EP0335570A1

EP0335570A1 - Transmission Line

Info

Publication number: EP0335570A1
Application number: EP89302820A
Authority: EP
Inventors: Fujiko Akiba; Hiromi Yasumoto
Original assignee: Junkosha Co Ltd
Current assignee: Junkosha Co Ltd
Priority date: 1988-04-01
Filing date: 1989-03-21
Publication date: 1989-10-04
Also published as: JPH01254002A; GB2217115A; GB8906464D0; AU3154289A

Abstract

A transmission line (1) having an electromagnetic wave energy transmitting core (2) formed of unsintered or partially sintered polytetrafluoroethylene, the core (2) being rectangular in cross-section, and the line having an electrically conductive layer (4) disposed outside the core, preferably on the outside surface of at least a portion thereof. The electrically conductive layer is preferably formed by polytetrafluoroethylene tape containing carbon fibres.

Description

The present invention relates to wave energy transmission lines such as dielectric lines, surface-wave lines, including image lines and insular lines and dielectric-packed or internal metal waveguides, as well as combinations of these structures.
The applicant has been actively engaged in the development of transmission lines utilizing dielectrics. Results of this development work have been disclosed in Japanese Patent Publication No. 56-24241, Japanese Laid-Open Patent Application No. 58-73501 and Japanese Laid-Open Patent Application No. 58-166804. However, in cases where the cross-sectional shape of the wave energy transmitting part of a transmission line is circular, the plane of polarization cannot be preserved when a twist is applied to the line. As a result, a so-called "reflection", involving a return of the transmitted signal, occurs and the transmission efficiency deteriorates.
The present invention seeks to solve this problem and to provide a transmission line which substantially preserves the plane of polarization and which has good transmission efficiency.
According to the present invention there is provided a transmission line having an electromagnetic wave energy transmitting core formed of unsintered or partially sintered polytetrafluoroethylene, the core having a rectangular cross-section, and the transmission line including an electrically conductive layer disposed outside the core.
The electrically conductive layer is preferably disposed on the outside surface of at least a portion of the core, and may be formed by polytetrafluoroethylene tape containing carbon fibres.
In a preferred embodiment of the invention the transmission line is equipped with a wave energy transmitting core portion which is formed from an unsintered or partially sintered polytetrafluoroethylene (PTFE) resin moulding and which is rectangular in cross-section, and a conductive layer which is formed on the outside of this transmitting portion.
As described above, the wave energy transmitting portion of a transmission line in accordance with the invention is formed from an unsintered or partially sintered PTFE moulding which is rectangular in cross-section. Accordingly, in the case of electromagnetic wave propagation, the electric field E and magnetic field H are mutually perpendicular, and are also in a perpendicular relationship with the side surfaces of the wave energy transmitting portion. This relationship is constant for the cross-section taken at any point along the entire length of the transmission line. Accordingly, even if the transmission line is twisted, the plane containing the electric field vector and the direction of propagation, i.e. the plane of polarization, remains constant. Since a conductive layer is formed on the outside of the wave energy transmitting portion, any reflection loss generated when a twist is applied to the transmission line will be absorbed by the conductive layer. Accordingly, there are substantially no problems associated with reflection, and the transmission efficiency is high.
Embodiments of the transmission line in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a schematic cross-sectional view of a first embodiment;
Figure 2 is a cross-sectional view of a second embodiment;
Figure 3 is an illustration of the relationship between the electric field and the magnetic field in the waveenergy transmitting portion of a transmission line in accordance with the invention; and
Figure 4 is a view similar to that of Figure 3, illustrating the operation of the wave-energy transmitting portion of the transmission line shown in Figure 1.

