JP3433914B2 - Bandpass filter and method for adjusting passband of bandpass filter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bandpass filter and a method for adjusting the passband width of the filter, and more particularly to a narrow bandpass composed of a plurality of microstrip line resonators using a high temperature superconductor film. The present invention relates to a filter and a method of adjusting its pass bandwidth.

[0002]

2. Description of the Related Art A microstrip line resonator having an extremely high Q value can be manufactured by using a low-loss high-temperature superconductor film as a strip conductor and a ground conductor. By using a plurality of such resonators, a bandpass filter having a very narrow band with a relative bandwidth of several percent can be manufactured.

In such a narrow band filter, since the coupling coefficient between the resonators is extremely small, the frequency characteristics of the filter are influenced even by an extremely weak electromagnetic field. Therefore, the frequency characteristic of the filter is strongly influenced by the metal casing. Therefore, when a metal case of a normal conductor, which has a larger loss than a superconductor, is used, an electromagnetic field loss occurs on the inner wall of the case, and the Q value of the resonator using the superconductor film decreases. As a result, the narrow band pass characteristic of the filter also deteriorates.

For this reason, for example, the document "IEE Applied Super Conductivity Magazine, No. 2"
Pp. 571-2574, 1995 ", a proposal has been made to manufacture a housing from a bulk body of a superconductor, and Japanese Patent Laid-Open No. 7-22810 discloses a dielectric material. A microstrip line filter having a high Q value is formed by using oxide superconductors for the strip conductor and the ground conductor formed on both sides of the substrate and the constituent material of the shield casing or the inner surface of the shield casing. Is described.

[0005]

As described above, the conductor forming the filter is made of a superconductor and the casing for the shield is also made of a superconductor, so that a high Q value and high performance can be obtained. Although it is possible to realize a filter, when a housing is made of a bulk body of superconductor, a bulk body large enough to install a dielectric substrate on which a high-temperature superconductor film is formed inside is used. I need.
A bulk body of a high-temperature superconductor satisfying such a size and having good superconducting high frequency characteristics has not yet been developed.

Further, when a substance exhibiting superconductivity at a temperature lower than that of a high-temperature superconductor such as niobium is used, the operating temperature is also lowered, and the increase in cost is inevitable in terms of size and price of the refrigerator. .

As described above, constructing the shield casing itself or the inner surface of the shield casing with a superconductor has a problem in that it is difficult to manufacture and the manufacturing cost cannot be ignored.

In the narrow band pass filter as described above, the rough frequency characteristic is determined by the pattern of the strip conductor produced. However, the frequency characteristics of the filter also vary depending on the processing accuracy of the pattern and the substrate thickness and the variation of the dielectric constant in the substrate.

In particular, when the characteristic of the filter is a very narrow band of several percent of the specific band, the adjustment process after the pattern formation is essential. In that case, the center frequency of the pass band can be adjusted relatively easily by changing the resonator length by trimming or etching, but to adjust the pass band width, it is necessary to change the coupling coefficient between the resonators. There was, and it was extremely difficult.

An object of the present invention is to provide a means capable of realizing a band-pass filter composed of a plurality of microstrip line resonators at a relatively low cost, using a high-temperature superconductor film having a narrow band-pass characteristic less deteriorated. To provide.

Another object of the present invention is to provide a method capable of easily adjusting the frequency characteristics, particularly the pass band width, of the filter having the above structure.

[0012]

DISCLOSURE OF THE INVENTION The present invention provides a dielectric substrate having a plurality of microstrip line resonators using a high temperature superconductor film formed on both sides as a strip conductor and a ground conductor, and a ground conductor surface thereof. Is installed so that it is grounded to the inner wall of a metal casing made of a normal conductor, and a high-temperature superconductor film is formed that is grounded at high frequency only on the inner wall opposite to the inner wall on which the dielectric substrate is installed. Is characterized by.

Further, according to the present invention, in the above-mentioned bandpass filter, the passband of the bandpass filter is changed by changing a gap between the strip conductor and the high-frequency superconductor film which is opposed to the strip conductor and grounded at a high frequency. It is characterized by adjusting the width.

According to the present invention, the strip conductors and the ground conductors of the plurality of microstrip line resonators formed on the dielectric substrate are constituted by the high temperature superconductor film, and the ground conductors of the dielectric substrate are also provided. Since the inner wall of the metal casing facing the metal casing inner wall of the normal conductor installed so that its surface is grounded is formed of a high-temperature superconductor film grounded at high frequency, The ground conductor portion occupying a large area and the inner wall of the housing facing the ground conductor portion are both covered with the high temperature superconductor film.

Therefore, the region occupied by the normal conductor on the inner wall of the casing is only an extremely narrow region on the side wall of the casing, and the deterioration of the narrow bandpass characteristic of the filter due to the inner wall of the metal casing of the normal conductor can be reduced. .

Further, according to the present invention, by adjusting the gap between the high temperature superconductor film grounded at a high frequency and the surface of the filter, it is possible to adjust the amount of electromagnetic field coupling between the existing resonators. Therefore, the coupling coefficient between the resonators can be adjusted, and the pass bandwidth can be adjusted.

