JPH1168405A - Filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly switch a microwave input signal by a low magnetic field. SOLUTION: In a co-planer band pass filter provided with a substrate 7 and a transmission line, a band passing half wavelength resonator 3 and a ground conductor 4 formed on the substrate 7, conductor parts of the line 1, the resonator 3 and the conductor 4 are formed by thin films having superconductivity. A layer 6 consisting of a magnetic substance (LaCa)MnO3 , a layer 6 obtained by substituting Sr for a part of Ca in the (LaCa)MnO3 or a layer 6 obtained by substituting Nd or Pr for a part or all of La in the (LaCa)MnO3 is formed between the line 1 and the conductor 4, wherein an external magnetism impressing means 8 for impressing a magnetic field is formed on the upper part of the magnetic substance layer 6. When a magnetic field is impressed from the means 8, the layer 6 is switched to conductive and a microwave input signal is reflected to execute switching control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a filter,
In particular, the present invention relates to a coplanar filter which is a superconducting applied technology in a satellite communication field, a mobile communication field, and the like.

[0002]

2. Description of the Related Art As a microwave filter in a microwave communication device, a planar circuit filter such as a microstrip formed on a dielectric substrate is used together with a waveguide filter or the like.

[0003] Waveguide filters are useful as low-loss narrow-band filters because of their high Q characteristics. However, most of them are generally three-dimensional, and are suitable for communication equipment that requires small size and light weight. Not. On the other hand, a planar circuit filter such as a microstrip circuit using a normal conductive metal such as gold for the conductor portion is suitable for reducing the size and weight, but has a low Q value as compared with the waveguide type filter, and thus has a low Q value. It is not suitable for application to microwave filters that require narrow band characteristics due to loss.

Therefore, a superconducting planar circuit filter having a higher Q value than a conventional waveguide filter has been developed by using a superconductor for the conductor portion of the planar circuit. As a result, a low-loss narrow-band filter that could not be realized conventionally can be realized with a planar circuit, and a very great advantage can be expected in terms of reducing the size and weight of communication devices. If an oxide superconductor having a high critical temperature is used as the superconductor, a superconducting microwave filter that can be easily cooled with a small refrigerator can be provided. Such a microwave filter may be used alone, but in general, it is often used in combination with a large number of filters to pass a plurality of signals having different frequencies, and a band corresponding to a plurality of frequencies is often used. It is used as a component of a filter bank composed of filters having pass characteristics.

In general, the above-mentioned band-pass filter merely shows a band-pass effect. However, when the band-pass filter is used as a filter bank, a signal of a specific frequency required by a radio signal environment or the like is generated at another time. Therefore, it is necessary to be able to selectively pass and block a radio signal by an external signal depending on circumstances such as being unnecessary, and the simple filter as described above cannot cope with the situation.

Therefore, a method of adding a switching function to a filter has been proposed. For example, JP-A-7-14
This is a method using a thermal switch as described in Japanese Patent Publication No. 2905. It takes advantage of the fact that the loss of the superconductor increases as the temperature rises. In the example of the microstrip bandpass filter shown in FIG. 4, a thermal switch 12 is provided near the end of the half-wavelength resonator 3 composed of a superconductor. In a state where current is not passed through the thermal switch 12, the superconducting filter passes a signal in a predetermined band, and in a state where current is passed through the thermal switch 12, a passing loss increases due to a decrease in superconducting characteristics due to a rise in temperature of the filter. Block signals in the band. However, such a switching band-pass filter has a problem that the switching speed is very slow, on the order of msec or more, because it utilizes heat generation and heat conduction. Further, this filter has a problem that the signal in the pass band is reduced to about -40 dB in the cut-off state, but the blocking state is insufficient and the influence of the signal of a minute level remains.

Therefore, switching is not performed by heat. For example, Japanese Patent Application Laid-Open Nos. 5-206705, 2-101801, and 1-1900
A filter has been proposed in which a mechanism for applying a magnetic field is provided as in the filter described in Japanese Patent Application Publication No. 01-301, and the switching of the passage or blocking of a microwave signal is performed by turning on and off the magnetic field. This utilizes the fact that when a magnetic field is applied so that a magnetic flux penetrates into the superconductor, the superconductor increases the conductor loss in the microwave band. Since the switching by the magnetic field is faster than the switching by the heat, the problem that the switching speed is slow can be improved.

For example, the filter described in Japanese Patent Laid-Open No. 5-206705 is a band rejection filter having a stripline or microstripline structure. When a magnetic field applying element is installed near the half-wavelength resonator and a superconducting characteristic is degraded by applying a magnetic field of several tens Oe (Oersted), the passing loss of the filter increases. Switching is performed according to a signal passing state at the time of application.

