Compensation of Diffraction Effects in SAW Filters Using the Uniform Asymptotic Expansion

Abstract

Abstruct-The uniform asymptotic expansion (UAE) previously developed for the calculation of the diffracted SAW beam profile is extended to the calculation of diffraction effects in the frequency response of a SAW filter. The method provides a fast and accurate method of calculating the effects of diffraction in the frequency response of SAW filters even in the very near field region (z < 2.5 A,,). Accuracy and speed comparisons between the UAE and a direct numerical integration algorithm are given. For transducer separations greater than 25 X. the relative difference between the two methods is less than 0.1 dB in the frequency range of interest. In addition, the computation speed of the UAE is greater than that of the numerical integration algorithm by at least a factor of 60 and continues to increase with increasing transducer separation. This technique is used in conjunction with well-known wide-band compensation procedures to design diffraction compensated SAW filters. Experimental results of diffraction compensated SAW filters constructed on 128 rotated Y-cut X-propagating LiNbO, are given.