Patent Description:
Dielectric waveguides, waveguides, coaxial cables, and similar devices are used to transmit high frequency signals such as microwaves and millimeter waves. In particular, dielectric waveguides and waveguides are used as transmission lines for high frequency band electromagnetic waves such as millimeter waves. A common dielectric waveguide is composed of an inner layer and an outer layer and it utilizes the difference in permittivity between the layers to transmit electromagnetic waves by side reflection. The outer layer may be the air. Still, in order to stabilize the permittivity and to achieve easy handling, the outer layer is usually a soft structure made of, for example, resin foam having low tanδ and low permittivity. In practical implementation, transmission lines of different kinds are often coupled with each other. A dielectric waveguide may be coupled with a waveguide or a coaxial cable, or coaxial cables of different shapes may be coupled with each other. In order to reduce the return loss at a connection point of these different transmission lines, the impedances or modes of the transmission lines are to be matched to each other. Such matching of impedances or modes and conversion thereof for the matching are achieved using a special transformer or using a special structure. A rapid change in impedance may cause reflection of high frequency signals, resulting in loss of transmission efficiency.

Patent Literature <NUM> discloses a resonator with a dielectric waveguide. This resonator has a structure in which one or two dielectric waveguides are inserted in one or two holes made in a reflector of a Fabry-Perot resonator, wherein a tip of the dielectric waveguide inserted to stick to the resonator through the hole of the reflector is tapered with a conical shape, for example.

Patent Literature <NUM> discloses a coaxial waveguide transformer for connecting a circular coaxial line and a rectangular coaxial line. The coaxial waveguide transformer includes a ridge waveguide whose inner and outer conductors are monolithic, and the inner conductor is changed in a stepwise or tapering manner in the longitudinal direction.

Patent Literature <NUM> discloses a nonradiative dielectric line including dielectric lines between conductor plates. The dielectric lines include at least a dielectric line (line <NUM>) made of a material of a prescribed dielectric constant and a dielectric line (line <NUM>) made of a material of a dielectric constant lower than the material of the line <NUM>.

Patent Literature <NUM> describes a dielectric waveguide in cable form fabricated from polytetrafluoroethylene. An embodiment of cable is a composite of partially sintered PTFE and sintered and unsintered expanded PTFE arranged in such a fashion that the specific gravity of cable decreases from the core to the outer surface.

Patent Literature <NUM> describes a dielectric line to be used for transmitting energy of electromagnetic waves such as millimetric or submillimetric waves and, more particularly, to a dielectric line equipped with means for emitting electromagnetic waves directly from one end portion thereof into space without the use of a metallic waveguide.

Patent Literature <NUM> relates to a measuring jig which is used to measure characteristics of a device with a nonradiative dielectric waveguide which operates in a microwave band or in a millimeter wave band.

Patent Literature <NUM> describes a probe antenna for terahertz waveband near-field imaging and specifically relates to surface metallized coating on a narrow edge of an antenna on the basis of polymethyl methacrylate (PMMA) material manufacture. The antenna comprises a terahertz signal couple input part, a terahertz resonant cavity and a PMMA surface metallized thin film coating layer.

Non-Patent Literature <NUM> discloses preparation of a polyethylene waveguide that has a circular cross section and is provided with a conical horn at each end, and measurement of the HE<NUM> transmission loss thereof.

The methods of using a special shape as disclosed in Patent Literature documents <NUM> and <NUM> have difficulty in processing a narrow dielectric waveguide into such a special shape, and thus cannot be used as methods for transmitting millimeter waves or sub-millimeter waves. Further, improved transmission efficiency is awaited. In the method of inserting a tapered dielectric waveguide and fixing it to a converting portion as disclosed in Patent Literature <NUM>, the dielectric waveguide portion is bent and a stress is applied, so that the tip of the tapered structure is displaced. This causes a change in properties of reflecting high frequency signals at the converting portion, resulting in unstable performance.

Patent Literature <NUM> also discloses the following. In the method disclosed therein with the use of the dielectric line (line <NUM>) made of a material of a high dielectric constant, electromagnetic waves are not directly input to/output from the dielectric line (line <NUM>) made of a material of a high dielectric constant but are input/output via the dielectric line (line <NUM>) made of a material of a low dielectric constant. This can reduce reflection of electromagnetic waves toward the line <NUM> and enables easy input/output of electromagnetic waves. This method involves bonding of two dielectric lines of different materials, and forming an interface having low reflection is difficult unfortunately.

In the method disclosed in Non-Patent Literature <NUM>, horn-shaped jigs are attached to a dielectric waveguide.

The invention therefore aims to provide a dielectric waveguide which is easily processed and connected even when having a small diameter and can provide a connection structure exhibiting low transmission and return losses of high frequency signals.

The invention also aims to provide a connection structure for connecting a dielectric waveguide and a waveguide which enables easy processing and connection even when having small diameters and shows low transmission and return losses of high frequency signals.

The invention also aims to provide a method for producing a dielectric waveguide enabling easy production of a dielectric waveguide that includes a dielectric waveguide end having a lower permittivity or density than a dielectric waveguide body, that is easily processed and connected even when having a small diameter, and that can provide a connection structure exhibiting low transmission and return losses of high frequency signals.

A dielectric waveguide provided in the invention includes a dielectric waveguide as it is disclosed in the present claims.

In one embodiment, the dielectric waveguide end has a lower permittivity than the dielectric waveguide body.

The dielectric waveguide is preferably obtainable by stretching an end of a resin line in a longitudinal direction.

Preferably, the dielectric waveguide body has a permittivity of <NUM> or higher and <NUM> or lower and the dielectric waveguide end has a permittivity of <NUM> or lower.

