Patent ID: 6104260
Filing Date: 2000-08-15
Classification: H03H

Abstract:
A surface acoustic wave filter, comprising:a piezoelectric substrate; a first filter track having a first input interdigital transducer, a first reflector, and a first output interdigital transducer disposed therebetween; and a second filter track having a second input interdigital transducer, a second reflector, and a second output interdigital transducer disposed therebetween on said piezoelectric substrate,wherein said first filter track and said second filter track are substantially arranged in parallel to each other,the distance between said first input interdigital transducer and said first output interdigital transducer is equal to the distance between said second input interdigital transducer and said second output interdigital transducer,the distance between said first output interdigital transducer and said first reflector differs from the distance between said second output interdigital transducer and said second reflector by (n.lambda.+.lambda./4) (n: natural number), assuming that the wavelength of the surface acoustic wave is .lambda.,an electrical connection mutually in opposite phase is established for any one of between said first input interdigital transducer and said second input interdigital transducer, or between said first output interdigital transducer and said second output interdigital transducer, while an electrical connection mutually in phase is established for the other, andeach positive electrode and negative electrode of respective output interdigital transducers of said first and second filter tracks are both so configured that,electrode fingers are arranged in groups of two in a cycle of .lambda., each of the electrode fingers has a width along the surface acoustic wave propagation direction of approximately .lambda./8, while the center-to-center distance between the two electrode fingers of the one group is .lambda./4, and the space between adjacent, one pair of electrode fingers of said positive electrode and one pair of electrode fingers of said negative electrode is .lambda./2;wherein both said first input interdigital transducer and said second input transducer are unidirectional transducers.