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In this article, a 1-THz traveling-wave tube (TWT) based on flat-roofed sine waveguide (SWG) slow wave structure (SWS) has been studied theoretically and experimentally, and parts of the component have been fabricated. First, the flat-roofed SWG SWS has been optimized for working at 1 THz, the normalized phase velocity is around 0.287, and the interaction impedance is over $3.5~\Omega $ in the frequency range of 1.02–1.04 THz. Meanwhile, the performance of the designed TWT has been simulated, whose saturated output power is 720 mW and the corresponding gain is 28.57 dB. What is more, to decrease the transmission loss of the high-frequency structure, the input and output structures have been designed and a transition structure that transforms the waveguide to standard rectangular waveguide has been proposed. The simulation results show that the reflection coefficient of the novel proposed transmission system is less than −20 dB, and the insertion losses of the transition structure with the input and output waveguides are 2.45 and 1.68 dB, respectively. Finally, the designed SWS has been fabricated by deep reactive-ion etching (DRIE) and tested; ${S}_{{11}}$ is generally less than −10 dB in the frequency range of 1020–1040 GHz.

The $W$ -band flat-roofed sine waveguide (SWG) slow wave circuit was designed and processed in this article. Considering the limitations on present practical fabrication level, sensitivity analysis was performed on the potential influencing factors for the performance of the flat-roofed SWG slow wave structure (SWS). As indicated by the calculation results, the gap between the SWSs and the side-wall strips could have a significant impact on the dispersion, interaction impedance, and the transmission of the entire slow wave circuit. Based on the theoretical analysis, two types of $W$ -band flat-roofed SWG slow wave circuits were fabricated and tested. The side-wall strips of the two circuits are processed with/without rounded corner. The circuit without rounded corner may cause a large gap and severe reflection. In comparison, the other one with rounded corners can make the parts fit tighter, thus minimizing the potential gap. The test results demonstrate that the $W$ -band flat-roofed SWG traveling-wave tube (TWT) possesses a voltage standing wave ratio less than 1.8, which is basically consistent with the simulation results.

In this article, a potentially pseudoperiodic slow wave structure (SWS) for a broadband, high-power, helix traveling-wave tube (TWT) is studied. The structure considered here suppresses the back-wave oscillations caused by a large working current. These oscillations do not have conventional uniform pitch distributions in the radial dimension; rather, the two configurations studied in this article are a uniform pitch gradient and a conical helix. Through a reasonable design and a large number of calculations, the entire tube consists of four tapered, pitch-varying SWSs. In addition, to achieve an 8–18-GHz broadband, high-power output, a double-ridged waveguide window output coupler is designed, fabricated, and tested. The 3-D electromagnetic simulation software CST STUDIO SUITE is used to verify the performance of the tube. The simulation results show that the potentially pseudoperiodic SWS can adequately suppress the backward-wave oscillations, and the tube is capable of achieving an output power of over 6 kW, even with a very wide bandwidth of 8–18 GHz. Additionally, the electronic efficiency varies from 21.5% to 25.8%. The maximum output power is 7.45 kW, corresponding to an electronic efficiency of 25.8% at 14 GHz.

In this article, two types of compact and effective input and output couplers for a 6–18 GHz 5-kW-level helix traveling wave tube (TWT) are designed, fabricated, and cold- tested. The input coupler section includes an impedance transformer, a conical coaxial window, and a transition to a subminiature version A (SMA) connector for a radio frequency (RF) input. For achieving a high-power output, a new type of double-ridged waveguide window is used in the output coupling section. The output coupling structure consists of a standard double-ridged waveguide (WRD650), an impedance transformer, a square sapphire window, and a coaxial to double-ridged waveguide transition. The commercially available 3-D electromagnetic simulation software package CST is used to further optimize these structures, including couplers terminated with an actual complex helix slow-wave structure (SWS). According to the simulation results, the input and output couplers are fabricated and tested. The experimental results of the optimized coupled structures are presented, and both couplers show excellent transmission performance for a 6–18-GHz high-power helix TWT.

