SAW duplexers without λ/4 phase shifter for PDC cellular phone systems

This paper describes a design technique for SAW duplexer. We developed a front-end SAW duplexer for Japanese PDC 800MHz cellular phone. Wide channel separation of 130MHz between Tx and Rx band is required for the PDC duplexer. It is difficult to realize such a wide channel separation by conventional design method. To solve this issue, we controlled frequencies of pole and zero arbitrary by adding outer inductor and/or capacitor to SAW resonator. By using this technique, a very low loss and high attenuation duplexer for PDC system was realized. As the feature of the duplexer, it can minimize insertion loss deterioration in duplex mode due to bulk wave radiation loss. Moreover, the developed duplexer has the advantage that λ/4 phase shifter and matching circuit are not needed. The duplexer achieved less than 25% in the area ratio toward conventional dielectric duplexer.