An elastic wave device includes a piezoelectric substrate, an IDT electrode on the piezoelectric substrate, and a silicon oxide film arranged on the piezoelectric substrate to cover the IDT electrode. The IDT electrode includes first and second electrode layers laminated on each other, the first electrode layer is made of metal or an alloy with a density higher than a density of metal of the second electrode layer and a density of silicon oxide of the silicon oxide film, the piezoelectric substrate is made of LiNbO.sub.3 and θ is in a range of equal to or greater than about 8° and equal to or less than about 32° with Euler Angles (0°±5°, θ, 0°±10°) of the piezoelectric substrate, and the silicon oxide film contains hydrogen atoms, hydroxyl groups, or silanol groups.

A filter includes a series arm resonator that defines at least a portion of a signal path connected between first and second terminals, a parallel arm resonator including one end that is grounded, a first inductor including one end that is connected to one end of the series arm resonator and another end that is connected to another end of the parallel arm resonator, and a second inductor including one end that is connected to another end of the series arm resonator and another end that is connected to the other end of the parallel arm resonator. A relative band width of the parallel arm resonator is smaller than a relative band width of the series arm resonator.

An antenna includes a piezoelectric disc. The antenna further includes a first electrode disposed on a first surface of the piezoelectric disc and a second electrode disposed on a second surface of the piezoelectric disc that is opposite to the first surface. The first electrode and the second electrode are to receive a time-varying voltage to excite a mechanical vibration in the piezoelectric disc, and the piezoelectric disc is to radiate electromagnetic energy at a particular frequency responsive to the mechanical vibration.

When a current flowing in a series circuit including an equivalent resistance, an equivalent inductor, and an equivalent capacitance in an electric equivalent circuit of a specific resonator in each filter is defined as an acoustic path current, under conditions that a phase of an acoustic path current of a first transmission filter at a side of a common terminal at a frequency within a first pass band is represented as θ1.sub.Tx1, a phase of an acoustic path current of the first transmission filter at the side of the common terminal at a frequency within a second pass band is represented as θ2.sub.Tx1, a phase of an acoustic path current of a second transmission filter at the side of the common terminal at a frequency within the first pass band is represented as θ1.sub.Tx2, and a phase of an acoustic path current of the second transmission filter at the side of the common terminal at a frequency within the second pass band is represented as θ2.sub.Tx2, a multiplexer satisfies a first condition: |(2.Math.θ1.sub.Tx1−θ2.sub.Tx1)−(2.Math.θ1.sub.Tx2−θ2.sub.Tx2)|=180°±90°, or a second condition: |(2.Math.θ2.sub.Tx1−θ1.sub.Tx1)−(2.Math.θ2.sub.Tx2−θ1.sub.Tx2)|=180°±90°.

An acoustic wave device includes a support substrate made of silicon, a piezoelectric body provided directly or indirectly on the support substrate, the piezoelectric body including a pair of main surfaces facing each other, and an interdigital transducer electrode provided directly or indirectly on at least one of the main surfaces of the piezoelectric body, a wave length that is determined by an electrode finger pitch of the interdigital transducer electrode being λ. An acoustic velocity V.sub.Si=(V.sub.1).sup.1/2 of bulk waves that propagate in the support substrate, which is determined by V.sub.1 out of solutions V.sub.1, V.sub.2, V.sub.3 of x derived from the expression, Ax.sup.3+Bx.sup.2+Cx+D=0, is higher than or equal to about 5500 m/s.

An acoustic wave filter device includes at least one series arm resonator and a parallel arm resonator. The series arm resonators and the parallel arm resonator are defined by acoustic wave resonators, an interdigital transducer electrode of the series arm resonators is an apodized interdigital transducer electrode subjected to apodization weighting, in the interdigital transducer electrode of the parallel arm resonator, an intersecting portion includes a central region and low acoustic velocity regions provided at both outer side portions of the central portion, an acoustic velocity of an acoustic wave in the low acoustic velocity region is lower than an acoustic velocity of an acoustic wave in the central region, and a high acoustic velocity region where an acoustic velocity of an acoustic wave is higher than that of the low acoustic velocity region is provided at an outer side portion of each of the low acoustic velocity regions.

In an acoustic wave device, an antenna end resonator that is electrically closest to a first terminal is a first acoustic wave resonator. In each of the first acoustic wave resonator and a second acoustic wave resonator, a thickness of a piezoelectric layer is about 3.5λ or less when a wavelength of an acoustic wave is denoted as λ. The first acoustic wave resonator and the second acoustic wave resonator satisfy at least one of a first condition, a second condition, and a third condition. The first condition is a condition that the first acoustic wave resonator further includes a dielectric film provided between the piezoelectric layer and an interdigital transducer electrode, and the second acoustic wave resonator does not include the dielectric film.

A radio-frequency circuit is capable of simultaneously transmitting a radio-frequency signal of a middle high band group (MHB) including B1 and B3, and a radio-frequency signal of a ultra-high band group (UHB) including n77, and includes: a first transfer circuit that transfers the MHB radio-frequency signal and a radio-frequency signal of a low band group (LB); and a second transfer circuit that transfers the UHB radio-frequency signal. The first transfer circuit includes: a power amplifier for B1 signals; a diplexer that demultiplexes and/or multiplexes the MHB radio-frequency signal and the LB radio-frequency signal; a transmission filter that is connected to the power amplifier and has, as a passband, a transmission band of B1; and a band-elimination filter that is disposed between the diplexer and the transmission filter, and has, as an attenuation band, a transmission band of n77. The second transfer circuit includes a power amplifier for n77 signals.

Aspects of this disclosure relate to a surface acoustic wave device. The surface acoustic wave device includes a piezoelectric layer and an interdigital transducer. The interdigital transducer electrode includes a pair of electrodes, each electrode having a bus bar and fingers extending from the bus bar. The interdigital transducer electrode has an interdigital region defined by a portion of the fingers of the electrodes that interdigitate with each other. A dielectric layer is disposed over the interdigital transducer electrode outside the interdigital region and configured to reduce a loss of the surface acoustic wave device.

A radio-frequency filter includes a series-arm circuit on a circuit path that connects a first input/output terminal and a second input/output terminal. A parallel-arm circuit is connected to a node on the path and ground. The series-arm circuit includes a first impedance element, a first switch element connected to the first impedance element, and a series-arm resonator connected in parallel to the first impedance element and the first switch element. The parallel-arm circuit includes a first parallel-arm resonator, and a first switch circuit connected in series to the first parallel-arm resonator, the first switch circuit includes a second switch element. The first and second switch elements and the second switch elements include one or more transistors, and a gate width of the transistors included in the second switch element is larger than that of at least one of the transistors included in the first switch element.