JP3023874B2 - High frequency transmission line - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application field] The present invention relates to a feed line to a broadcasting antenna, or a waveguide or a high frequency wave mainly transmitting a VHF band or higher, such as a microwave relay facility or a radar facility. The present invention relates to improvement of a high-frequency transmission line such as a coaxial cable.

[Prior Art] In the frequency range from microwave to millimeter wave,
Waveguides that have smaller transmission loss than coaxial waveguides and that can transmit more power than coaxial waveguides are widely used.

On the other hand, in the VHF to UHF band, a coaxial tube or a coaxial cable that can have a wide transmission frequency band and can be smaller in size than a waveguide is frequently used.

FIG. 1 shows an elliptical flexible waveguide 10 which is an embodiment of a waveguide.
It is an explanatory perspective view showing the configuration of, the conductor 11 is corrugated and molded so as to have flexibility, is provided with an anticorrosion sheath 12 made of polyethylene or the like, can be transported by drums, and bend parts It has excellent laying and wiring workability such as being able to bend and lay without using.

On the other hand, FIG. 3 is an explanatory perspective view showing the configuration of the flexible high-frequency coaxial cable 20, and shows the inner conductor 21 and the corrugated outer conductor (when corrugating is also performed on the inner conductor 21 depending on the size). 23) are arranged coaxially with a spiral insulator 22 interposed therebetween, and an anticorrosion sheath 24 made of polyethylene or the like is provided on the outer periphery thereof. Such a coaxial cable is also widely used as a feeder to a broadcast antenna or the like because it can be transported by a drum and can be easily bent and laid.

[Problems to be Solved by the Invention] In the above-mentioned conventional flexible waveguide or flexible coaxial cable, oxygen-free copper having excellent electrical characteristics is used as a conductor.

However, recently, for example, the transmission power of television broadcasts and the like tends to be further increased, and the power supply power capacity to the high-frequency transmission line and the like for supplying the power to a transmission antenna also increases.
Heat generation of the feeder line accompanying this has been regarded as a problem.

For this reason, in order to cope with large-capacity transmission power, an attempt is made to increase the size of the power supply line, or to cool the power supply line by air cooling or water cooling.
If the size is increased, the cost naturally rises greatly. Even if the air cooling or the water cooling is performed, the equipment cost required for the cooling becomes very large.

One of the major reasons why the size of the power supply line is increased and the cooling by the cooling device is forced is that all the conductors are made of oxygen-free copper.

That is, FIG. 5 shows an example of an isochronous softening curve of pure copper. Even if hard copper is used, its tensile strength is half of the tensile strength at room temperature at 150 ° C.
It turns out that it falls to the extent.

In this way, if the tensile strength is greatly reduced due to the temperature rise, the structural dimensions of the long and laid feeder line will change, and the electric power such as VSWR (standing wave ratio) will be changed. This results in a decrease in the mechanical characteristics, which is extremely undesirable in practical use.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, an object of the present invention is to maintain the strength of a conductor in a high-temperature region, and furthermore, there is not much difference in electric characteristics from the conventional case, and therefore, the transmission power capacity increases in the same size It is also an object of the present invention to provide a new high-frequency transmission line capable of reducing the size of the power supply line if the transmission power capacity is the same, thereby achieving cost reduction and weight reduction. .

[Means for Solving the Problems] The gist of the present invention resides in that a material in which pure copper is formed on the surface of brass is used as a material of a conductor in a waveguide type high-frequency transmission line.

In a high-frequency transmission line in which an inner conductor and an outer conductor are coaxially arranged, both the inner conductor and the outer conductor are made of brass, and pure copper is formed on at least opposing surfaces of the inner and outer conductors. Is to be.

[Action] Brass itself, which is a copper-zinc alloy, has poor electrical properties but very good mechanical properties, and does not soften as easily as pure copper even at high temperatures.

On the other hand, the higher the frequency, the higher the frequency,
Due to the so-called skin effect, it has the property of intensively flowing only in a very shallow layer on the surface of the conductor, and in the VHF frequency band, it can be around 10 μm in the surface area and the 10 GHz band where the waveguide is used. At most, only a portion of about 2 to 3 μm of the surface layer is involved.

With this depth, it is easy to evaporate zinc from the surface of brass and make it pure copper, and the high-frequency current is made pure copper in this way, and the electrical characteristics are almost equivalent to oxygen-free copper. If brass is used as the material as long as it flows through the changed surface layer, there is no risk that the electrical characteristics will be affected.

[Example] Hereinafter, the present invention will be described with reference to examples.

Since the boiling point of zinc at atmospheric pressure is 930 ° C., and the boiling point of copper at atmospheric pressure is 2582 ° C., the temperature difference between zinc and zinc is very large. Therefore, it is possible to heat brass, evaporate only zinc from its surface layer, and then form a pure copper layer.

