| 摘要 |
PURPOSE:To obtain a filter whose stop hand attenuation is large by excluding the uniformity of a pitch of of a reflector strip of the filter so as to exclude the spurious response of a low frequency region near the pass band. CONSTITUTION:IDTs 2, 2' and reflectors 7, 7', 8, 8' are arranged closely in parallel onto a piezoelectric substrate 1 and the pitch of each strip constituting the reflectors 7, 7', 8, 8' is not made uniform but increased gradually toward the outside. The spurious of the longitudinal harmonic mode is suppressed without almost giving any effect to the pass band in the characteristic as shown in figure. As shown in the figure clearly, the spurious response near the center frequency is almost host. The reflector strips are selected as 7.004mum for the first 10 strips from the inside, 7.008mum for next 20 strips, 7.012mum for next 40 strips, 7.016mum for next 80 strips, 7.02mum for next 160 strips and 7.024mum for last 90 strips.
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