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In this work, a Spindt cold cathode electron gun with a PPM (periodic permanent magnet) focusing system for a terahertz TWT (traveling wave tube) was designed and simulated based on the Pierce electron gun structure. More specifically, a new 3D (three dimensional) emission model was used, where the cathode radius of the electron gun was 1 mm and the cathode current was 30 mA, with an emitting half angle of about 28°. It was demonstrated that the electron beam was well focused with an electron beam radius of 0.3 mm and a filling ratio of 0.5 when the maximum value of the PPM field along with the axis was 0.122T. According to the simulation results, a planar cold cathode electron gun was developed. Measurements demonstrated that the I/V characteristics of the cold cathode gun were consistent with that of a cold cathode, revealing that the electrons emitted from the cathode are not intercepted when passing through the electron gun.

A traveling-wave tube (TWT) with a sheet electron beam and staggered double-grating slow-wave structure (SWS) is a promising high-power, wideband terahertz amplifier. In such tubes, electron-optical systems (EOSs) with a converging sheet beam are mostly used, which allow a reduction of the cathode load, increase the lifetime, and enable operation in a continuous-wave (CW) mode. This paper presents the results of a 3D particle-in-cell (PIC) simulation of the 0.22 THz TWT driven with a converged sheet beam, which is compressed to less than 100 μm thickness in the EOS with a magnetically shielded cathode. The beam with high compression has a significant transversal velocity spread and essentially non-uniform current density distribution over the cross-section. These factors significantly affect the beam–wave interaction. We compare the performance of the TWT driven by the compressed sheet beam and by an idealized initially rectilinear beam without any velocity spread.

In this article, the first 237 GHz traveling wave tube (TWT) is presented as a high-power amplifier for the terahertz (THz) cloud radar. As is common with previous G-band traveling wave tubes developed at Beijing Vacuum Electronics Research Institute, the 237 GHz traveling wave tube employs a 20 kV, 50 mA pencil electron beam focused using periodic permanent magnets (PPMs) to achieve compactness. A folded waveguide (FWG) slow-wave structure (SWS) with modified circular bends is optimized to provide high impedance and eliminate sideband oscillations. Limited by insufficient drive power, this device is not saturated. The measured maximum output power and gain are 8.9 W and 35.7 dB, and the 3 dB gain bandwidth achieves 4 GHz.

The applications of terahertz (THz) devices in communication, imaging, and plasma diagnostic are limited by the lack of high-power, miniature, and low-cost THz sources. To develop high-power THz source, the high-harmonic traveling wave tube (HHTWT) is introduced, which is based on the theory that electron beam modulated by electromagnetic (EM) waves can generate high harmonic signals. The principal analysis and simulation results prove that amplifying high harmonic signal is a promising method to realize high-power THz source. For further improvement of power and bandwidth, two novel dual-beam schemes for high-power 346 GHz TWTs are proposed. The first TWT is comprised of two cascaded slow wave structures (SWSs), among which one SWS can generate a THz signal by importing a millimeter-wave signal and the other one can amplify THz signal of interest. The simulation results show that the output power exceeds 400 mW from 340 GHz to 348 GHz when the input power is 200 mW from 85 GHz to 87 GHz. The peak power of 1100 mW is predicted at 346 GHz. The second TWT is implemented by connecting a pre-amplification section to the input port of the HHTWT. The power of 600 mW is achieved from 338 GHz to 350 GHz. The 3-dB bandwidth is 16.5 GHz. In brief, two novel schemes have advantages in peak power and bandwidth, respectively. These two dual-beam integrated schemes, constituted respectively by two TWTs, also feature rugged structure, reliable performance, and low costs, and can be considered as promising high-power THz sources.

A novel chamfered V-shaped microstrip meander line (MML) slow-wave structure (SWS) based on the V-shaped MML SWS for W-band traveling-wave tube (TWT) is proposed to decrease the transmission loss and thus to improve the output power and beam-wave interaction efficiency. The high-frequency characteristics, transmission characteristics, and the beam-wave interaction processes of the novel structure are investigated by simulations. The simulation results show that the S 21 parameters of the chamfered V-shaped MML SWS are improved by 4.3 dB for 100 periods compared with that of the traditional V-shaped MML SWS at 95 GHz. Besides, the particle-in-cell simulations indicate that the output power of the TWT with the novel structure is 30% higher than the V-shaped MML SWS in W-band. Finally, two types of SWSs with 100 periods are fabricated, assembled, and experimentally tested. According to the experimental test results, while the S 11 parameters are below − 20 dB, the “cold” S 21 parameters are − 17.04 dB vs − 20.74 dB at 95 GHz, which shows potential advantages of the proposed novel SWS in millimeter wave and even terahertz spectrum.