The dielectric waveguide body has a hardness of <NUM> or higher.

The dielectric waveguide body preferably has a loss tangent at <NUM> of <NUM> × <NUM>-<NUM> or lower.

The dielectric waveguide of the invention is preferably formed from polytetrafluoroethylene.

The invention also relates to a connection structure including a hollow metallic tube and the aforementioned dielectric waveguide, the dielectric waveguide end being inserted in the hollow metallic tube and thereby the hollow metallic tube and the dielectric waveguide being connected to each other.

Preferably, the hollow metallic tube of the connection structure of the invention has a cavity filled with gas and the gas has a lower permittivity than the dielectric waveguide end.

The invention also relates to a method for producing a dielectric waveguide as defined above, including a step (<NUM>) of providing a resin line formed from polytetrafluoroethylene; a step (<NUM>) of heating an end of the resin line; and a step (<NUM>) of stretching the heated end in a longitudinal direction to provide a dielectric waveguide.

The heating in the step (<NUM>) is preferably performed at a temperature of <NUM> or higher and <NUM> or lower.

The dielectric waveguide of the invention may be connected to a hollow metallic tube for use. The connection of the dielectric waveguide to the hollow metallic tube can be achieved by inserting the dielectric waveguide into the hollow metallic tube. Thus, the hollow metallic tube and the dielectric waveguide can be easily connected to each other. The dielectric waveguide includes a dielectric waveguide body and a dielectric waveguide end having a lower density than the dielectric waveguide body. This can reduce a rapid change in impedance between the dielectric waveguide and the hollow metallic tube and enables a connection structure exhibiting low transmission and return losses. The dielectric waveguide body and the dielectric waveguide end are seamlessly and monolithically formed from the same material. This can eliminate the need for processing to form an interface and lead to excellent transmission efficiency. Accordingly, a change in impedance at an interface does not occur even when the dielectric waveguide is bent and a stress is applied. Thus, the dielectric waveguide can exhibit stable properties even when bent.

The connection structure of the invention can provide a connection between a hollow metallic tube and a dielectric waveguide by insertion of the dielectric waveguide into the hollow metallic tube. Thus, the hollow metallic tube and the dielectric waveguide can be easily connected to each other. The dielectric waveguide includes a dielectric waveguide body and a dielectric waveguide end having a lower density than the dielectric waveguide body. This can reduce a rapid change in impedance between the dielectric waveguide and the hollow metallic tube and enables low transmission and return losses. The dielectric waveguide body and the dielectric waveguide end are seamlessly and monolithically formed from the same material. This can eliminate the need for processing to form an interface and lead to excellent transmission efficiency.

The production method of the invention having the above features enable easy production of a dielectric waveguide that includes a dielectric waveguide end having a lower permittivity or density than a dielectric waveguide body, that is easily processed and connected even when having a small diameter, and that can provide a connection structure exhibiting low transmission and return losses of high frequency signals.

<FIG> is a cross-sectional view of an example of the dielectric waveguide of the invention. A dielectric waveguide <NUM> of <FIG> includes a dielectric waveguide body <NUM> and a dielectric waveguide end <NUM>, and the dielectric waveguide end <NUM> has a density than the dielectric waveguide body <NUM>. The dielectric waveguide body <NUM> and the dielectric waveguide end <NUM> have different densities, but they are not formed by bonding different materials. Thus, the dielectric waveguide <NUM> has no interface.

The dielectric waveguide body <NUM> is preferably a portion having the maximum density among the fragments obtained by cutting the dielectric waveguide at <NUM>-mm intervals, for example, or a portion where the percent change in density from the maximum density is within <NUM>%.

Letting the length of the dielectric waveguide end <NUM> be L (mm) and the diameter of the dielectric waveguide body <NUM> be D (mm), L and D preferably satisfy the following conditions:.

In the dielectric waveguide of the invention, preferably, the dielectric waveguide body <NUM> has a permittivity of <NUM> or higher and <NUM> or lower and the dielectric waveguide end <NUM> has a permittivity of <NUM> or lower. In the dielectric waveguide of the invention, more preferably, the permittivity of the dielectric waveguide body <NUM> is <NUM> or higher and <NUM> or lower and the permittivity of the dielectric waveguide end <NUM> is <NUM> or lower.

The permittivity of the dielectric waveguide body <NUM> is preferably <NUM> or higher and <NUM> or lower. The permittivity is more preferably <NUM> or higher, still more preferably <NUM> or higher.

In order to achieve high transmission efficiency, the permittivity of the dielectric waveguide end <NUM> is preferably <NUM> or lower, more preferably <NUM> or lower, still more preferably <NUM> or lower.

In order to reduce a rapid change in permittivity, the permittivity of the dielectric waveguide end <NUM> may also preferably decrease gradually or stepwise toward the tip. For the dielectric waveguide end <NUM> having a permittivity that decreases toward the tip, the permittivity of the tip of the dielectric waveguide end <NUM> preferably falls within the above range. The reduction rate in permittivity of the dielectric waveguide end <NUM> toward the tip per <NUM> is preferably <NUM>% or higher, more preferably <NUM>% or higher, while preferably <NUM>% or lower, more preferably <NUM>% or lower.

The dielectric waveguide end <NUM> has a lower density than the dielectric waveguide body <NUM>. Such a difference in density can easily reduce a rapid change in permittivity, can reduce the return loss, and can lead to high transmission efficiency.

The density of the dielectric waveguide body <NUM> is <NUM>/cm<NUM> or higher and <NUM>/cm<NUM> or lower. The density is preferably <NUM>/cm<NUM> or higher. The density of the dielectric waveguide body <NUM> is preferably <NUM>/cm<NUM> or lower.

