JPH04152701A - Magnetostatic surface wave filter - Google Patents

Abstract

PURPOSE:To suppress spurious response by placing a spacer whose thickness is a multiple of 0.75 or over and 5 or below of an electrode pitch of each of parallel strip transducer between the parallel strip transducer and a ferromagnetic substance single crystal thin film. CONSTITUTION:A coupling quantity between a magnetostatic surface wave and a high frequency signal of a magnetostatic surface filter depends on the thickness of a spacer placed between a parallel strip transducer and a ferromagnetic substance single crystal thin film. A glass plate is adopted for the material of the spacer 3. The electrode pitch of each of the said transducers 6, 7 is selected normally to be 100-1000mum, and in this embodiment, the pitch is selected to be 600mum. That is, when the spacer whose thickness is 0.45mm (a multiple of 0.75), no spurious response is observed. Thus, it is required to select the thickness of the spacer 3 to be a multiple of 0.75 of the electrode pitch of each of the said transducers 6, 7. On the other hand, the insertion loss with a desired response is increased by selecting the thickness of the spacer to be a multiple of 5 of the pitch or over especially.

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 with improved spurious characteristics.

(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 is a spacer, 4 is a metal thin film pattern formed on the dielectric substrate 1, and 5 is a ground conductor. , 6 is an input side parallel strip transducer, and 7 is an output side parallel strip transducer.

As sample 2, for example, an indium-iron-garnet (Y, r, G,) I film was formed on a gadolinium-gallium-garnet (C, C, C,) substrate.
Y, I, (:,,\iI are arranged with the spacer 3 in between so that the film side faces the dielectric substrate 1.

The dielectric substrate 1 is made of, for example, Marumina ceramic.

The metal thin film pattern 4, the input side parallel strip transducer 6, and the output side parallel strip transducer 7 are formed, for example, on the dielectric substrate 1 using a photoetching method, and the metal thin film pattern 4, the dielectric substrate l and the ground conductor 5 constitute a microstrip line. The spacer 3 is made of a material with low magnetic permeability and low dielectric constant.

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 6 installed below the sample 2. Here, sample 2 is magnetized by applying a DC magnetic field parallel to the plane of the ferromagnetic single crystal thin film in the longitudinal direction of the parallel strip transducer. A high frequency magnetic field generated from the input parallel strip transducer 6 excites magnetostatic surface waves on the ferromagnetic thin film of the sample 2, and the magnetostatic surface waves propagate toward the output parallel strip knob transducer 7. Next, the output side parallel strip transducer 7 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.

(Problems to be Solved by the Invention) In the filter having the above configuration, the amount of coupling between the high frequency signal and the magnetostatic surface wave is controlled by the thickness of the spacer. This is because by appropriately selecting the amount of coupling between the high frequency signal and the magnetostatic surface wave, only the desired frequency band can be excited and unnecessary spurious responses can be suppressed. However, conventional surface wave filters, such as -, l5hak, E, Ree
se, R, Beer and Gate, Foimler's IEE
E Transaction on Magnetic
s Vol.

20 No., 5 pp., 1229-1231 “Tunable magnetostatic”
wave oscillator sustaining pure
and doped YIG films, the spacer thickness is set to 0.65 times the wavelength of the magnetostatic surface wave to be excited, that is, the electrode period length of the parallel strip transducer.With this spacer thickness, A spurious response is observed on the high frequency side of the passband.This is because the amount of coupling between the energy of the high frequency magnetic field and the energy of the magnetostatic surface wave in the parallel strip transducer does not depend on the actual spacer thickness (i.e., This is because it is determined by the thickness of the spacer relative to the wavelength of the magnetostatic wave.

In the above-mentioned paper, the electrode period length of the parallel strip transducer is 600 μm, whereas the spacer thickness is set to 390 μm.

As described above, conventional magnetostatic surface wave filters have the disadvantage that spurious responses cannot be suppressed sufficiently.

Therefore, an object of the present invention is to provide a magnetostatic surface wave filter that can sufficiently suppress spurious responses.

