The output/input circuit is a core component in all high-power millimeter-wave (MMW) radiation sources, and its performance specifications and reliability directly impact upon the performance of the radiation source device. Central to achieving high power is the development of efficient mode converters. Here, we report on the development of a compact Ka-band circular TM ₀₁ to rectangular TE ₁₀ mode converter. The present mode converter adopts an all-metal waveguide structure and facilitates notable improvement in the system power capacity and is capable of realizing high-power propagation. The mode converter realizes effective mode conversion between high-order and fundamental modes, as well as allowing longitudinal and transverse transmission. Our simulation and empirical findings have shown mode purity ≥99.5% in the frequency range of 32.7-34.6 GHz, and the mode conversion efficiency is more than 96% at a center frequency of 32.9 GHz with a return loss S ₁₁ of -19.3 dB. The bandwidth of the converter is 2.4 GHz with transmission coefficient S ₂₁ ≥ -1 dB.

A four-cavity, large-sized beam tunnel, G-band extended interaction Klystron (EIK) is here proposed. A three-hole coupling cavity has been optimized to ensure a sufficient beam–wave interaction. The beam conductance and the total quality factor of each cavity have been analyzed to evaluate the stability of the beam–wave interaction for a 0.2-A beam current and 14.5-kV operating voltage. The particle-in-cell (PIC) simulation results show that the maximum output power is 134.5 W, with a gain of 30.3 dB and an efficiency of 4.6%, with a 3-dB bandwidth of 1 GHz.

This article presents the demonstration of several compact millimetre wave sources driven both by a pencil or sheet electron beam from a pseudospark (PS) discharge. The millimetre wave sources include two pencil beam extended interaction oscillators (EIO) in W‐band (75–110 GHz), two sheet beam EIOs in W‐ and G‐bands, two pencil beam backward wave oscillators (BWO) in W‐ and G‐bands, and one pencil beam Cherenkov maser in Ka‐band. These devices can generate up to kilowatts of output power, which are very attractive for many important applications.

To develop miniaturized and compact vacuum electron devices, new approaches to device manufacturing must be embraced. Here, a terahertz oscillator based on carbon nanotube (CNT) cold cathode is investigated through particle-in-cell (PIC) simulations. The studies show that the high-frequency (HF) field excited by the device can modulate the field emission current efficiently, with an output power of 4.6 W at 139.4 GHz obtained at an operating voltage of 2.9 kV and an initial emission current and current density of 15.8 mA and 7.65 A/cm², respectively, and the efficiency is 10.0%.

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.