Swif with transducers having varied duty factor fingers for trap enhancement

Claim 2

An acoustic surface wave filter having a predetermined transfer function which defines a major passband essentially centered about a synchronous frequency and adjacent traps, said filter comprising: a piezoelectric surface wave propagating medium having an attenuation characteristic and defining a propagating surface; and a transmitting transducer and a receiving transducer formed on said surface for respectively launching and receiving surface waves, each transducer including a pair of interdigitated comblike arrays of spaced electrically conductive fingers, said attenuation characteristic resulting in substantial reduction of surface waves propagating across said transducers, at least one of said transducers having a duty factor gradient having a maximum for conductive fingers farthest from the other of said transducers and a minimum for those nearest said other transducer, said gradient compensating for said surface wave reduction.

Claim 3

An acoustic surface wave filter as in claim 1, wherein said attenuation characteristic is constant at any given frequency and said duty factor gradient is linear.

Claim 4

An acoustic surface wave filter having a predetermined transfer function comprising: a piezoelectric surface wave propagating medium having a predetermined attenuation characteristic; a transmitting transducer and a receiving transducer formed on said surface for respectively launching and receiving surface waves, each transducer including a pair of interdigitated comb-like arrays of electrically conductive fingers spaced on said medium such that signals propagating across said arrays, having frequencies within a selected range defining a passband, are reinforced by successively encountered conductive fingers, while signals adjacent said selected range defining adjacent traps are cumulatively cancelled by successively encountered conductive fingers; and at least one of said transducers having a varied duty factor which is maximum for conductive fingers most remote from the other of said transducers compensating for surface wave amplitude reduction caused by said attenuation characteristic and enhancing said cumulative cancellation of signals at said trap frequencies.

Claim 5

An acoustic surface wave filter having a predetermined transfer function comprising: a piezoelectric surface wave propagating medium having a predetermined attenuation characteristic; a transmitting transducer and a receiving transducer formed on said surface for respectively launching and receiving surface waves, each transducer including a pair of interdigitated comb-like arrays of electrically conductive fingers spaced on said medium such that signals propagating across said arrays, having frequencies within a selected range defining a passband, are reinforced by successively encountered conductive fingers, while signals adjacent said selected range defining adjacent traps are cumulatively cancelled by successively encountered conductive fingers; and at least one of said transducers having a varied duty factor which is maximum for conductive fingers most remote from the other of said transducers compensating for surface wave amplitude reduction caused by said attenuation characteristic and enhancing said cumulative cancellation of signals at said trap frequencies.

Claim 6

An acoustic surface wave filter as in claim 3, wherein one of said transducers has a duty factor gradient selected to optimize said cumulative cancellation of signals at one of said adjacent trap frequencies and the other of said transducers has a duty factor gradient selected to optimize said cumulative cancellation of signals at the other of said adjacent trap frequencies.