The filter described in Japanese Patent Application Laid-Open No. Hei 2-101801 is a band rejection filter in which a superconductor and a normal conductor are overlapped to constitute a half-wavelength resonator. When the conductor loss of the superconductor increases due to the application of a magnetic field, only the normal conductor portion operates as a half-wavelength resonator. Therefore, the resonance frequency of the superconducting resonator and the normal conduction resonator are designed to be different from each other to turn on and off the magnetic field. In this method, a signal is blocked and passed in a certain band.

Further, the filter described in Japanese Patent Application Laid-Open No. 1-190001 is a band-pass filter in which a half-wavelength resonator is formed by combining two superconductors having different critical magnetic fields. When an intermediate magnetic field of two large and small critical magnetic fields is applied, the conductor loss of the superconductor having a small critical magnetic field increases, and the resonance frequency of the half-wave resonator changes from that of the zero magnetic field. By utilizing this, switching is performed by shifting the pass frequency band of the filter between the state of the zero magnetic field and the state of the applied magnetic field.

[0011]

The prior art has a structure in which a magnetic field applying element is provided in the vicinity of a half-wavelength resonator that controls the filter characteristics, and a magnetic field is applied to the half-wavelength resonator. Then, by applying a high magnetic field of several tens Oe such that a magnetic flux penetrates into the superconductor to the half-wavelength resonator, the superconducting characteristics of the half-wavelength resonator are deteriorated, and the loss of the filter is increased.

However, if a magnetic flux enters the superconductor as described above, the magnetic flux remains in the superconductor even if the magnetic field is returned to zero by the pinning effect. When the magnetic flux enters, the loss in the superconductor increases even in the same zero magnetic field state in the frequency range of the microwave band as compared with the state where the magnetic flux does not enter. That is, in the filter having such a configuration, once a magnetic field of several tens Oe is applied, the filter does not completely return to the original low-loss state, and has a problem that the low-loss characteristic of the superconducting filter cannot be used.

As described above, in the prior art, by using the on / off of the magnetic field for the switching of the filter, there is a feature that the switching can be performed at a higher speed than when the thermal switch is used, but the characteristics of the filter are deteriorated. There was a problem.

(Object) It is an object of the present invention to provide a filter using a superconducting filter which enables a high-speed switching operation without deteriorating characteristics.

Another object of the present invention is to provide a low-loss filter using a superconducting filter capable of performing switching in a low magnetic field.

[0016]

In order to achieve the above object, a microwave band pass filter according to the present invention comprises a substrate, an input / output transmission line formed on the substrate, a band-pass half-wavelength resonator, A coplanar filter having a ground conductor, wherein the transmission line, the half-wavelength resonator, and each conductor portion of the ground conductor are formed of a thin film having superconductivity,
A part of the magnetic material (LaC) between the input transmission line and the ground conductor
a) A MnO ₃ layer is formed, and external magnetic applying means for applying a magnetic field is provided above the MnO ₃ layer.

In the magnetic layer, (LaC
a) It is assumed that a part of Ca in the MnO ₃ layer is replaced with Sr, or a part or all of La is replaced with Nd or Pr.

Further, in the above-mentioned filter, the external magnetic applying means is a coil provided on the upper inner wall of the package.

(Function) The conductor portion is used in a superconductive state by cooling. On / off control of a magnetic field applied from an external magnetic application means is performed. By setting the magnetic layer in a non-conductive state at zero magnetic field to a conductive state when a magnetic field is generated, a microwave input to the transmission line is made to be in a state of total reflection, thereby enabling a switching operation.

[0020]

Next, an embodiment in which the filter of the present invention is configured as a band-pass filter of a microwave filter will be described with reference to the drawings. 1 and 2
3A and 3B are cross-sectional views each showing a circuit pattern of the band-pass filter according to the present embodiment and a state where the filter is mounted on a package.

1 and 2, 1 is an input transmission line, 2 is an output transmission line, 3 is a half-wave resonator for bandpass, 4 is a ground conductor, 5 is a space between the transmission line and the ground conductor, Reference numeral 6 denotes a magnetic layer, 7 denotes a low-loss dielectric substrate, 8 denotes a magnetic field generating coil, and 9 denotes a package.

