JP2015185858A - flexible waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-weight waveguide, having flexibility, excellent in workability by winding a flat foil yarn having conductivity by making a flexible dielectric body as a core.SOLUTION: By winding a conductive flat foil yarn by making a flexible dielectric body having continuous cross sections of the same shape to be a core, a conductor layer is formed at an outer surface of the dielectric body. By compressively deforming the dielectric body with tension of the flat foil yarn and utilizing a restoring force with regard to the compressive deformation of the dielectric body, a cross section shape of the conductor layer is maintained.

Description

  The present invention relates to a waveguide that is a kind of line for transmitting high-frequency radio waves and electrical signals.

In recent years, the frequency of electrical signals has increased due to the necessity of high-capacity high-speed communication, and the microwave band is generally used, and the number of used frequency bands has been increased to some millimeter waves.
Since these waveguides used for high-frequency transmission have poor flexibility and poor workability, there is a need for lightweight waveguides that are as flexible and flexible as ordinary cables. .

  In Patent Document 1, a core is formed by bundling a plurality of yarns, and since this dielectric is not elastically compressed, there is no restoring force, and there is no pressure toward the outside from the inside of the dielectric. When the waveguide is bent, there is no force that resists deformation of the cross-sectional shape, so that wrinkles occur in the conductor layer outside the dielectric, and the transmission loss of the waveguide increases.

  In the flexible waveguide of Patent Document 2, a bellows tube whose movable part is shaped into a corrugated metal is used as the outer conductor of the waveguide, and the flexible part is limited to a part of the waveguide, and the mass Is larger than conventional waveguides.

In Patent Document 3, the outer conductor of the waveguide is wound only in one direction clockwise or counterclockwise with a dielectric rod as a core, with a flat metal foil tape having a wide width. Since the dielectric is not elastically compressed and deformed in advance, there is no restoring force and there is no pressure to push the outer conductor from the inside to the outside, so wrinkles are generated in the outer conductor when the waveguide is bent However, transmission loss increases.
In addition, since the metal foil tape is wound in one direction, the direction of the wrinkles on the outer conductor differs depending on whether the waveguide is bent rightward or leftward, which affects transmission loss. To do.

JP 2008-28523 A JP 2008-271333 A JP-A-8-195605

  The present invention provides a flexible waveguide that is lightweight and flexible with excellent workability and suppresses an increase in transmission loss.

In high frequency transmission in the microwave band and millimeter wave band, the transmission loss of the waveguide is smaller than that of the coaxial cable. For this reason, in a communication system that handles minute power, a waveguide is installed as a transmission line instead of a coaxial cable.
For example, in an antenna system that needs to receive a small amount of power, such as a ship or aircraft radar or satellite communication, a metal waveguide is used as a transmission line for supplying power to the antenna.

However, metal waveguides are heavy, inflexible, and have the disadvantage of poor workability. When it is necessary to bend and construct a conventional metal waveguide, it is necessary to use a bent metal waveguide called a curved tube and screw it together with a straight waveguide and a flange.
Also, since it is heavy and not flexible and cannot be wound, there is a limit to the length of a single metal waveguide, and many metal cables are required to construct long-distance transmission lines. It was necessary to connect the waveguides with flanges. Further, as the number of waveguides to be connected increases, an increase in transmission loss at the flange portion is unavoidable, which causes a deterioration in quality as a transmission line.

  Moreover, the construction of a waveguide, which often feeds an antenna directly, can be a work at a high place, and the work at a high place with heavy objects is dangerous. For this reason, it is necessary to reduce the weight of the waveguide in order to reduce the load on workers.

In the waveguide of Patent Document 1, the core dielectric is only a material in which yarns are bundled and has no restoring force against compression. Therefore, when the waveguide is bent, the conductor layer in the bent portion is irregular. As a result, the transmission loss increases due to scattering in the electromagnetic field propagating inside.
Further, the waveguide of Patent Document 2 is a flexible metal waveguide made of a bellows-like outer conductor only in a portion that needs to be bent, and is the same as a conventional metal waveguide except for the bent tube. Yes, workability will not be improved.

