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°.

Multi-mode surface acoustic wave filters are disclosed. A multi-mode surface acoustic wave filter can include a plurality of interdigital transducer electrodes that are longitudinally coupled to each other and acoustic reflectors on opposing sides of the plurality of interdigital transducer electrodes. The acoustic reflectors include acoustic reflector fingers arranged to suppress a spurious response due to shear horizontal mode of the multi-mode surface acoustic wave filter. For example, the acoustic reflector fingers can include stepped lengths and/or slanted pitches to suppress the spurious response due to shear horizontal mode.

In an elastic wave resonator, a first IDT electrode, a second IDT electrode, a first reflector, and a second reflector are located on a piezoelectric substrate. The first IDT electrode and the second IDT electrode share a shared bus bar. Between a first terminal and a second terminal, the first IDT electrode and the second IDT electrode are connected in parallel. The shared bus bar and the first reflector are connected to the first terminal. A first bus bar and a second bus bar are connected to the second reflector, and are further connected to the second terminal.

An elastic wave includes a piezoelectric substrate having a polarization direction denoted by an arrow Px, and first and second IDT electrodes arranged on the substrate in an elastic wave propagation direction with a shared reflector therebetween. A first bus bar of the first IDT electrode and a first end portion bus bar of a second reflector are connected to a wiring electrode to define a first terminal. A second bus bar of the first IDT electrode and a second end portion bus bar of the shared reflector are connected to each other to define a second terminal. A first end portion bus bar and a first bus bar are electrically connected to each other. A second bus bar and a second end portion bus bar are electrically connected to each other, and the first and second IDT electrodes and are connected in parallel between the first and second terminals.

A surface acoustic wave filter device includes surface acoustic wave filters, one of which includes a longitudinally coupled resonator-type first filter section and a longitudinally coupled resonator-type second filter section. The second filter section is electrically connected in parallel or series with the first filter section on at least one of an input signal side and an output signal side. The first filter section includes a first IDT group including three IDTs. The second filter section includes a second IDT group including three IDTs. Another surface acoustic wave filter includes a third IDT group that is cascade connected to the first filter section and the second filter section and includes IDTs arranged in order in a line in a surface acoustic wave propagation direction.

Surface acoustic wave (SAW) devices and methods of fabricating SAW devices are disclosed. The disclosed SAW device includes a piezoelectric layer. The SAW device also includes at least one transducer coupled to the piezoelectric layer. The transducer includes a first set of electrodes and a second set of electrodes. Each electrode in the first set of electrodes is directly adjacent to at least one electrodes in the second set of electrodes along a wave propagation axis, and the first and second set of electrodes are separated from each other along a depth axis.

A ladder filter includes series-arm resonators each including an IDT electrode and a reflector, and a parallel-arm resonator. In at least one of the series-arm resonators, where a wavelength that is determined by an electrode finger pitch of the IDT electrode is λ, an electrode finger center-to-center distance between an electrode finger located closest to the reflector among electrode fingers of the IDT electrode and an electrode finger located closest to the IDT electrode among electrode fingers of the reflector is less than about 0.5λ, and an anti-resonant frequency of the at least one of the series-arm resonators is higher than an anti-resonant frequency of at least another one of the series-arm resonators.

Multi-mode surface acoustic wave filters are disclosed. A multi-mode surface acoustic wave filter can include a plurality of interdigital transducer electrodes that are longitudinally coupled to each other and stepped acoustic reflectors on opposing sides of the plurality of interdigital transducer electrodes. The acoustic reflectors include acoustic reflector fingers with stepped lengths.

Multi-mode surface acoustic wave filters are disclosed. A multi-mode surface acoustic wave filter can include a plurality of interdigital transducer electrodes that are longitudinally coupled to each other and slanted acoustic reflectors on opposing sides of the plurality of interdigital transducer electrodes. The acoustic reflectors include acoustic reflector fingers with slanted pitches.

Multi-mode surface acoustic wave filters are disclosed. A multi-mode surface acoustic wave filter can include a plurality of interdigital transducer electrodes that are longitudinally coupled to each other and stepped acoustic reflectors on opposing sides of the plurality of interdigital transducer electrodes. The acoustic reflectors include acoustic reflector fingers with stepped lengths.