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In order to reduce the ohmic losses in the slow wave structure (SWS), an elliptical pillar defected photonic crystal waveguide (EPDPCW) is proposed as a SWS for the terahertz traveling wave tube (TWT). Compared with rectangular pillar defected photonic crystal waveguides (RPDPCW), the EPDPCW shows better high-frequency characteristics and lower ohmic losses. According to the particle-in-cell (PIC) results, in the frequency range of 188 GHz to 218 GHz, the saturated output power of EPDPCW is greater than 13.4 W, and the maximum saturated output power is 26.8 W at 196 GHz at a voltage of 9.78 kV and a beam current of 150 mA. Compared to the RPDPCW-TWT, the performance of the EPDPCW-TWT has been significantly improved. [ABSTRACT FROM AUTHOR]

For the purpose of improving performance and reducing the fabrication difficulty of terahertz traveling wave tubes (TWTs), this paper proposes a novel single-section high-gain slow wave structure (SWS), which is named the symmetrical quasi-synchronous step-transition (SQSST) folded waveguide (FW). The SQSST-FW SWS has an artificially designed quasi-synchronous region (QSR) to suppress self-oscillations for sustaining a high gain in an untruncated circuit. Simultaneously, a symmetrical design can improve the efficiency performance to some extent. A prototype of the SQSST-FW SWS for 650 GHz TWTs is designed based on small-signal analysis and numerical simulation. The simulation results indicate that the maximum saturation gain of the designed 650 GHz SQSST-FW TWT is 39.1 dB in a 34.3 mm slow wave circuit, occurring at the 645 GHz point when a 25.4 kV 15 mA electron beam and a 0.43 mW sinusoidal input signal are applied. In addition, a maximum output power exceeding 4 W is observed at the 648 GHz point using the same beam with an increased input power of around 2.8 mW. [ABSTRACT FROM AUTHOR]

A new slow wave structure (SWS), named E-plane loaded sine waveguide (EPLSW) SWS is proposed for the development of G-band traveling wave tubes (TWTs). The structure, derived from the sine waveguide (SW) SWS, features staggered rectangular gratings on the two E-planes, intersecting with the sine-shaped gratings. The natural electron beam tunnel lies between these gratings. The EPLSW-SWS offers improved characteristics compared to the conventional SW-SWS. High-frequency simulation studies reveal that the passband of the EPLSW-SWS extends by more than 33 GHz over the SW-SWS under identical dispersion conditions. Additionally, the interaction impedance of EPLSW-SWS surpasses that of the SW-SWS in the frequency range of 195–255 GHz. Further analysis through particle-in-cell (PIC) results presents that when operating at 19.5 kV and 145 mA for the sheet beam current, it attains a maximum saturated power of 132.7W and a 3 dB bandwidth exceeding 50 GHz. [ABSTRACT FROM AUTHOR]

A staggered vane-shaped slot-line slow-wave structure (SV-SL SWS) for application in W-band traveling wave tubes (TWTs) is proposed in this article. In contrast to the conventional slot-line SWSs with dielectric substrates, the proposed SWS consists only of a thin metal sheet inscribed with periodic grooves and two half-metal enclosures, which means it can be easily manufactured and assembled and has the potential for mass production. This SWS not only solves the problem of the dielectric loading effect but also improves the heat dissipation capability of such structures. Meanwhile, the SWS design presented here covers a −15 dB S11 frequency range from 87.5 to 95 GHz. The 3-D simulation for a TWT based on the suggested SWS is also investigated. Under dual-electron injection conditions with a total voltage of 17.2 kV and a total current of 0.3 A, the maximum output power at 90 GHz is 200 W, with a 3 dB bandwidth up to 4 GHz. With a good potential for fabrication using microfabrication techniques, this structure can be a good candidate for millimeter-wave TWT applications. [ABSTRACT FROM AUTHOR]

