JP2006080873A - Surface acoustic wave device and communication device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a longitudinally coupled multiple mode surface acoustic wave filter whose pass band is wide, and insertion loss in the pass band is small. <P>SOLUTION: In a longitudinally coupled multiple mode surface acoustic wave apparatus, a plurality of interdigital electrodes are closely arranged on a piezoelectric substrate along the propagation direction of an exciting surface acoustic wave, and reflectors are arranged on both sides of this row of interdigital electrodes. A dummy electrode finger is formed between each electrode finger of an interdigital electrode and a bus bar, and an acoustic velocity in each reflector corresponding to the dummy electrode finger of the interdigital electrode and the air gap between the electrode finger and the dummy electrode finger, is made slower than the acoustic velocity of a uniform metallized region, so as to suppress unnecessary radiation of the surface acoustic wave at the reflectors. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface acoustic wave device used for a communication device such as a mobile radio terminal (for example, a mobile phone), and more particularly to a surface acoustic wave device having a wide passband and a small insertion loss in the passband, and a communication device using the same. It is about.

  In recent years, with an increase in data communication speed of mobile phones, communication systems are being shifted to ones having a wide transmission / reception band. In order to effectively use the frequency, the interval between the transmission and reception bands is narrowing, and a high-angle filter having a wide band and a steep cut-off characteristic is required.

  As a method for realizing a surface acoustic wave device having a wide passband and low loss while maintaining a large attenuation outside the passband in the vicinity of the high frequency side of the passband, the elasticity as described in Patent Document 1 below is used. Surface wave devices have been proposed.

  A surface acoustic wave device described in Patent Document 1 includes a surface acoustic wave filter having at least two comb electrodes (IDT) on a piezoelectric substrate, and a surface acoustic wave connected in series to the surface acoustic wave filter. The surface acoustic wave resonator is characterized in that spurious due to SSBW is shifted to the resonance frequency.

  One embodiment of the surface acoustic wave device described in Patent Document 1 is shown in FIG. As shown in the figure, this surface acoustic wave device includes two 3IDT type longitudinally coupled double mode surface acoustic wave filters 131 and 137, and four surface acoustic wave resonators 143, 147 and 151 connected in series thereto. 155.

  At this time, at least one of the surface acoustic wave resonators 143, 147, 151, and 155 has a resonance frequency within the pass band of the 3IDT type longitudinally coupled double mode surface acoustic wave filters 131 and 137 and an antiresonance frequency of 3IDT type. The longitudinally coupled double mode surface acoustic wave filters 131 and 137 are set to be located outside the passband.

  In addition, the dummy electrode finger 154 is provided between the electrode finger 152 of the IDT and the bus bar 153 in the surface acoustic wave resonators 151 and 155. In the figure, 155 is an unbalanced input terminal, and 156 and 157 are balanced output terminals.

In this configuration, by providing the dummy electrode finger 154, the spurious attributed to the SSBW of the surface acoustic wave resonator can be shifted to the resonance frequency side, and while maintaining a large attenuation outside the passband, A surface acoustic wave device having a small insertion loss on the inner high frequency side and a wide pass band is obtained.
JP 2003-309448 A

  However, if dummy electrode fingers 154 are provided on the surface acoustic wave resonators 151 and 155 as in this surface acoustic wave device, it is difficult to improve the insertion loss in the entire pass band, particularly on the low frequency side. Further, in a surface acoustic wave device having no surface acoustic wave resonator, it is not an effective means.

  The object of the present invention is to eliminate such drawbacks, and in a longitudinally coupled multimode surface acoustic wave device, while reducing the insertion loss on the high frequency side in the pass band, the loss is also reduced on the low frequency side in the pass band. The present invention is to propose a surface acoustic wave device having a wide pass band and good shoulder characteristics, and a communication device using the same.

In order to achieve the above object, the first means of the present invention is arranged on the piezoelectric substrate in close proximity along the propagation direction of the surface acoustic wave exciting the plurality of comb electrodes, and reflectors on both sides of the comb electrode rows. In a longitudinally coupled multimode surface acoustic wave device using a plurality of vibration modes generated by acoustic coupling between the plurality of comb electrodes,
A dummy electrode finger that does not contribute to excitation is formed between the electrode finger of the comb electrode and the bus bar, and the dummy electrode finger portion and the electrode finger of the comb electrode are suppressed so as to suppress unnecessary radiation of the surface acoustic wave in the reflector. The sound speed of the reflector corresponding to the gap between the electrode and the dummy electrode finger is made slower than the sound speed of the uniform metallized region.

