The present invention concerns a sputtering magnetron assembly comprising a rotatable tubular target cathode and a magnetic field generating device installed within the tubular target cathode. At least part of the magnetic field generating device is configured to move within the tubular target cathode so as to maintain within a predetermined range a magnetic field strength at an outer surface of the tubular target cathode during erosion of said outer surface. The present invention also relates to a physical vapour deposition method using such a sputtering magnetron assembly.