Coaxial Cable

Abstract

A coaxial cable, an inner conductor formed by twisting together one central strand and six outer strands arranged around the central strand; an insulator covering the outer periphery of the internal conductor; a shield conductor covering an outer periphery of the insulator; In a cross section perpendicular to the longitudinal direction of the coaxial cable, The sum of the areas of the first regions, which are gaps formed between the central strand and two adjacent peripheral strands, of the inner conductor external The ratio to the area of ​​the circle is 0.5% or more and 2.0% or less, A coaxial cable in which the ratio of the total area of ​​the second region, which is a gap formed between the surfaces of two adjacent outer wires and the surface of the insulator, to the area of ​​the circumscribed circle of the inner conductor is 2.0% or more and 5.0% or less.

Description

[Technical field]

[0001] The present disclosure relates to coaxial cables.

[0002] This application claims priority to Japanese Application No. 2020-155643, filed on September 16, 2020, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0003] Patent Document 1 describes an internal conductor, an insulator provided to cover an outer periphery of the internal conductor; an outer conductor provided so as to cover an outer periphery of the insulator; The outer conductor is a first outer conductor formed of a horizontally wound shield in which a first wire is wound in a spiral shape around an outer periphery of the insulator; A second outer conductor is provided so as to cover an outer periphery of the first outer conductor and is made of a braided shield formed by braiding second wires. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-175781 A Summary of the Invention

[0005] The coaxial cable of the present disclosure is a coaxial cable, An inner conductor formed by twisting together one central strand and six peripheral strands arranged around the central strand; an insulator covering an outer periphery of the internal conductor; a shield conductor covering an outer periphery of the insulator; In a cross section perpendicular to the longitudinal direction of the coaxial cable, a ratio of a total area of ​​first regions, which are gaps formed between the central strand and two adjacent peripheral strands, to an area of ​​a circumscribed circle of the inner conductor is 0.5% or more and 2.0% or less; The ratio of the total area of ​​second regions, which are gaps formed between the surfaces of two adjacent outer strands and the surface of the insulator, to the area of ​​the circumscribing circle of the inner conductor is 2.0% or more and 5.0% or less. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a cross-sectional view of a coaxial cable according to one embodiment of the present disclosure taken along a plane perpendicular to the longitudinal direction. [Diagram 2] FIG. 2 is a cross-sectional view of an inner conductor of a coaxial cable according to one embodiment of the present disclosure, taken along a plane perpendicular to the longitudinal direction thereof. [Diagram 3] FIG. 3 is an enlarged view of region A in FIG. [Figure 4] FIG. 4 is an explanatory diagram of the bending test. [Diagram 5] FIG. 5 is a photograph of a cross section perpendicular to the longitudinal direction of the inner conductor used in Experimental Example 1. [Figure 6] FIG. 6 is a photograph of a cross section perpendicular to the longitudinal direction of the inner conductor used in Experimental Example 2. [Figure 7] FIG. 7 is a photograph of a cross section perpendicular to the longitudinal direction of the inner conductor used in Experimental Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] [Problem that this disclosure aims to solve]

[0008] As disclosed in Patent Document 1, coaxial cables for transmitting high-speed signals have been studied for some time. However, data transfer speeds between electronic devices are becoming faster day by day. Accordingly, the transmission speeds and frequency bands required for coaxial cables connecting electronic devices are also gradually becoming faster and higher frequency.

[0009] Skew, which is defined as the difference in delay time between two coaxial cables of the same length and type, is known as a characteristic value for evaluating coaxial cables for high-speed transmission.

[0010] Thunderbolt 3, a high-speed general-purpose data transfer technology that has already been put to practical use, requires a skew of less than 10 ps / m. It is highly likely that a data transfer standard faster than Thunderbolt 3 will require a skew of less than 10 ps / m.

[0011] In order to achieve such a skew, the variation in skew in the coaxial cable must also be made smaller than the conventional required value.

[0012] In addition, since coaxial cables may be repeatedly bent depending on the installation location and the manner of use, they are also required to have excellent bending resistance.

[0013] Therefore, an object of the present disclosure is to provide a coaxial cable that has excellent bending resistance and suppresses skew variation.

