Search

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 novel chamfered V-shaped microstrip meander line (MML) slow-wave structure (SWS) based on the V-shaped MML SWS for W-band traveling-wave tube (TWT) is proposed to decrease the transmission loss and thus to improve the output power and beam-wave interaction efficiency. The high-frequency characteristics, transmission characteristics, and the beam-wave interaction processes of the novel structure are investigated by simulations. The simulation results show that the S21 parameters of the chamfered V-shaped MML SWS are improved by 4.3 dB for 100 periods compared with that of the traditional V-shaped MML SWS at 95 GHz. Besides, the particle-in-cell simulations indicate that the output power of the TWT with the novel structure is 30% higher than the V-shaped MML SWS in W-band. Finally, two types of SWSs with 100 periods are fabricated, assembled, and experimentally tested. According to the experimental test results, while the S11 parameters are below − 20 dB, the "cold" S21 parameters are − 17.04 dB vs − 20.74 dB at 95 GHz, which shows potential advantages of the proposed novel SWS in millimeter wave and even terahertz spectrum. [ABSTRACT FROM AUTHOR]

Analysis of the performance degradation for W-band lossy ceramic-loaded gyrotron traveling wave tubes (gyro-TWTs) caused by ionization of the released gas molecules is presented in this paper. The gas is released from the lossy ceramics during high average or continuous wave operation and ionized by colliding with the high-energy gyrating electrons. A potential well will be formed by the diffusion and accumulation of the ionization particles after the collision and then degrade the gyro-TWT performance. This process has been simulated based on a simplified model by introducing an equivalent ionization source combining ions and electrons. With a vacuum of 5.1 × 10 - 5 Pa, the theoretically calculated initial energy and equivalent ionization current are 0.01 eV and 0.5 A, respectively. It leads to a deterioration in the output power stability of the gyro-TWT. The performance degradation including spectrum and field pattern caused by gas ionization is also given and analyzed. One of the primary causes is the quality (pitch factor and velocity spread) degradation of the electron beam. According to the simulation and hot test experiments, the vacuum should be maintained below 2.1 × 10 - 6 Pa for stabilizing the amplified operation. [ABSTRACT FROM AUTHOR]

In this paper, the design of different dielectric advanced ceramic materials of RF windows for dual-band K-band and Q-band Gyro-TWT has been described. The design methodology of quartz, magnesium aluminate (MgAl2O4) and sapphire dielectric windows of operating TE01 mode for K-band and Q-band Gyro-TWT has been discussed. The simulation result predicts that these windows can handle 100 kW output power and return loss −58.5 dB and insertion loss −0.02 dB. This paper presents the electrical design and thermal analysis of K-band and Q-band dual-band Gyro-TWT amplifier. In the thermal analysis, the maximum temperature has been obtained at the centre of the dielectric disc. The electro-mechanical analysis has also been carried out on the different dielectric windows to achieve stress and displacement. A new type and unique advance transparent dielectric material magnesium aluminate (MgAl2O4) disc window has been used to improve the bandwidth performance of Gyro-TWT. [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]

We present the quasi-analytical spatiotemporal theory of the resonant traveling-wave tube scheme of a gyrotron based on the transverse amplifications of the operating wave and on the use of a remote delayed feedback. The main idea is to implement a system with a dense spectrum of eigenmodes, which makes it possible to smoothly adjust the generation frequency by switching from mode to mode when the operating magnetic field changes. On the basis of a simple 2D three-mirror model, we show the possibility of achieving the stable single-frequency generation regime in this system if the excess of the operating current above the starting threshold is not too high. The mechanism of loss of stability of the single-frequency generation with an increase in operating current is also described. [ABSTRACT FROM AUTHOR]

Classical Cherenkov radiation is a celebrated physics phenomenon of electromagnetic (EM) radiation stimulated by an electric charge moving with constant velocity in a three-dimensional dielectric medium. Cherenkov radiation has a wide spectrum and a particular distribution in space similar to the Mach cone created by a supersonic source. It is also characterized by the energy transfer from the charge's kinetic energy to the EM radiation. In the case of an electron beam passing through the middle of an EM waveguide, the radiation is manifested as collective Cherenkov radiation. In this case, the electron beam can be viewed as a one-dimensional non-neutral plasma, whereas the waveguide can be viewed as a slow wave structure. This collective radiation occurs, in particular, in traveling wave tubes (TWTs), and it features the energy transfer from the electron beam to the EM radiation in the waveguide. Based on a first principles Lagrangian field theory, we develop a convincing argument that the collective Cherenkov effect in TWTs is, in fact, a convective instability, that is, amplification. We also recover Pierce's theory as a high-frequency limit of our generalized Lagrangian theory. Finally, we derive for the first time expressions identifying low- and high-frequency cutoffs for amplification in TWTs. [ABSTRACT FROM AUTHOR]

