JP2001036379A - Saw filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize a device and to obtain superior frequency stability by arranging a horizontal elastic coupling type reflector, which has the function of transmitting surface acoustic wave on a first-class propagation path onto a second-class propagation path via a horizontal elastic coupling phenomenon and reflects it, in an adjacent relation to a waveguide, which propagates the surface acoustic wave which a transmission side interdigital electrode generates. SOLUTION: An input voltage of a signal source 118 is applied to an IDTI (transmission) 105, and a surface acoustic wave thus excited is propagated to an X-axis 119 direction orthogonal to electrode fingers 112, 115, 114 or the like and is made incident to a wave guide 101. After this, the surface acoustic wave is transmitted to reflectors 1 102 and 2 103 by using a horizontal elastic coupling phenomenon, is further reflected in the -X direction and is propagated to an IDT 2 (reception 1) 105 and an IDT 3 (reception 2) 107. The propagated surface acoustic wave is received by these IDT and becomes an electrical signal among terminal impedance terminals ZL 117. Thus, the total length of an element can be shortened by about 30%, and an satisfactory small-sized SAW filter can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transversal SAW filter constructed by utilizing surface acoustic waves, and comprises an interdigital transducer and a transverse elastic coupling type reflector.
The present invention relates to a technology for realizing miniaturization of an AW filter.

[0002]

2. Description of the Related Art As a conventional transversal type SAW filter, there is a well-known one using a pair of interdigital electrodes. In this method, the IDT on the transmitting side is weighted and the IDT on the receiving side is of the normal type, but the length of the IDF weighting function required to realize the frequency characteristics of the filter is used. (Time length of the impulse response function) is long, and miniaturization is difficult. To improve this, there is an example in which a pair of interdigital transducers and a reflector are arranged in a straight line, the reflector is weighted to realize a desired filter frequency characteristic, and the element is reduced in size ( References: A. Bergmann et al; "TWO-TRACK-REFLECT
OR-FILTERS FOR CDMA MOBILE TELEPHONES ", IEEE ULTRAS
ONICS SYMPOSIUM pp.57-60, (1996)).

[0003]

However, the above-mentioned conventional technology using a pair of interdigital transducers and a reflector is used for a CDMA small and light mobile phone, which has been remarkably developed in recent years. The required size of the intermediate frequency filter (IF filter) of about 200 MHz, which is within 5 × 5 mm of the plane size of the container, can achieve satisfactory performance with ST cut substrates having a small electromechanical coupling coefficient such as quartz. could not. This is because when analyzing the cause that cannot be realized, the length becomes about 7 mm in order to arrange the pair of interdigital transducers and reflectors in a line in the propagation direction of the surface acoustic wave.

Therefore, the present invention solves such a problem, and an object of the present invention is to use a substrate having an excellent frequency-temperature characteristic and a material having an excellent Q value, such as a quartz crystal ST-cut, and a conventional method. An object of the present invention is to provide an IF filter having a small size, excellent frequency stability, and a high S / N ratio to the market.

[0005]

(1) A SAW filter according to the present invention comprises a transmitting interdigital transducer for transmitting at least a surface acoustic wave on a piezoelectric flat plate and an elastic surface on which the transmitting interdigital transducer is generated. A first type of propagation path comprising a waveguide for propagating a wave; and a second type of propagation path parallel to and adjacent to the first type of propagation path, and having a lateral elasticity adjacent to the waveguide. A coupling-type reflector is arranged, and on the propagation path of the surface-acoustic-wave radiated by the lateral-elastic-coupling-type reflector, a reception-side interdigital electrode for receiving the surface-acoustic-wave is configured. And a function of transmitting and reflecting the surface acoustic wave on the first type of propagation path to the second type of propagation path via a lateral elastic coupling phenomenon.

(2) In the above (1), the first propagation path of the surface acoustic wave generated by the transmitting interdigital transducer (first
The second and third propagation paths, which are the second type of propagation path, in which the receiving-side interdigital electrodes for receiving the surface acoustic waves are located at the center of the first type of propagation path, The lateral elastic coupling type reflector is disposed on both sides of the path, and has a function of transmitting and reflecting the surface acoustic wave on the first propagation path to the second and third propagation paths via a lateral elastic coupling phenomenon. It is characterized by having.