The dried blood spot (DBS) is a novel alternative matrix used in 2022 Beijing Winter Olympics and Paralympics. It is capable of distinguishing anabolic androgenic steroid (AAS) esters without the gas chromatography–combustion–isotope ratio mass spectrometry (GC‐C‐IRMS) confirmation. In this study, a method for detection of 22 anabolic steroid esters in DBS based on ultra‐high liquid chromatography–mass spectrometry (UPLC‐MS) with parallel reaction monitoring (PRM) was developed and validated. Methoxylamine was used as the derivatization reagent to improve the sensibility. Specificity, limit of detection (LOD), linearity, stability, robustness, and carryover were evaluated. Steroid esters are nine testosterone esters, six nandrolone esters, five boldenone esters, methenolone enanthate, and trenbolone acetate. UV spectra were determined by HPLC. And density functional theory (DFT) calculation methods could provide theoretical UV spectra data. Three basis set of B3LYP/6‐31G(d), B3LYP/6‐31+G(d, p), and WB97XD/6‐31+G(d, p) were used for the geometry optimizations and TD‐DFT calculation. The average deviation (%RD) of B3LYP/6‐31+G(d) for all 44 ester oximes are less than 3.0%. This study for the first time provides a method to tentatively identify the 44 E/Z configurations of steroid oxime products. [ABSTRACT FROM AUTHOR]

In this paper, a series of experimental and numerical studies were carried out to investigate the effect of multiple cracks on concrete fracture behavior. Seven groups of double-crack concrete three-point bending (TPB) experiments with different crack lengths and different crack distances were carried out. The experimental results showed that the bearing capacity of double-crack specimens was slightly larger than the standard specimen with one central crack. Additionally, with an increase in the second crack length or with a crack distance reduction, the concrete's bearing capacity increased correspondingly. Based on the experiments, a numerical meso-model was developed based on applying cohesive elements. The aggregate, mortar, interface transition zone (ITZ), and potential fracture surfaces were explicitly considered in the model. In particular, cohesive elements were used to characterize the mechanical behavior of the ITZ and potential fracture surfaces. A modified constitutive concrete model was developed by considering the potential fracture surfaces' damage relation and friction effect. The accuracy of the developed meso-model was validated through a comparison between simulation and experiments. Based on meso-models, the influence of multiple cracks on the concrete bearing capacity was investigated by analyzing the energy evolution. The analysis results showed that the bearing capacity has a linear relation with the proportion of mode II energy consumption during the fracture process, which explains why specimens with multiple cracks have a slightly larger bearing capacity than the standard specimens. In summary, this study has found that in three-point bending fracture tests primarily characterized by mode I fractures, the presence of multiple cracks near the main crack slightly enhances the load-bearing capacity of the specimens. This is attributed to a slight increase in internal energy dissipation associated with the presence of these multiple cracks. [ABSTRACT FROM AUTHOR]

Based on the reversed Cherenkov radiation excited in metamaterials, a novel S-band reversed Cherenkov radiation amplifier (RCRA) with two output ports is proposed in this paper. Its metamaterial slow-wave structure (MSWS) consists of a hollow circular waveguide periodically loaded with all-metal double-ridge complementary electric split-ring resonators (CeSRRs). The CeSRR exhibits subwavelength and strong resonance characteristics, which lead to miniaturization and high interaction impedance of the MSWS. The period of the MSWS is optimized using the phase velocity jump technique to further increase the output power and electronic efficiency. The simulation results demonstrate that when the microwave signal of 7.8 W at 2.286 GHz is inputted at port 2, the output power at port 1 is 307 W, and the saturated output power and saturated gain at port 3 are 5.48 kW and 28.47 dB, respectively. Notably, the total electronic efficiency of the RCRA is predicted as 33.84%. The RCRA features high electronic efficiency and miniaturization and may meet special application scenarios that require two output microwave signals at the same frequency. [ABSTRACT FROM AUTHOR]

In this paper, a novel staggered double-segmented grating slow-wave structure (SDSG-SWS) is developed for wide-band high-power submillimeter wave traveling-wave tubes (TWTs). The SDSG-SWS can be considered as a combination of the sine waveguide (SW) SWS and the staggered double-grating (SDG) SWS; that is, it is obtained by introducing the rectangular geometric ridges of the SDG-SWS into the SW-SWS. Thus, the SDSG-SWS has the advantages of the wide operating band, high interaction impedance, low ohmic loss, low reflection, and ease of fabrication. The analysis for high-frequency characteristics shows that, compared with the SW-SWS, the SDSG-SWS has higher interaction impedance when their dispersions are at the same level, while the ohmic loss for the two SWSs remains basically unchanged. Furthermore, the calculation results of beam–wave interaction show that the output power is above 16.4 W for the TWT using the SDSG-SWS in the range of 316 GHz–405 GHz with a maximum power of 32.8 W occurring at 340 GHz, whose corresponding maximum electron efficiency is 2.84%, when the operating voltage is 19.2 kV and the current is 60 mA. [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]

