JP2894245B2 - High frequency transmission line - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates in planar transmission line such as a microstrip transmission line using a superconducting material,
The present invention relates to a high-frequency transmission line capable of dramatically improving its transmission power , and a filter circuit using the same .

[0002]

2. Description of the Related Art A planar transmission line such as a microstrip transmission line is frequently used as a transmission line for transmitting a high frequency such as a microwave. Attempts have been made to use superconducting materials in tracks. The conductor constituting the planar transmission line is usually a planar conductor having a constant width, and generally, when a current flows through a planar conductor made of a superconducting material, the so-called Meissner effect causes
Current flows only near the surface of the conductor. In particular, in a microstrip transmission line, current concentrates on the cross-sectional end of the conductor film, and this is shown in FIGS.

In FIG. 4, a ground conductor film 3 of a superconductive material is formed on the entire lower surface of a dielectric plate 2, while a strip conductive film 1 of a predetermined width is formed on the upper surface by a single film of a superconductive material. Is formed. Assuming that the width direction of the strip conductor film 1 is x, the longitudinal direction is y, and the film thickness direction is z, the distribution of the current density Jy in the y direction in the flat rectangular film cross section is as shown in FIG.

That is, as is known from FIG. 5, the current density Jy shows a maximum at both ends (B in the drawing) in the cross section of the film, and particularly on the side in contact with the dielectric plate 2 (the front side in the drawing). It becomes a non-uniform thing showing a large value. Therefore, the current density is extremely small in the middle part (A in the figure) of the film cross section excluding the both ends, and as a result, the current transport efficiency of the entire conductor film 1 is poor. In addition, the same phenomenon appears due to a so-called skin effect even when a high-frequency current flows through a conductor of a normal conductive material.

In particular, each superconducting material has its own critical current. Even if the superconducting material is cooled below the critical temperature, if a current exceeding the critical current (critical current density) flows,
The superconducting state is destroyed in this part. Therefore, when a superconducting material is used, it is necessary to keep the maximum value of the current density Jy below the critical current density, and the effect of improving the current transport efficiency by the superconducting material is greatly reduced.

Therefore, in the filter (resonator) of the microstrip transmission line, as shown in FIG. 6, by making the shape of the filter F disc-shaped, the peak value of the current density in the resonance region is suppressed. A proposal for increasing the input power (current) has been proposed (IEICE Technical Report SCE93).
−53 The Institute of Electronics, Information and Communication Engineers).

[0007]

However, when the shape of the filter is a disk, the line width becomes very large in the filter portion. In particular, when the filter is multi-staged to obtain a steep filter characteristic, etc. There is a problem that a communication circuit becomes large. In view of the above, an object of the present invention is to provide a high-frequency transmission line capable of transporting a larger current while suppressing an increase in line width and improving input power. .

[0008]

Since the present invention SUMMARY OF] is to achieve the above object, in the invention according to claim 1, the dielectric base
The plate (2) and the upper surface of the dielectric substrate (2)
A constant width (W1) and a constant adjacent distance (d)
Lines that are formed in parallel to each other to form a planar transmission line
And a conductor (11), wherein the plurality of linear conductors are formed.
(11) is made of a superconducting material, and its longitudinal direction
At the both ends of the shape with the above-mentioned constant adjacent distance (d) maintained.
It is characterized by being made. In this case, the conductor width of the linear conductor is set to about 1 μm, and the adjacent distance between these linear conductors is set to about 0.8 to about the same as the conductor width.
It is preferable to set the thickness to 1.5 μm.

According to the second aspect of the present invention, the dielectric material
On the substrate (2) and the upper surface of the dielectric substrate (2),
Formed in parallel with the longitudinal direction to form a flat transmission line
And the plurality of formed wires are provided.
The conductor (11) is made of a superconducting material and has a long length.
The state where both ends in the hand direction are not connected to each other
It is characterized by being formed while maintaining. Claim 3
In the invention described in (1), the linear shape according to claim 1 or 2
Characterized in that the conductor (11) is used as a filter (F)
And

[0010] The symbols in parentheses of the above means indicate the correspondence with the concrete means described in the embodiments described later.

