Coaxial cable

Abstract

This coaxial cable comprises an inner conductor, an insulator covering an outer circumference of the inner conductor, an outer conductor covering an outer circumference of the insulator, and a sheath covering an outer circumference of the outer conductor, wherein: the inner conductor is a compressed conductor including a central wire and a plurality of outer circumferential wires surrounding the central wire; and the inner conductor has a compression ratio which, as a percentage, lies between 23.0% and 35.0% inclusive, calculated by means of formula (B) from a cross-sectional area S1, calculated by means of formula (A) from a diameter D of the central wire and a total number n of the central wire and the outer circumferential wires, and a cross-sectional area S2 of the compressed conductor, and where an outer diameter of the insulator is at least equal to 1.25 mm and less than 1.75 mm. (A): S1=n×π×0.25×D2 (B): Compression ratio=[1-S2 / S1]

Description

Technical Field

[0001] This disclosure relates to coaxial cables.

[0002] This application claims priority based on Japanese Application No. 2021-061964 filed on March 31, 2021, and incorporates by reference all the descriptions set forth in the said Japanese application.

Background Art

[0003] Patent Document 1 discloses a shielded cable including an inner conductor, an insulator provided so as to cover the outer periphery of the inner conductor, and an outer conductor provided so as to cover the outer periphery of the insulator, where the outer conductor includes a first outer conductor formed of a horizontally wound shield in which a first stranded wire is spirally wound around the outer periphery of the insulator, and a second outer conductor formed of a braided shield provided so as to cover the outer periphery of the first outer conductor and formed by braiding second stranded wires.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] The coaxial cable of this disclosure includes an inner conductor, an insulator covering the outer periphery of the inner conductor, an outer conductor covering the outer periphery of the insulator, and a sheath covering the outer periphery of the outer conductor, where the inner conductor is a compressed conductor having a central stranded wire and a plurality of outer peripheral stranded wires surrounding the central stranded wire, The inner conductor has a cross-sectional area S1 calculated from the outer diameter D of the central strand and the total number n of the central strand and the outer strands using the following formula (A), and a compressibility ratio calculated from the cross-sectional area S2 of the compression conductor using the following formula (B), where the compressibility ratio is 23.0% or more and 35.0% or less in percentage terms. S1 = n × π × 0.25 × D 2 ...(A) Compression ratio=[1-S2 / S1] (B) The outer diameter of the insulator is 1.25 mm or more and less than 1.75 mm. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 is a cross-sectional view of a coaxial cable according to one aspect of the present disclosure, in a plane perpendicular to the longitudinal direction. [Figure 2] Figure 2 is an explanatory diagram of the stranded state of the internal conductor of a coaxial cable according to one aspect of the present disclosure before compression. [Figure 3] Figure 3 is an explanatory diagram of the bending resistance test. [Modes for carrying out the invention]

[0007] [Issues this disclosure aims to address]

[0008] As disclosed in Patent Document 1, coaxial cables for transmitting high-speed signals have been considered for some time.

[0009] Incidentally, while the communication speeds required for coaxial cables have increased in recent years, conventional coaxial cables suffer from significant signal attenuation, which can lead to communication failures. Therefore, there is a need to suppress signal attenuation.

[0010] Furthermore, since coaxial cables may be repeatedly bent depending on their installation location and usage, they also need to have excellent bending resistance.

[0011] Therefore, the present disclosure aims to provide a coaxial cable that has suppressed attenuation and excellent flexibility.

[0012] [Effects of the Present Disclosure]

[0013] According to the present disclosure, a coaxial cable with suppressed attenuation and excellent bending resistance can be provided.

[0014] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description thereof will not be repeated.

[0015] (1) The coaxial cable according to one aspect of the present disclosure includes an inner conductor, an insulator covering the outer periphery of the inner conductor, an outer conductor covering the outer periphery of the insulator, and a sheath covering the outer periphery of the outer conductor. The inner conductor is a compressed conductor having a central strand and a plurality of outer strands surrounding the central strand. The inner conductor has a cross-sectional area S1 calculated by the following formula (A) from the outer diameter D of the central strand and the total number n of the central strand and the outer strands, and a compression ratio calculated by the following formula (B) from the cross-sectional area S2 of the compressed conductor is 23.0% or more and 35.0% or less in percentage. S1 = n × π × 0.25 × D 2 ···(A) Compression ratio = [1 - S2 / S1] ···(B) The outer diameter of the insulator is 1.25 mm or more and less than 1.75 mm.

[0016] The inventor of the present invention has studied a coaxial cable with suppressed attenuation and excellent bending resistance. From the viewpoint of enhancing the bending resistance, it is preferable to use a stranded wire formed by twisting a plurality of conductor strands as the inner conductor. However, when a conventional stranded wire is used, there is a problem that the attenuation amount becomes very large.

[0017] Therefore, the coaxial cable of this disclosure can use a stranded wire containing multiple conductor strands, that is, a compressed conductor obtained by twisting together multiple conductor strands and compressing it from the outer side.

[0018] By compressing a stranded wire containing multiple conductor strands to create a compressed conductor, it is possible to create a coaxial cable with excellent bending resistance inherent to the stranded wire.

[0019] Furthermore, by using a compressed conductor as the internal conductor, the proportion of the conductor portion (the area occupied solely by the conductor portion) in the cross-section of the internal conductor (the area of ​​the circumscribed circle of the internal conductor), i.e., the proportion of the conductor strand portion, can be increased compared to the case where stranded wire before compression is used as the internal conductor. For this reason, by using a compressed conductor as the internal conductor, the conductor strands can function not as individual, independent conductors, but as a single conductor with a larger outer diameter, thereby suppressing conductor loss and attenuation.

[0020] Furthermore, when the outer diameter of the insulator is 1.25 mm or more and less than 1.75 mm, the compression ratio of the internal conductor can be set to 23.0% or more, thereby sufficiently suppressing attenuation, especially for 6.0 GHz signals where suppression of attenuation is particularly required.

[0021] Furthermore, by limiting the compression ratio of the internal conductor to 35.0% or less, the productivity of coaxial cables can be increased, and the characteristic impedance of the coaxial cable can be easily set to within 50Ω ± 2Ω.

[0022] (2) A coaxial cable according to one aspect of the present disclosure comprises an internal conductor and An insulator covering the outer circumference of the aforementioned internal conductor, An outer conductor covering the outer circumference of the insulator, The outer conductor comprises a sheath that covers the outer circumference of the outer conductor, The aforementioned internal conductor is a compression conductor having a central strand and a plurality of outer strands surrounding the central strand. The inner conductor has a cross-sectional area S1 calculated from the outer diameter D of the central strand and the total number n of the central strand and the outer strands using the following formula (A), and a compression ratio calculated from the cross-sectional area S2 of the compression conductor using the following formula (B), where the compression ratio is 24.0% or more and 37.0% or less in percentage terms. S1 = n × π × 0.25 × D 2 ...(A) Compression ratio=[1-S2 / S1] (B) The outer diameter of the insulator is 1.75 mm or more and less than 2.25 mm.

[0023] When the outer diameter of the insulator is 1.75 mm or more and less than 2.25 mm, the compression ratio of the internal conductor can be set to 24.0% or more, which allows for sufficient suppression of attenuation, especially for 6.0 GHz signals where suppression of attenuation is particularly important.

[0024] Furthermore, by limiting the compression ratio of the internal conductor to 37.0% or less, the productivity of coaxial cables can be increased, and the characteristic impedance of the coaxial cable can be easily set to within 50Ω ± 2Ω.