Volcano-structured field emitter arrays (FEAs) have achieved high-beam focusing and have been applied in electron beam lithography and image sensors. However, high current operation on the order of milliamperes is necessary for applications such as x-ray sources and traveling wave tubes. Thus, this study applied a TiN coating to a volcano-structured Si-FEA, which has a high melting point favorable for high-current operation. Transmission electron microscopy and x-ray photoelectron spectroscopy revealed that TiN was uniformly deposited on the Si tip by DC magnetron sputtering with the atomic ratio of Ti to N being 1:1. The TiN-coated volcano-structured FEA exhibited excellent electron emission property (7.7 mA/1027 tips) and an electron emission stability of >6 mA for 60 min in pulse operation. These results are expected to aid in the development of next-generation electron sources that can realize high-current operations under high-beam-focusing conditions. [ABSTRACT FROM AUTHOR]

We present a technique for generating multiple electron beams with different energies and comparable currents from a single cathode stalk at a single potential using nested magnetically insulated coaxial diodes (MICDs). The application is for a multi-stream traveling wave tube. Particle-in-cell simulations are performed for an experimental parameter-based geometry where two thin-walled intense relativistic electron beams immersed in a strong uniform magnetic field propagate through a cylindrical vacuum channel. The analytically derived results are obtained by extending Fedosov's solution for generating a hollow electron beam from an MICD on a cathode stalk in an infinite magnetic field. Two electron beams are generated and accelerated downstream assuming zero initial kinetic energy of the electrons from the cathodes. Results show both electron beam currents ranging from 66 to 2.8 kA with an energy difference ranging from 6% to 27% depending on voltages applied from 100 to 600 kV and the geometry of the two MICDs. An optimal geometry is a crucial factor in achieving the maximum energy difference between the electron beams for comparable currents. The analytical and numerical simulation results show good agreement. We are currently in the process of planning experiments using the electron beam accelerator (SINUS-6 at UNM) to validate the analytical and simulation results. [ABSTRACT FROM AUTHOR]

The article formulates equations for longitudinally irregular waveguide excitation by three-dimensionally phased electron flows taking into account the finite wall conductivity. A.G. Sveshnikov's method based on using non-orthogonal coordinates for Maxwell's equations to formulate the excitation equations, which makes it possible to transpose the irregular boundary of the electrodynamic structure to a regular one. Then, Galerkin's projection method is used for the transformed regular region with a priori known complete system of vector basis functions for this region. A special approach allows one to solve the difficulty arising due to the boundary conditions for the vector basis functions and the solution on the waveguide surface in the case of finite conductivity. As a result, the original three-dimensional boundary value problem is derived to a one-dimensional (two-point) boundary value problem for the amplitudes of normal coupled waves of the electrodynamic structure. This problem formulates an ordinary differential equation (ODE) system with boundary conditions of the third kind on the first and final sections of the waveguide. The excitation equations, together with the equations of electron motion, form a self-consistent mathematical model for calculating and optimizing high-power electronic devices using irregular waveguides: relativistic traveling wave tubes (TWTs), backward wave oscillators (BWOs), klynotrons, gyro-TWTs, gyro-BWOs, and gyrotons. [ABSTRACT FROM AUTHOR]

Based on the rigorous nonlinear theory of relativistic traveling wave tubes (TWTs) and backward wave oscillators BWOs on irregular hollow waveguides with cathode filter-modulators, taking into account both propagating and supercritical waves, taking into account losses in the walls of the waveguide and the inhomogeneity of the magnetostatic field guiding the electron flow, the influence of dynamic stratification of the electron flow on the efficiency of the generator is determined. The article shows a full compensation possibility on the influence of dynamic layering on efficiency by optimizing an electronic beam in inhomogeneous high frequency and magnetic fields and the corrugated irregular waveguide characteristics when electron beam layers depositing on it. [ABSTRACT FROM AUTHOR]

As the central component of the traveling wave tube (TWT), the thermal deformation of the electron gun is a critical concern. This paper presents a method for analyzing the electromagnetic characteristics of electron gun after thermal deformation. The method adopts multiple grid acceleration technology. Based on this method, a three-dimensional thermal stress analysis tool called the Thermal Stress Simulator (TSS) is developed. In addition, the TSS can be seamlessly coupled with the Thermal Simulator (TS) and the Electron Optical Simulator (EOS) previously developed by our team to realize the analysis of electromagnetic characteristics changes after thermal deformation and provide support for the reliable design of TWT. [ABSTRACT FROM AUTHOR]