  According to a second means of the present invention, in the first means, the opening length of the reflector includes an intersection of the electrode fingers of the comb-shaped electrode and an opening between the electrode finger and the dummy electrode finger. It is characterized in that it is set longer than the length of the part.

  According to a third means of the present invention, in the first or second means, the opening of the reflector includes an intersection of electrode fingers of a comb-shaped electrode, a gap between the electrode finger and a dummy electrode finger, and a dummy. The position is set on the same straight line as the opening including the electrode finger.

  A fourth means of the present invention is the surface acoustic wave device according to any one of the first to third means, wherein the surface acoustic wave device is disposed adjacently along the propagation direction of the surface acoustic wave exciting the three comb electrodes. A three-comb electrode-type longitudinally coupled dual-mode elastic surface using reflectors on both sides of these comb-shaped electrode arrays and utilizing the first and third vibration modes generated by acoustic coupling between the three comb-shaped electrodes. It is a wave device.

  According to a fifth means of the present invention, in any one of the first to fourth means, a piezoelectric substrate having an electromechanical coupling coefficient in the range of 1 to 30% is used as the piezoelectric substrate. .

  According to a sixth means of the present invention, in any one of the first to fifth means, if the wavelength defined by the pitch of the comb electrodes is λ, the length of the dummy electrode is 0.2λ-3. It is characterized by being defined in the range of 0λ.

  According to a seventh means of the present invention, the surface acoustic wave device according to any one of the first to sixth means is used for a communication device.

  As described above, the present invention can suppress the oblique emission of the surface acoustic wave by providing the dummy electrode finger between the IDT electrode finger and the bus bar of the longitudinally coupled multimode surface acoustic wave filter. Thus, the loss in the passband can be greatly reduced and the bandwidth can be increased.

  Furthermore, it becomes possible to suppress unnecessary radiation of the surface acoustic wave in the reflector, and it is possible to further reduce the loss and increase the bandwidth on the low frequency side in the passband.

  In a longitudinally coupled multimode surface acoustic wave filter, by providing a dummy electrode finger between the electrode finger of the comb electrode and the bus bar, oblique emission of the surface acoustic wave can be suppressed and confined in the lateral direction (cross width direction). it can.

  In order to confine the surface acoustic wave in the lateral direction (cross width direction) in the comb-shaped electrode, the gap 402 and the bus bar located outside the surface acoustic wave velocity Vi in the intersecting portion of the comb-shaped electrode 401 in FIG. It is necessary to slow down the speeds Vg and Vb at 403. In practice, however, as shown in the figure, the velocity Vg in the gap 402 is higher than the surface acoustic wave velocity Vi at the crossing portion of the comb electrode 401, and the velocity Vb in the outer bus bar 403 is higher (see FIG. Vi <Vg <Vb). Therefore, it is considered that the surface acoustic wave leaks from the tip of the electrode finger 404 as indicated by an arrow.

  As shown in FIG. 4, by providing the dummy electrode finger 406 between the electrode finger 404 of the comb-shaped electrode 405 and the bus bar 403, a region where the surface acoustic wave velocity is slower than the gap portion 402 is created outside the gap portion 402. The surface acoustic wave can be confined in the lateral direction (cross width direction).

  Next, 1st Embodiment of this invention is described with a comparative example. As an example of this embodiment, a reception filter for a 1.9 GHz band PCS (Personal Communications System) having a balanced-unbalanced conversion function (impedance on the unbalanced side is 50Ω and impedance on the balanced side is 150Ω) will be described as an example. .

  FIG. 1 is an electrode pattern diagram for explaining the surface acoustic wave device according to the first embodiment of the present invention, and FIG. 2 is an electrode pattern diagram in Comparative Example 1.

  In these figures, 201 and 207 are 3IDT type longitudinally coupled double mode surface acoustic wave filters, 202, 203, 204, 208, 209, 210, 214, and 218 are comb-shaped electrodes, and 205, 206, 211, 212, 215, and 216, respectively. 219 and 220 are reflectors, 213 and 217 are surface acoustic wave resonators, 221 are unbalanced input terminals, 222 and 223 are balanced output terminals, 202a and 202b are electrode fingers, and 224 is a dummy electrode finger.

