JPH02170610A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To improve an attenuation quantity in trapping frequencies by not arranging an edge part in the cross width direction of an interdigital electrode on the same straight line with respect to a surface acoustic wave propagating direction, but fixing an unnecessary diffracting wave generated at each electrode finger edge part so as to be suppressed especially by means of the frequencies of the electrode on a high frequency side. CONSTITUTION:A cross width W1 of a normal type interdigital electrode 1 is set larger than a maximal cross width W2 of the weighting interdigital electrode. These electrodes consist of the aluminum thin films at a film width 6000Angstrom prepared on a 128 deg.-rotated Y-axis-cut X-axis-propagated niobic acid lithium monocrystal substrate by a depositing method, and formed by means of photolithograph technique. For the floating electrode designing condition in order to improve the trap attenuating quantity, a distance (g) from the center between the first electrode and the floating electrode to the center between the said floating electrode and the second electrode is fixed by a following expression. g=lambda/2{1-(lambda/2d)<2>}<1/2> (lambda is the wavelength of the surface acoustic wave, and (d) is the repeating cycle of the electrode finger).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a surface acoustic wave device having interdigital electrodes, and in particular suppresses unnecessary diffraction waves generated from the ends of electrode fingers in the cross width direction. The present invention relates to a surface acoustic wave device suitable for improving attenuation (trap) at a pole frequency.

[Conventional technology]

Conventionally, regarding the deterioration of frequency characteristics caused by the diffraction phenomenon of surface acoustic waves, IE Transaction Nis. 21 (1974) pp. 114 to 119 (ll1iEE, Trans8U-21)
1974, pp. 4-119), a method is known in which the influence of diffraction phenomena is considered in advance and corrected.

In addition, Shioyo et al. solved the above problem by creating periodicity in the excitation wave in the cross-width direction of the electrode fingers, and by controlling the center-to-center distance between the input and output electrodes of the surface acoustic wave device. [Diffraction phenomenon and frequency characteristics of surface acoustic waves in interdigital electrodes] (IEICE, Ultrasonic Research Group Materials, U 8-7
5-37, 1975).

[Problem to be solved by the invention]

The above conventional technology requires a lot of time to design in the former paper, and does not take into account cases where the number of electrodes is relatively large, such as filters with complex amplitude characteristics. The problem is that the structure becomes complicated or the degree of freedom in design is reduced.

An object of the present invention is to suppress the above-mentioned diffracted waves using a relatively simple design method and to obtain a surface acoustic wave device having a sufficient amount of attenuation of an attenuation pole (trap).

[Means to solve the problem]

The above purpose is to make the ends of the transverse width direction of the interdigital electrodes elastic surface r.
This is achieved by not arranging them on the same straight line with respect to the fi-wave propagation direction, but by arranging them so that unnecessary diffracted waves generated at the ends of each electrode finger are suppressed, especially at the frequency of the pole on the high frequency side.

[Effect]

By providing a floating electrode at the end of the cross width direction of the interdigital electrode, the excitation source of the unwanted diffracted wave can be distributed two-dimensionally, and the radiation direction $ and intensity of the unwanted diffracted wave can be considered.

As a result, the diffracted waves do not affect the interdigital electrodes facing each other, and the amount of attenuation at the trap frequency can be improved.

〔Example〕

A first embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 is a schematic plan view of an input interdigital electrode according to a first embodiment of the present invention. The interdigital electrode 1 is constructed as follows. The intersecting width Wl of the electrode fingers is constant at 1500 μm, the width of the electrode fingers 5.6 connected to the common electrodes 3 and 4 is 17.2 μm, and the repetition period d is 34.4 μm.
This is a solid regular type electrode.

The electrode fingers 5, 6 are each connected to a common electrode 3.4. In addition, the length of the '1 pole finger or the end in the width direction is Ld.
Floating electrodes 7 and 8 with a diameter of 30 μm are arranged. The center frequency is 56.5 MHz, and the number of logarithms of the surface acoustic wave excitation source is 15.

