1. O. Ya. Usikov Institute for Radio, Physics and Electronics of NASU,Department of Vacuum Electronics,Kharkiv,Ukraine
2. O. Ya. Usikov Institute for Radio, Physics and Electronics of NASU,Kharkiv,Ukraine
3. O. Ya. Usikov Institute for Radio, Physics and Electronics of NASU,Department of Diffraction Theory and Diffraction Electronics,Kharkiv,Ukraine