In this work, a Spindt cold cathode electron gun with a PPM (periodic permanent magnet) focusing system for a terahertz TWT (traveling wave tube) was designed and simulated based on the Pierce electron gun structure. More specifically, a new 3D (three dimensional) emission model was used, where the cathode radius of the electron gun was 1 mm and the cathode current was 30 mA, with an emitting half angle of about 28°. It was demonstrated that the electron beam was well focused with an electron beam radius of 0.3 mm and a filling ratio of 0.5 when the maximum value of the PPM field along with the axis was 0.122T. According to the simulation results, a planar cold cathode electron gun was developed. Measurements demonstrated that the I/V characteristics of the cold cathode gun were consistent with that of a cold cathode, revealing that the electrons emitted from the cathode are not intercepted when passing through the electron gun. [ABSTRACT FROM AUTHOR]

The results of the development of a meander-line slow-wave system (SWS) with metal supports for a miniature high-power W-band traveling-wave tube (TWT) with two sheet electron beams are presented. Using a three-dimensional finite element software package, the electromagnetic parameters of the SWS were studied. A two-section model of a TWT amplifier with a sever to prevent self-excitation has been developed. Three-dimensional modeling of the beam–wave interaction has been carried out. It was found that with a total beam current of 200 mA in the linear mode, the gain exceeds 30 dB in the frequency band 95.4–97.75 GHz, and the output power in the saturation mode reaches 120 W. A technology for manufacturing SWSs based on laser micromachining of thin copper plates is proposed. Test samples of the SWS were fabricated and verified using optical and scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Based on the double-periodic characteristics of a sine waveguide, the dispersion equation, interaction impedance, and transmission losses of slow-wave structures are derived. The dispersion equation indicates that the waves propagating in the sine waveguide should belong to two mode types, which can exist independently rather than as "pseudo-modes." The dispersion equation, interaction impedance, and transmission losses are obtained using a theoretical model. A 220 GHz traveling wave tube (TWT) is used as an illustrative example to verify the validity of the analytical model. The calculated results show that the dispersion curve is in good agreement with that given by the Ansys high-frequency simulation software over the entire frequency range and that the theoretical numerical calculation time is less than 2% of that of the Ansys software package. In addition, the results demonstrate that the interaction impedance of the symmetric φ0 + π mode is much higher than that of the asymmetric φ0 mode. Therefore, the symmetric φ0 + π mode should be used for propagation in sine waveguide traveling-wave tubes. Moreover, when the conductivity is set at 1.6 × 107 S/m, the loss of the sine waveguide is ∼1.15 dB/cm for 220 GHz. The equivalent conductivity of the metal can be used appropriately in the design of the mm-wave and the THz TWT. [ABSTRACT FROM AUTHOR]

Solid-state power amplifiers using semiconductor technology have the advantages of small size and high stability, and have replaced traditional travelling wave tube amplifiers in many microwave applications. Among all types of semiconductor materials, the third-generation semiconductor material GaN(Gallium Nitride) has been widely used in power amplifiers because of its advantages of wide band gap, high electron mobility, and high breakdown voltage. Based on the development of power amplifiers, this study describes the development history of solid-state power amplifiers, summarizes the performance comparison between GaN technology and other semiconductor technologies, and focuses on power amplifiers using GaN HEMT(GaN High Electron Mobility Transistor) technology. This study discusses various types of GaN HEMT power amplifiers, including class A, B, C, D, and E, etc., introduces the efficiency and linearity improvement techniques applied to GaN power amplifiers, including Doherty power amplifiers and envelopes tracking technology, and digital pre-distortion technology, etc., and makes a summary and comparison of related technologies. [ABSTRACT FROM AUTHOR]

We experimentally study the dynamics of a K-band continuous wave gyro-resonant traveling wave tube (gyro-TWT) with strong output reflections. By varying system parameters, we have obtained transitions from periodic self-modulation regimes with line spectra to more complex oscillation regimes. We present the analysis of experimental data verifying the experimental observation of chaotic oscillation regimes. We have shown that chaotic oscillation regimes emerge in a fairly narrow parameter area, about 0.5% of magnetic field strength and about 10% of reflectivity. Maximum oscillation power reaches 0.5 kW at about 2% efficiency. For a gyro-TWT with output reflections operating in the CW mode, the chaotic oscillations are being experimentally observed and systematically analyzed for the first time. [ABSTRACT FROM AUTHOR]

