High-Power Vacuum Electronic Devices from Microwave to THz Band: Way Forward

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Vacuum Electronic Devices and Applications

This issue of Defence Science Journal (DSJ) contains a collection of nine manuscripts from National Symposium on Vacuum Electronic Devices and Applications (VEDA-2019). Vacuum Electronic Devices and Applications Society organises VEDA symposium/conference/workshop every year at different locations of India. VEDA has established itself as a leading platform for active and innovative research of microwave tubes. It provides a forum for knowledge sharing and exhibition of theoretical and technological development in the general areas of vacuum electronics devices and its system applications. It organises special session to enhance Research Institutes – Industries and Academia Interaction.

Over-Size Pill-Box Window for Sub-Terahertz Vacuum Electronic Devices

The pill-box window is one of the important components of microwave vacuum electronic devices (VEDs), and research into it is of great significance. As the operating frequency increases, the problems associated with the reduction in the structure size include the reduction of the brazing plane and the reduction in the tolerance of the pill-box window. These problems will cause traditional pill-box windows to be unsuitable in high-frequency bands, especially in terahertz and sub-terahertz regions. The most influential factor is the length of the circular waveguide in the box window. The welding plane of the over-size pill-box window is the annular bottom surface on both sides of the dielectric sheet, which is larger than the circular waveguide, and the operating frequency does not directly affect the area of the brazing surface. Choosing a suitable diameter for the dielectric sheet can effectively increase the tolerance to the length of the pill-box window circular waveguide. Therefore, an over-size pill-box window would be a practicable approach to improve the performance compared to the traditional pillow-box in high-frequency bands. This paper describes, in detail, the theoretical design, simulation optimization and experimental process of this improved pill-box window. An over-size pill-box window suitable for G band VEDs was successfully developed. The experimental result in the 215–225 GHz band is that the maximum transmission loss is −1 dB, and the overall transmission loss is close to −0.5 dB. The overall reflection is less than −11 dB.

Investigation on Symmetric and Asymmetric Broadband Low-Loss W-Band Pillbox Windows

In order to develop wide-band low-loss windows for W-band vacuum electronic devices and easily fabricate them, symmetric and asymmetric pillbox windows are investigated and reported in this paper. A symmetric pillbox window and an asymmetric pillow-box window were designed, simulation optimized, fabricated, and tested. The initial parameters for the two pillbox windows were designed by equivalent circuit theory. Computer simulation technology (CST) three-dimensional (3D) electromagnetic simulation software was used to verify and optimize the design. Because of the uncontrollability of welding during the experiment, this article provides two solutions. One is to measure and reprocess the symmetrical pillbox window with the dielectric sheet welded to reduce the influence of welding on the measurement results; the other is an asymmetrical box window which is designed to avoid the error caused by the welding of the box window. The best experimental results for the symmetric pillbox window were |S21| close to 1 dB and reflection parameter |S11| close to 10 dB in the frequency range of 77–110 GHz. The experimental results for the asymmetric pillbox window were |S21| < 1 dB nearly in the frequency range of 76–109.5 GHz. The experimental results show that both solutions efficiently complete the design of broadband pillbox windows and would potentially be operated in the gigahertz millimeter-wave region.