Frequency characteristic optimization in surface acoustic wave filters by DFP approaches

Abstract

This chapter considers transmission characteristic of surface acoustic wave (SAW) filters. The apodization in the input interdigital transducer (IDT) is adopted to achieve the desired frequency bandwidth, and the attenuation for the central frequency of the stopband given. The present paper proposes the design procedure to meet the requirement. The frequency characteristic of a SAW filter is characterized by a delta-function model, and an equivalent circuit model. The apodization is made by varying each electrode length of the input IDT. The objective function or the error norm between the required frequency characteristic and the calculated is defined. The calculation is repeated to minimize the objective function using the Davidon‑Fletcher‑Powell (DFP) method. The study demonstrates the design methodology of the SAW filters with a couple of worked examples and with some discussions.