The dispersion equation for a rectangular tape helix with four rectangular dielectric support rods was derived using precise boundary conditions and field-restricting functions. The dispersion equation is a simplified conjoint expression obtained for the axial and transverse directions, derived by solving an infinite set of linear homogeneous simultaneous equations, represented as an infinite-order matrix whose determinant is zero. The dispersion characteristics plotted from the simplified dispersion equation consist of dominant and additional higher-order modes, similar to an open rectangular slow-wave structure (SWS), but with the existence of ß0a(k0a) roots everywhere without the limitations of the forbidden region boundary. The phase velocity curves obtained for the corresponding mode of the dispersion characteristics exhibit comparable behavior to the free-space rectangular helix SWS, especially in the third "allowed" region, which offers a wider beam-wave interaction region with phase speed equivalent to the speed of light at higher operating frequencies. The numerically computed dispersion curves and their corresponding phase velocities were plotted. Similar dimensional variations of the structure with discrete support rods were simulated using three-dimensional simulation software. The dispersion characteristics obtained from the simplified dispersion equation along with the dimensional variation of the dielectric-loaded rectangular tape helix SWS determine the capability and limitations of such minuscule traveling wave tubes (TWTs) as planar TWTs suitable for fabrication using micro-machining techniques. [ABSTRACT FROM AUTHOR]

A dual-band (K/Ka) TE01/TE02 mode gyrotron traveling wave tube is presented in this article. To suppress parasitic oscillations, a lossy-dielectric-loaded interaction circuit is employed. The particle-in-cell simulation results show that when it operates in K-band, the operating mode is the TE01 mode, with a peak output power of 87.1 kW, a saturated gain of 42.74 dB, and a −3 dB bandwidth of 0.7 GHz, and when it operates in Ka-band, the operating mode is the TE02 mode, with a peak output power of 62 kW, a saturated gain of 60.76 dB, and a −3 dB bandwidth of 2 GHz. Moreover, in the operating frequency range of the Ka-band, the overall gain is greater than 57 dB. To meet the requirements of dual-band operating, a dual-state magnetic injection gun is designed, a dual-mode coaxial cavity input coupler is proposed, and a dual-band output system is developed. All of these components showed excellent performance in simulations. [ABSTRACT FROM AUTHOR]

A miniaturized traveling wave tube (TWT) was studied by proposing a novel metamaterial (MTM) slow wave structure (SWS). The dispersion results show that n = −1 space harmonic of the fundamental mode exhibits the "forward" wave properties, which is the foundation of the MTM-inspired TWT. Meanwhile, the interaction impedance for mode 2 of the novel MTM SWS can be sharply decreased by introducing four blend edges to weaken the corresponding longitudinal electric field. Also, two coaxial couplers are presented to input/output the signals. The transmission results show that the reflection is as low as −15 dB from 2.90 GHz to 3 GHz, which ensures the amplified signal can be effectively outputted. The MTM-inspired TWT exhibits miniaturized superiority for its compact high frequency structure including the MTM SWS and the coaxial couplers. Especially, for the high-frequency structure, the transverse and longitudinal sizes are ~λ/5 and ~3λ, respectively (λ is the free-space wavelength at the operating frequencies). The simulation of the beam wave interaction shows that the proposed MTM-inspired TWT yields output powers of kW levels from 2.90 GHz to 3 GHz, with a gain of 23.5–25.8 dB and electronic efficiency of 14–22% when the beam current is 0.5 A and the beam voltage is 13 kV. The results indicate that the gain per wavelength is as high as 8.5 dB in the operating bands. The simulation results confirm that it is possible to weaken the backward wave oscillation from the higher mode in the miniaturized MTM-inspired TWT. [ABSTRACT FROM AUTHOR]

In this paper, a novel K/Ka dual-band input coupler for the gyrotron traveling wave tube is theoretically and experimentally investigated. This input coupler mainly consists of three modules, a Y-type power division coupler, a coaxial cavity coupler, and a Bragg reflector. When the dual-band coupler operates in K-band, the Y-type coupler couples out the TE11 mode, and simulation results show the −1 dB bandwidth is 3.3 GHz in the frequency range of 17.9–21.2 GHz. In Ka-band, the TE21 mode coupled out by the coaxial cavity coupler, the −1 dB bandwidth is 3.5 GHz within 33.7–37.2 GHz, and the reflection coefficient keeps a pretty low level. The prototype was fabricated and measured to further verify the designed dual-band input coupler's performance. The back-to-back cold test results show that the −3 dB bandwidth of the K-band is about 2.5 GHz, and the −3 dB bandwidth of the Ka-band is 2.44 GHz. [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 article, the first 237 GHz traveling wave tube (TWT) is presented as a high-power amplifier for the terahertz (THz) cloud radar. As is common with previous G-band traveling wave tubes developed at Beijing Vacuum Electronics Research Institute, the 237 GHz traveling wave tube employs a 20 kV, 50 mA pencil electron beam focused using periodic permanent magnets (PPMs) to achieve compactness. A folded waveguide (FWG) slow-wave structure (SWS) with modified circular bends is optimized to provide high impedance and eliminate sideband oscillations. Limited by insufficient drive power, this device is not saturated. The measured maximum output power and gain are 8.9 W and 35.7 dB, and the 3 dB gain bandwidth achieves 4 GHz. [ABSTRACT FROM AUTHOR]

