Patent Application
20220028582
The present disclosure relates to a high-frequency coaxial cable.
The present application is based on and claims priority to Japanese Patent Application No. 2019-047870, filed on Mar. 15, 2019, the entire contents of the Japanese Patent Application are hereby incorporated herein by reference.
The data transfer speed between electronic devices is increasing day by day.
Accordingly, for cables connecting electronic devices, the required transmission speed and the required frequency band are also increasing.
Thus, as a coaxial cable for performing high-speed transmission at a high-frequency band, there is a known shield cable that includes an inner conductor that is a stranded wire conductor made of tin-plated copper alloy wires, an insulator provided to cover the outer periphery of the inner conductor, and an outer conductor provided to cover the outer periphery of the insulator, wherein the outer conductor includes a first outer conductor covering the outer periphery of the insulator and including a served shield with first element wires iii spirally wound, and a second outer conductor covering the outer periphery of the first outer conductor and including a braided shield with second element wires braided (for example, Patent Document 1).
[Patent Document 1] Japanese Patent No. 6409993
According to one aspect of the present disclosure, a high-frequency coaxial cable used for high-frequency signal transmission includes: an inner conductor; an insulator surrounding an outer periphery of the inner conductor; a shield conductor surrounding an outer periphery of the insulator; and a covering surrounding an outer periphery of the shield conductor, wherein the inner conductor is a compressed conductor having a plurality of silver-plated soft copper element wires compressed.
As a characteristic value of evaluating such a coaxial cable for high-speed transmission, skew that is a value defined by the difference in the delay time of two coaxial cables of the same length and the same type is known. Also, 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 Thunderbolt 3, which is one of the high-speed general-purpose data transfer technologies and which has already been put into practical use, the required skew is less than 10 ps/m. In data transfer standards faster than Thunderbolt 3, skew having a value smaller than 10 ps/m is likely to be required.
Therefore, the variation in skew is also required to be smaller than the conventional requirement.
In order to reduce the variation in skew, it is required to reduce the variation in the delay time of coaxial cables. 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 the restrictions of standards or the like, it is required to reduce the variation in the capacitance of the coaxial cable in order to reduce the variation in skew.
However, because the coaxial cable disclosed in Patent Document 1 uses a stranded wire conductor as the inner conductor, voids are easily generated at random between the inner conductor and the insulator, and it is difficult to suppress the variation in skew.
In view of the above, the present disclosure has an object to provide a high-frequency coaxial cable with a small variation in skew.
According to the above, it is possible to provide a high-frequency coaxial cable with a small variation in skew.
First, aspects of the present disclosure will be listed and described.
According to one aspect of the present disclosure, (1) a high-frequency coaxial cable used for high-frequency signal transmission includes: an inner conductor; an insulator surrounding an outer periphery of the inner conductor; a shield conductor surrounding an outer periphery of the insulator; and a covering surrounding an outer periphery of the shield conductor, wherein the inner conductor is a compressed conductor having a plurality of silver-plated soft copper element wires compressed.
Thereby, in addition to reducing voids between the silver-plated soft copper element wires and voids between the inner conductor and the insulator, the durability of the inner conductor against repeated stresses is increased. Therefore, it is possible to reduce the variation in skew while maintaining the durability as a cable.
(2) In the high-frequency coaxial cable described above, an outer shape of the inner conductor is circular, and the silver-plated soft copper element wires are composed of a plurality of outer shape forming element wires that form the outer shape of the inner conductor and a core element wire that is in contact with only the outer shape forming element wires, and respective centers of iii virtual circles passing through outer shapes of the outer shape forming element wires toward the insulator match.
Thereby, because voids between the inner conductor and the insulator are further reduced, the variation in capacitance as the high-frequency coaxial cable can be reduced and the variation in skew can be reduced.
(3) In the high-frequency coaxial cable described above, the core element wire of the silver-plated soft copper element wires is hexagonal in a cross-section view, and the outer shape forming element wires are six wires.
