New Design of High Order Modes Electronics in MTCA.4 Standard for FLASH and the European XFEL

At free-electron linear accelerators, various High Order Modes (HOM) - both monopole and dipole - are excited. Extensive studies at DESY have shown that monitoring and analysis of some of these modes can be used for different applications including Beam Position Monitors (BPMs) and the reduction of wake-fields, the measurement of the beam phase with-respect-to RF signal in cavities, and the measurement of cavity alignment in the 1.3 GHz cryo-modules. Three frequencies were chosen for further experiments: the 1.3 GHz base frequency from the klystron, the 1.7 GHz dipole mode and the 2.4 GHz monopole mode. In order to realize the monitoring and analysis requirements, very high resolution measurements in amplitude, phase and shape (time resolution) are required for all three frequencies simultaneously. In this paper, we present the new HOM electronics prototype including a microstrip and stripline RF tri-passband filter design and measurements and the specialized MTCA.4 Rear Transition Module for HOM measurements with an ultra-fast high-resolution AMC digitizer