JP2004140738A - Surface acoustic wave filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a means which improves an attenuation gradient near the passband of a cascaded multiplex mode SAW filter and the amount of stop band attenuation near the passband. <P>SOLUTION: In the surface acoustic wave filter, one or a plurality of cascaded multiplex mode surface acoustic wave filters having a plurality of IDTs and grating reflectors arranged on both sides of the IDTs are cascade-connected, and at least one single-terminal paired SAW resonator is connected in series or parallel to the cascaded multiplex mode surface acoustic wave filters. Further, a comb shaped capacitor is connected in parallel to the single-terminal paired SAW resonator. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surface acoustic wave filter, and more particularly to a surface acoustic wave filter with improved stopband attenuation near a pass band.
[0002]
[Prior art]
2. Description of the Related Art In recent years, surface acoustic wave filters have been widely used in the field of communications and have excellent characteristics such as high performance, small size, and mass productivity, and thus are particularly frequently used in mobile phones and the like. FIG. 8 is a plan view of an electrode pattern showing a configuration of a conventional cascade-connected primary-tertiary longitudinally coupled surface acoustic wave filter (hereinafter, referred to as a dual mode SAW filter). The IDTs 42, 43, 44 on the three screens are arranged close to each other along the propagation direction of the surface wave, and grating reflectors 45a, 45b (hereinafter, referred to as reflectors) are arranged on both sides of the IDTs. Filter. Each of the IDTs 42, 43, and 44 is constituted by a pair of comb-shaped electrodes having a plurality of electrode fingers interposed therebetween, and a comb-shaped electrode near an end of the substrate 41 of the IDT 42 is an electrode pad provided near the outside of the electrode. The other comb-shaped electrode is connected to a ground electrode pad E1 provided near the center of the substrate 41 in the vicinity of the electrode. Then, the comb-shaped electrodes of the IDTs 43 and 44 near the ends of the substrate 41 are connected to grounding electrode pads E2 and E3 provided near the outside of the electrodes. Further, lead electrodes L1 for cascade connection extend from the other comb-shaped electrodes of the IDTs 43 and 44 to the next stage.
[0003]
The second double mode SAW filter, which is substantially line-symmetric with respect to the first double mode SAW filter at the center of the substrate, that is, a double mode SAW filter including IDTs 46, 47 and 48 and reflectors 49a and 49b disposed on both sides thereof. Are formed along the propagation direction of the surface wave. The IDT 46 has a comb-shaped electrode near the center of the substrate 41 connected to a grounding electrode pad E4 provided near the outside of the electrode, and the other comb-shaped electrode of the IDT 46 used for an output provided near the outside of the electrode. Connect to electrode pad P2. Further, the comb-shaped electrodes of the IDTs 47 and 48 near the end of the substrate 41 are connected to grounding electrode pads E5 and E6 provided near the outside of the electrodes. Further, lead electrodes L2 for cascade connection extend from the other comb-shaped electrodes of the IDTs 47 and 48 toward the front stage.
[0004]
An IDT 50 and reflectors 51a and 51b on both sides thereof are provided along one output terminal of the first dual mode SAW filter, that is, a lead electrode L1 extending from a bus bar inside the substrate 41 of the IDT 43 along the propagation direction of the surface wave. One terminal of the disposed SAW resonator (hereinafter, SAW resonator A) is connected in series, and the other output terminal of the dual mode SAW filter is connected to the lead electrode L1 extending from the bus bar inside the substrate 41 of the IDT 44. One terminal of a SAW resonator (hereinafter, SAW resonator B) in which the IDT 52 and the reflectors 53a and 53b are arranged is connected in series. The lead electrodes L2 extend from the other terminals of the SAW resonators A and B, respectively, and are respectively connected to bus bars near the center of the substrate 41 of the IDTs 47 and 48 of the second dual mode SAW filter. I do.
[0005]
As is well known, the operation of the dual mode SAW filter shown in FIG. 8 is that the surface waves excited by the IDTs 42, 43, and 44 are confined between the reflectors 45a and 45b and acoustically coupled, and the first order is formed by the electrode pattern. , And two longitudinal resonance modes of the third order are strongly excited, and a dual-mode SAW filter is constructed using these two modes. Further, by setting the anti-resonance frequencies of the SAW resonators A and B to be higher than the pass band of the dual mode SAW filter, the attenuation pole due to the anti-resonance frequency of the SAW resonator is higher in the pass band. Is generated, and the attenuation gradient and the amount of attenuation in the stop band on the high band side of the pass band are improved.