(3) In the above (1), the lateral elastic coupling type reflector is such that the frequency f1 of the waveguide arranged in the first type of propagation path is the same as that of the reflector arranged in the second type of propagation path. (F1> f2) so as to transmit a surface acoustic wave on the first type of propagation path to the second type of propagation path via a lateral elastic coupling phenomenon. I do.

(4) In the above (1), in the transverse elastic coupling type reflector, a large number of conductor strips made of a metal such as aluminum are arranged in parallel on a piezoelectric flat plate in a direction orthogonal to the phase propagation direction of the surface acoustic wave. The width of the conductor strip is variably formed by a width weighting method with respect to the reflection coefficient κm of the conductor strip so that a predetermined filter frequency characteristic can be realized.

(5) In the above (4), in the lateral elastic coupling type reflector, a large number of conductor strips made of a metal such as aluminum are arranged in parallel on a piezoelectric flat plate in a direction orthogonal to the phase propagation direction of the surface acoustic wave. The width of a part of the conductor strip is approximately (1), where λ is the wavelength of the surface acoustic wave.
/ 8) λ.

(6) In the above (1), the piezoelectric flat plate is a quartz ST cut made of a Y-plate rotated by 30 to 35 degrees.
9.6 degree rotation Y plate and in-plane rotation angle 32.43 from X axis
It is characterized by being a K-cut made of degrees or an LST cut made of a Y-plate rotated from -72 to -76 degrees.

(7) In the above (3), the lateral elastic coupling type reflector may be arranged such that the frequency f1 of the waveguide arranged in the first type of propagation path is equal to the frequency of the waveguide arranged in the second type of propagation path. (F1> f2), and the frequency f2 is formed by oxidizing or anodizing the surface of the conductor strip of the reflector to reduce the frequency due to the mass adding effect. Has the function of transmitting and reflecting the surface acoustic wave on the second propagation path to the second type of propagation path via the transverse elastic coupling phenomenon.

(8) In the above item (3), the reflector constituting the lateral elastic coupling type reflector is characterized in that a ratio H / H of the thickness H of the conductor strip made of aluminum to the wavelength λ of the surface acoustic wave is obtained.
λ is in the range of 0.01 to 0.05.

(9) In the above (1), the waveguide comprises a conductor strip made of a metal such as aluminum.
A large number of the conductor strips are arranged in parallel on a piezoelectric flat plate perpendicular to the phase propagation direction of the surface acoustic wave, and the width of the conductor strip is substantially (1/8) λ, where λ is the wavelength of the surface acoustic wave. It is characterized by.

[0014]

(Embodiment 1) Embodiments of the present invention will be described below in order from FIG. FIG. 1 is a plan view showing an electrode pattern used in a transversal type SAW filter according to the first embodiment of the present invention. The names of the respective parts in FIG. 1 are as follows: 100 is a piezoelectric flat plate, 101 surrounded by a broken line is a waveguide of the first propagation path (the line width of the conductor strip of the waveguide is ８λ), 102 and 103 Are the first and second reflector portions of the transverse elastic coupling type reflector, respectively, 104 is a ground (GND) conductor, and 105 is enclosed by a broken line.
Is a transmitting IDT (IDT1) (hereinafter abbreviated as ID
T: Interdigital Transducer. ), 106 and 107 are receiving-side IDT2 and IDT3, 108 and 109 are transmitting-side IDT input pads, and 110 and 111 are receiving-side common pads obtained by connecting the receiving-side IDT2 and IDT3 in parallel. 112, 113, 114, 115
And the like are electrode fingers having a ８λ line width of the IDT.
116 is a ground portion outside the element, 117 is the terminal impedance of the SAW filter, and 118 is an input signal source. The operation of the first embodiment according to FIG.
Vin is applied to the transmitting side IDT 1, and the surface acoustic wave excited by this is propagated in the X-axis direction (arrow 119) orthogonal to the electrode fingers 112, 115, 114, etc., and the waveguide ( After being incident on the reflector 101 (101), the surface acoustic wave is transmitted to the reflector 1 (102) and the reflector 2 (103) using the transverse elastic coupling phenomenon, and is further reflected in the -X direction to be received by the receiving IDT 2 (106). , IDT3 (107). The propagated surface acoustic wave is received by these IDTs, and the electric signal Vo between the 117 terminal impedance terminals is output.
ut. The transmission characteristic of the SAW filter is G (f) = 2
0 log ₁₀ (Vin / Vout) (dB). In addition, the piezoelectric flat plate 100 includes a quartz crystal ST cut (30 to 35 degree rotation Y plate-X propagation), a quartz crystal K cut (9.6 degree rotation Y plate and in-plane rotation angle of 32.43 degree X propagation),
Quartz LST cut (-72 to -76 rotation Y-plate-X propagation), or a single crystal having piezoelectricity such as lithium tantalate, lithium tetraborate, langasite, and Z
It is composed of a substrate or the like on which a piezoelectric thin film such as nO is formed. The IDT1, IDT2, IDT formed on the 100
The horizontal elastic coupling type reflector 3 and the like are formed by forming a conductive metal film such as aluminum and gold into a thin film by means of vapor deposition, sputtering or the like, and then forming a pattern by photolithography. A large number of the IDTs and a group of electrode fingers such as reflectors are arranged in parallel and periodically at right angles to the phase traveling direction (longitudinal direction X) of the surface acoustic waves (Rayleigh waves, leaky waves, etc.) to be used. . As the IDT in this case, a non-reflection type IDT having an electrode finger width of １ ／ wavelength (λ) uniformly, or a unidirectional IDT composed of an IDT that radiates a surface acoustic wave only in one direction is used. May be used.

