Diplexer separates two different frequency bands in the receive path and combines them in the transmit path, with bands being widely separated, such as separating GSM and WCDMA. Duplexer uses a single antenna for both transmit and receive simultaneously for bands closer together, such as uplink and downlink DCS. Duplexers have higher Tx-Rx isolation around 90-95 dB and use bandpass filters or switching to separate transmit and receive signals on the same channel.

1. Diplexer v.s. Duplexer
Diplexer
Separates two different freq. bands in Rx path and combines them in Tx path.
These freq. bands will be wide apart in freq. domain. Ex: separate EGSM, DCS or GSM, WCDMA.
Tx-Rx isolation ~ 50-60 dB.
One HPF and one LPF HPF負責High-Band TRx, LPF負責Low-Band TRx.
Smart phone always use the LC Diplexer.
Use single antenna by both Tx and Rx at the same time.
Both Tx and Rx paths have freq. bands very nearer, hence narrow BPF are used. Ex: DCS uplink and downlink.
Two types of duplexer, one by using PIN diode switches and the other using circulators.
Tx-Rx isolation very important ~ 90-95 dB.
兩個頻段不同的BPF 一個負責Tx, 一個負責Rx.
Smart phone always use the SAW Duplexer.
EGSM + DCS
EGSM 900
880-915 MHz
920-965 MHz
DCS 1800
1710-1785 MHz
1805-1880 MHz
DCS
1710-1785 MHz 1805-1880 MHz
Duplexer
收發都走同通道收發都走同通道收發都走同通道收發都走同通道
收發分別從兩個通道收發分別從兩個通道收發分別從兩個通道收發分別從兩個通道走走走走