JPH04152702A - Magnetostatic surface wave filter - Google Patents

Abstract

PURPOSE:To suppress a ripple within a pass band by selecting the width of a ferromagnetic substance single crystal thin film to be a multiple of 10 or over and 20 or below of an electrode pitch of each of parallel strip transducer. CONSTITUTION:The electrode pitch of each of parallel strip transducers 7, 8 is usually selected to be 100-1000mum. In this embodiment, the pitch is selected to be 600mum and individual four inputs and outputs are provided to this filter. Moreover, a glass plate whose thickness is 450mum is employed for spacers 3, 4. When the width of the single crystal thin film is selected to be, e.g. a multiple of 13 (8mm) of the electrode pitch (600mum) of the parallel strip transducers 7, 8, no ripple is observed and an excellent pass band characteristic is realized. Moreover, when the width of a Y. I. G. electrode is selected to be a multiple of 20 or over and 30 or below of the electrode pitch of the parallel strip transducers 7, 8, this is in consistent with miniaturization being substantial characteristic of the magnetostatic surface wave filter and not practical.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetostatic surface wave filter used in a microwave radio device, and more particularly to a magnetostatic surface wave filter that reduces ripple within a passband.

(Prior Art) An example of the configuration of a normal magnetostatic surface wave filter is shown in FIG. 1
2 is a dielectric substrate, 2 is a single crystal substrate with a ferromagnetic single crystal thin film formed on one side (hereinafter referred to as sample), 3 and 4 are spacers, 5 is a metal thin film pattern formed on dielectric substrate 1, 6 is
is a ground conductor, 7 is an input parallel strip transducer, and 8 is an output parallel strip transducer. As sample 2, for example, a thin film of yttrium, iron, garnet (Y, 1.G,) is formed on a gallium, gallium, garnet (G, G, G, ) substrate, and the thin film side is placed on a dielectric substrate. 1 with a spacer 3.4 in between.

The dielectric substrate I is, for example, Marumina ceramic.

The metal thin film pattern 5, the input side parallel strip transducer 7, and the output side parallel strip transducer 8 are formed, for example, on a dielectric substrate l using a photoetching method, and the metal thin film pattern 5, the dielectric substrate 1 and the ground conductor 6 constitute a microstrip line. The spacer 3.4 is made of a material with low magnetic permeability and low permittivity.

In such a configuration, the high frequency signal input from point A is transmitted along the microstrip line to the input side parallel strip transducer 7 installed below the sample 2. Here, sample 2 is magnetized by applying a DC magnetic field parallel to the Y, I, G films and parallel to the longitudinal direction of the electrodes of the parallel strip transducer. 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 7, and the magnetostatic surface wave propagates in the direction of the output side parallel strip transducer 8. Next, the output side parallel strip transducer 8 converts the magnetostatic surface wave energy into a high frequency magnetic field, which is transmitted to point B along the microstrip line. Therefore, the transmission characteristic from point A to point B is a bandpass characteristic in which only the frequency band determined by the magnitude of the applied DC magnetic field, the magnitude of saturation magnetization of the ferromagnetic thin film, and the shape of the input/output parallel strip transducer passes. shows.

(Problem to be solved by the invention) In the filter with the above configuration, Y, 1. G.

The width of the thin film has a large effect on the propagation characteristics of the widthwise mode of magnetostatic surface waves. This is Y, 1. G, If the width of the thin film is sufficiently wider than the wavelength of the magnetostatic surface wave, the difference in propagation speed between each width direction mode is small, but Y, 1. G.
This means that when the width of the thin film becomes comparable to the wavelength of the magnetostatic surface wave, there will be a large difference in propagation speed between each radial mode. For this reason, in a magnetostatic surface wave filter in which y, r, c, and the width of the thin film are about the same as the wavelength of the magnetostatic surface wave, there is a ripple pull in the passband caused by the difference in propagation speed between each widthwise mode. arise.

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The sample width is set to eight times the wavelength of the magnetostatic surface wave to be excited, that is, the electrode period of the parallel strip transducer. Here, the electrode period of the parallel strip transducer and the wavelength of the excited magnetostatic surface wave match.

Y, 8 times wider than the electrode period of the parallel strip amplifier transducer used here, 1. G.

As described above, in a thin film, ripple occurs within the passband due to the widthwise mode.

As described above, conventional magnetostatic surface wave filters have the drawback that ripples within the passband cannot be suppressed sufficiently.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a magnetostatic surface wave filter that can sufficiently suppress the ripple within the passband.

