Surface acoustic wave resonator filter

摘要

The invention provides a surface acoustic wave resonator filter having not only a wide bandwidth and a low-loss characteristic but also a sharp attenuation characteristic at edges of the passband. The surface acoustic wave resonator filter includes first and second longitudinally coupled resonator filters formed on a piezoelectric substrate, wherein: the first and second longitudinally coupled resonator filters each have first, second, and third resonance modes; the phases of the output signals of the first and second longitudinally coupled resonator filters are opposite to each other for an input signal at frequencies higher than the passband; the difference in frequency between the first resonance mode of the first longitudinally coupled resonator filter and the first resonance mode of the second longitudinally coupled resonator filter is smaller than the difference in frequency between the first resonance mode and any other resonance modes in the first and second longitudinally coupled resonator filters; and the difference in frequency between the third resonance mode of the first longitudinally coupled resonator filter and the third resonance mode of the second longitudinally coupled resonator filter is smaller than the difference in frequency between the third resonance mode and any other resonance modes in the first and second longitudinally coupled resonator filters.