This paper explores the thermal characteristics of a helix traveling wave tube (TWT) in the Ka-band (26.5-40 GHz) based on rectangular semi-metallic rods formed by welding boron nitride and copper. The results reveal that the maximum temperature of the helix during TWT operation for this supporting rod structure is 339.2°C. A comparison of the thermal characteristics about this structure with those of a conventional dielectric rod shows that the helix temperature of the former is about 40°C lower than that of the latter during operating conditions.

A high-frequency structure that can be used for the G-band high-power traveling wave tube is proposed to analyz and the slow-wave characteristics of the quasi flat-roofed sine waveguide(QFRSWG). The PIC method is used to obtain the interaction characteristics of the sheet electron beam and the electromagnetic wave in this structure. The calculation results show that the traveling wave tube can produce over 110 W output power in the frequency range of 212 GHz-232 GHz, the gain is greater than 33.94 dB and the maximum electronic efficiency is 5.25 %.

Driven by success in areas such as computer vision and natural language processing, attempts have been made in this work to combine deep learning with the large signal of the Traveling Wave Tube (TWT) to assist in predicting the output performance of the tube and advancing the pre-design of TWT. By feeding the trained artificial neural network with several feature parameters, the output power with the tube length can be predicted.

The development of a 340GHz modified sine waveguide vacuum electron amplifier is presented here. Output power from this structure is predicated to exceed 10W with a pencil beam electron gun at 17 kV and 38mA. Design, fabrication and test of slow wave structure (SWS) and pillbox window are discussed respectively. The cold test results show a good agreement with the simulation, which verified the properties of low loss and wide bandwidth of the high frequency system.

In order to make the design results of the traveling wave tube (TWT) coincide with the experiments very well, we need to build a bridge between the actual electron situation and the beam-wave interaction. In this paper, considering the actual magnetic field distribution, the macro particle data at the waist position is processed by MATLAB to meet the needs of the interaction calculation model, so as to realize the integrated design of electron gun, magnetic system and interaction calculation using CST studio suite.

In this paper, the high frequency characteristics of Trapezoidal Staggered Grating Slow-wave Structure for 1THz Traveling Wave Tube has been studied. The transmission structure has been simulated, the reflection coefficient is less than -20dB in the frequency of 1015GHz to 1055GHz and the loss of the structure is over 58dB. The PIC simulation shows that the saturation output power is 405mW at the frequency of 1030GHz, and the corresponding gain is 19.08dB.

This paper describs a fan-shaped metal loaded helix traveling wave tube working at Ka–band. It has the gain of 37.3-48.7dB, electronic efficiency of 15.18%-19.42% and output power is greater than 286W when it works at a voltage of 9KV and a current of 210mA. The simulation results of VSWR for its coaxial energy coupler are below 1.35, and the test results of it is below 2.1 at the working frequency range.

In order to predict the saturation output power of traveling wave tubes rapidly, analytical expression has been worked out. This theory is verified by comparison with two of large signal theory.

The high frequency characteristics and beam wave interaction characteristics of a Ka-band (26-40GHz) helix traveling wave tube (TWT) with rectangular semi-metallic rod are presented. The design results show that the TWT has the gain of more than 42dB, the output power of more than 220W and the electronic efficiency of more than 19% in the working bandwidth. Now the high frequency structure of the TWT are manufactured, the preparation for the transmission test is in progress.

This paper introduces a high-stability electron optical system for millimeter wave traveling wave tubes. Firstly, a circular electronic injection Pierce electron gun is designed. The electron channel radius is 0.2mm, the current is 90mA. Then the immersed flow method was used to design a ppm focusing system with a magnetic field period of 7.3 mm and a peak value of 4900 Gauss. The stability of the immersed flow electron gun is compared with the gun under a conventional ppm magnetic field in consideration of thermal deformation and assembly errors.

A W-band multi-beam traveling-wave tube (TWT) based on sine slow-wave structure is designed. The cold bandwidths of the fundamental and higher-order modes in the slow-wave circuit are analyzed using HFSS software. Through reasonable structural design, the fundamental mode and low-order mode are suppressed. The beam-wave interaction capability of the multi-beam TWT is analyzed based on the high-order mode transmission design. At the voltage of 11.7 kV, the current density of the sheet electron beam is 96 A/cm2 which can be produced by the non-convergent electron gun, and the output power is over 150 W in the operating frequency 90 GHz-100 GHz.

