Piezoelectric surface acoustic wave device with suppression of reflected signals

Claim 1

A surface acoustic wave device comprising a piezoelectric substrate, first and second interdigital transducers each having a pair of comb-like electrode fingers overlapped with each other arranged on said substrate, and a propagation path between said first and second interdigital transducers on said substrate for propagating a surface acoustic wave, one of said first and second interdigital transducers converting an electric signal to a surface acoustic wave signal, the other interdigital transducer converting said surface acoustic wave signal to an electric signal, at lest one of said first and second interdigital transducers having a weighted overlap length without dummy electrode fingers, wherein each of the electrode fingers of said at least one of said first and second interdigital transducers includes a first finger portion not contributing to generation or reception of said surface acoustic wave and a second finger portion contributing to generation or reception of said surface acoustic wave, lengths of said first and second finger portions defining said weighted overlap length, the envelopes defined by said weighted overlap length are substantially symmetric about the center line of said propagation path for said surface acoustic wave, the width of said first finger portions and the length of the spaces existing between adjacent first finger portions measured widthwise of said first finger portions are approximately equal to one-half of the wavelength of said approximately equal to one-half of the wavelength of said surface acoustic wave, and said first finger portions and said spaces between said first finger portions are in opposite positional relation about said center line of said propagation path of the surface acoustic wave.