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Abstract
A fully three-dimensional (3-D) helix traveling-wave tube (TWT) simulation model has been developed using a commercial electromagnetic (EM) finite-element-method (FEM) code. The model is used to simulate the π-mode stopband characteristics caused by asymmetries of support rods and metal loading in helix TWTs. Compared with the previous analytical method, the present simulation method can calculate the natural stopband of the π-mode, the absolute π-mode frequency, and the asymmetric effect of metal loading.