1.9 GHz range ultra-low-loss and steep cut-off double mode SAW filter for the Rx band in the PCS antenna duplexer

This paper describes the DMS (double mode SAW) filter design techniques to achieve the ultra-low-loss and steep cut-off characteristics required for the Rx filter in the PCS (personal communications service) duplexer. It is the first attempt to employ DMS filters for antenna duplexers in mobile phones. It is demonstrated that the common ground inductance L_g and the coupling capacitance C_c between the input and output terminals of the DMS filters dramatically enhances the skirt steepness and the attenuation for the lower frequency side of the pass band. Based on this result, we propose a novel DMS filter structure that easily controls the L_g and C_c values. Moreover, we propose a compact DMS filter structure connected in parallel, which reduces the insertion loss. Applying these technologies to the Rx filter, we develop a DMS-employing PCS antenna duplexer.