[0014] [Effects of this disclosure]

[0015] According to the present disclosure, it is possible to provide a coaxial cable having excellent bending resistance and suppressed skew variation.

[0016] The embodiments for carrying out the invention are described below.

[0017] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be 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.

[0018] (1) A coaxial cable according to one embodiment of the present disclosure is a coaxial cable, An inner conductor formed by twisting together one central strand and six peripheral strands arranged around the central strand; an insulator covering an outer periphery of the internal conductor; a shield conductor covering an outer periphery of the insulator; In a cross section perpendicular to the longitudinal direction of the coaxial cable, a ratio of a total area of ​​first regions, which are gaps formed between the central strand and two adjacent peripheral strands, to an area of ​​a circumscribed circle of the inner conductor is 0.5% or more and 2.0% or less; The ratio of the total area of ​​second regions, which are gaps formed between the surfaces of two adjacent outer strands and the surface of the insulator, to the area of ​​the circumscribing circle of the inner conductor is 2.0% or more and 5.0% or less.

[0019] The ratio of the total area of ​​first regions, which are gaps formed between the central strand and two adjacent peripheral strands, to the area of ​​the circumscribing circle of the inner conductor is defined as the area ratio of the first regions.

[0020] In this case, by setting the area ratio of the first region to 2.0% or less, the inner conductor is sufficiently compressed, and the unevenness occurring on the outer surface of the inner conductor can be suppressed. Therefore, when an insulator is disposed on the outer periphery of the inner conductor, the occurrence of a gap between the inner conductor and the insulator can be suppressed, and the variation in the amount of the gap can be suppressed. As a result, the variation in the capacitance of the coaxial cable can be suppressed, and the variation in the skew can be suppressed.

[0021] However, excessive compression of the internal conductor requires multiple steps, which may reduce productivity. For this reason, the area ratio of the first region is preferably 0.5% or more. By making the area ratio of the first region 0.5% or more, productivity can be increased.

[0022] The area ratio of the second region is the ratio of the total area of ​​the second region, which is the gap formed between the surfaces of the two adjacent peripheral strands and the surface of the insulator, to the area of ​​the circumscribing circle of the inner conductor.

[0023] The area ratio of the second region indicates the degree to which the insulator fills the unevenness of the surface of the internal conductor. Therefore, by setting the area ratio of the second region to 5.0% or less, it is shown that the amount of void between the internal conductor and the insulator is sufficiently suppressed. As a result, the variation in the capacitance of the coaxial cable can be suppressed, and the variation in skew can be suppressed.

[0024] However, it is difficult to completely fill the unevenness of the surface of the internal conductor with the insulator. For this reason, the area ratio of the second region is preferably 2.0% or more. By making the area ratio of the second region 2.0% or more, productivity can be improved.

[0025] (2) A ratio of a total length of a contact portion where the circumference of the circumscribing circle of the internal conductor is in contact with the circumference of the circumscribing circle of the internal conductor may be 40% or more and 70% or less.

[0026] The ratio of the contact portion to the circumference of the circumscribing circle of the internal conductor is defined as the total length of the contact portion where the circumference of the circumscribing circle and the internal conductor are in contact with each other.

[0027] When the inner conductor is completely compressed, the cross section perpendicular to the longitudinal direction becomes circular and completely overlaps with the circumscribed circle, i.e., the proportion of the contact area is 100%.

[0028] However, excessive compression of the internal conductor may increase the number of steps and reduce productivity. Therefore, the ratio of the contact portion is preferably 70% or less. By setting the ratio of the contact portion to 70% or less, productivity can be increased.

[0029] In addition, by making the contact area ratio 40% or more, it means that the inner conductor is sufficiently compressed. Therefore, when an insulator is arranged around the inner conductor, the amount of the gap between the inner conductor and the insulator can be sufficiently reduced. As a result, the variation in the capacitance of the coaxial cable can be reduced, and the variation in skew can be reduced.

[0030] (3) The inner conductor The aboveThe outside diameter of the circumscribing circle may be 0.1 mm or more and 0.4 mm or less.