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.

A novel ridge-loaded staggered single-slot rectangular coupled-cavity traveling-wave tube (CC-TWT) operating at $X$ -band is presented. It features large interaction impedance and good thermal dissipation with a moderate bandwidth. Compared with the existing staggered single-slot rectangular CC-TWT and Hughes-type TWT, this structure has the advantage of large coupled impedance and high electron efficiency, which makes it potentially useful for miniaturization in CC-TWT. The electromagnetic characteristics and the beam–wave interaction based on this slow-wave structure are investigated. The calculation results predict that it potentially could provide saturated output power over 20 kW from 8.5 to 9.8 GHz when the cathode voltage is set from 25.4 to 26.4 kV and the beam current is 5 A, respectively. The corresponding saturated gain and the electron efficiency can reach over 34.4 dB and 15.2%. From 8.6 to 9.5 GHz, the gain is even over 38.6 dB, and the electron efficiency is more than 16.9%. The cold test results show that the voltage standing wave ratio of the high-frequency structure is below 2 at the range of 8.5–10 GHz.

A two-section Folded rectangular groove waveguide (FRGWG) Slow wave structure (SWS) Traveling wave tube (TWT) with large dimension of beam tunnel is studied. Compared with the Folded waveguide (FWG) under the same size parameters conditions, the interaction impedance and center frequency of the FRGWG are higher. The advantage is that a beam tunnel with large dimension can be applied to the FRGWG without the influence caused by signal decrease, reflection and oscillation. The microwave amplification capability based on beam-wave interaction is obtained through the particle-in-cell method. This circuit structure can produce an output power of over 100W ranging from 136 to 142GHz when the operation voltage and beam current are set as 18.4kV and 150mA, respectively, for a 95mm long circuit.

A wideband coaxial line to double-ridge waveguide window for broadband high power THz TWT has been studied in this paper, which can cover the 270–370 GHz with a ultra-bandwidth over 0.1 THz. Based on the mode conversion theories and impedance matching techniques, the broadband transition of coaxial line to double ridge waveguide is designed. In addition, the diamond is adopted to design the broadband double ridged waveguide window. The characteristics of the transition are analyzed by using the full-wave analysis software. According to the simulated results, the reflection coefficient is less than −20 dB and the VSWR is less than 1.2 in the 270–370 GHz.

A 0.65 THz traveling-wave tube was designed based upon truncated sine waveguide slow-wave structure. The high frequency characteristics and transmission characteristics are analyzed and calculated by Ansoft High frequency simulation software. We have also studied and simulated the beam-wave interaction of this truncated sine waveguide traveling-wave tube. The results show that the peak output power is 270 mW from 640 GHz to 660 GHz with synchronous voltage of 18.9 kV, operation current of 11 mA and input power of 1.25 mW.

The ridge loaded azimuthal supported angular log-periodic strip meander line slow wave structure (SWS) is presented in this paper. The dispersion characteristics and coupling impedance of the SWS are calculated. According to the simulation results of beam wave interaction, the planar travelling wave tube(TWT) with SWS can give the output power of 136.3W, the electron efficiency and gain approach 5.6% and 9.6dB, respectively, at 39GHz under a single fan-shaped radial sheet beam voltage of5250Vand current of 0.46A.

A new slow wave structure (SWS) of azimuthal support angular log-periodic strip line SWS is presented in this paper. An attractive property of the new structure is that the ability of resistance to electron bombardment is better than microstrip SWS. Applied a single radial sheet beam with the work voltage of 5920V and the current of 0.6A, the beam-wave interaction results show that the maximum output power, gain and electron efficiency are 300.3W, 14.8dB and 8.46%, respectively, in Ka band.

