| 摘要 |
A surface acoustic wave filter includes IDTs on an input side and on an output side, the Inter Digital Transducers (IDTs) are formed by depositing a thin film made of aluminum and the like on a piezoelectric substrate made of crystal, and disposed on the substrate with a spacing interposed therebetween. The width of each electrode digit of each IDT is +E,fra 1/4+EE of the wavelength of the surface acoustic wave during resonance. A reflection coefficient epsilon per electrode digit and the total number N of pairs of the electrode digits constituting the IDTs on the input side and on the output side are set to satisfy N epsilon >/=0.55. Also, the aperture width W lambda of a surface acoustic wave transmission path, the center frequency of the filter f in units of Hertz , and the thickness of the electrode digits H in units of meters, are set to satisfy fH</=-17.5W+210.
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