In this paper, a stacked dual beam electron gun and the associated electron optical system are proposed. The stacked dual beam electron gun includes two compact focusing electrodes which help to achieve dual sheet beams. As an application of this dual beam electron gun, a 340 GHz integrated dual beam traveling wave tube (TWT) based on the staggered dual vane slow-wave structure (SWS) is also put forward. In order to reduce the length of the TWT, a novel input/output coupler is introduced. The overall transmission characteristics of the SWS structure together with the input/output couplers show a wide bandwidth covering a frequency range of 306 GHz to 360 GHz. Based on the parameters obtained for the integrated TWT, a stacked dual-beam electron gun with dual focusing electrodes is designed to achieve a beam current of 43 mA, a beam voltage of 21.4 kV, and a cross-sectional size of each beam of 0.3 mm × 0.08 mm. A uniform magnetic field of 0.52 T is utilized to focus the dual electron beams, and a beam transmission efficiency of 97.1% is achieved over a length of 50 mm. Finally, particle in cell simulation results show that the integrated dual-beam TWT can generate an output power of 5 W over the frequency range of 315 GHz to 350 GHz, with the maximum output power of 24.5 W at 330 GHz.

This paper puts forward a novel dual-beam overmoded folded waveguide (FW) slow-wave structure (SWS), which is loaded with photonic crystals. In this novel structure, the two electron beams pass through the small gaps between the photonic crystal structures and the FW; the dimension of the FW is twice larger than that of the fundamental mode structure. The novel dual-beam photonic crystal overmoded FW traveling-wave tube (TWT) is proposed on the basis of the SWS. And, a mode converter is introduced to achieve the connection between the SWS and the input/output structure, and the mode transformation. At the operating voltage of 21.2 kV and the operating current of 320 mA, the proposed TWT can generate 128 W of output power at 220 GHz, and its 3-dB bandwidth is 7 GHz, ranging from 216 to 223 GHz.

A novel modified angular log-periodic folded waveguide slow wave structure (MALPFW-SWS) is proposed for high-gain traveling wave tubes (TWTs). Each unit of the MALPFW-SWS has different dispersion characteristics and thus it has the ability to suppress oscillations in TWTs. The dispersion equation of the MALPFW-SWS is derived and a Ka-band MALPFW-SWS is designed according to the dispersion equation for verification. The particle-in-cell (PIC) simulation indicated that the output signal is steady even the gain of the designed MALPFW-TWT reaches 40 dB. The frequency spectrum of the output signal also proved that the MALPFW-SWS can suppress oscillations. The cold test experiment results show that the transmission characteristics of the fabricated MALPFW-SWS are good and are in good agreement with the simulation results.

A novel concept of hybrid dispersion slow wave structure (HD SWS) is reported. It is realized by alternatively connecting SWSs operating at the regions of relatively strong dispersion (SD) and relatively weak dispersion (WD). In this way, the HD SWS will be characterized by high interaction efficiency over a moderate bandwidth. The equivalent dispersion of the HD SWS is calculated, which is affected by the periods’ proportion of the WD and SD SWSs. Driven by an ideal beam of 16.0 kV, 20 mA, and an input power of 1 mW, the hot performance of the HD SWS is conducted by using particle-in-cell (PIC) method. Compared with the SD SWS, the 3dB bandwidth and maximum power have been expanded and improved by 51.6% and 32.6%, without significantly increasing the circuit length. Compared with the WD SWS, the saturated interaction length has decreased by 31.1% at 0.661 THz, releasing the electro-optical system constraints. The HD SWS shows great potential to improve the terahertz (THz) vacuum electron devices’ performance.

A semi-analytic numerical algorithm for general pillbox windows, named the pillbox window mode-matching algorithm (PWMMA), is proposed in this letter. The PWMMA shows quite consistent calculation results with CST Microwave Studio (CST-MWS) within a remarkably reduced time than CST-MWS. Four pillbox windows, each consists of a double-side metalized diamond disk, were fabricated and tested at the frequency bands of 0.21 THz-0.25 THz and 0.32 THz-0.36 THz. The experimental results of the transmission characteristics are consistent well with the calculation results of the PWMMA.

A novel planar meander slot-line slow-wave structure (MSL-SWS) configuration for a Q-band traveling wave tube (TWT) is proposed and investigated. Consisting of a thin metal sheet graved with a meander slot and a metal enclosure, the MSL-SWS can combine massive production and good heat dissipation. The high-frequency characteristics are obtained by numerical simulation and validated by experiment. The PIC simulation results suggest that for an 8.2 kV and 0.1 A sheet electron beam, the output power can reach 49 W at 40 GHz with a gain of 26.9 dB. A 3-dB bandwidth of roughly 15% centered at 40 GHz is also indicated. The proposed configuration is manufactured using laser cutting and computer numerical control (CNC) milling technology. Experimental confirmation that insertion losses can be reduced to 0.043 dB/mm by plating the MSL-SWS with copper. With a good potential for fabrication, this structure can be good candidate for millimeter TWT applications.