JP2019087439A - High frequency cable - Google Patents

Abstract

To provide an inexpensive cable for microwaves and quasi-millimeter waves.SOLUTION: A high frequency cable is formed by surrounding a central conductor 30 with an insulator 20 and an external conductor 10. The external conductor 10 comprises: a first coil 11 wound in a direction substantially orthogonal to a cable central axis in the longitudinal direction; and a second coil 12 wound on the outer side of the first coil 11 along between the conductors of the first coil 11. The second coil 12 is wound so as to shift by approximately 1/2 pitch from the first coil 11.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a high frequency cable for transmitting, for example, a high frequency signal of a frequency higher than a microwave band.

  As a means for transmitting a high frequency signal, a high frequency cable (sometimes referred to as a "coaxial cable") in which the central conductor and the outer conductor therearound are coaxial is widely used. A general structural example of this type of high frequency cable is shown in FIG. The conventional general high-frequency cable 8 is one in which a central conductor 830 having a circular cross-sectional shape is covered with an insulator 820 and the outer side is covered with an outer conductor 810 and a sheath 840. The outer conductor 810 is preferably a metal tube such as a semi-rigid cable from the point of view of transmission characteristics, but such metal tube is less flexible. Therefore, for example, in the high frequency cable disclosed in Patent Document 1, the outer conductor 810 is made of a flexible material such as aluminum foil, copper foil, braided copper wire (braided wire), etc., whereby the flexibility of the entire high frequency cable 8 is obtained. Improve. Moreover, the high frequency cable currently disclosed by patent document 2 corrugates the outer conductor 810 in a wavelike form, and improves flexibility.

JP, 2006-221842, A JP, 2005-158502, A

  In order to obtain good transmission characteristics in a high frequency cable, it is important that the distance between the central conductor and the outer conductor does not change when the high frequency cable is bent, that is, it does not deform or collapse. In the high frequency cable disclosed in Patent Document 1, the outer conductor is soft, and the mechanical strength and flexibility are mainly borne by the insulating material. Therefore, the outermost shape of the insulator needs to be round and smooth, and there are many limitations in terms of material and shape, such as the need to use a foam material to lower the dielectric constant of the insulator. The

On the other hand, in the high frequency cable described in Patent Document 2, the corrugated structure is formed by welding with copper tape or the like, and the pitch of the peak and the valley is fixed to a certain degree.
The main object of the present invention is to provide a high-frequency cable with a simple structure that suppresses the increase in loss while alleviating the above-mentioned limitations, and has higher flexibility than before.

  A high frequency cable which achieves the above object comprises a central conductor provided along a cable central axis and an outer conductor surrounding the central conductor, the outer conductor being substantially orthogonal to the cable central axis And a second spiral conductor wound along the space between the conductors of the first spiral conductor on the outside of the first spiral conductor.

  The first helical conductor and the second helical conductor have a mechanical strength of at least a certain level. Therefore, restrictions on the strength and shape of the insulator are reduced. When the entire high-frequency cable is bent, the distance between the conductors of the first helical conductor changes according to the degree of bending, so that the bendable range can be made larger than that of a planar one, and the second helical conductor (1) Since the space between the conductors of the spiral conductor is closed, it is possible to provide a high-frequency cable with a simple structure in which the flexibility is increased compared to the conventional one while suppressing an increase in loss during transmission.

(A) is a structure perspective view of the high frequency cable concerning this embodiment, (b) is front sectional drawing. Longitudinal sectional view of a high frequency cable. Transmission characteristics of the high frequency cable. (A)-(d) is a fragmentary sectional view which shows the modification of an outer conductor. (A), (b) is a structural perspective view which shows the other example of a center conductor. (A), (b) is front sectional drawing which shows the modification of an insulator. (A), (b) is front sectional drawing which shows the other modification of an insulator. The structural perspective view of the conventional coaxial cable.

Hereinafter, an embodiment of the high frequency cable of the present invention will be described with reference to the drawings. FIG. 1A is a structural perspective view of a high frequency cable according to the present embodiment, and FIG. 1B is a front cross-sectional view of the high frequency cable 1. The high frequency cable 1 is a coaxial cable whose frontal cross section is circular, and has an outer conductor 10, an insulator 20, a central conductor 30, and a sheath 40. The "circular shape" is not limited to a circular shape, but refers to a shape regarded as a circular shape.
In this specification, the central axis of the high frequency cable 1 is “cable central axis”, the direction of the cable central axis is “longitudinal direction”, and the direction away from the cable central axis in the plane orthogonal to the cable central axis is “outside” The direction approaching the central axis of the cable is called "inside".

