Longitudinal leaky surface waves for high frequency SAW device applications

Abstract

Longitudinal leaky surface waves with a phase velocity of 6700 m/s and low propagation loss on lithium tetraborate (LBO) are reviewed. Moreover, the dispersion properties of longitudinal leaky surface waves propagating under the periodic Al strip grating on LBO are described theoretically and experimentally, for applications of the mode to the high frequency SAW devices. The theoretical method is based on Floquet's theorem using space harmonics as an orthogonal function set. It is found that the propagation loss at the lower edge of the first Bragg stopband for shorted gratings is relatively low. The parameters used in the electrical equivalent circuit model for designing the SAW filters, are obtained from the calculated dispersion curves. A 1.5 GHz SAW filter using the mode has been designed and fabricated for the filter of the global positioning system (GPS). A low loss SAW filter can be obtained easily without submicron fabrication techniques, by using the longitudinal leaky surface waves on LBO.