A network model for arbitrarily oriented IDT structures

A network model approach for analyzing arbitrarily oriented short-circuited SAW grating structures is extended to include interdigital transducers (IDTs) that are also arbitrarily oriented. The IDT structure is divided into cells, each modelled by a sequence of mismatched transmission lines consisting of a metallized and unmetallized region. The model includes: the impedance difference between metallized and free regions, the reflection coefficient at the metallization upstep, the reflection coefficient at the downstep for a counterpropagating wave, all deduced from the Datta-Hunsinger perturbation formula; the velocity difference between the free and metallized regions obtained using SAW propagation calculation software for arbitrarily oriented multilayers; and the energy storage susceptance at each finger discontinuity. Since only ordinary network elements are combined in accordance with the IDT geometry, this model permits good physical insight into the structure's characteristics and allows simple procedures for finding high directivity orientations.