b one edge of which coincides with one of the curved edges of the microstrip provided in the dielectric is a slot 4 into which the gas is injected and in which the plasma 5 is generated a substrate 6 to be treated on average perpendicular to the plane of the microstrip and having a warped shape matching the curvature of the dielectric and of the microstrip is driven beneath the device in the direction indicated by the arrow according to this embodiment the substrate is perpendicular to the microstrip the treatment is a post discharge plasma treatment fig2 a and 2 b illustrate schematically a device 7 according to the invention in which the microstrip 8 of warped shape is connected to a very high frequency generator this microstrip 8 is fixed to the actual warped surface of a dielectric 9 b the gas is fed in close to the face 9 a 2 of the dielectric 9 a 1 a 2 and the plasma 10 is generated beneath the face 9 a 2 opposite the microstrip 8 a substrate 11 to be treated having a warped shape matching that of the dielectric 9 b and of the microstrip 8 is driven beneath the device 7 in the direction indicated by the arrow in this embodiment since the substrate 11 is perpendicular to the microstrip the treatment is a direct plasma treatment fig3 a to 3 d show schematically the various ways of connecting the microstrip conductor to the very high frequency power supply thus according to a first embodiment.