[0025] (3) A coaxial cable according to one aspect of the present disclosure comprises an internal conductor and An insulator covering the outer circumference of the aforementioned internal conductor, An outer conductor covering the outer circumference of the insulator, The outer conductor comprises a sheath that covers the outer circumference of the outer conductor, The aforementioned internal conductor is a compression conductor having a central strand and a plurality of outer strands surrounding the central strand. The inner conductor has a cross-sectional area S1 calculated from the outer diameter D of the central strand and the total number n of the central strand and the outer strands using the following formula (A), and a compressibility ratio calculated from the cross-sectional area S2 of the compression conductor using the following formula (B), where the compressibility ratio is 20.0% or more and 33.0% or less in percentage terms. S1 = n × π × 0.25 × D 2 ...(A) Compression ratio=[1-S2 / S1] (B) The outer diameter of the insulator is 2.25 mm or more and 2.80 mm or less.

[0026] When the outer diameter of the insulator is between 2.25 mm and 2.80 mm, the compression ratio of the internal conductor can be set to 20.0% or higher, which allows for sufficient suppression of attenuation, especially for 6.0 GHz signals where suppression of attenuation is particularly important.

[0027] Furthermore, by limiting the compression ratio of the internal conductor to 33.0% or less, the productivity of coaxial cables can be increased, and the characteristic impedance of the coaxial cable can be easily set to within 50Ω ± 2Ω.

[0028] (4) The insulator may have one to three insulating layers.

[0029] Having one or more insulating layers in the insulator makes it easier to adjust the relative permittivity and thickness of the entire insulator, thus allowing the characteristic impedance of the coaxial cable to be easily adjusted to the desired range. Furthermore, by using a configuration with three or fewer insulating layers, the productivity of coaxial cables can be increased.

[0030] (5) The insulator may include a layer of foamed polyolefin.

[0031] By having a layer of foamed polyolefin in the insulator, the dielectric constant of the insulator can be reduced, making it possible to reduce the thickness of the insulator required to achieve the desired characteristic impedance of the coaxial cable. This makes it possible to reduce the diameter of the coaxial cable, making it lighter and easier to handle.

[0032] (6) The insulator has, in order from the inner conductor side, a first insulating layer, a second insulating layer, and a third insulating layer. The thickness of the second insulating layer is greater than the thickness of the first insulating layer and the thickness of the third insulating layer. The first and third insulating layers may consist solely of non-foamed polyolefin, and the second insulating layer may consist solely of foamed polyolefin.

[0033] When an insulator has a first to third insulating layer, the first and third insulating layers located on the surface side of the insulator are made only of non-foamed polyolefin, which prevents damage to the insulator due to friction with other components. Furthermore, by making the second insulating layer, located in the middle of the thickness direction of the insulator, made only of foamed polyolefin, the properties of the insulator, such as the relative permittivity, can be easily controlled by adjusting, for example, the degree of foaming. By making the film thickness of the second insulating layer thicker than that of the first and third insulating layers, the influence of the second insulating layer on the properties of the insulator, such as the relative permittivity, can be greatly increased, making it particularly easy to control the properties of the insulator.

[0034] (7) The insulator may have a relative permittivity of 2.4 or less.

[0035] The lower the dielectric constant of the material used as the insulator, the higher the characteristic impedance of the coaxial cable. Conversely, the thinner the insulator, the lower the characteristic impedance of the coaxial cable.

[0036] Coaxial cables are required to have a characteristic impedance of 50Ω ± 2Ω, that is, between 48Ω and 52Ω. To achieve this characteristic impedance, using a material with a relative permittivity of 2.4 or less as the insulating material makes it easy to achieve the required characteristic impedance even when the thickness of the insulating material is reduced, i.e., when the diameter of the coaxial cable is reduced.

[0037] Therefore, by using a material with a relative permittivity of 2.4 or less as the insulating material, it becomes possible to reduce the diameter of the coaxial cable, thereby making the coaxial cable lighter and improving its handling.

[0038] (8) The central strand and the outer strand of the inner conductor are made of soft copper wire. The outer conductor comprises, in order from the insulator side, a first outer conductor and a second outer conductor. The first outer conductor may be a copper-clad polyester tape, and the second outer conductor may be a braided shield of tin-plated soft copper wire.

[0039] By using soft copper wire for the central and outer conductor strands of the internal conductor, a coaxial cable with particularly high reliability and excellent high-frequency characteristics can be produced.

[0040] By stacking the above-mentioned components as the first and second external conductors, a particularly high noise shielding effect can be achieved. In other words, the intrusion of noise from the outside and the emission of noise to the outside can be particularly effectively shielded.

[0041] [Details of the embodiments of this disclosure] A specific example of a coaxial cable according to one embodiment of this disclosure (hereinafter referred to as "this embodiment") will be described below with reference to the drawings. However, the present invention is not limited to these examples and is intended to be shown by the claims, with all modifications within the meaning and scope of the equivalents of the claims being included. (Coaxial cable) Figure 1 shows an example of a cross-sectional view of the coaxial cable of this embodiment, perpendicular to its longitudinal direction. Figure 2 shows a cross-sectional view of the stranded wires of the internal conductor before they are compressed. Figures 1 and 2 are schematic representations of the components to explain the structure of the coaxial cable and internal conductor of this embodiment, and the size and other characteristics are not limited to those shown in Figures 1 and 2.

[0042] As shown in Figure 1, the coaxial cable 10 of this embodiment may include an inner conductor 11, an insulator 12 covering the outer circumference of the inner conductor 11, an outer conductor 13 covering the outer circumference of the insulator 12, and a sheath 14 covering the outer circumference of the outer conductor 13.

[0043] Each component is described below. (1) Internal conductor (1-1) About the materials The internal conductor 11 may include a plurality of conductor strands 111, as shown in Figure 1. The internal conductor 11 may have a central strand 111A positioned in the center and a plurality of outer strands 111B arranged around the outer circumference of the central strand 111A so as to surround the central strand 111A.

[0044] The internal conductor 11 is a compressed conductor formed by twisting together multiple conductor strands 111 and compressing the stranded wire from the outer side.

[0045] The material of the conductor strands 111 constituting the inner conductor 11 is not particularly limited, but soft copper wire or copper alloy wire can be suitably used as the conductor strands 111, i.e., the central strand 111A and the outer strand 111B, with soft copper wire being more suitably used. By using soft copper wire or copper alloy wire as the conductor strands 111, a coaxial cable with particularly high reliability and excellent high-frequency characteristics can be made.

[0046] Furthermore, from the viewpoint of transmitting high-frequency signals, it is preferable that the conductor strands 111 do not have a plating film on their surface. (1-2) Regarding the structure As described above, the internal conductor 11 can be a compressed conductor obtained by compressing a stranded wire containing multiple conductor strands 111.

[0047] The inventors of the present invention have investigated a coaxial cable that suppresses attenuation and has excellent bending resistance. From the viewpoint of improving bending resistance, it is preferable to use a stranded wire made by twisting together multiple conductor strands as the internal conductor 11. However, when conventional stranded wires are used, there is a problem that the attenuation becomes very large.

[0048] Therefore, the coaxial cable 10 of this embodiment can use a stranded wire containing multiple conductor strands 111, that is, a compressed conductor obtained by twisting together multiple conductor strands 111 and compressing the stranded wire from the outer side.

[0049] By compressing a stranded wire containing multiple conductor strands 111 to form a compressed conductor, a coaxial cable with excellent bending resistance inherent to the stranded wire can be produced.

[0050] Here, Figure 2 shows a cross-sectional view perpendicular to the longitudinal direction of a stranded wire 21, which is made by twisting together multiple conductor strands 211 before compression.

