Dielectric Waveguide

Abstract

To provide a dielectric waveguide that can suppress transmission loss when transmitting electromagnetic waves in a quasi-millimeter wave band or millimeter wave band and has excellent flexibility.SOLUTION: A dielectric waveguide 1 that transmits electromagnetic waves with frequencies of 20GHz or more and 200GHz or less includes a core 2 in which a plurality of dielectric waveguides 21 made of a dielectric material made of resin or quartz are bundled together.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a dielectric waveguide for transmitting electromagnetic waves in the quasi-millimeter wave band and millimeter wave band. [Background technology]

[0002] Dielectric waveguides that transmit electromagnetic waves using a core made of a dielectric material have been known. For example, Patent Document 1 discloses a dielectric waveguide that transmits microwave or millimeter wave electrical signals. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6355094 [Non-patent literature]

[0004] [Non-Patent Document 1] Katsunari Okamoto, "Fundamentals of Optical Waveguides," Corona Publishing, October 1, 1992 Summary of the Invention [Problem to be solved by the invention]

[0005] Dielectric waveguides are required to have low bending loss so that transmission loss does not become too large when they are bent and installed. To reduce bending loss, it is necessary to increase the normalized frequency (V) to concentrate the electromagnetic wave distribution inside the core, and accordingly, the diameter of the core of the dielectric waveguide must be increased. However, a dielectric waveguide with a core with a large diameter is difficult to bend, making installation difficult.

[0006] More specifically, to reduce bending loss, it is desirable to set the normalized frequency V to at least 1.0 (more preferably 1.7 or greater). For example, when the normalized frequency V is set to 1.7, if a PTFE (polytetrafluoroethylene) jacket is provided around the core, and the core is covered with the jacket, and the relative refractive index difference between the core and the jacket is set to the same level as that of a standard optical fiber (approximately 0.3%), the core diameter of the dielectric waveguide must be 4.2 cm or greater at a frequency of 20 GHz in the quasi-millimeter wave band. Furthermore, under the same conditions as above, the core diameter of the dielectric waveguide must be 4.2 mm or greater at a frequency of 200 GHz in the millimeter wave band. Dielectric waveguides with such thick cores are difficult to bend.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a dielectric waveguide that can suppress transmission loss when transmitting electromagnetic waves in the quasi-millimeter wave band or millimeter wave band and has excellent flexibility. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention provides a dielectric waveguide that transmits electromagnetic waves with a frequency of 20 GHz or more and 200 GHz or less, the dielectric waveguide having a core in which a plurality of dielectric waveguide lines made of a dielectric material such as resin or quartz are bundled together. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a dielectric waveguide that can suppress transmission loss when transmitting electromagnetic waves in the quasi-millimeter wave band or millimeter wave band and has excellent flexibility. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a graph showing the ratio of the power of an electromagnetic wave propagating inside a core to the total power of the propagating electromagnetic wave in a conventional dielectric waveguide. [Figure 2] 1 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of a dielectric waveguide according to an embodiment of the present invention. [Figure 3] 10(a) and 10(b) are cross-sectional views showing a cross section perpendicular to the longitudinal direction of a dielectric waveguide according to a modified example of the present invention. [Figure 4] FIG. 10 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of a dielectric waveguide according to a modified example of the present invention. [Figure 5] 10(a) and 10(b) are diagrams illustrating an evaluation test of transmission loss. [Figure 6] FIG. 10 is a graph showing measurement results of transmission loss. [Figure 7] FIG. 10 is a graph showing a simulation result of insertion loss. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Embodiment Mode] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0012] (Problems with using a single core) Before describing the embodiments of the present invention, we will first explain the problems associated with conventional dielectric waveguides using a single cylindrical core (hereinafter referred to as conventional dielectric waveguides). In conventional dielectric waveguides, the power (so-called electric power) of electromagnetic waves propagating through the dielectric waveguide must be concentrated inside the core to reduce bending loss. As shown in the aforementioned Non-Patent Document 1 and FIG. 1, the ratio (so-called power ratio) of the power of electromagnetic waves propagating inside the core to the total power (so-called total power) of electromagnetic waves propagating through the dielectric waveguide increases as the normalized frequency V (so-called V value) increases. The graph shown in FIG. 1 indicates that the power of electromagnetic waves propagating inside the core increases as the power ratio increases; for example, when the power ratio is 1.0, all electromagnetic waves propagate inside the core.