(Embodiment 2) FIG. 2 shows another embodiment of the present invention, in which the surface acoustic wave has two propagation paths. In the figure, 200 is a piezoelectric flat plate, 201 is a transmitting side IDT1 and 202 is a receiving side IDT2 surrounded by a fine broken line. Numerals 203 and 204 are a waveguide and a reflector, respectively, of the transverse elastic coupling type reflector. Reference numeral 205 denotes an external connection conductor for anodizing, 206 and 208 denote positive power supply conductors (bus bars), and 209 denotes a negative power supply conductor. Reference numeral 207 denotes an electrode finger having a line width of 1 / 8λ. 21
Numeral 0 denotes a ground conductor, and solid lines 211, 212, 214 and the like illustrate the flow of surface acoustic waves. Further, 215 is an input signal power supply, and 216 is a terminating impedance. The operation of the element according to the second embodiment is as follows. The surface acoustic wave excited in the IDT 1 201 by the voltage Vin of the signal source 215 is incident on the incident side waveguide (203) of the transverse elastic coupling type reflector, and the transverse elastic The light propagates to the reflector 204 via the coupling phenomenon. Thereafter, the light is reflected, enters the receiving-side IDT 2 (202), becomes an electric signal Vout, and is detected as a terminal-to-terminal voltage of the termination impedance 216. The frequency characteristic (operating transmission amount Sb) of the SAW filter is G (f) = 20 log.
₁₀ (Vin / Vout) (dB). In this case, the IDT may be a 1/8 wavelength (λ) electrode finger width or a one-way IDT. Further, as the above-mentioned waveguide, it is preferable to form an open type or a short type using a conductor width of １ ／ wavelength (λ) so that reflection does not occur.

Next, referring to FIG. 3, FIG. 5, FIG. 6, and FIG.
The configuration and operation of the transverse elastic coupling type reflector which is an important component of the present invention will be described in detail. First, FIG. 3 illustrates the state of the surface acoustic wave amplitude in the operating state of the lateral elastic coupling type reflector described in the embodiment of FIG.

