Fractional efficiency coupler

Claim 2

A fractional efficiency surface acoustic wave coupling device, comprising: a substrate of piezoelectric material having a surface capable of supporting propagating surface acoustic wave energy; input means including an input transducer disposed on said surface for launching surface acoustic wave energy along a first track on said surface in response to an electrical input signal; output means including an output transducer disposed on said surface for detecting surface acoustic wave energy propagating along a second track on said surface and producing a corresponding electrical output signal; and coupler means including a multistrip coupling array of a predetermined number N of conductive strips disposed on said surface, said coupling array having a tapping portion in said first track and an approximately equal length launching portion in said second track for launching along said second track only a portion of said surface acoustic wave energy incident on said tapping portion, the strip period p 1 of said strips in said tapping portion being different than the strip period p 2 of said strips in said launching portion, the strip period difference being defined by a predetermined strip period ratio p 1 /p 2 which in conjunction with said predetermined strip number N provides a broadband device having a desired transfer efficiency less than unity at a desired center frequency, the downstream end of said launching portion of said multistrip coupling array being offset by a distance d in an upstream direction relative to the downstream end of said tapping portion to provide a desired phase shift characteristic.

Claim 3

The fractional efficiency coupling device according to claim 1, wherein said input transducer is a first port and said output transducer is a fourth port, and also comprising a second port in the form of a third transducer disposed on said surface in alignment with said second track on the same side of said multistrip coupling array as said first port, and further comprising a third port in the form of a fourth transducer disposed on said surface in alignment with said first track on the side of said multistrip coupling array opposite that of said first port, said distance d being selected to provide a 90° phase shift between output signals provided at said third and fourth ports.

Claim 4

The fractional efficiency coupling device according to claim 1, also comprising a selected additional number of said multistrip coupling arrays disposed downstream of said first mentioned multistrip coupling array and each having their tapping portions disposed in said first track and having their launching portions in separate additional tracks essentially parallel to said second track, a separate output transducer being disposed on said surface and associated with each of said additional multistrip coupling arrays downstream of their respective launching portions, and a separate surface acoustic wave absorber being disposed on said surface and associated with a different one of said launching portions and on the side thereof opposite an associated one of said output transducers, to provide a nonreflecting tapped delay line.

Claim 5

The fractional efficiency coupling device according to claim 1, wherein said multistrip coupling array provides -3 dB coupling between said tapping and launching portions, and also comprising a second output transducer and associated load matching the characteristics of said first mentioned output transducer, said second output transducer being disposed on said surface in said first track directly opposite said first output transducer, and further comprising a surface acoustic wave absorber disposed in axial alignment with said second track on the side of said launching portion opposite that of said first output transducer, said distance d being selected to provide a 90° phase shift between surface acoustic wave energy incident on said first and second output transducers, to provide an echo trap.

Claim 6

A fractional efficiency surface acoustic wave reflecting track changer, comprising: a substrate of piezoelectric material having a surface capable of supporting propagating surface acoustic wave energy; input means including an input transducer disposed on said surface for launching surface acoustic wave energy along a first track on said surface in response to an electrical input signal; output means including an output transducer disposed on said surface for detecting surface acoustic wave energy propagating along a second track on said surface and producing a corresponding electrical output signal; coupler means including a first, second, and third multistrip coupling array, each of a predetermined number N of conductive strips disposed on said surface, said coupling arrays each having a tapping portion in an associated input track and an approximately equal length launching portion for launching along an associated track only a portion of said surface acoustic wave energy incident on said tapping portion, the strip period p 1 of said strips in said tapping portion being different than the strip period p 2 of said strips in said launching portion, the strip period difference being defined by a predetermined strip period ratio p 1 /p 2 which in conjunction with said predetermined strip number N provides a broadband multistrip coupling array having a desired transfer efficiency less than unity at a desired center frequency, said tapping portions of said first and second arrays being disposed in said first track, the latter being downstream of the former, said launching portion of said first array and said tapping portion of said third array being disposed in said second track, the latter being on the same side of the former as said second array and on the side of said former opposite said output transducer, said second and third arrays being U-shaped whereby said launching portion of said second array is in said first track and said launching portion of said third array is in said second track, the downstream end of said launching portion of said multistrip coupling array being offset by a distance d in an upstream direction relative to the downstream end of said tapping portion to provide a desired phase shift to compensate for the phase shift caused by said predetermined strip period ratio p 1 /p 2 .

Claim 7

A fractional efficiency surface acoustic wave reflecting track changer, comprising: a substrate of piezoelectric material having a surface capable of supporting propagating surface acoustic wave energy; input means including an input transducer disposed on said surface for launching surface acoustic wave energy along a first track on said surface in response to an electrical input signal; output means including an output transducer disposed on said surface for detecting surface acoustic wave energy propagating along a second track on said surface and producing a corresponding electrical output signal; coupler means including a first, second, and third multistrip coupling array, each of a predetermined number N of conductive strips disposed on said surface, said coupling arrays each having a tapping portion in an associated input track and an approximately equal length launching portion for launching along an associated track only a portion of said surface acoustic wave energy incident on said tapping portion, the strip period p 1 of said strips in said tapping portion being different than the strip period p 2 of said strips in said launching portion, the strip period difference being defined by a predetermined strip period ratio p 1 /p 2 which in conjunction with said predetermined strip number N provides a broadband multistrip coupling array having a desired transfer efficiency less than unity at a desired center frequency, said tapping portions of said first and second arrays being disposed in said first track, the latter being downstream of the former, said launching portion of said first array and said tapping portion of said third array being disposed in said second track, the latter being on the same side of the former as said second array and on the side of said former opposite said output transducer, said second and third arrays being U-shaped whereby said launching portion of said second array is in said first track and said launching portion of said third array is in said second track, the downstream end of said launching portion of said multistrip coupling array being offset by a distance d in an upstream direction relative to the downstream end of said tapping portion to provide a desired phase shift to compensate for the phase shift caused by said predetermined strip period ratio p 1 /p 2 .