1. O. Ya. Usikov Institute for Radio Physics and Electronics of NASU,Department of Vacuum Electronics,Kharkiv,Ukraine
2. Ukraine Max Planck Institute for Plasma Physics,Greifswald,Germany
3. Institute of Radio Astronomy of NASU,Microwave Electronics Department,Kharkiv,Ukraine
4. School of Radiophysics, Biomedical Electronics and Computer Systems V. N. Karazin Kharkiv National University,Kharkiv,Ukraine