• D. Lipka, D. Nölle, M. Siemens, S. Vilcins
  DESY, Hamburg
• F. Caspers
  CERN, Geneva
• H. Maesaka, T. Shintake
  RIKEN/SPring-8, Hyogo
• M. Stadler, D.M. Treyer
  PSI, Villigen

XFELs require high precision orbit control in the long undulator sections. Due to the pulsed operation of these systems the high precision has to be reached by single bunch measurements. So far cavity BPMs achieve the required performance and will be used at the European XFEL between each of the 116 undulators. Coupling between the orthogonal planes limits the precision of beam position measurements. A first prototype build at DESY shows a coupling between orthogonal planes of about -20 dB, but the requirement is lower than -40 dB (1%). The next generation Cavity BPM was build with tighter tolerances and mechanical changes, the orthogonal coupling is measured to be lower than -43 dB. This report discusses the various observations, measurements and improvements which were done.