[0013] Here, the normalized frequency V is defined by the following equation (1), where f is the frequency of the transmitted electromagnetic wave, b is the radius of the core, ε1 is the relative dielectric constant of the core, ε2 is the relative dielectric constant of the cladding (outer covering) made of a dielectric material surrounding the core, and c is the speed of light in a vacuum. V = 2π × b × f × (ε1 - ε2) 1 / 2 / c···(1) As shown in Figure 1, in the HE11 mode, which is the fundamental mode of a cylindrical dielectric waveguide, the normalized frequency V must be 1.7 or higher in order for the power of the electromagnetic wave propagating inside the core to be more than half of the total power.

[0014] Furthermore, the magnitude of bending loss also varies depending on the bending radius, but in a practical dielectric waveguide, it is desirable to set the normalized frequency V to at least 1.0 or more to sufficiently reduce bending loss during installation. Therefore, from the perspective of reducing bending loss, it is desirable for the V value of the dielectric waveguide to be at least 1.0 or more (more preferably 1.7 or more). Note that, if the frequency of the electromagnetic wave propagating inside the core and the relative dielectric constant of the dielectric waveguide are constant, in order to satisfy this condition, the diameter of the core of the dielectric waveguide (diameter = 2 × core radius b) must be larger than the value determined by the following formula (2): b=V×c / (2π×f×(ε1-ε2) 1 / 2 )···(2) However, V>1.0

[0015] On the other hand, it is desirable to set the normalized frequency V of the dielectric waveguide to a suitable condition depending on the application of the signal transmission.

[0016] (Single-mode transmission and its optimal conditions) In signal transmission applications, dielectric waveguides are sometimes used under single-mode transmission conditions, i.e., conditions under which the eigenmode of the electromagnetic wave is single (excluding the degree of freedom of polarization), in order to suppress degradation of the signal waveform. To satisfy the single-mode transmission conditions, it is desirable to set the normalized frequency V to 2.4 or less. Therefore, in order to achieve transmission with low bending loss under single-mode transmission conditions in a dielectric waveguide, it is desirable to set the normalized frequency V to 1.0 or more and 2.4 or less (more preferably 1.7 or more and 2.4 or less).

[0017] In single-mode transmission, the higher the normalized frequency V, the smaller the bending loss. Therefore, a suitable condition for single-mode transmission is to set the normalized frequency V to approximately 2.3 to 2.4. Furthermore, higher-order modes of a dielectric waveguide experience greater bending loss than the fundamental mode, which satisfies the conditions for single-mode transmission. Therefore, taking into account the attenuation of higher-order modes due to bending loss, it is preferable to set the normalized frequency V to approximately 2.4 to 2.5, so as to virtually satisfy the conditions for single-mode transmission.

[0018] (Multimode transmission and its favorable conditions) Furthermore, in applications where some degradation of the signal waveform can be tolerated or in applications where power is to be transmitted, dielectric waveguides are sometimes used under multimode transmission conditions to facilitate coupling of external electromagnetic waves. In multimode transmission, any number of eigenmodes can exist, so there is no upper limit to the normalized frequency V. In other words, in multimode transmission, there is no upper limit to the diameter of the dielectric waveguide.

[0019] For these reasons, in order to reduce bending loss in a conventional dielectric waveguide using a single cylindrical core, the diameter of the dielectric waveguide must be set to a size that satisfies the normalized frequency V≧1.0 (preferably the normalized frequency V≧1.7). In particular, for single-mode transmission, it is preferable to set the diameter of the dielectric waveguide to a size that satisfies the normalized frequency V=2.3 to 2.4.

