Expansion joint for wave guides

An expansion joint for wave guides, said expansion joint including first and second aligned components which have the same inside dimensions as the wave guide and which are free to move longitudinally with respect to each other, the improvement wherein said first component comprises a tube, said second component includes a trap positioned at least partially between said components and radially outside the first component, the electric length of said trap being equal to half the wavelength of the central frequency transmitted by the wave guide, and means for separating said components longitudinally at the trap by a distance which varies as the length of the wave guide varies, and wherein said trap is folded so as to obtain two transmission lines which have the same electric length, and said trap includes a first transmission line constituted by a space comprised between the first component and the first longitudinal branch of the second component, a second transmission line constituted by a space comprised between said first branch and said second longitudinal branch, one of whose ends has a radially inwardly turned lip facing said other surface of said first component and covering one end of said first branch, and wherein said second transmission line is wider than that of the first transmission line and having therefore a greater impedance.