| 摘要 |
PROBLEM TO BE SOLVED: To obtain a filter which has boardband low loss and also improves attenuation quality on the side of a high frequency in the neighborhood of a pass band by making parts of two IDT electrodes adjacent to grating reflectors split electrodes. SOLUTION: Three IDT electrodes 2 to 4 are arranged adjacently on the principal plane of a piezoelectric substrate 1 along the propagation direction of a surface wave, and grating reflectors 5a and 5b are arranged on both sided of them. The IDT electrodes 3 and 4 consist of normal electrodes 3n and 4n and split electrodes 3s and 4s. That is, in this filter, pass-band characteristics are maintained, while the number of pairs of the IDT electrodes 3 or 4 including the split electrodes 3s and 4s and the pole position of a main lobe formed by them is shifted toward a center frequency by making the central IDT electrode 2 and the inner sides of the IDT electrodes 3 and 4 on both sides normal type electrodes which are equivalent in the conventional practice. Thus, attenuation characteristics are made steep, and also blocking attenuation quality in the neighborhood of a pass band is improved.
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