Regarding RF passive componenst, we always use duplexer and diplexer, which maybe confused. what is the difference between duplexer and diplexer?

RF Diplexers are 3-port RF devices, which allow the use of two signal paths on the same transmission line (such as an antenna). This is achieved through filters that separate the frequencies of interest, allowing signals at two different frequencies to be sent and received from the same antenna. High performance Diplexers rely on the selectivity and attenuation of the filter structures and their performance over temperature.

RF Duplexers are also a 3-port RF devices, and their function is to separate the transmit and receive signals from the antenna into two different signal paths based on the direction of travel (e.g. if the antenna is port A, then ‘forward’ signals move from B to A, and ‘backward’ signals move from A to C). The transmit and receive signals can operate at the same frequency, enabling true Full Duplex communication on a single antenna.