| 摘要 |
In a longitudinally coupled resonator type surface acoustic wave filter device having a serially weighted IDT, a structure for reducing ripple in the passband is provided. In the longitudinally coupled resonator type surface acoustic wave filter device, at least in one part where IDTs (113, 114) are mutually adjacent to each other, at least one of the IDTs (113, 114) has a dummy electrode (116, 118) and is serially weighted. The longitudinally coupled resonator type surface acoustic wave filter device includes at least one of a metallization ratio decreasing means and a metallization ratio increasing means. The metallization ratio decreasing means is provided on a first acoustic track so as to reduce, at least in the one part where the serial weighting is performed, the difference between the metallization ratio of the first acoustic track passing through a link portion (116c) of the dummy electrode (116) and the metallization ratios of second and third acoustic tracks located on both sides in the acoustic wave propagation direction of the first acoustic track. The metallization ratio increasing means is provided on the second acoustic track.
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