[0031] By making the outer diameter of the circumscribing circle of the inner conductor 0.4 mm or less, the outer diameter of the coaxial cable can be reduced, resulting in a coaxial cable that is easy to handle. Also, by making the outer diameter of the circumscribing circle of the inner conductor 0.1 mm or more, a coaxial cable with high reliability can be obtained.

[0032] (4) The insulator may have an outer diameter of 0.25 mm or more and 1.5 mm or less.

[0033] By setting the outer diameter of the insulator to 0.25 mm or more, it is possible to particularly improve bending resistance, and by setting the outer diameter of the insulator to 1.5 mm or less, it is possible to make a coaxial cable with a small diameter, which improves handling properties.

[0034] (5) The central wire and the peripheral wire may be silver-plated annealed copper wires.

[0035] By using silver-plated annealed copper wire as the material for the central wire and outer peripheral wire that make up the inner conductor, a coaxial cable with high reliability and excellent high-frequency characteristics can be obtained.

[0036] (6) The shield conductor may be horizontally wound.

[0037] By using a horizontally wound shield conductor, the coaxial cable can be made more flexible than a braided structure, and bending resistance can be improved.

[0038] (7) The ratio of the sum of the area of ​​a third region, which is a region surrounded by the circumscribing circle of the inner conductor and the surfaces of the two adjacent outer strands, to the area of ​​the circumscribing circle of the inner conductor may be 7% or more and 14% or less.

[0039] The area ratio of the third region is the ratio of the total area of ​​the third region, which is the region surrounded by the circumscribing circle of the inner conductor and the surfaces of the two adjacent peripheral strands, to the area of ​​the circumscribing circle of the inner conductor.

[0040] The area ratio of the third region is an index of the degree of unevenness of the outer surface of the inner conductor, and is also an index of the degree of compression of the inner conductor, and is smaller as the degree of compression increases.

[0041] By setting the area ratio of the third region to 14% or less, the inner conductor is sufficiently compressed, and the unevenness occurring on the outer surface of the inner conductor can be suppressed. Therefore, when an insulator is disposed around the outer periphery of the inner conductor, the occurrence of a gap between the inner conductor and the insulator can be suppressed, and the variation in the amount of the gap can be suppressed. As a result, the variation in the capacitance of the coaxial cable can be suppressed, and the variation in the skew can be suppressed.

[0042] However, excessive compression of the internal conductor may increase the number of steps and reduce productivity. Therefore, the area ratio of the third region is preferably 7% or more. By making the area ratio of the third region 7% or more, productivity can be increased.

[0043] In addition, by setting the area ratio of the third region to 7% or more, a suitable amount of unevenness can be left on the surface of the internal conductor, thereby improving the adhesion between the internal conductor and the insulator when the insulator is placed around the outer periphery of the internal conductor.

[0044] (8) The insulator may contain a fluororesin.

[0045] By using a fluororesin as the insulating material, the coaxial cable can be made heat-resistant and oil-resistant while also being easily bendable.

[0046] [Details of the embodiment of the present disclosure] Specific examples of coaxial cables according to an embodiment of the present disclosure (hereinafter, referred to as the present embodiment) will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. (Coaxial cable) Fig. 1 shows an example of a cross section perpendicular to the longitudinal direction of a coaxial cable according to this embodiment. Fig. 2 shows an enlarged view of an inner conductor 11. Fig. 3 shows an enlarged view of a region A in Fig. 1.

[0047] As shown in FIG. 1, a coaxial cable 10 of this embodiment can include an inner conductor 11, an insulator 14 covering the outer periphery of the inner conductor 11, and a shield conductor 15 covering the outer periphery of the insulator 14.

[0048] The inner conductor 11 has one central strand 12 and six outer peripheral strands 13 arranged around the central strand 12. The inner conductor 11 can be a stranded wire in which the one central strand 12 and the six outer peripheral strands 13 are twisted together.

[0049] Each component will be described below. (1) Inner conductor (1-1) Materials The material of the central strand 12 and the outer circumferential strand 13 constituting the inner conductor 11 is not particularly limited, but a silver-plated soft copper wire can be preferably used.

