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The paper describes how leaky surface acoustic wave (LSAW) propagation characteristics on LiTaOi depend upon its rotation angle when the AI electrode thickness is increased.It is shown that the propagation loss arising from leaky nature changes parabolically with both the film thickness and rotation angle, and becomes zero when they are properly chosen. This means that even when the relatively thick electrodes are needed, zero propagation loss is always achieved by properly determining the rotation angle for LiTOl When the electrode thickness is 0.07 -0.1 wavelengths, for example, LSAWs on the 40-42" Y-X LiTaOi offer zero propagation loss without deteriorating other characteristics.Ladder filters for 800MHz range were fabricated, which essentially need thick AI electrodes. As is predicted by theoretical calculation, experimental results showed that if the rotation angle B is increased to circa 42" from the conventional value of 36' , the insertion loss and shape factor are improved by 0.7dB and 0.26, respectively. The result gives a valuable guideline for determining the optimal rotation angle of LiTaOi to be used for high performance LSAW filters, which are one of the key components in RF sections of mobile communication systems 1. INTRODUCTlON Because of their attractive features such as compactness, light weight and low price, surface acoustic wave (SAW) filters are widely used in both RF and IF sections of mobile communications hand set units. For RF filter applications, adding to high stop-band rejection, ultimately low insertion loss is required for reduced power consumption or to realize better reception sensitivity in these terminals. For this purpose, leaky SAWS (LSAU's) on 36" Y-X LiTaO? [ l ] and 64' Y-X LiNb03 [ 2 ] have extensively been usedI3-61 because of their very large electromechanical coupling factor K' and low propagation loss. In modem mobile communication systems, their operation frequencies are becoming higher and higher: 800-900MHz range is employed in AMPS and GSM, while I~5GHz range in PDC1500, 1.8-I.9GHz range in PHs, PCS and PCN, and 2.4Gl-I~ range in wireless LAN When designing LSAW 0-7803-3615-1/96/$5.00 0 1996 IEEE 19% IEEE ULTRASONICS SYMPOSIUM -71

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In this paper we propose a method of analysing surface acoustic waves (SAWs) propagating obliquely under a metallic grating with finite thickness. The discrete Green function originally developed for SAWs longitudinally propagating under the metallic grating is modified, and applied to the characterisation of obliquely propagating SAWs. The method is applied to the analysis of Rayleigh SAWs obliquely propagating on 128° Y X-LiNbO3 (128-LN), and the result is shown to be in good agreement with experiments. Leaky SAWs obliquely propagating on 36° Y X-LiTaO3 (36-LT) are also analysed and compared with the result obtained for 128-LN.