In Patent Document 3, the waveguide has a flexible dielectric rod as the core, but the metal tape is wound in one direction, either rightward or leftward, and in addition, the dielectric rod is restored to compression. When there is no force and the waveguide is bent, a problem similar to that of the waveguide of Patent Document 1 occurs.
In addition, since the metal foil tape is wound in one direction, directionality occurs in the flexibility of the waveguide, and it is easy to bend when the waveguide is bent to the right and to the left. As well as the transmission characteristics.

  In order to achieve the above object, it is possible to solve the problem by forming an outer conductor with a conductive flat foil thread with a dielectric having a restoring force against compression deformation as a core.

  That is, (1) a waveguide having a flexible dielectric having a cross section of the same shape continuous in the longitudinal direction as a core and the outer surface of the dielectric covered with a conductor layer, the dielectric being compressed and deformed The conductor layer is formed by winding a required number of flat foil yarns having conductivity in a flat cross-sectional shape around the dielectric, and the conductor layer is formed of a material having a restoring force. Half of the foil is wound clockwise so as to be inclined with respect to the longitudinal direction of the dielectric, and the remaining half of the flat foil yarn is at the same angle as the clockwise flat foil yarn, and the longitudinal direction of the dielectric. Since the coil is wound counterclockwise so as to be inclined, the dielectric is in a waveguide that maintains the state in which the dielectric is compressed and deformed by the tension of the flat foil yarn.

  (2) The waveguide according to 1 above, wherein the flat foil yarn is formed by laminating a metal foil and a film.

  (3) The waveguide according to (2) above, wherein the film has conductivity.

  (4) In the waveguide according to any one of (1) to (3), the dielectric is made of a material having a relative dielectric constant smaller than 2.

  Since the waveguide of the present invention is configured as described above, it is possible to realize a waveguide that is lightweight, flexible, and excellent in workability.

In the waveguide of the present invention, since the conductor layer covers the outer surface with a dielectric material as a core, an electromagnetic field propagates through the inside of the dielectric and operates as a waveguide. Moreover, the core dielectric is a material that is flexible and has a restoring force against compression, and is compressed by the tension of the flat foil yarn forming the conductor layer, so that the cross-sectional shape of the dielectric is Since the elastic contraction is similar, the dielectric has a restoring force.
Therefore, a pressure is generated to push the conductor layer from the inside of the dielectric toward the outside, and the cross-sectional shape of the conductor layer is maintained even against bending by balancing this force with the tension of the flat foil yarn.

  The dielectric as the core has a cross-sectional area reduced by several percent due to the tension when winding the flat foil yarn, and a conductor layer depending on the conductivity of the flat foil yarn is formed on the outside thereof. The conductivity and cross-sectional shape of the conductor layer and the relative dielectric constant of the compressed dielectric determine the transmission characteristics of the waveguide.

  The conductor layer formed of the flat foil yarn is maintained with a constant and stable cross-sectional shape of the waveguide by applying pressure from the inside due to the restoring force of the compressed dielectric. The pressure from the inside to the outside is effective even when the waveguide is bent, and the change in the shape of the waveguide cross section can be suppressed and an increase in transmission loss can be suppressed.

  Also, since the conductor layer is composed of the same number of clockwise and counterclockwise flat foil yarns, the difference in distortion due to the bending direction of the waveguide is reduced, and the flexibility of the waveguide is reduced. The workability is improved by not depending on the bending direction.

Since the waveguide of the present invention is flexible and has virtually no limitation on the length that can be manufactured, it has the advantage that it can be produced, shipped, transported, and constructed in the same manner as a normal coaxial cable.
The advantage of reducing the number of waveguide connection points is beneficial not only in construction but also in reducing transmission loss.

In the waveguide of the present invention, since the electromagnetic field propagates through the dielectric, it is attenuated by the dielectric loss of the dielectric during propagation. For this reason, a propagation loss becomes small, so that the dielectric constant of a dielectric material is small.
A dielectric such as an ordinary plastic has a relative dielectric constant of 2 or more, but a dielectric including an air layer exhibits a relative dielectric constant of 2 or less and is suitable as a core material for a waveguide.

