Finite element methods for integrated circuits of LTCC and equivalent circuit models for SAW chips are applied to SAW duplexer analysis. We improve this composite method with considering feed through. A good agreement with this improved composite simulation and experiment is obtained. We have found that magnetic interaction between a phase-shifter and a matching element for Tx circuit becomes a worse of Tx-Rx isolation. We have also found an improved shape of element to suppress the magnetic interaction between these circuits by try and error method. An isolation value of 48 dB in Rx band is observed at an improved duplexer. Consequently it is verified that a improved composite model is effective for analyzing Tx-Rx isolation of a miniature SAW duplexer. And high isolation characteristic for SAW duplexer is also obtained by using improved structure.