SURFACE ACOUSTIC WAVE FILTER DEVICE

摘要

PROBLEM TO BE SOLVED: To reduce a cross length at the end of a weighting electrode and to reduce the diffraction of surface acoustic waves after suppressing the change of frequency characteristics as much as possible. SOLUTION: This surface acoustic wave filter device is provided with a piezoelectric substrate and a weighting electrode 20 and a normal electrode are arranged side by side in the propagation direction of the surface acoustic waves on the substrate. The cross length ai (i is an even number) of respective cross parts where the adjacent electrode fingers of the weighting electrode 20 cross each other is set to a value designed by a design method for optimizing the frequency characteristics, a mini-max method for instance. At the time, even at the time of respectively reducing the cross lengths ai and ai+2 of both cross parts so as to keep the difference ai-ai+2 of the cross lengths of the adjacent cross parts fixed at the end part of the weighting electrode 20, frequency components obtained by the cross parts are maintained almost the same in a desired frequency band.