Acoustical filter, especially surface wave filter

摘要

The SAW filter has an interdigitated transducer region (f) with a large aperture. The phase velocity at the transversal outer regions (g) is selected to lie between the phase velocity in the interdigitated transducer region and the higher phase velocity at the free non-metallised surface. The phase velocity at the outer regions can be selected to ensure a loss-free propagation of the required lower order modes within the interdigitated transducer region, by determining the metallisation of the grid structure forming the outer regions.