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An innovative complementary electric split-ring resonator metamaterial (MTM) structure applied as the slow-wave circuit for a cascade backward-wave oscillator (CBWO) operating in C-band is studied in this paper. The idea of a drift tube in a multiresonant cavity extended interaction klystron is borrowed to design a novel backward-wave oscillator (BWO). The construction of this device features two BWOs separated by a short cutoff waveguide for permitting the flow of the electron beam and stopping the electromagnetic wave. The high-frequency characteristics are analyzed and optimized by using a high-frequency structure simulator and computer simulation technology (CST). Meanwhile, the S-parameter retrieval approach is used to retrieve the effective permittivity and permeability. In addition, the CST code is adopted to investigate the performance of the MTM-based CBWO. The particle-in-cell simulation results show that the novel CBWO is capable of achieving over 51.77% electronic efficiency from 4.8344 to 4.8687 GHz. Meanwhile, the maximum electronic efficiency can reach 82.44%, corresponding to a peak output power of 14.51 MW at 4.8466 GHz. These results indicate that the MTM-based CBWO proposed in this paper has the characteristic of miniaturization, manufacturability, and high electronic efficiency.

In this paper, multiphysics field simulation is applied to analyze the temperature distribution of Ka-band U-shaped microstrip line planar TWT considering the thermal losses induced by ohmic loss and electron collision losses. The beam-wave interaction of the planar TWT is analyzed by using CST particle-in-cell (PIC) solver, at the same time the thermal losses distribution is recorded, which will be the heat source. The simulation results show that the high temperature with a peak value of 263 °C.

3-D printed Ka-band sine waveguide (SWG) slow wave structures (SWSs) are presented in this paper. A kinds of 3-D printing technologies, rapid investment casting (RIC) with brass, have been considered. The VSWR of the assembled 3-D printed brass SWG SWS is less than 1.37, and the dissipative attenuation ranges between 0.025 and 0.054 dB/mm at 33-40 GHz. The 3-D printing technologies appear as a promising fabrication method for vacuum electron devices fabrication with the advantages of low-cost and rapid-prototyping compared with traditional machining processes.