In the figure, reference numeral 300 denotes a relative amplitude V (Y) of the surface acoustic wave.
Vertical axis representing frequency potential 301
P (Y), 302 is the coordinate axis Y in the lateral width direction, 303 is the frequency potential function P (Y), 30 which the transverse elastic coupling type reflector has.
4 is the amplitude distribution of the surface acoustic wave of the lateral elastic coupling type reflector
V (Y), the area 305 is half of the first propagation path (Track # 1) on the side where the surface acoustic wave is incident, and the area 306 is the second propagation path (Trac
k # 2), a region 307 is a power supply conductor region (corresponding to B in FIG. 1), a reference numeral 308 is a free surface region where the conductor film is not covered, and a region 309 is a conductor covering region between the Track # 1 and Track # 2 ( (Corresponding to G in FIG. 1). The frequency potential P (Y) is determined by the frequency f1 of the waveguide forming the transverse elastic coupling type reflector and the frequency f2 of the reflector. These have a line width L of the conductor strip forming the waveguide of 1.
Since the wavelength is / 8, f1s = Vs / (8 × L) (where Vs is the velocity of the elastic surface on the free surface). Further, using the period length PR between the conductor strips of the reflector (see FIG. 5), f2s = Vs / (2 × PR) = f1
The frequency defined as s (corresponding to P (Y) = 0 in FIG. 3) is given by the fact that the frequency decreases due to the mass and perturbation effects of the aluminum conductor, and f1s becomes f1 and f2s becomes f2. η1 = (f1s−f1) / f1s, η2
= (F2s−f2) / f2s, in the case of FIG. 3, P (Y) = 1 corresponds to η1 of Track # 1, and P (Y) of Track # 2 is P2 = η2 / η1. It is standardized as follows. Therefore, in FIG. 3, the first propagation path (Track #
The waveguide frequency f1 of 1) is the second propagation path (Track #).
2) greater than the reflector frequency f2 (f1> f2). The conditions are the above-mentioned crystal ST cut, K cut, LST
It can be applied to a substrate having a positive coefficient of lateral anisotropy such as a cut substrate. As the condition of the P (Y), P2 = 1.2, P1
= 1 (η1 = 0.01) and the half width of Track # 1 is 1
When 6 wavelengths and the width of Track # 2 is 34 wavelengths, T
The calculation result of the amplitude of the surface acoustic wave existing on rack # 1 and the amplitude of Track # 2 is displayed as V (Y) of 304. The amplitude V (0) at the center position of Track # 1, which is the origin 0 of the coordinate Y in the width direction, is 0.01, while the amplitude at the center position of Track # 2 is 7, and a relative difference of about 700 times occurs. ing. If this is interpreted physically, assuming that a surface acoustic wave is incident on Track # 1, the surface acoustic wave is unidirectionally moved from Track # 1 on the higher frequency side to Track # 2 on the lower frequency side. Means lateral propagation. This is an example, but depending on the setting of P (Y), Track # 1 and Track # 2
Can be set in any manner. FIG.
In this case, the smaller the width of Track # 1 and Track # 2, the stronger the lateral elastic coupling between the two Tracks. Therefore, FIG. 1 of the first embodiment described above is of the first type compared to FIG. 2 of the second embodiment. Since there is an advantage that the surface acoustic wave can be efficiently transmitted from the propagation path to the second type propagation path, the insertion loss of the SAW filter of the present invention is improved.

Next, FIGS. 5 and 6 show a method of setting the frequency characteristics of each reflector used in the transverse elastic coupling type reflector. SA configured as in the present invention
In the case of the W filter, the creation of the frequency characteristics of the SAW filter mainly requires the use of a reflector.
This is because the frequency characteristic H (f) of the SAW filter is obtained by the Fourier transform of the impulse response function h (t) generated by the IDT or the reflector. In the IDT,
The excitation amplitude of the surface acoustic wave is h (t). In the reflector, the generation amplitude of the reflected wave or the reflection coefficient function κm (X)
= H (t). Therefore, in FIG. 5, the entirety of 605 is a reflector, and 603 in the 605 region is a conductor strip or the like. The width L (Xi) of the conductor strip is (where X is the propagation direction of the surface acoustic wave). Position coordinates (60
1), Xi is the coordinates of the center position of the electrode finger), and the line width L (X) corresponding to the desired reflection coefficient function κm (Xi) (602)
i). FIG. 6 gives this correspondence. The horizontal axis in the figure is the conductor coverage ε, and ε = L (Xi).
/ PR. The vertical axis is the reflection coefficient κm of the conductor strip having the L (Xi). Curve 700 is crystal S
This is the reflection coefficient of the aluminum conductor strip on the T-cut substrate. However, the aluminum film thickness H is H / λ =
This is the case under the condition of 0.03. As far as the characteristic curve 600 is concerned, the reflection coefficient κm has a negative value when ε is in the range of 0 to 0.2. Therefore, it is possible to cope with a case where h (t) has a negative value. The state having this negative value is H / λ =
It is generated in the range of 0.01 or more and 0.05, and can be used to realize sharp SAW filter frequency characteristics. Further, when constructing the lateral elastic coupling type reflector of the present invention, it is important that Track # 1 and Track # 1 are used.
Although it is necessary to form a frequency difference in # 2, in the present invention, this frequency difference is created by anodizing the reflector 2 of Track # 2. In this processing method, only the reflector 2 is immersed in an aqueous solution of phosphoric acid to oxidize the surface of the aluminum conductor strip. Alternatively, an oxidation treatment in plasma may be used. As a result, the above-mentioned frequency potential difference ΔP = P2−P1 is set to 0.2 to 0.5 (η2−η1 = 0.002 to 0.
005). This processing can be performed in the presence of the aluminum conductor strip, but it is difficult to secure ΔP especially when the line width is small. FIG. 7 shows an example in which this problem is solved by using a conductor strip having a width of 1/8 wavelength whose reflection coefficient is known to be zero in a region where the reflection coefficient κm = 0. In the figure, 800 and 802 surrounded by broken lines are conductor strips having a reflection coefficient of zero, 801 is a conductor strip having a non-emission coefficient, and 803 in a region 800 is 1/8. The conductor strip 804 having a wavelength width also has a space of 1/8 wavelength width. Also, 80 in the area 801
5 and 806 are wider conductor strips having a non-zero reflection coefficient, 807, 808, 809, 810, 811
Is the reflection coefficient function κm (X) as a whole, 813 is the X axis indicating the propagation direction of the surface acoustic wave, and 807 and 811 are the areas of the free surface. 812 is a connection conductor used for anodizing. In the above-mentioned conductor strip having a 1/8 wavelength width,
The method of scattering the conductor strips having a quarter wavelength width with frequency weighting is a method similar to the thinning method known as the IDT weighting method.

