Abstract: A transmission path between a source of microwaves, such as a radar transceiver, and a load rectilinearly movable with reference thereto, such as an aerial mounted on a retractable mast of a submarine periscope, comprises two relatively movable parallel waveguides respectively connected to a pair of coaxial ancillary guide portions with mating extremities which are separated from each other in one relative position and are interfitted in another relative position of the source and the load. The male guide portion is externally grooved to form microwave chokes whose effect is enhanced by a peripheral layer of energy-absorbent coating disposed beyond these chokes as seen from the female guide portion. The main waveguides may be coaxial with the interfitting guide portions or may extend parallel thereto and be connected to them by respective elbows.