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Abstract

Selected transducer geometries including unbalanced split electrode and three electrode per wavelength structures are employed for use in wide band tapered SAW devices. Combining geometries useful in narrow bandwidth SAW filters for canceling reflected waves leading to triple transit interference, and electrode tapering useful in wide bandwidth SAW filters for permitting transduction of a wide range of surface acoustic wavelengths has the unexpected result of significantly reducing insertion loss and improving triple transit suppression over wider bandwidths than can be achieved with SPUDT designs on non-tapered devices. The interdigitized electrode fingers of opposing bus bars in the transducer have a tapered alignment wherein a period of electrode finger portions along an acoustic wave propagation axis decreases along a transducer dimension. In one embodiment, the transducer has spacing between the electrode fingers which provides two pairs of unbalanced split electrodes within a spacing length equal to its respective acoustic wavelength. The positions and widths of the fingers are such that SPUDT transduction and reflection conditions are satisfied. In an alternate embodiment, the transducer has three electrodes per acoustic wavelength wherein the electrode widths and gaps between electrodes vary to satisfy the SPUDT transduction and reflection conditions. The performance of each transducer is further enhanced with subtransducers for providing series-block weighting. The three electrode per wavelength finger geometry further includes line-width weighting for providing a fine weighting control to complement the inherently coarse weighting control of the series-block weighted transducer.

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