| 摘要 |
PURPOSE:To suppress the increase in a direct wave spurious radiation by making a passing phase amount of two stages of surface acoustic wave filters different by pi(2n+1) radians (where; n=0, + or -1, + or -2,...) substantially. CONSTITUTION:The 1st reed screen transducer input IDT32 transducing an electrical signal into a surface wave and the 1st output IDT33 transducing the surface acoustic wave into the electrical signal are provided to a piezoelectric substrate 30 so as to constitute a surface acoustic wave filter F1. A surface acoustic wave filter F2 is constituted by providing the 2nd inout IDT42 and the 2nd outout IDT43 on the piezoelectric substrate 31. The input IDTs 32, 42 are weighted by apodized form, the output IDTs 33, 43 are of normal type and have identical structure. In the distance between the input and output IDTs, the filter F2 is shifted from the filter F1 by (2n+1)lambda0/2 (where; n=0, + or -1, + or -2,...). |
