Abstract
To realize wideband surface acoustic wave (SAW) filters, a weighted single-phase-unidirectional transducer (SPUDT) has been analyzed by direct numerical analysis of the coupling-of-modes equations. It was found that the directivity was obtained over a wide frequency range when the reflection coefficient of the SPUDT was weighted using a sinc function in order to distribute the positive and negative reflection elements into the SPUDT; this was called a wideband SPUDT. This paper also describes a high-performance wideband SPUDT, with both the reflection and transduction coefficients weighted on 128°Y-X LiNbO3 substrates, and a new wideband natural-SPUDT (NSPUDT) on 50°Y-23°X La3Ga5SiO14 substrates, which has recently attracted much attention for intermediate frequency (IF) SAW filters.