The band-pass filter of the present embodiment is a strip-shaped input transmission line 1 formed on a dielectric substrate 4.
An output transmission line 2, a strip-shaped half-wavelength resonator 3 formed between the input / output transmission lines 1 and 2, and a ground conductor 4 formed with a space 5 between each of the transmission lines. A coplanar bandpass filter is constructed.
Also, the conductor portions of the input / output transmission line 1, the half-wave resonator 3, and the ground conductor 4 are formed of a thin film having superconductivity such as an oxide superconductor to constitute a low-loss microwave filter. Further, the microwave filter includes a space between the input transmission line 1 and a ground conductor 4 near the input transmission line 1, and a thin magnetic material for switching between passing and non-passing of the input microwave signal so as to cover both of them. The layer 6 is formed.

The microwave filter formed with such a superconductive thin film and a magnetic material is mounted and installed in a package 9 having a magnetic field generating coil 8 as an external magnetic application means as shown in FIG. A filter that can be switched is constructed by attaching a connector or the like not shown. Here, the magnetic field generating coil 8 is provided so as to be located above the magnetic layer, and generates a magnetic field of a predetermined value when a current is applied to the coil 8 from the outside. Here, as the magnetic material, for example, (LaCa) Mn is used for the magnetic material layer.
When O ₃ is used, the magnetic layer shows the characteristics of a paramagnetic insulator when there is no magnetic field near the operating temperature of the oxide superconductor, and shows the characteristics of a ferromagnetic metal when a magnetic field is applied. .

Therefore, this microwave filter
When the magnetic field from the magnetic field generating coil 8 is not applied, the magnetic layer is an insulator and the thickness of the magnetic layer is thin, so that there is almost no influence on the characteristic impedance of the coplanar circuit. It operates, and only a signal in a specific frequency band of the microwave input signal passes with low loss. When a magnetic field is applied from the magnetic field generating coil 8, the input transmission line 1 is short-circuited to the ground conductor 4 because the magnetic layer becomes metallic. For this reason, the microwave input signal is completely reflected at the short-circuited portion, and signals of all frequencies are blocked.

In particular, in this microwave filter, since a superconductor is used for the transmission line 1 and the ground conductor 4, the magnetic flux is eliminated at the superconductor portion and concentrated in a narrow space of the coplanar structure. Even at the level, the magnetic flux density of the magnetic layer can be sufficiently increased. For this reason, the magnetic layer 6 transitions from an insulator to a metal even at a relatively low external magnetic field level of 10 Oe or less, so that switching can be performed at a lower external magnetic field level than in the prior art, and magnetic flux enters the superconductor. Thus, it is possible to prevent the superconducting characteristics from deteriorating.

As described above, the band-pass filter according to the present embodiment can completely control the passage and rejection of the microwave signal by applying and not applying a magnetic field. The switching operation can be performed by the / off signal.

As the magnetic layer used in the filter of the present invention, it is possible to select a different magnetic material depending on the setting of the transition temperature and the like according to the embodiment. In place of the (LaCa) MnO ₃ layer as the magnetic layer, part of Ca (calcium) is replaced by Sr (strontium), and La
A magnetic layer in which part or all of (lanthanum) is substituted with Nd (neodymium) or Pr (praseodymium) can be used. The transition temperature of the magnetic layer can be adjusted by such substitution. For example, by replacing La with Nd, the transition temperature is slightly lowered, so that the switching filter can be used up to a lower temperature than in the case of the (LaCa) MnO ₃ layer.

Also, in the filter of the present invention, a low magnetic field of 10 Oe or less can be generated with high accuracy by providing the magnetic field generating coil 8 as an external magnetic applying means on the upper inner wall of the package.

[0029]

Next, an example of the configuration of a 10 GHz band coplanar filter will be described as an embodiment of the present invention employing the basic configuration shown in FIGS. This coplanar waveguide filter has a center frequency 10GH _Z, fractional bandwidth of 2%, ripple 0.1dB
Are configured by a six-stage bandpass filter.

In manufacturing the filter, an MgO substrate is used as the low-loss dielectric substrate 7. An oxide superconductor having a critical temperature of about 90 K on a MgO substrate YBa ₂ Cu ₃ O
_x Form a thin film. The YBa ₂ Cu ₃ O _x thin film is formed on an MgO substrate to a thickness of about 5 mm by a laser vapor deposition method.
Further, the YBa ₂ Cu ₃ O _x thin film is processed into a filter circuit pattern as shown in FIG. 1 using ordinary lithography and argon ion milling. Next, the upper part of the input transmission line 1, the ground conductor 4 and the space 5 of the filter is
As shown in the figure, the magnetic material (LaCa) MnO ₃ was
The magnetic layer 6 having a Curie point of about 80K is formed by vapor deposition using a metal mask to a thickness of about 0 nm by a laser vapor deposition method. Finally, the produced filter is mounted and installed on a package 9 having a lid at the upper part of the package and a coil 8 for generating a magnetic field at the lower part of the lid as shown in FIG. 2 and necessary connectors are attached to complete the filter. Let it.