FIG. 4 shows a schematic plan view of a surface acoustic wave device using this interdigital electrode. It is configured. The distance 2 between the centers of these input interdigital electrodes and output interdigital electrodes is 2600 μm.
And so. Further, as shown in FIG. 4, the intersection width W1 of the regular interdigital electrode 1 is the maximum intersection 1@W of the weighted interdigital electrode.

is set larger than .

These electrodes are made of aluminum thin films with a thickness of 6,000 yen produced by vapor deposition on a lithium niobate single crystal substrate (not shown) of a 128 degree rotated Y #l cut X axis transmission, and are made using photolithography technology. It is formed by

FIG. 5 shows the width frequency characteristic 12 of this embodiment.

According to this example, 52.75MHz and 60.25MHz
The attenuation amount (peak ratio) at MHz is 68 dB, respectively.
, 63dB, and good characteristics were obtained.

Here, floating electrode 7.8 for improving trap attenuation
Find the design details.

The unnecessary excitation source at the end of the electrode finger is non-directional, and the excitation source is arranged at one end of the electrode finger as shown in FIG. In addition,
The width of each excitation source is equal.

The respective composite waves E1+B1 are generated by the excitation source group 10 at the end of the electrode finger and the new excitation source group 11 generated by the floating electrode.
is given by the following equation.

B, =1+e'ψ1+ej2ψkara+ ,・+ e J
(n-1) ψkura (1) E@=ejψt B,
cutting) 2π
13) ψs ” 2 ” d-(2) θ
+π2π (4)ψ,
=Niku・g−10 However, λ is the wavelength of the surface acoustic wave at a specific frequency.

Therefore, the composite wave E of these excitation sources is given by the following equation.

E=E, +E,
(51, therefore, the directivity DI(θ) due to this excitation source group
is normalized and given by the following formula.

The trap frequency on the high frequency side of this example (60, 25M1
The directivity 9 of the unnecessary excitation source at iz) is shown in Fig. 2.
In this way, the directivity is high at maximum, and (θ) is 0.25. This indicates that the excitation source is suppressed to 1/4 of the case where all excitation sources are added in the same phase.

The influence of unnecessary excitation sources due to the conventional electrode configuration will be explained using FIGS. 6 to 8. FIG. 6 is a schematic plan view of a conventional regular electrode, in which the unnecessary wave excitation source 10 is 1
They are arranged as shown in Figure 1g8.

Directivity DI(θ) is given by the following equation.

As shown in FIG. 7, at 0120 degrees, the directivity 9 is 1, so all the excitation sources are added in the same phase, causing an adverse effect.

In this configuration, the trap attenuation amount is 66 dB on the low frequency side.

The high frequency side is 52 dB, and the high frequency side trap is particularly deteriorated.

From equation (9), the condition for θm that gives the maximum value of DI(θ) is, on the other hand, equation (81) can be expressed as follows.

Dt(θ) = am9 ・DB(θ)
(b) Therefore, at θ□ where Ds(θ) is maximum, (
2) If the force is zero, unnecessary excitation is suppressed, and this condition is expressed by the following formula 7.% The influence of unnecessary diffracted waves is particularly large on the high frequency side, and at the trap frequency on the high frequency side, %D, (θ) In the 0-line example in which g is determined so that the value is zero, g is 96 μm.

According to the present invention, since unnecessary diffracted waves can be suppressed, a sufficient amount of trap attenuation can be obtained with a relatively simple design method, and an improvement of about 11 dB can be achieved compared to the conventional method.

