Filter device and multiplexer

A filter device comprising:

• a first terminal;
• a second terminal;
• a first acoustic wave resonator in a first line that connects the first terminal and the second terminal;
• and
• a second acoustic wave resonator in a second line that branches off from the first line and connects the first line and ground;
• wherein
• one of the first acoustic wave resonator and the second acoustic wave resonator includes:
• a piezoelectric substrate;
• a dielectric layer on the piezoelectric substrate;
• a first IDT electrode on the dielectric layer;
• and
• a pair of first reflectors on the dielectric layer on two opposing sides of the first IDT electrode;
• another of the first acoustic wave resonator and the second acoustic wave resonator includes:
• a piezoelectric substrate;
• a second IDT electrode on the piezoelectric substrate without the dielectric layer interposed therebetween;
• and
• a pair of second reflectors on the piezoelectric substrate without the dielectric layer interposed therebetween on two opposing sides of the second IDT electrode;
• the first acoustic wave resonator and the second acoustic wave resonator are side by side in a propagation direction of an acoustic wave generated in the piezoelectric substrate;
• in planar view seen from a surface side of the piezoelectric substrate on which the dielectric layer is provided, the dielectric layer includes an edge portion between the pair of first reflectors and the pair of second reflectors;
• in the planar view of the dielectric layer, the edge portion is closer to the pair of second reflectors than to the pair of first reflectors;
• and
• a distance L between one of the pair of the first reflectors and one of the pair of the second reflectors is less than or equal to 10λ, where λ is a wavelength corresponding to a lower frequency of the first acoustic wave resonator or the second acoustic wave resonator.