[0020] As an example, consider the case where the normalized frequency V is 2.4 and the frequency f of the electromagnetic wave to be transmitted is 28 GHz, which is in the quasi-millimeter wave band. For example, if the core of a dielectric waveguide is made of PTFE (polytetrafluoroethylene) with a dielectric constant of 2.1 and no outer sheath is provided (the core is surrounded by air), the diameter of the single core is 7.8 mm, as calculated by equation (2), which is a large core diameter. Also, if the core of a dielectric waveguide is made of PTFE (polytetrafluoroethylene) with a dielectric constant of 2.2 and the outer sheath is also made of PTFE (polytetrafluoroethylene) with a dielectric constant of 2.1, which protects the core, the diameter of the single core is 26 mm, as calculated by equation (2), which is a very large core diameter. Furthermore, if the normalized frequency V is set to a value that satisfies the conditions for multimode transmission in order to reduce the bending loss of the dielectric waveguide, the diameter of the single core will be even larger.

[0021] Furthermore, for example, in a dielectric waveguide, if the core is made of quartz with a relative dielectric constant of 3.8 and no jacket is provided (the core is surrounded by air), the diameter of the single core is 4.9 mm, according to the above formula (2), which is a large core diameter. Also, if the core and jacket are both made of quartz and the core is protected by the jacket, and the relative refractive index difference between the core and jacket is 0.3%, the same as that of a standard single-mode optical fiber, then the diameter of the single core is 54 mm, according to the above formula (2), which is an extremely large core diameter.

[0022] The above-described dielectric waveguides having a core made of a thick, single cylindrical dielectric material such as PTFE or quartz are difficult to bend, and may break if forcibly bent at room temperature. Therefore, when bending and laying the waveguide, the dielectric waveguide must be heated at a high temperature to soften it before bending, which makes the laying work difficult. In consideration of these circumstances, the present inventors conducted extensive research into a dielectric waveguide that is easy to bend and lay while suppressing transmission loss, and as a result, they arrived at the present invention.

[0023] (Dielectric Waveguide 1) Fig. 2 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of a dielectric waveguide 1 according to this embodiment. As shown in Fig. 2, the dielectric waveguide 1 has a core 2 in which a plurality of dielectric waveguide lines 21 made of a dielectric material such as resin or quartz are bundled together, and an outer jacket 3 that covers the periphery of the core 2. The dielectric waveguide 1 is used to transmit electromagnetic waves with frequencies of 20 GHz or more and 200 GHz or less (electromagnetic waves in the quasi-millimeter wave band and millimeter wave band).

[0024] In the dielectric waveguide 1, the core 2 is made up of a plurality of thin dielectric waveguides 21 (for example, having a diameter of 3.5 mm or less), which allows the core 2 to have a large diameter while still making the dielectric waveguide 1 easy to bend. As a result, it is possible to realize a dielectric waveguide 1 that is easy to bend and install while reducing transmission loss. Furthermore, manufacturing a thick dielectric waveguide 21 is technically difficult and requires dedicated equipment. In contrast, a thin dielectric waveguide 21 can be manufactured relatively easily, and can even be manufactured using existing optical fiber or electric wire manufacturing equipment. This reduces equipment costs and manufacturing costs, contributing to lower costs for the dielectric waveguide 1.

