We present the mathematical models, computer code and numerical analysis for modeling linear operation regimes of broadband helix travellingwave tube (TWT) with the inhomogeneous slow wave structure along the interaction space. Onedimensional model of the interaction of the forward and reflected electromagnetic waves with an electron beam in a inhomogeneous section of the slow wave structure was researched. The calculation method of the linear gain and selfexcitation conditions of multisection TWT was suggested.
