Surface wave low filter loss having coupling transducers

Claim 2

A surface wave filter, comprising: interdigital transducers and coupling transducers disposed at selected distances from one another on a substrate in two tracks, said distances being selected relative to a wavelength, λ of a surface wave on said substrate, wherein differences of effective center-to-center distances d1, d2, d3, d4, which are dimensioned between each of said coupling transducers and respective ones of the interdigital transducers associated therewith: d1-d2=n1·λ+k.sup.* (1) d3-d4=n2·λ+k.sup.** (2) d1-d3=n3·λ±(2n'-1)·λ/4(3) d2-d4=n4·λ±(2n"-1)·λ/4,(4) where n1, n2, n3, n4, n', n" are natural numbers and the following holds true for correction quantities k * , k ** : k * =0 if the transducers of path distances d1, d2 of equation (1) are symmetric or antisymmetric transducers and k ** =0 if the transducers of path distances d3, d4 of equation (2) are symmetric or antisymmetric transducers, or k * =(2n * -1)·λ/2 (n * =natural number) if the transducer pair of one path distance d1 or d2 of equation (1) consists of a symmetric and an antisymmetric transducer and, in addition, the transducer pair of the other path distance d1 and d2, respectively, are transducers of the same type of symmetry, and k ** =(2n ** -1)·λ/2 (n ** =natural number), if the transducer pair of one path distance d3 and d4, respectively, of equation (2) consists of a symmetric or an antisymmetric transducer and, in addition, the transducer pair of the other path distance d4 and d3, respectively, are transducers of the same type of symmetry.

Claim 3

A surface wave filter, comprising: a substrate first and second interdigital transducers with a first coupling transducer disposed therebetween mounted on said substrate to define a first center-to-center distance d1 between said first interdigital transducer and said first coupling transducer and a second center-to-center distance d2 between said first coupling transducer and said second interdigital transducer; third and fourth interdigital transducers with a second coupling transducer disposed therebetween mounted on said substrate to define a third center-to-center distance d3 between said third interdigital transducer and said second coupling transducer and a fourth center-to-center distance d4 between said second coupling transducer and said fourth interdigital transducer, said first and second coupling transducers being electrically connected to one another; said center-to-center distances conforming to the following relationships: d1-d2=n1·λ+k.sup.* d3-d4=n2·λ+k.sup.** d1-d3=n3·λ±(2n'-1)·λ/4 d2-d4=n4·λ±(2n"-1)·λ/4, where n1, n2, n3, n4, n', and n" are natural numbers, λ is a wavelength of a surface wave in said substrate, and k * and k ** are corrective factors defined as follows: k * =0 is said first and second interdigital transducers and said first coupling transducer are all one of symmetric and asymmetric transducers, k ** 0 is said third and fourth interdigital transducers and said second coupling transducer are all one of symmetric and asymmetric transducers, k * =(2n * -1)·λ/2 if said transducers defining one of said first and second center-to-center distances d1 and d2 are both either symmetric or asymmetric transducers and said transducers defining another of said first and second center-to-center distances d1 and d2 are symmetric and asymmetric transducers, respectively, where n * is a natural number; and k ** =(2n ** -1)·λ/2 if said transducers defining one of said third and fourth center-to-center distances d3 and d4 are both either symmetric or asymmetric transducers and said transducers defining another of said third and fourth center-to-center distances d3 and d4 are symmetric and asymmetric transducers, where n ** is a natural number.

Claim 4

A surface wave filter, comprising: a substrate first and second interdigital transducers with a first coupling transducer disposed therebetween mounted on said substrate to define a first center-to-center distance d1 between said first interdigital transducer and said first coupling transducer and a second center-to-center distance d2 between said first coupling transducer and said second interdigital transducer; third and fourth interdigital transducers with a second coupling transducer disposed therebetween mounted on said substrate to define a third center-to-center distance d3 between said third interdigital transducer and said second coupling transducer and a fourth center-to-center distance d4 between said second coupling transducer and said fourth interdigital transducer, said first and second coupling transducers being electrically connected to one another; said center-to-center distances conforming to the following relationships: d1-d2=n1·λ+k.sup.* d3-d4=n2·λ+k.sup.** d1-d3=n3·λ±(2n'-1)·λ/4 d2-d4=n4·λ±(2n"-1)·λ/4, where n1, n2, n3, n4, n', and n" are natural numbers, λ is a wavelength of a surface wave in said substrate, and k * and k ** are corrective factors defined as follows: k * =0 is said first and second interdigital transducers and said first coupling transducer are all one of symmetric and asymmetric transducers, k ** 0 is said third and fourth interdigital transducers and said second coupling transducer are all one of symmetric and asymmetric transducers, k * =(2n * -1)·λ/2 if said transducers defining one of said first and second center-to-center distances d1 and d2 are both either symmetric or asymmetric transducers and said transducers defining another of said first and second center-to-center distances d1 and d2 are symmetric and asymmetric transducers, respectively, where n * is a natural number; and k ** =(2n ** -1)·λ/2 if said transducers defining one of said third and fourth center-to-center distances d3 and d4 are both either symmetric or asymmetric transducers and said transducers defining another of said third and fourth center-to-center distances d3 and d4 are symmetric and asymmetric transducers, where n ** is a natural number.