SURFACE ACOUSTIC WAVE FILTER

摘要

PROBLEM TO BE SOLVED: To provide a surface acoustic wave filter with low impedance and an excellent cut-off frequency characteristic without causing spurious radiation even when the impedance is reduced by widening the width of guide paths. SOLUTION: In this surface acoustic wave filter, two grating reflectors 1, 2 and input and output interdigital electrodes 3, 4 inserted between the reflectors are formed on a piezoelectric substrate 10. Spurious radiation resulting from other undesired vibration modes than the Si mode and the Ai mode is suppressed by apodizing the cross width of the electrode fingers of the interdigital electrodes 3, 4 based on a weight function F(x) expressed as the sum of vibration displacement distribution functionsΨSi(x) andΨAi(x) of the i-th symmetry mode Si and the asymmetry mode Ai used for the filter.