[0025] The core 2 is preferably formed of a concentric twisted wire in which a plurality of dielectric waveguides 21 are twisted concentrically, a bunched twisted wire in which a plurality of dielectric waveguides 21 are bunched twisted, or a concentric twisted wire in which a plurality of child twisted wires, such as a twisted pair wire, a concentric twisted wire, or a bunched twisted wire, are twisted together, each of which is made up of a plurality of dielectric waveguides 21. This prevents the core 2 from being deformed by an external force or the like, maintains the overall cross-sectional shape of the core 2 in a circular shape, and suppresses a decrease in transmission loss due to deformation of the cross-sectional shape. Note that, in order to easily maintain the circular cross-sectional shape of the core 2, the core 2 is more preferably formed by concentrically twisting a plurality of dielectric waveguides 21. Furthermore, by forming the core 2 from a bunched twisted wire in which a plurality of dielectric waveguides 21 are bunched twisted or a concentric twisted wire using a plurality of such bunched twisted wires, the diameter of the core 2 can be increased while further improving the flexibility of the dielectric waveguide 1.

[0026] The diameter a of the core 2 may be determined so that the bending loss is small at the frequency of the electromagnetic wave to be transmitted. More specifically, it is desirable that the diameter a of the core 2 be in a range where the normalized frequency V is 1.0 or more (preferably 1.7 or more). For example, the diameter a of the core 2 is 23 mm or less. The normalized frequency V of the dielectric waveguide 1 is such that the frequency of the electromagnetic wave is f, the radius of the core 2 is b eq , and the spatial average value of the relative permittivity inside the entire core 2 is ε eq , and it can be calculated by the following formula (3). V = 2π × b eq × f × (ε eq − ε2) 1 / 2 / c ··· (3) Therefore, the diameter a of the core 2 (diameter a = 2 × radius b of the core eq ) is determined by the following formula (4) according to the required normalized frequency V. b eq = V × c / (2π × f × (ε eq − ε2) 1 / 2 ) ··· (4) V > 1

[0027] In particular, for single - mode transmission applications, at the frequency of the electromagnetic wave to be transmitted, the core 2 may satisfy the conditions for single - mode transmission. More specifically, it is preferable that the normalized frequency V is 2.5 or less. Therefore, for single - mode transmission applications, in the above formula (4), the normalized frequency V may be set in the range of 1 < V < 2.5.

[0028] In addition, in single - mode transmission applications, in order to minimize the bending loss as much as possible, within the range where the core 2 satisfies the conditions for single - mode transmission and the normalized frequency V is made as large as possible. Therefore, in single - mode transmission applications, in order to minimize the bending loss as much as possible, in the above formula (4), the normalized frequency V may be set in the range of 2.3 < V < 2.5.

[0029] Furthermore, in applications for multimode transmission, there is no upper limit to the normalized frequency V. Therefore, in applications for multimode transmission, the normalized frequency V needs to be at least 1.0 or more, preferably 1.7 or more, and the diameter a of the core 2 can be arbitrarily large.

[0030] If the diameter d of the dielectric waveguide 21 used in the core 2 is too thick, it will be difficult to bend and will also be difficult to manufacture, so it is desirable to make it thin enough to bend and to be easy to manufacture (for example, a diameter of 3.5 mm or less, more preferably a diameter of 2.0 mm or less, and even more preferably a diameter of 1.5 mm or less). In this embodiment, the cross-sectional shape of the dielectric waveguide 21 is circular, but the cross-sectional shape of the dielectric waveguide 21 is not limited to this and may be other shapes, such as an ellipse.

[0031] The number of dielectric waveguides 21 used in the core 2 is determined according to the diameter d of the dielectric waveguide 21 and the required normalized frequency V (required diameter a of the core 2). In this embodiment, 37 dielectric waveguides 21 each having a diameter d of 1.4 mm are concentrically twisted to form the core 2 having a diameter a of 9.8 mm. The number of dielectric waveguides 21 used in the core 2 is not particularly limited. However, as described above, it is preferable that the core 2 be configured with concentric twisting. For example, the number of dielectric waveguides 21 used in the core 2 may be 19 as shown in FIG. 3(a), or the number of dielectric waveguides 21 used in the core 2 may be 7 as shown in FIG. 3(b).

