| 摘要 |
PURPOSE:To improve the filtrating capacity of a piezoelectric base plate, by enclosing an inner case and its lid, in which the piezoelectric base plate mounted on an earth electrode is enclosed, in an outer case made of a resin mixed with metallic power composed mainly of ferrite powder. CONSTITUTION:A piezoelectric base plate 1 is mounted on an earth electrode 10 and is covered with an inner case 8, its lid 11, and outer case 12, all of which are molded with a resin mixed with ferrite powder having an electromagnetic shielding effect. When the piezoelectric base plate is put in the cases in such a way, a shielding effect equivalent to one obtained when an expensive package having a metallic can structure is used can be obtained, even when this surface wave device is used in frequency bands of >=10MHz. As a result, the guaranteed damping quantity of the outside of a passing band can be obtained sufficiently and the selectivity characteristics of the filter is improved. At the same time, no ripple is produced in the passing band.
|