Next, a second embodiment of the present invention will be explained using FIG.
In this embodiment, the electrode end portions are configured so that they are not aligned on the same straight line with respect to the surface acoustic wave propagation direction.0 Region W where surface acoustic waves are generated in all electrodes. 41
It is 1200 μm. The embodiment shown in FIG. 9 is an example of a configuration in which the crossing width of the electrodes changes sequentially (pseudo-normal electrode). Since the single electrode configuration has a configuration in which the crossing width changes sequentially, the group delay characteristic becomes flat. Furthermore, if the electrode of the embodiment shown in FIG. 9 is used as an input electrode and the first electrode 2 shown in FIG. 4 is configured as an output electrode, the surface acoustic waves shown in FIG. If the region (minimum crossing width of the IIE pole) W (1) is set larger than the maximum crossing width of the opposing weighting electrode, this electrode can be operated in the same way as a regular electrode.

In this embodiment as well, the difference g between the lengths of the electrode fingers 5a and 5b was set to 75 μm using the same design method as in the first embodiment of the present invention. At this time, the directivity D(θ)let of the unnecessary diffracted wave is the first
As shown in Figure 1, the trap attenuation was suppressed to 0.2 compared to the conventional configuration, and the trap attenuation was improved by more than 6 dB.

Since this embodiment can be realized without having a floating electrode, it has the advantage that stable characteristics can be obtained even with variations in the photolithography process.

Next, a third embodiment of the present invention will be explained with reference to FIG. The configuration is such that they are not lined up on the same straight line.

Electrodes 5a', 5b', 6a', and 6b' are split-connect type electrodes with an electrode finger width of 8.6 μm,
Even in the zero-wire configuration in which the crossing width % of the electrodes 5a' and 6b' is constant at 1283 μm, the area Wt where surface acoustic waves are generated in all electrodes is determined by the maximum crossing width W of the opposing weighted electrodes. also needs to be set large. Here W
5 was 1200 μm.

Note that this embodiment has a feature that the geometrically reflected wave suppression effect is high due to the presence of the electrode portion and the free surface portion.

In this configuration, since the intersecting width of the electrode fingers is constant, it has the same frequency characteristics as a conventional regular electrode.

Here, the length of the electrode fingers 5a' and 5b' is 8 kg.
3 μm, and the directivity D(θ) of the unnecessary diffracted waves at this time was as shown in FIG. According to this embodiment, the directivity D(θ) was suppressed to 0.2 or less, and the trap attenuation was improved by 6 dB or more compared to the conventional configuration.

According to experiments by the present inventors, 0.1λ<g<3λ. When set within the range of , there is an effect of suppressing unnecessary diffracted waves compared to the conventional configuration.

Next, a fourth embodiment of the present invention is shown in FIG.
An example of this is shown in FIG.

In the embodiments shown in Figure WJ13 and Figure 14, the ends of the electrode fingers in the cross width direction are arranged in - rows, and the straight line connecting the ends of each electrode finger is 28 mm with respect to the surface acoustic wave propagation direction.
degree (θ5=28 L).

In the conventional regular electrode, unnecessary diffracted waves are emitted in the direction of the angle tjm shown in the diagram. Therefore, the straight line connecting the positions of the electrode finger ends is θs with respect to the propagation direction of the surface acoustic wave.
By configuring it so that it can be tilted by degrees, the angle at which unnecessary diffracted waves are radiated can be changed.

The angle θ at which the unnecessary diffracted waves are radiated can be expressed by the following equation with respect to the surface acoustic wave propagation direction (X-axis).

Frog = ctj' (S・mutual 1) ±θs 2d ” In Fig. 13, when there is a weighting electrode in the input direction,
In order for the diffracted waves generated above the electrodes to not be received by the weighting electrodes, the following condition is met.

,=-1(2,7331185)-05<Oα◆d On the other hand, the angle θ□ at which the diffracted wave generated at the lower part of the electrode is radiated can be expressed by the following equation.

0-1(!-・ase5)+θskuθ□
(2) d In other words, equation (2) indicates that the radiation angle of the diffracted wave at the lower part of the electrode becomes larger, which means that it is less likely to be received by the weighting electrode and is suppressed more than by the conventional regular electrode.