[0050] By using silver-plated annealed copper wire as the material for the central strand 12 and the outer strand 13 that constitute the inner conductor 11, a coaxial cable having high reliability and excellent high-frequency characteristics can be obtained. (1-2) Structure The inner conductor 11 can be a compressed conductor compressed from the outer periphery. Although each strand is shown in a schematic circular shape in Figures 1 and 2, it is compressed as described above, and therefore has a compressed and distorted shape rather than a perfect circle.

[0051] The delay time of a coaxial cable is generally determined by three parameters: the outer diameter of the inner conductor, the outer diameter of the insulator, and the capacitance of the coaxial cable. In order to suppress the variation in the skew of a coaxial cable, it is necessary to suppress the variation in the delay time of the coaxial cable. However, because there is little room for adjustment in the outer diameter of the inner conductor and the outer diameter of the insulator due to restrictions such as standards for coaxial cables, suppressing the variation in the capacitance of the coaxial cable is considered to reduce the variation in skew.

[0052] When a twisted wire is used as the inner conductor 11, the variation in capacitance of the coaxial cable is caused by the unevenness of the surface of the twisted wire causing random gaps to form between the inner conductor 11 and the insulator 14. Therefore, by suppressing the occurrence of such gaps and suppressing the variation in the amount of the generated gaps, the variation in capacitance of the coaxial cable can be suppressed.

[0053] Furthermore, by using a compressed conductor of twisted wire as the inner conductor 11, it is possible to suppress unevenness occurring on the outer surface of the inner conductor. Therefore, it is possible to suppress the occurrence of voids between the inner conductor 11 and the insulator 14, while suppressing variation in the amount of voids that occur. Furthermore, by using a twisted wire as the inner conductor 11 as described above, it is possible to obtain a coaxial cable with excellent bending resistance.

[0054] The outer diameter D11 of the circumscribing circle C11 of the inner conductor 11 is not particularly limited, but is preferably 0.1 mm to 0.4 mm, and more preferably 0.15 mm to 0.3 mm. By setting the outer diameter D11 of the circumscribing circle C11 of the inner conductor 11 to 0.4 mm or less, the outer diameter of the coaxial cable can be reduced, resulting in a coaxial cable with excellent handleability. In addition, by setting the outer diameter D11 of the circumscribing circle C11 of the inner conductor 11 to 0.1 mm or more, a coaxial cable with high reliability can be obtained.

[0055] The outer diameter D11 of the circumscribing circle C11 of the inner conductor 11 corresponds to the outer diameter of the inner conductor 11.

[0056] (1-2-1) Area ratio of the first region Here, in a cross section perpendicular to the longitudinal direction of the coaxial cable 10, the ratio of the total area of ​​the first region 21 (see FIG. 2), which is a gap formed between the central strand 12 and two adjacent outer strands 13, to the area of ​​the circumscribing circle C11 of the inner conductor 11, is defined as the area ratio of the first region. The areas of the first region 21 and the circumscribing circle C11 are areas found in a cross section perpendicular to the longitudinal direction of the coaxial cable 10, as described above. The area of ​​the circumscribing circle C11 is the area of ​​a circle calculated from the outer diameter D11 of the circumscribing circle C11. In the coaxial cable of this embodiment, the area ratio of the first region is preferably 0.5% to 2.0%, and more preferably 0.6% to 1.9%.

[0057] 2, a gap formed between the central strand 12 and two adjacent peripheral strands 131, 132 is defined as a first region 21. The inner conductor 11 has six such first regions 21 along the circumferential direction of the central strand 12, and the total area of ​​the six first regions 21 is the total area of ​​the first regions 21.

[0058] The area ratio of the first region can be calculated by the following formula (1). (Area ratio of the first region) = (Total area of ​​the first region) ÷ (Area of ​​circumscribed circle C11) × 100 (1) By setting the area ratio of the first region to 2.0% or less, the inner conductor 11 is sufficiently compressed, and irregularities occurring on the outer surface of the inner conductor 11 can be suppressed. Therefore, when the insulator 14 is disposed on the outer periphery of the inner conductor 11, it is possible to suppress the occurrence of gaps between the inner conductor 11 and the insulator 14, while suppressing variations in the amount of gaps. As a result, it is possible to suppress variations in the capacitance of the coaxial cable, and to suppress variations in skew.