Thereby, because the inner conductor has a close-packed structure, voids in the inner conductor are further reduced, and the variation in skew can be further reduced.
(4) In the high-frequency coaxial cable described above, the insulator is made of a fluoropolymer. Thereby, it is possible to easily bend while having heat resistance and oil resistance.
(5) In the high-frequency coaxial cable described above, the shield conductor is formed of a plurality of shield element wires.
Thereby, because the durability of the shield conductor against repeated stresses is increased, the durability as a cable can be increased.
(6) In the high-frequency coaxial cable described above, an outer diameter of the inner conductor is 0.1 mm or more and 0.5 mm or less, and an outer diameter of the insulator is 0.2 mm or more and 2.0 mm or less.
A high-frequency coaxial cable according to an embodiment of the present disclosure will be described with reference to
It should be noted that the present disclosure is not limited to these examples, and is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.
The high-frequency coaxial cable 100 according to the embodiment of the present disclosure is a high-frequency coaxial cable for high-speed data transmission using a high-frequency band with a transmission rate of 40 Gbps and an attenuation frequency band of 35 GHz or the like.
As illustrated in
The inner conductor 110 is a compressed conductor formed by compressing a plurality of silver-plated soft copper wires and has a substantially circular shape as the outer shape.
As illustrated in
Accordingly, the core element wire 111, which is a silver-plated soft copper element wire, is in contact with only the outer shape forming element wires 112.
The outer shape forming element wires 112, which are silver-plated soft copper element wires, have a trapezoidal shape as a cross-sectional shape in a cross-sectional view.
This trapezoidal cross-sectional shape is defined by an inner peripheral side 112a that is in contact with the core element wire 111, an outer peripheral side 112b that is opposite to the inner peripheral side 112a and that is in contact with the insulator 120, and a left side 112c and a right side 112d extending in directions toward the insulator 120.
The centers of virtual circles P1, P2, P3, P4, P5, and P6 passing through the outer peripheral sides 112b, which are the outer shapes of the outer shape forming element wires 112 toward the insulator 120, substantially match.
The radii r1, r2, r3, r4, r5, and r6 of the virtual circles P1, P2, P3, P4, P5, and P6 are approximately equal.
The insulator 120 is made of FEP (tetrafluoroethylene-propylene hexafluoride copolymer), i.e., made of a fluoropolymer.
The insulator 120 is coated on the inner conductor 110 by a drawdown molding. Here, because the inner conductor 110 is a compressed conductor, voids between the inner conductor 110 and the insulator 120 are iii very few, and the variation in the composite dielectric constant of the high-frequency coaxial cable 100 can be reduced.
Therefore, the variation in the delay time can be reduced, and the value of skew can be reduced.
The shield conductor 130 is made by transversely winding a plurality of shield element wires 131.
The material of the shield element wires 131 is, for example, hard copper wire.
The covering 140 is composed of a shield layer (not illustrated) that is in contact with the shield conductor 130 and a jacket layer that is in contact with the shield layer.
The shield layer may be, for example, a lap wound copper-deposited polyester tape. The jacket layer may be, for example, a wound polyester tape.
Next, Example of the present disclosure will be described with reference to
It should be noted that the Example is merely an example and is not intended to limit the scope of the present disclosure.
A high frequency coaxial cable of Example 1 is an Example of the present disclosure. The inner conductor is a compressed conductor formed by compressing a plurality of silver-plated soft copper element wires and has an outer diameter of 0.16 mm.
The insulator is made of FEP and has an outer diameter of 0.45 mm. Thus, the impedance of the high-frequency coaxial cable of Example 1 is 45Ω.
The shield conductor is made by laterally winding shield element wires of hard copper wires, and the diameter of the shield element wires is 0.45 mm.
The shield layer of the covering is made of a copper deposited polyester tape.
The jacket layer of the covering is made of a polyester tape and the outer diameter of the jacket layer of the covering (that is, the outer diameter of the covering) is 0.55 mm.