It is the figure which showed the structure of the typical waveguide of this invention. FIG. 3 is a view of a typical flat foil yarn forming a conductor layer covering the outside of the waveguide of the present invention. It is the Example which measured the transmission characteristic with respect to the 25 GHz band waveguide of this invention. It is a comparative example for comparing the transmission characteristic of the 25 GHz band waveguide comprised by patent document 1 with FIG. It is the Example which measured the transmission characteristic when a conductor layer was formed with the flat foil thread | yarn of width 1mm with respect to the waveguide of 15 GHz band of this invention. It is the Example which measured the transmission characteristic when a conductor layer was formed with the flat foil thread | yarn of width 1.5mm with respect to the waveguide of 15 GHz band of this invention. It is the Example which measured the transmission characteristic with respect to the 50 GHz band waveguide of this invention. It is the Example which compared the waveguide loss of this invention, the waveguide made from a pure copper, and each transmission loss and mass.

  Hereinafter, embodiments will be described in detail with reference to the drawings. FIG. 1 is a typical cross-sectional view of a waveguide according to the present invention, and a thin flat foil yarn 2, 3 is wound around the outside of a dielectric with a dielectric 1 having a restoring force against compressive deformation as a core. Thus, a waveguide is formed.

  The core dielectric 1 is a material having a restoring force and flexibility and having a low dielectric constant. The dielectric is rod-shaped and the cross-sectional shape is constant in the longitudinal direction.

A required number of flat foil yarns 2 and 3 are wound around the outside of the dielectric 1. Half of the flat foil yarns 2 are wound around the dielectric counterclockwise, and the remaining half of the flat foil yarns 3 are wound around the dielectric clockwise.
The flat foil yarns 2 and 3 are wound while being inclined at the same angle both counterclockwise and clockwise with respect to the longitudinal direction of the rod-shaped dielectric material, and cover the outer surface of the dielectric material without a gap.

  As a material of the dielectric 1, for example, there is a rod-like foamed polyethylene, and the elasticity when the cross-sectional area is reduced by several percent by the tension at the time of winding the flat foil yarn, and since the dielectric constant is included because of including the air layer It is a flexible material that is small and exhibits a low dielectric constant of about 1.2.

Normally, when a long product with a constant cross-sectional shape is bent, a tensile force works on the outside of the curved portion and a compression force works on the inside, so that the cross-sectional shape orthogonal to the long axis direction of the long product is Deforms flat so that it collapses.
In a transmission line such as a coaxial cable or a waveguide, a change in the cross-sectional shape of the transmission line perpendicular to the direction in which the electromagnetic field propagates affects the transmission characteristics of the electromagnetic field. Therefore, it is determined that a general coaxial cable is used within the curvature range in which the influence of the change in the cross-sectional shape of the transmission line can be ignored with respect to the transmission characteristics of the electromagnetic field.

In the case of a coaxial cable, the conductor layer outside the dielectric is formed by wrapping the required number of fine metal wires, and there are gaps between the metal wires. The force is dispersed in many fine metal wires, and the strain is relaxed in the gaps, thereby suppressing the change in the cross-sectional shape of the conductor layer.
Along with the bend, the dielectric layer of the coaxial cable is deformed so that the cross section of the curved portion is crushed, and the curvature within an allowable value that the crushed manner affects the transmission characteristics of the coaxial cable is the bending limit of the coaxial cable.

  The conductor layer formed of the flat foil yarn of the waveguide shown in the examples to be described later and the conductor layer formed of a thin metal wire of a general coaxial cable have the same braided structure. However, the conductor layer covering the outer surface of the dielectric of the coaxial cable has a feature that there is no mechanical interaction with the dielectric and a mechanism for reducing strain against bending. And different.

The conductor layer outside the dielectric of a general coaxial cable is formed by bundling a plurality of fine metal wires having a circular cross section into a single fine metal wire strand, and then finishing it into a braided structure using the required number of strands. . Further, the metal thin wire strand is not tensioned enough to shrink the inner dielectric, and the cross-sectional shape is maintained only by the metal thin wire.
Therefore, there are many gaps in the conductor layer of the coaxial cable, and the distortion generated in the curved portion when the coaxial cable is bent is alleviated by the movement of the individual fine metal wires through the gap.