[0059] However, excessive compression of the internal conductor 11 requires multiple steps, which may reduce productivity. For this reason, the area ratio of the first region is preferably 0.5% or more. By setting the area ratio of the first region to 0.5% or more, productivity can be increased. (1-2-2) Area ratio of the second region The area ratio of the second region is defined as the ratio of the total area of ​​the second region 31 (see FIG. 3), which is a gap formed between the surfaces of the two adjacent outer peripheral wires 131, 132 and the surface of the insulator 14, to the area of ​​the circumscribing circle C11 of the inner conductor 11. The area of ​​the second region 31 is an area obtained in a cross section perpendicular to the longitudinal direction of the coaxial cable 10. In the coaxial cable of this embodiment, the area ratio of the second region is preferably 2.0% or more and 5.0% or less, and more preferably 2.5% or more and 4.5% or less.

[0060] As shown in FIG. 3, which is an enlarged view of region A in FIG. 1, the surfaces of two adjacent peripheral wires 131 and 132 and the insulator 14 Surface The gap formed by these is defined as the second region 31. The internal conductor 11 has six such second regions along the circumferential direction of the internal conductor 11, and the total area of ​​the six second regions 31 is the total area of ​​the second regions 31.

[0061] The area ratio of the second region can be calculated by the following formula (2). (area ratio of the second region) = (total area of ​​the second region) ÷ (area of ​​circumscribed circle C11) × 100 (2) The area ratio of the second region indicates the degree to which the insulator 14 fills the unevenness on the surface of the inner conductor 11. Therefore, by setting the area ratio of the second region to 5.0% or less, it is shown that the amount of the gap between the inner conductor 11 and the insulator 14 is sufficiently suppressed. As a result, the variation in the electrostatic capacitance of the coaxial cable can be suppressed, and the variation in skew can also be suppressed.

[0062] However, it is difficult to completely fill the unevenness on the surface of the internal conductor 11 with the insulator 14. For this reason, the area ratio of the second region is preferably 2.0% or more. By making the area ratio of the second region 2.0% or more, productivity can be increased. (1-2-3) Area ratio of the third region A third region is a region surrounded by the circumscribing circle C11 of the inner conductor 11 and the surfaces of the two adjacent outer strands 13. 22 (See Figure 2)The ratio of the total area of ​​the third region 22 to the area of ​​the circumscribing circle C11 of the inner conductor 11 is defined as the area ratio of the third region. The area of ​​the third region 22 is an area obtained in a cross section perpendicular to the longitudinal direction of the coaxial cable 10. In the coaxial cable of the present embodiment, the area ratio of the third region is preferably 7% or more and 14% or less, and more preferably 9% or more and 13.5% or less.

[0063] 2 , a region surrounded by the circumscribing circle C11 of the inner conductor 11 and the surfaces of the two adjacent outer strands 131, 132 is defined as a third region 22. The inner conductor 11 has six such third regions along the circumferential direction of the inner conductor 11, and the total area of ​​the six third regions 22 is the total area of ​​the third regions 22.

[0064] The area ratio of the third region can be calculated by the following formula (3). (Area ratio of the third region) = (Total area of ​​the third region) ÷ (Area of ​​circumscribed circle C11) × 100 (3) The area ratio of the third region 22 is an index of the degree of unevenness of the outer surface of the internal conductor 11. The area ratio of the third region 22 is also an index of the degree of compression of the internal conductor 11, and decreases as the degree of compression increases.

[0065] By setting the area ratio of the third region to 14% or less, the inner conductor 11 is sufficiently compressed, and unevenness occurring on the outer surface of the inner conductor 11 can be suppressed. Therefore, when the insulator 14 is disposed on the outer periphery of the inner conductor 11, it is possible to suppress the occurrence of a gap between the inner conductor 11 and the insulator 14 while suppressing the variation in the amount of the gap. As a result, it is possible to suppress the variation in the capacitance of the coaxial cable and the variation in skew.

[0066] However, excessive compression of the internal conductor 11 may increase the number of steps, which may reduce productivity. Therefore, the area ratio of the third region is preferably 7% or more. By setting the area ratio of the third region to 7% or more, productivity can be increased.

