Surface acoustic wave filter
AssigneeRockwell International Corporation
InventorsTeong C. Lim, Umit Tarakci, Carmine F. Vasile
Life of this patent
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Abstract
A surface acoustic wave filter has a Lithiumniobate substrate of parallelogram configuration, which is bonded to a header having similar acoustic impedance. The substrate has three transducers arranged along its long sides at particular spacings destined to suppress triple transit echoes. The short sides are oblique and surface portions adjacent thereto are covered by surface waves attenuating paddings. Two such filters are cascaded on the same header.
Claims12
A surface acoustic wave filter for use in connection with an amplifier having a particular pulse response recovery time, comprising:
- a flat, piezoelectric substrate having elongated extension in one direction and a parallelogram elevational contour, there being a plurality of interdigitized fingers establishing at least two transducers respectively for transmitting and receiving acoustic surface waves propagating in the one direction, the wavelength of the passband center frequency being determined by the spacing on said interdigitized fingers, particular surface areas being free from these fingers adjacent to short side edges of the parallelogram, said edges having an angle of less than 90.degree. relative to one direction;
- a damping material covering at least a portion of the said surface areas for a width in the said direction equivalent to about ten wavelengths of the transmitted surface waves;
- and
- the edge-to-edge spacing between the transducers being greater than about four wavelengths, the center-to-center spacing between the two transducers being smaller than one half the distance a surface wave propagates during said recovery time.
In a filter circuit which includes a surface acoustic wave filter connected to an amplifier to establish a band pass amplifier system, the amplifier having a particular pulse response recovery time, the improvement for the acoustic wave filter, comprising:
- a flat piezoelectric substrate carrying on one surface a plurality of interdigitized fingers establishing at least one transmitting transducer for surface waves and at least one transducer for receiving surface waves, the two transducers having a center-to-center spacing which is less than one half the distance an acoustic surface wave travels during said recovery time, the two transducers having an edge-to-edge distance in excess of the dimensions of the acoustic storage field of each said transducers, being about four wavelengths.
A surface acoustic wave filter comprising:
- a flat, piezoelectric substrate carrying on one surface a plurality of interdigitized metallization fingers for establishing plural transducers, at least one of the plural transducers for transmitting acoustic surface waves in a direction extending transversely to said fingers, thereby inherently producing bulk waves propagating into the interior of the substrate, at least one of the plural transducers for receiving said waves;
- a support element having an acoustic impedance which is closely matched to the acoustic impedance of said piezoelectric substrate;
- and
- a bonding layer for bonding the substrate at its surface opposite said finger carrying surface to said support element, the bonding layer being electrically conductive and having a thickness being uniformly less than the wavelength of said surface and bulk waves.
Dependencies are inferred from the claim text.