On the other hand, in the waveguide of the embodiment described later, the flat foil yarn forming the conductor layer has no gap in the braided structure. Flat foil yarns having flat cross sections are combined without gaps to form a braided structure, and the absence of gaps in the conductor layer improves the propagation characteristics of the waveguide.
In the waveguide of the present invention, the dielectric is compressed by the tension of the flat foil yarn forming the conductor layer, and as a reaction, the dielectric applies pressure to the conductor layer, and these forces are balanced. The mechanism in which the cross-sectional shape is stable is different from the conductor layer forming the coaxial cable.

  When the waveguide of the present invention is bent, a change in tension occurs in the flat foil yarn forming the conductor layer so that the tension increases outside the curved portion and decreases in the inner flat foil yarn. Since there is no gap in the braided structure forming the conductor layer, the flat foil yarn can only move in the long axis direction of the flat foil yarn, and the tension generated in the conductor layer as each flat foil yarn moves in this direction To alleviate changes.

In addition, the core dielectric is also subjected to a force that expands outside the curved portion and compresses inside due to bending of the waveguide. Therefore, a pressure in a positive direction from the inside of the dielectric toward the outside is generated in the portion to be compressed, and a pressure in a negative direction inward is generated in the portion that is expanded.
In the waveguide of the present invention, the core dielectric is compressed from the beginning by the winding of a flat foil yarn, and a positive pressure is generated. For this reason, even in a portion where a negative pressure is generated by expansion of the dielectric due to the bending of the waveguide, the positive pressure is maintained in a range where the bending curvature of the waveguide is small, and the conductor layer may be wrinkled. There is little change in the cross-sectional shape.
If the dielectric is not compressed from the beginning, the dielectric is stretched by bending the waveguide, and the dielectric pressure is in the negative direction. Occurs, the change in the cross-sectional shape increases and the transmission loss increases.

  Similarly to other transmission lines, the waveguide of the present invention can be used within a range in which a change in cross-sectional shape due to bending does not affect transmission characteristics.

FIG. 2 shows an example of a typical flat foil yarn, in which a metal foil 5 and a film 4 are bonded and cut into a narrow width. A flat foil yarn using only the metal foil 5 without the film 4 being bonded is also possible.
Further, by making the film 4 conductive, the conductivity of the conductor layer can be made higher than when the insulating film 4 is bonded to the metal foil 5, so that the transmission loss of the waveguide can be reduced. it can.

Normally, an electromagnetic field propagating in a dielectric is subjected to transmission loss due to dielectric loss of the dielectric. Therefore, the material filling the inside of the waveguide is desirably a material that is electromagnetically close to vacuum, and a material having a relative dielectric constant close to 1 is preferable.
The foamed dielectric includes an air layer and can have a relative dielectric constant of 2 or less, which has the effect of reducing the dielectric loss of the electromagnetic field propagating therein, and can further reduce transmission loss.

In the following examples, the transmission loss of the waveguide of the present invention was measured by attaching a specially developed connector to both ends of the waveguide and measuring with a network analyzer. The measured value is converted into the transmission loss per 1 m of the waveguide length by subtracting the transmission loss of only the connector.
The waveguide is placed at one place, bent at 180 degrees with a radius of curvature of 100 mm, connected to a network analyzer, and transmission characteristics are measured.

<Example 1>
FIG. 3 shows an example in which the transmission loss per meter of a 25 GHz band waveguide is measured. A flat foil yarn having a width of 1 mm is wound around a foamed polyethylene shaped into a cross section of 4 mm in length and 9 mm in width.
In the conductive layer forming step, 16 flat foil yarns were used and wound by a braiding machine (manufactured by Kokbun Limited: 101-C medium-sized carrier blader).
This flat foil yarn is obtained by bonding a 9 μm thick copper foil and a 25 μm thick PET (polyethylene terephthalate) film. The minimum transmission loss of this waveguide is -1.6 dB / m.
This value is larger than the theoretical value of transmission loss of pure copper 25 GHz band waveguide -0.4 dB / m, but considering the advantages in construction as described above, the waveguide of the present invention is used. In this case, there are advantages in reducing the construction cost, operation and maintenance of the entire device (FIG. 3).