[0067] Furthermore, by making the area ratio of the third region 7% or more, it is possible to leave a suitable amount of unevenness on the surface of the internal conductor, thereby improving the adhesion between the internal conductor 11 and the insulator 14 when the insulator 14 is placed around the outer periphery of the internal conductor 11. (1-2-4) The ratio of the total length of the contact area between the circumference of the circumscribing circle and the inner conductor to the circumference of the circumscribing circle of the inner conductor It is preferable that the ratio of the total length of the contact portion 23, where the circumference of the circumscribing circle C11 and the inner conductor 11 contact each other, to the circumference of the circumscribing circle C11 of the inner conductor 11 is 40% or more and 70% or less. The length of the contact portion 23 is the length measured in a cross section perpendicular to the longitudinal direction of the coaxial cable 10.

[0068] 2, for example, the contact portion 23 refers to a portion where the inner conductor 11 contacts the circumference of the circumscribing circle C11 of the inner conductor 11. The inner conductor 11 has six such contact portions along the circumscribing circle C11. Therefore, the total length of the six contact portions 23 is the total length of the contact portion 23 where the inner conductor 11 contacts the circumference of the circumscribing circle C11 (hereinafter, also referred to as the "total length of the contact portions").

[0069] The ratio of the total length of the contact portion where the circumference of the circumscribing circle and the internal conductor are in contact with each other to the circumference of the circumscribing circle of the above-mentioned internal conductor (hereinafter also referred to as the "contact portion ratio") can be calculated by the following formula (4).

[0070] (Proportion of contact area) = (Total length of contact area) ÷ (Circumference length of circumscribed circle C11) × 100 (4) When the inner conductor 11 is completely compressed, the cross section perpendicular to the longitudinal direction becomes circular and completely overlaps with the circumscribing circle C11. In other words, the proportion of the contact portion is 100%.

[0071] However, as mentioned above, excessive compression of the internal conductor 11 may increase the number of steps and reduce productivity. Therefore, the ratio of the contact portion is preferably 70% or less. By setting the ratio of the contact portion to 70% or less, productivity can be increased.

[0072] Moreover, by making the ratio of the contact portion 40% or more, it means that the inner conductor is sufficiently compressed. Therefore, when the insulator 14 is disposed on the outer periphery of the inner conductor 11, the amount of the gap between the inner conductor 11 and the insulator 14 can be sufficiently reduced. As a result, the variation in the capacitance of the coaxial cable can be reduced, and the variation in the skew can be reduced. (2) Insulator (2-1) Materials The material of the insulator 14 is not particularly limited, but for example, a fluororesin can be used. That is, the insulator 14 can contain a fluororesin.

[0073] By using fluororesin as the material for the insulator 14, it is possible to provide heat resistance and oil resistance while also making it easy to bend.

[0074] As the fluororesin, for example, one or more types selected from ethylene-tetrafluoroethylene copolymer (ETFE), polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyvinylidene fluoride resin (PVDF), etc. can be used.

[0075] Insulation 14 may be applied to inner conductor 11 by, for example, draw forming. (2-2) Outer diameter The outer diameter D14 of the insulator 14 is not particularly limited, but is preferably 0.25 mm or more and 1.5 mm or less, and more preferably 0.4 mm or more and 1.2 mm or less.

[0076] By setting the outer diameter D14 of the insulator 14 to 0.25 mm or more, it is possible to particularly improve bending resistance. Also, by setting the outer diameter D14 of the insulator 14 to 1.5 mm or less, it is possible to make the coaxial cable small in diameter, which improves the handleability. (3) Shield conductor The shield conductor 15 has a structure in which shield wires 151 are arranged in a horizontal winding or braided structure around the outer periphery of the insulator 14. The shield conductor 15 is preferably horizontally wound. By using the shield conductor 15 in a horizontal winding structure, a more flexible coaxial cable can be obtained than when the shield conductor 15 has a braided structure, and bending resistance can be improved.

[0077] The shielding wires 151 of the shielding conductor 15 can be made of copper, aluminum, copper alloy, or the like. Therefore, the shielding wires 151 can be made of hard copper wire or the like. The surface of the shielding wires 151 can be plated with silver or tin. Therefore, the metal wire of the shielding conductor can be made of, for example, a silver-plated copper alloy or a tin-plated copper alloy.

