SURFACE ACOUSTIC WAVE FILTER, AND SAW DUPLEXER

摘要

A plurality of surface acoustic wave resonators (15 through 20) including a comb electrode and a grating reflector are coupled on piezoelectric substrate (12). Dielectric film (14) is formed on the surface of at least one surface acoustic wave resonator, of surface acoustic wave resonators (15 through 20). No dielectric film (14) is formed on the surface of at least another surface acoustic wave resonator. Thus, an SAW filter where the insertion loss into a band is small, the steepness is sufficient, and the band is wide can be obtained.