The embodiment shown in FIG. 14 is constructed based on the same concept as the fourth embodiment shown in FIG. 13 above. 14th
The feature of the embodiment shown in the figure is that the crossing width of the electrodes changes sequentially, the frequency characteristics are different from those of regular electrodes, and the degree of out-of-band suppression can be improved.

In the embodiment shown in FIG. 13 and the embodiment shown in FIG. 14, the area Wa in which one surface acoustic wave is generated in all electrodes is made larger than the maximum crossing width W of the opposing weighting electrodes. Here, W was set to 1200 μm. At this time,
The trap attenuation was suppressed by more than 5 dB. Also, the 14th
In the fifth embodiment of the present invention shown in the figure, the degree of out-of-band suppression is improved by about 7 dB compared to the conventional one.

Next, a sixth embodiment of the present invention is shown in FIG.

Further, a seventh embodiment of the present invention is shown in FIG.

With conventional regular electrodes, the radiation angle θ is the maximum of unwanted diffracted waves. is the surface acoustic wave wavelength λ
is determined by the electrode finger repetition period d.

Since this repetition period d is determined by the center frequency of the device, θ□ in a conventional regular electrode is uniquely determined.

In the sixth embodiment of the present invention shown in FIG. 15, the repetition period d of the surface acoustic wave excitation portion W0 is
The repetition period d' of the tip of the electrode finger is increased. According to the configuration of the embodiment shown in FIG. 15, the radiation angle of the unnecessary diffracted wave is larger than that of the conventional method, according to formula at).
Unwanted diffracted waves are less likely to be received by the weighting electrode, and unnecessary waves are suppressed.

On the other hand, when d is λ/2, the most strongly radiated frequency is higher than the trap frequency on the high frequency side, and is suppressed at the trap frequency. In the embodiment of FIG. 16, d'=
In this embodiment, the diameter is 30 μm, and the maximum value of the directivity at the high-frequency side trap frequency of this embodiment is 0.22.

In the sixth embodiment shown in FIG. 15 and the seventh embodiment shown in FIG. It needs to be convex when viewed from above.

This embodiment has the advantage that the surface acoustic waves propagating outside the maximum crossing width of the weighting electrodes have a shifted wavefront, so that they are less likely to affect the extraction electrode portion (not shown) of the weighting electrodes.

Next, an eighth embodiment of the present invention will be described using FIG. 17. FIG. 17 is a diagram showing only the shape of the tip of the electrode finger.

In the first to seventh embodiments of the present invention described above, the electrode finger 1
The size of the diffracted waves generated at the edges of the book is the same as in the conventional method, and the arrangement of the electrode fingers has been devised to suppress the combined waves.

This embodiment is an embodiment in which diffracted waves generated at the end of each electrode finger are suppressed. In other words, the diffraction wave generated at the electrode end has the amplitude of the surface acoustic wave excited by the electrode finger pair.
This is due to discontinuous changes at the ends of the electrode fingers. Therefore, by slowing down the change in the electric field at the tip of the electrode finger, the diffracted waves can be suppressed.

This can be realized, for example, by making the tips of the electrode fingers thinner, as shown in FIG. 17(a). Similarly (bl
The tip of the electrode as shown in FIG. 6, which may have a shape like # (cl), is shown in FIG.
(If the shape is as shown in cl, unnecessary waves generated at the electrode shoulders will be reduced.

In addition, in a split-connect type surface acoustic wave device, the shape of the electrode finger tip may be the shape shown in FIG. 17(d) or (a), or the electrode finger tip as shown in FIG. It goes without saying that the shape of the portion may be applied to the first to seventh embodiments of the present invention.

Note that the configuration and concept of the present invention can be applied to any of a solid electrode, a split connect type electrode, and a split isolated electrode.

It is clear that the present invention can also be used with phase weighting electrodes in which the repetition period of a surface acoustic wave device source is not constant, and with unidirectional electrodes in which signals of different phases are added to reduce loss.