Common resin lines are known to have a lower permittivity as the density becomes lower. The density is a value determined by hydrostatic weighing in accordance with JIS Z8807.

In order to achieve high transmission efficiency, the density of the dielectric waveguide end <NUM> is preferably as low as possible, and is <NUM>% or less, preferably <NUM>% or less, more preferably <NUM>% or less of the density of the dielectric waveguide body <NUM>. In order to achieve good strength of the dielectric waveguide end <NUM>, the density thereof is preferably <NUM>% or more, more preferably <NUM>% or more of the density of the dielectric waveguide body <NUM>.

In order to reduce a rapid change in permittivity, the density of the dielectric waveguide end <NUM> preferably decreases gradually or stepwise toward the tip. For the dielectric waveguide end <NUM> having a density that decreases toward the tip, the density of the tip of the dielectric waveguide end <NUM> preferably falls within the above range. The reduction rate in density of the dielectric waveguide end <NUM> toward the tip per <NUM> is preferably <NUM>% or higher, more preferably <NUM>% or higher, still more preferably <NUM>% or higher. In order to achieve good strength of the dielectric waveguide end <NUM>, the reduction rate in density of the dielectric waveguide end <NUM> toward the tip per <NUM> is preferably <NUM>% or lower, more preferably <NUM>% or lower, still more preferably <NUM>% or lower.

The dielectric waveguide body <NUM> has a hardness of <NUM> or higher. The hardness is more preferably <NUM> or higher, particularly preferably <NUM> or higher. The upper limit thereof may be, but is not limited to, <NUM>. The dielectric waveguide body <NUM> having a hardness falling within the above range can have a high permittivity and can easily provide a dielectric waveguide having a low loss tangent. This dielectric waveguide is less likely to be damaged and is less likely to suffer blockage or breakage.

The hardness is determined by the spring hardness standardized in JIS K6253-<NUM>.

The hardness greatly contributes to the strength and bending stability of the dielectric waveguide. A higher hardness can lead to a higher strength and can further reduce a change in permittivity in bending and an increase in loss tangent.

The dielectric waveguide body <NUM> preferably has a loss tangent (tanδ) at <NUM> of <NUM> × <NUM>-<NUM> or lower. The loss tangent (tanδ) is more preferably <NUM> × <NUM>-<NUM> or lower, still more preferably <NUM> × <NUM>-<NUM> or lower. The lower limit of the loss tangent (tanδ) may be, but is not limited to, <NUM> × <NUM>-<NUM> or <NUM> × <NUM>-<NUM>.

The loss tangent is determined at <NUM> using a cavity resonator available from Kanto Electronic Application and Development Inc. The lower the loss tangent is, the better the transmission efficiency of the dielectric waveguide is.

The dielectric waveguide may have either a rectangular shape or a circular shape. Still, it more preferably has a circular shape because a circular dielectric waveguide can more easily be produced than rectangular one.

<FIG> is also a cross-sectional view of an example of the dielectric waveguide of the invention. The dielectric waveguide <NUM> of <FIG> includes the dielectric waveguide body <NUM> and the dielectric waveguide end <NUM>. In this embodiment, the dielectric waveguide end <NUM> has a smaller cross-sectional area than the dielectric waveguide body <NUM>. The dielectric waveguide end <NUM> having a smaller cross-sectional area than the dielectric waveguide body <NUM> can further reduce a rapid change in permittivity. The dielectric waveguide end <NUM> may have a shape of cone, truncated cone, pyramid, or truncated pyramid. A conical shape is easy to produce.

The cross-sectional area of the dielectric waveguide body <NUM> is preferably <NUM><NUM> (φ0. <NUM>: <NUM> THz) or larger and <NUM><NUM> (φ150 mm: <NUM>) or smaller, more preferably <NUM><NUM> (φ0. <NUM>: <NUM>) or larger and <NUM><NUM> (φ9 mm: <NUM>) or smaller.

In order to achieve high transmission efficiency, the cross-sectional area of the dielectric waveguide end <NUM> is preferably <NUM>% or more, more preferably <NUM>% or more, still more preferably <NUM>% or more of the cross-sectional area of the dielectric waveguide body <NUM>. The cross-sectional area of the dielectric waveguide end <NUM> is also preferably <NUM>% or less, more preferably <NUM>% or less, still more preferably <NUM>% or less of the cross-sectional area of the dielectric waveguide body <NUM>.

In order to reduce a rapid change in permittivity, the cross-sectional area of the dielectric waveguide end <NUM> may also preferably decrease gradually or stepwise toward the tip. The reduction rate in cross-sectional area of the dielectric waveguide end <NUM> toward the tip per <NUM> is preferably <NUM>% or higher, more preferably <NUM>% or higher, still more preferably <NUM>% or higher. The reduction rate in cross-sectional area of the dielectric waveguide end <NUM> toward the tip per <NUM> is also preferably <NUM>% or lower, more preferably <NUM>% or lower, still more preferably <NUM>% or lower.

The dielectric waveguide <NUM> is preferably formed from polytetrafluoroethylene (PTFE). PTFE may be a homo PTFE consisting only of tetrafluoroethylene (TFE), or may be a modified PTFE consisting of TFE and a modifying monomer. The modifying monomer may be any monomer copolymerizable with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene (HFP); chlorofluoroolefins such as chlorotrifluoroethylene (CTFE); hydrogen-containing olefins such as trifluoroethylene and vinylidene fluoride (VDF); perfluoroalkyl ethylene; and ethylene. One modifying monomer may be used, or a plurality of modifying monomers may be used.