[0017]

1 is an exploded perspective view showing the configuration of a narrow band pass filter for explaining an embodiment of the present invention, and FIG. 2 is a casing band pass filter of the present invention. FIG. As shown in FIG. 1, the dielectric substrate 2 (first dielectric substrate)
A plurality of microstrip resonators composed of a ground conductor 3 and a strip conductor 4 of a high temperature superconductor film are formed on a plate) , and the dielectric substrate 2 is connected to the normal conductor metal casing 1
It is installed inside so that the ground conductor surface 3 is grounded to the inner wall of the metal housing 1.

Next, the dielectric substrate 5 (second dielectric substrate)
The high-temperature superconductor film 6 formed on the bottom surface of the casing is installed so as to be electrically connected to the metal casing 1 at its periphery and grounded at a high frequency to form a casing upper lid. Therefore, as shown in FIG. 2, the high temperature superconductor film 6 covers the inner wall of the upper surface of the housing, which is opposed to the ground conductor portion that occupies a larger area than the side wall portion of the inner wall of the housing 1. Become. As a result, the normal conductor occupies only the side wall in the inner wall of the housing, and deterioration of the narrow band pass characteristic of the filter due to the inner wall of the housing located on the upper surface of the strip conductor 4 being the normal conductor can be reduced.

As described above, according to the present invention, the high temperature superconductor film, which is grounded only on the inner wall surface facing the surface on which the microstrip resonator is installed, may be formed, so that the cost can be reduced. A high-performance bandpass filter can be realized.

By changing the height of the side wall of the metal casing 1, the pass band width of the filter can be adjusted. For example, when the height of the side wall of the metal housing 1 is reduced to narrow the gap between the strip conductor 4 and the high temperature superconductor film 6 on the opposing inner wall surface, the electromagnetic field coupling between the resonators is reduced. Therefore, the coupling coefficient between the resonators becomes smaller and the pass band width becomes narrower.

On the other hand, if the height of the side wall of the metal casing 1 is increased to widen the gap between the strip conductor 4 and the high temperature superconductor film 6 on the inner wall surface facing the strip conductor 4, the electromagnetic field coupling between the resonators increases. As a result, the coupling coefficient between the resonators becomes large, and the pass band width becomes wide.

By the way, when the inner wall of the upper surface of the housing is also covered with the normal conductor, a loss of the electromagnetic field occurs in the inner wall of the upper surface of the housing and the Q value of the resonator is lowered, so that the pass band width is widened. Therefore, it becomes difficult to obtain a desired narrow pass band width.

That is, the bandwidth adjusting method according to the present invention is an extremely effective method as means for adjusting the pass bandwidth in a narrow band pass filter including a plurality of microstrip resonators.

[0024]

FIG. 3 is a diagram showing the configuration of a narrow band pass filter for explaining the first embodiment of the present invention. A double-side polished magnesium oxide single crystal (100) substrate was used as the dielectric substrate, and a 0.8 μm thick c-axis oriented epitaxially grown YBa ₂ Cu ₃ O _7-δ thin film was used as the high temperature superconductor film.

Magnesium oxide substrate (first dielectric substrate
A plurality of hairpin type resonators made of strip conductors 10 are formed on the plate 8 by processing a high temperature superconductor film, and a ground conductor 9 of the high temperature superconductor film is formed on the bottom surface of the substrate 8. . This ground conductor 9 was soldered through a 0.1 mm thick indium sheet in a metal casing 7 in which brass was plated with 3 μm of gold.

Next, an indium wire 11 having a diameter of 1 mm was laid in the recess formed in the side wall of the housing 7 to form a high temperature superconductor film 13 formed on the bottom surface of the magnesium oxide substrate (second dielectric substrate) 12. The peripheral portion was soldered to form a housing upper lid made of a high-temperature superconductor film grounded at a high frequency.

This narrow band filter has a center frequency of 1.97.
At 1 GHz with a bandwidth of 1%, the unloaded Q value of the resonator is 1
A value of 50,000 was shown. This value is slightly lower than the value of 190,000 when the niobium housing is used, but is extremely high compared to the value of 40,000 when the gold-plated housing is used.

In other words, it is possible to reduce the loss of the electromagnetic field due to the inner wall of the metal case of the normal conductor, and to manufacture the filter with less deterioration of the narrow band pass characteristic. Further, by changing the height of the concave portion on the side wall of the metal casing 7, the substrate 8
The gap between the substrate 12 and the substrate 12 was adjusted to adjust the pass band width. When the gap was 3 mm, the specific bandwidth was 1%, but when the gap was 7 mm, the specific bandwidth was expanded to 1.5%.

FIG. 4 is a diagram showing the configuration of a narrow band pass filter for explaining the second embodiment of the present invention. As for the dielectric substrate and the high temperature superconductor film, the double-sided polished magnesium oxide single crystal (100) substrate and 0.8 as in the first embodiment.
Micron-thick c-axis oriented epitaxial growth YBa ₂ Cu
_{A 3} O _7-δ thin film was used.

