Abstract:
Background Advanced sheet electron beam vacuum electron devices, particularly Ka-band traveling-wave tubes, are required to meet increasingly stringent broadband operational demands. However, energy leakage and impedance mismatch at millimeter-wave output interconnections remain major challenges that limit transmission efficiency and bandwidth performance.
Purpose To address these challenges, this work aims to design and validate a broadband, high-efficiency output circuit for a Ka-band sheet beam TWT. A novel non-contact double-layer choke-mode output circuit with an air-gap configuration is proposed to suppress leakage and enable broadband operation.
Methods The design is based on the fundamental theory of conventional rectangular waveguides. The output circuit structure is carefully optimized, and matching stepped waveguides are introduced to improve impedance matching and reduce reflections. A comprehensive electromagnetic simulation model is developed and analyzed using High-Frequency Structure Simulator (HFSS). Furthermore, cold-test measurements are conducted on a fabricated prototype to experimentally verify the design.
Results HFSS simulation results show that the choke grooves effectively suppress parasitic leakage while enabling broadband transmission. The proposed output circuit achieves an absolute bandwidth of 11.9 GHz with a return loss better than −20 dB. The simulated transmission efficiency reaches 93.3%, corresponding to a relative bandwidth of 36.9%, which satisfies broadband operation requirements. Experimental cold-test results are in good agreement with the simulations, confirming the validity of the design.
Conclusions Both simulation and experimental results demonstrate that the proposed choke-mode output circuit exhibits wide operating bandwidth, high transmission efficiency, low reflection, and effective voltage depression capability. The structure also shows strong anti-interference performance and operational reliability, making it well suited for high-power, broadband millimeter-wave sheet beam TWT applications.
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