The modified PTFE preferably contains a unit of the modifying monomer in an amount of <NUM>% by mass or less, more preferably <NUM>% by mass or less, still more preferably <NUM>% by mass or less of all monomer units. In order to improve the moldability and the transparency, this amount is preferably <NUM>% by mass or more. The term "unit of the modifying monomer" herein means a moiety that is part of a molecular structure of the modified PTFE and is derived from the modifying monomer. The term "all monomer units" herein means the moieties derived from any of all monomers in the molecular structure of the modified PTFE.

The polytetrafluoroethylene may have a standard specific gravity (SSG) of <NUM> or higher and <NUM> or lower, preferably <NUM> or higher and <NUM> or lower. It may have non melt-processibility, and may have fibrillatability. The standard specific gravity is a value determined by the water replacement method in conformity with ASTM D-<NUM> using a sample prepared in conformity with ASTM D-<NUM><NUM>.

In an aspect of the invention, a connection structure is provided. The connection structure includes a hollow metallic tube and the dielectric waveguide of the invention, and the dielectric waveguide end is inserted in the hollow metallic tube and thereby the hollow metallic tube and the dielectric waveguide are connected to each other. <FIG> is a cross-sectional view of an example of the connection structure of the invention. The connection structure of <FIG> includes a hollow metallic tube <NUM> and a dielectric waveguide <NUM>. The dielectric waveguide end 12c is inserted in the hollow metallic tube <NUM> and thus the dielectric waveguide end 12c is placed in the hollow metallic tube, whereby the hollow metallic tube <NUM> and the dielectric waveguide <NUM> are connected to each other. The dielectric waveguide <NUM> includes the dielectric waveguide body 12b and the dielectric waveguide end 12c, and the dielectric waveguide end 12c has a lower permittivity or density than the dielectric waveguide body 12b. The dielectric waveguide body 12b and the dielectric waveguide end 12c have different densities, but they are not formed by bonding different materials. Thus, the dielectric waveguide <NUM> has no interface. The dielectric waveguide <NUM> is the same as the aforementioned dielectric waveguide <NUM>.

Further, in <FIG>, the cross section in the circumferential direction of the cavity of the hollow metallic tube <NUM> and the cross section in the circumferential direction of the dielectric waveguide <NUM> have the same shape and substantially the same size. Thus, the dielectric waveguide <NUM> is in close contact with the inner wall of the hollow metallic tube <NUM> and the dielectric waveguide <NUM> is fixed to the hollow metallic tube <NUM>. Accordingly, the cavity of the hollow metallic tube <NUM> and the dielectric waveguide <NUM> having the same cross-sectional shape in the circumferential direction enable easy alignment of the center of the hollow metallic tube and the center of the dielectric waveguide. They also can prevent misalignment of the centers during use, and thus can much further reduce the return loss.

The dielectric waveguide <NUM> is not inserted to fill completely the cavity of the hollow metallic tube <NUM>. Thus, the connection structure of <FIG> has a cavity <NUM>. The cavity <NUM> is filled with gas and the gas may be the air.

The dielectric waveguide end 12c has a lower permittivity than the dielectric waveguide body 12b, and the gas inside the cavity <NUM> (the gas inside the hollow metallic tube <NUM>) preferably has a lower permittivity than the dielectric waveguide end 12c. In other words, the dielectric waveguide end 12c having a permittivity lower than that of the dielectric waveguide body 12b and higher than that of the gas can reduce a rapid change in permittivity, reduce the return loss, and lead to high transmission efficiency.

The dielectric waveguide end 12c may also preferably have a lower density than the dielectric waveguide body 12b.

Common resin lines are known to have a lower permittivity as the density becomes lower. In the invention, the density of the dielectric waveguide end 12c is lower than the density of the dielectric waveguide body 12b, so that the dielectric waveguide end 12c has a reduced permittivity and the return loss at the interface between the cavity <NUM> and the gas is reduced. The density is a value determined by hydrostatic weighing in accordance with JIS Z8807.

The hollow metallic tube and the dielectric waveguide each may have either a rectangular shape or a circular shape. Still, for the above reasons, they preferably have the same shape. Each of them more preferably has a circular shape because a circular dielectric waveguide can more easily be produced than rectangular one.

In order to insert and fix the dielectric waveguide <NUM> in the hollow metallic tube <NUM>, an inserted portion 12a of the dielectric waveguide <NUM> inserted in the hollow metallic tube <NUM> preferably has a certain degree of length. Too long an inserted portion may not only fail to exert an effect that corresponds to the length but also result in a large product. Thus, the length of the inserted portion 12a is preferably <NUM> or longer and <NUM> or shorter. Further, in order to reduce a rapid change in permittivity and to achieve downsizing, the length of the dielectric waveguide end 12c is preferably <NUM> or longer and <NUM> or shorter.

<FIG> is also a cross-sectional view of an example of the connection structure of the invention. In an embodiment of <FIG>, the connection structure includes the hollow metallic tube <NUM> and the dielectric waveguide <NUM>. The dielectric waveguide end 12c is inserted in the hollow metallic tube <NUM> and thereby the hollow metallic tube <NUM> and the dielectric waveguide <NUM> are connected to each other. The dielectric waveguide <NUM> includes the dielectric waveguide body 12b and the dielectric waveguide end 12c, and the dielectric waveguide end 12c has a smaller cross-sectional area than the dielectric waveguide body 12b. The dielectric waveguide end 12c having a smaller cross-sectional area than the dielectric waveguide body 12b can further reduce a rapid change in permittivity, further reduce the return loss, and lead to much higher transmission efficiency. In comparison with the cases without a change in cross-sectional area, the dielectric waveguide end 12c can be shorter, resulting in downsizing. The dielectric waveguide end 12c may have a shape of cone, truncated cone, pyramid, or truncated pyramid. A conical shape is easy to produce.

