 includes an inner conductor 2, an insulator 3 that covers the inner conductor 2, and an outer conductor 4 that covers the insulator 3 and has at least one slot 4a formed therein. Then, the total length of the internal conductor 2 (leakage coaxial cable 1) in the longitudinal direction is set to 10 m or less, the longitudinal dimension W1 of the slot 4a is set to 10 mm or more, and the peripheral dimension W2 of the slot 4a is set with respect to the total length in the circumferential direction of the outer conductor 4. The range is 35 to 95%, and the outer diameter D of the insulator 3 is 5 mm or more. As a result, the coupling loss can be reduced to 40 dB or less. This makes it possible to provide a leaky coaxial cable 1 that can be used as an antenna for performing RFID communication in the UHF band.

Further, a plurality of slots 4a may be formed in the outer conductor 4 at intervals in the longitudinal direction. In this case, it is possible to provide a leaky coaxial cable 1 capable of performing RFID communication in a wider range in the longitudinal direction.

Further, the peripheral dimension W2 of each of the plurality of slots 4a may gradually increase in the propagation direction in which the signal propagates. In this case, the coupling loss can be made more even in the longitudinal direction.

Further, a plurality of slots 4a may be formed in the outer conductor 4, and the plurality of slots 4a may be repeatedly arranged in the longitudinal direction. When the repeating dimension (slot pitch) of the arrangement of the slot 4a in the longitudinal direction is P, the longitudinal dimension of the slot 4a is W1, the wavelength of the signal transmitted by the leaky coaxial cable 1 is λ, and the wavelength shortening rate is ν. , 0.97 × λν ≦ P ≦ 1.03 × λν and 0.97 × P / 2 ≦ W1 ≦ 1.03 × P / 2. In this case, the -1st order radiation from the leaky coaxial cable 1 can be made perpendicular to the longitudinal direction, and an electric field with little fluctuation in the longitudinal direction can be obtained.

The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

For example, in the above embodiment, it has been explained that the leaky coaxial cable 1 is used as an antenna for communicating with a passive RFID tag. However, the application of the leaky coaxial cable 1 is not limited to such an application. The leaky coaxial cable 1 of the present embodiment is suitable for, for example, an application in which a coupling loss of 40 dB or less is required with a certain distance (for example, 0.5 m or more) from a communication object. Available. Depending on the application of the leaky coaxial cable 1, the leaky coaxial cable 1 may have a configuration other than the inner conductor 2, the insulator 3, the outer conductor 4, and the sheath.

In addition, it is possible to replace the constituent elements in the above-described embodiment with well-known constituent elements as appropriate without departing from the spirit of the present invention, and the above-described embodiments and modifications may be appropriately combined.

1 ... Leakage coaxial cable 2 ... Internal conductor 3 ... Insulator 4 ... External conductor 4a ... Slot D ... Insulator outer diameter Z ... Longitudinal direction W1 ... Longitudinal dimension (dimension in longitudinal direction) W2 ... Circumferential dimension (dimension in circumferential direction) )

Claims

With the inner conductor,
The insulator that covers the inner conductor and
An external conductor covering the insulator and having at least one slot formed therein.
The total length of the internal conductor in the longitudinal direction is 10 m or less.
The dimension of the slot in the longitudinal direction is 10 mm or more.
The dimension of the slot in the circumferential direction of the outer conductor is in the range of 35 to 95% with respect to the total length of the outer conductor in the circumferential direction.
A leaky coaxial cable having an outer diameter of the insulator of 5 mm or more.
A plurality of slots including the slot are formed in the outer conductor at intervals in the longitudinal direction.
The leaky coaxial cable according to claim 1, wherein the dimension of each of the plurality of slots in the circumferential direction is gradually increased in the propagation direction in which the signal propagates.
A plurality of slots including the slot are formed in the outer conductor at intervals in the longitudinal direction.
The plurality of slots are repeatedly arranged in the longitudinal direction, and the plurality of slots are repeatedly arranged in the longitudinal direction.
When the repeating dimension of the plurality of slots is P, the dimension of each of the plurality of slots in the longitudinal direction is W1, the wavelength of the signal transmitted by the leaky coaxial cable is λ, and the wavelength shortening rate is ν. , 0.97 × λν ≦ P ≦ 1.03 × λν and 0.97 × P / 2 ≦ W1 ≦ 1.03 × P / 2, the leaky coaxial cable according to claim 1 or 2.