Dual track low-loss reflective saw filter

摘要

A dual track, low signal loss surface acoustic wave filter includes tapered transducers and tapered reflectors within an axis of propagation for each track to achieve an improved pass band response associated with tapered transducers. The bandwidth of the filter is achieved by adjusting the taper of periodicity normal to the propagation axis. Each track includes reflector gratings mounted on the filter substrate for reflecting a surface acoustic wave propagating from a transducer mounted within each track back to the transducer. Input and output transducers are positioned between the reflectors within each track for providing a direct surface acoustic wave propagation path within the track between the transducers. Alternate parallel tracks have the reflector with an input transducer, and a reflector with an output transducers mounted in an offset alignment with a corresponding adjacent track reflector and transducer for constructively adding surface acoustic wave signals detected within the adjacent track. Both the reflectors and transducers within each track include a similar set of electrode fingers mounted on the substrate generally transverse to the longitudinal propagation axis. In addition, each finger set has adjacent fingers positioned such that a spacing between the adjacent fingers continuously increases or decreases monotonically from point to point transversely to the propagation axis, along the fingers, and the spacing between adjacent fingers along lines parallel to the axis of propagation are substantially equal.