Optimized cut of lithium niobate for HVPSAW filters with different metalization ratio in element resonators

The propagation loss of high-velocity pseudo-surface (leaky) waves (HVPSAW) propagating in orientations of LiNbO₃ defined by the Euler angles (0°, μ, 90°), with periodic Al grating, has been numerically analyzed as function of three parameters, Euler angle μ, electrode thickness and metalization ratio. It was found that there is no combination of these parameters giving non-attenuated HVPSAW simultaneously at resonant and antiresonant frequencies, but there exists a wide area, within which the propagation losses at resonance and at antiresonance are both less than 0.001 dB/Λ. This area is located between orientations (0°, 78.5°, 90°) and (0°, 81°, 90°), with normalized Al thickness between 0.079 and 0.0875 and metalization ratio between 0.4 and 0.8. Orientation (0°, 80°, 90°) was found to be the best choice to provide low propagation loss within wide interval of Al thicknesses. Metallization ratios of individual resonators within one resonator (ladder) filter can be varied to allow the propagation loss for each individual resonator to be minimized at predetermined individual frequency and provide improved performance of the HVPSAW filter.