An apparatus for depositing a thin film on a substrate, comprising: a substrate support having an outer surface for guiding the substrate in a transport direction along a surface of the substrate support through a first vacuum processing region and at least one second vacuum processing region, wherein the outer surface of the substrate support is a curved surface of a coating drum; a first deposition source (130, 630, 730) corresponding to the first vacuum processing region and at least one second deposition source (130, 630, 730) corresponding to the at least one second vacuum processing region, wherein at least the first deposition source (130, 630, 730) comprises: an electrode (531, 602, 702) having a curved surface, wherein the surface of the electrode opposes the surface of the substrate support; a processing gas inlet (612, 712) and a processing gas outlet (614, 714), wherein the processing gas inlet (612, 712) and the processing gas outlet (614, 714) are arranged at opposing sides, with respect to the transport direction, of the surface of the electrode (531, 602, 702); and at least one separation gas inlet (842, 1842) having one or more separation gas inlet openings, wherein the one or more separation gas inlet openings are provided at opposing sides, with respect to the transport direction, of the surface of the electrode (531, 602, 702) such that the processing gas inlet (612, 712) and the processing gas outlet (614, 714) are provided between the one or more separation gas inlet openings and the surface of the electrode (531, 602, 702); the apparatus further comprising: one or more vacuum flanges (1142, 402) providing at least a further gas outlet between the first deposition source (130, 630, 730) and the at least one second deposition source (130, 630, 730). a substrate support having an outer surface for guiding the substrate in a transport direction along a surface of the substrate support through a first vacuum processing region and at least one second vacuum processing region, wherein the outer surface of the substrate support is a curved surface of a coating drum; a first deposition source (130, 630, 730) corresponding to the first vacuum processing region and at least one second deposition source (130, 630, 730) corresponding to the at least one second vacuum processing region, wherein at least the first deposition source (130, 630, 730) comprises: an electrode (531, 602, 702) having a curved surface, wherein the surface of the electrode opposes the surface of the substrate support; a processing gas inlet (612, 712) and a processing gas outlet (614, 714), wherein the processing gas inlet (612, 712) and the processing gas outlet (614, 714) are arranged at opposing sides, with respect to the transport direction, of the surface of the electrode (531, 602, 702); and at least one separation gas inlet (842, 1842) having one or more separation gas inlet openings, wherein the one or more separation gas inlet openings are provided at opposing sides, with respect to the transport direction, of the surface of the electrode (531, 602, 702) such that the processing gas inlet (612, 712) and the processing gas outlet (614, 714) are provided between the one or more separation gas inlet openings and the surface of the electrode (531, 602, 702); an electrode (531, 602, 702) having a curved surface, wherein the surface of the electrode opposes the surface of the substrate support; a processing gas inlet (612, 712) and a processing gas outlet (614, 714), wherein the processing gas inlet (612, 712) and the processing gas outlet (614, 714) are arranged at opposing sides, with respect to the transport direction, of the surface of the electrode (531, 602, 702); and at least one separation gas inlet (842, 1842) having one or more separation gas inlet openings, wherein the one or more separation gas inlet openings are provided at opposing sides, with respect to the transport direction, of the surface of the electrode (531, 602, 702) such that the processing gas inlet (612, 712) and the processing gas outlet (614, 714) are provided between the one or more separation gas inlet openings and the surface of the electrode (531, 602, 702); the apparatus further comprising: one or more vacuum flanges (1142, 402) providing at least a further gas outlet between the first deposition source (130, 630, 730) and the at least one second deposition source (130, 630, 730).