An acoustic wave device includes a piezoelectric substrate, a first band pass filter that is on the piezoelectric substrate and has a first pass band, and a second band pass filter that is on the piezoelectric substrate and has a second pass band at a higher frequency than the first pass band. The first and second band pass filters include resonators that include respective IDT electrodes. When a first total average metallization ratio is defined as an average of metallization ratios of all of the IDT electrodes included in the first filter and a second total average metallization ratio is defined as an average of metallization ratios of all of the IDT electrodes included in the second filter, the first total average metallization ratio is greater than the second total average metallization ratio.

A filter includes a transmission filter circuit and an additional circuit that is electrically connected in parallel with at least a portion of the transmission filter circuit. The additional circuit includes a resonator group including a plurality of interdigital transducer electrodes provided adjacent to or in a vicinity of each other in an acoustic wave propagation direction, a first capacitive element electrically connected between the resonator group and one end of the additional circuit, and a second capacitive element connected between a ground and a signal path electrically connecting the resonator group and the first capacitive element. A capacitance of the second capacitive element is greater than about 0 pF and less than or substantially equal to about 2.0 pF.

A filter includes a ladder filter portion formed on a first piezoelectric substrate; and a multi-mode filter portion connected to the ladder filter portion and formed on a second piezoelectric substrate different from the first piezoelectric substrate. The ladder filter portion and the multi-mode filter portion constitute a single passband.

A filter device includes a first filter and a second filter. The first filter and the second filter are disposed in parallel between a first terminal and a second terminal. A first passband of the filter device includes at least part of a second passband of the first filter. The first passband includes at least part of a third passband of the second filter. The second passband is narrower than the first passband. The third passband is narrower than the first passband. The third passband has a center frequency higher than a center frequency of the second passband. The first filter includes multiple elastic wave resonators and a first capacitive element. The first capacitive element is connected in parallel with the first elastic wave resonator.

A bandpass acoustic wave filter device includes an IDT electrode and a dielectric film disposed on a piezoelectric substrate including a LiNbO.sub.3 layer, and an acoustic wave resonator is defined by the IDT electrode. The acoustic wave resonator utilizes the Rayleigh wave, and a response of an SH wave excited by the acoustic wave resonator is outside a pass band of the acoustic wave filter device.

A filter device includes: a common terminal; a first input/output terminal; a second input/output terminal; a first filter connected to a first path that connects the common terminal and the first input/output terminal, and having a passband that is a first band; a second filter connected to a second path that connects the common terminal and the second input/output terminal, and having a passband that is a second band having a frequency range that is different from and does not overlap a frequency range of the first band; a first switch element connected between a first node on the first path between the first filter and the first input/output terminal and a second node on the second path between the second filter and the second input/output terminal; and a second switch element on the second path, which is connected between the second node and the second input/output terminal.

A longitudinally coupled resonator acoustic wave filter includes first and second IDT electrodes on a piezoelectric substrate. A direction in which electrode fingers of the IDT electrodes extend is a first direction, a direction perpendicular or substantially perpendicular to the first direction is a second direction, a ground-side busbar of the first IDT electrode and a hot-side busbar of the second IDT electrode face each other in the second direction, and the longitudinally coupled resonator acoustic wave filter includes a projecting portion, connected to the ground-side busbar of the first IDT electrode, that extends in the second direction toward the second IDT electrode beyond an interdigitated region of the first IDT electrode.

An electromechanical device includes a piezoelectric support delimited by a surface, or by two surfaces parallel to each other, and, on this support, a resonator for elastic waves propagating parallel to the surface or surfaces, the resonator including two reflectors that delimit the resonator and which are reflective for the waves, several interfacing transducers, to generate the waves from an electrical signal, and several transducers for controlling the resonance frequency, each transducer including a first electrode and a second electrode that are interdigitated, the transducers being arranged along the propagation path followed by the waves in the resonator, with, along the path, an alternation between interfacing transducer and tuning transducer.

A resonator includes: interdigital transducer (IDT) including first electrode including first base on piezoelectric substrate and extended in reference direction, and first protrusions connected to the first base and extended in direction intersecting with the reference direction, and second electrode including second base on the piezoelectric substrate and extended in the reference direction, and second protrusions connected to the second base and extended in direction intersecting with the reference direction, each of the second protrusions extended to have one of the first protrusions inserted between the second protrusion and another second protrusion adjacent to the second protrusion, wherein a width of each of first specific protrusions included between one end of the IDT and first position at first distance from the one end, among the first protrusions and the second protrusions, decreases from first specific protrusion closest to the first position toward first specific protrusion closest to the one end.

A double mode SAW (DMS) filter includes: a plurality of interdigital transducers (IDTs), each having a plurality of Type 1 electrode fingers and a plurality of Type 2 electrode fingers formed on a piezoelectric substrate, wherein one Type 2 electrode finger among the plurality of Type 2 electrode fingers is disposed between two adjacent Type 1 electrode fingers among the plurality of Type 1 electrode fingers, and in a first IDT and a second IDT included in the plurality of IDTs to be adjacent to each other, one Type 1 electrode finger of the second IDT is disposed between two Type 1 electrode fingers of the first IDT. Accordingly, it is possible to provide a DMS filter capable of improving the amount of attenuation in an attenuation band adjacent to the wide band side for the passband and miniaturizing a product by saving space.