[0011]

According to the first and second aspects of the present invention, the high-frequency current flowing through both ends of the conventional single conductor can be diverted to the respective cross-sectional ends of the plurality of linear conductors. Therefore, a necessary high-frequency current can be caused to flow with low loss through the entire planar transmission line made of a normal conductive material. In this case, if the distance between the linear conductors in the line width direction is set to an appropriate range in which mutual electromagnetic influences are reduced, it is possible to keep the current carrying efficiency high and suppress an increase in the line width.

When the conductor width of the linear conductor is set to about 1 μm and the distance between adjacent conductors is set to about 0.8 to 1.5 μm, the line width can be increased while minimizing the electromagnetic effect between the conductor films. Can be suppressed .

Further, in the superconducting material critical current density is present, while reducing the current density below the critical current density at each linear conductor, increases the overall maximum current without enlarging increase the line width of the transmission line be able to.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 shows an example in which the present invention is applied to a microstrip transmission line using a superconducting material.
A ground conductor film 3 is formed on the entire lower surface. On the other hand, on the upper surface of the dielectric substrate 2, a large number of linear conductor films 11 having a width W1 are formed in parallel with each other in the high-frequency propagation direction (front-rear direction in the drawing) while maintaining the adjacent distance d. Make up. The width of the entire strip conductor film 1 is W
It is.

At this time, the current density distribution in the section of each linear conductor film 11 is as shown in FIG. As can be seen from the figure, since each linear conductor film 11 has a sufficiently small line width, an intermediate portion (part A in FIG. 5) where the current density is small as in a conventional strip conductor film formed of a single film. Hardly occurs, portions where the current density is high due to the Meissner effect appear at both ends of each linear conductor film 11, and the current amount greatly increases in the entire strip conductor film 1.

In the following, when this is theoretically examined, the Samir, which examines the characteristics of the microstrip transmission line, is described.
M. Report of El-Ghazally et al. (IEEE TRA
NSACTIONS ON MICROWAVE TH
EORY AND TECHNIQUES, Vol. 4
0, No. 3 1992 p. According to 499 to 508), when a single film of a superconducting material is used as the strip conductor film of the line, the relationship between the maximum current ImaxU flowing through the conductor film and the film width W ′ is approximated by Expression 1.

[0017]

[Number 1] ImaxUarufaW' ^1/2 way, a dielectric constant of about 10, using a dielectric substrate substrate thickness is 500 [mu] m, in order to realize the characteristic impedance 50Ω line, the strip conductor of the conventional single layer In the film, the film width W ′ (FIG. 4) needs to be about 500 μm.
Therefore, the film width W1 (FIG. 1) and the adjacent distance d of the linear conductor film 11 are both set to 1 .mu.m and 1 .mu.m at 1 .mu.m intervals.
When 250 linear conductor films 11 having a width are formed in parallel so that the entire width W of the strip conductor film 1 is about 500 μm, the maximum current Imaxs flowing through each linear conductor film 11 is expressed by the following equation. W1 ^1/2 = (W '/ 500) ^1/2

At this time, the maximum current ImaxC of the entire strip conductor film 1 is as shown in Expression 2.

[0019]

ImaxC = Imaxs × 250∝ (W ′ / 500) ^1/2 × 250 = (125 W ′) ^1/2 Therefore, a strip having a line width of 500 μm constituted by 250 linear conductor films of superconducting material The maximum current that can be carried by the conductor film 1 is 125 ^1/2 times (= ImaxC / ImaxU) that of a strip conductor film having the same line width formed of a single film (that is, the inputtable power is 125 times). Becomes).

