Super-Isolation Duplexer Aiming for Removing Rx Inter-stage Filter in W-CDMA Handsets

A significant improvement in the Tx to Rx isolation of an antenna duplexer intended to remove the need for the Rx interstage filter in CDMA handsets is presented. A developed prototype of the W-CDMA (Band Class I) duplexer achieves 70 dB of isolation in the Tx band, while the isolation of conventional miniaturized duplexers is limited to about 50 dB. The developed "super-isolation duplexer" helps to remove the need for the Rx interstage filter, because the leakage signal from the transmitter, which is the largest interferer for the receiver, is mostly suppressed by the duplexer.