Coupled-cavity traveling wave tube (CCTWT) is a high power microwave vacuum electronic device used to amplify radio frequency signals. CCTWTs have numerous applications, including radar, radio navigation, space communication, television, radio repeaters, and charged particle accelerators. Microwave-generating interactions in CCTWTs take place mostly in coupled resonant cavities positioned periodically along the electron beam axis. Operational features of a CCTWT, particularly the amplification mechanism, are similar to those of a multicavity klystron. We advance here a Lagrangian field theory of CCTWTs with the space being represented by one-dimensional continuum. The theory integrates into it the space-charge effects, including the so-called debunching (electron-to-electron repulsion). The corresponding Euler–Lagrange field equations are ordinary differential equations with coefficients varying periodically in the space. Utilizing the system periodicity, we develop instrumental features of the Floquet theory, including the monodromy matrix and its Floquet multipliers. We use them to derive closed form expressions for a number of physically significant quantities. Those include, in particular, dispersion relations and the frequency dependent gain foundational to the RF signal amplification. Serpentine (folded, corrugated) traveling wave tubes are very similar to CCTWTs, and our theory applies to them also. [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]

In this article, a Ka-band broadband analog predistortion (APD) microwave monolithic integrated circuit (MMIC) with independent tunability based on a 0.15 μm GaAs pHEMT process is proposed, which can be cascaded in front of traveling wave tube amplifiers (TWTAs) to improve their linearity. The influence of different diode sizes on the parameters of Schottky diodes is analyzed and used to design the gain and phase nonlinear branches. The broadband APD MMIC is realized based on a dual-branch vector synthesis design and nonlinear frequency adjust module (NFAM). The independent tunability and broadband characteristics of the APD MMIC are verified by simulated and measured results with an error of less than 5%. Furthermore, a Ka-band 60 W TWTA is linearized by the APD MMIC, and the gain and phase compressions are reduced from 8 dB and 50° to within 3 dB and 12°, respectively. The third-order intermodulation (C/IM3) is greater than 28 dBc and noise power ratio (NPR) is greater than 15.7 dBc at 3 dB output power backoff (OPBO) over the operating band of 25.1~27.5 GHz, indicating that the APD MMIC can improve the nonlinearity of TWTA effectively under broadband signals. [ABSTRACT FROM AUTHOR]

This paper investigates the mode excited, evolved, and propagating properties of the lossy dielectric-loaded waveguide (DLW) used in a Ku-band TE11-mode gyrotron traveling wave tube (gyro-TWT). Theoretical calculation and numerical simulation show that different DLW eigenmodes can be excited by the hollow circular waveguide as a single or hybrid-mode. This study clearly reveals the transformation conditions of the single and hybrid-mode, and the mechanism of the resulting specific dispersion, loss, and electromagnetic field distribution. According to the mode excitation principle and its evolution laws, the propagating properties can be accurately controlled by adjusting the dielectric thickness, which can effectively suppress the potential oscillations and improve the electron bunching phase in the gyro-TWT. As a result, the dielectric loading scheme can be optimized by properly arranging the DLWs, thus enhancing the stability and gain of the gyro-TWT. The theory and simulation are verified by the vector network analyzer measurement at Ku-band, and the results show a good agreement. [ABSTRACT FROM AUTHOR]

This study showed the possibility of using a sub-terahertz (THz) traveling-wave tube (TWT) via measuring the transmission characteristics and TWT performance of the circuit by applying X-ray LIGA, a micro-fabrication process, to the interaction circuit. The applied circuit type, an E-bend folded waveguide, is a simple structure most suitable for lithography. A total of three applied frequencies were used the W-band, G-band, and 850 GHz. Among the manufactured circuits, the W-band circuit was applied to the TWT, one of the vacuum electronics devices (VEDs). This was done to prove the manufacturing accuracy of the circuit by comparing the nonlinear characteristics of the circuit with the prediction results. Through such testing, the small signal gain was measured as 13 ± 2 dB under the conditions of 13.96-kV and 24.2-mA electron beam energy. The frequency bandwidth was extremely wide, about 9 GHz, and showed similar characteristics to the simulation predictions. The maximum output of the device was obtained up to 1 W or more at 87.12 GHz by slightly increasing the beam current. These characteristic achievements showed the suitability of the TWT for very small circuits fabricated using the X-ray LIGA process, further suggesting the applicability of other sub-THz bands. [ABSTRACT FROM AUTHOR]