[0051] As is clear from comparing the ratio of the area occupied by the conductor strands 211 within the circumscribed circle 21A of the stranded wire 21 in Figure 2 with the ratio of the area occupied by the conductor strands 111 within the circumscribed circle 11A of the internal conductor 11 in Figure 1, the proportion occupied by the conductor strands 111 within the circumscribed circle 11A is larger for the internal conductor 11. In other words, by using a compressed conductor as the internal conductor 11, the proportion of the conductor portion (the area occupied only by the conductor portion) in the cross-section of the internal conductor 11 (the area of ​​the circumscribed circle of the internal conductor), i.e., the proportion of the conductor strand portion, can be increased compared to the case where the stranded wire 21 before compression is used as the internal conductor 11. Therefore, by using a compressed conductor as the internal conductor 11, the conductor strands 111 can function not as individual independent conductors, but as a single conductor with a larger outer diameter, thereby suppressing conductor loss and attenuation. (1-3) Regarding compression ratio The compression ratio can be calculated using the following formula (B) from the cross-sectional area S1, which is calculated from the outer diameter D of the central wire 111A and the total number n of the central wire 111A and outer wire 111B, and the cross-sectional area S2 of the compressed conductor, and can be expressed as a percentage. That is, the compression ratio can be expressed as a percentage by multiplying the value calculated using the following formula (B) by 100.

[0052] S1 = n × π × 0.25 × D 2 ...(A) Compression ratio=[1-S2 / S1] (B) In equations (A) and (B), S1 is the cross-sectional area of ​​the conductor strands 211 in the stranded wire 21 before it is compressed. In equation (B), S2 is the cross-sectional area of ​​the conductor strands in the compressed conductor.

[0053] Therefore, the compression ratio can also be defined as the reduction in the cross-sectional area of ​​the conductor strands when the stranded wire 21 is converted into the compressed inner conductor 11.

[0054] If the cross-sectional area S1 of the conductor strands 211 in the stranded wire 21 before compression is known, it can be calculated from equation (B) above. If the cross-sectional area S1 of the conductor strands 211 in the stranded wire 21 before compression is unknown, it can be calculated from the cross-sectional shape of the compressed inner conductor 11 using equation (A) by the following procedure.

[0055] In the case of the compression ratio of the inner conductor 11 in the coaxial cable 10 of this embodiment, the central strand 111A among the conductor strands 111 of the inner conductor 11 maintains a partially circular cross-sectional shape. Partially means that although it maintains a circular shape overall, a part of it (especially the part in contact with the outer strands 111B) is crushed due to compression. Therefore, the maximum width of the central strand 111A passing through the center of its cross-section can be considered as the outer diameter D of the central strand 111A. Then, the cross-sectional area of ​​the central strand 111A can be calculated from the outer diameter D of the central strand 111A.

[0056] Next, by multiplying the cross-sectional area of ​​the central strand 111A by the number of conductor strands 111, the cross-sectional area S1 of the portion of the stranded wire 21 containing conductor strands 211 before it is compressed can be calculated. That is, S1 can be calculated using the above formula (A). In the case of the coaxial cable 10 shown in Figure 1, the total number n of the central strand 111A and outer strands 111B of the inner conductor 11 is 7.

[0057] The cross-sectional area S2 of the compressed conductor can be calculated from a cross-section perpendicular to the longitudinal direction of the coaxial cable, using image processing software or similar methods as needed. In other words, the cross-sectional area S2 of the compressed conductor is the area of ​​the net conductor portion excluding the air gap.

[0058] The compression ratio of the internal conductor 11 of the coaxial cable in this embodiment is preferably 20.0% or more and 37.0%, and more preferably 20.5% or more and 36.0%.

[0059] This is because, by setting the compression ratio of the internal conductor 11 to 20.0% or higher, the attenuation of 6.0 GHz signals, for which suppression of attenuation is particularly required in recent years, can be sufficiently suppressed.

[0060] However, if the compression ratio of the internal conductor 11 is increased excessively, productivity may decrease, and it may become difficult to satisfy the characteristic impedance of the coaxial cable, which is normally required to be within 50Ω ± 2Ω. For this reason, it is preferable that the compression ratio of the internal conductor 11 be 37.0% or less.

[0061] The characteristics required for the coaxial cable 10 in this embodiment, and the corresponding range of suitable compression ratios for the internal conductor 11, also vary depending on the size of the coaxial cable 10. Since the sizes of each component constituting the coaxial cable 10 vary by approximately the same proportion depending on the size of the coaxial cable 10, the suitable range of compression ratios will be explained below based on the outer diameter D12 of the insulator 12. (1-3-1) When the outer diameter of the insulator is 1.25 mm or more and less than 1.75 mm In particular, when the outer diameter D12 of the insulator 12 is 1.25 mm or more and less than 1.75 mm, the compressibility of the internal conductor 11 is preferably 23.0% or more and 35.0% or less, and more preferably 24.0% or more and 34.0% or less.

[0062] When the outer diameter D12 of the insulator 12 is 1.25 mm or more and less than 1.75 mm, the compression ratio of the internal conductor 11 can be set to 23.0% or more, thereby sufficiently suppressing attenuation, especially for 6.0 GHz signals where suppression of attenuation is required.

[0063] Furthermore, by setting the compression ratio of the internal conductor 11 to 35.0% or less, the productivity of coaxial cables can be increased, and the characteristic impedance of the coaxial cable can be easily set to within 50Ω ± 2Ω. (1-3-2) When the outer diameter of the insulator is 1.75 mm or more and less than 2.25 mm In particular, when the outer diameter D12 of the insulator 12 is 1.75 mm or more and less than 2.25 mm, the compressibility of the internal conductor 11 is preferably 24.0% or more and 37.0% or less, and more preferably 25.0% or more and 36.0% or less.

[0064] When the outer diameter D12 of the insulator 12 is 1.75 mm or more and less than 2.25 mm, the compression ratio of the internal conductor 11 can be set to 24.0% or more, thereby sufficiently suppressing attenuation, especially for 6.0 GHz signals where suppression of attenuation is required.

[0065] Furthermore, by setting the compression ratio of the internal conductor 11 to 37.0% or less, the productivity of coaxial cables can be increased, and the characteristic impedance of the coaxial cable can be easily set to within 50Ω ± 2Ω. (1-3-3) When the outer diameter of the insulator is 2.25 mm or more and 2.80 mm or less In particular, when the outer diameter D12 of the insulator 12 is 2.25 mm or more and 2.80 mm or less, the compressibility of the internal conductor 11 is preferably 20.0% or more and 33.0%, and more preferably 20.5% or more and 32.0%.

[0066] When the outer diameter D12 of the insulator 12 is 2.25 mm or more and 2.80 mm or less, the compression ratio of the internal conductor 11 can be set to 20.0% or more, thereby sufficiently suppressing attenuation, especially for 6.0 GHz signals where suppression of attenuation is required.

[0067] Furthermore, by setting the compression ratio of the internal conductor 11 to 33.0% or less, the productivity of coaxial cables can be increased, and the characteristic impedance of the coaxial cable can be easily set to within 50Ω ± 2Ω. (2) Insulator (2-1) About the materials The material of the insulator 12 is not particularly limited, but polymer materials can be suitably used, and materials with a relative permittivity of 2.4 or less can be suitably used.

[0068] Materials with low molecular polarity, particularly nonpolar materials, can be suitably used as the material for the insulator 12. For example, one or more materials selected from polyolefins such as polyethylene and polypropylene, or fluoropolymers such as polytetrafluoroethylene, can be preferably used as the material for the insulator 12, with polyolefins being more preferable.

[0069] The material of the insulator 12 may be crosslinked or foamed. Foaming can reduce the dielectric constant of the insulator.

[0070] The insulator 12 may also contain various additives such as flame retardants in addition to the polymer material described above.

[0071] The lower the dielectric constant of the material used for the insulator 12, the higher the characteristic impedance of the coaxial cable 10. Conversely, the thinner the insulator 12, the lower the characteristic impedance of the coaxial cable 10.

[0072] The coaxial cable 10 is required to have a characteristic impedance of 50Ω ± 2Ω, that is, between 48Ω and 52Ω. To achieve this characteristic impedance, by using a material with a relative permittivity of 2.4 or less as the material for the insulator 12, the required characteristic impedance can be easily achieved even when the thickness of the insulator 12 is reduced, i.e., when the diameter of the coaxial cable 10 is reduced.