[0006]
FIG. 9 shows a case where a dual mode SAW filter having a thickness of 4100 ° and a thickness of an aluminum alloy is formed on a 39 ° Y-cut X-propagation LiTaO ₃ substrate to form a dual mode SAW filter having a center frequency of 836.5 MHz and a pass bandwidth of 25 MHz. 18.5 pairs of IDTs 42 and 46, 12.5 pairs of IDTs 43, 44 and 47 and 48, and 120 reflections 45a and 45b and 49a and 49b, respectively, and SAW resonators A and B FIG. 7 is a diagram showing pass characteristics of a dual mode SAW filter when the number of IDTs 50 and 52 is 63 pairs and the number of reflectors 51a and 51b and 53a and 53b is 4 each.
[Problems to be solved by the invention]
[0007]
In recent years, with the further improvement of communication quality, the required specifications from the market have become strict, and in particular, the need for higher attenuation in the stop band near the passband has become remarkable. To meet these demands, for example, as disclosed in JP-A-2000-349590, JP-A-7-307641, JP-A-7-30366, and JP-A-7-30367, Although a one-port SAW resonator is connected to the filter, the attenuation gradient near the pass band and the attenuation of the stop band have been improved. However, in these conventional surface acoustic wave filters, the attenuation characteristics of the stop band near the pass band have been improved. Improvement has reached its limit, and it has become difficult to satisfy the required specifications from the market.
[0008]
SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a surface acoustic wave filter having improved attenuation gradient and attenuation in a stop band, particularly in the vicinity of a pass band, among various characteristics improvement requests from the market. The purpose is to do.
[Means for Solving the Problems]
[0009]
In order to achieve the above object, a surface acoustic wave filter according to the present invention according to claim 1 comprises one or more longitudinally coupled multimode surface acoustic wave filters in which a plurality of IDTs and reflectors are arranged on both sides thereof. In a surface acoustic wave filter in which a plurality of cascade-connected and at least one one-port SAW resonator are connected in series to the longitudinally-coupled multi-mode surface acoustic wave filter, a capacitor is connected in parallel to the one-port SAW resonator. This is a surface acoustic wave filter characterized by the following.
[0010]
According to a second aspect of the present invention, one or a plurality of longitudinally coupled multimode surface acoustic wave filters having a plurality of IDTs and reflectors disposed on both sides thereof are cascaded, and the longitudinally coupled multimode surface acoustic wave filter is connected to the longitudinally coupled multimode surface acoustic wave filter. A surface acoustic wave filter in which at least one one-port SAW resonator is connected in parallel, wherein a capacitor is connected in parallel to the one-port SAW resonator.
[0011]
According to a third aspect of the present invention, in the surface acoustic wave filter according to the first or second aspect, the capacitor is a comb-shaped capacitor in which a comb-shaped electrode is arranged on a piezoelectric substrate. It is.
[0012]
According to a fourth aspect of the present invention, in the surface acoustic wave filter according to the third aspect, the comb capacitor is formed on the same piezoelectric substrate as the longitudinally coupled multi-mode surface acoustic wave filter or the one-port SAW resonator. Wherein a surface acoustic wave filter is arranged so as not to transmit / receive a surface acoustic wave to / from these.
[0013]
According to a fifth aspect of the present invention, in the surface acoustic wave filter according to the third or fourth aspect, when a plurality of the comb capacitors are provided on the same piezoelectric substrate, no surface acoustic waves are transmitted and received between the comb capacitors. A surface acoustic wave filter comprising the comb capacitor.