Finally, SA obtained by the configuration of the present invention
The frequency characteristics of the W filter will be described with reference to FIG. FIG. 4 shows the operation transmission amount Sb (dB) for the configuration of FIG.
, The piezoelectric flat plate 100 is a quartz ST cut, the operating frequency is 200 MHz, and the IDT
1 (105), IDT2 (106), IDT3 (10
7) The number of pairs of positive and negative electrode fingers is 80, the number of conductor strips of the reflector is 300, the total element width is 50λ, and the film thickness ratio H / λ = 0.
03. At this time, the chip size is as small as about 4 × 2 mm. (The above setting conditions are an example, but IDT
May be weighted by increasing or decreasing the logarithm, and filter characteristics can be obtained even when the number of reflectors is set to about 100. )
As can be seen in FIG. 4, the 3 dB pass bandwidth is 4 MHz,
The insertion loss is as good as 10 dB and the attenuation outside the band is as large as 50 dB or more. This is interpreted as that only the surface wave energy is transmitted from Track # 1 to Track # 2 due to the transverse elastic coupling effect, and the bulk wave excited by Track # 1 is not transmitted.

The configuration and characteristics of the SAW filter according to the present invention have been described above. Configuration example is 30-35 degree rotation Y
Although shown as a quartz ST cut from the plate, it is another cut-
LST cut which is a Y-plate rotated from -72 to -76 degrees,
9.6 degree rotation Y plate and in-plane rotation angle 32.43 from X axis
It should be noted that a K-cut, which is a degree, may be used, and a piezoelectric material other than quartz may be used.

[0021]

As described above, according to the present invention, when the size of a SAW filter is reduced using, for example, a quartz substrate, the transmitting and receiving sides of the SAW filter are reduced.
Since the DTs are formed on separate propagation paths, the energy transfer of the surface acoustic wave between the propagation paths is performed by the transverse elastic coupling type reflector formed over both propagation paths. The overall length of the element can be shortened by about 30%, and the S
An AW filter can be realized. Further, since the propagation path of the surface acoustic wave of the transmission / reception IDT is different, and there is no direct bulk wave, there is an advantage that a large amount of attenuation outside the pass band can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view showing a conductor pattern included in an embodiment of a SAW filter according to the present invention.

FIG. 2 is a plan view showing a second embodiment of the SAW filter according to the present invention.

FIG. 3 is a characteristic diagram of a lateral elastic coupling type reflector which is a component of the present invention.

FIG. 4 is a frequency characteristic diagram of the SAW filter shown in FIG. 1 of the present invention.

FIG. 5 is a configuration diagram of a reflector included in the lateral elastic coupling type reflector of the present invention.

FIG. 6 is a characteristic diagram of the reflector of the present invention.

