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Surface acoustic wave filter having unidirectional and bidirectional transducers

  • US 6,127,904 A
  • Filed: 11/30/1998
  • Issued: 10/03/2000
  • Est. Priority Date: 10/31/1994
  • Status: Expired due to Fees
First Claim
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1. A surface acoustic wave filter device comprising:

  • a piezoelectric substrate;

    an input side transducer formed on said substrate, for exciting a surface acoustic wave;

    an output side transducer formed on said substrate, for receiving and converting the surface acoustic wave excited by said input side transducer;

    one of said transducers comprising a unidirectional transducer and the other of said transducers comprising a bidirectional transducer,wherein said unidirectional transducer comprises at least one electrode comprising a plurality of sets of first and second electrode fingers, said sets of electrode fingers being periodically arranged at a pitch λ

    which is the propagation wavelength of said surface acoustic wave, said first electrode finger having a width λ

    /8, said second electrode finger having a width 3λ

    /8, and said first and second electrode fingers being spaced from each other at a center distance 3λ

    /8;

    wherein said bidirectional transducer comprises electrode fingers of a split-structure, said electrode fingers of the bidirectional transducer each having a width λ

    /8; and

    wherein said unidirectional transducer comprises a normal electrode and said bidirectional transducer comprises a weighted electrode.

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