US-PCS SAW duplexer using high-Q SAW resonator with SiO/sub 2/ coat for stabilizing temperature characteristics

We have successfully developed SAW resonators with a SiO/sub 2/ coat, which have both high-Q characteristics and stable temperature characteristics. We realized a SAW duplexer for the US PCS band (US-PCS) using these resonators. The frequency characteristics variation due to temperature change is usually taken into design consideration. However, in case of the US-PCS duplexer, which has a difficult frequency allocation for the transmission (Tx) band and the reception (Rx) band. A temperature coefficient (TC) reduction technology is essential to realize the US-PCS SAW duplexer. Of course, this TC reduction technique should not deteriorate the filter characteristics, such as insertion loss. In this report, we explain the TC reduction technique using a SiO/sub 2/ layer and the US-PCS SAW duplexer employing these resonators. It shows good performance over the temperature range -30/spl deg/C to +85/spl deg/C.