Computer aided design of low-loss SAW filters employing IIDT for high performance mobile radio duplexer

The authors describe a computer-aided design method to optimize all the design parameters of the IIDT (interdigitated interdigital transducer)-type SAW (surface acoustic wave) filter so that it satisfies the required frequency and electrical characteristics. By connecting the admittance matrices of each IDT, each SAW propagation path, and each IIDT-track, a dual IIDT-track configuration is represented by a six-port admittance matrix in an equivalent circuit model. A merit function, which is defined as the sum of squared of deviations from the target specifications, is introduced to evaluate filter characteristics. By iterating calculations of the equivalent circuit model, the design parameters are determined so as to minimize the merit function. A high-performance filter which satisfies the requirement is thus achieved. Some design examples are given, and they are verified by experimental results