In order to improve the performance of sine waveguide (SW) traveling wave tube (TWT), an elliptical beam-tunnel sine waveguide (EBTSW) slow wave structure (SWS) is proposed. EBTSW-SWS not only has high interaction impedance in a relatively wide frequency band but also has an elliptical beam-tunnel. The simulation results of high-frequency characteristics show that, under the same dispersion, the passband of EBTSW-SWS increases by 30% compared to the SW-SWS, and the average interaction impedance of EBTSW-SWS is higher than that of SW-SWS in almost the whole passband. Moreover, the particle-in-cell (PIC) simulation results reveal that under the operating voltage of 20.8 kV and beam current of 150 mA, EBTSW-TWT can provide more than 70 W of saturated output power in the frequency range of 200-260 GHz, reaching the maximum power of 151 W at 220 GHz with the maximum electronic efficiency of 4.85%. [ABSTRACT FROM AUTHOR]

An accurate quantitative method for four prohibited ephedrine substances in human urine has been established, based on ultra-performance liquid chromatography tandem mass spectrometry (UPLC–MS/MS). The quantitative bias caused by pretreatment operations and matrix effects was reduced by the dilute and shoot pretreatment method. The good separation of isomers was achieved with the advantages of the UPLC instrument and Agilent Poroshell 120 EC-C8 UPLC column. Stable quantitative ions were selected during the analysis with MS/MS. The result of the method validation experiment showed an excellent linearity between 50% and 200% threshold concentration with a correlation coefficient (r 2) greater than 0.999. The coefficient of variation at the limit of quantification and threshold was <20% and 10%, respectively. The uncertainty was below the maximum uncertainty specified in the technical document of the World Anti-Doping Agency (WADA). The analytical result using this method has passed the WADA-external quality assessment scheme. The anti-doping laboratory has applied the method in routine tests and reported adverse analytical finding. [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]

Enormous concerns focus on the high-power and wide bandwidth traveling-wave tube (TWT) for its outstanding performance. In this article, a shape-optimized staggered double-vane slow-wave structure (SWS) for terahertz (THz) sheet beam TWT is proposed. The shape-optimized staggered double-vane SWS takes the advantages of higher interaction impedance, lower transmission loss, and lower phase velocity than conventional staggered double-vane SWSs. The shape-optimized staggered double-vane SWS with 85 periods is designed, fabricated, and cold tested. The measured transmission loss of the shape-optimized staggered double-vane SWS is less than 0.79 dB/cm in the frequency range of 0.211–0.26 THz, which is in good agreement with the simulation results. Furthermore, the beam–wave interaction analysis of a sheet beam TWT with this SWS is given. The output power is predicted to be >100 W with 3-dB bandwidth of >50 GHz. The results show that the shape-optimized staggered double-vane SWS is a very promising scheme to construct a high-power and wideband THz TWT for future applications such as communication and imaging. [ABSTRACT FROM AUTHOR]

In the particle-in-cell simulation study of this paper, it is found that the high-power terahertz radiation at twice the plasma frequency can be generated by the interaction between a weakly relativistic, large-radius, focused electron beam and an overdense plasma. The terahertz radiation is emitted from a multi-filament structure in the electron beam, which is caused by the coupling of the longitudinal two-stream instability and the transverse filamentation instability. The analysis of the k space of the plasma waves indicates that the radiation can be explained by the mode coupling among a forward oblique mode, a backward oblique mode, and a second harmonic radiation mode. The influences of the beam Lorentz factor and plasma density on the radiation power, efficiency, and coherence are also investigated. The present results not only contribute to the development of novel megawatt-level narrowband terahertz radiation sources, but also propose a potential terahertz radiation mechanism for the fundamental research of the beam-plasma system. [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]

It is found that the plasma waves driven by an electron beam rotating in a magnetized overdense plasma can be converted into terahertz electromagnetic radiation by new mechanisms. According to the particle-in-cell simulation results, the radiation modes include a dominant extraordinary (X) mode at twice the plasma frequency 2 f p and a subordinate X mode at f p . The 2 f p radiation can be generated by the coupling of a beam mode and a scattered upper-hybrid (UH) mode, or by the coupling of a beam mode and a right-handed X mode. Here, the beam mode can be a UH mode or a left-handed X mode driven by the beam under the Cherenkov condition, and the right-handed X mode can be induced by high-order electron cyclotron maser instability. The f p radiation is the right- or left-handed fundamental X mode escaping from the plasma boundary. This study also shows that the breakdown of beam modulation is responsible for the radiation attenuation. The scheme proposed in this paper can be applied in high-power THz radiation sources and diagnosis of magnetized plasmas. [ABSTRACT FROM AUTHOR]

