Patent ID: 6897744

Claim:
A longitudinally-coupled multi-mode piezoelectric bulk wave filter comprising: at least four excitation electrodes extending substantially parallel to each other; a laminated piezoelectric body including a plurality of piezoelectric layers arranged between the excitation electrodes and polarized in a direction that is substantially perpendicular to or substantially parallel to the excitation electrodes, the laminated piezoelectric body having first and second end surfaces facing in a direction that is substantially perpendicular to the plurality of the piezoelectric layers and first through fourth side surfaces connecting the first and second end surfaces; an input electrode disposed on the first side surface of the laminated piezoelectric body closer to the first end surface; an output electrode disposed on the first side surface of the laminated piezoelectric body closer to the second end surface; and a ground electrode disposed on the second side surface of the laminated piezoelectric body opposite from the first side surface, wherein the plurality of excitation electrodes include a first group which is electrically connected to the input electrode, a second group which is electrically connected to the output electrode, and a third group which is electrically connected to the ground electrode; wherein when an input signal is input between the input electrode and the ground electrode, vibration modes of different orders are excited and coupled so that an output signal is output between the output terminal and the ground terminal; and wherein T/D is equal to or smaller than about 0.9 where T represents the dimension of the width between the opposed first and second side surfaces of the laminated piezoelectric body and D represents the distance between the adjacent excitation electrodes.