JPH10247426A - Coaxial cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the mismatching of characteristic impedance caused by the change of a outer diameter size generated by a thermal effect and allow good signal transmission by applying an inclined gradient to the outer diameter in response to the temperature gradient generated on a coaxial cable used to connect the devices installed in different thermal environments. SOLUTION: This coaxial cable 10 is formed so that the outer diameter size is gradually increased from one end side to the other end direction. The outer diameter size of the coaxial cable 10, i.e., the inner diameter of an outer conductor 11, is formed to complement the expansion/shrinkage quantity of the outer diameter size generated on a dielectric 13 in particular based on the temperature gradient generated in the cable 10 according to the temperature environment in an operating state of the coaxial cable 10. The layer thickness of the dielectric 13 is inclinatorily changed in advance so that the outer size of the coaxial cable 10 becomes constant from one end to the other end. The outer diameter of the dielectric 13 is set to 2R0 on one end side and to 2R1 (>2R0 ) on the other end side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coaxial cable and, more particularly, to a coaxial cable which is suitable for transmitting a signal to a device installed under a predetermined temperature environment.

[0002]

2. Description of the Related Art In general, a known coaxial cable is constituted by coaxially bundling a cylindrical outer conductor, a center conductor at the center of the coaxial cable, and an insulator as a dielectric between both conductors.
Compared to a balanced cable, it has excellent characteristics such as low transmission loss at high frequency, high heat insulation, and easy impedance uniformity due to its structure. Can be effectively applied as a transmission line for input / output signals to / from a high-frequency device.

FIG. 2 is a conceptual diagram showing an example of use of a coaxial cable. In this use example, one end of a coaxial cable 10 having a structure in which a cylindrical outer conductor 11, a center conductor 12 at the center thereof, and a dielectric 13 that insulates the two conductors 11 and 12 from each other are coaxially bundled (FIG. (Right side) is connected to a device (not shown) provided inside the thermostat 15.

FIG. 3 shows a more specific configuration example to which such a coaxial cable is applied. Here, a low-temperature holding body that holds an extremely low temperature state is shown as the above-mentioned constant temperature bath, and a device that performs a specific operation under an extremely low temperature environment is, for example, a filter circuit using a superconducting substance (hereinafter, superconducting material) And a low-noise amplifier circuit. These devices can be expected to improve operating characteristics such as sharp cut characteristics, low loss characteristics, and low noise characteristics under extremely low temperature conditions.

[0005] In FIG. 3, reference numeral 21 denotes a low-temperature holding body which blocks conduction of heat due to an external temperature environment to the inside and maintains an extremely low temperature state inside; A cold head 23 comprising a heat diffusion plate 22a to be mounted and a regenerator 22b for providing a predetermined cryogenic state to the superconducting filter circuit 32 and the low noise amplifier circuit 33. An input connector for electrically connecting an input pad of the filter circuit 32 via a coaxial cable serving as a signal input line 23a;
4 is an output pad of the low-noise amplifier circuit 33 and the low-temperature holding body 21.
This is an output connector for electrically connecting to the outside through a coaxial cable as a signal output line 24a. Although not shown, the low-temperature holding body 21 is provided with a cooling source such as liquid helium or liquid nitrogen for maintaining a predetermined cryogenic state, and vacuum holding means such as a rotary pump and a diffusion pump. .

[0006]

[Problems to be Solved by the Invention] Low temperature holding body (constant temperature bath)
In the example shown in FIG. 3, the input / output connectors 21 and 24 are provided with input / output connectors 23 and 24 which are thermally affected by the external temperature environment. The heat is transmitted to the superconducting filter circuit 32 or the low-noise amplifier circuit 33 cooled to the cryogenic state via the signal input / output lines 23a and 24a formed by coaxial cables. That is, a gradient (temperature gradient) occurs in the temperature distribution in the coaxial cable. Specifically, the input / output connectors 23 and 24 exposed under the external temperature environment
The device (superconducting filter circuit 32, low noise amplifier circuit 3)
Assuming that the cooling temperature in 3) is the liquid nitrogen temperature (about 77 K) required to realize the superconducting state, the temperature gradient is 20
Over 0K.

