JP6865106B2 - Flexible waveguide - Google Patents

Description

The present invention relates to a flexible waveguide that transmits high frequency signals in the microwave band or millimeter wave band.

In recent years, consumer devices using high frequencies in the millimeter wave band have rapidly become widespread due to the demand for higher resolution of radars and sensors, or large-capacity high-speed communication represented by 5th generation mobile communication systems. In these consumer devices, a flat transmission line, a coaxial cable, a waveguide, etc. formed on a printed circuit board are used as means for transmitting an electric signal. A dielectric material such as PTFE is used as a printed circuit board material in a flat type transmission line and as a support material for holding a central conductor in a coaxial cable. These dielectric materials are generally expensive, and deterioration of transmission characteristics due to dielectric loss is unavoidable. Therefore, there is a high demand for a hollow waveguide that does not use a dielectric material.
However, the conventional waveguide for the millimeter wave band is made of a hard metal wall and therefore lacks flexibility. In addition, it tends to be expensive because high processing accuracy is required. Therefore, there is a demand for a lightweight and inexpensive waveguide that is highly flexible like a coaxial cable.

As conventional flexible waveguides of this type, those having a bellows structure on the tube wall (Patent Document 1) and those wound with a strip-shaped metal body having a fitting structure (Patent Document 2) are known. Further, a rod-shaped low-loss dielectric having a structure in which a ribbon-shaped metal foil (Patent Document 3) or a conductive flat foil thread is wound around is known (Patent Document 4).

Japanese Patent No. 2800636 US US3331400 Gazette Japanese Unexamined Patent Publication No. 8-195605 Japanese Unexamined Patent Publication No. 2015-185858

The frequency band in which a waveguide can be transmitted is limited by its diameter size. Therefore, it is necessary to reduce the diameter size as the frequency increases. In particular, the diameter size required for transmission in the millimeter wave band is approximately 3 mm or less. The flexible waveguide disclosed in Patent Document 1 and Patent Document 2 has a problem that it is difficult to realize a diameter size of about 3 mm or less due to a problem of machining accuracy, and even if it is realized, it is expensive. The flexible waveguide disclosed in Patent Document 3 and Patent Document 4 uses an expensive dielectric material, and there remains a problem that the dielectric loss cannot be improved.
An object of the present invention is to provide an inexpensive and low-loss flexible waveguide suitable for use in the millimeter wave band.

A flexible waveguide according to an embodiment of the present invention has a tube wall having a hollow structure, and the tube wall is wound in a direction substantially orthogonal to a longitudinal tube axis. It is characterized in that it is formed including a one spiral conductor and a second spiral conductor wound around the outside of the first spiral conductor along between the conductors of the first spiral conductor.

Since it has a hollow structure, it has a lower loss than when a dielectric material is used, and even if a gap is created between the conductors of the first spiral conductor when curved, the second spiral conductor closes the gap, so it is flexible. Low loss transmission is possible while keeping it.

(A) is a structural perspective view of the flexible waveguide according to the first embodiment, and (b) is a partial cross-sectional view in the longitudinal direction. (A) is a structural perspective view when the flexible waveguide according to the first embodiment is curved, and (b) is a partial cross-sectional view in the longitudinal direction. The electric field distribution diagram of the flexible waveguide according to the first embodiment. (A) and (b) are transmission characteristic diagrams of the flexible waveguide according to the first embodiment. (A) and (b) are transmission characteristic diagrams of a cylindrical waveguide as a comparative example. (A) to (c) are partial cross-sectional views showing a modification of the flexible waveguide according to the first embodiment. The structural perspective view of the flexible waveguide according to the 2nd Embodiment. The structural perspective view of the flexible waveguide according to the 3rd Embodiment.

Hereinafter, examples of embodiments of the flexible waveguide of the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1A is a structural perspective view of the flexible waveguide according to the first embodiment, and FIG. 1B is a partial cross-sectional view thereof in the longitudinal direction. The flexible waveguide 1 of the present embodiment has a hollow tube wall 10 having a circular cross section for transmitting electromagnetic waves in the millimeter wave band. The central axis of the tube wall 10 in the longitudinal direction is called a tube axis. In this embodiment, the tube wall 10 is formed by two types of spiral conductors, an inner one and an outer one. The tube wall 10 acts as an inner wall of the waveguide, and the electromagnetic wave propagates in the tube axis direction while being repeatedly reflected by the tube wall 10.