  First, Comparative Example 1 will be described with reference to FIG. Three comb-shaped electrodes 202, 203, and 204 are arranged close to each other along the propagation direction of the surface acoustic wave to be excited on the piezoelectric substrate, and reflectors 205 and 206 are disposed on both sides of the comb-shaped electrodes 202, 203, and 204 rows. The 3IDT type longitudinally coupled double mode surface acoustic wave filter 201 is arranged so as to use first and third order vibration modes generated by acoustic coupling between the three comb electrodes 202, 203, 204. A surface acoustic wave resonator 213 is connected in series between the 3IDT type longitudinally coupled double mode surface acoustic wave filter 201 and the unbalanced input terminal 221.

  Similarly, reflectors 211 and 212 are arranged on both sides of the comb-shaped electrodes 208, 209, and 210 rows to constitute a 3IDT type longitudinally coupled double mode surface acoustic wave filter 207. A surface acoustic wave resonator 217 is connected in series between the 3IDT type longitudinally coupled double mode surface acoustic wave filter 207 and the unbalanced input terminal 221. The surface acoustic wave filter 207 includes a comb-shaped electrode 208 in which the phase of the comb-shaped electrode 202 at the center of the surface acoustic wave filter 201 is reversed to reverse the phase.

  In the first embodiment, as shown in FIG. 1, dummy electrode fingers 224 are provided between the electrode fingers 202 a and 202 b of the surface acoustic wave filters 201 and 207 and the bus bar.

The detailed design of the surface acoustic wave device according to the first embodiment is as follows.
(Piezoelectric substrate)
42 ° Y-XLiTaO ₃ : electromechanical coupling coefficient 7 to 11%
(3IDT type longitudinally coupled double mode surface acoustic wave filters 201, 207)
IDT wavelength λ _I1 : 2.03 μm
Reflector wavelength λ _R1 : 2.04 μm
Comb electrode cross length W _I : 31.5λ _I1
Dummy electrode length L: 1.2λ _I1
Gap length L _g : 0.6 μm
(Surface acoustic wave resonators 213 and 217)
IDT wavelength λ _I2 : 2.006 μm
Reflector wavelength λ _R2 : 2.006 μm
Comb electrode cross length W _I : 37.5λ _I2
IDT logarithm: 100 pairs Air gap length: 1.0 μm

Next, the effect of the first embodiment will be described. The comparison results of the characteristics of Comparative Example 1 (without dummy electrodes) and the first embodiment (with dummy electrodes) are shown in FIGS. FIG. 5 is a transmission characteristic diagram, and FIG. 6 is a square ratio characteristic table.

  As can be seen from these figures, the insertion loss of Comparative Example 1 is 2.26 dB, whereas in the first embodiment, the 2.19 dB and 0.07 dB insertion losses are improved.

  Further, the loss at the end of the pass band is 1.75 dB in Comparative Example 1 at 1930 MHz, whereas the improvement in the first embodiment is 1.59 dB and 0.16 dB, and Comparative Example 1 at 1990 MHz. Is 2.24 dB, whereas the improvement effect of 1.98 dB and 0.26 dB is obtained in the first embodiment.

  In addition, it can be seen that also in the squareness ratio (−10 dB bandwidth / −3 dB bandwidth), Comparative Example 1 is steep as 1.207, and 1.163 in the first embodiment.

  Next, FIGS. 7 and 8 show changes in insertion loss (FIG. 7) and squareness ratio (FIG. 8) when the length L (see FIG. 4) / λ of the dummy electrode fingers is changed. The wavelength λ is a wavelength defined by the pitch of the comb electrodes.

The length L of 0.2λ _I1 ~3.0λ dummy electrode fingers as is clear from these figures _I1, preferably 0.6λ _{I1 ~3.0λ I1,} more preferably 1.0λ _I1 ~2.0λ _I1 As a result, good results with low loss and high squareness ratio can be obtained.

