| 摘要 |
PROBLEM TO BE SOLVED: To obtain the double-mode filter having spurious radiation of the this mode suppressed by making the opening parts of IDT electrodes with different sizes. SOLUTION: IDT electrodes 2 and 3 are formed of a couple of comb-shaped electrodes having electrode fingers which are inserted between each other, and the IDT electrode 2 has one comb-type electrode connected to an input terminal IN and the other comb-type electrode, i.e., the comb-type electrode connected to a common bus bar 4 is grounded. The opening lengths W1 and W2 and crossing lengths X1 and X2 of those IDT electrodes 2 and 3 are made different from each other. Consequently, the amount by which the IDT electrodes 2 and 3 gather electric charges generated by vibration displacement of tertiary mode is different from the amount of electric charges that the IDT electrodes of a conventional double-mode filter gather. Namely, the spurious radiation of the third mode can be suppressed more than before, so characteristics of an intermediate-frequency part can be improved.
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