Filter, duplexer and communication module

A filter having at least one series resonator and parallel resonators,

• the at least one series resonator and the parallel resonators including excitation electrodes and reflectors,
• the parallel resonators having different resonance frequencies, and
• at least one of the parallel resonators other than the parallel resonator having the highest resonance frequency being configured so that a ratio (Pref/Varef) of a pitch Prefof the reflectors to a velocity Varefof an acoustic wave propagated through the reflectors is smaller than a ratio (Pres/Vares) of a pitch Presof the excitation electrodes to a velocity Varesof an acoustic wave propagated through the excitation electrodes,
• wherein in at least one of the parallel resonators configured so that the ratio (Pref/Varef) is smaller than the ratio (Pres/Vares), a lower-end frequency of a rejection band of a reflector of said at least one of the parallel resonators is arranged between a resonance point of said at least one of the parallel resonators and an anti-resonance point of the parallel resonator having the highest resonance frequency.

A filter having series resonators and at least one parallel resonator,

• the series resonators and the at least one parallel resonator including excitation electrodes and reflectors,
• the series resonators having different anti-resonance frequencies, and
• at least one of the series resonators other than the series resonator having the lowest anti-resonance frequency being configured to have a pitch of the reflectors larger than that of the excitation electrodes,
• wherein in at least one of the series resonators configured so that the pitch of the reflectors is larger than that of the excitation electrodes, an upper-end frequency of a rejection band of a reflector of said at least one of the series resonators is arranged between an anti-resonance point of said at least one of the series resonators and a resonance point of the series resonator having the lowest anti-resonance frequency.

A filter having series resonators and at least one parallel resonator,

• the series resonators and the at least one parallel resonator including excitation electrodes and reflectors,
• the series resonators having different anti-resonance frequencies, and
• at least one of the series resonators other than the series resonator having the lowest anti-resonance frequency being configured so that a ratio (Pref/Varef) of a pitch Prefof the reflectors to a velocity Varefof an acoustic wave propagated through the reflectors is larger than a ratio (Pres/Vares) of a pitch Presof the excitation electrodes to a velocity Varesof an acoustic wave propagated through the excitation electrodes,
• wherein in at least one of the series resonators configured so that the ratio (Pref/Varef) is larger than the ratio (Pres/Vares), an upper-end frequency of a rejection band of a reflector of said at least one of the series resonators is arranged between an anti-resonance point of said at least one of the series resonators and a resonance point of the series resonator having the lowest anti-resonance frequency.