By separating the transmitted and received signals, which occurs at different times, the same antenna can be used for the transmitter and receiver. To ensure that the radiated transmit frequency, whose transmit power is much higher than the receive field strength, does not affect the received signal, the RF filters must have a high selectivity. In terms of transmission technology, the transmit and receive frequencies are separated from each other by steep-edged filters. To achieve the required high selectivity of duplexers, narrowband bandpass filters are combined with notch filters.
Duplexers are used in filters, resonators and radar systems, where they separate the outgoing radio wave from the reflected radio wave.