Background In millimeter-wave and terahertz traveling-wave tubes (TWTs), nonlinear effects including nonlinear phase shift and AM/PM conversion can substantially degrade the transmission quality of communication signals.
Purpose In the design of slow-wave structures (SWSs), simultaneously satisfying requirements of high output power and low nonlinear distortion is generally a challenge. Furthermore, conventional simulation-based iterative approaches incur high computational costs when applied to multi-parameter, multi-objective optimization problems.
Methods In this article, a collaborative optimization method, which integrates a multi-section phase velocity jump with the Non-dominated Sorting Genetic Algorithm II (NSGA-II), is proposed. Based on a one-dimensional (1-D) large-signal beam-wave interaction model, the proposed method conducts three-objective optimization on three key performance metrics: saturated output power, nonlinear phase shift, and AM/PM conversion coefficient. An E-band folded waveguide (FWG) TWT is adopted as an example, and a final design is selected from the Pareto-optimal solution set. Variable sensitivity analyses were also conducted on the optimal solution set, which clarified the key parameters that affect optimization.
Results 1-D calculation results indicate that, within the 71-76 GHz frequency band, the optimized scheme achieves a maximum saturated output power of 130.1 W. The maximum electronic efficiency is enhanced to 10.2%. The nonlinear phase shift and AM/PM conversion coefficient are controlled within 40.5 ° and 4.7 °/dB, respectively, representing improvements of over 38.5% and 37.0% compared to the baseline design. Additionally, 3-D particle-in-cell (PIC) simulations validate the effectiveness of the proposed optimization scheme. Simulation results are in good agreement with 1-D calculation results.
Conclusions The proposed method offers an efficient optimization solution and provides valuable design guidance for the high-linearity design of high-frequency TWTs.
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