The transition frequency band between Tx (transmission) and Rx (receiving) pass bands of the Personal Communication Services (PCS) handy phone in US is relatively narrow (20MHz) compared with similar systems' handy phones. The antenna duplexer for the PCS needs a good temperature stability of frequency and a steep cut-o® frequency characteristics in the transition band. Up to the present, there exists no substrate for the surface acoustic wave (SAW) having both the good temperature stability and the optimum electromechanical coupling factor to realize the required bandwidth of the PCS duplexer. So, the PCS SAW duplexer has been developed with the only steeper cut-o® characteristics to eke out its insu±cient temperature stability. The PCS duplexers consisting of FBAR (-Im bulk acoustic resonator) have also been designed as another approach, but their temperature characteristics are not enough. This paper describes a new substrate having both the good temperature stability and the suitable electromechanical coupling factor and a US-PCS SAW duplexer constructed of this substrate.
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