A conformai microstrip angular log-periodic meander line(ALPML) traveling wave tube(TWT) based on quartz substrate is studied in this paper. In order to decrease the attenuation of dielectric substrate and eliminate the charge accumulation, a conformal microstrip is adopted. Conformal microstrip remove the unnecessary dielectric substrate and remain the dielectric substrate in the microstrip metal layer below. The remained dielectric substrate is as same shaped as the metal layer. By simulation, this traveling wave tube can reach 25W power output in 32GHz, which in condition of voltage 2300V and current 0.2A. The gain and efficiency is 14dB and 5.6%, respectively. The 3dB bandwidth is 10GHz from 27.5GHz to 37.5 GHz.

A novel slow-wave structure (SWS) named angular log-periodic folded groove waveguide was proposed in this paper, which mainly used in traveling wave tube (TWT) for G-band. Due to the design idea owing the combination of folded groove waveguide and log-periodic form, this new SWS possess several advantages from them. Low operation voltage and weak dispersion of electromagnetic wave are merits of them. In addition, a modified equation to calculate the phase velocity in radial direction was proposed. In the end, one angular log-periodic folded groove waveguide was designed which owing 38.8W output power at 198GHz, the gain is 18.8dB when operation voltage is set to 8080V.

The paper describes the design of an X-band coupled-cavity traveling-wave tube (CC-TWT) based on the reentrant double-staggered ladder coupled-cavity slow wave structure (SWS) using High Frequency Structure Simulator (HFSS) and particle-in-cell (PIC) code in Computer Simulation Technology (CST) Particle Studio. When the cathode voltage and cathode current are 25.9 kV and 5 A, respectively, the PIC simulation results show that the corresponding saturated output power is over 20kW from 8.6 to 9.7 GHz, the maximum output power can reach 28.8 kW at 9.2 GHz, and the electronic efficiency and the gain can reach over 15.6% and 40 dB.

The design of fan-shaped metal loaded helix slow wave structure for a dual-band (Ka/Q) traveling wave tube is presented in this paper. The beam-wave interaction simulation predicts a minimum output power of 199/191 W, minimum electronic efficiency 15.1%/12.5%, and maximum gain of 50.1/49.9 dB, respectively, for Ka-band(29-31GHz) and Q-band(43.5-45.5GHz).

A 1D frequency-domain nonlinear model for illustrating the beam-wave interactions of sine waveguide (SWG) traveling-wave tubes (TWTs) was studied. Our model considered space-charge fields and Ohmic losses to make the model closer to practical situations. The sheet beam was split into a series of rectangular electron plates in the axial direction, and the space-charge field was calculated by solving Green's function. The dynamic equations and relativistic equations of motion were solved self-consistently to obtain the nonlinear characteristics of the power saturation, as well as the electron velocity, phase space distributions, etc. A 0.22 THz SWG TWT was used to illustrate and verify the validity of the theoretical model. The output power and gain results were in good agreement with those from the Computer Simulation Technology (CST) 3D particle-in-cell simulation. In addition, the code developed based upon the theoretical model produced faster results than the CST simulation.

A new type of folded frame slow-wave structure (SWS) is introduced and used in the design of a low-voltage, high-efficiency, and widebandwidth millimeter-wave traveling-wave tube (TWT). The high-frequency characteristics of the folded frame structure, including dispersion properties, coupling impedances, and reflection characteristics are investigated. The beam-wave interaction of the TWT with the folded frame SWS working at the millimeter-wave frequency range is also calculated using 3-D particle-in-cell algorithms. The simulation results reveal that with sheet electron beam parameters of 6000 V and 0.2 A, the average output power and electron efficiency can reach 196 W and 16.3%, respectively. Compared with the symmetric double V-shaped microstrip meander-line SWS, the folded frame SWS has larger coupling impedances and can generate higher output power.

A novel ridge-loaded folded waveguide slow-wave structure has been firstly employed to manufacture a W-band continuous wave traveling wave tube (TWT). This letter reports the processes of the design and experimental test for this TWT. From the experimental results, over 25-W output power are produced within the operation bandwidth from 93.1 to 94.8 GHz, which is in accordance with the simulation results.

