SAW Duplexer with High Isolation Based on Rejection Resonator and Cross Coupled Capacitor

A novel surface acoustic wave (SAW) Band-1 duplexer with high isolation is proposed and studied in this paper. A cross coupled capacitor connected between the series resonator on receiving (Rx) path and the ground on the transmitting (Tx) path can substantially enhance the isolation. This Tx ground pad is bonded to a coil inductor on the HTCC substrate. And a parallel rejection resonator on the Tx path is introduced to further improve the isolation, whose resonant frequency is set at the Rx band. The duplexer is fabricated on a standard 42° Y-X Lithium Tantalate (LiTaO₃) substrate. When the above two approaches are combined simultaneously, the isolation at the Rx band could achieve 60 dB or even higher. The proposed design method is also proven to be beneficial to the miniaturization of the duplexer, which greatly enhances the design flexibility. The measured results are in good agreement with the simulation.