| 摘要 |
PROBLEM TO BE SOLVED: To provide a surface acoustic wave filter that has a balanced- unbalanced conversion function, whose input impedance differs from its output impedance and that is excellently in-band balanced. SOLUTION: This invention provides the surface acoustic wave filter 100 where a center interval between input and output interdigital transducers(IDTs) of a 2nd surface acoustic wave filter element 102 is selected greater than that of a 1st surface acoustic wave filter element 101 by about 0.5 wavelength of a surface acoustic wave so as to attain phase inversion between outputs of the surface acoustic wave filter elements 101, 102 and the balanced-unbalanced conversion function is provided, and the total sum of static capacitances of a plurality of the IDTs of the 2nd surface acoustic wave filter element 102 is selected greater than the total sum of static capacitances of a plurality of the IDTs of the 1st surface acoustic wave filter element 101.
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