New SPUDT cells including fingers and gaps wider than a quarter wavelength

The basic types of SPUDT cells like DART, EWC, Hanma-Hunsinger, FEUDT and TF include quite narrow fingers and gaps. For application in GHz SAW devices these fingers are too narrow to implement the electrode structures in the required quality by means of the available technologies. Solutions of SPUDT cells with sufficiently wide fingers and gaps on YZLiNbO₃ and 128°YXLiNbO₃ with 3, 4, 5 fingers and with lengths of 2, 3, 3 wavelengths (in the same order) are presented. The cells have been found by means of an optimization procedure. Due to bulk wave generation there is a relatively big loss. This can be a problem if the SPUDTs are too long. In order to achieve a sufficient unidirectional effect in spite of the small number of fingers big reflection factors per wavelength are needed. The experimental study of a cell type with five fingers on YZLiNbO₃ confirms the existence of a strong unidirectional effect pointing really to a big reflection factor per wavelength.