  In the longitudinally coupled multimode surface acoustic wave filter in which the dummy electrode finger is provided between the electrode finger of the comb electrode and the bus bar, the present invention is configured so that the opening length of the reflector is set to the cross electrode finger length of the comb electrode and the dummy electrode finger. The electrode finger length and the length of the opening including the gap between the electrode finger and the dummy electrode finger are set to be the same. According to this configuration, unnecessary radiation of the surface acoustic wave in the reflector can be suppressed and confined in the lateral direction (cross width direction).

  As described above, by making the velocity of the surface acoustic wave in the non-waveguide slower than the velocity of the surface acoustic wave in the waveguide, the surface acoustic wave can be confined in the lateral direction (cross width direction), and unnecessary radiation is generated. The same applies to the reflector. Therefore, the structure of the reflector is set so as to suppress unnecessary radiation of the surface acoustic wave in the reflector.

  FIG. 11 shows a structure in which the length of the opening of the reflector 501 is set to be the same as the length WI of the crossing portion of the comb electrode 502. In such a structure, the surface acoustic wave that has excited the crossing portion of the comb electrode 502 reaches the reflector 501 and is radiated into the uniformly metallized bus bar 508 having a high surface acoustic wave velocity. In the figure, 504 is the bus bar of the comb-shaped electrode 502, 507 is the electrode finger of the reflector 501, Vr is the surface acoustic wave velocity at the electrode finger 507 of the reflector 501, and Vb is the surface acoustic wave velocity at the bus bar 508 of the reflector 501. .

  In FIG. 12, the opening of the reflector 501 is on the same straight line as the opening including the cross electrode finger of the comb-shaped electrode 502 and the dummy electrode finger 506 and the gap 503 between the electrode finger 505 and the dummy electrode finger 506. And including the length W of the opening of the reflector 501, the cross electrode finger of the comb electrode 502 and the dummy electrode finger 506, and the gap 503 between the electrode finger 505 and the dummy electrode finger 506. This is the same structure as the length WR of the opening (W = WR).

  With such a structure, the sound velocity (Vr) of the reflector corresponding to the dummy electrode finger portion of the comb-shaped electrode and the gap portion between the electrode finger and the dummy electrode finger is set to the sound velocity (Vb) of the uniform metallized region. ) (Vr <Vb), and the surface acoustic wave that has excited the crossing portion of the comb-shaped electrode 502 is suppressed in velocity within the reflector 501 and the generation of unwanted wave mode is reliably suppressed.

In particular, in a piezoelectric substrate having a large electromechanical coupling coefficient of 1 to 30%, such as a LiTaO ₃ piezoelectric substrate, the velocity of the surface acoustic wave propagating through the crossing portion of the comb-shaped electrode and the velocity of the surface acoustic wave propagating outside thereof The difference becomes larger and the confinement effect becomes stronger.

  Next, a second embodiment of the present invention will be described together with a comparative example 2. As an example of this embodiment, a receiving filter for 900 MHz band EGSM (Extended Global System for Mobile Communication) having a balanced-unbalanced conversion function (impedance on the unbalanced side is 50Ω and impedance on the balanced side is 150Ω) will be described as an example. Do.

  FIG. 9 is an electrode pattern diagram for explaining the surface acoustic wave device according to the second embodiment of the present invention, and FIG. 10 is an electrode pattern diagram in Comparative Example 2.

  In these figures, reference numerals 301, 307, 313, and 319 denote 3IDT type longitudinally coupled dual mode surface acoustic wave filters, 302, 303, 304, 308, 309, 310, 314, 315, 316, 320, 321, and 322, respectively. Comb electrodes 305, 306, 311, 312, 317, 318, 323, 324 are reflectors, 325 are unbalanced input terminals, 326, 327 are balanced output terminals, 328 are dummy electrode fingers, 329 is a gap, 308a, 308b is an electrode finger.

  Four 3IDT type longitudinally coupled double mode surface acoustic wave filters 301, 307, 313, 319 are formed on the piezoelectric substrate so as to have a balance-unbalance conversion function.

  The surface acoustic wave filter 301 is disposed in the vicinity of the propagation direction of the surface acoustic wave that excites the three comb-shaped electrodes 302, 303, and 304 on the piezoelectric substrate, and reflectors 305 are provided on both sides of the comb-shaped electrodes 302 to 304. , 306 are arranged and primary and tertiary vibration modes generated by acoustic coupling between the three comb electrodes 302 to 304 are used.

