| 摘要 |
PROBLEM TO BE SOLVED: To provide the ladder connection type surface acoustic wave filter in which an out-pass band attenuation is increased without much deteriorating other characteristics. SOLUTION: In the ladder connection type surface acoustic wave filter formed by connecting plural numbers of 1-terminal twin resonators consisting of interdigital electrode transducers in series and in parallel electrically on a piezoelectric substrate 3, let capacitance of a series arm resonator 1 be CS, capacitance of a parallel arm resonator 21 be CP, and a pitch of electrode fingers beλg , then the capacitance ratio CP/CS of the parallel arm resonator 2 with respect to the series arm resonator 1 is selected to be 1.5 or over and 2.2 or below, and a height (h) from an upper face of the piezoelectric substrate to an upper side of the electrode is selected to be 10% or over and 13% or below with respect to a mean value of the electrode finger pitch of the series arm resonator 1 and the parallel arm resonator 2,λ=(λP+λS)/2.
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