[0073] Therefore, by using a material with a relative permittivity of 2.4 or less as the material for the insulator 12, that is, by making the relative permittivity of the insulator 12 2.4 or less, it becomes possible to reduce the diameter of the coaxial cable 10. Consequently, the coaxial cable 10 can be made lighter and its handling can be improved. It is more preferable that the relative permittivity of the material for the insulator 12 be 1.65 or less.

[0074] The lower limit of the relative permittivity of the insulator material 12 is not particularly limited, but it can be, for example, 1.2 or higher.

[0075] As will be described later, the insulator 12 may have, for example, one or more insulating layers. Furthermore, the material of the insulator 12 may be foamed as described above. For this reason, the insulator 12 may have, for example, a layer of foamed polymer material or a layer of foamed polyolefin. By having a layer of foamed polyolefin in the insulator 12, the relative permittivity of the insulator 12 can be reduced, and the thickness of the insulator 12 required to make the coaxial cable 10 have the desired characteristic impedance can be reduced. As a result, it becomes possible to make the coaxial cable 10 smaller in diameter, making the coaxial cable 10 lighter and improving its handling. (2-2) About the structure The insulator 12 can consist of a single insulating layer, or it can consist of multiple insulating layers.

[0076] The statement that the insulator 12 has multiple insulating layers means, for example, as shown in Figure 1, that the insulator 12 has multiple layered insulating layers, such as the first insulating layer 121, the second insulating layer 122, and the third insulating layer 123, in order from the inner conductor 11 side. Figure 1 shows an example with three insulating layers, but the configuration is not limited to this.

[0077] When the insulator 12 has multiple insulating layers, the number of insulating layers is not particularly limited. However, if the configuration has an excessive number of insulating layers, productivity may decrease. Therefore, it is preferable that the number of insulating layers be five or less, and more preferably three or less.

[0078] Therefore, it is preferable that the insulator 12 has one to three insulating layers.

[0079] Having one or more insulating layers in the insulator 12 makes it easier to adjust the relative permittivity and thickness of the entire insulator 12, thus allowing the characteristic impedance of the coaxial cable 10 to be easily adjusted to a desired range. Furthermore, by configuring the insulator 12 to have three or fewer insulating layers, the productivity of the coaxial cable 10 can be increased.

[0080] When the insulator 12 has multiple insulating layers, the configuration of each insulating layer is not particularly limited, but each insulating layer can be an insulating layer that differs in, for example, the materials it contains, and whether or not it is foamed or crosslinked.

[0081] For example, the insulator 12 may have, in order from the inner conductor 11 side, a first insulating layer 121, a second insulating layer 122, and a third insulating layer 123.

[0082] In this case, it is preferable that the film thickness T122 of the second insulating layer 122 is thicker than the film thickness T121 of the first insulating layer and the film thickness T123 of the third insulating layer 123. That is, it is preferable that T122 > T121 and T122 > T123 are satisfied.

[0083] Furthermore, it is preferable that, for example, the first insulating layer 121 and the third insulating layer 123 consist only of unfoamed polyolefin, and the second insulating layer 122 consists only of foamed polyolefin.

[0084] If the insulator 12 has a first insulating layer 121 to a third insulating layer 123, the first insulating layer 121 and the third insulating layer 123 located on the surface side of the insulator 12 are made only of non-foamed polyolefin, thereby preventing damage to the insulator 12 due to friction with other components. Furthermore, by making the second insulating layer 122 located in the middle of the thickness direction of the insulator 12 made only of foamed polyolefin, the properties of the insulator 12, such as the relative permittivity, can be easily controlled by adjusting, for example, the degree of foaming. As described above, by satisfying the relationships T122>T121 and T122>T123, the influence of the second insulating layer 122 on the properties of the insulator 12, such as the relative permittivity, can be greatly increased, making it particularly easy to control the properties of the insulator 12.

[0085] Furthermore, "non-foamed polyolefin" means that it is intentionally not foamed. Therefore, for example, in a cross-section perpendicular to the longitudinal direction of the coaxial cable 10, it means that multiple bubbles cannot be seen with the naked eye in a layer composed solely of non-foamed polyolefin. (2-3) Outer diameter of the insulator The outer diameter D12 of the insulator 12 can be selected according to the characteristic impedance required for the coaxial cable 10. The outer diameter D12 of the insulator 12 is preferably 1.25 mm or more and 2.80 mm or less, and more preferably 1.50 mm or more and 2.70 mm or less.

[0086] The outer diameter D12 of the insulator 12, as shown in Figure 1, is the outer diameter of the outermost insulating layer among the insulating layers that make up the insulator 12 covered by the outer conductor 13 in the coaxial cable 10. Therefore, in the case of the coaxial cable 10 shown in Figure 1, the outer diameter D12 of the insulator 12 is the outer diameter of the third insulating layer 123, which is the outermost layer among the insulating layers 12 covered by the outer conductor 13.

[0087] The coaxial cable of this embodiment can be used, for example, as an in-vehicle cable, and by setting the outer diameter D12 of the insulator 12 to 1.25 mm or more and 2.80 mm or less, it can be kept within the allowable outer diameter range of an in-vehicle connector.

[0088] The outer diameter D12 of the insulator 12 can be measured in accordance with JIS C 3005 (2014). Specifically, the outer diameter of the insulator 12 can be measured at two or more locations in the same plane perpendicular to the central axis of the coaxial cable 10, and the average value of these measurements can be taken as the outer diameter of the insulator.

[0089] Furthermore, when measuring the outer diameter of the insulator 12 at two or more locations within a single plane perpendicular to the central axis of the coaxial cable 10, that is, within a single cross-section perpendicular to the central axis of the coaxial cable 10, the outer diameter will be measured along the diameter of the insulator. When performing the above measurement, it is preferable to select the measurement locations such that the angles between the multiple diameters of the insulator being measured are approximately equal. Specifically, for example, the outer diameter of the insulator 12 can be measured along the diameters of two orthogonal insulators 12 in a plane perpendicular to the central axis of the coaxial cable 10 being measured, and the average value can be used as the outer diameter of the insulator. The outer diameters D11, D13, and D14 of the inner conductor 11, outer conductor 13, and sheath 14 can be measured in the same manner. (3) Outer conductor The outer conductor 13 can be arranged to cover the outer circumference of the insulator 12. The outer conductor 13 may consist of one layer, or it may consist of two or more layers. From the viewpoint of particularly enhancing the noise shielding effect in the coaxial cable 10, it is preferable that the outer conductor 13 has two or more layers. However, from the viewpoint of productivity, it is preferable that the outer conductor 13 has two layers. That is, it is preferable that the outer conductor 13 has a first outer conductor 131 and a second outer conductor 132 in that order from the insulator 12 side.

[0090] By stacking a first outer conductor 131 and a second outer conductor 132 as the outer conductor 13, the volume of conductive material surrounding the outer circumference of the inner conductor 11 increases, achieving a higher noise shielding effect compared to using only one type of outer conductor. In other words, having two layers of outer conductors 13 effectively shields against the intrusion of noise from the outside and the emission of noise to the outside.

[0091] As will be described later, the coaxial cable 10 of this embodiment can use, for example, a composite material of a base material and a metal film as the first outer conductor 131, and a braided shield (braided shield) made of metal strands as the second outer conductor 132. By arranging the metal film of the first outer conductor 131 and the braided shield of the second outer conductor 132 to be in direct contact, the noise shielding performance of the outer conductor 13 can be particularly effectively enhanced.

[0092] The configuration of the coaxial cable 10 having two layers of outer conductors as the outer conductor 13, consisting of a first outer conductor 131 and a second outer conductor 132, is described below. (3-1) First outer conductor The first outer conductor 131 can be, for example, a film-like member having a metal film. Due to the presence of the metal film, the first outer conductor 131 plays a role in shielding the inner conductor 11 from the intrusion of external noise and the emission of external noise.

