A noise suppression filter includes a resonator, a ground plane, and a set of differential transmission lines. The set of differential transmission lines includes a first meander line and a second meander line formed in a first circuit layer. The resonator is formed in a second circuit layer and includes a first long arm, a second long arm, and a short arm extended form a same point to form a T-shape. The ground plane is formed in a third circuit layer and is coupled to the first long arm and the second long arm through vias. The first meander line is detoured along the inner sides of the first long arm and the short arm, and the second meander line is detoured along the inner sides of the second long arm and the short arm.

A noise suppression filter includes a resonator, a ground plane, and a set of differential transmission lines. The set of differential transmission lines includes a first meander line and a second meander line formed in a first circuit layer. The resonator is formed in a second circuit layer and includes a first long arm, a second long arm, and a short arm extended form a same point to form a T-shape. The ground plane is formed in a third circuit layer and is coupled to the first long arm and the second long arm through vias. The first meander line is detoured along the inner sides of the first long arm and the short arm, and the second meander line is detoured along the inner sides of the second long arm and the short arm.

An elastic wave device includes a piezoelectric substrate made of lithium niobate, an interdigital transducer electrode on the piezoelectric substrate, and a silicon oxide layer that covers the interdigital transducer electrode. The interdigital transducer electrode includes an AlCu layer and a metal layer disposed closer to the piezoelectric substrate than the AlCu layer, the metal layer having a higher density than the silicon oxide layer. The AlCu layer has a Cu concentration of about 13% or more by weight.

A high-frequency module that performs filtering of signals transmitted and received through an antenna includes an antenna terminal, a transmission terminal, a reception terminal, a reception filter connected between the antenna terminal and the reception terminal, a transmission filter connected between the antenna terminal and the transmission terminal, a first element connected between the antenna terminal and the transmission filter, and a second element connected in series between the transmission terminal and the transmission filter. The first element and the second element are capacitively coupled to each other.

A tunable filter includes a series-arm resonant circuit, and a parallel-arm resonant circuit. The series-arm resonant circuit includes a group of acoustic wave resonant circuits that have different resonant frequencies, a variable capacitor, and switching circuits. The parallel-arm resonant circuit includes another group of acoustic wave resonant circuits that have different resonant frequencies, a variable capacitor, and switching circuits. For example, the difference in pass-band frequency caused by the difference in resonant frequency between the acoustic wave resonant circuit in the group and the acoustic wave resonant circuit in the other group is greater than the maximum difference in pass-band frequency resulting from the variable range of capacitance of the variable capacitor.

A multiplexer includes a filter (10) arranged between a common terminal and an input/output terminal (110) and configured to pass a radio frequency signal in a first frequency band, and a filter (20) arranged between the common terminal and an input/output terminal (120) and configured to pass a radio frequency signal in a second frequency band. The filter includes series arm circuits (31 and 32) connected in series, a series arm circuit (33) connected in parallel to the series arm circuit (32), and a parallel arm circuit. The series arm circuit (32) includes a series arm resonator that is an acoustic wave resonator. The series arm circuit (33) includes a switch arranged on a second path connecting nodes. In a CA mode, the switch is OFF. In a non-CA mode, the switch is ON.

An elastic wave apparatus includes a piezoelectric substrate, a first dielectric film provided on the piezoelectric substrate, an IDT electrode provided on the first dielectric film, and a capacitor that includes a pair of comb-shaped electrodes provided directly on the piezoelectric substrate and is electrically connected to the IDT electrode. An elastic wave resonator including the IDT electrode is provided.

An elastic wave device includes a first filter including an elastic wave resonator and a second filter connected to an antenna common terminal via a common node. When a first pass band of the first filter and second pass bands of the second filters are F1 and F2, respectively, F1<F2. The first filter includes at least one elastic wave resonator, and the elastic wave resonator uses Rayleigh waves propagating on a piezoelectric substrate made of LiNbO.sub.3, IDT electrodes including a Pt film on a piezoelectric layer made of LiNbO.sub.3, and a silicon oxide film covering the IDT electrodes. The thickness of the silicon oxide layer is about 33% or less of the wavelength of the IDT electrodes.

A radio frequency module includes a module substrate, a plurality of passive components disposed on a main surface of the module substrate, and a filter component disposed over the plurality of passive components, wherein the filter component includes series arm resonators that constitute an acoustic wave filter, the series arm resonator is connected between the series arm resonators, and a region of the filter component formed with the series arm resonator does not overlap the plurality of passive components and at least a part of the other region of the filter component overlaps at least a part of each of the plurality of passive components in a plan view of the module substrate.

An acoustic wave device includes a substrate, an interdigital transducer electrode including electrode fingers on a main surface of the substrate, and a protection film covering the main surface of the substrate, and side surfaces and upper surfaces of the electrode fingers. The protection film includes a portion covering the main surface of the substrate, an intermediate portion between two of the electrode fingers adjacent to each other, and a vicinity portion of the electrode fingers. The intermediate portion is thicker than the vicinity portion.