In the transmission line 1 of Figure 1, electrically conductive layers 4 are formed by causing a PTFE tape containing carbon fibres to adhere tightly to the surfaces on the shorter sides of a rectangular section dielectric core 2 consisting of PTFE and manufactured by the method described in Japanese Patent Publication No. 56-24241. An outer dielectric layer or cladding 3 is then formed by wrapping an unsintered PTFE tape around the outside of the dielectric core 2 and conductive layers 4 along the entire length of the line. The transmission line 1 is completed by an outer covering or sheath 5 consisting of polyvinylchloride.
Since electromagnetic waves are propagated within the medium of the rectangular dielectric core 2, the electric field E and magnetic field H are in a mutually perpendicular relationship, and are also in a perpendicular relationship with the side surfaces of the rectangular dielectric core 2, as is shown in Figure 3. This relative positional relationship is constant at the cross-section taken at any point along the entire length of the transmission line 1. Accordingly, even if the transmission line is twisted, the plane containing the electric field vector and the direction of propagation, i.e. the plane of polarization remains constant. Unwanted modes E′ which are generated when the transmission line 1 is twisted, and which are not perpendicular to the magnetic field H as shown for example by the dotted line in Figure 4, are absorbed by the conductive layers 4. Accordingly, there are substantially no problems associated with reflection, and the transmission efficiency of the line is high.
Figure 2 illustrates a different example of the transmission line in accordance with the invention. The materials and construction of the rectangular dielectric core 2, the dielectric cladding 3 and outer sheath 5 are the same as in the first example described above, and further detailed description of these parts is omitted here. The transmission line 6 of this example differs from the first example in that a conductive layer 7 is installed around the core 2 by weaving it, e.g. from a silver-plated soft copper wire, into the outer dielectric layer 3 instead of installing conductive layers along the side surfaces of the rectangular dielectric core 2. By using such a structure, it is possible not only to absorb unwanted modes, but also to use the conductive layer 7 to prevent external noise voltages from having a deleterious effect on the electric field vector. In this example, the plane of polarization is preserved when the transmission line 6 is twisted, just as described for the first example.
As described above, the wave energy transmitting portion of a transmission line in accordance with the invention is formed from an unsintered or partially sintered PTFE moulding which is rectangular in cross-section. Accordingly, in the propagation of electromagnetic waves, the electric field and magnetic field are perpendicular to each other, and both fields are in a perpendicular relationship with the side surfaces of the wave energy transmitting portion. This relationship is constant along the entire length of the transmission line. If the transmission line is twisted, the plane of polarization is preserved. Furthermore, since the transmission line is constructed with a conductive layer formed outside of the wave energy transmitting portion, unnecessary modes generated when a twist is applied to the line are absorbed by the conductive layer, so that high-efficiency transmission is possible.
The present invention is not limited to the examples described above, and various modifications are possible within the scope of the invention. For example, the material or method of construction of the conductive layer may be altered, or a multi-core cable may be constructed.

Claims

1. A transmission line, (1; 6) having an electromagnetic wave energy transmitting core (2) formed of unsintered or partially sintered polytetrafluoroethylene, characterised by said core (2) having a rectangular cross-section, and said transmission line (1;6) including an electrically conductive layer (4;7) disposed outside the core (2).

2. A transmission line according to claim 1, wherein the electrically conductive layer (4) is disposed on the surface of at least a portion of the core (2).

3. A transmission line according to claim 2, in which the electrically conductive layer (4) is disposed on the shorter sides of the rectangular section of the core (2).

4. A transmission line according to any one of claims 1 to 3, in which the electrically conductive layer (4) is formed by polytetrafluoroethylene tape containing carbon fibres.

5. A transmission line according to any one of the preceding claims, in which the core (2) is surrounded by a cladding (3) of dielectric material.

6. A transmission line according to claim 5, in which the cladding (3) is formed by unsintered polytetrafluoroethylene tape wrapped around the core (2) along the length of the transmission line.

7. A transmission line according to claim 5 or claim 6 when dependent on claim 1, in which the electrically conductive layer (7) surrounds the core (2) and is embedded in the cladding (3).

8. A transmission line according to claim 7, in which the electrically conductive layer (7) is woven into the cladding (3).