JPH05175710A - Temperature compensation type magnetostatic surface wave filter - Google Patents

Abstract

PURPOSE:To prevent a center frequency from being increased due to the rise to a temperature by forming the temperature characteristic in the magnetic field of a permanent magnet to be opposite in the polarity to the temperature characteristic of the strength of the magnetization of a ferromagnetic single crystal thin film. CONSTITUTION:A metallic thin film pattern 3, an input side strip transducer 4, an output strip transducer 5 are formed on a dielectric board 1. Moreover, a single crystal plate 2 with a ferromagnetic single crystal thin film formed to its one side is fitted onto the board 1. A single crystal base 2 with a ferromagnetic single crystal thin film formed onto its one side is fitted to the board 1. Permanent magnets 7, 8 for DC outer magnetic field application are fitted to the inside of both legs of a yoke 10. Then magnet 8 is connected to the magnet 7 so that the magnetic field formed on the ferromagnetic single crystal thin film by the magnet 8 is opposite to the magnetic field formed on the ferromagnetic single crystal thin film by the magnet 7. Thus, the composed magnetic field has the positive temperature characteristic and the increase in the center frequency of the filter due to the rise of the temperature is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetostatic surface wave filter used in microwave radio equipment, and more particularly to a temperature compensation type magnetostatic surface wave filter having improved temperature characteristics.

[0002]

2. Description of the Related Art FIG. 2 shows a configuration example of a conventional magnetostatic surface wave filter. The dielectric substrate 1 is made of alumina ceramic, and a metal thin film pattern 3, an input side strip (parallel strip in this conventional example) transducer 4, and an output side strip (this conventional substrate) are formed on the dielectric substrate by using, for example, a photoetching method. (Parallel strip in the example)
The transducer 5 is formed. Further, a single crystal substrate (hereinafter referred to as a sample) 2 having a ferromagnetic single crystal thin film formed on one surface is attached to the dielectric substrate 1. This sample 2 is, for example, a yttrium / iron / garnet (YIG) thin film formed on a gadolinium / gallium / garnet (GG) substrate, and the thin film side faces the dielectric substrate 1. Arranged to do. A permanent magnet for applying a DC external magnetic field, for example, a ferrite magnet 6 is attached to the inside of both legs of the U-shaped yoke 10 in section, and the ferrite magnet 6 is attached to the ferromagnetic thin film of the sample 2. A DC magnetic field is applied parallel to the plane and parallel to the longitudinal direction of the parallel strip transducer. In addition,
The arrow indicates the magnetization direction of the permanent magnet.

The operation of the magnetostatic surface wave filter thus constructed will be described below. A high frequency signal input from the point A is transmitted along the metal thin film pattern 3 and then to the input side parallel strip transducer 4. Transmitted along. A magnetostatic surface wave is excited on the ferromagnetic thin film of the sample 2 by the high frequency magnetic field generated from the input side parallel strip transducer 4, and the magnetostatic wave is propagated in the direction of the output side parallel strip transducer 5. Next, the output side parallel strip transducer 5 converts the energy of the magnetostatic wave into a high frequency magnetic field and transmits it to point B along the microstrip line. Therefore, from point A to B
The transmission characteristic to the point is a bandpass characteristic in which only the frequency band determined by the magnitude of the applied magnetic field, the magnitude of the magnetization of the ferromagnetic thin film and the shape of the input / output parallel strip transducer passes.

[0004]

In the above-described conventional filter, the magnitude of the magnetization of the ferromagnetic single crystal thin film becomes smaller as the ambient temperature of the filter rises. Further, the magnitude of magnetization of the permanent magnet 6 which is a ferrite magnet is also reduced, and thus the magnitude of the DC external magnetic field is also reduced. Generally, the center frequency of the magnetostatic surface wave filter is determined by the propagation velocity of the magnetostatic surface wave and the electrode period length of the parallel strip transducer. And the propagation velocity of the magnetostatic surface wave described above, when the magnitude of the magnetization of the ferromagnetic single crystal thin film or the magnitude of the DC external magnetic field increases,
It fluctuates such that it becomes larger and becomes smaller as it becomes smaller.

Here, the electrode period length of the parallel strip transducer has a small variation with respect to temperature as compared with the propagation velocity of the magnetostatic surface wave and can be ignored. Therefore, the fluctuation of the center frequency of the magnetostatic surface wave with respect to the temperature is due mainly to the magnitude of the magnetization of the ferromagnetic single crystal thin film and the magnitude of the DC external magnetic field. Has a drawback that the transmission speed is reduced, and as a result, the center frequency of the filter is significantly increased.

Therefore, an object of the present invention is to provide a temperature-compensated magnetostatic surface wave filter which prevents the center frequency of the magnetostatic surface wave filter from increasing due to temperature rise.

