Selfexcitation of wideband traveling-wave tubes near "π" point under conditions of presence the stopband in system dispersion

Special attention is paid to problem of selfexcitation in wideband TWTs. Such problem is connected with necessity of generating signal stability in practice for any application. However, there are several mechanisms, responsible for unwanted oscillations origination. Among principal mechanism one can mention following: oscillation near driven signal frequency or one of its harmonics, oscillations near the edge of the band, generating of backward wave harmonic and others. To mentioned mechanisms one can also refer the parasitic oscillations, connected with opportunity of simultaneous effective between electron beam interaction with forward and backward waves near frequency of π point (the point of synchronism of fundamental spatial harmonic and (-1) harmonic of backward wave). We examine the linear theory of TWT selfexcitation with stopband in dispersion near π point.