| 摘要 |
A surface acoustic wave filter having a first surface acoustic wave resonator 10 which is a two-port resonator utilizing longitudinal mode coupling and a second surface acoustic wave resonator 20 connected to a series arm of the first surface acoustic wave resonator 10 on a piezoelectric substrate. The duty of the second surface acoustic wave resonator 20 is set to be smaller than the duty of the first surface acoustic wave resonator 10. Consequently the reflectance per electrode finger of the second surface acoustic wave resonator 20 can be smaller than that of the first surface acoustic wave resonator 10. Therefore, even when the effect of the inductance component is added to the characteristics of the second surface acoustic wave resonator 20, the increase of the difference between the resonance frequency fr and the anti-resonance frequency far can be suppressed. Therefore, the filter loss is low at the high frequency side of the pass band of the surface acoustic wave filter, and an excellent attenuation characteristics are obtained in a vicinity of the high frequency side of the pass band.
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