High-frequency SAW duplexer with low-loss and steep cut-off characteristics

In CDMA (code division multiple access), analog, and partly TDMA (time division multiple access) cellular phone systems, transmitting and receiving are carried out simultaneously. Thus, an antenna duplexer is needed. An antenna duplexer using ladder-type SAW filters was first applied in an AMPS (Advanced Mobile Phone System)-CDMA system in 1998. The package size was 9.5 × 7.5 × 2 mm. The development of SAW antenna duplexers will require SAW filter designs that enable lower loss and a sharper cut-off, electrode materials that provide higher power durability, and package designs that enable lower loss and a smaller size. The miniaturization of this duplexer has been achieved by improving the filter chip and reducing the package size to 5 mm square. However, SAW duplexer with low-loss and steep cut-off characteristics is needed for high frequency applications. Through improved SAW filter characteristics, a duplexer for a 1.9 GHz PCS (personal communication services)-CDMA system has been realized. This paper describes these advanced technologies.