A novel slow-wave structure called ridge-vane-loaded folded waveguide combined with pencil electron beam has been proposed for millimeter-wave traveling-wave tubes. The high-frequency characteristics including the dispersion properties and the interaction impedance of this kind of structure have been analyzed by means of an equivalent circuit based on the transmission-line cascading network. The theoretical results agree well with those obtained by the 3-D electromagnetic high-frequency simulation software. The nonlinear interaction between the electron beam and the electromagnetic field is investigated with the help of the Computer Simulation Technology Particle Studio 3-D particle-in-cell (PIC) code. The PIC simulation results revealed that this kind of structure could produce about 56 W of peak output power at 0.22-THz when the cathode voltage and current of the pencil electron beam are set to 14.65 kV and 50 mA, respectively. Moreover, the maximum gain and interaction efficiency can reach 37.5 dB and 7.7% at 0.22 THz, respectively. A simulated 3-dB bandwidth of ~ 30 GHz is demonstrated.

A novel slotted helix slow-wave structure (SWS) is proposed to develop high power, wide-bandwidth, high reliability millimeter-wave traveling-wave tube (TWT). This structure, which can improve the heat dissipation capability of the helix SWS, evolves from conventional helix SWS with three parallel rows of rectangular slots made in the outside of the helix. In this paper, thermal stress analysis, the electromagnetic characteristics and the beam-wave interaction of this structure are investigated. The conclusions of this paper will be a great help for the design of millimeter-wave traveling-wave tube.

A method to estimate output power for sheet-beam traveling-wave amplifiers is presented. Two traveling-wave tubes are calculated by this method, and the results are compared with those of particle-in-cell simulation.

This paper describes a fan-shaped metal-loaded helix slow-wave structure (SWS) to develop ultra-wideband traveling-wave tube with low gain fluctuation. The electromagnetic characteristics and beam-wave interaction of this structure are calculated. The simulation results show that the helix TWT gain is more than 42dB and the signal gain fluctuation of the TWT is less than 2.5dB in a frequency range from 15 to 35 GHz. In addition, the maximum output power can reach 199 W at 21 GHz, corresponding to the maximum electronic efficiency is 16.6%.

A novel slow-wave structure called V-shape folded rectangular groove waveguide is proposed to develop high-power, wide-bandwidth, and high-efficiency millimeter-wave traveling-wave tube. This structure evolves from a conventional rectangular groove waveguide bending the groove with V-shape along its longitudinal direction, which can operate with the sheet electron beam. In this paper, the electromagnetic characteristics and the beam-wave interaction of this structure operating in the V-band are obtained. From our calculations, this circuit structure possesses low transmission loss and can produce an output power of over 900 W ranging from 56 to 65 GHz when the cathode voltage and beam current are set to 12.8 kV and 500 mA, respectively. The corresponding gain and electron efficiency can reach over 36.5 dB and 14%, respectively.

In this paper, a new simple equivalent circuit model for analysis of dispersion and interaction impedance characteristics of ridge-loaded folded-waveguide slow-wave structure is presented. In order to make the computational results more accurately, the efiects of the presence of the beam-hole and discontinuity due to the waveguide bend and the narrow side dimension change of this kind of structure were considered. The dispersion characteristics and the interaction impedance are numerical calculated and discussed. The analytical results agree very well with those obtained by the 3-D electromagnetic high-frequency simulation software. It is indicated that the equivalent circuit methods are reliable and high e-ciency.

This paper presents a tapered ridge-loaded folded waveguide (FWG) slow-wave structure (SWS) for broadband and high power millimeter wave traveling wave tube (TWT). The radio-frequency characteristics including dispersion properties, interaction impedance, S-parameters are analyzed. And based upon these results, the nonlinear large signal performance of the tapered ridge-loaded folded waveguide TWT working in W-band is simulated by 3-D particle-in-cell code. In the same ridge length, the tapered FWG has lower reflection and radio-frequency loss than the normal ridge-loaded FWG. Besides, the tapered ridge-loaded FWG TWT also has higher electron efficiency and larger bandwidth, which is more suitable for millimeter-wave TWT.

