K.A. Zaitsev, V.M. Pikunov, A.N. Sandalov

Multibeam klystrons (MBKs) are used in different branches of science and engineering where high level of output power in wide band is necessary, especially for modern radar systems and particle accelerators. Traditional floating-drift klystron is narrow-band with bandwidth about 1.5% and its broadening is important problem for designers of high-power microwave electron systems. Creation of powerful and wideband klystrons is concerned with investigating of electrodynamic characteristics of its cavities. In powerful MBK parameters of cavities have to correspond to requirements of high-performance electron bunching to realize high efficiency. 3D simulating code CST Microwave Studio allow to calculate basic parameters of cavities in rapid and comfortable way. Different ways to determine the parameters of open output cavities such as resonant frequencies, Q-factors and R/Q values are described. Such techniques are applicable for lossfree structures. First five modes for C-band MB output system are considered. The influence of nonoperating mode oscillations is estimated. The methods to expand the bandwidth for structure under research are suggested.