[0032] The dielectric waveguide 21 is made of a dielectric material made of resin or quartz. The resin used for the dielectric waveguide 21 can be any of fluororesin, foamed fluororesin, polyethylene, foamed polyethylene, polypropylene, and foamed polypropylene. In this embodiment, the dielectric waveguide 21 is made of FEP (tetrafluoroethylene-hexafluoropropylene copolymer), a fluororesin. In order to make the diameter of the dielectric waveguide 21 uniform, as shown in FIG. 4, the dielectric waveguide 21 may have a tensile strength fiber 22 such as aramid fiber in its center, and a dielectric material made of resin or quartz around the tensile strength fiber 22.

[0033] When manufacturing the dielectric waveguide 21, a manufacturing method can be used in which a large-diameter base material is heated and melted to draw out the small-diameter dielectric waveguide 21. Alternatively, the small-diameter dielectric waveguide 21 can be manufactured by feeding the above-mentioned resin into an extruder, and extruding the heated and melted resin inside the extruder to form a small diameter.

[0034] The jacket 3 protects the core 2 and serves to hold the dielectric waveguide 21 that constitutes the core 2 so that it does not come apart (so that its cross-sectional shape does not collapse). In this embodiment, the jacket 3 is formed by winding a tape member made of fluororesin (PTFE) spirally around the core 2. However, this is not limiting, and the jacket 3 may be formed by extruding a resin made of fluororesin by extrusion molding such as tube extrusion. Note that the jacket 3 may not be provided depending on the application of signal transmission.

[0035] (Transmission loss evaluation) As shown in Figure 5(a), the transmission loss of the dielectric waveguide 1 shown in Figure 2 was evaluated using a network analyzer 11. The dielectric waveguide 1 had a core 2 formed by concentrically twisting 37 dielectric waveguides 21 made of FEP with a diameter of 1.4 mm, and a sheath 3 formed by spirally wrapping a PTFE tape around the core 2. Coaxial lines 12 extended from two ports 11a (PORT1, PORT2) of the network analyzer 11, and the ends of these coaxial lines 12 were connected to both ends of the dielectric waveguide 1 via conversion jigs 13 that convert between electrical signals and electromagnetic waves. The length of the dielectric waveguide 1 was 10.8 m, and the signal frequency was 20 to 40 GHz. The normalized frequency V of the core 2 was 1.7 at 22 GHz, 2.2 at 28 GHz, and 3.1 at 40 GHz. The S21 measurement results obtained using the network analyzer 11 are shown in Figure 6. Furthermore, in order to investigate the influence of the coaxial cable 12 and the converter 13, similar measurements were carried out by directly connecting the converter jigs 13 to each other as shown in Fig. 5(b). The results are also shown in Fig. 6.

[0036] 6, for example, at a frequency of 28 GHz (= when the frequency of the transmitted electromagnetic wave is 28 GHz), the loss due to the dielectric waveguide 1 is 23.1-11.3=11.8 dB, and the loss per unit length in the dielectric waveguide 1 is 11.8 / 10.8=1.1 dB / m. From this result, it can be considered that the transmission loss in the dielectric waveguide 1 is sufficiently suppressed.

[0037] Next, we performed simulations to determine the insertion loss for Example 1 (see FIG. 3(a)), in which the core 2 was formed by concentrically twisting 19 dielectric waveguides 21 with a diameter of 2.0 mm; Example 2 (see FIG. 3(b)), in which the core 2 was formed by concentrically twisting 7 dielectric waveguides 21 with a diameter of 3.3 mm; and a conventional example having a single cylindrical core with a diameter of 10 mm. In all cases, the core 2 was not surrounded by a jacket 3 (the core 2 was surrounded by air), the dielectric constant of the dielectric constituting the core 2 was 2.1, the dielectric loss tangent was 0.0003, and the core diameter was approximately 10 mm. The twist pitch in Examples 1 and 2 was 150 mm, and the frequency of the transmitted electromagnetic waves was 28 GHz. The simulation results are summarized in FIG. 7.