A folded-waveguide (FW) traveling-wave tube (TWT) with two electron beams, which operates at the higher order mode, is simulated. Operating with two electron beams means that a larger beam current can be used for a higher output power. Meanwhile, the electric field density of the fundamental mode is not the strongest at the center of the beam channel, so the competition of the fundamental mode is significantly suppressed. A four-section two-beam FWTWT at 140 GHz is designed to get 100 W of average power. From the simulation results, we can see that this kind of tube is unstable if the gain per section is over 11 dB, because both fundamental and band-edge modes are strongly excited. Then, another way for a stable FWTWT operation with two electron beams by loading with dielectric is also presented in this paper. The results presented here can provide a new way to obtain high power radiation at the terahertz frequency.

The design and simulated performance of a traveling-wave tube (TWT) constructed by combining a folded-waveguide (FW) slow-wave circuit with arrays of 2-D photonic crystals (PhC) are presented. Numerical results reveal that the Pierce interaction impedance of the FW circuit with PhCs is similar to the circuit without PhC arrays. The gain, output power, and efficiency of TWTs with and without PhCs are also similar when the circuit dimensions are identical; however, the TWT with PhCs can filter out nonoperating modes, which may improve the stability of the circuit shielded with PhCs when compared to the same circuit shielded by metal walls.

Properties of traveling wave-beam interaction in a centered dielectric-rod loaded, arbitrarily-shaped helical groove slow-wave structure (SWS) are investigated for a thin annular electron beam. The “hot” dispersion equation is obtained by means of the self-consistent field theory, and the small signal analysis is carried out including the effects of the dielectric-rod parameters and the groove shapes. The numerical results show that the bandwidth of the helical groove TWT is expanded by loading dielectric-rod, however, the small-signal gain is reduced; and when the groove shape changes from the swallow-tail shape to the triangle shape, the working frequency increases , while the peak gain decreases.

A simple but reasonable approach to the cold dispersion analysis of a coaxial arbitrary-shaped groove cylindrical waveguide is presented in the fast-wave regime for potential application in wideband gyro-traveling-wave tubes (gyro-TWTs). The unified dispersion equation of this structure is obtained by using an approximate field-theory analysis, in which the profile of the groove is approximately replaced by a series of rectangular steps, and the continued relation of the fields between two adjacent steps and the matching conditions at the interface between the groove region and central region are investigated. The dispersion characteristics of the disk-loaded structure obtained by modifying above results have been validated against those reported by Kesari et al. Meanwhile, the dispersion characteristics of arbitrary-shaped groove, such as the triangle-groove-loaded one are proved to agree well with computer simulation technology (CST) microwave studio simulation. The results of numerical calculations of the dispersion relation shows that the adjustment of structure parameters led to the possibility of widening the straight-line portion of omega-beta dispersion characteristics, which is required for wideband TWT performance in view of widening the bandwidth of resonance between the beam-mode and the waveguide-mode. Comparison of several different shape groove-loaded structures shows that the coaxial inverted trapezoid groove one shows the most potential application in wideband gyro-TWT because its transverse electric field is the greatest so that can interact effectively with the electron beam.

The analysis of the novel coupled-cavity traveling-wave tube(CC-TWT) operating at X-band is presented for the purpose of gaining higher power with a smaller size compared with the existing coupled cavity circuit. The electromagnetic characteristics, and the beamwave interaction based on the ridge-loaded staggered single-slot rectangular coupled-cavity slow-wave structure(SWS) are investigated. Compared with the existing staggered single-slot rectangular coupled cavity TWT, our designed TWT has the advantage in coupled impedance and electron efficiency, which makes it has the potential of miniaturization in CC-TWT. The calculation results reveal that it can produce saturated output power over 23 kilowatts from 8.6 to 9.5GHz when the cathode voltage are set from 25.9kV to 26.9kV and beam current is 5A, respectively. The corresponding saturated gain and electron efficiency can reach over 39dB and 17.4%.

A novel and simple helix slow-wave structure (SWS) with low gain fluctuation is present. The high frequency characteristics and beam-wave interaction of this structure are calculated. The simulation results show that the gain of the novel helix traveling wave tube (TWT) is more than 58dB at Ka-band. At the same time, the gain fluctuation of the TWT is less than 6.2dB.

