Installation for depositing, by means of a microwave plasma, a barrier coating on thermoplastic containers (5), this installation comprising treatment stations (1) each comprising a treatment enclosure (2) and a cover (3) and including a vacuum pumping chamber in which connection means (4) for sealed connection to the container comprise a sleeve (6) co-axial with the neck (7) of the container, each cover (3) also supporting an injector (8) co-axial with the sleeve (6) for injecting a reactive fluid into the container; the sleeves (6) and/or the injectors (8), of several adjacent stations are fastened to a single support plate (15, 20) that extends in the form of a bridge over the covers (3) of these stations (1), whereby the plate (15, 20) and the sleeves and/or injectors of the stations (1) constitute a unitary assembly (16, 21) that can be maneuvered as one piece.