| 摘要 |
PROBLEM TO BE SOLVED: To provide a compact surface acoustic wave filter with a high degree of freedom in the design of a frequency characteristic and with an excellent out of band characteristic. SOLUTION: The surface acoustic wave filter is the resonator-type one characterized in such a way that an IDT (interdigital converter) 10 which is arranged on a piezoelectric substrate so as to permit surface acoustic wave propagating directions to coincide and a reflector which is arranged on the piezoelectric substrate so as to sandwich IDT 10 along the surface acoustic wave propagating direction are disposed, IDT 10 is provided with a first area 11 having equal to or more than a half of electrode fingers which constitute IDT 10 and the second area 12 other than the first one and the phase of surface acoustic wave excited by the first area 11 is opposite to the one excited by the second area 12. The frequency characteristic and susceptance characteristic of the filter are controlled by selecting the pitch and the number of pairs of the electrode fingers 12f of the second area and, then, the characteristic is improved.
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