"Spiral conductor" refers to a component in which linear, planar, and strip-shaped (one aspect of planar) conductors, which can be regarded as one or one, are spirally wound with the same inner diameter or outer diameter. .. Since it is spirally wound and extends in the elongated direction, the winding direction has a slight inclination with respect to the plane orthogonal to the pipe axis, but is substantially on the plane orthogonal to the pipe axis. In this embodiment, an example in which a helical coil is used as the spiral conductor is shown. Hereinafter, the inner spiral conductor is referred to as the first coil 11, and the outer spiral conductor is referred to as the second coil 12.

Since the first coil 11 is hollow, it is desirable that the first coil 11 is not easily crushed by an external force and that a large gap is not formed between the conductors during tension. Therefore, it is desirable to manufacture the first coil 11 using a hard material having a Young's modulus of 100 GPa or more, for example, a metal material, which is used as a spring material, for example. Examples of such metal materials 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.

Further, when the first coil 11 is used as the flexible waveguide 1, the magnitude of the conductivity in the tube wall 10 is closely related to the quality of the transmission characteristics, particularly the magnitude of the insertion loss. Therefore, the first coil 11 is manufactured using a metal material having a conductivity (about 30 × 10 ⁶ S / m) or more, which is at least 50% of the conductivity of pure copper (59.5 × 10 ^{6 S / m).} Is desirable. Examples of such metal materials include silver, copper, gold, aluminum, and copper alloys. Further, it may be a rigid material which is plated with a conductivity of about 30 × 10 6 ^{S /} m or more metallic materials on the surface.

In the present embodiment, the first coil 11 is manufactured by winding a metal material having a rectangular cross section of 0.3 mm in length × 0.3 mm in width in a direction substantially orthogonal to the tube axis. The inner diameter D1 of the pipe wall 10 is 2.6 mm. As the metal material, a gold-plated copper alloy was used. The pitch (distance between the centers of the conductors, the same applies hereinafter) P11 is preferably twice or less the conductor width (0.3 mm) from the viewpoint of preventing leakage of electromagnetic waves, which will be described later. In the present embodiment, the pitch P11 in the non-bent state is set to 0.35 mm.
The second coil 12 is a coil of the same material and the same conductor width as the first coil 11, and is wound while being loosely adhered to the outer surface between the conductors of the first coil 11. The inner diameter D2 of the second coil 12 is 3.2 mm. The second coil 12 has a role of closing the gap between the conductors of the first coil 11. Therefore, the pitch P12 of the second coil 12 is the same as the pitch P11 of the first coil 11, but is substantially 1/2 pitch deviated from the first coil 11. The “loosely adhered” means a state in which the first coil 11 and the second coil 12 themselves are in close contact with each other by the urging force and the urging force, but the contact portion can be displaced according to the degree of bending. Further, "substantially 1/2" means that it does not have to be exactly 1/2.

FIG. 2 is a structural perspective view of the flexible waveguide 1 when it is curved, and FIG. 2B is a partial cross-sectional view of the flexible waveguide 1 in the longitudinal direction. When the flexible waveguide 1 is curved, the pitches P11 and P12 between the conductors of the first coil 11 and the second coil 12 change. That is, the curved inner pitch is partially narrowed, the outer pitch is partially widened, and a gap is created between the conductors. Even in such a state, the gap generated between the conductors of the first coil 11 remains closed by the second coil 12. That is, since the second coil 12 closes between the conductors of the first coil 11 regardless of the presence or absence of bending, leakage of electromagnetic waves from the pipe wall 10 to the outside is prevented, and transmission with low loss is possible.

Next, the transmission characteristics of the flexible waveguide 1 will be described. Generally, when the transmission frequency of a waveguide becomes high, a high-order mode is generated and the transmission efficiency is lowered. Therefore, it is designed so that only the lowest-order mode, that is, the basic mode can be transmitted. The basic mode of the waveguide with a circular cross section is called the TE11 mode shown in FIG. 3, and it is possible to transmit a high frequency signal when the wavelength in the tube is in the range of about 1.316 times to about 1.706 times the inner diameter D1. Become. In the case of the flexible waveguide 1 according to the present embodiment, since the inner diameter D1 is 2.6 mm, for example, the usable frequency in which the TE11 mode can exist is about 70 GHz to 85 GHz.

