| 摘要 |
PROBLEM TO BE SOLVED: To obtain a means for improving the attenuation amount at the low- frequency-side image frequency of a high-frequency double-mode piezoelectric filter. SOLUTION: In the double-mode piezoelectric filter on one principal surface of whose piezoelectric substrate first and second electrodes are provided and on the other principal surface of whose piezoelectric substrate third and fourth electrodes are provided, the sizes of the first, second, third electrodes are made nearly equal to each other, and the size of the fourth electrode is made larger than the other electrodes. Further, the third electrode is so provided more near the end portion of the piezoelectric substrate than the opposite position to the first electrode, and the fourth electrode is so provided more near the center of the gap between the first and second electrodes than the opposite position to the second electrode as to configure the filter.
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