A magnetron source comprises a target (39) with a sputtering surface and a back surface. A magnet arrangement (30, 32, 19a, 19b) is drivingly moved along the backside of the target (39). A tunnel-shaped magnetron magnetic field is generated between an outer loop (30) and an inner loop (32) of the magnet arrangement. Elongated pivotable or rotatable permanent magnet arrangements (19a, 19b) of the magnet arrangement are provided in an interspace between the outer and inner loops (30, 32) of the overall arrangement.