FIG. 4 shows the transmission characteristics of the flexible waveguide 1 per coil length of 10 mm. FIG. 4A is a transmission characteristic diagram when there is no bending, and FIG. 4B is a transmission characteristic diagram when the curvature radius is 16 mm and is curved by 30 degrees. The horizontal axis is frequency (GHz) and the vertical axis is insertion loss (dB). For example, in the case of 80 GHz, the insertion loss when there is no bending is −0.06 dB, and the insertion loss when curved is also −0.06 dB, which is a sufficiently small insertion loss.
For comparison, FIG. 5 shows the transmission characteristics of a cylindrical waveguide having the same inner diameter as the flexible waveguide 1 (2.6 mm) and made of a metal material having the same conductivity. FIG. 5A is a transmission characteristic diagram when there is no bending, and FIG. 5B is a transmission characteristic diagram when the curvature radius is 16 mm and the curvature is 30 degrees. The vertical axis and the horizontal axis are the same as those in FIG. For example, in the case of 80 GHz, the insertion loss when there was no bending was −0.04 dB, and the insertion loss when curved was also −0.04 dB. That is, it can be seen that the flexible waveguide 1 is capable of low-loss transmission, which is almost the same as the cylindrical waveguide (less than −0.02 dB per 10 mm coil length).

As described above, in the flexible waveguide 1 according to the first embodiment, since the second coil 12 is wound between the conductors of the first coil 11 to form the tube wall 10, an arbitrary diameter size, particularly millimeter wave, is formed. A flexible waveguide that requires a small diameter such as a band can be manufactured at low cost. Since the tube wall 10 is more easily bent than the cylindrical waveguide and easily returns to the original shape, there is also an effect that the connection between high frequency components is easier than that of the cylindrical waveguide.
Further, since the waveguide has a hollow structure, low-loss transmission is possible as compared with a waveguide in which a dielectric is inserted. Further, even if the pitch P11 of the first coil 11 is partially changed by an external force, it is blocked by the second coil 12, so that low-loss transmission is possible while maintaining flexibility.

The above has described an example in which the first coil 11 and the second coil 12 are both manufactured of a metal material having the same cross-sectional size and a rectangular cross-section, but the present invention is not limited to this example. For example, as shown in the partial cross-sectional view of FIG. 6A, the flexible waveguide may be composed of the first coil 21 and the second coil 22 having the same diameter and a circular cross section. The pitch P21 of the first coil 21 and the pitch P22 of the second coil 22 on the outer side thereof are not more than twice the outer diameter of the coil and are substantially 1/2 pitch deviated from each other.

Further, as shown in the partial cross-sectional view of FIG. 6B, the first coil 31 may have a rectangular cross section, and the second coil 32 outside the first coil 32 may have a circular cross section. The first coil 31 may have a circular cross section, and the second coil 32 may have a rectangular cross section. Also in this example, the pitch P31 of the first coil 31 and the pitch P32 of the second coil 32 on the outer side thereof are not more than twice the outer diameter of the coil or the conductor width, and are substantially 1/2 pitch deviated from each other.

Further, as shown in the partial cross-sectional view of FIG. 6C, the first coil 41 has a rectangular cross section having a large conductor width, and the second coil 42 outside the first coil 42 has a rectangular cross section having a relatively small conductor width. Is also good. The size of the conductor width may be reversed. In the case of these examples, the pitch P41 of the first coil 41 and the pitch P42 of the second coil 42 outside the pitch P41 are set to be twice or less the larger conductor width.

[Second Embodiment]
A second embodiment of the present invention will be described. FIG. 7 is a structural perspective view of the flexible waveguide according to the second embodiment. The flexible waveguide 7 of the second embodiment is a rectangular waveguide having a hollow structure having a rectangular surface (diameter) orthogonal to the tube axis. That is, the first coil 71 wound in a rectangular shape in a direction substantially orthogonal to the tube axis, and the first coil 71 wound outside the first coil 71 along the conductors of the first coil 71. The tube wall 70 is formed by the two coils 72. The relationship between the material, cross-sectional shape, pitch, conductor width (or outer diameter) of the first coil 71 and the second coil 72, the pitch of the first coil 71, and the pitch of the second coil 72 is the first embodiment (FIG. 6 (a) to (c) are the same as those described in (including the modified examples shown in).
As described above, the cross-sectional shape of the waveguide may be substantially circular or rectangular, and may be, for example, elliptical.

