Patent ID: 7215224

Claim:
A longitudinally coupled resonator type surface acoustic wave filter, comprising: a surface acoustic wave resonator including: a piezoelectric substrate; a plurality of interdigital transducer electrodes disposed adjacent to each other on the piezoelectric substrate along the propagating direction of a surface acoustic wave, each interdigital transducer electrode including a pair of electrode terminals that are opposite to each other and a plurality of electrode fingers that extend from each electrode terminal toward the opposite electrode terminal to define an interdigitated configuration; and reflecting members provided at two opposing ends of the plurality of interdigital transducer electrodes; wherein the piezoelectric substrate is made of a rotated Y-cut X-propagating LiTaO 3 , one of the electrode terminals of said pair of electrode terminals includes a plurality of dummy electrode fingers extending therefrom toward the opposite electrode terminal of said pair of electrode terminals, said dummy electrode fingers are arranged opposite to the electrode fingers extending from the opposite electrode terminal, and the gap length between the tips of the dummy electrode fingers extending from the one of the electrode terminals and the tips of the electrode fingers extending from the opposite electrode terminal is less than or equal to 0.3λ, where λ is the wavelength of the surface acoustic wave.