The cross-sectional area of the dielectric waveguide body 12b is preferably <NUM><NUM> (φ0. <NUM>: <NUM> THz) or larger and <NUM><NUM> (φ150 mm: <NUM>) or smaller, more preferably <NUM><NUM> (φ0. <NUM>: <NUM>) or larger and <NUM><NUM> (φ9 mm: <NUM>) or smaller.

As described above, the connection structure of the invention enables connection of a dielectric waveguide having a small diameter and a hollow metallic tube having a small diameter.

In order to easily fix the dielectric waveguide to the hollow metallic tube, the dielectric waveguide body 12b preferably has a length of <NUM> or longer and <NUM> or shorter. In order to achieve downsizing and to reduce a rapid change in permittivity, the dielectric waveguide end 12c preferably has a length of <NUM> or longer and <NUM> or shorter.

The hollow metallic tube <NUM> may be any metallic tube having a hollow portion, and may be a converter or a hollow waveguide. An embodiment in which a converter is used as a hollow metallic tube will be described in detail later.

<FIG> illustrates an embodiment in which a circular hollow metallic tube as illustrated in <FIG> constitutes part of a converter. The hollow metallic tube <NUM> in <FIG> constitutes part of a converter <NUM>, and the circular dielectric waveguide <NUM> is inserted therein. The dielectric waveguide <NUM> constitutes an inner layer of the dielectric waveguide <NUM> that includes an outer layer. The dielectric waveguide <NUM> is surrounded by an outer layer <NUM> having a lower permittivity than the dielectric waveguide <NUM>. The dielectric waveguide <NUM> is inserted in the hollow metallic tube <NUM> so that the inserted portion 12a of the dielectric waveguide <NUM> is placed in the hollow metallic tube <NUM> and the hollow metallic tube <NUM> is inserted between the inserted portion 12a and the outer layer <NUM>. Thereby, the dielectric waveguide <NUM> including the outer layer and the converter <NUM> are firmly connected to each other. The converter <NUM> includes a flange <NUM>, and can be connected to a component such as a hollow waveguide (not illustrated) via the flange. The outer layer <NUM> may have an inner diameter of <NUM> or greater and <NUM> or smaller, preferably <NUM> or greater and <NUM> or smaller. The outer layer <NUM> may have an outer diameter of <NUM> or greater and <NUM> or smaller, preferably <NUM> or greater and <NUM> or smaller.

The following describes a method of forming the dielectric waveguide including the dielectric waveguide end having a lower density from polytetrafluoroethylene (PTFE). This dielectric waveguide may be obtainable by stretching an end of a resin line in the longitudinal direction.

The resin line may be obtainable by molding PTFE by a known molding method. Specifically, a PTFE line may be obtainable by mixing PTFE powder with an extrusion aid, molding the mixture into a pre-molded article using a pre-molding machine, and then paste extrusion molding the pre-molded article.

The paste extrusion molding may be performed without pre-molding. Specifically, a PTFE line may be obtainable by mixing PTFE powder with an extrusion aid, directly putting the mixture into a cylinder of a paste extruder, and then paste extrusion molding the mixture.

Then, an end of the resulting resin line is stretched in the longitudinal direction. This can provide a dielectric waveguide whose end has a lower permittivity than the other portions or a dielectric waveguide whose end has a lower density than the other portions. In this process, heating only a portion to be stretched facilitates production of a desired dielectric waveguide end. The stretch ratio may be <NUM> times or higher and <NUM> times or lower.

The method of stretching an end of a resin line in the longitudinal direction can provide the aforementioned dielectric waveguides whose dielectric waveguide end has a smaller cross-sectional area than the dielectric waveguide body.

The stretching may be performed by holding an end of a resin line with a tool such as pliers and stretching the resin line in the longitudinal direction. If the held portion is not stretched, this portion may be cut off. This can easily provide a truncated-cone-shaped dielectric waveguide end having a permittivity or a density that gradually or stepwise decreases toward the tip and having a cross-sectional area that gradually or stepwise decreases toward the tip.

In an aspect of the invention, a method for producing a dielectric waveguide is provided. This method includes a step (<NUM>) of providing a resin line formed from polytetrafluoroethylene, a step (<NUM>) of heating an end of the resin line, and a step (<NUM>) of stretching the heated end in the longitudinal direction to provide a dielectric waveguide.

The respective steps are described hereinbelow.

The production method of the invention preferably includes a step (<NUM>) of mixing polytetrafluoroethylene (PTFE) powder with an extrusion aid to provide a pre-molded article of PTFE before the step (<NUM>).

The PTFE powder is produced from a homo PTFE consisting only of tetrafluoroethylene (TFE), a modified PTFE consisting of TFE and a modifying monomer, or a mixture thereof. The modifying monomer may be any monomer copolymerizable with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene (HFP); chlorofluoroolefins such as chlorotrifluoroethylene (CTFE); hydrogen-containing olefins such as trifluoroethylene and vinylidene fluoride (VDF); perfluoroalkyl ethylene; and ethylene. One modifying monomer may be used, or a plurality of modifying monomers may be used.

The modified PTFE preferably contains a unit of the modifying monomer in an amount of <NUM>% by mass or less, more preferably <NUM>% by mass or less, still more preferably <NUM>% by mass or less of all monomer units. In order to improve the moldability and the transparency, this amount is preferably <NUM>% by mass or more.

The PTFE may have a standard specific gravity (SSG) of <NUM> or higher and <NUM> or lower, preferably <NUM> or higher and <NUM> or lower. It may have non melt-processibility, and may have fibrillatability. The standard specific gravity is a value determined by the water replacement method in conformity with ASTM D-<NUM> using a sample prepared in conformity with ASTM D-<NUM><NUM>.

