Minmization of diffraction effects in SAW devices using a wide aperture

A simple and elegant method is presented for the minimization of diffractive effects in SAW filters. It is shown that diffraction effects can be almost completely eliminated by merely increasing the aperture of the receiving unapodized transducer. From the leading terms of the Uniform Asymptotic Expansion (UAE) of the diffraction integrals, we can obtain a physical interpretation of the diffraction process in terms of the Geometric Theory of Diffraction GTD). An explanation of this diffraction minimization tec h nique is obtained using the physically intuitive language of the GTD. A simple formula for the necessary dimension of the receiving aperture which yields a desired level of diffraction error for a given transducer separation is given. The validity of the method is confirmed experimentally for devices fabricated on 128 degree rotated Y-cut X-propagating LiNb03. This technique can be applied to a wide class of highly anisotropic materials.