Abstract: A duplexer, useable to interlink the receiver, transmitter and antenna units of a microwave transmit/receive system takes the form of a "T" junction coupling device and three coaxial lines extending from junction ends at such device to coaxial end connectors on the ends of such lines away from such device. The "T" junction coupling device comprises a copper block having a central cavity and three bores leading into such cavity, a copper cap to close the top of such cavity, a copper disc disposed in said cavity away from its walls and containing a central space and three passages leading into said spaces and corresponding to said bores, and three brass ferrules for such lines. The ferrules are seated on the junction ends of such lines and are soldered to their outer conductors and are pressed fitted into the three bores. The inner conductors are received in the three passages in the disc and are all soldered thereto.