The effect of such a temperature gradient on the signal characteristics of the coaxial cable will be described. The dielectric layer interposed between the outer conductor and the center conductor of the coaxial cable is made of a polymer resin material such as polyethylene, and the ratio of expansion and contraction due to thermal influence is determined by the conductor portion (for example, Copper) about 10 times higher. Therefore, when a temperature gradient of 200 K or more occurs as described above, a difference occurs in the amount of contraction between the input / output connectors 23 and 24 of the coaxial cable and the device, and the outer diameter (diameter) changes. .
That is, as shown in FIG. 4A, the dielectric 1 having the outer diameter 2R ₀ set to have a uniform layer thickness at room temperature.
As shown in FIG. 4B, one end (left side in the drawing) of the coaxial cable 10 having the outer conductor 11 in close contact with the outer periphery thereof has a normal temperature T _H and the other end side (in the drawing). If the temperature on the right side is the liquid nitrogen temperature _TL and a coaxial cable, especially a dielectric 13 has a temperature gradient having a uniform slope, the outer diameter of the dielectric is 2R ₂ (<2) at the other end of the low-temperature end.
(R ₀ ), a gradient change occurs in the outer diameter dimension.

Here, the outer diameter (diameter) of the center conductor 12 is 2
r, the inner diameter of the outer conductor 11 (outer diameter of the dielectric 13) is 2R,
When the insulator interposed between the central conductor 12 and outer conductor 11 of the dielectric constant of the (dielectric 13) and epsilon _r, the characteristic impedance Z ₀ of the general coaxial cable is expressed by the following equation.

[0009]

(Equation 1)

Therefore, when a gradient change occurs in the outer diameter of the dielectric 13, R in equation (1) decreases, and the characteristic impedance Z ₀ changes. Usually, the characteristic impedance between the coaxial cable and the device side to be connected is configured to increase the matching so as not to cause reflection of the transmitted signal. In this case, there is a problem that a step of characteristic impedance is generated between the first and second transmission lines, and a favorable signal transmission is not performed. Such a problem becomes more remarkable as the transmitted signal becomes faster and has a higher frequency.

Accordingly, the present invention suppresses mismatching of characteristic impedance due to a change in outer diameter dimension caused by thermal effects in a coaxial cable used to connect devices installed in different temperature environments. It is an object of the present invention to provide a coaxial cable capable of performing good signal transmission.

[0012]

According to the present invention, in order to achieve the above-mentioned object, an invention according to claim 1 comprises a cylindrical outer conductor, a center conductor located at the axis of the outer conductor, In a coaxial cable having a dielectric interposed between both conductors, one end of the coaxial cable is in a first thermal environment and the other end is in a second thermal environment different from the first thermal environment. When installed, the outer diameter is changed and set in accordance with the thermal gradient generated by the first and second thermal environments.

According to such a configuration, the outer diameter dimension is changed in advance, ie, contracted, in response to a temperature gradient generated in a coaxial cable used in a configuration for connecting devices installed in different thermal environments. By adding a gradient to the outer diameter dimension so as to increase the outer diameter of the direction or the specific location where the amount becomes higher, complement the gradient change of the outer diameter dimension due to the temperature gradient generated in the coaxial cable, Since a uniform outer diameter can be obtained in a use state, a change in characteristic impedance can be suppressed, consistency with a device to be connected can be maintained, and good signal transmission can be realized. .

According to a second aspect of the present invention, there is provided the coaxial cable according to the first aspect, wherein the change in the outer diameter is interposed between the outer conductor and the center conductor in accordance with the thermal gradient. A gradient is set in the thickness of the dielectric layer. According to such a configuration,
By forming the layer thickness of the dielectric composed of a polymer resin with a high degree of shrinkage due to thermal effects with a gradient, a uniform outer diameter in the use condition can be easily obtained. The change can be suppressed, the consistency with the device to be connected can be maintained, and good signal transmission can be realized.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing an embodiment of a coaxial cable according to claim 1 or 2. In FIG. 1A, a coaxial cable 10 has a structure in which a cylindrical outer conductor 11, a center conductor 12 at the center thereof, and a dielectric 13 that insulates between the two conductors 11 and 12 are coaxially bundled. doing. The feature of this embodiment is that the outer diameter of the coaxial cable 10 is formed so as to gradually increase from one end (left side in the drawing) to the other end (right side in the drawing).

Here, the outer diameter of the coaxial cable 10, that is, the inner diameter of the outer conductor 11, depends on the temperature gradient generated in the coaxial cable due to the temperature environment in the use condition of the coaxial cable 10, especially the outer conductor 11 and the center conductor. The layer thickness of the dielectric 13 is set in advance so that the expansion and contraction of the outer diameter generated in the dielectric 13 interposed between the 12 and the outer diameter from the one end to the other end of the coaxial cable 10 are constant. It is formed by changing it inclining. Here, by setting the inner diameter of the outer conductor 11 (the outer diameter of the dielectric 13) at one end 2R _0, the 2R ₁ (> 2R ₀₎ at the other end.