BEST MODE FOR CARRYING OUT THE INVENTION
[0014]
Hereinafter, the present invention will be described in detail based on an embodiment illustrated in the drawings. FIG. 1 is a plan view showing a configuration of a dual mode SAW filter according to a first embodiment of the present invention, in which three IDTs 2, 3 and 3 are arranged on a main surface of a piezoelectric substrate 1 along a propagation direction of a surface wave. 4 are arranged close to each other, and reflectors 5a and 5b are arranged on both sides thereof to form a first filter. Each of the IDTs 2, 3, and 4 is constituted by a pair of comb-shaped electrodes having a plurality of electrode fingers interposed therebetween, and the comb-shaped electrode outside the IDT 2 is connected to an electrode pad P1 provided near the outside of the electrode. The other comb-shaped electrode is connected to a grounding electrode pad E1 provided near the center of the substrate 1 near the electrode. The comb electrodes outside the IDTs 3 and 4 are connected to ground electrode pads E2 and E3 provided near the outside of the electrodes. Further, lead electrodes L1 for cascade connection are respectively extended from the other comb-shaped electrodes of the IDTs 3 and 4 toward the next stage.
[0015]
The second double mode SAW filter, which is substantially line-symmetric with respect to the first double mode SAW filter at the center of the substrate, that is, a double mode SAW including IDTs 6, 7, 8 and reflectors 9a, 9b disposed on both sides thereof. Form a filter. The bus bar inside the IDT 6 is connected to the ground electrode pad E4 provided near the center of the substrate 1 near the electrode, and the bus bar outside the IDT 6 is connected to the output electrode pad P2 provided near the outside of the electrode. Connect with Further, the bus bars near the ends of the substrate 1 of the IDTs 7 and 8 are connected to the grounding electrode pads E5 and E6, respectively. Further, lead electrodes L2 for cascade connection are respectively extended from the other comb-shaped electrodes of the IDTs 7 and 8 toward the front stage.
[0016]
IDT 10 and reflectors 11a and 11b are arranged on one output terminal of the first dual mode SAW filter, that is, on lead electrode L1 extending from the bus bar inside substrate 1 of IDT 3 along the propagation direction of the surface wave. Lead terminal extending from a bus bar inside the substrate 1 of the IDT 4 which is the other output terminal of the first dual mode SAW filter, while connecting one terminal of the SAW resonator (hereinafter, referred to as SAW resonator C) in series. One terminal of a SAW resonator (hereinafter, SAW resonator D) in which the IDT 12 and the reflectors 13a and 13b are arranged in L1 is connected in series. The lead electrodes L2 extend from the other terminals of the SAW resonators C and D, respectively, and are connected to bus bars near the center of the substrate 1 of the IDTs 7 and 8 of the second dual mode SAW filter. .
[0017]
The wavelength λr defined by the pitch of the interdigitated electrode fingers of the IDTs 10 and 12 constituting the SAW resonators C and D is the wavelength defined by the pitch of the interdigitated electrode fingers of the IDTs 2 to 4 and 6 to 8. λ, the anti-resonance frequency is set so as to be located on the high frequency side near the pass band of the first and second dual mode SAW filters connected in cascade, and the SAW resonance A trap having an anti-resonance frequency of the daughters C and D as an attenuation pole is configured. A feature of the present invention is that a comb capacitor 14 in which an IDT is arranged in a direction orthogonal to a propagation direction of a surface wave so that excitation reception of the surface wave is not performed is parallel to the SAW resonator C via a lead electrode L3. The SAW resonator is connected in parallel with the SAW resonator D via the lead electrode L4 to form a SAW filter.
[0018]
Next, the relationship between a one-port SAW resonator such as the SAW resonators C and D and a capacitor connected in parallel to the SAW resonator will be described. FIG. 2 is a diagram showing the impedance-frequency characteristics of the one-port SAW resonator. The broken line shows the characteristics of the one-port SAW resonator alone, and the solid line shows a capacitor equivalent to 1 pF in parallel with the one-port SAW resonator. This is the characteristic when connected. By connecting a capacitor to the one-port SAW resonator in parallel as shown in the figure, the anti-resonance frequency fa moves to the resonance frequency fr side and becomes fa ′, and the interval between the resonance frequency and the anti-resonance frequency is reduced. Understand.
[0019]
The inventor of the present application pays attention to this point, and in a longitudinally coupled multimode SAW filter, a one-port SAW resonator is connected in series to the SAW filter, and the anti-resonance frequency of the SAW resonator is shifted to a higher pass band side. When a trap is formed as an attenuation pole, a capacitor is connected in parallel to the one-port SAW resonator, so that the attenuation pole set on the high band side of the pass band moves to the low frequency side as shown in FIG. We thought that the attenuation gradient on the high band side might be further improved.
