SURFACE ACOUSTIC WAVE FILTER, AND SHARED DEVICE FOR ANTENNA

摘要

The present invention relates to a surface acoustic wave filter for use in a mobile communication device such as a portable telephone. As for the surface acoustic wave filter provided with a plurality of serially connected surface acoustic wave resonators, the invention aims at realizing the filter that is simple to design. The invention comprises a grounding electrode 12, serially connected surface acoustic wave resonators 15a through 15c, coupling electrodes 16a through 16d for the resonators, and inter-digital electrodes 20a through 20d formed from the coupling electrodes 16a through 16d, all formed on a surface of a piezoelectric substrate 11. The surface acoustic wave resonators 15a through 15c and capacitances 19a through 19d can be designed independently with respect to each other, as the capacitances 19a through 19d are formed by the inter-digital electrodes 20a through 20d and the grounding electrode 12. <IMAGE>