Low loss and high performance SAW filters for 800 MHz mobile telephone transceiver

Propagation characteristics of leaky SAW under a metallic‐grating structure (grating mode) on 36° YX‐LiTaO3 (36‐LTO) are analyzed and compared with experimental results. First, the velocity dispersion and attenuation for the grating mode are theoretically analyzed. The results show that although the velocity dispersion is similar to that for an SAW, the stopband width of the grating changes with the electrical boundary of the grating. The attenuation depends on how strongly the grating mode couples to bulk waves and leaks its energy into the bulk. The interaction of the grating mode with slow shear waves is markedly weak on 36‐LTO. Hence, the attenuation due to bulk wave radiation is negligible at frequencies where the grating mode couples only to slow shear waves. However, the attenuation increases at frequencies slightly higher than the stopband, where the grating mode strongly couples to fast shear waves. Next, transmission and reflection characteristics are experimentally investigated about the stopband of a metallic‐grating fabricated on 36‐LTO. The results are in good agreement with the theoretical prediction.

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