[0093] When the first outer conductor 131 is made of a film-like material having a metal film, the first outer conductor 131 may consist only of the metal film, or it may be a composite material in which the metal film is laminated onto a substrate or the like.

[0094] When the first outer conductor 131 is made of a composite material, it may have a polymer film as a base material and a metal film disposed on the surface of the base material.

[0095] The method for arranging the metal film on the substrate surface is not particularly limited, and it can be formed and fixed to the substrate by vapor deposition, plating, adhesive, etc. By making the first outer conductor 131 a composite material of the substrate and the metal film, the mechanical strength can be increased and handling can be improved compared to the case in which the first outer conductor 131 is composed of the metal film alone. By increasing the mechanical strength of the first outer conductor 131, the first outer conductor 131 becomes less likely to be damaged when the coaxial cable 10 is bent, thus particularly enhancing the bending resistance of the coaxial cable 10.

[0096] When the first outer conductor 131 is a film-like member having a metal film as described above, the type of metal film is not particularly limited, but examples include metal materials such as copper, copper alloys, aluminum, and aluminum alloys. The metal film may consist of a film of a single metal type, or layers of two or more metal types may be laminated. In addition, a non-metallic material, such as a protective film made of an organic material, may be placed on the surface of the metal film as needed.

[0097] The first outer conductor 131 may have a base material as described above. The material of the base material is not particularly limited. Examples of base material materials include polyester resins such as polyethylene terephthalate (PET), polyolefin resins such as polypropylene, and vinyl resins such as polyvinyl chloride. The base material may also contain various polymer species and various additives. From the viewpoint of excellent mechanical strength and flexibility, polyester resin can be suitably used as the polymer species.

[0098] When the first outer conductor 131 is a composite material of a substrate and a metal film, the thickness of the substrate, the metal film, and the first outer conductor 131 are not particularly limited.

[0099] For example, from the viewpoint of ensuring the small diameter and flexibility of the coaxial cable 10, the overall thickness of the first outer conductor 131 is preferably 500 μm or less, and more preferably 100 μm or less.

[0100] Furthermore, from the viewpoint of ensuring sufficient mechanical strength and handling of the first outer conductor 131, the substrate is preferably thicker than the metal film, and particularly preferably 10 μm or more.

[0101] The thickness of the metal film is preferably 1 μm or more from the viewpoint of exhibiting sufficient noise shielding. On the other hand, from the viewpoint of ensuring flexibility, the thickness of the metal film is preferably 30 μm or less. The metal film may be provided on one side or both sides of the substrate. However, when the first outer conductor 131 is bonded to the insulator 12, it is preferable to provide an adhesive layer with adhesive on the side of the substrate facing the insulator. And it is preferable to provide the metal film on the side of the substrate opposite to the side facing the insulator. (3-2) Second outer conductor The second outer conductor 132 may have a structure formed into a hollow cylindrical shape by braiding together thin metal strands made of a metal material such as copper, copper alloy, aluminum, or aluminum alloy, or a material with a plating applied to the surface of such metal materials. In other words, the second outer conductor 132 can be a braided shield made of braided metal strands. As the metal strands, soft copper wire or hard copper wire can also be used. As mentioned above, the metal strands may have a plating treatment on their surface, such as silver or tin plating. For this reason, as the metal strands, for example, silver-plated soft copper wire or tin-plated soft copper wire can be used, and a braided shield of silver-plated soft copper wire or tin-plated soft copper wire can be used.

[0102] The second outer conductor 132 plays a role in shielding the inner conductor 11 from the intrusion of noise from the outside and the emission of noise to the outside.

[0103] The combination of the first outer conductor 131 and the second outer conductor 132 of the coaxial cable outer conductor 13 in this embodiment is not particularly limited, and each can have the materials and structures described above. For example, the first outer conductor 131 can be a copper-clad polyester tape, and the second outer conductor 132 can be a braided shield of tin-plated soft copper wire.

[0104] By stacking the above-mentioned components as the first external conductor 131 and the second external conductor 132 of the external conductor 13, a particularly high noise shielding effect can be achieved. In other words, the intrusion of noise from the outside and the emission of noise to the outside can be shielded particularly effectively. (4) Sheath The material of the sheath 14 is not particularly limited, and the sheath 14 can be positioned to cover the outer circumference of the outer conductor 13. The sheath 14 serves to physically protect the outer conductor 13 and the inner conductor 11.

[0105] The sheath 14 may contain a polymer material. The polymer material is not particularly limited, but for example, one or more selected from polyolefins such as polyethylene and polypropylene, polyvinyl chloride, polystyrene, polytetrafluoroethylene, and polyphenylene sulfide can be used.

[0106] The sheath 14 may be composed solely of polymer materials, but it may also contain additives such as flame retardants in addition to polymer materials.

[0107] The polymer material contained in sheath 14 may be foamed or cross-linked.

[0108] The outer diameter D14 of the sheath 14 is not particularly limited, but is preferably 2.90 mm or more and 4.20 mm or less, and more preferably 3.00 mm or more and 4.00 mm or less.

[0109] The coaxial cable of this embodiment can be used, for example, as an in-vehicle cable, and by setting the outer diameter D14 of the sheath 14 to 2.90 mm or more and 4.20 mm or less, it can be kept within the allowable outer diameter range of an in-vehicle connector.

[0110] Although embodiments have been described in detail above, the invention is not limited to any particular embodiment, and various modifications and changes are possible within the scope described in the claims. (Note) As can be seen from the embodiments described above, this specification includes disclosures of the following aspects. (1) Internal conductor and An insulator covering the outer circumference of the aforementioned internal conductor, An outer conductor covering the outer circumference of the insulator, The outer conductor comprises a sheath that covers the outer circumference of the outer conductor, The aforementioned internal conductor is a compression conductor having a central strand and a plurality of outer strands surrounding the central strand. The inner conductor has a cross-sectional area S1 calculated from the outer diameter D of the central strand and the total number n of the central strand and the outer strands using the following formula (A), and a compression ratio calculated from the cross-sectional area S2 of the compression conductor using the following formula (B), where the compression ratio is 20.0% or more and 37.0% or less in percentage terms. S1 = n × π × 0.25 × D 2 ...(A) Compression ratio=[1-S2 / S1] (B) A coaxial cable having an outer diameter of 1.25 mm or more and 2.80 mm or less. [Examples]

[0111] The present invention will be described with specific examples below, but it is not limited to these examples. (Evaluation method) First, we will explain the evaluation method for the coaxial cable fabricated in the following experimental example. (1) Outer diameter of inner conductor D11, outer diameter of insulator D12, outer diameter of outer conductor D13, outer diameter of sheath D14 The outer diameter D11 of the inner conductor, the outer diameter D12 of the insulator, the outer diameter D13 of the outer conductor, and the outer diameter D14 of the sheath were measured according to JIS C 3005 (2014).

[0112] Specifically, the outer diameter of the inner conductor 11 was measured at two locations in the same plane perpendicular to the central axis of the coaxial cable 10, and the average value of these measurements was taken as the outer diameter D11 of the inner conductor 11. Furthermore, the outer diameter D11 of the inner conductor 11 was measured along two orthogonal diameters in a plane perpendicular to the central axis of the coaxial cable 10, and the average value of these measurements was taken as described above.

[0113] Although the internal conductor 11 was used as an example in this explanation, the outer diameters of the insulator 12, external conductor 13, and sheath 14 were measured in the same manner. (2) Compression ratio of the internal conductor The compression ratio is calculated using the following formula (B), which is derived from the cross-sectional area S1 of the conductor before compression (calculated using formula (A) from the outer diameter D of the center strand and the total number n of the center and outer strands) and the cross-sectional area S2 of the compressed conductor, and can be expressed as a percentage. In other words, the compression ratio can be expressed as a percentage by multiplying the value calculated using the following formula (B) by 100.