[0078] The shield conductor 15 can be formed by, for example, winding copper-deposited polyester tape or the like over the outer surface of the insulator 14 . (4) Outer covering The coaxial cable 10 may also include an outer jacket 16 around the shield conductor 15 .

[0079] The material of the outer sheath 16 is not particularly limited, but examples of the material that can be used include fluororesins such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and ethylene-tetrafluoroethylene copolymer (ETFE), and polyester resins such as polyethylene terephthalate (PET).

[0080] For example, the outer sheath 16 can be formed by wrapping a polyester tape or the like around the outer periphery of the shield conductor 15 .

[0081] Although the embodiments have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes are possible within the scope of the claims. EXAMPLES

[0082] The present invention will be described below with reference to specific examples, but is not limited to these examples. (Evaluation method) First, the method for evaluating the coaxial cables produced in the following experimental examples will be described. (1) Outer diameter D11 of circumscribing circle C11 of inner conductor 11, outer diameter D14 of insulator The outer diameter D11 of the circumscribing circle C11 of the inner conductor 11 was obtained by observing an arbitrary cross section perpendicular to the longitudinal direction of the coaxial cable with a microscope, drawing the circumscribing circle C11 of the inner conductor 11, and measuring its diameter. The outer diameter D11 of the circumscribing circle C11 of the inner conductor 11 corresponds to the outer diameter of the inner conductor 11.

[0083] The outer diameter D14 of the insulator 14 was also obtained by observing the above cross section with a microscope, drawing a circumscribing circle of the insulator 14, and measuring the diameter thereof.

[0084] The area percentage of the first region, the area percentage of the second region, the area percentage of the third region, and the percentage of the contact portion described below were also measured on the same cross section. (2) Area ratio of the first region, area ratio of the second region, area ratio of the third region, and contact area ratio An arbitrary cross section perpendicular to the longitudinal direction of the coaxial cable produced in the following experimental example was observed with a microscope to measure the area of ​​the first region, the second region, and the third region. Then, the area ratio of the first region, the second region, and the third region to the area of ​​the circumscribing circle C11 obtained from the outer diameter D11 of the circumscribing circle C11 of the inner conductor 11, which was measured in advance, was calculated.

[0085] In addition, in the observed image, the internal conductor 11 Outside Measure the total length of the contact area where the circumference of the tangent circle C11 and the internal conductor 11 are in contact, Occupying the circumference of circumscribing circle C11 The percentage of contact areas was calculated. (3) Maximum skew Two coaxial cables were prepared for each sample, as described in the following experimental example. Electrical pulses were then sent to the two high-frequency coaxial cables of a given length using a digital serial analyzer, and the delay time per meter was measured.

[0086] From the delay time measurement results for the 10 samples, the value obtained by subtracting the minimum delay time from the maximum delay time was calculated, and this value is shown in Table 1 as the "maximum skew value." (4) Bending test 4, the coaxial cable 10 to be evaluated was placed and sandwiched between two mandrels 411, 412 with a diameter of 4 mm that were arranged horizontally and parallel to each other, and a load of 200 g 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 as to abut against the upper side of one mandrel 411, and then repeatedly bent horizontally by 90° so as to abut against the upper side of the other mandrel 412.

[0087] The number of times the coaxial cable was bent was counted until it broke. Note that one bending count is defined as bending the coaxial cable to the left, then to the right, and then back to the left. The higher the bending count, which is the result of the bending test, the better the bending resistance.

[0088] The coaxial cables in each of the experimental examples are described below. Experimental examples 1 and 2 are working examples, and experimental example 3 is a comparative example. (Experimental Example 1) The coaxial cable was produced according to the following procedure.

[0089] A stranded wire was prepared by stranding seven silver-plated soft copper wires each having a wire diameter of 0.102 mm. The stranded wire was compressed to form a compressed conductor, which was used as the inner conductor 11.

[0090] The stranded wire has a configuration in which six outer peripheral wires are arranged around one central wire. The central wire and the outer peripheral wire are made of the same wire.