From a practical point of view, heating above 930 ° C. is slightly too high. Therefore, the pressure within the heating room temperature should be 10 ^-2 ~
If the vacuum is drawn to about 10 ^-4 Torr and the vacuum heating is performed, the boiling point is lowered under the above high vacuum of about 10 ^-2 to 10 ^-4 Torr, and heating of zinc at about 500 to 900 ° C is sufficient. Can be evaporated.

According to the experiments of the inventors, using a brass strip having a thickness of 4 mm,
When heated and dezinced in the above vacuum heating furnace,
As shown in the enlarged sectional view of FIG.
A pure copper layer 3 having a thickness of about μm was formed, a transition layer 2 from brass to pure copper was formed, and a material having a state of brass 1 inside could be obtained.

As described above, in a high-frequency band in which a waveguide or a coaxial cable is used as a transmission line, a high-frequency current flows only through the surface layer, and the depth at which it actually participates is 3 as described above. About 10 μm. This depth matches the thickness of the pure copper layer 3 formed by the above-described dezincing. The brass material whose surface has been dezincified and made pure copper is, for example, an elliptical waveguide as shown in FIG. Tube 10
Alternatively, for example, it can be seen that the present invention can be sufficiently applied as a conductor of the high-frequency coaxial cable 20 as shown in FIG.

In the case of the coaxial cable shown in FIG. 3, current flows only through the outer surface of the inner conductor 21 and only through the inner surface of the outer conductor 23 due to the proximity effect other than the skin effect. As for 21, at least only the outer surface of the pipe-shaped conductor needs to be subjected to pure copper treatment 3 as shown in FIG. 4, and at least only the inner surface facing the outer conductor 23 has to be pure copper treated. It would be good if it was. However, this means that the opposing surface of the conductor may be subjected to pure copper treatment in practice, and does not mean that the conductor must be limited to that.

It is to be noted that the pure copper layer 3 on the surface subjected to the pure copper treatment becomes porous by dezincification, and there is a concern that, as it is, it becomes a starting point of stress corrosion cracking due to a stress load due to subsequent processing.

On the other hand, it is preferable that the pure copper layer 3 is formed into a solid layer by an appropriate treatment such as performing rolling such as skin pass rolling on the surface subjected to the pure copper treatment to form a solid layer by sealing deformation of the porous layer. Desirably, such a solid body can improve electrical characteristics.

If a high-frequency transmission line such as a waveguide or a high-frequency coaxial cable or a coaxial tube is formed by using brass having a pure copper layer 3 formed on the surface as described above, a high-frequency current flows through the depth of the conductor due to the skin effect. Has a pure copper layer having excellent electrical characteristics, and there is no great difference in electrical characteristics from the case where only conventional oxygen-free copper is used. On the other hand, most of the parts other than the surface layer are made of brass having excellent mechanical strength, so that even if the transmission power capacity is increased and the temperature of the transmission line rises, it is easily softened like oxygen-free copper. It keeps high mechanical strength without fear. Therefore, a highly reliable high-frequency transmission line can be configured without a risk of deterioration of electrical characteristics such as VSWR.

[Effects of the Invention] As described in detail above, according to the transmission line of the present invention,
Maintains the strength of the conductor in the high-temperature region, and there is not much difference in the electric characteristics from the conventional case, and the transmission power capacity can be increased for the same size, while the size of the power supply line for the same transmission power capacity This makes it possible to achieve a significant feature that the cost can be reduced and the cost and the weight can be reduced accordingly.

[Brief description of the drawings]

FIG. 1 is an explanatory perspective view showing the configuration of a flexible elliptical waveguide, and FIG.
The figure is an enlarged sectional view of a brass strip with a pure copper layer formed on the surface after dezincification, FIG. 3 is an explanatory perspective view showing the configuration of a high frequency coaxial cable, and FIG. 4 is a pure copper layer obtained by dezincing the outer surface of a brass pipe. FIG. 5 is an isochronous softening curve diagram of pure copper. 1: Brass layer, 2: Brass-pure copper transition layer, 3: Pure copper layer, 10: Elliptical waveguide, 11: Conductor, 12: Anticorrosive sheath, 20: High frequency coaxial cable, 21: Inner conductor, 22: Insulator, 23: outer conductor, 24: anticorrosion sheath.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Harushiro Ohashi 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture Inside the Hidaka Works, Hitachi Cable Co., Ltd. (72) Inventor Takashi Yagi Hidaka, Hitachi City, Ibaraki Prefecture (1-1) Mitsu Onishi 5-1-1, Hidakacho, Hitachi City, Ibaraki Pref.

Claims (2)

(57) [Claims] 1. A high-frequency transmission line of a waveguide type using a material in which pure copper is formed on the surface of brass as a material forming a conductor. 2. A high-frequency transmission line in which an inner conductor and an outer conductor are coaxially arranged, wherein both the inner conductor and the outer conductor are made of brass and at least opposing surfaces of the inner and outer conductors. High-frequency transmission line made of pure copper.