Development of a new design technique for surface acoustic wave ladder filters

Design of surface acoustic wave (SAW) ladder filters has been performed by trial and error, that is, by modifying the design variables step by step until performance of the filter satisfies given specifications. In this work, a new design method is developed that automatically determines the detailed pattern of a SAW ladder filter to meet all the given specifications. As a first step for the development, an analysis tool for the SAW ladder filter is produced by means of the Smith equivalent circuit analysis technique, and its validity is verified through comparison of calculated results with experimental data. With the analysis tool, we investigate variation of the filter performance in relation to the change in its design factors, and the results lead to the design algorithm. Validity and efficiency of the algorithm are illustrated with an exemplary design of a SAW ladder filter for cellular phones. The design scheme developed in this paper is so general that it can be applied to any other types of SAW filters too.