Green´s function approach to the design of SAW filters, containing long unidirectional transducers

Green´s function approach (GFA) allows one to evaluate such characteristics of an interdigital transducer (IDT) as the insertion loss and input admittance both in an electrostatic approximation and taking into account surface acoustic waves (SAW) generation. To do this it is necessary to evaluate the charge distribution (CD) along the electrodes of the IDT. This approach makes it possible to evaluate the CD for a single phase unidirectional transducer (SPUDT), having arbitrary types of electrodes (split, floating, nonequidistant etc.). The main disadvantage is the necessity of solving very large (practically more than 500×500) systems of linear equations for each frequency point, which makes this approach impossible to use for a long SPUDT. A procedure for dramatically reducing the computational time is described. It is based on the evaluation of the CD for a long SPUDT from the CD of a short test transducer. The procedure proposed allows one to determine the insertion loss and impedance of a SPUDT, having arbitrary types of electrodes and arbitrary number of periods, taking into account electrostatic CD and SAW generation. Examples discussed show a good agreement of the approximation proposed with the exact GFA solution