RF Diplexers and Duplexers

Diplexers are three-port frequency-dependent devices that may be used as a separator or a combiner of signals. The device consists of two fixed tuned bandpass filters sharing a common port. The common port and the output of the two filters (RX and TX) form the three terminals of the diplexer. Signals applied to common port are separated in accordance with their passband frequencies of the filters. Signals applied to either uncommon port are isolated from the other uncommon port and are combined at the common port. Diplexers are the simplest form of a multiplexer.  Duplexers allow a transmitter operating on one frequency and a receiver operating on a different frequency to share one common antenna with a minimum of interaction and degradation of the different RF signals.