[0114] S1 = n × π × 0.25 × D 2 ...(A) Compression ratio=[1-S2 / S1] (B) As mentioned above, n in equation (A) is the total number of strands, including the center strand and the outer strand. Therefore, in the case of the coaxial cable 10 shown in Figure 1, n = 7.

[0115] In equation (B), S1 is the cross-sectional area of ​​the conductor before compression, i.e., the cross-sectional area of ​​the conductor strands 211 in the stranded wire 21 before it is made into a compressed conductor. In equation (B), S2 is the cross-sectional area of ​​the conductor strands in the compressed conductor.

[0116] The cross-sectional area S1 of the conductor strands 211 in the stranded wire 21 before it was compressed was calculated using the following procedure.

[0117] In the following experimental example, the outer diameter D of the central strand 111A was measured in an arbitrary cross-section perpendicular to the longitudinal direction of the coaxial cable fabricated. Within the compression range of the coaxial cable in the experimental example below, the central strand 111A partially maintains a circular shape. Therefore, the maximum width of the central strand 111A passing through the center of its cross-section was determined as the outer diameter D of the central strand 111A.

[0118] Then, the cross-sectional area of ​​the central strand 111A was calculated from the outer diameter D of the central strand 111A, and by multiplying this by the number of conductor strands 111 in the internal conductor 11, the cross-sectional area of ​​the conductor before compression, i.e., S1, which is the cross-sectional area of ​​the portion of the conductor strands 211 in the stranded wire 21 before it is made into a compressed conductor, was calculated.

[0119] The cross-sectional area S2 of the conductor strands in a compressed conductor was calculated using image processing software (Simpleware Software, manufactured by JSOL Corporation) from a cross-section perpendicular to the longitudinal direction of the coaxial cable.

[0120] Using S1 and S2, which were measured and calculated as described above, the compressibility of the internal conductor of each experimental example was calculated using equation (B) above. (3) Characteristic impedance The characteristic impedance of the coaxial cables fabricated in the following experimental examples was measured using time-domain reflectionometry (TDR).

[0121] If the characteristic impedance was within 50Ω ± 2Ω, it was evaluated as a pass and given an A rating. If the characteristic impedance was outside the above range, it was evaluated as a fail and given a B rating.

[0122] If the characteristic impedance evaluation result was satisfactory (i.e., grade A), the following attenuation and bending resistance tests were performed. If the characteristic impedance evaluation result was unsatisfactory (i.e., grade B), the following attenuation and bending resistance tests were not performed on most samples, and the evaluation was terminated. (4) Attenuation Measurements were taken using a network analyzer on 5m long coaxial cables fabricated in each of the following experimental examples. The attenuation of a 6.0GHz signal was measured.

[0123] If the outer diameter D12 of the insulator 12 was 1.25 mm or more and less than 1.75 mm, it was considered acceptable if the attenuation was 1.90 dB / m or less, and unacceptable if the attenuation exceeded 1.90 dB / m.

[0124] If the outer diameter D12 of the insulator 12 was 1.75 mm or more and less than 2.25 mm, it was deemed acceptable if the attenuation was 1.65 dB / m or less, and unacceptable if the attenuation exceeded 1.65 dB / m.

[0125] If the outer diameter D12 of the insulator 12 is between 2.25 mm and 2.80 mm, it was deemed acceptable if the attenuation was 1.29 dB / m or less, and unacceptable if the attenuation exceeded 1.29 dB / m.

[0126] A passing grade was given, and a failing grade was given, both of which were graded as A. (5) Flexural resistance test As shown in Figure 3, the coaxial cable 10 to be evaluated was placed between two mandrels 311 and 312, each with a diameter of 12.5 mm and positioned horizontally and parallel to each other, and a load of 500 gf (4.9 N) was applied vertically downward to the coaxial cable 10. In this state, the upper end of the coaxial cable 10 was bent horizontally by 90° so that it abutted against the upper side of one mandrel 311, and then bent horizontally by 90° so that it abutted against the upper side of the other mandrel 312, and this process was repeated.

[0127] The number of bends until the internal conductor 11 broke and conductivity was lost was counted. One bend was defined as bending the coaxial cable to the left, then to the right, and then back to the left. The bending resistance test was conducted so that the number of bends was 60 per minute. A higher number of bends in this bending resistance test indicates better bending resistance.

[0128] If the number of flexions was 500 or more, it was evaluated as a pass and given an A rating. If the number of flexions was less than 500, it was evaluated as a fail and given a B rating.

[0129] The bending resistance test was conducted at room temperature (23°C). (6) Overall evaluation If the damping evaluation results and the bending resistance test evaluation results were satisfactory, the rating was A; if at least one of them was unsatisfactory, the rating was B.

[0130] An overall rating of A indicates that the coaxial cable has suppressed attenuation and excellent flexibility.

[0131] The coaxial cables used in each experimental example are described below. [Experimental Example 1] The coaxial cables described in Experimental Examples 1-1 to 1-9 below were fabricated and evaluated.

[0132] Experimental Examples 1-2 to 1-4 are examples, while Experimental Examples 1-1, 1-5 to 1-9 are comparative examples. [Experimental Example 1-1] A coaxial cable having the cross-sectional shape shown in Figure 1 was fabricated using the following procedure. (Internal conductor 11) A stranded wire was prepared by twisting together seven strands of soft copper wire, each with a strand diameter of 0.254 mm. This compressed stranded wire was then used as the internal conductor 11. The size of the die used for compression was selected so that the compression ratio would be the value shown in Table 1.

[0133] The internal conductor 11 has a configuration in which six outer strands 111B are arranged around one central strand 111A. The central strand and the outer strands are made of the same wire. (Insulator 12) An insulator 12 was placed on the outer circumference of the internal conductor 11. The insulator 12 has a first insulator layer 121, a second insulator layer 122, and a third insulator layer 123. For the first insulator layer 121 and the third insulator layer 123, non-foamed polyolefin was used and crosslinked by electron beam irradiation. For the second insulator layer 122, foamed polyolefin was used and crosslinked by electron beam irradiation. The thickness of the insulator 12 was adjusted so that the outer diameter D12 of the insulator 12 was the value shown in Table 1. The electron beam irradiation to crosslink the first insulator layer 121, the second insulator layer 122, and the third insulator layer 123 was performed on all three layers at once after the formation of the first insulator layer 121, the second insulator layer 122, and the third insulator layer 123.

[0134] Note that in Table 1 and in Tables 2 and 3 described later, the columns for the material and foaming rate of the insulator 12 only show the composition of the second insulator layer 122, which has the largest film thickness among the insulators. For example, in Experimental Example 1-2, the film thickness T121 of the first insulator layer 121 was 0.02 mm, the film thickness T122 of the second insulator layer 122 was 0.41 mm, and the film thickness T123 of the third insulator layer 123 was 0.10 mm. The thickness of each insulator layer was measured at a total of four locations along two orthogonal diameters in the same plane perpendicular to the central axis of the coaxial cable 10, and the average value was used. The relative permittivity, thickness, and outer diameter D12 are values ​​for the entire insulator 12. (Outer conductor 13) A copper-clad polyester tape, having a copper layer on the first main surface of a polyester resin substrate and an adhesive layer on the second main surface located opposite the first main surface of the substrate, is bonded to the outer circumference of the insulator 12 by an adhesive layer to form the first outer conductor 131.

[0135] A second outer conductor 132 was formed by arranging tin-plated soft copper wires in a braided structure around the outer circumference of the first outer conductor 131. The second outer conductor 132 was formed by using 16 units, each consisting of five tin-plated soft copper wires with an outer diameter of 0.1 mm arranged in parallel, to form a braided shield. In Table 1, the configuration of the second outer conductor is listed in the "Configuration" column, in the order of number of units / number of tin-plated soft copper wires constituting one unit / outer diameter of the tin-plated soft copper wires. (Sheath 14) A polyvinyl chloride (PVC) sheath 14 was formed around the outer circumference of the outer conductor 13 to manufacture the coaxial cable used in this experiment. In the table, polyvinyl chloride is abbreviated as PVC.