[0020]
FIG. 4 shows an electrode pattern as shown in FIG. 1 formed on a 39 ° Y-cut X-propagation LiTaO ₃ substrate to form a dual-mode SAW filter having a center frequency of 836.5 MHz and a pass bandwidth of 25 MHz. FIG. 7 is a diagram showing a comparison of measured data when a capacitor is connected in parallel to a one-terminal SAW resonator (solid line) and when a conventional structure without a comb capacitor is used (broken line). In the actual measurement data, the thickness of the aluminum alloy is 4100 ° for both the solid line and the broken line, IDT2 is 18.5 pairs, IDT3 and IDT4 are 12.5 pairs, and the number of reflectors 5a and 5b is 120 each. The number of IDTs 10 and 12 of the SAW resonator is 63, and the number of reflectors 11a, 11b and 13a, 13b is 4. The wavelength λ defined by the pitch of the electrode fingers constituting the IDTs 2, 3, and 4 And the ratio (λr / λ) of the wavelength λr defined by the pitch of the electrode fingers constituting the one-terminal SAW resonator was set to 0.99193. In the solid line data, the number of comb-shaped capacitors 14 and 15 is 33, the cross width of the comb-shaped electrodes is 53 μm, and a capacitor corresponding to 0.85 pF is connected in parallel to the one-terminal SAW resonator. If the comb capacitor is simply connected in parallel to the one-port SAW resonators C and D, the filter as a whole filter is affected by the narrowing of the resonance frequency-anti-resonance frequency interval of the one-port SAW resonator. Since the pass band width is slightly narrowed, in the measured data shown in FIG. 4, the one-port SAW resonator having the comb capacitors connected in parallel is compared with the one-port SAW resonator having no comb capacitors connected. The period of the IDT and the reflector is shortened, and the resonance frequency is increased by 2 MHz. As can be seen from the figure, by connecting the comb capacitor in parallel to the one-port SAW resonator, the attenuation gradient and the stopband attenuation near the high band side of the passband are improved.
[0021]
The electrode finger arrangement period of the comb capacitor is not necessarily required to be equal to that of the IDT or the reflector of the one-port SAW resonator, as long as a desired reactance can be obtained. Since they can be formed at the same time, no additional steps are required in the manufacturing process.
[0022]
In the method of arranging the comb capacitors, in FIG. 1, the comb capacitors are arranged in a direction orthogonal to the IDT. However, it is not always necessary to make them orthogonal and any direction may be used so long as the surface waves of the IDT are not transmitted and received. . However, in consideration of the chip size, a structure in which comb capacitors are arranged orthogonally to the IDT shown in FIG. 1 is desirable. Also, when a plurality of comb capacitors are provided on the SAW chip, it is necessary to arrange the comb capacitors so that surface waves are transmitted and received between the comb capacitors and no spurious is generated outside the pass band.
[0023]
FIG. 5 shows a second embodiment according to the present invention, in which three IDTs 21, 22, and 23 are arranged close to each other along the propagation direction of a surface acoustic wave on a piezoelectric substrate 1, and reflectors 24a and 24b are provided at both ends thereof. In the longitudinally coupled dual mode SAW filter arranged, one comb-shaped electrode of the IDT 21 is connected to the input electrode pad P1, and the other comb-shaped electrode of the IDT 21 is connected to the ground electrode pad E1. Also, one of the IDTs 22 and 23 is connected to the ground electrode pads E2 and E3, respectively, and the other of the IDTs 22 and 23 is connected to one side of the one-terminal SAW resonator 25 on one side. Then, the other comb-shaped electrode of the SAW resonator 25 is connected to the output electrode pad P2. The anti-resonance frequency of the one-port SAW resonator 25 is designed to be higher than the pass band of the dual mode SAW filter. A feature of this embodiment is that in the structure in which the one-port SAW resonator 25 is connected in series to the dual mode SAW filter, a comb capacitor 26 is connected in parallel to the one-port SAW resonator 25.
