| 摘要 |
In a balanced-type surface acoustic wave filter, IDTs in the center of each of first and second longitudinally coupled resonator type surface acoustic wave filter sections are connected to an unbalanced input terminal, first and third IDT sections on both the sides of the center IDT are connected to first and second balanced output terminals, respectively, the first and third IDTs have narrow pitch electrode finger sections N, and when an electrode finger pitch of the narrow pitch electrode finger section of the second IDT is P1, an electrode finger pitch of the narrow pitch electrode finger section of the first and third IDTs is P2, the number of electrode fingers of the second IDT except for the narrow pitch electrode finger section of the IDT is K1, and the number of electrode fingers of the first and third IDT except for the narrow pitch electrode finger section is K2, P1>P2 and 1.12<=K1/K2<=1.65 are satisfied.
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