Direct numerical analysis of SAW coupling-of-modes equations and its applications to weighted single-phase unidirectional transducers and weighted reflectors

To realize wideband SAW filters, a weighted single-phase unidirectional transducer (SPUDT) has been analyzed by direct numerical analysis of the coupling-of-modes equations using an algorithm combined with the Runge-Kutta and the Newton method. It is found that the directivity is obtained over a wide frequency range when the reflection coefficient of the SPUDT was weighted using a sine function in order to distribute the positive and negative reflection elements into the SPUDT. This paper also describes weighted reflectors, a weighted SPUDT with both the reflection and transduction coefficients, and a weighted natural-SPUDT (NSPUDT) on a langasite (La₃Ga₅SiO₁₄) and a langanite (La₃Ga_5.5Nb_0.5O₁₄) substrates, which have recently attracted much attention for IF SAW filters.