[0007]

In order to achieve the above-mentioned object, the present invention provides a single crystal substrate on which a ferromagnetic single crystal thin film is formed, and a DC external magnetic field on the ferromagnetic single crystal thin film. A magnetostatic surface wave filter comprising a permanent magnet for applying a magnetic field, wherein at least two or more permanent magnets are combined so as to have different magnetizing directions, and the temperature characteristic of the magnitude of the magnetic field of the combined permanent magnets is increased by the strong magnetic field. A temperature-compensated magnetostatic surface wave filter is adopted which is configured so as to have a polarity opposite to the temperature characteristic of the magnitude of magnetization of the magnetic single crystal thin film.

[0008]

The magnetostatic surface wave filter of the present invention utilizes that the center frequency of this filter mainly depends on the magnitude of the magnetization of the ferromagnetic single crystal thin film and the magnitude of the DC external magnetic field. ..

Generally, when the magnitude of the magnetization of the ferromagnetic single crystal thin film increases, the propagation velocity of the magnetostatic surface wave increases, and when the magnitude of the DC external magnetic field increases, the propagation velocity of the magnetostatic surface wave also increases. Also grows. Therefore, if the magnitude of the magnetization of the ferromagnetic single crystal thin film and the magnitude of the DC external magnetic field have opposite polarities as the temperature characteristics, the propagation velocity of the magnetostatic surface wave becomes constant with respect to the change of the ambient temperature, As a result, the center frequency of the filter does not change. In the present invention, the magnitude of the magnetization of the ferromagnetic single crystal thin film becomes smaller as the temperature rises, that is, the magnitude of the DC external magnetic field changes with the temperature in consideration of having the negative temperature characteristic. It is configured such that it becomes larger as the temperature rises, that is, it has a positive temperature characteristic. Specifically, a permanent magnet that applies a DC external magnetic field is made by combining at least two permanent magnets so that the magnetization directions are different, and the combined magnetic field is configured to have a positive temperature characteristic.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described with reference to the drawings.

Referring to FIG. 1, which illustrates an embodiment of the present invention,
A magnetostatic surface wave filter of the present invention is shown. This filter is the same as the conventional filter except that two permanent magnets 7 and 8 are used instead of the permanent magnet 6, and therefore detailed description of the same components will be omitted.

Ferrite magnets, for example, are used as the above-mentioned permanent magnets 7 and 8. For example, the magnetic field produced on the ferromagnetic single crystal thin film of the permanent magnet 7 is 1000 Oe, its temperature coefficient is 0.1% / ° C, and the magnetic field produced on the ferromagnetic single crystal thin film of the permanent magnet 8 is 300 Oe. And its temperature coefficient is 0.4
% Of the permanent magnet 7 is used, the magnetic field created on the ferromagnetic single crystal thin film of the permanent magnet 8 is the ferromagnetic material of the permanent magnet 7 as shown in the magnetization direction of the arrow in FIG. The connection is made in the direction opposite to the magnetic field created on the single crystal thin film. Then, the magnitude of the synthetic magnetic field formed on the ferromagnetic single crystal thin film is 700 (1000-300) Oe, and the synthetic temperature coefficient is -0.029% [(0.1X1000-
0.4 × 300) / 700].

[0013]

[Experimental Example] Next, an experimental example using the permanent magnet configured as described above will be described. In this experimental example, Y. I. G
A material having a saturation magnetization of 1750 gauss and a film thickness of 20 μm was used for the thin film, and a magnetic field of 780 oersted was applied to the sample 2 by the magnet described above. The pass band was 3.8 GHz, and the temperature coefficient of its center frequency was about 100 ppm / ° C.
This value is significantly improved as compared with the temperature coefficient of the center frequency of the conventional magnetostatic surface wave filter of 1000 ppm / ° C to 3000 ppm / ° C.

[0014]

As described in detail above, the present invention provides a temperature-compensated magnetostatic surface having a temperature characteristic of a DC external magnetic field that suppresses fluctuations in the center frequency of a magnetostatic surface wave filter against fluctuations in ambient temperature. A wave filter can be provided.

[Brief description of drawings]

FIG. 1 is a plan view of a magnetostatic surface wave filter according to an embodiment of the present invention.

FIG. 2 is a plan view of a conventional magnetostatic surface wave filter.

[Explanation of symbols]

 1 Dielectric Substrate 2 Sample 3 Metal Thin Film Pattern 4 Input Side Parallel Strip Transducer 5 Output Side Parallel Strip Transducer 6 Permanent Magnet 7 Permanent Magnet 8 Permanent Magnet 10 Yoke

Claims (1)

[Claims] 1. A magnetostatic surface wave filter comprising a single crystal substrate on which a ferromagnetic single crystal thin film is formed, and a permanent magnet for applying a DC external magnetic field to the ferromagnetic single crystal thin film, By combining at least two permanent magnets with different magnetization directions, the temperature characteristics of the magnetic field magnitude of the combined permanent magnets are opposite to the temperature characteristics of the magnetization magnitude of the ferromagnetic single crystal thin film. A temperature-compensated magnetostatic surface wave filter, which is configured so as to have a polarity.