  The surface acoustic wave filter 307 has the same characteristics as the surface acoustic wave filter 301. The surface acoustic wave filter 307 is arranged such that the surface acoustic wave propagation direction of the surface acoustic wave filter 307 is parallel to the surface acoustic wave propagation direction of the surface acoustic wave filter 301 and the propagation direction is The symmetrical line is symmetrical with respect to the surface acoustic wave filter 301.

  The surface acoustic wave filter 313 has the same characteristics as the surface acoustic wave filter 301. The surface acoustic wave filter 313 is arranged such that the propagation direction of the surface acoustic wave of the surface acoustic wave filter 313 is parallel to the propagation direction of the surface acoustic wave in the surface acoustic wave filter 301 and is in the propagation direction. The surface acoustic wave filter 301 is symmetric with respect to the surface acoustic wave filter 301 with a direction perpendicular to the surface as a symmetric line.

  The surface acoustic wave filter 319 is arranged such that the surface acoustic wave propagation direction of the surface acoustic wave filter 319 is parallel to the surface acoustic wave propagation direction of the surface acoustic wave filter 313 and the propagation direction is The surface acoustic wave filter 313 is symmetrical with respect to the surface acoustic wave filter 313, and the center comb-shaped electrode 320 of the surface acoustic wave filter 319 is inverted so that the phase is inverted. .

  A dummy electrode finger 328 is provided between the electrode fingers 308a and 308b of each of the comb electrodes 302, 303, 304, 308, 309, 310, 314, 315, 316, 320, 321, and 322 and the bus bar.

In this embodiment, as shown in FIG. 9, the opening length W of each reflector 305, 306, 311, 312, 317, 318, 323, 324 is set to the cross width W _I of the comb electrodes 308a, 308b (see FIG. 10). And the length of the dummy electrode finger 328 and the opening length WR including the gap 329 between the dummy electrode finger 328 and the comb-shaped electrodes 308a and 308b are set to the same length (same position W = WR). .

The detailed design of the surface acoustic wave device according to this embodiment is as follows.

(Piezoelectric substrate)
42 ° Y-XLiTaO ₃ : electromechanical coupling coefficient 7 to 11%
(3IDT type longitudinally coupled double mode surface acoustic wave filters 301, 307, 313, 319)
IDT wavelength λ _I : 4.188 μm
Reflector wavelength λ _R : 4.236 μm
Comb electrode cross length WI: 29.5λ _I
Reflector aperture length W : W _I (29.5λ _I ) + L _d (0.944 μm × 2)
+ L _g (1.0λ _I × 2)
Dummy electrode length L : 1.0λ _I
Gap length : 0.944 μm

On the other hand, in Comparative Example 2, as shown in FIG. 10, the openings of the reflectors 305, 306, 311, 312, 317, 318, 323, and 324 are set to be the same as the crossing width WI of the comb-shaped electrode.

  A characteristic comparison between the second embodiment of the present invention and Comparative Example 2 is shown in FIGS. FIG. 13 shows transmission characteristics, and FIG. 14 shows loss improvement characteristics.

  As is apparent from these figures, the insertion loss of Comparative Example 2 is 1.81 dB, whereas in the present embodiment, it is not different from 1.81 dB, but the minimum insertion loss is improved by 0.04 dB.

  Furthermore, the loss at the end of the passband is 925 MHz, and Comparative Example 2 is 1.77 dB, whereas the second embodiment is 1.65 dB, which is an improvement of 0.12 dB. In contrast to 2 being 1.69 dB, the improvement effect of 1.68 dB and 0.01 dB was obtained in the second embodiment. It can be seen that the structure of the present invention has an effect of improving the loss particularly on the low frequency side in the passband.

  FIG. 15 is an electrode pattern diagram for explaining the surface acoustic wave device according to the third embodiment of the present invention. In the surface acoustic wave filter according to this embodiment, the opening length W of the reflectors 305, 306, 311, 312, 317, 318, 323 and 324 is set to the cross length WI of the electrode fingers 308 a and 308 b in the comb electrode 308 ( And the opening WG including the gap 329 between the electrode fingers 308a and 308b and the dummy electrode finger 328, and the same length (the same position W = WG) and the position on the same straight line. . With this configuration, the loss improvement effect is slightly reduced, but the effect of the present invention can be obtained.

  Although the above embodiment is a surface acoustic wave filter having a balance-unbalance conversion function, the effect of the present invention can be obtained even in a configuration without a balance-unbalance conversion function.