[Third Embodiment]
A third embodiment of the present invention will be described. FIG. 8 is a structural perspective view of the flexible waveguide according to the third embodiment. The flexible waveguide 8 of the third embodiment is a waveguide having a circular cross section, and has a hollow tube wall 80. The pipe wall 80 includes a first coil 81 wound in a direction substantially orthogonal to the pipe axis in the longitudinal direction, and a strip-shaped conductor foil 82 wound outside the first coil 81. Is formed by. The material, cross-sectional shape, and size of the first coil 81 are the same as those of the flexible waveguide 1 of the first embodiment.

The strip-shaped conductor foil 82 is a kind of spiral conductor, and corresponds to the second coil 12 in the flexible waveguide 1 described in the first embodiment. The thickness of the conductor foil 82, the width in the short side direction, and the pitch at the time of winding are not particularly fixed and can be arbitrarily selected. The width may be several times the conductor width (outer diameter) of the first coil 81. A part of the conductor foil 82 may overlap as long as it is wound in close contact with the conductors of the first coil 81.

As the material of the conductor foil 82, for example, copper foil, aluminum foil, metal tape, or the like can be used. From the viewpoint of low loss, a metal material having high conductivity is desirable. A material having a highly conductive metal plating on the surface may also be used. The conductor foil 82 does not necessarily have to be a hard material, and may be a soft metal material. At that time, the outer surface of the soft metal material (conductor foil 82) may be coated with a resin film, a metal film, or the like.

In the flexible waveguide 8 of the third embodiment, the conductor foil 82 prevents the leakage of electromagnetic waves between the conductors of the first coil 81 that occurs when the coil 81 is curved, so that the flexible waveguide 8 of the first embodiment is prevented. Similar to the flexible waveguide 7 of the first and second embodiments, transmission with low loss is possible. When the conductor foil 82 is made of a soft metal material and its outer surface is covered with a resin or the like, the influence of the outside air is maintained while maintaining higher flexibility than in the first embodiment using the hard second coil 12. It is possible to realize a circular waveguide that is less susceptible to damage.
Although the example of the waveguide having a circular cross section has been described in the third embodiment, it may be applied to a waveguide having a rectangular cross section. That is, in the flexible waveguide 7 of the second embodiment, a strip-shaped conductor foil may be used instead of the second coil 72. Further, the outer surface of the conductor foil may be coated with a resin film or a metal film.

In the first to third embodiments, examples of the flexible waveguides 1, 2, 7, and 8 used in the millimeter wave band have been described, but the same applies to the flexible waveguides used in the microwave band. It can be applied to.

1, 2, 7, 8 ... Flexible waveguide, 11, 21, 31, 41, 71, 81 ... 1st coil, 12, 22, 32, 42, 72 ... 2nd coil, 82 ... Conductor foil.

Claims (8)

A first spiral conductor that forms a hollow tube wall by being spirally wound,
A second spiral conductor having the same conductor width as the first spiral conductor, which is wound around the outside of the first spiral conductor along between the conductors of the first spiral conductor, is included.
Flexible waveguide. The first spiral conductor is wound at a pitch of twice or less the width of the conductor.
The second spiral conductor is wound with a deviation of approximately 1/2 pitch between the conductors of the first spiral conductor.
The flexible waveguide according to claim 1. At least one of the first spiral conductor and the second spiral conductor is characterized in that its cross section is circular or rectangular.
The flexible waveguide according to claim 1 or 2. It said second helical conductor is characterized in that in intimate wear between the conductors of the first spiral conductor,
The flexible waveguide according to claim 3. At least one of the first spiral conductor and the second spiral conductor is a linear conductor.
The flexible waveguide according to any one of claims 1 to 4. Said first helical conductor is plating the conductivity of ^{30 × 10 6 [S / m} ] or more metallic materials or conductivity on the surface of ^{30 × 10 6 [S / m} ] or more metallic material has been applied materials It is characterized by being composed of
The flexible waveguide according to any one of claims 1 to 5. The first spiral conductor is made of a metal material having a Young's modulus of 100 [GPa] or more.
The flexible waveguide according to any one of claims 1 to 6. The plane orthogonal to both sides of the pipe wall is circular or rectangular.
The flexible waveguide according to any one of claims 1 to 7.

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