A miniaturized 3 × 3-mm SAW antenna duplexer for the US-PCS band with temperature-compensated LiTaO3/sapphire substrate

This paper describes a temperature-stable and miniaturized SAW antenna duplexer for the 1.9 GHz US-PCS band that uses a temperature-compensated 42° Y-X:LiTaO₃/sapphire bonded substrate. In this duplexer, the temperature coefficient of frequency is reduced to half or two-thirds of that of a conventional LiTaO₃ substrate. Also, it is shown that our new duplexer has a smaller insertion loss and offers sufficient power durability. These improvements are mainly due to the characteristics of sapphire, such as its larger thermal conductivity and smaller dielectric constant. Furthermore, the performance of our SAW duplexer is compared with that of two kinds of BAW duplexers, which are competitive technologies. As a result, it is shown that our newly developed SAW duplexer offers equal or better performance in a smaller package. This implies that our SAW duplexer is the best and the smallest PCS duplexer.