Analysis of the performance degradation for W-band lossy ceramic-loaded gyrotron traveling wave tubes (gyro-TWTs) caused by ionization of the released gas molecules is presented in this paper. The gas is released from the lossy ceramics during high average or continuous wave operation and ionized by colliding with the high-energy gyrating electrons. A potential well will be formed by the diffusion and accumulation of the ionization particles after the collision and then degrade the gyro-TWT performance. This process has been simulated based on a simplified model by introducing an equivalent ionization source combining ions and electrons. With a vacuum of 5.1 × 10 - 5 Pa, the theoretically calculated initial energy and equivalent ionization current are 0.01 eV and 0.5 A, respectively. It leads to a deterioration in the output power stability of the gyro-TWT. The performance degradation including spectrum and field pattern caused by gas ionization is also given and analyzed. One of the primary causes is the quality (pitch factor and velocity spread) degradation of the electron beam. According to the simulation and hot test experiments, the vacuum should be maintained below 2.1 × 10 - 6 Pa for stabilizing the amplified operation.

A vacuum window used for W-band traveling wave tube (TWT) featured with excellent thermal capacity, low insert loss, and wide operation band is investigated in this paper. The window sheet material is upgraded to single crystal diamond. The microwave characteristic simulation, thermal analysis, and the structure design are deeply and successively carried out before the fabrication. The microfabrication of the window frame, the produce and surface treatment of the diamond sheet, the metallization, and the vacuum brazing are demonstrated. According to the experimental test results with a vector network analyzer, the S 21 parameters are larger than − 0.8 dB and S 11 parameters are lower than − 18 dB in a 25 GHz with more than 25% relative bandwidth, which shows great advantages of the single crystal diamond vacuum window in millimeter wave and even terahertz spectrum.

Since the electronic power conditioner (EPC) is a crucial part of a space traveling-wave tube amplifier (STWTA), its reliability issue must be considered. The most effective way to prevent insulation breakdown is potting. Silicone elastomers are commonly used as an encapsulant for the EPC because of their good physical and electrical properties. The properties of the encapsulant and the interfaces change under the influence of γ-radiation, which may result in the failure of the potted modules. In this work, a comprehensive evaluation methodology is proposed for silicone-based potted modules, where besides physical and electrical properties, the effect of γ-radiation on the encapsulated interface is also considered. The results show that with the increase of the irradiation dose, the crosslinking density, hardness, elastic modulus, volume resistivity, dielectric constant, and storage modulus are increased by 301.6%, 76.3%, 289.7%, 396.1%, 5.0%, and 589.8%, respectively. In contrast, the elongation at break and dielectric loss factor are decreased by 83.8% and 57.8%. In addition, the tensile strength and breakdown strength first increase and then decrease, while the coefficient of thermal expansion of the interface shows the opposite trend. Since the interface bonding state does not change and the electric field strength of the tip decreases slightly with an increasing dielectric constant, the average value of the partial discharge inception voltage increased slightly.

A double-staggered grating waveguide slow wave structure (DSGW–SWS) is designed for a 340 GHz traveling wave tube (TWT). Input and output couplers were also designed to isolate the electron beam source from the electromagnetic (EM) signal. Transition sections in the SWS circuits were made by tapering the height of the DSWG to improve the matching of the circuit with the couplers. The reflection coefficient has a wide range from 326 GHz to 364 GHz below −15 dB. Particle-in-cell (PIC) simulation is performed using an ideal particle source for sheet electron beam (SEB), considering the filling factor to be around 50%. The average input power of a 340 GHz signal is said to be 0.19 W, which is amplified to 17.4 W with a gain of 19.55 dB.

The demands for equalization accuracy in traveling wave tube power amplifiers (TWTAs) are increasingly stringent, and traditional analog equalizers are no longer sufficient. Furthermore, the low level of digitization in TWTAs makes the direct application of digital equalization techniques difficult. This study designs a digital equalizer system for Ka-band TWTAs that controls high-precision digital step attenuators (DSAs). By processing the RF link, the dynamic analog power signal was converted into a digital square wave, and digital equalization control was achieved using an STM32F103 microcontroller (STMicroelectronics, Geneva, Switzerland; Origin: Taiwan, China). Simulation and experimental results show that the system operates stably within the input dynamic power range of −20 to 0 dBm, with an overall control delay of approximately 2 ms, a frequency measurement error of less than 0.02%, and an equalization accuracy better than 0.25 dB. This work addresses the critical interface bottleneck between high-frequency analog TWT chains and digital control circuits, offering a reusable engineering solution for the digital upgrade of TWTA products.