  For example, as shown in FIG. 16, there is no balanced-unbalanced conversion function, but a longitudinally coupled dual mode elasticity of a 3IDT configuration having a dummy electrode finger 224 between the surface acoustic wave resonator filter 213 and the unbalanced output terminal 222. A configuration in which surface wave filters 201 are connected in series (fourth embodiment), or a configuration in which two 3IDT type longitudinally coupled dual mode surface acoustic wave filters 301 and 307 having dummy electrode fingers 328 are connected in cascade as shown in FIG. In the fifth embodiment, the effects of the present invention can be obtained.

  FIG. 18 is an electrode pattern diagram for explaining the surface acoustic wave device according to the sixth embodiment of the present invention. In the case of this embodiment, the opening length W of each reflector 305 (306, 311, 312, 317, 318, 323, 324) is set to the cross length WI (see FIG. 10) of the comb electrodes 308a, 308b and the dummy electrode finger. The length 328 is longer than the opening length WR including the gap 329 between the dummy electrode finger 328 and the comb electrodes 308a and 308b (W> WR), and is set on the same straight line.

  FIG. 19 is a block diagram of a mobile radio terminal including the surface acoustic wave device according to the embodiment. The receiver side of this communication apparatus includes an antenna 1, an antenna duplexer 2, an amplifier 3, an Rx interstage filter 4, a mixer 5, a 1st IF filter 6, a mixer 7, a 2nd IF filter 8, a 1st + 2nd local synthesizer 9, a crystal oscillator 10, and a divider 11. And a local filter 12 and the like.

  The transceiver side includes a TxIF filter 13, a mixer 14, an Fx interstage filter 15, an amplifier 16, a coupler 17, an automatic output control unit 18, an isolator 19, an antenna duplexer 2, an antenna 1, and the like.

The surface acoustic wave device according to the embodiment is applied to the Rx interstage filter 4, the 1stIF filter 6, the TxIF filter 13, and the Fx interstage filter 15. In the above embodiment, LiTaO ₃ is used as the piezoelectric substrate having an electromechanical coupling coefficient in the range of 1 to 30%. However, for example, LiNbO ₃ or Li ₂ B ₄ O ₇ can also be used.

It is an electrode pattern figure for demonstrating the surface acoustic wave apparatus which concerns on 1st Embodiment of this invention. 6 is an electrode pattern diagram for explaining a surface acoustic wave device according to Comparative Example 1. FIG. It is an electrode pattern enlarged view for demonstrating the surface acoustic wave apparatus of a prior art example. It is an electrode pattern enlarged view for demonstrating the surface acoustic wave apparatus which concerns on this invention. It is a frequency characteristic figure of the surface acoustic wave device concerning a 1st embodiment of the present invention, and the surface acoustic wave device concerning comparative example 1. 5 is a table comparing the squareness ratios of the surface acoustic wave device according to the first embodiment of the present invention and the surface acoustic wave device according to Comparative Example 1. It is a characteristic view which shows the change of insertion loss when changing the length of the dummy electrode finger of the surface acoustic wave apparatus concerning 1st Embodiment of this invention. It is a characteristic view which shows the change of the squareness ratio when changing the length of the dummy electrode finger of the surface acoustic wave device concerning a 1st embodiment of the present invention. It is an electrode pattern figure for demonstrating the surface acoustic wave apparatus which concerns on 2nd Embodiment of this invention. It is an electrode pattern figure for demonstrating the surface acoustic wave apparatus which concerns on the comparative example 2. FIG. FIG. 3 is an enlarged view of an electrode pattern of a surface acoustic wave device in which the opening length of a reflector is the same as the length of a crossing portion of a comb-shaped electrode. FIG. 4 is an enlarged electrode pattern diagram of a surface acoustic wave device in which the opening length of the reflector is the same as the total length of the crossing portion, the gap portion and the dummy electrode of the comb electrode. It is a frequency characteristic figure of the surface acoustic wave device concerning a 2nd embodiment of the present invention, and the surface acoustic wave device concerning comparative example 2. It is the table | surface which compared the squareness ratio of the surface acoustic wave apparatus which concerns on 2nd Embodiment of this invention, and the surface acoustic wave apparatus which concerns on the comparative example 2. It is an electrode pattern figure for demonstrating the surface acoustic wave apparatus which concerns on 3rd Embodiment of this invention. It is an electrode pattern figure for demonstrating the surface acoustic wave apparatus which concerns on 4th Embodiment of this invention. It is an electrode pattern figure for demonstrating the surface acoustic wave apparatus which concerns on 5th Embodiment of this invention. It is an electrode pattern figure for demonstrating the surface acoustic wave apparatus which concerns on 6th Embodiment of this invention. 1 is a block diagram of a communication device to which a surface acoustic wave device according to an embodiment of the present invention is applied. It is an electrode pattern figure for demonstrating the surface acoustic wave apparatus proposed conventionally.

