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Terahertz backward wave oscillators based on double corrugated waveguides are enabling devices for modern satellite communication systems. This research focuses on the design of a 0.34 THz double corrugated waveguide-based interaction structure using a sheet beam. This choice allows the use of shorter pillars along with a narrow gap between pillar rows. Shorter pillars are easier to manufacture and a narrow gap is required for better interaction impedance. Circular beams restrict the use of larger pillars and narrow gap between pillars. The performance of this interaction structure is compared with a folded waveguide. Under the same operating conditions involving a 20 kV beam voltage and a 30 mA beam current, the double corrugated waveguide interaction structure exhibits impressive performance in simulations, featuring an interaction impedance of 0.52 Ω at 0.34 THz, an output power of 3.2 W, and a bandwidth extending to approximately 20 GHz. In contrast, the folded waveguide, as per simulation results, registers values of 0.43 Ω , 2.6 W, and a 12 GHz bandwidth, respectively. The proposed double corrugated waveguide-based interaction structure is fabricated using modern CNC machining. Experimental validation reinforces the effectiveness of this design, with measurements indicating reflection below −20 dB and transmission exceeding −2 dB. [ABSTRACT FROM AUTHOR]

In this paper, an angular radial extended interaction amplifier (AREIA) that consists of a pair of angular extended interaction cavities is proposed. Both the convergence angle cavity and the divergence angle cavity, which are designed for the converging beam and diverging beam, respectively, are investigated to present the potential of the proposed AREIA. They are proposed and explored to improve the beam–wave interaction capability of W-band extended interaction klystrons (EIKs). Compared to conventional radial cavities, the angular cavities have greatly decreased the ohmic loss area and increased the characteristic impedance. Compared to the sheet beam (0°) cavity, it has been found that the convergence angle cavity has a higher effective impedance and the diverging beam has a weaker space-charge effect under the same ideal electron beam area; the advantages become more obvious as the propagation distance increases. Particle-in-cell (PIC) results have shown that the diverging beam (8°) EIA performs better at an output power of 94 GHz under the condition of lossless, while the converging beam (−2°) EIA has a higher output power of 6.24 kW under the conditions of ohmic loss, an input power of 0.5 W, and an ideal electron beam of 20.5 kV and 1.5 A. When the loss increases and the beam current decreases, the output power of the −2° EIA can be improved by nearly 30% compared to the 0° EIA, and the −2° EIA has a greatly improved beam–wave interaction capacity than conventional EIAs under those conditions. In addition, an angular radial electron gun is designed. [ABSTRACT FROM AUTHOR]

This article studies and summarizes the operating characteristics of a ${G}$ -band folded waveguide traveling wave tube (TWT) amplifier enhanced by the $\pi $ -mode extended interaction cavities. Compared with conventional ${G}$ -band TWTs, the proposed amplifier can at once obtain a higher gain in a shorter interaction circuit length and ensure a proper operating bandwidth. The key of the design is introducing the $\pi $ -mode multigap resonant cavity with alternating wide and narrow slots, which will improve the working performance of the whole device by shortening the length of the interaction circuit, enhancing its interaction effect, and improving its gain of unit length. In this design, the operation bandwidth is expanded by stagger tuning technique. In addition, the influence of cavity loss is examined so that the optimal performance is achieved. The PIC simulation results show that when the operating voltage is 21 kV and the operating current 80 mA, the maximum average output power of the designed TWT amplifier is 65.78 W at 217.4 GHz, which is corresponding to the maximum gain and efficiency of 37.38 dB and 3.9%, respectively. The gain per unit length is 12.64 dB/cm and the 3-dB bandwidth is 3.5 GHz. [ABSTRACT FROM AUTHOR]

A $Q$ -band traveling-wave tube (TWT) with profiled helix pitches and profiled inner diameters of slow wave structure (SWS) is proposed. The transmission characteristics of the $Q$ -band TWT are simulated by the Computer Simulation Technology (CST). In the operating frequency band (36.5–41.5 GHz), the simulated voltage standing wave ratio (VSWR) is less than 1.5. In addition, the beam–wave interaction is simulated to predict the performance of the $Q$ -band TWT when the beam voltage and beam current are 8.5 kV and 60 mA, respectively, and the axial focusing magnetic field is 0.4 T. In the operating frequency band, the self-oscillation is well suppressed, and the device efficiency of the $Q$ -band TWT exceeds 63.5%, and the saturated output power and gain exceed 83 W and 45 dB, respectively, especially the device efficiency can reach the maximum of 69.5% at 37 GHz. When it is backed off 6 dB from the saturation, the device efficiency exceeds 40.5%, up to 42.7% at 39 GHz. Preliminary experiments have confirmed the design. These results show that the proposed $Q$ -band TWT has important applications to the next generation wireless communication system with high efficiency. [ABSTRACT FROM AUTHOR]