Next, a high-frequency coaxial cable of Comparative Example 1 will be described.
The inner conductor is a single conductor composed of a single silver-plated soft copper element wire and has an outer diameter of 0.16 mm.
The insulator is made of FEP and has an outer diameter of 0.45 mm.
Thus, the impedance of the high-frequency coaxial cable of Comparative Example 1 is 45
The shield conductor is made by laterally winding shield element wires of hard copper wires, and the diameter of the shield element wires is 0.45 mm.
The shield layer of the covering is made of a copper deposited polyester tape.
The jacket layer of the covering is made of a polyester tape and the outer diameter of the jacket layer of the covering (that is, the outer diameter of the covering) is 0.55 mm.
Next, a high-frequency coaxial cable of Comparative Example 2 will be described.
The inner conductor is a stranded wire conductor formed by twisting seven silver-plated soft copper element wires and has an outer diameter of 0.19 mm.
The insulator is made of FEP and has an outer diameter of 0.45 mm.
Thus, the impedance of the high-frequency coaxial cable of Comparative Example 2 is 43Ω.
The shield conductor is made by laterally winding shield element wires of hard copper wires, and the diameter of the shield element wires is 0.45 mm.
The shield layer of the covering is made of a copper deposited polyester tape.
The jacket layer of the covering is made of a polyester tape and the outer diameter of the jacket layer of the covering (that is, the outer diameter of the covering) is 0.55 mm.
In order to evaluate Example and Comparative Examples described above, electrical pulses were sent to two high-frequency coaxial cables having predetermined lengths by a digital serial analyzer to measure the delay time per 1 m.
From a plurality of samples, the value was obtained by subtracting the minimum delay time from the maximum delay time, and this value is indicated in
As indicated in
In order to evaluate Example and Comparative iii Examples described above, the high-frequency coaxial cable of each example was sandwiched with a mandrel having a mandrel diameter of 2 mm, and with a load of 200 g applied vertically downward, an operation of 90 degrees bending was repeatedly given to the high-frequency coaxial cable.
It should be noted that for the “number of bends”, when bending is reciprocated once, it is counted as once.
As indicated in
In order to evaluate Example and Comparative Examples described above, the attenuation (S parameter S21) at 5 GHz of the high-frequency coaxial cable for each example was measured.
As indicated in
When Example and Comparative Examples described above are evaluated by the evaluation methods 1 to 3, it is confirmed that Example 1 (compressed conductor) is equivalent to Comparative Example (single wire conductor) in the maximum value of skew and the attenuation and has flexural durability similar to that of Comparative Example (stranded wire conductor).
Accordingly, for Example 1, it can be confirmed that both electrical characteristics and mechanical characteristics are achieved, and it can be said that the high-frequency coaxial cable of Example 1 has superior characteristics to the conventional high-frequency coaxial cables.
It should be noted that, in the cross-sectional photograph of the inner conductor, voids were not found inside Example 1. In Example 1, the cross-sectional shape of the core element wire was hexagonal, and the respective outer peripheral sides of the six outer shape forming element wires formed a concentric circle.
Further, constrictions C were identified between the respective outer peripheral sides of the six outer shape forming element wires in Example 1.
Although the outer shape of the inner conductor was 0.16 mm in Example of the present disclosure, the inner conductor may have an outer shape of 0.1 mm or more and 0.5 mm or less as long as the inner conductor is a compressed conductor.
Although the outer shape of the insulator was 0.45 mm in Example of the present disclosure, the outer shape of the insulator may be 0.2 mm or more and 2 mm or less as long as the impedance of the coaxial cable is in the range of 30Ω to 60Ω.
Although the embodiment of the present disclosure has been described above, the present disclosure is not limited to the above.
Also, each element of the embodiment described above can be combined as far as it is technically possible, and combinations thereof are included within the scope of iii the present disclosure as long as they include features of the present disclosure.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/009455 | 3/5/2020 | WO | 00 |
