LONGITUDINALLY-COUPLED RESONATOR SURFACE-ACOUSTIC WAVE FILTER AND COMMUNICATIONS APPARATUS USING THE SAME

摘要

PURPOSE: A longitudinally-coupled resonator surface-acoustic wave(SAW) filter is provided which substantially reduce the transversal response compared to the known SAW filter, and has the function of balance/unbalance signal conversion. CONSTITUTION: A longitudinally-coupled resonator surface-acoustic-wave(SAW) filter(101) comprises a piezoelectric substrate(100), and at least two interdigital transducers(IDTs)(102,103,104) provided on the piezoelectric substrate along the direction in which a surface acoustic wave propagates. At least one of the IDTs has an electrode finger whose metallization ratio is different from that of other electrode fingers of the IDT.