Surface acoustic wave ladder filter utilizing parallel resonators with different resonant frequencies

摘要

A surface acoustic wave filter has a series resonator group and a parallel resonator group. The series resonator group includes a plurality of surface acoustic wave electrodes formed on a surface of a piezoelectric substrate and electrically disposed in series between an input terminal and an output terminal. The parallel resonator group includes a plurality of surface acoustic wave electrodes individually electrically disposed in parallel between an input- or output-terminal of the individual surface acoustic wave electrodes of the series resonator group and a ground electrode. A part number of the surface acoustic electrodes of the parallel resonator group is configured to deteriorate an obtained Q value and presents a resonant frequency which is lower than an antiresonant frequency and higher than a resonant frequency respectively formed by the other surface acoustic wave electrodes of the parallel resonator group.