The paper describes the design of an X-band coupled-cavity traveling-wave tube (CC-TWT) based on the ridge-loaded staggered single-slot rectangular coupled-cavity slow wave structure (SWS) using High Frequency Structure Simulator (HFSS) and particle-in-cell (PIC) code in Computer Simulation Technology (CST) Particle Studio. The working frequency range is from 8.6 to 9.5 GHz. The ridge can concentrate the longitudinal electric field in the structure so that the CC-TWT can produce 29.6 kW of saturated output power at 9 GHz with an electronic efficiency of 22.3 percent and a gain of 44.7 dB when the beam voltage is set to 26.9 kV and the beam current is set to 5 A.

The coaxial circular-arc-groove periodic slow-wave system for relativestic traveling wave tubes (RTWT) is presented in this paper. To analyze the field in the groove region, the continuous profile of the circular arc is approximately replaced by a series of rectangular steps and the field continuity at the neighboring steps is deduced. The dispersion equation of the coaxial circular-arc-groove slow-wave structure is derived by the matching conditions at the interface between the groove region and central region. The influence of various circuit parameters on the dispersion relation is investigated by the numerical calculation.

The coaxial ridged disk-loaded structure which is a new disk-loaded periodic system is presented and analyzed in this paper. As an all-metal slow-wave circuit, it has properties that can be used in high-power traveling wave tubes (TWT) and relativistic TWTs. The dispersion equation and coupling impedance of the structure are investigated in the first part of this paper. The results of numerical calculations of the dispersion relation and coupling impedance with different structure dimensions indicate that the interaction impedance of the ridged disk-loaded structure is higher than that of the disk-loaded structure without ridges in most frequency ranges. In the second part, the "hot" dispersion equation of this circuit with an annular electron beam is obtained according to a self-consistent linear theory. The influence of physical dimensions and beam parameters on the small signal gain is discussed.

A folded rectangular groove waveguide (FRGWG) slow wave structure (SWS) for 140 GHz traveling wave tube (TWT) has been investigated in this paper. The radio frequency characteristics and beam-wave interaction of the structure are calculated. The calculation results show that such amplifier can potentially be used in high power millimeter/THz wave radiation source, and a large dimension circle electron beam tunnel is suit for this structure.

A novel taper H-plane loaded folded waveguide (FWG) slow wave structure (SWS) for traveling wave tube (TWT) amplifier has been presented. The high-frequency characteristics and the amplification performance have been investigated. The results implied that this structure possessed higher transverse dimension and higher efficiency than those of the traditional FWG-SWS.

In this paper, a new approach based on the transmission line cascading network, is proposed. It is used to analyze the high-frequency characteristics of ridge-loaded folded-waveguide slow-wave structure. The analytical results agree with those obtained by the 3-D electromagnetic high-frequency simulation software HFSS. It is indicated that the equivalent circuit method is reliable and high efficiency.

The folded rectangular groove guide, an original slow-wave structure (SWS) , which is evolved from a conventional rectangular groove guide by bending the groove along its longitudinal direction, can operate with the sheet electron beam or the circular electron beam. The groove shape can be various,such as triangle, circle, trapezoid, etc. The electromagnetic characteristics, and the beam-wave interaction of a traveling wave tube based on this structure at 3mm wavelength are presented. Furthermore, the influences of different groove shape on the high-frequency characteristics are also discussed. From our calculations, the folded rectangular groove guide possesses larger interaction impedance and lower ohmic loss than those of a folded rectangular waveguide with the same size. Calculation results reveal the potential of the folded groove guide, which is easy to fabricate, for wideband, low-loss, and high-power millimeter-wave submillimeter-wave TWT applications.

In this paper, we study the novel sheet electron beam gun by using CST simulation. We can find that the rectangular sheet electron beam gun can easily generate the rectangular sheet electron beam, its electrode shape and cathode focusing electrode angle have obvious influences on the performances of the rectangular sheet electron beam, such as its height and current density. The simulation results can offer a basis for designing a sheet electron beam gun which can be used in the high-power millimeter wave sources, such as traveling wave tubes.