  The central conductor 30 transmits a high frequency signal having a frequency of microwaves or higher, and is formed of, for example, a single or multiple wires such as copper. The sheath 40 is for preventing injury to the cable, flooding, and the like, and can be made of, for example, vinyl chloride or heat resistant polyethylene. The central conductor 30 and the sheath 40 are, for example, of the same size as the central conductor 830 and the sheath 840 of the conventional high frequency cable 8 shown in FIG.

Unlike the outer conductor 810 of the conventional high frequency cable 8 shown in FIG. 8, the outer conductor 10 itself has a mechanical strength higher than a certain level and is configured to be flexible. As an example of such a structure, in the present embodiment, the outer conductor 10 is configured by two types of the inner spiral conductor 11 and the outer spiral conductor 12. Each of the spiral conductors 11 and 12 may be regarded as one to one linear, planar or strip (one form of planar) conductor spirally wound with the same inner diameter or outer diameter Say.
In addition, since it is spirally wound and extends along the cable center axis, the winding direction has a slight inclination with respect to a plane orthogonal to the cable center axis, but a plane substantially orthogonal to the cable center axis On top. In the present embodiment, an example in the case of using a helical coil is shown as the helical conductor. In the following description, the inner spiral conductor 11 is referred to as a first coil 11 and the outer spiral conductor 12 is referred to as a second coil 12 for convenience.

The insulator 20 is a soft insulating material that supports the central conductor 30 while keeping the distance between the inner side of the outer conductor 10, that is, the first coil 11, constant, and it is possible to use, for example, one formed of polytetrafluoroethylene (PTFE) it can. Unlike the insulator 820 of the conventional high-frequency cable 8 shown in FIG. 8, the insulator 20 according to the present embodiment has a square cross section in its front cross section, and a portion corresponding to a corner contacts the inside of the first coil 11. I did it. That is, a space (a gap in which air exists) is formed between the surface of the insulator 20 and the inner side of the first coil 11. This is to reduce the relative dielectric constant between the first coil 11 and the central conductor 30 as much as possible. The “square shape” is not limited to a square shape, and refers to a shape regarded as a square shape (a part or all of a portion corresponding to a corner includes an R shape). For example, the shape having a quadrangle, a concave quadrilateral, a double-centered quadrilateral, a trapezoid, a wedge, a diagonal quadrilateral, a parallelogram, etc., having a portion corresponding to four sides and four corners becomes a quadrilateral.
Since the dielectric constant is the lowest in air (about 1.0), a wider space enables transmission with lower loss.

  The first coil 11 and the second coil 12 constituting the outer conductor 10 are manufactured by a member which does not easily collapse with respect to an external force, and a large gap does not occur between the conductors at the time of tension. For example, it is desirable to manufacture the first coil 11 and the second coil 12 using a hard metal material having a Young's modulus of 100 GPa or more, which is used as a spring material. Examples of such a metal material include stainless steel (SUS), piano wire, phosphor bronze, beryllium copper, brass, platinum, nickel, gold, platinum iridium alloy, platinum tungsten alloy, platinum nickel alloy, and the like.

Since the first coil 11 and the second coil 12 constitute the high frequency cable 1 together with the central conductor 30, the magnitude of the conductivity is closely related to the quality of the transmission characteristics of the high frequency signal, particularly to the magnitude of the insertion loss. Therefore, the first coil 11 and the second coil 11 are made of a metal material having a conductivity (about 30 × 10 ⁶ S / m) or more at least 50% of the conductivity (59.5 × 10 ⁶ S / m) of pure copper. It is desirable to manufacture the coil 12. Examples of such metal materials include silver, copper, gold, aluminum, copper alloys and the like. In addition, you may use the hard resin material etc. which were plated with the metal material whose electric conductivity is about 30 * 10 < ⁶ > S / m or more on the surface.

  FIG. 2 is a longitudinal sectional view of the high frequency cable 1 for explaining the structure of the outer conductor 10. The insulator 20 is omitted for convenience. In the present embodiment, as one size example, the first coil 11 is formed by winding a metal material having a rectangular shape with a cross section of 0.1 mm long × 0.3 mm wide in a direction substantially orthogonal to the cable central axis. Manufactured. The inner diameter D1 of the outer conductor 10 is, for example, 0.8 mm. The metal material used was a copper alloy plated with gold. The pitch (the distance between the centers of the conductors, the same applies hereinafter) P11 is preferably not more than twice the conductor width (0.3 mm) from the viewpoint of preventing the leakage of the electromagnetic wave described later. In the present embodiment, the pitch P11 in the undeflected state is 0.35 mm.