<Comparative Example 1>
FIG. 4 is a comparative example in which the conductor layer of the waveguide of Patent Document 1 is formed by the same manufacturing method as that of the present invention. The 25 GHz band waveguide of FIG. 3 has the same configuration as the waveguide of FIG. 3 except that the core dielectric is changed from foamed polyethylene to a polypropylene fiber bundle. When the waveguide is bent, there is no restoring force in the core fiber bundle of the dielectric, so that the conductor layer formed of flat foil yarn has wrinkles and the transmission loss is significantly increased compared to FIG. (FIG. 4).

<Example 2>
FIG. 5 shows an example in which the transmission loss of the 15 GHz band waveguide of the present invention was measured. The cross-sectional shape of the foamed polyethylene was 9 mm long and 17 mm wide, and a conductor layer was formed with a flat foil yarn having a width of 1 mm. The minimum transmission loss per meter of length is -1.3 dB / m (FIG. 5).

<Example 3>
FIG. 6 shows that when a conductor layer is formed of a flat foil thread having a width of 1.5 mm, the transmission loss of a 15 GHz band waveguide is converted per 1 m, and the minimum transmission loss is about −0.8 dB / m. is there. The width of the flat foil yarn forming the conductive layer is different from the waveguide of FIG. 5 which is the same 15 GHz band waveguide. If the flat foil yarn has the same structure, the flat foil having a larger width is used. Forming the conductor layer using yarn is advantageous in reducing transmission loss (FIG. 6).

  FIG. 7 is an example in which the transmission loss of the 50 GHz band waveguide of the present invention was measured. When the cross-sectional shape of the foamed polyethylene was 3 mm long and 5 mm wide, and a conductor layer was formed with a flat foil thread having a width of 0.5 mm, The minimum transmission loss is -3.4 dB / m. This example shows that the waveguide of the present invention can also be used in the millimeter wave band (FIG. 7).

  FIG. 8 is an example in which the relationship between transmission loss and mass is compared in terms of length per meter for the waveguide of the present invention and the waveguide made of pure copper. The waveguide of the present invention is lighter by one digit or more than a pure copper waveguide (FIG. 8).

  Waveguides are used in aircraft, marine radar, and communication equipment that use microwaves and millimeter waves, and their construction requires flexibility. In addition, a lightweight waveguide is required for aircraft.

Communication equipment is required to have high reliability, and the waveguide of the present invention has advantages in that it has fewer connection parts than a metal waveguide, and is light and flexible. And has strong features.
As described above, the communication equipment using the waveguide according to the present invention has remarkably high reliability against a disaster such as an earthquake as compared with a case where a heavy metal waveguide is screwed using a flange.

With the generalization of wireless communication, the frequency usage of radio waves has shifted to the high frequency side, and there is a tendency that communication facilities using microwaves and millimeter waves will increase in the future.
The transmission line used in such communication equipment is a waveguide, and the lightweight and flexible waveguide of the present invention is useful for constructing these equipment inexpensively and quickly.

1 Dielectric
2 Flat foil yarn 3 Flat foil yarn 4 Film 5 Metal foil

Claims (4)

  A waveguide having a flexible dielectric with a cross section of the same shape continuous in the longitudinal direction as a core and the outer surface of the dielectric covered with a conductor layer, the dielectric having a restoring force against compressive deformation The conductor layer is formed by winding a required number of flat foil yarns having a flat cross-sectional shape and conductivity around the dielectric, and half of the flat foil yarns are formed of the dielectric material. Wrapped clockwise to incline with respect to the longitudinal direction of the body, and the remaining half of the flat foil yarns incline with respect to the longitudinal direction of the dielectric at the same angle as the clockwise flat foil yarns. Thus, the waveguide is maintained in a state where the dielectric is compressed and deformed by the tension of the flat foil yarn. The waveguide according to claim 1, wherein the flat foil yarn is formed by laminating a metal foil and a film. The waveguide according to claim 2, wherein the film has conductivity. The waveguide according to any one of claims 1 to 3, wherein the dielectric is made of a material having a relative dielectric constant smaller than 2.