The above-mentioned Samir M. El-Gha
Zally et al. consider the use of electrically isolated microstrip transmission lines. When a large number of linear conductor films are formed close to each other, the above theoretical value is obtained due to electromagnetic interference between adjacent conductor films. Rather, the current magnification becomes smaller to some extent. By the way, when a microstrip transmission line is constituted by a large number of linear conductor films, there is a concern that the circuit constant fluctuates and the line impedance changes. In this regard, the simulation results of the inventor show that a transmission line consisting of a single film having a width of 500 μm and a large number (250
It was confirmed that the line impedance hardly changed between the transmission line having a width of 500 μm as a whole by arranging the linear conductive films of the superconducting material of the present invention in parallel.

Although such a microstrip transmission line can be applied to various devices constituting a high-frequency circuit, it is particularly effective when applied to a filter circuit in that the size can be avoided. That is, FIG. 3 shows a filter F using the line structure of the present invention.
Is provided in the microstrip transmission line L,
This filter F has a width equal to the entire line width W and a length m equal to a half wavelength of the used high frequency. In such a filter F, a large resonance current flows in the central portion in the longitudinal direction. However, since the maximum allowable current amount is sufficiently large, the filter is formed into a disk shape (see FIG. 6).
Without this, the input power can be made sufficiently large. Therefore, it is possible to avoid a problem that the line width becomes excessive at the filter installation portion.

[0022] Samir M. According to the report by El-Ghazally et al., If the film width of the linear conductor film 11 is reduced and more conductor films are provided, the maximum current amount can be increased. The width of the linear conductor film is about 1 μm because the magnetic flux passing through the cross section is saturated at about 1 μm and the current density cannot be further uniformed, and the film formation by etching becomes difficult. Good to do.

It is advantageous to increase the distance between adjacent linear conductor films in that the mutual electromagnetic influence can be reduced. However, in order to suppress an increase in line width, the distance between adjacent lines is preferably smaller. . Therefore, in response to this reciprocal request, as described above, the adjacent distance is set to 0.8 to about the same as the film width.
When the thickness is about 1.5 μm, an increase in the line width can be suppressed while minimizing the electromagnetic influence between the adjacent conductor films.

Although the application of the present invention to a microstrip transmission line made of a superconducting material has been described in the above embodiment, the present invention can be widely applied to a flat transmission line having a flat conductor. Also, as described above, the present invention has an excellent effect of dramatically improving the transmission power of a transmission line using a superconducting material as a conductor material,
Even in a transmission line using a normal conductive material for the conductor material,
This has the effect that the loss during high frequency transmission can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a cutaway perspective view showing one embodiment of a microstrip transmission line to which the present invention is applied.

FIG. 2 is a graph showing a current density distribution of each linear conductor film.

FIG. 3 is a cutaway perspective view of a filter installation portion of a microstrip transmission line to which the present invention is applied.

FIG. 4 is a cutaway perspective view showing one embodiment of a conventional microstrip transmission line.

FIG. 5 is a graph showing a current density distribution of a conventional microstrip transmission line.

FIG. 6 is a cutaway perspective view of a filter installation portion of a conventional microstrip transmission line.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Strip conductor film (flat conductor), 11 ... Linear conductor film, 2 ... Dielectric plate, 3 ... Ground conductor film, L ... Microstrip transmission line (flat transmission line)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01P 3/08 H01P 1/203 JICST file (JOIS)

Claims (3)

(57) [Claims] A constant width (W1) is defined between a dielectric substrate (2) and an upper surface of the dielectric substrate (2 ).
In certain adjacent spacing (d) a Chi coercive, linear conductors longitudinally formed in plurality in parallel to constitute a planar transmission line (11)
With the door, said plurality formed linear conductor (11) is configured with a superconducting material
And the same constant at both ends in the longitudinal direction.
A high-frequency transmission line formed so as to keep the adjacent distance (d) . 2. A dielectric substrate (2) and an upper surface of the dielectric substrate (2) which is parallel to a longitudinal direction.
Conductors that are formed in a plurality to form a planar transmission line
(11), wherein the plurality of linear conductors (11) are made of a superconductive material.
At both ends in the longitudinal direction.
A high-frequency transmission line formed so as not to be connected. 3. The linear conductor (1 ) according to claim 1 or 2,
A filter circuit using 1) as a filter (F).