SURFACE ACOUSTIC WAVE FILTER

摘要

PROBLEM TO BE SOLVED: To obtain a means for improving deterioration in attenuation, to solve the problem there is a frequency region, where the attenuation is deteriorated in a low pass side of the neighborhood of the passband in a longitudinally- coupled multi-mode SAW (surface acoustic wave) filter using reflection inverted type IDT (interdigital transducer) electrodes. SOLUTION: A longitudinally-coupled multi-mode SAW filter provided with a plurality of reflection inverted type IDT electrodes on a piezoelectric substrate and reflectors on both the sides thereof, and an SAW rosonator provided with IDT electrodes on the same substrate and reflectors on both the sides of the IDT electrodes are connected in series. A resonance frequency fs and an antiresonance frequency fa of a composite resonator in which an electric element is connected to the SAW resonator in series are made to meet the relation of fa