The angular log-periodic meander-line traveling wave tube (TWT) is a kind of low voltage, small-sized, high power, low cost, on chip amplifiers, and considered as a key part of the advanced communication systems, the future biomedical applications and the next electronic counter measure (ECM) instruments et al. Here, an angular log-periodic meander-line TWT is presented in this article. The angular log-periodic meander-line slow wave structure (SWS) is supported by two diamond rods. The dispersion and the impedance characteristics are analyzed in detail. In order to reduce the reflection loss, a gradual ridged waveguide is connecting the input–output standard rectangular waveguide to the meander-line SWS. The particle in cell (PIC) simulations show that the output power of the TWT can reach 55 W at 34 GHz with the operation voltage of 1800 V and the beam current of 0.2 A. The SWS is manufactured by a laser machine with Molybdenum sheet. The assembled TWT is tested and the results show that the ${S}_{{11}}$ is less than −10 dB at 30–39 GHz. The ${S}_{{21}}$ mismatch between the simulated and the measurement is discussed at the end. [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]

In this article, an improved model for the beam–wave interaction of sheet beam in traveling wave tubes (TWTs) considering ohmic losses and reflections is presented. The ohmic losses are obtained by field analysis and equivalent method. The space charge magnetic field is derived from the active Helmholtz’s equation. An algorithm to obtain the S-matrix by the equivalent circuit method is presented. The relativistic Boris method is applied to accelerate macroparticles. The exchanged power is computed by the work the electromagnetic field applied to the macroparticles. The theoretical model is applied for validation to a G-band staggered double vane TWT and validated in comparison with CST Particle Studio and simulations without losses and reflections. The convergence of this algorithm is also discussed. The simulation time of the model is substantial faster than 3-D particle-in-cell (PIC) simulations. [ABSTRACT FROM AUTHOR]

A novel electron-optical system is proposed for dual azimuthally stacked radial sheet electron beams (ARSEBs). The two sheet beams are emitted from curved surfaces of two cathodes and are focused by a focusing electrode, which is carefully designed to produce a symmetric field distribution for the two beams and to avoid interference between the beams. A common tunable periodic cusped magnetic focusing system is also designed to focus the two ARSEBs. The dual sheet beams are used in a traveling wave tube (TWT) consisting of a cascade of two azimuthally supported angular log-periodic strip-line (ASALS) slow-wave structures (SWSs). The transmission efficiency in the presence of beam–wave interaction is 93%. The particle-in-cell simulation results show that for a beam voltage of 4400 V and a current of 0.39 A, the proposed cascaded TWT has a maximum gain of 32.5 dB at 35 GHz and a maximum output power of 180 W; this is a significant gain improvement over a TWT using a single ASALS SWS. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A novel sine groove waveguide slow wave structure (SGW-SWS), originated from the sine waveguide (SW), is proposed for a wideband terahertz (THz) traveling wave tube (TWT). SGW-SWS not only has high interaction impedance in a relatively wide frequency band, but also has a wide beam tunnel. In addition, it can be fabricated using the Nano-Computer Numerical Control (CNC) milling techniques. The high-frequency simulation results show that, under the same dispersion, the passband of SGW-SWS is 23 GHz wider than that of SW-SWS, and the average interaction impedance of SGW-SWS is higher than that of SW-SWS in the whole passband. And the transverse dimension of beam tunnel is independent of the dispersion characteristics of SGW-SWS, so the beam current can be further increased by enlarging the size of beam tunnel. Moreover, the particle-in-cell (PIC) simulation results reveal that the saturated power and electronic efficiency of SGW-TWT in the frequency range of 201–260 GHz are more than 84.9 W and 2.72%, respectively, when the operating voltage is 20.8 kV and the beam current is 150 mA. [ABSTRACT FROM AUTHOR]