[0024]
Also in the second embodiment, by connecting the comb capacitor in parallel to the one-port SAW resonator, the attenuation gradient and the stop band attenuation near the high band side of the pass band are improved as in the first embodiment. Is done. Although FIG. 5 shows a structure in which one one-port SAW resonator is connected in series to the output side of the dual-mode SAW filter, a plurality of one-port SAW resonators are connected in series to the dual-mode SAW filter. It is apparent that the same effect can be obtained by the structure or the structure in which the one-port SAW resonator is connected in series to the input / output side of the dual mode SAW filter.
[0025]
FIG. 6 shows a third embodiment according to the present invention. Since the dual mode SAW filter has the same configuration as that of FIG. 5, the same reference numerals as in FIG. 5 are used. The feature of this embodiment is that in a structure in which a one-port SAW resonator 27 is connected in parallel to the output side of a dual-mode SAW filter, a comb-shaped capacitor 28 is connected in parallel to the one-port SAW resonator 27. The design is such that the resonance frequency of the terminal pair SAW resonator 27 is positioned lower than the pass band of the dual mode SAW filter.
[0026]
In the third embodiment, in a structure in which a one-port SAW resonator is connected in parallel to a dual-mode SAW filter, a low pass band is achieved by connecting a comb capacitor in parallel to the one-port SAW resonator. The attenuation gradient near the band side and the amount of attenuation in the stop band are improved. Although FIG. 6 shows a structure in which one one-port SAW resonator is connected in parallel to the output side of the dual-mode SAW filter, a plurality of one-port SAW resonators are connected in parallel to the dual-mode SAW filter. It is apparent that the same effect can be obtained also in the structure or the structure in which the one-port SAW resonator is connected in parallel to the input / output side of the dual mode SAW filter.
[0027]
FIG. 7 shows a fourth embodiment according to the present invention. This embodiment is characterized in that a one-port SAW resonator 29 is connected in series on the input side of a dual-mode SAW filter, and a one-port SAW resonator 31 is connected in parallel on the output side of the dual-mode SAW filter. In this structure, the comb capacitors 30 and 32 are connected in parallel to the one-port SAW resonators 29 and 31, respectively, and the anti-resonance frequency of the one-port SAW resonator 29 is set higher than the pass band of the dual mode SAW filter. Are designed to be located on the high frequency side, and the resonance frequency of the one-port SAW resonator 31 is located on the lower frequency side than the pass band of the dual mode SAW filter.
[0028]
In the fourth embodiment, a one-port SAW resonator is connected in series to the input side of a dual-mode SAW filter, and a one-port SAW resonator is connected in parallel to the output side of the dual-mode SAW filter. In the structure, by connecting a comb capacitor in parallel with the one-port SAW resonator, the attenuation gradient and the amount of attenuation in the stop band on both sides near the low band side and near the high band side of the pass band are improved. FIG. 6 shows a structure in which one one-port SAW resonator is connected in series to the input side of the dual-mode SAW filter and one one-port SAW resonator is connected in parallel to the output side. Obviously, the same effect can be obtained when a plurality of SAW resonators are connected in series or in parallel.
[0029]
As described above, a feature of the present invention is that, in a surface acoustic wave filter in which a one-port SAW resonator is connected to a multimode longitudinally coupled SAW filter, a comb capacitor is connected to the one-port SAW resonator. This means that the attenuation gradient near the pass band is steeper than when no comb capacitor is provided.
[0030]
Although the above description has been made with reference to the example in which the first-order and third-order longitudinally coupled dual-mode SAW filters are cascaded in one or two stages, the present invention is not limited to this. It goes without saying that the present invention can be applied to filters and the like. Also, the explanation has been made using the 39 ° Y-cut X-propagation LiTaO ₃ substrate as the piezoelectric substrate, but other cuts may be used, and the present invention can be applied to other piezoelectric materials such as lithium niobate, quartz, langasite, and lithium tetraquarate. Needless to say.
[0031]
【The invention's effect】
The surface acoustic wave filter according to the present invention has the following excellent effects because it is configured as described above. The invention according to claim 1 or 2, wherein one or a plurality of longitudinally coupled multimode surface acoustic wave filters having a plurality of IDTs and reflectors arranged on both sides thereof are connected in cascade, and the longitudinally coupled multimode surface acoustic wave filter is provided. In a surface acoustic wave filter in which at least one one-port SAW resonator is connected in series or in parallel to a filter, by connecting a capacitor in parallel with the one-port SAW resonator, the attenuation gradient near the pass band is steep. It has an excellent effect that it can be made.