In addition, conventionally, in order to reduce the influence of unnecessary diffracted waves, the aperture length of the regular electrode was set 1 or 2 times longer than the aperture length of the weighted electrode.
It was made 1.5 times larger. However, according to the present invention, since the diffracted waves themselves are suppressed, the aperture lengths of the two electrodes can be made equal. As a result, the size of the chip can be reduced by 20 to 40 mm.

In addition, although the case where the single excitation source is non-directional and there is no anisotropy in the surface acoustic wave velocity is shown here, a configuration similar to the present invention can be realized by rigorous analysis that takes these into consideration. It is clear that it is possible.

Next, another example of a method for creating a floating electrode as an actual example of the present invention will be explained using Figure @18.

FIG. 18 is a schematic plan view of the main part showing the method for producing a regular type electrode of the present invention.

In the first embodiment of the present invention, as described in the description, it is stated that the floating single pole is produced simultaneously with the interdigital electrode by a photolithographic process. In the example shown in FIG. 18, a floating electrode is formed using a laser cutter. That is, a regular type electrode 1 having a conventional configuration is created by a photolithographic process (FIG. 18(a)) - After that, the part A is cut with a laser cutter to form the floating electrode 7 of the regular type electrode 1' in the figure. (Fig. 18(b)).

According to the method of forming a floating electrode as shown in FIG.
Adjustments are possible because the regular electrodes that have already been created are processed. Therefore, there is an advantage that adjustment can be made so that sufficient characteristics can be obtained even when the trap attenuation degree is degraded due to other causes (for example, direct waves, pulse waves, etc.).

Note that it is clear that other means such as an ultrasonic cutter may be used to cut the electrode.

Next, a case will be described in which the surface acoustic wave device of the present invention is applied to an intermediate frequency filter of a color television receiver. The surface acoustic wave filter used as the intermediate frequency filter is the same as in the first embodiment of the present invention.

This surface acoustic wave filter is connected in cascade between a channel selection device (tuner) of a color television receiver and a video signal amplification stage PIF amplifier. The function of this surface acoustic wave filter is to suppress signals other than the desired signal among the signals selected by the tuner that include the desired channel, and also to suppress each of the video carrier, f-voice carrier, and chroma subcarrier of the desired signal. This is to set the signal level to an appropriate value. In particular, the amount of attenuation of the video carrier (upper adjacent video trap) and audio carrier (lower adjacent audio trap) of adjacent channels greatly affects the desired signal to interference signal ratio (DA), and sufficient performance is required.

When the surface acoustic wave filter of the present invention was used, in particular, the lower adjacent sound trap was improved by 1 ldB compared to the conventional one, and the sound carrier of the adjacent channel was improved by 11 dB, resulting in good image quality.

The method of improving the attenuation pole of the present invention is required not only for color televisions but also for other communication devices. In other words, so-called bandpass filters that extract the signal of a desired channel from signals of multiple channels, such as the intermediate frequency filter of an ATV receiver or the first or second intermediate frequency filter of a satellite broadcasting receiver, cannot remove interference signals. important and the invention, or
A surface acoustic wave filter using the present invention provides a significant performance improvement.

〔Effect of the invention〕

As explained above, according to the present invention, unnecessary diffracted waves generated from the ends of the electrode fingers in the cross width direction can be suppressed, so that particularly sufficient out-of-band attenuation can be obtained, and the filter performance can be improved. Effective for improvement. Furthermore, there is an effect that the size of the chip can be reduced by about 20 to 40 m.

