Abstract: A filter device includes a piezoelectric substrate, a dielectric layer on the piezoelectric substrate, a first IDT electrode on the dielectric layer, a second IDT electrode positioned on the piezoelectric substrate in an area where the dielectric layer is not provided such that the first and second IDT electrodes are side by side in an acoustic wave propagation direction extending along a principal surface of the piezoelectric substrate, a first reflector on the dielectric layer and adjacent to the first IDT electrode on a side of the second IDT electrode, and a second reflector on the piezoelectric substrate and adjacent to the second IDT electrode on a side of the first IDT electrode. The dielectric layer includes an edge portion between the first and second reflectors in planar view seen from a stacking direction of the piezoelectric substrate and the dielectric layer.

Abstract: A multiplexer includes a band pass filter configured to pass a signal in a predetermined frequency band between a first terminal and a common terminal connected to an antenna, and a band elimination filter configured to attenuate a signal in the predetermined frequency band between a second terminal and the common terminal and includes resonators connected in series with a line between the second terminal and the common terminal. The resonators include a first resonator having a lowest resonant frequency and a second resonator disposed on a side of the common terminal from the first resonator.

Abstract: An acoustic wave resonator includes: a piezoelectric substrate; and 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.

Abstract: A filter device includes a first series line, one or more first parallel lines extending from the first series line, two or more first series IDT electrodes on the first series line, and one or more first parallel IDT electrodes on the one or more first parallel lines. At least one of the two or more first series IDT electrodes is a first-type electrode. A dielectric layer is between the first-type electrode and a substrate. At least one of the two or more first series IDT electrodes except the first-type electrode and the one or more first parallel IDT electrodes is a second-type electrode directly contacting the substrate. A first series IDT electrode of the two or more first series IDT electrodes that has a largest pitch of electrode fingers is the first-type electrode.

Abstract: A filter device includes a first substrate, a first input electrode and a first output electrode on the first substrate, a first ground electrode on the first substrate and receiving a ground potential, an electrically open portion in or on the first substrate, a second substrate mounted on the first substrate, a second input electrode on a surface of the second substrate and connected to the first input electrode, a second output electrode on the surface of the second substrate and connected to the first output electrode, a second ground electrode on the surface of the second substrate and connected to the first ground electrode, and at least one first functional electrode on the second substrate and disposed on a first connecting path connecting the second input electrode and the second output electrode. The open portion is connected to the first connecting path.

Abstract: A multiplexer includes a band pass filter configured to pass a signal in a predetermined frequency band between a first terminal and a common terminal connected to an antenna, and a band elimination filter configured to attenuate a signal in the predetermined frequency band between a second terminal and the common terminal and includes resonators connected in series with a line between the second terminal and the common terminal. The resonators include a first resonator having a lowest resonant frequency and a second resonator disposed on a side of the common terminal from the first resonator.

Abstract: An acoustic wave resonator includes: a piezoelectric substrate; and 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.