In this embodiment, YBa ₂ Cu ₃ O _x is used as the oxide superconductor. However, other oxide superconductors having a high Tc such as Bi-based or T1-based may be used. In addition, as the substrate, other than MgO, LaAlO ₃
It is possible to use a substrate on which an oxide superconductor such as the above can be epitaxially grown.

In evaluating the filter characteristics, the packaged filter is placed in a small refrigerator that can be cooled to about 50 K, and is about 80 K lower than the critical temperature of the YBa ₂ Cu ₃ O _x oxide superconductor. Then, microwave power transmission measurement and reflection measurement were performed by a vector network analyzer.

Firstly, when no current flows to the magnetic field generating coil 8, i.e., in the state of zero magnetic field, as in the filter characteristics 10 at a temperature 80K shown in FIG. 3, the filter in the vicinity of f ₀ ~10GHz It shows the characteristics of a normal band-pass filter that passes only necessary signals and blocks signals outside the band. Also, the amplitude characteristic is flat within the pass band,
The transmission loss shows a good filter characteristic of 0.5 dB or less.

When the same filter is manufactured using gold, 3
A large passage loss of dB or more is observed. The reason why the filter of this embodiment has a small loss is that the superconductor has a very small surface resistance. In addition, the reflection loss within the band is also 20 dB.
This is the level at which there is no problem. In addition, the filter characteristics in this case are almost the same as those without the magnetic layer and the coil, so it can be confirmed that the above-described magnetic field applying mechanism hardly affects the filter characteristics.

Next, when a current is passed through the magnetic field generating coil 8 to generate a magnetic field of 10 Oe or less, the magnetic material (L
The aCa) MnO ₃ layer undergoes a phase transition from paramagnetism to ferromagnetic, and the electrical properties of the (LaCa) MnO ₃ layer undergo a phase transition from eclipse to metal.

When the (LaCa) MnO ₃ layer is an insulator, the input transmission line 1 and the ground conductor 4 are electrically insulated, so that the input transmission line 1 and the ground conductor 4 are almost the same as the case without the (LaCa) MnO ₃ layer. However, when the (LaCa) MnO ₃ layer becomes metallic, the input transmission line 1 and the ground conductor 4 are short-circuited. In this case, the microwave signal input to the filter is completely reflected. As shown in the filter characteristic 11 of FIG. 3, the characteristic of the filter in the completely rejected state can be obtained even near the pass band. When the current of the magnetic field generating coil 8 is returned to zero, the filter again shows normal band pass characteristics as shown by a characteristic 10.

As described above, in this embodiment, the characteristic of the band-pass filter is switched between the normal passing state and the completely blocking state by turning on / off a very low magnetic field of 10 Oe or less by the coil. be able to. In a conventional switching filter using a magnetic field,
Although a magnetic field of about several tens of Oe was required, and a completely blocked state of a signal could not be realized, the filter of the present invention employs a configuration in which a magnetic layer is provided between an input / output transmission line and a ground conductor. These problems can be solved.

Next, regarding the magnetic layer 6, (LaCa)
A filter using a magnetic layer in which a part of Ca was replaced by Sr instead of the MnO ₃ layer was prototyped, and the characteristics were measured. As a result, the Curie point increased to about 85K. In this case, the magnetic field sensitivity having the same switching characteristics as in FIG. 3 is improved. That is, the temperature at which switching in a low magnetic field is possible is about 85 K, and switching at a higher temperature and in a low magnetic field can be realized.

As a result of experimentally producing a filter in which a part of La of the (LaCa) MnO ₃ layer was replaced with Nd and measuring the characteristics, the Curie point was reduced to about 70K. Switching characteristics similar to those in FIG. 3 were observed for this filter. Considering that the characteristics of the superconducting filter improve as the temperature decreases and the pass loss in the band decreases, there is a great merit that the filter can be switched around 70K.

In the above embodiments and the like, the filter characteristics are described as band-pass filter characteristics. However, it is apparent that the present invention can be applied to other filter characteristics. The position where the magnetic layer is formed is not limited to the input transmission line, but may be the output transmission line or a filter portion such as a half-wavelength resonator in consideration of the influence on the filter characteristics. In essence, it is apparent that it is sufficient to form the transmission line portion so as to extend between a portion of the transmission line portion where the signal is transmitted and the adjacent ground conductor portion via the space and the space. Further, it is needless to say that the magnetic layer is not limited to a single layer, and a plurality of magnetic layers may be formed at appropriate portions of the coplanar filter.