Furthermore, when the present device is used in a communication device, the degree of suppression of adjacent signals is improved, and the desired signal to interference signal ratio (ry/u) is improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of a regular electrode according to a first embodiment of the present invention, FIG. 2 is a diagram showing the directivity of unnecessary diffracted waves in the embodiment shown in FIG. 1, and FIG. 1 is a layout diagram of an excitation source for unwanted diffracted waves in the embodiment shown in FIG. 1, FIG. 4 is a schematic plan view of the surface acoustic wave device in the embodiment shown in FIG. Fig. 6 is a schematic plan view showing a conventional regular electrode, and Fig. 7 shows the directivity of the conventional unwanted diffracted wave shown in Fig. 6. The figure shown in Fig. 8 is the 6th
FIG. 9 is a schematic plan view of a regular electrode according to a second embodiment of the present invention, and FIG. 10 is a schematic plan view of a regular electrode according to a third embodiment of the present invention. A schematic plan view of the mold electrode, FIG. 11 is a directivity diagram of unnecessary diffracted waves of the second embodiment of the present invention shown in FIG. 9, and FIG. 12 is a schematic plan view of the second embodiment of the present invention shown in FIG. Fig. 13 is a schematic plan view of the electrode of the fourth embodiment of the present invention; Fig. g14 is a schematic plan view of the electrode of the fifth embodiment of the present invention; FIG. 15 is a schematic plan view of the interdigital electrode according to the sixth embodiment of the present invention, and FIG.
The figure is a schematic plan view of the interdigital electrode according to the seventh embodiment of the present invention, FIG. 17 is a schematic plan view showing the tip of the interdigital electrode according to the eighth embodiment of the present invention, and FIG. FIG. 7 is a schematic plan view of main parts showing another example of the invention electrode manufacturing method. <Explanation of symbols> l... Input interdigital electrode 2... Output interdigital electrode 3.4... Common electrode 5, 6... Electrode finger 7.8
...Floating electrode 9...Directivity of unnecessary diffracted waves 10
, 11... Excitation source of unnecessary diffracted waves 12... Amplitude frequency characteristic Agent Patent attorney Ogawa Uo 〒5 Figure kan r'' 1 Figure blade O ri O θ (dei) Almost δ Figure 4 Figure 45 Figure 11 mark j0 θ (den) Closed Figure 12 θCde child) Closed 1j Figure 1 1'7 (Q, ) (b) (C) (d) (e) 〒 Figure 16

Claims (1)