In this embodiment, the magnesium oxide substrate (first
Dielectric Substrate 1) 14 is formed with a half-wave resonator composed of a strip conductor 15 by processing a high-temperature superconductor film, and a ground conductor of the high-temperature superconductor film is formed on the bottom surface of the substrate 14. 16 was formed. The grounding conductor 16 is connected to a metal housing 17 made of brass and plated with gold of 3 .mu.
It was soldered through a 1 mm thick indium sheet.

Next, as with the case 17, a magnesium oxide substrate is attached to a top lid 18 made of brass plated with 3 microns of gold.
(Second Dielectric Substrate) The high temperature superconductor film 20 formed on 19 is soldered to form a case upper lid made of the high frequency superconductor film grounded at a high frequency, and the upper lid is screwed to the case 17. did.

The forward-coupled narrow bandpass filter manufactured in this manner showed good narrow band pass characteristics, which were almost the same as those of the first embodiment. Furthermore, for example, the metal housing 1
The pass band width was adjusted by interposing a frame-shaped metal plate having a desired thickness between 7 and the upper lid 18 and screwing it to change the distance between the strip conductor 15 and the high temperature superconductor film 20. As a result, when the gap was 3 mm, the relative bandwidth was 0.8%, and when the gap was 7 mm, the relative bandwidth was 2.1%, and the adjustment range was wider than that of the first embodiment.

The present invention is not limited to the above embodiments, and within the scope of the technical idea of the present invention,
It can be appropriately changed and implemented.

[0034]

According to the present invention, the grounding conductor surface of the dielectric substrate having a plurality of microstrip line resonators using the high temperature superconductor film as the strip conductor and the grounding conductor on both sides is made of a normal metal casing. Since it is installed so as to be grounded to the inner wall of the body, and only the inner wall facing the wall is formed by another high-temperature superconductor film that is grounded at high frequency, the cost can be reduced, and the inner wall of the housing In, the area occupied by the normal conductor becomes narrower, the electromagnetic field loss due to the inner wall of the metal case of the normal conductor can be suppressed, and the deterioration of the narrow band pass characteristic can be reduced.

Further, in the band pass filter, the pass band width of the filter can be easily adjusted by changing the gap between the strip conductor and the high frequency superconductor film which is grounded at a high frequency and which faces the strip conductor. it can.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a bandpass filter according to an embodiment of the present invention.

FIG. 2 is a sectional view of a bandpass filter showing an embodiment of the present invention.

FIG. 3 is an exploded perspective view showing the first embodiment of the present invention.

FIG. 4 is an exploded perspective view showing a second embodiment of the present invention.

[Explanation of symbols]

1 metal housing 2 Dielectric substrate 3 Ground conductor of high temperature superconductor film 4 Strip conductor of high temperature superconductor film 5 Dielectric substrate 6 High temperature superconductor film 7 Brass metal casing with 3 micron gold plating 8 Magnesium oxide substrate 9 High temperature superconductor film 10 strip conductor 11 Indium wire with a diameter of 1 mm 12 Magnesium oxide substrate 13 High temperature superconductor film 14 Magnesium oxide substrate 15 Strip conductor 16 Ground conductor 17 metal housing 18 Top lid 19 Magnesium oxide substrate 20 High temperature superconductor film

Claims (3)

(57) [Claims] 1. A first dielectric substrate having a plurality of microstrip line resonators in which a strip conductor and a ground conductor are formed of a high-temperature superconductor film, and the first dielectric substrate .
The grounding conductor surface of the plate is installed in contact with its inner bottom surface
A metal housing having an open top surface and an upper lid covering the top surface of the metal housing.
In the band pass filter having bets, the metal housing is composed of a normal conductor, the
The upper lid is composed of a second dielectric substrate having a high-temperature superconductor film grounded only on the inner surface of the metal housing facing the inner bottom surface on which the first dielectric substrate is installed.
A band-pass filter characterized by being provided. 2. A first dielectric substrate strip conductor and the ground conductor has a high-temperature superconductor film plurality of micro-strip line resonator formed by the ground conductor surface of the first dielectric substrate and the metal housing of the open top which is placed in contact with its inner bottom, in the band pass filter and a lid covering an upper surface of the metal casing, said metal casing is composed of a normal conductor, the The upper lid has a second surface on which a high temperature superconductor film is formed.
A dielectric substrate and the high dielectric layer formed on the second dielectric substrate.
Of a normal conductor with a warm superconductor film in contact with its inner surface
A band-pass filter comprising a metal plate . 3.High temperature superconductivity for strip conductors and ground conductors
Multiple microstrip lines formed by conductor film
The first dielectric substrate having a resonator and the normal conductor
The grounding conductor surface is grounded to its inner bottom surface before
A metal housing on which a first dielectric substrate is installed;
High temperature facing the dielectric substrate of
Band having a second dielectric substrate on which a superconductor film is formed
A method for adjusting a pass bandwidth of a pass filter, comprising: The strip conductor formed on the first dielectric substrate
And the high temperature superconductor formed on the second dielectric substrate
Adjust the passband width by changing the membrane spacing
A method for adjusting the passband width of a bandpass filter characterized by
Law.