[0041]

According to the present invention, the conductor layer of the coplanar filter is formed of a superconductor, a magnetic (LaCa) MnO ₃ layer or the like is formed between the transmission line and the ground conductor, and an on / off magnetic field is applied to the upper portion. Since the external magnetic applying means is provided, the blocking and passage of the microwave signal can be completely controlled by applying and not applying a low magnetic field, thereby enabling a high-speed switching operation of the filter characteristics.

That is, since a superconductor is used for the transmission line and the ground conductor, the magnetic flux is eliminated in the superconductor portion and concentrated in a narrow space of the coplanar structure. Density can be increased. For this reason, the magnetic layer transitions from an insulator to a metal even at a relatively low external magnetic field level of 10 Oe or less, so that switching can be performed at a lower external magnetic field level than in the prior art. In addition, since a magnetic field is used for switching, the speed is higher than that of a switching principle using a thermal switch or the like. Furthermore, since the magnetic layer is an insulator and the thickness of the magnetic layer is thin, there is almost no influence on the characteristic impedance of the coplanar circuit, and the operating characteristics of the band-pass filter and the like are not deteriorated.

Since the filter of the present invention can be operated at a relatively low external magnetic field level, there is no disadvantage that a magnetic flux penetrates into the superconductor and deteriorates the superconducting characteristics. Further, the magnetic material (LaCa) MnO ₃ layer is
By using a magnetic layer in which part of a is substituted with Sr or a magnetic layer in which part or all of La is substituted with Nd or Pr, the boiling point and the Curie point characteristics and the like can be adjusted.

Further, in the filter of the present invention, the magnetic layer and the magnetic field generating portion required for switching do not always need to be provided near the half-wavelength resonator, but are provided in the input / output transmission line, so that the filter characteristics can be improved. There is also an advantage that the filter characteristic is hardly affected because the half-wavelength resonator part which governs the distance is separated from this mechanism.

Since such a filter can selectively pass and block a required signal of a specific frequency at a high speed, it is suitable for use as a filter bank and contributes to high performance of microwave communication equipment. .

In particular, the oxide superconductor has a feature that the surface resistance in a frequency band of a microwave band used for communication equipment such as satellite communication is about three orders of magnitude lower than that of a normal metal such as gold. In addition, since the critical temperature for superconductivity is higher than the boiling point of liquid nitrogen, 77 K, the filter of the present invention can be easily and inexpensively cooled with a small refrigerator, and is applied to microwave band communication equipment. Can be expected.

[0047]

[Brief description of the drawings]

FIG. 1 is a diagram showing a circuit pattern of a pass band filter according to an embodiment of the present invention.

FIG. 2 is a diagram showing a cross-sectional structure in which the passband filter according to the present embodiment is mounted and installed in a package.

FIG. 3 is a diagram showing frequency characteristics of a filter according to the present invention.

FIG. 4 is a diagram showing a circuit pattern of a conventional filter.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 input transmission line 2 output transmission line 3 half-wave resonator 4 ground conductor 5 space 6 magnetic layer 7 dielectric substrate 8 magnetic field generating coil 9 package 10 filter passing characteristic when magnetic field is zero 11 filter passing when magnetic field is applied Characteristic 12 Thermal switch

Claims (5)

[Claims] 1. A coplanar filter in which a conductor portion is formed of a thin film having superconductivity, wherein a magnetic layer formed using a magnetic material (LaCa) MnO ₃ between a transmission line and a ground conductor; An external magnetism applying means for applying a magnetic field to the magnetic layer. 2. A coplanar filter comprising a substrate and input and output transmission lines, a band-pass half-wave resonator and a ground conductor formed on the substrate, wherein the transmission line, the half-wave resonator and A magnetic layer formed by forming a conductor portion of a ground conductor from a thin film having superconductivity, and using a magnetic material (LaCa) MnO ₃ between an input transmission line or an output transmission line and the ground conductor; And an external magnetic applying means for applying a magnetic field to the filter. 3. The method according to claim 1, wherein the magnetic layer comprises a magnetic material (LaCa).
Instead of MnO ₃ magnetic (lacA) according to claim 1 or 2 filter further characterized in that a part of Ca of MnO ₃ using the magnetic material was replaced with Sr. 4. The magnetic material layer has a magnetic material (LaCa).
Magnetic instead of MnO ₃ (lacA) according to claim 1 or 2 filter further characterized in that some or all of the MnO ₃ of La using a magnetic material was replaced with Pr or Nd. 5. The filter according to claim 1, wherein the external magnetic applying means is a magnetic field generating coil provided on an upper inner wall of the package.