Acoustic wave filter and multiplexer

An acoustic wave filter comprising:

• an input terminal and an output terminal;
• a filter circuit on a first path connecting the input terminal and the output terminal;
• and
• an additional circuit on a second path connected in parallel with at least a portion of the first path;
• wherein
• the additional circuit includes an acoustically-coupled resonator including a plurality of interdigital transducers (IDTs) and a plurality of reflectors;
• the plurality of IDTs each include a pair of comb-shaped electrodes on a piezoelectric substrate;
• each of the comb-shaped electrodes includes a plurality of comb-shaped electrode fingers extending in a first direction parallel or substantially parallel to a main surface of the piezoelectric substrate and extending along a second direction intersecting the first direction;
• the plurality of IDTs are arranged along the second direction;
• the plurality of reflectors are located on both outer sides of the plurality of IDTs in the second direction and each includes a plurality of reflector electrode fingers extending in the first direction and arranged along the second direction;
• and
• a relationship of about 0.60+n≤G/(Pi+Pr)≤0.93+n is satisfied, where n is an integer of 0 or more, Pi denotes an array pitch of the plurality of comb-shaped electrode fingers arranged along the second direction, Pr denotes an array pitch of the plurality of reflector electrode fingers arranged along the second direction, and G denotes, in a boundary region between one of the plurality of IDTs and one of the plurality of reflectors adjacent to the IDT, an IDT-reflector gap, which is a center-to-center distance between one of the plurality of comb-shaped electrode fingers closest to the reflector and one of the plurality of reflector electrode fingers closest to the IDT.