Acoustic surface wave filter of longitudinal coupled resonator type

摘要

A longitudinally coupled resonator-type surface acoustic wave filter (1) includes a piezoelectric substrate (2) and at least three IDTs (13-15) provided on the piezoelectric substrate along the propagation direction of the surface acoustic wave and each having a plurality of electrode fingers. In at least one of the IDTs (e.g. 13), the electrode finger period of a first portion (13a,13b) that is adjacent to the side edge of another IDT (14) in the propagation direction of the surface acoustic wave is different from the electrode finger period of a second portion (13c-13g) that is the remaining part of the IDT.