Since the electronic power conditioner (EPC) is a crucial part of a space traveling-wave tube amplifier (STWTA), its reliability issue must be considered. The most effective way to prevent insulation breakdown is potting. Silicone elastomers are commonly used as an encapsulant for the EPC because of their good physical and electrical properties. The properties of the encapsulant and the interfaces change under the influence of γ-radiation, which may result in the failure of the potted modules. In this work, a comprehensive evaluation methodology is proposed for silicone-based potted modules, where besides physical and electrical properties, the effect of γ-radiation on the encapsulated interface is also considered. The results show that with the increase of the irradiation dose, the crosslinking density, hardness, elastic modulus, volume resistivity, dielectric constant, and storage modulus are increased by 301.6%, 76.3%, 289.7%, 396.1%, 5.0%, and 589.8%, respectively. In contrast, the elongation at break and dielectric loss factor are decreased by 83.8% and 57.8%. In addition, the tensile strength and breakdown strength first increase and then decrease, while the coefficient of thermal expansion of the interface shows the opposite trend. Since the interface bonding state does not change and the electric field strength of the tip decreases slightly with an increasing dielectric constant, the average value of the partial discharge inception voltage increased slightly. [ABSTRACT FROM AUTHOR]

The interaction characteristics of quasi-TEM mode and EHv1 mode with an electron beam in coaxial slow wave structures (SWSs) are analyzed and compared in this paper. Through theoretical analysis and simulation verification, we find that the asymmetric EHv1 quasi-π mode has high external Q-factor, low starting current, and high temporal growth. It is almost impossible to suppress the EHv1 mode when using single section SWSs. In order to solve this problem, a feasible method is proposed in this paper to suppress the EHv1 mode effectively, under the premise that all modes cannot be exited in single section SWSs, introducing the feedback to ensure that the quasi-TEM mode operates effectively. [ABSTRACT FROM AUTHOR]

An ultrashort H‐plane sheet beam traveling‐wave tube (SB‐TWT) coupler without transition structure is proposed. The coupler adopts a new idea of directly coupling the microwave from H‐plane of the slow‐wave circuit (SWC) and optimizes the matching by introducing an asymmetric circular ridge on the E‐plane of the coupled waveguide. As a result, the length of the SB‐TWT coupler is reduced from more than 3λ to 1λ. At the same time, the beam tunnel area is enlarged to twice that of the SWC beam tunnel. In the working band (90–100 GHz) of the SWC, the simulation results show that the reflection is less than −25 dB, the isolation is greater than −22 dB. And the influence of the dimensions and locations of ridge on the performance of the coupler is studied. Particle‐in‐cell simulation results also show that the new coupler can not only complete the microwave coupling well but also reduce the number of SWC periods. [ABSTRACT FROM AUTHOR]

A theoretical model is proposed for linear analysis of the beam–wave interaction in a sine waveguide (SWG) with slow-wave structure. The field expressions and "hot" dispersion equation are obtained by means of field matching. The ohmic loss and attenuation constant due to imperfect conductors are also derived using the theoretical model. Moreover, the effects of voltage, current, beam thickness, period, and oscillation amplitude on the linear gain and bandwidth are calculated. The results indicate a peak gain and 3-dB bandwidth of 6.82 dB/cm and 19.5%, respectively, for a 0.22-THz SWG traveling-wave tube upon selecting reasonable structural parameters and electron-beam dimensions. Furthermore, by considering the ohmic losses for the finite conductivities of 5.8 × 107 S/m and 2.2 × 107 S/m, the theoretical results are compared with those of particle-in-cell simulations performed using Computer Simulation Technology Particle Studio. [ABSTRACT FROM AUTHOR]

A traveling-wave tube (TWT) with a sheet electron beam and staggered double-grating slow-wave structure (SWS) is a promising high-power, wideband terahertz amplifier. In such tubes, electron-optical systems (EOSs) with a converging sheet beam are mostly used, which allow a reduction of the cathode load, increase the lifetime, and enable operation in a continuous-wave (CW) mode. This paper presents the results of a 3D particle-in-cell (PIC) simulation of the 0.22 THz TWT driven with a converged sheet beam, which is compressed to less than 100 μm thickness in the EOS with a magnetically shielded cathode. The beam with high compression has a significant transversal velocity spread and essentially non-uniform current density distribution over the cross-section. These factors significantly affect the beam–wave interaction. We compare the performance of the TWT driven by the compressed sheet beam and by an idealized initially rectilinear beam without any velocity spread. [ABSTRACT FROM AUTHOR]

