Surface acoustic wave resonator filters based on dispersive transducers

Abstract

The possibility of using interdigital transducers (IDTs) and reflecting lattices with electrode period modulation (dispersion) in resonator filters with longitudinal acoustic coupling on surface acoustic waves is considered. The experimental investigation of test structures with different directivities of the transducer dispersion shows that dispersive IDTs provide for unidirectional excitation. A model developed on the basis of the equivalent-circuit method makes it possible to calculate the characteristics of filters of the class under consideration. It is found that the use of dispersive IDTs and reflecting lattices makes it possible to reduce the insertion losses of devices, to extend their passbands, and to improve their selectivity. A set of filters is designed on the basis of lithium tantalate and lithium niobate acoustic ducts with insertion loss ranging from 1.5 to 3.0 dB and relative passbands ranging from 1 to 8%.