Acoustic wave resonator, filter, and multiplexer

A filter comprising:

• an acoustic wave resonator including:
• a piezoelectric substrate;
• an interdigital transducer (IDT) located on the piezoelectric substrate, the IDT including a pair of comb-shaped electrodes having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are coupled, the IDT having:
• a first region in which a pitch of electrode fingers is substantially constant;
• a second region in which a pitch of electrode fingers decreases at closer distances to an outer side;
• and a third region in which a pitch of electrode fingers increases at closer distances to an outer side, the second region being located outside the first region in an arrangement direction of the plurality of electrode fingers, and the third region being located outside the second region in the arrangement direction;
• and
• a reflector located on the piezoelectric substrate and located outside the IDT in the arrangement direction,
• wherein a region in which a pitch of electrode fingers is substantially constant is not located between the third region and the reflector.

A multiplexer comprising:

• a filter including an acoustic wave resonator, wherein
• the acoustic wave resonator includes:
• a piezoelectric substrate;
• an interdigital transducer (IDT) located on the piezoelectric substrate, the IDT including a pair of comb-shaped electrodes having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are coupled, the IDT having:
• a first region in which a pitch of electrode fingers is substantially constant;
• a second region in which a pitch of electrode fingers decreases at closer distances to an outer side;
• and a third region in which a pitch of electrode fingers increases at closer distances to an outer side, the second region being located outside the first region in an arrangement direction of the plurality of electrode fingers, and the third region being located outside the second region in the arrangement direction;
• and
• a reflector located on the piezoelectric substrate and located outside the IDT in the arrangement direction,
• wherein a region in which a pitch of electrode fingers is substantially constant is not located between the third region and the reflector.