In this article, a novel dielectric-supported staggered dual-meander-line (DS-SDML) planar slow-wave structure (SWS) is proposed for a traveling wave tube (TWT) working at ${E}$ -band. The proposed staggered arrangement of meander-lines (MLs) leads to a stronger beam–wave interaction and achieves higher output power as compared to the symmetric arrangement. The input–output couplers have been designed by using staggered stepped double ridge waveguide, to connect the standard ${E}$ -band rectangular waveguide and the DS-SDML SWS. An attenuator and pitch tapering have been applied to the proposed SWS to suppress the unwanted frequencies and to improve the output power. Particle-in-cell (PIC) simulation results show that for an 11.8-kV, 200-mA sheet-beam, the output power can reach 283 W at 75 GHz, with a maximum gain and electronic efficiency of 34.5 dB and 11.9%, respectively. [ABSTRACT FROM AUTHOR]

The miniaturized traveling wave tube (TWT) is a kind of high-efficiency, high-power, long-lifetime power amplifier which is an attractive choice for many applications, such as outer space exploration, phased array radar detection, unmanned aerial vehicle (UAV) communication, and on-chip application. In this article, a sheet beam miniaturized TWT with V-shaped meander-line slow wave structure (SWS) supported by two trapezoidal ceramic rods is designed. First, the dispersion characteristics, the impedance characteristics, and the S-parameters of the V-shaped meander-line SWS are analyzed in detail. Then, the particle-in-cell (PIC) simulation results predict that the TWT can produce 512-W output power driven by a 7.1 kV, 0.3-A sheet beam with a rectangular cross-sectional area of 3.5 mm $\times0.1$ mm. The TWT can cover the whole ${X}$ -band when the operation voltage shift from 7.1 to 9.1 kV. At last, the V-shaped meander-line SWS is manufactured, assembled, and tested. The good agreement between the simulated and the measured ${S} _{\mathbf {11}}$ has been achieved and the mismatch between the simulated and the measured ${S} _{\mathbf {21}}$ has been discussed at the end. [ABSTRACT FROM AUTHOR]

A dual-beam planar slow wave structure (SWS), named dielectric supported ring-bar SWS is proposed in this paper. The planar SWS is supported by two dielectric rods at the side edges, making it fit for dual sheet beam operation. The high frequency and transmission characteristics of the proposed SWS are investigated. The backward-wave oscillation and higher harmonic waves are effectively suppressed by setting two cathodes in the same plane parallel to the SWS and negative phase-velocity jumping. The hot performance of the proposed SWS is carried out by using particle-in-cell (PIC) simulation, in which two sheet electron beams (9.7 kV, 0.2 A) are employed to provide direct current power. With an input power of 1W, the output power is 180 W at 38 GHz and the corresponding gain is 22.6 dB. Besides, after adding dielectric rods to the output part, the entire structure dissipates heat well by thermal analysis. [ABSTRACT FROM AUTHOR]

A miniaturized, high electronic efficiency, S-band metamaterial extended interaction klystron (MEIK) is proposed. The metamaterial-based extended interaction resonant cavities were designed, fabricated, and tested, the assembled and cold-tested results confirm the feasibility of miniaturization in MEIK. Furthermore, the particle-in-cell (PIC) simulation predicts that, typically, when the beam voltage and current are 30 kV and 3 A, respectively, the focusing magnetic field is 1000 G, a 3-cavity MEIK yields the output power of 56 kW at 2.453 GHz, with the saturated gain of 47 dB and the electronic efficiency of 62%, and, importantly, with the cavity diameter of its interaction structure being ~1/2 of a conventional extended interaction klystron. As a power amplifier, the emerging MEIK with its miniaturization and high electronic efficiency has potential applications such as in future accelerators and microwave heating systems. [ABSTRACT FROM AUTHOR]

A novel slow wave structure (SWS), named staggered double corrugated waveguide (SDCW), is proposed for the development of wideband high-power terahertz (THz) traveling wave tubes (TWTs). The SDCW-SWS not only has the wideband characteristic of staggered double grating (SDG) but also has the high interaction impedance characteristic of symmetrical double grating. In addition, its tunnel width is independent of the lower cutoff frequency and can be further increased. Numerical Eigen mode calculations show that, under the same dispersion, the passband of SDCW-SWS is increased by more than 10 GHz compared with SDG-SWS, and the average interaction impedance at 195 GHz is increased by about 62%. A particle-in-cell simulation analysis confirms that the average output power, saturated gain, and electron efficiency of SDCW-TWT at 195 GHz are ~110 W, ~20.34 dB, and ~5.46%, respectively, when the operating voltage is 20 kV and the beam current is 100 mA. Therefore, SDCW is a promising slow wave circuit of wideband high-power THz traveling wave amplifier. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]