  The second coil 12 is, for example, a coil having the same conductor width as that of the first coil 11, and is wound while loosely in contact with the outer surface between the conductors of the first coil 11. In the case of this example, the inner diameter D2 of the second coil 12 is 1.0 mm. The pitch P12 of the second coil 12 is 0.35 mm, which is the same as the pitch P11 of the first coil 11, but the second coil 12 is wound so as to be offset from the first coil 11 by approximately 1⁄2 pitch. Thereby, the second coil 12 has a role of closing the gap between the conductors of the first coil 11. The term "loosely in close contact" means a state in which the close contact portion is displaceable according to the degree of bending although the close contact is achieved by the biasing force and the deenergizing force of the first coil 11 and the second coil 12 themselves. Also, "approximately 1/2" means that it is not necessary to be exactly 1/2.

When the high frequency cable 1 is bent, the pitches P11 and P12 between the conductors of the first coil 11 and the second coil 12 change. That is, the bent inner pitch partially narrows, the outer pitch partially widens, and a gap is created between the conductors. Even in such a state, changes in the pitch of the first coil 11 and the second coil 12 occur in the same manner. Therefore, the gap generated between the conductors of the first coil 11 remains blocked by the second coil 12. That is, since the second coil 12 closes the gap between the conductors of the first coil 11 regardless of the presence or absence of bending, leakage of the electromagnetic wave from the outer conductor 10 to the outside is prevented, and transmission with low loss is possible. Become.
In addition, since the first coil 11 and the second coil 12 are not fixed to each other and the pitch changes relatively freely, the range that can be bent while suppressing the loss during transmission is made larger than that of the conventional high frequency cable 8 be able to.

  An example of the transmission characteristic per 1 cm of the high frequency cable 1 is shown in FIG. In FIG. 3, the horizontal axis is frequency (GHz) and the vertical axis is insertion loss (dB / cm). For example, the insertion loss at 80 GHz is -0.15 dB, which is a sufficiently small insertion loss.

<Modification 1>
Although the above is an example at the time of producing the 1st coil 11 and the 2nd coil 12 by the metal material of the section square shape with the same section size, it is not limited to this example. For example, as shown in the partial cross-sectional view of FIG. 4A, the first coil 51 and the second coil 52 may be made of a metal material having the same diameter and a circular cross section. Also in this example, the pitch P51 of the first coil 51 and the pitch P52 of the second coil 52 outside the first coil 51 are equal to or less than twice the conductor diameter or the conductor width, and they are wound with an approximately 1/2 pitch deviation. Alternatively, as shown in the partial cross-sectional view of FIG. 4B, the first coil 61 may be made of a metal material having a circular cross section, and the second coil 62 on the outer side may be made of a metal material having a square cross section. . The pitch P61 of the first coil 61 and the pitch P62 of the second coil 62 outside the first coil 61 are equal to or less than twice the conductor diameter or the conductor width, and they are wound so as to be deviated from each other by about 1⁄2 pitch. Alternatively, as shown in the partial cross-sectional view of FIG. 4C, the first coil 71 may be made of a metal material having a square cross section, and the second coil 72 on the outside thereof may be made of a metal material having a circular cross section. . Also in this example, the pitch P71 of the first coil 71 and the pitch P72 of the second coil 72 outside the first coil 71 are equal to or less than twice the conductor diameter or the conductor width, and they are wound with an approximately 1/2 pitch deviation. Alternatively, as shown in the partial cross-sectional view of FIG. 4D, the first coil 81 is made of a metal material having a rectangular cross section with a large conductor width, and the second coil 82 outside thereof is a cross section with a relatively small conductor width. It may be a square metal material. In addition, the magnitude of the conductor width may be reversed. In these examples, the pitch P81 of the first coil 81 and the pitch P82 of the second coil 82 outside the first coil 81 are equal to or less than twice the width of the larger conductor.

  If at least one of the outside of the first coil 11, 51, 61, 71, 81 and the inside of the second coil 12, 52, 62, 72, 82 is flat or curved, the high frequency cable 1 is bent Sometimes, since the first coils 11, 51, 61, 71, 81 and the second coils 12, 52, 62, 72, 82 are smoothly displaced, their cross-sectional shapes may be arbitrary. For example, the cross-sectional shape may be a circular shape or an n-angular shape (n is a natural number of 3 or more) in which at least one side has a linear shape or a curved shape.

<Modification 2>
Although the central conductor 30 of the high frequency cable 1 has been described as a single or double wire such as copper provided along the cable central axis, it is not limited to this example. For example, as in the high-frequency cable 2 shown in the structural perspective view of FIG. 5A, the central conductor 30 may be a coplanar line 301 composed of three conductors arranged on the insulator 201. . Alternatively, as in the high-frequency cable 3 shown in the structural perspective view of FIG. 5 (b), the center conductor 30 is formed by arranging balanced lines 302 composed of four or more conductors on the insulator 202. It may be. Each of the insulators 201 and 202 has a frontal cross section in the form of a square (rectangular in the illustrated example) along the inner side of the first coil 11, and a portion corresponding to a corner portion corresponds to the inner side of the first coil 11. I am in touch.
Thus, the present invention is applicable to all high frequency cables having the outer conductor 10 regardless of the shape, structure, conductor arrangement and number of conductors of the central conductors 30, 301, 302.

