An acoustic wave filter includes a first filter circuit on a first path and an additional circuit connected to the first path. The first filter circuit includes a series arm resonator and a longitudinally coupled resonator. The longitudinally coupled resonator includes a first acoustic wave resonator and a first reflector. The additional circuit includes a second acoustic wave resonator on the opposite side of the first acoustic wave resonator with respect to the first reflector. The second acoustic wave resonator includes a first end connected to the first path through a second path and a second end connected to ground. The series arm resonator is connected to a portion of the first path between a connection node at which the second acoustic wave resonator is connected to the first path and the longitudinally coupled resonator.

A multiplexer includes a first filter disposed between an antenna common terminal and a first terminal, and a second filter that is disposed between the antenna common terminal and a second terminal and that has higher passband frequencies than the first filter. The second filter includes IDTs that are longitudinally coupled. Among IDT electrodes in the IDTs, first IDT electrodes are connected to the antenna common terminal side, and second IDT electrodes are connected to the second terminal side. The first and second IDT electrodes have different main pitches of the electrode fingers. At least one of the second IDT electrodes out of all of the electrode fingers has a maximum main pitch.

A filter device includes a first path, a second path, and a capacitor. The first path includes at least one ladder filter circuit and connects a first terminal and a second terminal. The at least one ladder filter circuit includes a parallel arm resonator connected to a ground terminal. The second path includes a grounded resonator and is connected in parallel with any of the at least one ladder filter circuit. One end of the capacitor is connected to the second path, and the other end of the capacitor is connected to a third path which connects the parallel arm resonator and the ground terminal.

An acoustic wave filter includes a first input terminal and a first output terminal, and a longitudinally coupled resonator coupled between the first input terminal and the first output terminal. The longitudinally coupled resonator includes one or more input-side resonators coupled to the first input terminal and one or more output-side resonators coupled to the first output terminal. A total electrostatic capacitance of the one or more input-side resonators is less than a total electrostatic capacitance of the one or more output-side resonators.

A filter includes a series resonator or a longitudinally coupled resonator on a path connecting a first input-and-output terminal and a second input-and-output terminal, and parallel resonators each connected between the path and a ground. Among the parallel resonators, a second parallel resonator and a first parallel resonator are connected in parallel without another resonator being interposed therebetween. An IDT electrode of the first parallel resonator includes different electrode finger pitches. An average of all the electrode finger pitches of the IDT electrode of the first parallel resonator is larger than an average of all the electrode finger pitches of an IDT electrode of the second parallel resonator.

A duplexer includes a transmission filter with a ladder circuit configuration and a reception filter including a ladder filter portion connected to an antenna terminal and a longitudinally coupled resonator-type surface acoustic wave filter. In the transmission filter, a coupling capacitor is connected between an end portion of an inductor nearer to parallel arm resonators and a wiring line connecting the series arm resonators of the ladder filter portion to each other in the reception filter.

A surface acoustic wave filter includes first and second signal terminals and first and second IDT electrodes that are adjacent to or in a vicinity of each other in an x-axis direction and that each includes a pair of comb-shaped electrodes each including a busbar electrode extending in the x-axis direction and electrode fingers extending in a y-axis direction. One of the comb-shaped electrodes in each of the first and second IDT electrodes is electrically connected to the first and second signal terminals, respectively. The surface acoustic wave filter further includes a bridging capacitance including a pair of comb-shaped electrodes arranged in a region outside an overlap region of the electrode fingers. One of the comb-shaped electrodes of the bridging capacitance is electrically connected to the comb-shaped electrode in the first IDT electrode. The other of the comb-shaped electrodes of the bridging capacitance is electrically connected to the comb-shaped electrode in the second IDT electrode.

In an arrangement having a DMS filter, it is provided to symmetrically divide at least one of the transducers (W) of the DMS filter (DMS) into two sub-transducers (T,T′) electrically connected in parallel and to shift them apart from each other by an amount of at least a half wavelength. This results in the signals of the two sub-transducers canceling each other out at a frequency in a stopband and thereby generating an attenuation pole in the upper blocking region.

An elastic wave filter has an unbalanced signal terminal, first and second balanced signal terminals, and first through fifth IDT electrodes arranged in ordinal order between a pair of grating reflectors. Wiring electrodes of the third and fifth IDT electrodes are disposed adjacent a ground electrode of the fourth IDT electrode, wiring electrodes of the second and third IDT electrodes are disposed adjacent one another, and ground electrodes of the first and second IDT electrodes are disposed adjacent one another. The unbalanced signal terminal is connected to the wiring electrodes of the first, third, and fifth IDT electrodes, and the first and second balanced signal terminals are connected to the wiring electrodes of the second and fourth IDT electrodes, respectively. A pitch gradation of pitch spacing between electrode fingers in each of the first, second, and third IDT electrodes on one side of a center line in the third IDT electrode is gradually reduced by a first spacing α, and a pitch gradation of pitch spacing between electrode fingers in each of the third, fourth, and fifth IDT electrodes on the other side of the center line is gradually reduced by a second spacing β (β≠α), as the distance from the center line increases.

An acoustic wave filter includes a surface acoustic wave resonator and a bulk acoustic wave resonator. The SAW resonator includes a piezoelectric substrate and an interdigital transducer electrode on the substrate. The IDT electrode includes a pair of comb-shaped electrodes interdigitated with each other. Each comb-shaped electrode includes electrode fingers extending in parallel or substantially in parallel in a direction crossing the SAW propagation direction and a busbar electrode connecting the electrode fingers to each other at one end of each of the electrode fingers. The BAW resonator includes a lower electrode defined by a portion of a busbar electrode, a piezoelectric film on the busbar electrode, and an upper electrode on the piezoelectric film.