Surface acoustic wave filter

摘要

A longitudinally coupled surface acoustic wave filter includes a first, second and third IDT electrodes and a first and second reflector electrodes on a piezoelectric substrate. The IDT electrodes each include a primary excitation region having lambda/2 electrode finger pitches, where lambda is the wavelength of a surface acoustic wave. The primary excitation region is phase-shifted by a certain amount in accordance with a desired passband frequency response. The IDT electrodes further include a plurality of secondary excitation regions each having electrode finger pitches different from the lambda/2 pitches. All of the electrode finger pitches of the surface acoustic wave filter thus range from 0.8lambda/2 to 1.2lambda/2, so that a loss increase caused by discontinuity between the IDT electrodes is prevented.