[0136] The obtained coaxial cables were evaluated as described above. The evaluation results are shown in Table 1. [Experimental Examples 1-2 to 1-5] Except for changing the conditions for compressing the internal conductor 11, the coaxial cable was manufactured and evaluated in the same manner as in Experimental Example 1-1.

[0137] The evaluation results are shown in Table 1.

[0138] [Experimental Examples 1-6] As the internal conductor, uncompressed stranded wire is used instead of a compressed conductor, and the strands used in this stranded wire have a diameter of 0.205 mm.

[0139] Except for the points mentioned above, the coaxial cable was manufactured and evaluated in the same manner as in Experimental Example 1-1.

[0140] The evaluation results are shown in Table 1. [Experimental Examples 1-7] As the internal conductor 11, a single solid wire with an outer diameter of 0.67 mm was used instead of stranded wire. Except for the points mentioned above, the coaxial cable was manufactured and evaluated in the same manner as in Experimental Example 1-1.

[0141] The evaluation results are shown in Table 1. [Experimental Examples 1-8, Experimental Examples 1-9] The conditions for manufacturing and compressing the internal conductor 11 were changed to those shown in Table 1. The material of the insulator 12 was also changed to the material shown in Table 1. In Experimental Examples 1-8 to 1-9, the insulator 12 consisted of a single insulating layer, and foaming and crosslinking were not performed. Note that in Table 1, PVC refers to polyvinyl chloride and PP refers to polypropylene. Except for the points mentioned above, the coaxial cable was manufactured and evaluated in the same manner as in Experimental Example 1-1.

[0142] The evaluation results are shown in Table 1.

[0143] [Table 1] From the evaluation results of Experimental Examples 1-1 to 1-5, it was confirmed that by using a compressed conductor, which is a stranded wire with a compression ratio within a predetermined range, as the internal conductor, it is possible to create a coaxial cable with electrical characteristics, specifically characteristic impedance and attenuation, within a predetermined range, and with excellent bending resistance.

[0144] In contrast, it was confirmed that the coaxial cable in Experimental Example 1-6, which used uncompressed stranded wire as the internal conductor, exhibited higher attenuation. Furthermore, it was confirmed that the coaxial cable in Experimental Example 1-7, which used solid wire instead of stranded wire as the internal conductor, had inferior bending resistance. [Experimental Example 2] The coaxial cables described in Experimental Examples 2-1 to 2-7 below were fabricated and evaluated.

[0145] Experimental Examples 2-2 to 2-4 are examples, while Experimental Examples 2-1, 2-5 to 2-7 are comparative examples. [Experimental Example 2-1] A coaxial cable having the cross-sectional shape shown in Figure 1 was fabricated using the following procedure. (Internal conductor 11) A stranded wire was prepared by twisting together seven strands of soft copper wire, each with a strand diameter of 0.32 mm. This compressed stranded wire was then used as the internal conductor 11. The size of the die used for compression was selected so that the compression ratio would be the value shown in Table 2.

[0146] The internal conductor 11 has a configuration in which six outer strands 111B are arranged around one central strand 111A. The central strand and the outer strands are made of the same wire. (Insulator 12) An insulator 12 was placed on the outer circumference of the internal conductor 11. The insulator 12 has a first insulator layer 121, a second insulator layer 122, and a third insulator layer 123. For the first insulator layer 121 and the third insulator layer 123, non-foamed polyolefin was used and crosslinked by electron beam irradiation. For the second insulator layer 122, foamed polyolefin was used and crosslinked by electron beam irradiation. The thickness of the insulator 12 was adjusted so that the outer diameter D12 of the insulator 12 was the value shown in Table 2. (Outer conductor 13) A copper-clad polyester tape, having a copper layer on the first main surface of a polyester resin substrate and an adhesive layer on the second main surface located opposite the first main surface of the substrate, is bonded to the outer circumference of the insulator 12 by the adhesive layer to form the first outer conductor 131.

[0147] A second outer conductor 132 was formed by arranging tin-plated soft copper wires in a braided structure around the outer circumference of the first outer conductor 131. The second outer conductor 132 was formed by using 16 units, each consisting of eight tin-plated soft copper wires with an outer diameter of 0.08 mm arranged in parallel, to form a braided shield. In Table 2, the configuration of the second outer conductor is listed in the "Configuration" column, in the order of number of units / number of tin-plated soft copper wires constituting one unit / outer diameter of the tin-plated soft copper wires. (Sheath 14) A polyvinyl chloride (PVC) sheath 14 was formed around the outer circumference of the outer conductor 13 to manufacture the coaxial cable used in this experiment. In the table, polyvinyl chloride is abbreviated as PVC.

[0148] The obtained coaxial cables were evaluated as described above. The evaluation results are shown in Table 2. [Experimental Examples 2-2 to 2-5] Except for changing the conditions for compressing the internal conductor 11, the coaxial cable was manufactured and evaluated in the same manner as in Experimental Example 2-1.

[0149] The evaluation results are shown in Table 2.

[0150] [Experimental Example 2-6] Instead of a compressed conductor, an uncompressed stranded wire was used as the internal conductor, and the strands used in this stranded wire had a diameter of 0.254 mm.

[0151] Except for the points mentioned above, the coaxial cable was manufactured and evaluated in the same manner as in Experimental Example 2-1.

[0152] The evaluation results are shown in Table 2. [Experimental Example 2-7] As the internal conductor 11, a single solid wire with an outer diameter of 0.78 mm was used instead of stranded wire.

[0153] Except for the points mentioned above, the coaxial cable was manufactured and evaluated in the same manner as in Experimental Example 2-1.

[0154] The evaluation results are shown in Table 2.

[0155] [Table 2] From the evaluation results of Experimental Examples 2-1 to 2-5, it was confirmed that by using a compressed conductor, which is a stranded wire with a compression ratio within a predetermined range, as the internal conductor, it is possible to create a coaxial cable with electrical characteristics, specifically characteristic impedance and attenuation, within a predetermined range, and with excellent bending resistance.

[0156] In contrast, the coaxial cable in Experimental Example 2-6, which used uncompressed stranded wire as the internal conductor, showed higher attenuation. Furthermore, the coaxial cable in Experimental Example 2-7, which used solid wire instead of stranded wire as the internal conductor, showed inferior bending resistance. [Experimental Example 3] The coaxial cables described in Experimental Examples 3-1 to 3-7 below were fabricated and evaluated.

[0157] Experimental Examples 3-2 to 3-4 are examples, while Experimental Examples 3-1, 3-5 to 3-7 are comparative examples. [Experimental Example 3-1] A coaxial cable having the cross-sectional shape shown in Figure 1 was fabricated using the following procedure. (Internal conductor 11) A stranded wire was prepared by twisting together seven strands of soft copper wire, each with a strand diameter of 0.40 mm. This compressed stranded wire was then used as the internal conductor 11. The size of the die used for compression was selected so that the compression ratio would be the value shown in Table 3.

[0158] The internal conductor 11 has a configuration in which six outer strands 111B are arranged around one central strand 111A. The central strand and the outer strands are made of the same wire. (Insulator 12) An insulator 12 was placed on the outer circumference of the internal conductor 11. The insulator 12 has a first insulator layer 121, a second insulator layer 122, and a third insulator layer 123. For the first insulator layer 121 and the third insulator layer 123, non-foamed polyolefin was used and crosslinked by electron beam irradiation. For the second insulator layer 122, foamed polyolefin was used and crosslinked by electron beam irradiation. The thickness of the insulator 12 was adjusted so that the outer diameter D12 of the insulator 12 was the value shown in Table 3. (Outer conductor 13) A copper-clad polyester tape, having a copper layer on the first main surface of a polyester resin substrate and an adhesive layer on the second main surface located opposite the first main surface of the substrate, is bonded to the outer circumference of the insulator 12 by the adhesive layer to form the first outer conductor 131.