The coaxial cable 10 according to the present embodiment is applied to the signal input line 23a shown in FIG.
The superconducting filter 3 whose input connector 23 is in a room temperature (first thermal environment: T _H ) state of K and whose other end is in a liquid nitrogen temperature state (second thermal environment: T _L ) of 77 K, for example.
2, the contraction of the outer diameter of the coaxial cable 10 gradually increases (the outer diameter decreases) from the input connector 23 toward the superconducting filter 32 due to a temperature gradient of 200 K or more. Occurs. Here, the coaxial cable 10 of the present embodiment has a 300K → 7
Inner diameter dimension of the outer conductor 11 caused by the temperature gradient of 7K,
That is, the amount of contraction of the thickness of the dielectric 13 is canceled out.
Since the outer diameter of the dielectric 13 is set in advance so as to increase in the direction of the superconducting filter 32 (the other end), in the use state, as shown in FIG. The difference in the outer diameter dimension becomes “0”, and the characteristic impedance uniform in the extending direction of the coaxial cable 10 can be realized from the above-described equation (1). Therefore, the coaxial cable 1
0 suppresses distortion and reflection of a signal transmitted, and obtains good signal transmission characteristics.

Specifically, the center conductor has a diameter of 1 mm, the outer diameter of the outer conductor is as thin as several mm, and the thickness of the outer conductor is as thin as several tens μm. In the coaxial cable in which is formed in close contact, when the outer diameter is made uniform and the characteristic impedance Z ₀ is set to, for example, 50 [Ω], under the above-described conditions,
The characteristic impedance Z at the device connection in the cryostat
_Since a phenomenon in which ₀ is reduced by about 1.5 [Ω] has been observed, the outer diameter of the dielectric may be formed with a gradient in advance so as to complement the 1.5 [Ω]. .

In the above-described embodiment, the case where the temperature gradient between the room temperature (300K) and the liquid nitrogen temperature (77K) occurs in the coaxial cable, but the present invention is limited to such a temperature setting. However, the present invention can be effectively applied to a coaxial cable used at a room temperature and a high temperature higher than the room temperature, for example, 500K, particularly a coaxial cable used in a temperature environment having a temperature gradient that causes a change in the outer diameter of the dielectric. .

[0020]

As described above, according to the coaxial cable of the first aspect, a coaxial cable used in a configuration for connecting devices installed in different thermal environments is preliminarily adapted to a temperature gradient generated in the coaxial cable. By changing the outer diameter dimension with a gradient, that is, by forming an outer diameter dimension with a slope gradient so as to increase the outer diameter at a direction where the amount of shrinkage increases or at a specific location, the outer diameter due to the temperature gradient generated in the coaxial cable Since a uniform outer diameter dimension can be obtained in a use state by compensating for a dimensional gradient change, a change in characteristic impedance can be suppressed, and consistency with a device to be connected can be maintained. Signal transmission can be realized.

Further, according to the coaxial cable of the second aspect, the layer thickness of the dielectric material made of the polymer resin having a high shrinkage amount due to the thermal influence is formed with an inclined gradient, so that it can be used. Since a uniform outer diameter dimension can be easily obtained, it is possible to suppress a change in the characteristic impedance, maintain the consistency with the device to be connected, and provide a good coaxial cable that suppresses the deterioration of the signal transmission characteristics. Can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a coaxial cable according to claim 1 or 2;

FIG. 2 is a conceptual diagram showing a usage example of a conventional coaxial cable.

FIG. 3 is a configuration diagram showing a specific usage example of a coaxial cable.

FIG. 4 is a configuration diagram illustrating a problem of a conventional coaxial cable.

[Explanation of symbols]

 10: Coaxial cable 11: Outer conductor 12: Central conductor 13: Dielectric 15: Constant temperature bath 21: Low temperature holder 22: Cold head 23: Input connector 23a: Signal input line 24: Output connector 24a: Signal output line 32: Super Conduction filter 33: Low noise amplifier circuit

Claims (2)

[Claims] 1. A coaxial cable comprising: a cylindrical outer conductor; a center conductor located at an axis of the outer conductor; and a dielectric material interposed between the two conductors. When the other end is installed in a second thermal environment different from the first thermal environment in the thermal environment, the other ends correspond to thermal gradients generated by the first and second thermal environments. A coaxial cable characterized by being set by changing its diameter. 2. The coaxial cable according to claim 1, wherein the change in the outer diameter dimension corresponds to the thickness of the dielectric layer interposed between the outer conductor and the center conductor corresponding to the thermal gradient. A coaxial cable characterized in that the slope is set.