The PTFE powder mixed with an extrusion aid may be aged at room temperature for about <NUM> hours to provide extrusion aid-mixed powder. This powder may be put into a pre-molding machine and pre-molded at <NUM> MPa or higher and <NUM> MPa or lower, more preferably <NUM> MPa or higher and <NUM> MPa or lower, for <NUM> minute or longer and <NUM> minutes or shorter. This can provide a pre-molded article of PTFE.

The extrusion aid may be hydrocarbon oil, for example.

The amount of the extrusion aid is preferably <NUM> parts by mass or more and <NUM> parts by mass or less, more preferably <NUM> parts by mass or more and <NUM> parts by mass or less, relative to <NUM> parts by mass of the PTFE powder.

This step is a step of providing a resin line formed from PTFE.

In the case where the step (<NUM>) is performed to provide a pre-molded article of PTFE, this pre-molded article may be extruded using a paste extruder to provide a resin line in the step (<NUM>).

In the case where no pre-molded article of PTFE is prepared before the step (<NUM>), PTFE powder may be mixed with an extrusion aid, the mixture may directly be put into a cylinder of a paste extruder, and the mixture may be paste extrusion molded to provide a resin line.

For the resin line containing an extrusion aid, the resin line is preferably heated at <NUM> or higher and <NUM> or lower for <NUM> hours or longer and <NUM> hours or shorter to evaporate the extrusion aid.

The resin line may have either a rectangular shape or a circular shape. Still, it preferably has a circular shape because a circular resin line can more easily be produced than rectangular one. The resin line may have a diameter of <NUM> or greater and <NUM> or smaller, preferably <NUM> or greater and <NUM> or smaller.

The production method of the invention may include a step (<NUM>) of heating the resin line obtained in the step (<NUM>).

Specific heating conditions are changed as appropriate in accordance with the shape and size of the resin line. For example, the resin line is preferably heated at <NUM> to <NUM> for <NUM> seconds to <NUM> hours. The heating temperature is more preferably <NUM> or higher and <NUM> or lower. The heating duration is more preferably one hour or longer and three hours or shorter.

Heating at the above temperature for a predetermined duration causes the air contained in the resin line to be released to the outside. This seems to enable a dielectric waveguide having a high permittivity. Further, the resin line is not completely baked. This seems to enable a dielectric waveguide having a low loss tangent. Further, heating at the above temperature for a predetermined duration can advantageously improve the hardness of the resin line and increase the strength thereof.

The heating may be performed using a salt bath, a sand bath, a hot air circulating electric furnace, or the like. In order to easily control the heating conditions, the heating is preferably performed using a salt bath. This can also advantageously shorten the heating time within the above range. The heating with a salt bath may be performed using a device for producing a coated cable disclosed in <CIT>, for example.

This is a step of heating an end of the resin line obtained in the step (<NUM>). This step may be a step of heating an end of the resin line obtained in the step (<NUM>).

In the step (<NUM>), an end of the resin line is heated, so that a desired dielectric waveguide end can easily be produced.

In the step (<NUM>), although not limited, a portion to be heated is preferably apart from a tip of the resin line by <NUM> or more and <NUM> or less, more preferably a portion to be heated is apart therefrom by <NUM> or less.

The heating temperature in the step (<NUM>) is preferably <NUM> or higher, more preferably <NUM> or higher, still more preferably <NUM> or higher. The heating temperature in the step (<NUM>) is preferably <NUM> or lower, more preferably <NUM> or lower, still more preferably <NUM> or lower.

This step is a step of stretching the heated end obtained in the step (<NUM>) in the longitudinal direction to provide a dielectric waveguide.

The stretching may be performed by holding the heated end obtained in the step (<NUM>) with a tool such as pliers and stretching the resin line in the longitudinal direction. If the held portion is not stretched, this portion may be cut off. This can easily provide a truncated-cone-shaped dielectric waveguide end having a density that gradually or stepwise decreases toward the tip and having a cross-sectional area that gradually or stepwise decreases toward the tip.

The stretch ratio is preferably <NUM> times or more, more preferably <NUM> times or more. The stretch ratio is preferably <NUM> times or less, more preferably <NUM> times or less.

The stretching speed is preferably <NUM>%/sec or higher, more preferably <NUM>%/sec or higher, still more preferably <NUM>%/sec or higher. The stretching speed is preferably <NUM>%/sec or lower, more preferably <NUM>%/sec or lower, still more preferably <NUM>%/sec or lower.

The production method of the invention may include a step (<NUM>) of inserting the dielectric waveguide obtained in the step (<NUM>) into an outer layer.

The outer layer may be formed from the same PTFE as for the dielectric waveguide.

The outer layer may be formed from a hydrocarbon resin such as polyethylene, polypropylene, or polystyrene, and may be formed from the resin in a foamed state.

The outer layer formed from PTFE may be produced by the following method, for example.

PTFE powder is mixed with an extrusion aid and is aged at room temperature for <NUM> hour or longer and <NUM> hours or shorter. The resulting extrusion aid-mixed powder is put into a pre-molding machine and pressurized at <NUM> MPa or higher and <NUM> MPa or lower for about <NUM> minutes. Thereby, a cylindrical pre-molded article of PTFE may be obtained. The pre-molded article of PTFE is extrusion molded using a paste extruder. Thereby, a hollow cylindrical molded article is obtained. When this molded article contains an extrusion aid, this molded article is preferably heated at <NUM> or higher and <NUM> or lower for <NUM> hours or longer and <NUM> hours or shorter so that the extrusion aid is evaporated. This molded article is stretched at <NUM> or higher and <NUM> or lower, more preferably <NUM> or higher and <NUM> or lower and at <NUM> times or more and <NUM> times or less, more preferably <NUM> times or more and <NUM> times or less. Thereby, a hollow cylindrical outer layer may be obtained.

