JPH073695Y2 - Surface acoustic wave reflector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a surface acoustic wave reflector which is a constituent element of a resonator and a filter using surface acoustic waves.

[Conventional technology]

FIG. 2 shows, for example, the journal of the Institute of Electronics and Communication Engineers, V01.J66-C, N.
FIG. 1 is a view showing a conventional surface acoustic wave reflector of this type shown in o.1 (1983), P.24. In FIG. 2, reference numeral 1 is a piezoelectric substrate, and 2 is a metal strip formed on the piezoelectric substrate 1. As shown in FIG. 2, a plurality of metal strips 2 are periodically arranged to form a surface acoustic wave reflector 3 as a whole.

Next, the operation will be described. In FIG. 2, when a surface acoustic wave is incident on the surface acoustic wave reflector 3 from the left side in the figure, for example, the portion where the metal exists on the piezoelectric substrate 1, that is, the portion of the metal strip 2, the metal strip 2 and the metal strip 2 Since the acoustic impedance with respect to the surface acoustic wave is different between the portion between which there is no metal, each metal strip 2 reflects a part of the surface acoustic wave.

Since the plurality of metal strips 2 are arranged periodically, the arrangement pitch of the metal strips 2 is about one half wavelength. At frequency, the surface acoustic waves reflected from each metal strip 2 overlap in phase. Therefore, a strong reflection occurs as a whole, and it operates as a reflector.

Although FIG. 2 shows a reflector using a plurality of electrically shorted metal strips 2, an electrically open metal strip 2 may be used. When using an electrically open metal strip 2, for example the document Uitrason
ics Symposium Proceedings, IEEE Cat. # 76 CH 1120-5s
As shown in u (1976), PP.297-302, the reflection amount of the surface acoustic wave per metal strip (2) is different from that when the electrically shorted metal strip 2 is used. However, also in this case, the surface acoustic wave is reflected by the same principle as described above and operates as a reflector.

FIG. 3 is an example of a two-terminal pair resonator using the conventional surface acoustic wave reflector 3 of this type. In FIG. 3, reference numeral 1 is a piezoelectric substrate. Reference numeral 4 is a comb-shaped electrode provided on the piezoelectric substrate 1. Reference numeral 3 is a surface acoustic wave reflector provided on both sides of the interdigital transducer 4. Reference numeral 2 is a metal strip forming the surface acoustic wave reflector 3. 5 is a lead wire. In FIG. 3, when a high frequency electric signal is applied to one of the interdigital transducers 4, a surface acoustic wave is excited on the piezoelectric substrate 1. The excited surface acoustic wave is repeatedly reflected between the surface acoustic wave reflectors 3 provided on both sides of the interdigital transducer 4, and a standing wave is generated at a frequency at which the multi-reflected surface acoustic waves are added in phase. Therefore, the electrode finger of the interdigital transducer 4 is placed at the antinode of the standing wave, a high frequency electric signal is applied to one interdigital electrode 4 to excite the surface acoustic wave, and the other interdigital electrode 4 is placed. If you receive a surface acoustic wave with
A large passing power is obtained only at a frequency that produces a standing wave, and the filter operates as a narrow band filter.

[Problems to be solved by the invention]

By the way, in the conventional surface acoustic wave reflector 3 of this kind, the reflection amount of the surface acoustic wave is equal in all parts of the surface acoustic wave reflector 3. For this reason, the frequency characteristic of the reflection coefficient of the surface acoustic wave reflector 3 is, for example, as shown in the document “Surface Acoustic Wave Engineering”, supervised by Inao Shibayama, edited by The Institute of Electronics and Communication Engineers (1983), PP. , The surface pitch is reflected at frequencies other than the frequency at which the arrangement pitch of the metal strips 2 is about one-half wavelength, that is, outside the band, and side lobes occur. Therefore, this type of conventional surface acoustic wave reflector 3
When a two-terminal pair resonator is configured by using, there is a problem that unnecessary side lobes and ripples are generated in the out-of-band pass characteristic.

This invention was made in order to solve the above-mentioned problems, and the reflection amount of the surface acoustic wave is determined by the surface acoustic wave reflector 3
By changing it in each place, compared to the conventional
An object of the present invention is to obtain a surface acoustic wave reflector 3 that can reduce the sidelobe level in the frequency characteristic of the reflection coefficient.