[0032]
According to a third aspect of the present invention, since the capacitor is a comb-shaped capacitor having a comb-shaped electrode disposed on a piezoelectric substrate, the capacitor can be formed simultaneously when an electrode pattern is formed on a main surface of a SAW chip. Has an excellent effect that no step is added.
[0033]
According to the fourth and fifth aspects of the present invention, since the comb capacitors are arranged so as not to transmit and receive surface waves between adjacent IDTs and other comb capacitors, an excellent effect that spurious noise is not generated outside the pass band. To play.
[Brief description of the drawings]
FIG. 1 is a plan view showing a configuration of a cascaded first-third-order longitudinally-coupled dual-mode SAW filter according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a comparison of impedance-frequency characteristics when a one-port SAW resonator alone and a comb capacitor are connected in parallel to the SAW resonator.
FIG. 3 is a diagram illustrating a relationship between an anti-resonance frequency of a SAW resonator used in a cascade-connected primary-tertiary-order longitudinally coupled dual-mode SAW filter and an attenuation pole of the filter.
FIG. 4 is a graph of measured data showing a comparison between the filter characteristics of a cascaded primary-tertiary-order longitudinally coupled dual-mode SAW filter according to the present invention and conventional filter characteristics.
FIG. 5 is a plan view showing a configuration of a cascaded primary-third-order longitudinally coupled dual mode SAW filter according to a second embodiment of the present invention.
FIG. 6 is a plan view showing a configuration of a cascaded primary-third-order longitudinally coupled dual-mode SAW filter according to a third embodiment of the present invention.
FIG. 7 is a plan view showing a configuration of a cascaded primary-third-order longitudinally coupled dual-mode SAW filter according to a fourth embodiment of the present invention.
FIG. 8 is a plan view showing the configuration of a conventional cascaded primary-tertiary-order longitudinally coupled dual-mode SAW filter.
FIG. 9 is a diagram showing filter characteristics of a conventional cascade-connected primary-tertiary-order longitudinally coupled dual-mode SAW filter.
[Explanation of symbols]
1, 41 ··· piezoelectric substrate 2, 3, 4, 6, 7, 8, 10, 12, 21, 22, 23, 42, 43, 44, 46, 47, 48, 50, 52 ··· IDT electrode 5a 5b, 9a, 9b, 11a, 11b, 13a, 13b, 24a, 24b, 45a, 45b, 49a, 49b, 51a, 51b, 53a, 53b, grating reflectors P1, P2, input / output electrode pads E1, E2, E3, E4, E5, E6... Ground electrode pads L1, L2, L3, L4... Lead electrodes 14, 15, 26, 28, 30, 32. A, B, C, D: 1 port pair SAW resonator

Claims (5)

One or a plurality of longitudinally coupled multimode surface acoustic wave filters having a plurality of IDTs and grating reflectors disposed on both sides thereof are connected in cascade, and the longitudinally coupled multimode surface acoustic wave filter has at least one terminal pair. A surface acoustic wave filter in which SAW resonators are connected in series, wherein a capacitor is connected in parallel to the one-port SAW resonator. One or a plurality of longitudinally coupled multimode surface acoustic wave filters having a plurality of IDTs and grating reflectors disposed on both sides thereof are connected in cascade, and the longitudinally coupled multimode surface acoustic wave filter has at least one terminal pair. A surface acoustic wave filter in which SAW resonators are connected in parallel, wherein a capacitor is connected in parallel to the one-port SAW resonator. 3. The surface acoustic wave filter according to claim 1, wherein the capacitor is a comb capacitor having a comb-shaped electrode disposed on a piezoelectric substrate. 4. The surface acoustic wave filter according to claim 3, wherein the comb capacitor is formed on the same piezoelectric substrate as the longitudinally coupled multimode surface acoustic wave filter or the one-port SAW resonator. A surface acoustic wave filter characterized by being arranged so as not to transmit and receive surface acoustic waves. 5. The surface acoustic wave filter according to claim 3, wherein when a plurality of the comb capacitors are provided on the same piezoelectric substrate, the comb capacitors are arranged so as not to transmit and receive surface acoustic waves between the comb capacitors. A surface acoustic wave filter characterized by the above-mentioned.

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