Two different excitation mechanisms of the frequency self-modulation (FSM) instability in a W-band dielectric-loaded gyrotron traveling-wave tube (gyro-TWT) were clearly revealed and explained. The FSM properties caused by the window reflection and collector 'bottleneck' versus operating beam current and pitch factor are respectively investigated. In order to solve the FSM instability, two improved gyro-TWT prototypes with broadband, low-reflection-level meta-surface window and a collector without 'bottleneck' were respectively fabricated and hot tested. The FSM excitation mechanism was well verified and excellent tube stability with a zero-driven signal was successfully achieved through our experiment. [ABSTRACT FROM AUTHOR]

Conventional analyses on dispersion tend to concentrate on the derivation and validation of closed-form solution, which is localized, viz. without an effective analysis pattern to uncover the full picture about dispersion space. This work shall provide a systematic treatment towards the panorama of dispersion space with the assistance of neural network. A thorough analysis pattern is presented to fully explore the dispersion space and gain some insight into it on the basis of several characterizations and rational-constrained analytic domain. The full picture of dispersion space and corresponding dispersion-manipulation capability are disclosed in this manner. The analysis pattern is of generality since the steps involved shall be easily transplanted to other periodic structures. [ABSTRACT FROM AUTHOR]

The dependence of overall traveling-wave tube (TWT) efficiency on the collector efficiency is of paramount importance. The objective of achieving high overall efficiency drives us to design a multi-stage depressed collector (MDC) with the theoretically highest possible efficiency with appropriate depressed potentials. Various design parameters, namely electrode geometry, depressed potentials, material parameters, etc., can be optimized to attain the desired theoretical maximum collector efficiency. But in a practical situation, the measured MDC efficiency is relatively less than the designed efficiency, which may be attributed to approximations involved in the nonlinear interaction of the electron beam and RF wave, fabrication inaccuracies, process limitations, simulation approximations, etc. This inexplicable practical decrease in MDC efficiency is typically accompanied by an increase in the backstreaming of electrons into the interaction structure. To compensate for this decrease, a permanent magnet has been suitably positioned on the base plate of the MDC, which results in an increase in collector efficiency. Simulation studies have been carried out to optimize the parameters of the magnet in terms of the geometrical dimensions, position, and magnetic field value, and has been validated experimentally. This technique of collector efficiency enhancement using an external magnet has proven to be very effective, contributing to a significant collector efficiency enhancement of > 5% from ~78% to ~83%, which in turn corresponds to an overall tube efficiency improvement of ~5.8% from 50.5% to 56.3%. [ABSTRACT FROM AUTHOR]

The article presents the optical manipulation of matter waves. It analysis the findings on inelastic interaction between free atoms and optical fields. It discusses optical manipulation as a tool for microscopy, spectroscopy, and exploration of fundamental phenomena associated with light-atom interactions.

We present the results of the studies aimed at developing small-size traveling-wave tubes (TWTs) with multiple sheet electron beams, which operate in the short-wavelength part of the millimeterwaverange. Two versions of such TWTs are considered. The TWT operating at frequencies near 0.22 THz with a triple sheet beam, which interacts with the higher transverse mode of the slow wave structure in the form of a dual comb, is studied. We describe the design of the electronoptical system which forms a beam consisting of several sheets with elliptical cross sections having an area compression of about 16 units. We also consider a TWT with a slow-wave structure in the form of a 3D meander line with several channels for electron beams, whichis placed in a rectangular waveguide. On each side, this structure is supported by dielectric supports. A slow-wave V-band (50–70 GHz) structure has been designed for a TWT with channels for four sheet electron beams. The results of calculating electrodynamic characteristics of the slow-wave structure are presented along with the results of three-dimensional simulation of the processes of the electron–wave interaction by the particle-in-cell method. [ABSTRACT FROM AUTHOR]

We present a version of the radiation input/output system with polarization division of signals and a single oversized window developed for a modification of the gyrotron-type traveling-wave tube (gyro-TWT) with ten helically corugated parallel waveguides, which was proposed earlier and, according to calculations, allows achieveing a pulse power of 200–400 kW in the frequency band 92–98 GHz. The key element of this system is the waveguide converter transforming the TE modes, which escape from each barrel, to a common linearly polarized quasioptical wave beam being a mixture of LP5, n modes of the corrugated waveguide. Spatial separation of the electron beam and microwave radiation takes place at the waveguide discontinuity of the collector insulated from the tube body. The radiation is injected into and ejected from the gyro-TWT via one oversized window. The input and output signals are divided spatially with respect to their polarization on an array of linear conductors. It is shown that using this system and a certain set of external quasioptical mirrors, one can ensure transformation of the output radiation of a gyro-TWT to the mode of an external transmission line (the HE mode of the corrugated waveguide or the TEM mode of the mirror line) with diffraction losses of about 3–4% at the bandwidth center and 12–15%, at its edges. [ABSTRACT FROM AUTHOR]

