SAW filter with an improved attenuation characteristic at a frequency any multiple of an attenuation pole frequency at one or both sides of a pass band

摘要

A SAW (Surface Acoustic Wave) filter includes serial arm resonators and parallel arm resonators interconnected in pairs in a multiple-stage, ladder configuration. A resonating device is serially connected to any one of the serial arm resonators and has an attenuation pole frequency higher than that of the serial arm resonator. At the attenuation pole frequency of the serial arm resonator, the resonating device functions as capacitance without performing attenuation. The resonating device has an antiresonance frequency 1.8 times or more but 2.2 times or less, or 2.7 times or more but 3.3 times or less, as high as the antiresonance frequency of the serial arm resonator.