FIG. 7 is another configuration diagram of the reflector of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 piezoelectric flat plate 101 waveguide 102 reflector 1 103 reflector 2 104 GND conductor 105 IDT1 106 IDT2 107 IDT3

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Makoto Furuhata 3-3-5 Yamato, Suwa City, Nagano Prefecture Seiko Epson Corporation F-term (reference) 5J097 AA05 AA29 BB11 CC01 CC15 DD08 DD15 DD17 DD20 DD28 GG02 HA02 HB02 KK01 KK04

Claims (9)

[Claims] 1. A first type propagation path comprising: a transmission-side interdigital electrode for transmitting at least a surface acoustic wave on a piezoelectric flat plate; and a waveguide for transmitting a surface acoustic wave generated by the transmission-side interdigital electrode. And a second parallel provided adjacent to and parallel to the first type of propagation path.
On a propagation path of a kind, a lateral elastic coupling type reflector is arranged adjacent to the waveguide, and on the propagation path of the surface acoustic wave radiated by the lateral elastic coupling type reflector, a receiving side for receiving the surface acoustic wave The transverse elastic coupling type reflector has a function of transmitting and reflecting a surface acoustic wave on a first type of propagation path to a second type of propagation path via a lateral elastic coupling phenomenon. A SAW filter, characterized in that: 2. A method according to claim 1, wherein a first interfacial path (a first type of propagating path) of the surface acoustic wave generated by the transmitting interdigital transducer is located at a center, and a receiving interdigital transducer receiving the surface acoustic wave is disposed at the center. The second and third propagation paths, which are disposed second type propagation paths, are disposed on both sides of the first type propagation path, and the lateral elastic coupling type reflector has an elastic surface on the first propagation path. 2. The SAW filter according to claim 1, wherein the SAW filter has a function of transmitting and reflecting a wave to the second and third propagation paths via a transverse elastic coupling phenomenon. 3. The lateral elastic coupling type reflector has a frequency f1 of a waveguide arranged in the first type of propagation path is higher than a frequency f2 of a reflector arranged in the second type of propagation path (f
1> f2), and has a function of transmitting a surface acoustic wave on the first type of propagation path to a second type of propagation path via a lateral elastic coupling phenomenon. SAW
filter. 4. The lateral elastic coupling type reflector is constituted by arranging a large number of conductor strips made of a metal such as aluminum on a piezoelectric flat plate in a direction orthogonal to the phase propagation direction of a surface acoustic wave. 4. The SAW filter according to claim 3, wherein the width of the strip is variably formed by a width weighting method with respect to the reflection coefficient κm of the conductor strip so that a predetermined filter frequency characteristic can be realized. 5. The lateral elastic coupling type reflector is configured by arranging a large number of conductor strips made of a metal such as aluminum on a piezoelectric flat plate in a direction orthogonal to the phase propagation direction of a surface acoustic wave. 5. The SAW filter according to claim 4, wherein the width of a part of the strip is (1/8) .lambda., Where .lambda. Is approximately the wavelength of the surface acoustic wave. 6. The piezoelectric flat plate is rotated by 30 to 35 degrees Y
Quartz ST cut consisting of a plate, K cut consisting of a 9.6 degree rotated Y plate and an in-plane rotation angle of 32.43 degrees from the X axis, or LST cut consisting of a -72 to -76 degree rotated Y plate The SAW filter according to claim 1, wherein: 7. The lateral elastic coupling type reflector has a frequency f1 of a waveguide arranged in the first type of propagation path is higher than a frequency f2 of a reflector arranged in the second type of propagation path (f
1> f2) The frequency f2 is formed by oxidizing or anodizing the surface of the conductor strip of the reflector to reduce the frequency due to a mass addition effect, and the elastic surface on the first type propagation path. 4. The SAW filter according to claim 3, wherein the SAW filter has a function of transmitting and reflecting the wave to the second type of propagation path via a transverse elastic coupling phenomenon. 8. The reflector constituting the transverse elastic coupling type reflector, wherein the ratio H / λ of the thickness H of the conductor strip made of aluminum to the wavelength λ of the surface acoustic wave is 0.01 to 0.05.
The SAW filter according to claim 3, wherein 9. The waveguide comprises a plurality of conductor strips made of metal such as aluminum, which are arranged in parallel on a piezoelectric flat plate at right angles to a phase propagation direction of a surface acoustic wave. 2. The SAW filter according to claim 1, wherein the wavelength is approximately (1/8) λ, where λ is the wavelength of the surface acoustic wave.