[0091] An insulator 14 made of FEP was disposed around the outer periphery of the internal conductor 11. The thickness of the insulator 14 was adjusted so that the outer diameter of the insulator 14 was 0.79 mm.

[0092] Next, a tin-plated soft copper wire was wound horizontally around the outer periphery of the insulator 14 to form a shield conductor.

[0093] Furthermore, a polyester tape was applied to the outer circumference of the shield conductor 15 to form the outer sheath 16, thereby producing the coaxial cable of this experimental example.

[0094] The obtained coaxial cable was evaluated as described above. The evaluation results are shown in Table 1. Figure 5 shows a photograph of a cross section perpendicular to the longitudinal direction of the inner conductor. (Experimental Example 2) Coaxial cables were produced and evaluated in the same manner as in Experimental Example 1, except that the degree to which the twisted wire was compressed was changed for the inner conductor 11 .

[0095] The results are shown in Table 1. Figure 6 shows a photograph of a cross section perpendicular to the longitudinal direction of the inner conductor. (Experimental Example 3) A coaxial cable was produced and evaluated in the same manner as in Experimental Example 1, except that a non-compressed stranded wire was used for the inner conductor 11.

[0096] The results are shown in Table 1. Figure 7 shows a photograph of a cross section perpendicular to the longitudinal direction of the inner conductor.

[0097] [Table 1] According to the results shown in Table 1, it was confirmed that the coaxial cables of Experimental Examples 1 and 2, in which the area ratio of the first region is 0.5% to 2.0% and the area ratio of the second region is 2.0% to 5.0%, had a maximum skew value of 7.5 ps / m or less. In other words, it was confirmed that the variation in skew could be suppressed compared to the coaxial cable of Experimental Example 3, in which the area ratio of the first region, etc. were not satisfied.

[0098] Moreover, the coaxial cables of Experimental Examples 1 and 2 were also bent more than 4,500 times in the bending test, and it was confirmed that they had sufficient bending resistance. [Explanation of symbols]

[0099] 10 Coaxial Cable 11 Inner conductor 12 Center strand 13, 131, 132 Outer wire 14 Insulators 15 Shielded Conductor 151 Shield wire 16 Outer cover 21 First area 22 Third area 23 Contact part 31 Second area 411, 412 Mandrel Area A C11 circumscribed circle D11 Outer diameter D14 outer diameter

Claims

1. A coaxial cable, an inner conductor formed by twisting together one central strand and six peripheral strands arranged around the central strand; an insulator covering an outer periphery of the internal conductor; a shield conductor covering an outer periphery of the insulator; In a cross section perpendicular to the longitudinal direction of the coaxial cable, a ratio of a total area of ​​first regions, which are gaps formed between the central strand and two adjacent peripheral strands, to an area of ​​a circumscribing circle of the inner conductor is 0.5% or more and 2.0% or less, A coaxial cable in which the ratio of the sum of the areas of second regions, which are gaps formed between the surfaces of two adjacent outer wires and the surface of the insulator, to the area of ​​the circumscribed circle of the inner conductor is 2.0% or more and 5.0% or less.

2. 2. The coaxial cable according to claim 1, wherein a ratio of a total length of a contact portion where the circumference of the circumscribing circle of the inner conductor is in contact with the circumference of the circumscribing circle of the inner conductor is 40% or more and 70% or less.

3. 3. The coaxial cable according to claim 1, wherein the outer diameter of the circumscribing circle of the inner conductor is 0.1 mm or more and 0.4 mm or less.

4. 4. The coaxial cable according to claim 1, wherein the insulator has an outer diameter of 0.25 mm or more and 1.5 mm or less.

5. 5. The coaxial cable according to claim 1, wherein the central wire and the outer peripheral wire are silver-plated annealed copper wires.

6. 6. The coaxial cable according to claim 1, wherein the shield conductor is wound in a cross-winding manner.

7. 7. A coaxial cable according to claim 1, wherein a ratio of the sum of the area of ​​a third region, which is a region surrounded by the circumscribing circle of the inner conductor and the surfaces of two adjacent outer wires, to the area of ​​the circumscribing circle of the inner conductor is 7% or more and 14% or less.

8. The coaxial cable according to claim 1 , wherein the insulator contains a fluororesin.

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