[0159] A second outer conductor 132 was formed by arranging tin-plated soft copper wires in a braided structure around the outer circumference of the first outer conductor 131. The second outer conductor 132 was formed by using 16 units, each consisting of 10 tin-plated soft copper wires with an outer diameter of 0.08 mm arranged in parallel, to form a braided shield. In Table 3, the configuration of the second outer conductor is listed in the "Configuration" column in the order of number of units / number of tin-plated soft copper wires constituting one unit / outer diameter of the tin-plated soft copper wires. (Sheath 14) A polyvinyl chloride (PVC) sheath 14 was formed around the outer circumference of the outer conductor 13 to manufacture the coaxial cable used in this experiment. In the table, polyvinyl chloride is abbreviated as PVC.

[0160] The obtained coaxial cables were evaluated as described above. The evaluation results are shown in Table 3. [Experimental Examples 3-2 to 3-5] Except for changing the conditions for compressing the internal conductor 11, the coaxial cable was manufactured and evaluated in the same manner as in Experimental Example 3-1.

[0161] The evaluation results are shown in Table 3. [Experimental Example 3-6] As the internal conductor, uncompressed stranded wire was used instead of a compressed conductor, and the strands used were 0.32 mm in diameter. In addition, the foaming ratio of the second insulating layer 122 was set to the values ​​shown in Table 3.

[0162] Except for the points mentioned above, the coaxial cable was manufactured and evaluated in the same manner as in Experimental Example 3-1.

[0163] The evaluation results are shown in Table 3. [Experimental Example 3-7] Instead of stranded wire, a single solid wire conductor with an outer diameter of 1.05 mm was used as the internal conductor 11. Aside from these points, the coaxial cable was manufactured and evaluated in the same manner as in Experimental Example 3-1.

[0164] The evaluation results are shown in Table 3.

[0165] [Table 3] From the evaluation results of Experimental Examples 3-1 to 3-5, it was confirmed that by using a compressed conductor, which is a stranded wire with a compression ratio within a predetermined range, as the internal conductor, it is possible to create a coaxial cable with electrical characteristics, specifically characteristic impedance and attenuation, within a predetermined range, as well as excellent bending resistance.

[0166] In contrast, the coaxial cable in Experimental Example 3-6, which used uncompressed stranded wire as the internal conductor, showed higher attenuation. Furthermore, the coaxial cable in Experimental Example 3-7, which used solid wire instead of stranded wire as the internal conductor, showed inferior bending resistance. [Explanation of symbols]

[0167] 10 Coaxial Cables 11 Inner conductor 11A Circumscribed circle of the inner conductor D11 Outer diameter of the inner conductor 111 Conductor strand 111A Center wire D: Outer diameter of the center wire 111B Outer wire 12 Insulators D12 Outer diameter of the insulator 121 First insulating layer 122 Second insulating layer 123 Third insulating layer T121 Film thickness of the first insulating layer T122 Film thickness of the second insulating layer T123 Film thickness of the third insulating layer 13 Outer conductor D13 Outer diameter of the outer conductor 131 First outer conductor 132 Second outer conductor 14 Sheath D14 outer diameter of the sheath 21 stranded wire 21A Circumscribed circle of stranded wire 211 Conductor strands 311, 312 Mandrels

Claims

1. Internal conductor and, An insulator covering the outer circumference of the aforementioned internal conductor, An outer conductor covering the outer circumference of the insulator, The outer conductor comprises a sheath that covers the outer circumference of the outer conductor, The aforementioned internal conductor is a compression conductor having a central strand and a plurality of outer strands surrounding the central strand. The inner conductor has a cross-sectional area S1 calculated from the outer diameter D of the central strand and the total number n of the central strand and the outer strands using the following formula (A), and a compression ratio calculated from the cross-sectional area S2 of the compression conductor using the following formula (B), where the compression ratio is 23.0% or more and 35.0% or less in percentage terms. S1=n×π×0.25×� ２ ・・・(A) Compression rate = [1-S2 / S1] ... (B) The outer diameter of the insulator is 1.25 mm or more and less than 1.75 mm. The outer diameter D of the central strand is the maximum width passing through the center of the cross-section of the central strand in the compressed conductor. The central wire and the outer wire are wires of the same outer diameter before compression. The cross-sectional area S2 of the compressed conductor is the total cross-sectional area of ​​the conductor portion excluding the air gap, in this coaxial cable.

2. Internal conductor and, An insulator covering the outer circumference of the aforementioned internal conductor, An outer conductor covering the outer circumference of the insulator, The outer conductor comprises a sheath that covers the outer circumference of the outer conductor, The aforementioned internal conductor is a compression conductor having a central strand and a plurality of outer strands surrounding the central strand. The inner conductor has a cross-sectional area S1 calculated from the outer diameter D of the central strand and the total number n of the central strand and the outer strands using the following formula (A), and a compression ratio calculated from the cross-sectional area S2 of the compression conductor using the following formula (B), where the compression ratio is 24.0% or more and 37.0% or less in percentage terms. S1=n×π×0.25×� ２ ・・・(A) Compression rate = [1-S2 / S1] ... (B) The outer diameter of the insulator is 1.75 mm or more and less than 2.25 mm. The outer diameter D of the central strand is the maximum width passing through the center of the cross-section of the central strand in the compressed conductor. The central wire and the outer wire are wires of the same outer diameter before compression. The cross-sectional area S2 of the compressed conductor is the total cross-sectional area of ​​the conductor portion excluding the air gap, in this coaxial cable.

3. Internal conductor and, An insulator covering the outer circumference of the aforementioned internal conductor, An outer conductor covering the outer circumference of the insulator, The outer conductor comprises a sheath that covers the outer circumference of the outer conductor, The aforementioned internal conductor is a compression conductor having a central strand and a plurality of outer strands surrounding the central strand. The inner conductor has a cross-sectional area S1 calculated from the outer diameter D of the central strand and the total number n of the central strand and the outer strands using the following formula (A), and a compressibility ratio calculated from the cross-sectional area S2 of the compression conductor using the following formula (B), where the compressibility ratio is 20.0% or more and 33.0% or less in percentage terms. S1=n×π×0.25×� ２ ・・・(A) Compression rate = [1-S2 / S1] ... (B) The outer diameter of the insulator is 2.25 mm or more and 2.80 mm or less. The outer diameter D of the central strand is the maximum width passing through the center of the cross-section of the central strand in the compressed conductor. The central wire and the outer wire are wires of the same outer diameter before compression. The cross-sectional area S2 of the compressed conductor is the total cross-sectional area of ​​the conductor portion excluding the air gap, in this coaxial cable.

4. The coaxial cable according to any one of claims 1 to 3, wherein the insulator has one to three insulating layers.

5. The coaxial cable according to any one of claims 1 to 4, wherein the insulator comprises a layer of foamed polyolefin.

6. The insulator has, in order from the inner conductor side, a first insulating layer, a second insulating layer, and a third insulating layer. The thickness of the second insulating layer is greater than the thickness of the first insulating layer and the thickness of the third insulating layer. The coaxial cable according to any one of claims 1 to 5, wherein the first insulating layer and the third insulating layer consist only of non-foamed polyolefin, and the second insulating layer consists only of foamed polyolefin.

7. The coaxial cable according to any one of claims 1 to 6, wherein the insulator has a relative permittivity of 2.4 or less.

8. The central strand and the outer strand of the inner conductor are made of soft copper wire. The outer conductor comprises, in order from the insulator side, a first outer conductor and a second outer conductor. The coaxial cable according to any one of claims 1 to 7, wherein the first outer conductor is a copper-clad polyester tape and the second outer conductor is a braided shield of tin-plated soft copper wire.

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