(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. A magnetostatic surface wave filter that excites waves, wherein a thickness between the parallel strip transducer and the ferromagnetic single crystal thin film is 0.75 times or more and 5 times or less the electrode period length of the parallel strip transducer. It is characterized by the fact that a spacer with a certain thickness is installed.

(Function) In the magnetostatic surface wave filter according to the present invention, the amount of coupling between the magnetostatic surface wave and the high frequency signal depends on the thickness of the spacer installed between the parallel strip transducer and the ferromagnetic single crystal thin film. I'm taking advantage of what I do. Generally, the amount of coupling is determined by the thickness of the spacer relative to the wavelength of the magnetostatic surface wave. The wavelength of the magnetostatic wave corresponding to the spurious response is 1/2 and 1/3 the length of the electrode period of the parallel strip transducer.

Therefore, the magnetostatic surface wave at a wavelength matching the electrode period of the parallel strip transducer, the desired filter response, will be longer than the wavelength of the magnetostatic surface wave that causes the spurious response. As a result, while the spacer has little effect on the desired response, spurious responses can be significantly suppressed.

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

The magnetostatic surface wave filter according to the present invention has main components, as shown in FIG.
, Sample 2 in which a ferromagnetic single crystal thin film was formed on a single crystal substrate
It's getting better. Here, sample 2 has, for example, G, G,
G, Y, I, G by liquid phase growth on a single crystal substrate
, a single crystal thin film is formed. In addition, the input side and output side parallel strip transducers 6.7 are
For example, after forming an aluminum thin film by vacuum evaporation, a pattern is formed by photoetching.

FIGS. 2(1) to 2(4) show changes in frequency characteristics when the thickness of the spacer is changed. Here, glass is used as the material of the spacer. Further, the electrode period of the parallel strip transducer is usually 100 μm to 1000 μm, but here it is set to 600 μm.

In Figure 2, the response near the center is due to magnetostatic surface waves with a wavelength that matches the electrode period, and the response on the higher frequency side is due to magnetostatic surface waves with wavelengths that are 1/2 and 1/3 of the electrode period. It is a response. As you can see from Figure 2, (
In cases 1) to (3), spurious responses are observed on the high frequency side of the desired response, but in case (4), spurious responses are observed on the high frequency side of the desired response, but in case (4), spurious responses are observed on the high frequency side of the desired response;
This is the case when a spacer of 0.45 m, which is 0.75 times μm, is used, but no spurious response is observed. This shows that the thickness of the spacer needs to be at least 0.75 times the electrode period of the parallel strip transducer. On the other hand, the spacer is made thicker (and
There is no particular change in response up to about 5 times the electrode period, but 3
It has been confirmed that increasing the insertion loss by a factor of at least 5 times, particularly by a factor of 5, increases the insertion loss of the desired response.

(Effects of the Invention) As described above, according to the present invention, by optimizing the thickness of the spacer for controlling the amount of coupling between the high frequency signal and the magnetostatic surface wave, the electrode period of the parallel strip transducer can be improved. It is possible to suppress the response due to magnetostatic surface waves with wavelengths of 1/2 and 1/3 of , and effectively excite and detect only magnetostatic surface waves with wavelengths that match the electrode period. Therefore, it is possible to construct a magnetostatic surface wave filter without spurious response, which is very effective industrially.

[Brief explanation of the drawing]

FIG. 1(a) is a perspective view of a magnetostatic surface wave filter. FIG. 1(b) is a plan view of FIG. 1(a). FIG. 1(c) is a sectional view taken along line nn in FIG. 1(b). FIGS. 2(1), (2), (3), and (4) are diagrams showing the relationship between spacer thickness and spurious response. 1...Alumina substrate, 2...C, C, Y on C1 substrate, 1. G, sample with tl film formed, 3... spacer, 4... metal thin film pattern, 5... ground conductor, 6...
・Input side parallel strip transducer, 7
...Output side parallel strip transducer. Patent applicant Sumitomo Metal Mining Co., Ltd. Figures (a) (b) (c) Vertical axis 10 dB/div. Horizontal axis 70MHz/div, OdB at the top of the diagram, OMHz at the left end

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 a spacer having a thickness of 0.75 to 5 times the electrode periodic length of the parallel strip transducer is installed between the magnetic single crystal thin film.