| 摘要 |
PROBLEM TO BE SOLVED: To provide a multimode SAW filter which has a wide band and also can significantly improve the stopping attenuation amount on the high frequency side near a pass band area by setting the film thickness of an electrode to the specific rate value of the wave length of an exciting surface wave. SOLUTION: The inter-center spaceα1 of the facing innermost electrode fingers facing to each other between respective gratings 4a to 4d is set to 3/4α, the inter-center spaceα2 of the innermost electrode fingers facing to each other between the electrodes 2 and 3 and the gratings 4a and 4d respectively is set to 3/4αand the electrode finger cycles of the gratings 4a to 4d are set equal to the finger cycles of both electrodes 2 and 3 respectively. Then an aluminum alloy is used as every electrode and the film thickness of the electrode is set within a range of 3%λto 12%λ. Thus, the satisfactory filter characteristic is secured. As a result, the attenuation amount become 20 dB or higher and is significantly improved compared with a conventional double mode filter on the high frequency side of a pass band. At the same time, the pass band width is increased. In addition, the attenuation gradient of a filter is also significantly improved.
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