[Means for solving problems]

Metal strip 2a electrically short-circuited on the piezoelectric substrate 1
And the electrically open metal strip 2b are arranged in parallel, and the reflection amount distribution of the incident surface acoustic wave is weighted based on the difference in reflectance between the metal strip 2a and the metal strip 2b. It is characterized in that it is configured as follows.

[Action]

The surface acoustic wave reflector 3 according to the present invention comprises an electrically short-circuited metal strip 2a and an electrically open metal strip 2a.
2b are arrayed and the reflection amount distribution of the incident surface acoustic wave is weighted based on the difference in reflectance between the metal strip 2a and the metal strip 2b. Therefore, the reflection amount of the surface acoustic wave is reflected by the surface acoustic wave reflector 3 It can be changed according to each place in
The side lobe level in the frequency characteristic of the reflection coefficient can be lowered.

[Example of device]

An embodiment of the present invention will be described below with reference to the drawings. First
In the figure, 1 is a piezoelectric substrate, and 2a is a piezoelectric substrate 1.
A metal strip formed above and electrically short-circuited by connecting both ends between common strips 2c, 2c, 2b is a metal strip that is electrically open and is arranged in parallel with metal strip 2b, and metal strip 2a , 2b are perpendicular to the incident direction of the surface acoustic wave. In this case, the number of arrayed metal strips 2a, 2b is different for each fixed section l, m, n with respect to the incident direction of the surface acoustic wave, and the metal strip 2a decreases from the section l in the section n direction, but the metal strip 2a decreases. 2b is constructed to increase.

In the surface acoustic wave reflector 3 according to the present invention, the number of arrayed metal strips 2a and 2b is determined based on the difference in reflectance between the electrically short-circuited metal strip 2a and the electrically open metal strip 2b. Distribution of surface reflector 3
Since it is configured to change the number of the metal strips 2a and 2b arrayed according to the section of the array, the surface acoustic wave incident on the surface acoustic wave reflector 3 can be changed. The reflection amount distribution can be weighted. Therefore, the side lobe level in the frequency characteristic of the reflection coefficient can be lowered as compared with the conventional uniform surface acoustic wave reflector 3 without weighting. Therefore, when the surface acoustic wave reflector 3 is used to form a two-terminal pair resonator as in the conventional case, for example, an unnecessary side lobe level outside the band in the pass characteristic can be reduced.

[Effect of device]

As described above, according to the present invention, the surface acoustic wave reflector is formed by arranging the electrically short-circuited metal strip 2a and the electrically open metal strip 2b, and reflecting the metal strip 2a and the metal strip 2b. Since the reflection amount distribution of the incident surface acoustic wave is weighted based on the difference in the coefficient, the side lobe level in the frequency characteristic of the reflection coefficient can be made lower than before. When a two-terminal pair resonator or the like is configured, there is an effect that unnecessary side lobe levels and ripples outside the band in the pass characteristic can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a surface acoustic wave reflector according to an embodiment of the present invention, FIG. 2 is a diagram showing a conventional surface acoustic wave reflector, and FIG. 3 is a two-terminal pair using the surface acoustic wave reflector. It is a figure which shows a resonator. Reference numeral 1 is a piezoelectric substrate, 2, 2a and 2b are metal strips, 3 is a surface acoustic wave reflector, 4 is a comb-shaped electrode, and 5 is a lead wire. In the drawings, the same reference numerals indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-54-87457 (JP, A) JP-A-55-47718 (JP, A) JP-A-61-220514 (JP, A)

Claims (2)

[Scope of utility model registration request] 1. A metal strip 2a electrically short-circuited and a metal strip 2b electrically open on a piezoelectric substrate 1.
And are arranged in parallel, and based on the difference in reflectance between the metal strip 2a and the metal strip 2b, the reflection amount distribution of the incident surface acoustic wave is weighted. Surface acoustic wave reflector. 2. The metal strips according to the section of the array.
The surface acoustic wave reflector according to claim 1, characterized in that it is configured so that the numbers of arrays of 2a and 2b are different.