Equivalent circuits for unidirectional SAW-IDTs based on thecoupling-of-modes theory

摘要

A three-port distributed-parameter equivalent circuit representingnthe whole structure of a unidirectional interdigital transducer (IDT) isnderived from generalized coupling-of-modes (COM) equations with complexnparameters. The circuit has a simple form similar to that of anbidirectional IDT, but involves two additional impedance elements ofnopposite signs. It is shown that the two additional elements expressnwell the behaviors of unidirectional IDTs and the directivity can easilynbe derived from the equivalent circuit. Some examples of calculations ofndevice characteristics using the circuit are also presented