The outer layer may have an inner diameter of <NUM> or greater and <NUM> or smaller, preferably <NUM> or greater and <NUM> or smaller. The outer layer may have an outer diameter of <NUM> or greater and <NUM> or smaller, preferably <NUM> or greater and <NUM> or smaller.

The connection structure of the invention may favorably be produced by a method including a step of connecting a hollow metallic tube and the dielectric waveguide obtained in the step (<NUM>) to provide a connection structure. The connection structure of the invention may favorably be produced by a method including a step of connecting a hollow metallic tube and the dielectric waveguide inserted in the outer layer obtained in the step (<NUM>) to provide a connection structure.

In these steps, for example, the dielectric waveguide obtained in the step (<NUM>) or the dielectric waveguide inserted in the outer layer obtained in the step (<NUM>) is inserted into a hollow metallic tube. Thereby, a connection structure may be obtained.

The hollow metallic tube may have either a rectangular shape or a circular shape. Still, in order to easily align the center of the hollow metallic tube and the center of the dielectric waveguide and to prevent misalignment of the centers during use, to thereby much further reduce the return loss, the shape of the hollow metallic tube is preferably the same as the cross-sectional shape in the circumferential direction of the dielectric waveguide. Further, the hollow metallic tube preferably has a circular shape because a circular dielectric waveguide can more easily be produced than rectangular one.

The hollow metallic tube may be formed from any material, such as copper, brass, aluminum, stainless steel, silver, or iron. One of the metals may be used alone, or a plurality thereof may be used in combination.

The hollow metallic tube may be any metallic tube having a cavity, and may be a converter or a hollow waveguide.

Even for a dielectric waveguide formed from a resin such as polyethylene resin, polypropylene resin, or polystyrene resin, stretching of an end of a resin line in the longitudinal direction can easily provide a dielectric waveguide whose dielectric waveguide end has a smaller cross-sectional area than the dielectric waveguide body.

The invention is described with reference to examples. These examples are not intended to limit the invention, the scope of which is determined by the claims.

PTFE fine powder (SSG: <NUM>) in an amount of <NUM> parts by mass was mixed with <NUM> parts by mass of Isopar G available from Exxon Mobil Corp. serving as an extrusion aid, and the mixture was aged at room temperature for <NUM> hours. Thereby, extrusion aid-mixed powder was obtained. This extrusion aid-mixed powder was put into a pre-molding machine and pressurized at <NUM> MPa for <NUM> minutes. Thereby, a cylindrical pre-molded article was obtained.

This pre-molded article was paste-extruded using a paste extruder, and then heated at <NUM> for one hour so that the extrusion aid was evaporated. Thereby, a resin line having a diameter of <NUM> was obtained.

This resin line was cut so as to have a total length of <NUM>.

PTFE fine powder was mixed with Isopar G available from Exxon Mobil Corp. serving as an extrusion aid, and the mixture was aged at room temperature for <NUM> hours. Thereby, extrusion aid-mixed powder was obtained. This extrusion aid-mixed powder was put into a pre-molding machine and pressurized at <NUM> MPa for <NUM> minutes. Thereby, a cylindrical pre-molded article was obtained.

This pre-molded article was paste-extruded using a paste extruder, and then heated at <NUM> for one hour so that the extrusion aid was evaporated. Thereby, a molded article having an outer diameter of <NUM> and an inner diameter of <NUM> was obtained. This molded article was stretched at a ratio of two times at <NUM>. Thereby, an outer layer having an outer diameter of <NUM> and an inner diameter of <NUM> was obtained.

The resin line was inserted into the outer layer. Thereby, a dielectric waveguide including an outer layer was obtained.

The resin line obtained in the experimental example was heated at <NUM> for <NUM> minutes. A portion (end) <NUM> or less apart from a tip of the resin line was heated at <NUM>. A portion <NUM> or less apart from the tip was then held and the end was stretched at a stretch ratio of two times and at a stretching speed of <NUM>%/sec in the longitudinal direction. Thereby, the end was stretched to <NUM>. After the stretching, a portion <NUM> or less apart from the tip held in the stretching was cut off. Thereby, a dielectric waveguide was obtained.

This dielectric waveguide was inserted into the outer layer obtained in the experimental example. Thereby, a dielectric waveguide including an outer layer was obtained.

Without heating the resin line obtained in the experimental example, a portion (end) <NUM> or less apart from a tip of the resin line was heated up to <NUM>. A portion <NUM> or less apart from the tip was then held and the end was stretched at a stretch ratio of two times and at a stretching speed of <NUM>%/sec in the longitudinal direction. Thereby, the end was stretched to <NUM>. After the stretching, a portion <NUM> or less apart from the tip held in the stretching was cut off. Thereby, a dielectric waveguide was obtained.

The resin line obtained in the experimental example was heated at <NUM> for <NUM> minutes. Thereby, a dielectric waveguide was obtained.

The physical properties of the resulting dielectric waveguides are shown in Table <NUM>.

The physical properties shown in Table <NUM> were determined by the following methods. A to D shown in Table <NUM> are illustrated in <FIG>. In <FIG>, the figures "<NUM>" indicate that the length of each of A to D is <NUM>.

Each of the resulting dielectric waveguides was cut at <NUM>-mm intervals from a tip and the diameter of the midpoint of each fragment was measured using vernier caliper. Thereby, the cross-sectional area was calculated.

The density was determined by hydrostatic weighing in accordance with JIS Z8807.