We study the dynamics of a W-band traveling-wave tube with delayed feedback on the basis of averaged equations and within the framework of three-dimensional simulation by the particle-in- cell method. The system parameters, which are optimal from the viewpoint of the width and uniformity of the chaotic-generation spectrum, are determined. It is shown that the chaotic noise-like radiation sources with the relative spectrum width exceeding 10% can be implemented using the experimentally realized traveling-wave tubes on the basis of a slow-wave system of the winding-waveguide type. [ABSTRACT FROM AUTHOR]

In many fields, such as space astrophysics, plasma and vacuum electronics, there are many nonlinear strong coupling physical problems. In order to solve the problem of electron beam–wave interaction in cylindrical Traveling wave tube (TWT) with symmetrical structure, a multi particle simulation algorithm for beam circuit is designed. The algorithm allows aperiodic time input, nonuniform linearity and large space diagnosis for different particles. In this algorithm, the field of coupled slow-wave transmission line is simulated by finite difference method. Assuming that there is strong coupling between the beam and the circuit, the space center equation of transmission along the line is obtained, and the space charge field is modeled considering the space charge effect, which can easily be ignored. The Particle In Cell (PIC) method of frog leaping step scheme is adopted to evaluate the electric field of each particle center, determine the circuit and space charge field, and design the termination part to compensate for the loss in order to avoid self-excited agitation. Finally, a simple numerical simulation is carried out for the electromagnetic problem and the accuracy of the code is checked against the electromagnetic simulator CHPIC. Therefore, the algorithm can be used to solve the problem of beam–wave interactions in a fixed structure (cylindrical) in multiple fields and can accurately record the data in the process. [ABSTRACT FROM AUTHOR]

Development of a G-band broadband continuous wave (CW) traveling wave tube (TWT) for wireless communications is described in this paper. This device provides the saturation output power over 8 W and the saturation gain over 30.5 dB with a bandwidth of 27 GHz. The maximum output power is 16 W and the bandwidth of 10 W output power is 23 GHz. The 3 dB bandwidth is greater than 12.3% of fc (center frequency). The gain ripple is less than 10 dB in band. A pencil beam of 50 mA and 20 kV is used and a transmission ratio over 93% is realized. The intercept power of the beam is less than 70 W and the TWT is conduction cooled through mounting plate and air fan, which makes the device capable of operating in continuous wave mode. A Pierce's electron gun and periodic permanent magnets are employed. Chemical vapor deposition diamond disc is used in the input and output radio frequency (RF) windows to minimize the loss and voltage standing wave ratios of the traveling wave tube. Double stages deeply depressed collector is used for improving the total efficiency of the device, which can be over 5.5% in band. The weight of the device is 2.5 kg, and the packaged size is 330 mm × 70 mm × 70 mm. [ABSTRACT FROM AUTHOR]

In this paper, we present the results of development and research of planar microstrip slow-wave structures (SWSs) on dielectric substrates for miniature low-voltage O-type traveling-wave tubes (TWTs) of the sub-terahertz frequency band. The main electromagnetic parameters of meander-line SWSs of various frequency bands (V-,W-,D-band) are studied. Using technology based on magnetron sputtering and laser ablation, samples of SWSs were fabricated and their S-parameters were measured. A three-dimensional simulation of the beam-wave interaction in a V-band TWT was performed. It is shown that at a beam current of 100 mA and a voltage of 5 kV, the gain can reach 33 dB while the power in the saturation mode is 23 W. [ABSTRACT FROM AUTHOR]

The results of study carried out at JSC NPP Almaz over the past ten years on the application and prospects for the use of carbon materials in heat-loaded units of TWTs and klystrons are presented. [ABSTRACT FROM AUTHOR]

Five studies [[1], [3], [5]] present key devices for terahertz communications, including terahertz reconfigurable intelligent surfaces [[1]], terahertz micro-electro-mechanical system (MEMS) switches [[2]], resonant triple-band terahertz thermal detectors [[3]], G-band continuous-wave traveling wave tubes [[4]], and wide-dynamic-range GaAs transceivers [[5]], which could effectively support broadband terahertz systems. The remarkable explosion of wireless devices and bandwidth-consuming Internet applications have boosted the demand for wireless communications with ultra-high data rate. Motivated by the potential of terahertz wireless communications, this Special Issue reports on recent critical technological breakthroughs in terms of broadband terahertz devices and communications, as well as novel technologies at other frequency bands that can also motivate terahertz research. In this Special Issue, three terahertz communicating systems were analyzed and demonstrated [[9], [11]], including a 144 Gbps photonics terahertz communication system working at 500 GHz [[9]], a W-band communication and sensing convergence system [[10]], and an analysis of secure terahertz communications with perfect electric conductor (PEC) and multiple eavesdroppers [[11]]. [Extracted from the article]