# US 6,720,847 B2 · Longitudinally-coupled resonator surface acoustic wave filter and communication apparatus using the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,720,847 B2 - Document ID: US6720847B2 - Status: Granted - Kind: B2 - Application number: 10/170,154 - Filed: 2002-06-12 - Published: 2002-12-26 - Granted: 2004-04-13 - Earliest claimed: 2001-06-12 - Assignees: Murata Manufacturing Co., Ltd. - Inventors: Katsuhiro Nako; Yuichi Takamine - Web page: https://patentgrep.com/patent/US6720847B2 ## CPC - H03H 9/0042: {the balanced terminals being on opposite sides of the track} - H03H 9/0038: {the balanced terminals being on the same side of the track} - H03H 9/0071: {the balanced terminals being on the same side of the tracks} - H03H 9/14582: {the last fingers having a different pitch} - H03H 9/14588: {Horizontally-split transducers} - H03H 9/6433: {Coupled resonator filters} - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) ## Abstract A longitudinally-coupled resonator surface acoustic wave (SAW) filter includes a piezoelectric substrate and at least two IDTs arranged in the direction along which a SAW propagates on the piezoelectric substrate. At least one of the IDTs has an electrode finger wherein the metallization ratio of the electrode finger is different from that of the other electrode fingers of the IDT. ## Claims ### Claim 1 A longitudinally-coupled resonator surface acoustic wave (SAW) filter comprising: a piezoelectric substrate; and at least two interdigital transducers (IDTs) provided on the piezoelectric substrate along the direction in which a surface acoustic wave propagates; wherein at least one of the IDTs has an electrode finger with a metallization ratio that is different from that of other electrode fingers of the IDT. ### Claim 2 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein at least one of adjacent IDTs has an electrode finger at a region extending from the adjacent portion of the IDT to an about one-fourth portion of the IDT wherein the metallization ratio of the electrode finger is different from that of other electrode finger of the IDT. ### Claim 3 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein at least one of the IDTs has electrode fingers wherein the metallization ratio of the electrode fingers is continuously varied in the direction along which a surface acoustic wave propagates. ### Claim 4 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein the SAW filter is an EGSM-Rx filter. ### Claim 5 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein the piezoelectric substrate is a 40±5° Y-cut X-propagating LiTaO3 substrate. ### Claim 6 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, further comprising reflectors disposed at opposite ends of the piezoelectric substrate. ### Claim 7 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein the at least two IDTs include electrode fingers and portions which are adjacent to each other, and the pitch of the electrode fingers of the adjacent portions of at least two IDTs are narrower than that of the electrode fingers of the other portions of the at least two IDTs. ### Claim 8 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein at least one of the at least two IDTs has electrode fingers wherein the metallization ratio of the electrode fingers is continuously varied from about 0.54 to about 0.73. ### Claim 9 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein the at least two IDTs have electrode fingers, and the electrode fingers of one of the at least two IDTs has a metallization ratio that is continuously varied from about 0.54 to about 0.73 in a direction along which a surface acoustic wave propagates and the electrode fingers of a second of the at least two IDTs has a constant metallization ratio. ### Claim 10 (depends on 9) A longitudinally-coupled resonator SAW filter according to claim 9, wherein the constant metallization ratio is about 0.73. ### Claim 11 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein the at least two IDTs have electrode fingers, and the electrode fingers of one of the at least two IDTs has a metallization ratio that is continuously varied from about 0.54 to about 0.73 in a direction along which a surface acoustic wave propagates and the electrode fingers of a second of the at least two IDTs has a metallization ratio that is continuously varied from about 0.73 to about 0.54 in the direction along which a surface acoustic wave propagates. ### Claim 12 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein at least one of the at least two IDTs has electrode fingers wherein the metallization ratio of the electrode fingers is non-continuously varied. ### Claim 13 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein the at least two IDTs have electrode fingers, and the electrode fingers of one of the at least two IDTs has a metallization ratio that is non-continuously varied in a direction along which a surface acoustic wave propagates and the electrode fingers of a second of the at least two IDTs has a constant metallization ratio. ### Claim 14 (depends on 13) A longitudinally-coupled resonator SAW filter according to claim 13, wherein the constant metallization ratio is about 0.73. ### Claim 15 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein the at least two IDTs have electrode fingers, and the electrode fingers of one of the at least two IDTs has a metallization ratio that is non-continuously varied from about 0.73 to about 0.584 in a direction along which a surface acoustic wave propagates. ### Claim 16 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein the interdigital width between the IDTs is about 35.8 times the wavelength of a surface acoustic wave propagated in the SAW filter. ### Claim 17 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein the interdigital width between the IDTs is about 40.5 the wavelength of a surface acoustic wave propagated in the SAW filter. ### Claim 18 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein the piezoelectric substrate is one of a 40±5° Y-cut X-propagating LiTaO3 substrate, a 64 to 72° Y-cut X-propagating LiNbO3 substrate, and a 41° Y-cut X-propagating LiNbO3 substrate. ### Claim 19 (depends on 1) A longitudinally-coupled resonator SAW filter according to claim 1, wherein the SAW filter has a balance/unbalance signal conversion function. ### Claim 20 (depends on 1) A communication apparatus comprising a longitudinally-coupled resonator SAW filter according to claim 1 mounted therein.