[0038] As shown in FIG. 7, the insertion loss of Examples 1 and 2 is almost the same as that of the conventional example, and it was confirmed that Examples 1 and 2 of the present invention result in almost the same transmission loss as that of the conventional example.

[0039] (Actions and Effects of the Embodiments) As described above, the dielectric waveguide 1 according to this embodiment includes the core 2 formed by bundling together a plurality of dielectric waveguides 21 made of a dielectric material such as resin or quartz. By configuring the core 2 from a plurality of thin dielectric waveguides 21, it is possible to suppress transmission loss when transmitting electromagnetic waves in the quasi-millimeter wave band or millimeter wave band in the same manner as in the past, and the dielectric waveguide 1 becomes easier to bend. As a result, it is possible to significantly improve the workability of installation work, and a dielectric waveguide 1 with improved handleability can be realized. Furthermore, by configuring the core 2 from a plurality of thin dielectric waveguides 21, it becomes possible to manufacture the core 2 using existing optical fiber or electric wire manufacturing equipment, and a dielectric waveguide 1 can be manufactured easily and at low cost.

[0040] (Summary of the embodiment) Next, the technical ideas grasped from the above-described embodiments will be described by using the reference numerals and the like in the embodiments. However, the reference numerals and the like in the following description do not limit the components in the claims to the members and the like specifically shown in the embodiments.

[0041] [1] A dielectric waveguide (1) that transmits electromagnetic waves with a frequency of 20 GHz or more and 200 GHz or less, comprising a core (2) that bundles together a plurality of dielectric waveguide lines (21) made of a dielectric material such as resin or quartz.

[0042] [2] The dielectric waveguide (1) according to [1], wherein the core (2) is formed by twisting together a plurality of the dielectric waveguides (21).

[0043] [3] The dielectric waveguide (1) according to [1] or [2], wherein the core (2) has a normalized frequency V of 1.0 or more at the frequency of the electromagnetic wave to be transmitted.

[0044] [4] The dielectric waveguide (1) according to any one of [1] to [3], wherein the core (2) has a normalized frequency V of 2.5 or less at the frequency of the electromagnetic wave to be transmitted.

[0045] [5] The dielectric waveguide (1) according to any one of [1] to [4], wherein the resin is made of any one of fluororesin, foamed fluororesin, polyethylene, foamed polyethylene, polypropylene, and foamed polypropylene.

[0046] [6] A dielectric waveguide (1) according to any one of [1] to [5], wherein the plurality of dielectric waveguides (21) have a tensile strength fiber (22) at their center and the dielectric is disposed around the tensile strength fiber (22).

[0047] Although the embodiments of the present invention have been described above, the invention according to the claims is not limited to the above-described embodiments. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention. Furthermore, the present invention can be appropriately modified and implemented within the scope of its spirit. [Explanation of symbols]

[0048] 1...Dielectric waveguide 2...Core 3...Outer cover 21...Dielectric waveguide 22...Tensile strength fiber

Claims

1. A dielectric waveguide that transmits electromagnetic waves having a frequency of 20 GHz or more and 200 GHz or less, The core is made up of a bundle of multiple dielectric waveguides made of a dielectric material made of fluororesin, The core is formed by concentrically twisting a plurality of the dielectric waveguides. Dielectric waveguide.

2. The core has a normalized frequency V of 1.0 or more and 2.5 or less at the frequency of the transmitted electromagnetic wave.

2. The dielectric waveguide according to claim 1.

3. The core is provided with an outer jacket formed by wrapping a tape member made of fluororesin around the core.

2. The dielectric waveguide according to claim 1.

4. The diameter of the dielectric waveguide is 3.5 mm or less.

2. The dielectric waveguide according to claim 1.

5. The plurality of dielectric waveguides have a tensile strength fiber at the center thereof, and the dielectric is disposed around the tensile strength fiber.

2. The dielectric waveguide according to claim 1.

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