In this article, a 1-THz traveling-wave tube (TWT) based on flat-roofed sine waveguide (SWG) slow wave structure (SWS) has been studied theoretically and experimentally, and parts of the component have been fabricated. First, the flat-roofed SWG SWS has been optimized for working at 1 THz, the normalized phase velocity is around 0.287, and the interaction impedance is over 3.5 Ω in the frequency range of 1.02-1.04 THz. Meanwhile, the performance of the designed TWT has been simulated, whose saturated output power is 720 mW and the corresponding gain is 28.57 dB. What is more, to decrease the transmission loss of the high-frequency structure, the input and output structures have been designed and a transition structure that transforms the waveguide to standard rectangular waveguide has been proposed. The simulation results show that the reflection coefficient of the novel proposed transmission system is less than -20 dB, and the insertion losses of the transition structure with the input and output waveguides are 2.45 and 1.68 dB, respectively. Finally, the designed SWS has been fabricated by deep reactive-ion etching (DRIE) and tested; S ₁₁ is generally less than -10 dB in the frequency range of 1020-1040 GHz.

This article reports a slow-wave structure (SWS) working at 1 THz which can be fabricated through nano-computer numerical control (nano-CNC) technology for the first time. First, a 1 THz deformed quasi sine waveguide (D-QSWG) SWS has been designed and simulated in this article. To reduce the metal loss of input and output waveguide, a coupler which transit the waveguide to over mode rectangular waveguide has been designed. The simulation result shows that input and output waveguides with this coupler have lower metal loss than that of WR1 rectangular waveguide. To fabricate the designed D-QSWG SWS, tungsten steel endmills have been used. The fabricated SWS has the surface roughness around 58–74 nm, the corresponding effective conductivity is around $2\times 10^{{7}}$ –1.85 $\times 10^{{7}}$ S/m. And the cold test results show that the insertion loss of the fabricated model is less than 30 dB while the reflection loss is less than −15 dB in the frequency range of 0.998–1.016 THz, which has a good consistency with the simulated results. The beam-wave interaction simulation results based on the cold test results show that the designed D-QSWG traveling wave tube (TWT) has the output power of 300 mW, and the 3 dB bandwidth is around 3 GHz.

The electron optical systems (EOS) play a vital role in vacuum electron devices (VED). This letter reported the design and experiments of the sheet EOS for the 1.03 THz traveling wave tube (TWT). A high-current-density sheet electron beam (SEB) electron gun generating up to 20.3-mA at 22.4-kV is designed, based on the requirements of this TWT. Due to the very high operating frequency, more than 1 THz, the miniature tunnel and beam waist with a dimension of 0.05 mm ^* 0.148 mm and 0.025 mm ^* 0.114 mm, respectively, will lead to a very high beam current density (906.9 A/cm ² ). Therefore, a 1-Telsa uniform magnetic system is designed, to ensure such a high-current-density SEB passes through the 27-mm tunnel. Finally, the primary experiments indicate that 7.56-mA current reaches the collector.

The design and simulated performance of a traveling-wave tube (TWT) constructed by combining a folded-waveguide (FW) slow-wave circuit with arrays of 2-D photonic crystals (PhC) are presented. Numerical results reveal that the Pierce interaction impedance of the FW circuit with PhCs is similar to the circuit without PhC arrays. The gain, output power, and efficiency of TWTs with and without PhCs are also similar when the circuit dimensions are identical; however, the TWT with PhCs can filter out nonoperating modes, which may improve the stability of the circuit shielded with PhCs when compared to the same circuit shielded by metal walls.

To achieve tens of kilowatt (kW) output power, W-band klystron usually employs a large beam tunnel to accommodate high current. The deteriorated effective impedance of the cavity could be reenhanced by adopting extended interaction (EI) cavities. In this article, a new approach utilizing simple fundamental modes in cascaded single-gap cavities for W-band klystron is proposed and discussed. Although the effective impedance of each cavity is far lower than its EI klystron (EIK) counterpart, this disadvantage could be efficiently compensated by densely populating those single-gap cavities using the kladistron technology previously conceived for the C-or X-band high-efficiency (HE) klystrons. However, kladistron is rarely reported and normally regarded as less a promising HE bunching technique overwhelmed by the self-excitation issues caused by adjacent mode coupling. Fortunately, such instability could be naturally suppressed in a higher frequency regime, so further exploration of kladistron technology is intriguing. In this article, an exemplary 30-kW W-band klystron equipped with big circular beam tunnel is designed using the kladistron technology, which finally shows no instability issues in 3-D particle-in-cell (PIC) simulation. This novel device delivers up to 37% electronic efficiency and 24% RF efficiency, validating that the kladistron concept is well suited for this millimeter-wave amplifier, which indicates possible HE substitutes for existing EIK technology.

In this letter, the modified flat-roofed sine waveguide slow-wave structure (FRSWG-SWS) is proposed for the wideband high-power sub-terahertz traveling-wave tube (sub-THz TWT), which possesses the advantages of wide operating bandwidth, low loss, minimal reflection, and ease of fabrication. The simulation results demonstrate that the transmission parameter is more than $-$ 5.0 dB in the frequency range between 210 and 250 GHz. The beam–wave interaction results indicate that the modified FRSWG can provide over 50 W of output power and 30 dB of gain from 205 to 250 GHz with sheet electron beam with a voltage of 20.8 kV and a current of 150 mA. Finally, we use high-speed milling to fabricate the modified FRSWG by the nano-Computer Numerical Control (CNC) technology. The cold test results demonstrate that the modified FRSWG has low loss and good reflection characteristics.