The applicant has already proposed, in French Patent FR-A-2608119, a system for transmitting broadband data and/or instructions between a railway vehicle and a traffic control station, and likewise proposed, in French Patent FR-A-2612715, a system for transmiting data and/or instructions between road vehicles and a contro station.  These systems however apply only to transmissions between a hollow tube forming a microwave guide and a vehicle following a path substantially parallel to and a short distance from the hollow tube, having lateral motions which connot exceed a few tens of centimeters.  The did not enable the transmission of data and/or instructions between a control station and an element moving in one plane, which might be at considerably varying distances from the hollow tube waveguide, of the order of several meters for example.