A 0.14 THz angular radial extended interaction oscillator (AREIO) is proposed in this article. The characteristic impedance (${R}/{Q}$), the normalized equivalent conductance (${g}_{e}$), and the starting condition of the cavity are calculated and analyzed. When the metal loss is considered, in order to achieve the starting condition, it is necessary to increase the period length (${p}$) to improve $\vert {g}_{e}\vert $. The performance of the AREIO is simulated by particle-in-cell (PIC). The voltage tuning range and the output performance under different angular angles of the cavity are investigated. Under the condition of lossless and the electron beam of 11.5 kV and 1.5 A, the peak output power and interaction efficiency of the AREIO (8°) are 5.46 kW and 31.7%, which have increased by 24.1% and 6.2% in comparison with conventional sheet beam. When considering the metal loss, the optimal angular angle will decrease to 4°. In addition, the cavity is fabricated and tested, and the results of ${S}_{{11}}$ in operating mode are consistent with the simulation. [ABSTRACT FROM AUTHOR]

We proposed an oversized coaxial multi-beam relativistic klystron amplifier (OCMB-RKA) with a new input coupler of lesser complexity giving enhanced input microwave power absorption rate for generating high power millimeter-wave radiation in Ka-band. The high-frequency structure of the OCMB-RKA was designed, fabricated, and cold-tested for results that agreed well with the simulated results. Furthermore, using the 3D particle-in-cell (PIC) code, the beam-wave interaction of the OCMB-RKA was simulated, considering two different materials (stainless steel and copper) making the interaction structure. When a 500 kV, 3 kA electron beam, and a focusing magnetic flux intensity of 1 T were adopted in the PIC simulation, a five-cavity OCMB-RKA yielded the output power of 610 MW at 30.525 GHz with the electronic efficiency of 40.7% and the saturated gain of 55.3 dB. Experimentally, the OCMB-RKA demonstrated its capability of generating high power Ka-band radiation typically of 390 MW power with the pulse width of 27 ns. [ABSTRACT FROM AUTHOR]

A novel electron-optical system (EOS) for ${G}$ -band traveling-wave tubes (TWT) is investigated by simulation and verified by experiment. The EOS includes a sheet beam electron gun, a tunable periodic cusped magnetic focusing (TPCMF), and a collector. An elliptical focus electrode (FE) featuring a simple geometry and easy fabrication is utilized to compress the pencil beam into the sheet beam with a cross section of 0.4 mm $\times0.1$ mm. The electron gun with a cylindrical cathode of 0.8 mm diameter generates the sheet beam with voltage of 22 kV and current of 115 mA. Based on the sheet beam electron gun, the TPCMF with easy assembly and compact size is then proposed. The experimental results show that the beam transmission is 92.1% within a beam tunnel (its length 21.2 mm and cross section 0.8 mm $\times0.15$ mm). The EOS is suitable for ${G}$ -band TWT. [ABSTRACT FROM AUTHOR]

In this article, we propose a simulation method to investigate the noise mechanism of traveling-wave tube (TWT). Based on the nonlinear theory of Lagrangian description, 1-D noise model is established to analyze the shot noise and the velocity noise of the electron beam in the drift space, which clearly shows that the beam noise propagates along the electron beam with standing wave shape. The shot noise and the velocity noise can be periodically converted into each other along electron beam transmission, which is consistent with the prediction of the classical noise theory developed by Pierce and Danielson (1954). Using the nonlinear beam–wave interaction theory, the evolution process of the shot noise and the velocity noise of the electron beam transforming to the electromagnetic wave in TWT is illustrated. The calculated results show that the input position of the slow wave circuit may affect the noise power spectral density (NPSD) of the device. The proposed method can provide more intuitive and simple images to explain the noise mechanism of TWT. [ABSTRACT FROM AUTHOR]

A new scheme for generating high power terahertz (THz) radiation by using two obliquely colliding electron beams in plasma is proposed. The particle-in-cell (PIC) simulation finds that a small beam intersection of high electron density is formed within a plasma wavelength when two thin electron beams collide. Meanwhile, the beam intersection can oscillate in a strong plasma wave driven by the two beams to produce THz radiation at double plasma frequency. A theoretical model is established showing that the radiation mechanism is the second-order current generated by the beam intersection oscillation. The angular distribution of the THz radiation is calculated by the theory, which agrees well with the PIC simulation. Compared with the existing high power THz sources, the scheme provided in this article has the advantages of a simple structure and no need for extreme parameter conditions, which is hopeful for applications in kilowatt-level coherent compact THz sources. [ABSTRACT FROM AUTHOR]

An attenuator supporting meander-line (ASML) slow wave structure (SWS) is proposed for a Ka-band traveling wave tube (TWT) and studied by simulations and experiments. The ASML SWS simplifies the fabrication and assembly process of traditional planar metal meander-lines (MLs) structures, by employing an attenuator to support the ML on the bottom of the enclosure rather than welding them together on the sides. To reduce the surface roughness of the molybdenum ML caused by laser cutting, the ML is coated by a thin copper film by magnetron sputtering. The measured S11 of the ML is below −20 dB and S21 varies around −8 dB to −12 dB without the attenuator, while below −40 dB with the attenuator. Particle-in-cell (PIC) simulation results show that with a 4.4-kV, 200-mA sheet electron beam, a maximum output power of 126 W is obtained at 38 GHz, corresponding to a gain of 24.1 dB and an electronic efficiency of 14.3%, respectively. [ABSTRACT FROM AUTHOR]