Explanation of symbols

201, 207, 301, 307, 313, 319: 3ID type longitudinally coupled double mode surface acoustic wave filter,
202, 203, 204, 208, 209, 210, 214, 218, 302, 303, 304, 308, 309, 310, 314, 315, 316, 320, 321, 322, 405: comb electrodes,
205, 206, 211, 212, 215, 216, 219, 220, 305, 306, 311, 312, 317, 318, 323, 324: reflector,
213, 217: surface acoustic wave resonators,
221 and 325: unbalanced input terminals,
222, 223, 326, 327: balanced output terminals,
202a, 202b, 308a, 308b, 404: electrode fingers,
224, 328, 406: dummy electrode fingers,
329, 402: void portion,
403: Bus bar,
Vi: surface acoustic wave velocity at the intersection of the comb electrodes,
Vg: surface acoustic wave velocity in the void,
Vb: surface acoustic wave velocity at the bus bar,
Vr: surface acoustic wave velocity at the electrode fingers of the reflector,
WI: Cross length of comb electrode,
WR: crossing length of comb electrode, dummy electrode finger length, opening length including gap between dummy electrode finger and comb electrode,
WG: crossing length of comb electrode and opening length including gap between electrode finger and dummy electrode finger,
W: Reflector aperture length,
L: Dummy electrode finger length.

Claims (7)

On the piezoelectric substrate, a plurality of comb electrodes are arranged close to each other along the propagation direction of the surface acoustic wave, and reflectors are arranged on both sides of the comb electrode rows, and acoustic coupling between the plurality of comb electrodes is performed. In a longitudinally coupled multimode surface acoustic wave device that uses a plurality of vibration modes to be generated,
Forming a dummy electrode finger that does not contribute to excitation between the electrode finger of the comb electrode and the bus bar;
In order to suppress unnecessary radiation of the surface acoustic wave in the reflector, the sound speed of the dummy electrode finger portion of the comb-shaped electrode and the reflector portion corresponding to the gap portion between the electrode finger and the dummy electrode finger is made uniform. A surface acoustic wave device characterized by being slower than the sound velocity in the metallized region.   2. The surface acoustic wave device according to claim 1, wherein an opening length of the reflector is determined by a length of an opening including an intersection of electrode fingers of the comb electrode and a gap between the electrode finger and the dummy electrode finger. The surface acoustic wave device is characterized in that it is set longer.   3. The surface acoustic wave device according to claim 1, wherein the opening of the reflector includes a crossing portion of electrode fingers of a comb-shaped electrode, a gap between the electrode finger and the dummy electrode finger, and a dummy electrode finger. A surface acoustic wave device characterized by being set at a position on the same straight line as the opening.   The surface acoustic wave device according to any one of claims 1 to 3, wherein the surface acoustic wave device is disposed adjacent to each other along the propagation direction of the surface acoustic wave that excites the three comb-shaped electrodes. A three-comb electrode type longitudinally coupled double mode surface acoustic wave device using reflectors disposed on both sides of an electrode array and utilizing first and third order vibration modes generated by acoustic coupling between the three comb electrodes. There is provided a surface acoustic wave device.   5. The surface acoustic wave device according to claim 1, wherein a piezoelectric substrate having an electromechanical coupling coefficient of 1 to 30% is used as the piezoelectric substrate.   6. The surface acoustic wave device according to claim 1, wherein the length of the dummy electrode is in the range of 0.2λ to 3.0λ, where λ is a wavelength defined by the pitch of the comb electrodes. A surface acoustic wave device characterized by the above.   A communication apparatus comprising the surface acoustic wave device according to claim 1.

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