(Means for Solving the Problem) In order to achieve this object, the present invention uses a single crystal substrate on which a ferromagnetic single crystal thin film is formed, and uses a parallel strip transducer to generate a magnetostatic surface. This magnetostatic surface wave filter excites waves, and is characterized in that the width of the ferromagnetic single crystal thin film is 10 times or more and 20 times or less the electrode period of the parallel strip transducer.

(Function) The magnetostatic surface wave filter according to the present invention utilizes the fact that the propagation speed of each width direction mode of the magnetostatic surface wave varies greatly depending on the width of the Y, I, C, and thin films used.

Figure 2 shows f//! ! A schematic diagram shows how the width direction mode propagates in the IM1 surface wave filter. The reason why the width direction mode is generated in this manner is that the efficiency of the magnetostatic surface waves needs to be attenuated exponentially at the ends of the Y, I, G, and thin films in the width direction.

The difference in propagation speed between these width direction modes is Y.

1. We theoretically investigated how much G changes by changing the width of the thin film. An example is shown in FIG.

This figure shows Y,1. It shows the dispersion characteristics of magnetostatic surface waves when the width of the G and L films is 1- and 8-hole. In this diagram,
The slope of each curve indicates the propagation speed of each width direction mode. Therefore, Y, I, G.

Compared to when the width of the thin film is 1 ml, when the width of the thin film is 8 m, the difference in the propagation speed of each width direction mode is smaller. As a result, the ripple within the passband caused by the difference in propagation speed of each width direction mode is Y, 1. G. This becomes noticeable when the width of the thin film is narrow.

The present invention was obtained as a result of intensive study of this result.

(Example) Next, the present invention will be explained with reference to the drawings.

Embodiments of the invention have the same major components as in FIG. 1, namely the input parallel strip transducer 7.
, an output side parallel strip transducer 8, and a sample 2 in which a ferromagnetic single crystal thin film was formed on a single crystal substrate. Here, sample 2 was prepared using G, G, G, Y, 1. G: A single crystal thin film was formed. Further, the input side and output side parallel strip transducers 7.8 are patterned by photoetching after forming a gold thin film by vacuum evaporation. The electrode period of a parallel strip transducer is usually 100 to 1000 μm, but here it was set to 600 μm, and there were four inputs and four outputs. Furthermore, a glass plate with a thickness of 450 μm was used as the spacer 3.4. In FIG. 4 (1) to (4), Y, 1. G shows the change in frequency characteristics of the magnetostatic surface acoustic wave filter when the width of the thin film is changed. In (2) to (4), ripples are observed near the peak of the passband. On the other hand, in (1), the electrode period of the parallel strip transducer is 600μ
In the case of a single crystal thin film with a width of 8f1 and 13 times m, no such pull was observed, indicating good passband characteristics.

Also Y, 1. When the width of the G, \iI film was made wider than the example shown in Fig. 4, no significant change was observed. but,
y, r, c, It is not realistic to make the width of the thin film more than 20 times the electrode period of the parallel strip transducer because it contradicts miniaturization, which is the original feature of magnetostatic surface wave filters.

(Effects of the Invention) As described above, according to the present invention, it is possible to construct a magnetostatic surface wave filter in which ripples do not occur within the pass band, and is industrially very effective.

[Brief explanation of the drawing]

FIG. 1(a) is a perspective view of a conventional magnetostatic surface wave filter. FIG. 1(b) is a plan view of FIG. 1(a). FIG. 1(c) is a cross-sectional view taken along the line ■-■ in FIG. 1(b). FIG. 2 shows a schematic diagram showing the propagation of the width direction mode, and FIG. 3 shows the dispersion characteristics of magnetostatic surface waves. Figure 4 is Y, 1. FIG. 6 is a diagram showing the frequency characteristics of the magnetostatic wave filter when the width of the G, \ii film is changed. DESCRIPTION OF SYMBOLS 1... Alumina substrate, 2... Sample in which a ferromagnetic single crystal thin film is formed on a single crystal substrate, 3-4... Spacer,
5... Microstrip line, 6... Ground conductor,
7... Parallel strip transducer on the input side, 8... Parallel strip transducer on the output side. Patent applicant: Sumitomo Metal Mining Co., Ltd. (b) (c) Figure 1゜, m' krrr+ Figure

Claims (1)

[Claims] A magnetostatic surface wave filter that excites magnetostatic surface waves using a parallel strip transducer using a single crystal substrate on which a ferromagnetic single crystal thin film is formed, A magnetostatic surface wave filter characterized in that the width is 10 times or more and 20 times or less the electrode period of the parallel strip transducer.