Longitudinally coupled resonator acoustic wave filter

A longitudinally coupled resonator acoustic wave filter comprising:

• a piezoelectric substrate;
• a plurality of IDT electrodes disposed on the piezoelectric substrate;
• and
• a pair of reflectors disposed in a propagation direction of an acoustic wave at opposite ends of an area in which the plurality of IDT electrodes are disposed;
• wherein
• each of the plurality of IDT electrodes includes:
• a first busbar and a second busbar that face each other;
• a plurality of first electrode fingers connected to the first busbar at one end of each of the plurality of first electrode fingers;
• and
• a plurality of second electrode fingers connected to the second busbar at one end of each of the plurality of second electrode fingers;
• wherein
• each of the plurality of first electrode fingers and each of the plurality of second electrode fingers are interleaved with each other;
• each of the plurality of IDT electrodes includes a narrow-pitch electrode finger portion and a remaining electrode finger portion, and a pitch between electrode fingers is narrower in the narrow-pitch electrode finger portion than in the remaining electrode finger portion;
• an area in which the plurality of first electrode fingers and the plurality of second electrode fingers overlap when viewed in the propagation direction of the acoustic wave defines an overlap area, and the overlap area includes a central area, a first edge area, and a second edge area arranged in a direction in which the plurality of first electrode fingers and the plurality of second electrode fingers extend, the first edge area and the second edge area being disposed at opposite ends of the central area in the direction in which the plurality of first electrode fingers and the plurality of second electrode fingers extend;
• in the remaining electrode finger portion, each of the plurality of first electrode fingers and each of the plurality of second electrode fingers include a wide portion in at least one of the first edge area and in the second edge area, the wide portion of each of the plurality of first electrode fingers being wider than a remaining portion of each of the plurality of first electrode fingers and the wide portion of each of the plurality of second electrode fingers being wider than a remaining portion of each of the plurality of second electrode fingers;
• and
• in the narrow-pitch electrode finger portion, none of the plurality of first electrode fingers and none of the plurality of second electrode fingers include a wide portion.