Which device uses circulators or diplexer filters to separate and combine the different transmit and receive RF paths?

A transceiver integrates transmitter and receiver functions but does not rely on circulators or diplexers as its defining mechanism for path separation.

A bidirectional amplifier boosts signals in both directions simultaneously but uses spatial or filter-based isolation rather than circulators as its primary defining characteristic.

Circulators are three-port passive devices that allow RF energy to flow in only one direction, making them the key component in a unidirectional amplifier for isolating the TX and RX signal paths and preventing oscillation or feedback. Diplexer filters complement this by separating the two paths based on frequency, allowing both TX and RX signals to share the same physical connection while remaining electrically distinct. Together these components define the unidirectional amplifier's ability to separate, amplify, and recombine both signal directions.

A repeater achieves TX/RX isolation through physical antenna separation and spatial diversity, not through internal circulators or diplexer filters.