Abstract: A longitudinally coupled resonator acoustic wave filter includes a piezoelectric substrate, IDT electrodes on the piezoelectric substrate along an acoustic wave propagation direction, and a pair of reflectors on the piezoelectric substrate on both sides of the IDT electrodes in the acoustic wave propagation direction. Each of the reflectors includes first and second reflector busbars, and first reflective electrode fingers connected to at least one of the first reflector busbar and the second reflector busbar. The reflector includes a first portion in which lengths of the first reflective electrode fingers change in the acoustic wave propagation direction.

Abstract: A longitudinally coupled resonator acoustic wave filter includes a piezoelectric substrate, IDT electrodes on the piezoelectric substrate along an acoustic wave propagation direction, and a pair of reflectors on the piezoelectric substrate on both sides of the IDT electrodes in the acoustic wave propagation direction. Each of the reflectors includes first and second reflector busbars, and first reflective electrode fingers connected to at least one of the first reflector busbar and the second reflector busbar. The reflector includes a first portion in which lengths of the first reflective electrode fingers change in the acoustic wave propagation direction.

Abstract: A radio frequency module includes an elastic wave filter and a low-noise amplifier that amplifies an RF signal output from the elastic wave filter. An output impedance of the elastic wave filter is positioned, on a Smith chart, closer to a noise matching impedance than to a gain matching impedance, at a frequency of at least one of a low frequency end and a high frequency end of a passband of the elastic wave filter. The noise matching impedance indicates the output impedance where a noise figure of the LNA becomes minimum. The gain matching impedance indicates the output impedance where a gain of the LNA becomes maximum.

Abstract: A high-frequency module includes a longitudinally coupled surface acoustic wave filter and a low-noise amplifier that is connected to the surface acoustic wave filter. The input impedance of the surface acoustic wave filter connected to the low-noise amplifier differs from the output impedance thereof. On a Smith chart, the output impedance in the pass band of the surface acoustic wave filter is present in a region between a first output impedance and a second output impedance, the first output impedance being the output impedance of the surface acoustic wave filter where a gain of the low-noise amplifier is maximum, the second output impedance being the output impedance of the surface acoustic wave filter where a noise figure of the low-noise amplifier is minimum.

Abstract: A high-frequency module includes a longitudinally coupled surface acoustic wave filter and a low-noise amplifier that is connected to the surface acoustic wave filter. The input impedance of the surface acoustic wave filter connected to the low-noise amplifier differs from the output impedance thereof. On a Smith chart, the output impedance in the pass band of the surface acoustic wave filter is present in a region between a first output impedance and a second output impedance, the first output impedance being the output impedance of the surface acoustic wave filter where a gain of the low-noise amplifier is maximum, the second output impedance being the output impedance of the surface acoustic wave filter where a noise figure of the low-noise amplifier is minimum.

Abstract: A radio frequency module includes an elastic wave filter and a low-noise amplifier that amplifies an RF signal output from the elastic wave filter. An output impedance of the elastic wave filter is positioned, on a Smith chart, closer to a noise matching impedance than to a gain matching impedance, at a frequency of at least one of a low frequency end and a high frequency end of a passband of the elastic wave filter. The noise matching impedance indicates the output impedance where a noise figure of the LNA becomes minimum. The gain matching impedance indicates the output impedance where a gain of the LNA becomes maximum.