From the viewpoint of the structure of the dielectric waveguide, the permittivity is difficult to measure directly. Thus, the permittivity of each of the dielectric waveguides obtained in Example <NUM>, Reference Example <NUM> and Comparative Example <NUM> was calculated by the following method. Resin lines each having a diameter of <NUM> were produced in the same manner as in the experimental example, except that the diameter of each resin line was <NUM>. The extrusion aid was then evaporated, and the resin lines were heated at <NUM> for <NUM> minutes and stretched at a ratio of <NUM> time or <NUM> times. Thereby, samples having a density of <NUM>/cm<NUM> or <NUM>/cm<NUM> were produced. Also, resin lines each having a diameter of <NUM> were produced in the same manner as in the experimental example, except that the diameter of each resin line was <NUM>. The extrusion aid was then evaporated, and the resin lines were stretched at a ratio of <NUM> time, <NUM> times, or <NUM> times in the longitudinal direction without heat treatment. Thereby, samples having a density of <NUM>/cm<NUM>, <NUM>/cm<NUM>, or <NUM>/cm<NUM> were produced. For the resulting samples, the permittivity was measured as follows and the correlation between the density and the permittivity was examined as shown in Table <NUM>. The permittivity at a density of <NUM>/cm<NUM> corresponds to the permittivity of the air. The density was determined by hydrostatic weighing in accordance with JIS Z8807. The permittivity was determined using a cavity resonator available from Kanto Electronic Application and Development Inc. (perturbation, <NUM>) and Network Analyzer HP8510C available from HP Inc. Based on the above values, the relation between the permittivity and the density was examined to find the following correlation between the density (X) and the permittivity (Y). With the following formula, the permittivity was calculated from the density of the dielectric waveguide.

The physical properties shown in Table <NUM> were determined by the following methods.

The hardness was measured using a spring type durometer (JIS type A) standardized in JIS K6253-<NUM>.

The loss tangent was determined using a cavity resonator (<NUM>) available from Kanto Electronic Application and Development Inc.

The dielectric waveguide body was cut to have a length of <NUM>. Thereby, a sample was produced. First, the density of the resulting sample was measured and the permittivity (A) was calculated from the density value. Then, as shown in <FIG>, a sample <NUM> obtained was placed between round bars 5a and 5b each having a diameter of <NUM> (<FIG>). The sample <NUM> was wound round the bar 5a and bent <NUM>° (<FIG>), and then the sample <NUM> was returned to a straight state (<FIG>). Next, the sample <NUM> was wound around the round bar 5b and bent <NUM>° (<FIG>), and then the sample <NUM> was returned to a straight state (<FIG>). This series of operations is taken as <NUM> process, and this process was repeated <NUM> times. After the above operations, the density of the sample <NUM> was measured and the permittivity (B) was calculated. For the bending stability, the permittivity change ratio (B/A) of the dielectric waveguide body before and after the bending was calculated. The conversion from the density (X) to the permittivity (Y) was performed using the following formula.

For the permittivity of the dielectric waveguide and the permittivity of the outer layer, the densities of the dielectric waveguide and the outer layer were measured and then converted by the following formula.

The density (X) and the permittivity (Y) show the following correlation.

The difference in permittivity between the dielectric waveguide and the outer layer is defined as the value obtained by subtracting the permittivity of the outer layer from the permittivity of the dielectric waveguide.

As shown in <FIG>, each end of the dielectric waveguide inserted in the outer layer was inserted into the hollow metallic tube <NUM> of each of two converters <NUM>. The flange <NUM> of each converter <NUM> was coupled with the circular waveguide side of a corresponding one of circular waveguide-rectangular waveguide converters <NUM> and <NUM> (not illustrated). The rectangular waveguide sides of the circular waveguide-rectangular waveguide converters <NUM> and <NUM> were respectively coupled with the rectangular waveguides <NUM> and <NUM>. These rectangular waveguides <NUM> and <NUM> were respectively connected to a first terminal (not illustrated) and a second terminal (not illustrated) of the network analyzer, and the parameter S11 was measured. The maximum reflection value between <NUM> and <NUM> was taken as the return loss. The zero-point adjustment was performed as follows. First, the circular waveguide sides of the circular waveguide-rectangular waveguide converters <NUM> and <NUM> were connected to each other in the absence of a dielectric waveguide in between. Next, the rectangular waveguide sides of the circular waveguide-rectangular waveguide converters <NUM> and <NUM> were respectively coupled with the rectangular waveguides <NUM> and <NUM>. Then, the rectangular waveguides <NUM> and <NUM> were respectively connected to the first terminal and the second terminal of the network analyzer.

As shown n <FIG>, the dielectric waveguide inserted in the outer layer obtained in each of Example <NUM>, Reference Example <NUM> and Comparative Example <NUM> was inserted into the hollow metallic tube of the converter, so that the dielectric waveguide inserted in the outer layer and the hollow metallic tube of the converter were connected to each other. Then, the transmission loss and the return loss were determined. The results are shown in Table <NUM>.

Claim 1:
A dielectric waveguide (<NUM>) comprising:
a dielectric waveguide body (<NUM>, 12b); and
a dielectric waveguide end (<NUM>, 12c) having a lower density than the dielectric waveguide body (<NUM>, 12b),
the dielectric waveguide body (<NUM>, 12b) and the dielectric waveguide end (<NUM>, 12c) being seamlessly and monolithically formed from a same material,
characterized in that the dielectric waveguide body (<NUM>, 12b) has a density of <NUM>/cm<NUM> or higher and <NUM>/cm<NUM> or lower,
the dielectric waveguide body (<NUM>, 12b) has a hardness of <NUM> or higher; and
the dielectric waveguide end (<NUM>, 12c) has a density that is <NUM>% or less of the density of the dielectric waveguide body.