Modified Green´s function approach to analysis of long SAW transducers

Low loss filters based on Single Phase Unidirectional Transducers (SPUDT) could be characterized as a separate class of Surface Acoustic Wave (SAW) filters because they overcome the main SAW filters limitation-6 dB bidirectional insertion loss. For the substrate with the high value of electroacoustic coupling coefficient k² the main effect used to obtain unidirectionality is electrical regeneration which could be treated directly by the Green´s Function Model (GFM). The GFM being applicable to an interdigital transducer (IDT) with arbitrary topology is difficult to be applied to the IDT with large number of periods because computation time increases in power law with growth of the IDT length reaching very quickly unacceptable values. In this paper we present the method for calculation of arbitrary SAW filter parameters based on the GFM. Symmetry consideration being used for presentation of the central region of the long IDT, computation time decreases dramatically. At the same time edge effects of the IDT are correctly taken into account. The method developed works both for high and low k ² value substrates. Results of calculation of SPUDT characteristics with the help of method proposed are presented