[Claims] 1. A first electrode having interdigitated electrodes as an input electrode and an output electrode on a piezoelectric substrate, wherein at least one of the input electrode or the output electrode is composed of a plurality of first electrode fingers extending from a first common electrode. a second electrode comprising an electrode and a plurality of second electrode fingers extending from a second common electrode and extending to intersect with the first electrode fingers; In a surface acoustic wave device that is a regular electrode in which the intersection width between the finger and the second electrode finger is constant, a floating electrode that is an extension of the electrode finger and is not electrically connected to other electrodes at the tip of the electrode finger is used. A surface acoustic wave device characterized by being provided with. 2. The distance g from the center between the first electrode and the floating electrode constituting the regular electrode to the center between the floating electrode and the second electrode is defined by the following formula. The surface acoustic wave device according to claim 1. g=λ/2・1/√{1-(λ/[2d])^2}where, λ: wavelength of surface acoustic wave d: repetition period of electrode fingers3. It has an input electrode composed of an interdigital electrode formed on a piezoelectric substrate, and an output electrode composed of an interdigital electrode formed at a position facing the input electrode, and one of these interdigital electrodes. The other interdigital electrode is composed of weighted electrodes in which the intersecting width of the electrode fingers that constitute the interdigital electrode changes sequentially, and the minimum intersecting width of the electrodes constituting the interdigital electrode is equal to the maximum intersecting width of the weighted electrode. A surface acoustic wave device which is a pseudo-normal electrode configured larger than the pseudo-normal electrode, wherein the length of the electrode fingers of the interdigital interdigital electrodes constituting the pseudo-normal electrode is different between adjacent electrode fingers of the same polarity, and A surface acoustic wave device characterized in that the difference in length between electrode fingers is 0.1 to 3 times the surface acoustic wave wavelength. 4. It has an input electrode composed of an interdigital electrode formed on a piezoelectric substrate, and an output electrode composed of an interdigital electrode formed at a position facing the input electrode, and one of these interdigital electrodes. The other interdigital electrode is composed of weighted electrodes in which the intersecting width of the electrode fingers that constitute the interdigital electrode changes sequentially, and the minimum intersecting width of the electrodes constituting the interdigital electrode is equal to the maximum intersecting width of the weighted electrode. A surface acoustic wave device that is a pseudo-normal electrode configured larger than the surface acoustic wave device, wherein the tip of each electrode finger constituting the pseudo-normal electrode is tilted by θs (degrees) with respect to the propagation direction of the surface acoustic wave. A surface acoustic wave device arranged on a straight line parallel to the straight line, and characterized in that θs is determined by the following formula. cos＾-＾1(λ/2・[cosθs]/[d]-θ
s)<05. It has an input electrode made up of interdigitated electrodes formed on a piezoelectric substrate, and an output electrode made up of interdigitated electrodes formed at a position facing the input electrode,
One of these interdigital electrodes is constituted by a weighted electrode in which the intersecting width of the electrode fingers constituting the interdigital electrode changes sequentially, and the other interdigital electrode is constituted by a weighted electrode in which the minimum intersecting width of the electrode fingers constituting the interdigital electrode is A surface acoustic wave device that is a pseudo-normal type electrode configured to be larger than a maximum crossing width of a weighting electrode, wherein the repetition period d of the electrode fingers of the pseudo-normal electrode is wider than the maximum crossing width of the weighting electrodes. Then, the surface acoustic wave wavelength λ determined by the center frequency of the surface acoustic wave device is
The electrode fingers are curved so that the repetition period d' of the electrode fingers outside the intersection is greater than 1/4 of the surface acoustic wave wavelength. surface acoustic wave device. 6. It has an input electrode composed of an interdigital electrode formed on a piezoelectric substrate, and an output electrode composed of an interdigital electrode formed at a position facing the input electrode, and one of these interdigital electrodes. The other interdigital electrode is composed of weighted electrodes in which the intersecting width of the electrode fingers that constitute the interdigital electrode changes sequentially, and the minimum intersecting width of the electrodes constituting the interdigital electrode is equal to the maximum intersecting width of the weighted electrode. In the surface acoustic wave device, which is a pseudo-normal type electrode configured to have a larger size than the surface acoustic wave device, the surface acoustic wave device is 1/ of the surface acoustic wave wavelength λ_0 at the center frequency of
4, and the repetition period d of the electrode fingers outside the intersection is
′ is the surface acoustic wave wavelength λ at the pole frequency of the surface acoustic wave device
A surface acoustic wave device characterized in that electrode fingers are curved to be smaller than 1/4 of _0. 7. Claim 1 or Claim 2, wherein the tip portion of the electrode finger of the regular electrode is formed to become gradually thinner.
Area surface acoustic wave device. 8. 3. The surface acoustic wave device according to claim 1, wherein the regular electrode is a phase weighting electrode in which the intersecting width of the electrode fingers is constant and the repetition period changes sequentially. 9. The normal type electrodes are arranged on the same propagation path with electrode centers separated by a specific distance in the surface acoustic wave propagation direction, and a voltage having a specific electrical phase difference corresponding to the distance at a specific frequency within the rated frequency band is generated. 3. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is a unidirectional electrode consisting of a set of a sending electrode and a reflecting electrode. 10. 7. The surface acoustic wave device according to claim 3, wherein the tip portion of the electrode finger of the pseudo-normal electrode is formed to become gradually thinner. 11. The pseudo-normal electrode has a constant intersecting width of electrode fingers,
The surface acoustic wave device according to any one of claims 3 to 6, characterized in that the surface acoustic wave device is a phase weighting electrode whose repetition period changes sequentially. 12. The pseudo-normal electrodes are arranged on the same propagation path with electrode centers separated by a specific distance in the surface acoustic wave propagation direction, and have a specific electrical phase difference corresponding to the distance at a specific frequency within the rated frequency band. 7. The surface acoustic wave device according to claim 3, wherein the surface acoustic wave device is a unidirectional electrode consisting of a set of a sending electrode and a reflecting electrode to which a voltage is applied.