Abstract: A cooling device for microwave circuits comprises a coaxial cable conveying very high power microwave energy, said cable consisting of a hollow, internal, central conductor with a predefined thickness and length and an external conductor within which there is placed the central conductor, said cooling device comprising an inlet channel and a return flow channel to enable the passage of a cooling fluid; said channels consisting of the central conductor which comprises, for this purpose, a strip which separates this conductor longitudinally into two conduits, each forming one of the two channels.