<Modification 3>
In the present embodiment, an example in which the front cross section of the insulator 20 has a square shape has been described, but the present invention is not limited to this example. Since it is desirable that a space with the largest possible volume be formed between the surface of the insulator 20 and the inner side of the outer conductor 10, the shape thereof is, for example, the shape shown in FIG. Also good. In FIGS. 6 and 7, the same components as those in FIGS. 1A, 1B, 5A, and 5B are denoted by the same reference numerals.
FIG. 6A shows an example in which the center conductor 30 is molded with an insulator 210 whose front cross section is substantially cruciform. The same (b) is an example similarly molded by the insulator 220 whose front cross section curved toward the central portion of the central conductor 30 is a triangle. The triangular shape includes, in addition to the illustrated shape example, a shape in which part or all of the portion corresponding to the corner has an R shape. Since the space between the insulators 210 and 220 and the inner side of the outer conductor 10 is large, an increase in transmission loss is suppressed. In addition to the above, it may be an insulator whose front cross section is star-shaped, saddle-shaped or similar.

FIG. 7A shows an example of the insulators 201, 231 and 232 in the case where the central conductor is the coplanar line 301 of FIG. 5A. Moreover, FIG.7 (b) is an example of the insulators 202,241,242 in case the center conductor is the balance line 302 of FIG.5 (b). In either case, the central conductor (coplanar line 301, balanced line 302) is sandwiched from above and below in the drawing.
7 (a) shows a structure in which the coplanar line 301 is supported by one insulator 231, but as shown in FIG. 7 (b), the three conductors constituting the coplanar line 301 are individually individually provided. It may be a supporting structure. Although FIG. 7 (b) shows a structure in which the four conductors constituting the balanced line 302 are individually supported, it may be a single support as shown in FIG. 7 (a). Further, in FIGS. 7A and 7B, the insulators 232 and 242 on the lower side in the drawing are integrally configured with the insulator 201 provided with the coplanar line 301 and the insulator 202 provided with the balanced line 302, respectively. It may be. The front cross-sectional shape in that case may be arbitrary.

Claims (12)

A central conductor provided along the cable central axis;
And an outer conductor surrounding the central conductor,
The outer conductor is wound around a first spiral conductor wound in a direction substantially orthogonal to the cable central axis and an outer side of the first spiral conductor along a space between the conductors of the first spiral conductor. High frequency cable having a second helical conductor. The central conductor is supported by the outer conductor via a flexible insulator, and a space is formed between the surface of the insulator and the inner side of the outer conductor.
The high frequency cable according to claim 1. The central conductor is any of a substantially cylindrical conductor, a coplanar line, and a balanced line.
The high frequency cable according to claim 1 or 2. The conductor width of the second helical conductor is larger than the gap between the conductors of the first helical conductor
The high frequency cable according to any one of claims 1 to 3. The conductor width of the first spiral conductor is larger than the conductor width of the second spiral conductor
The high frequency cable according to any one of claims 1 to 4.   The high frequency cable according to any one of claims 1 to 5, wherein at least one of the outer side of the first helical conductor and the inner side of the second helical conductor is flat or curved. The first helical conductor and the second helical conductor have a circular cross-sectional shape or an n-angular shape (n is a natural number of 3 or more) in which at least one side is linear or curved.
The high frequency cable according to any one of claims 1 to 6. The cross-sectional shape of the first helical conductor and the cross-sectional shape of the second helical conductor are the same.
The high frequency cable according to any one of claims 1 to 7. The first spiral conductor is wound at a pitch not more than twice the width of the conductor,
The high frequency cable according to any one of claims 1 to 8, wherein the second spiral conductor is wound around the conductors of the first spiral conductor with a shift of about 1⁄2 pitch. The second spiral conductor is in close contact with the conductors of the first spiral conductor.
The high frequency cable according to any one of claims 1 to 9. The first spiral conductor is a metal material having a conductivity of 30 × 10 ⁶ [S / m] or more, or a metal material having a conductivity of 30 × 10 ⁶ [S / m] or more plated on the surface thereof. The high frequency cable according to any one of claims 1 to 10, wherein   The high frequency cable according to any one of claims 1 to 11, wherein the first spiral conductor is made of a metal material having a Young's modulus of 100 [GPa] or more.

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