Folded Waveguide Traveling Wave Tube Research Articles

Study of the Slow-Wave Properties of a Rectangular Groove-Loaded Folded Waveguide for Millimeter Traveling-Wave Tubes

A novel slow-wave structure (SWS), called the rectangular groove-loaded folded waveguide SWS, is presented in this paper. Its high-frequency characteristics, which include the dispersion properties, normalized phase velocity, and the beam-wave interaction impedance, are analyzed by the field-matching method and calculated numerically. The calculation results by theory agree well with those obtained by the 3-D EM simulation software HFSS. The effects of the groove dimensions on the dispersion characteristics and interaction impedance are specifically studied. It is indicated from this investigation that the modified folded waveguide slow-wave structure with groove loading has the merit of higher interaction impedance but with narrower pass-band and sharper phase velocity dispersion compared to the conventional folded waveguide circuit. With proper groove dimensions, the higher gain and electron efficiency of a rectangular groove-loaded folded waveguide traveling wave tube could be obtained.

有限电导率模块在THz折叠波导行波管模拟中的验证和确认

有限电导率模块在THz折叠波导行波管模拟中的验证和确认

Theoretical and simulation study of 0.14 THz fundamental mode multi-beam folded waveguide traveling wave tube

To improve the current and output power of the THz traveling wave tube (TWT), a fundamental mode multi-beam folded waveguide (FMMBFW) TWT scheme is proposed. Firstly, an equivalent circuit model FMMBFW for calculating the high-frequency characteristic is established and compared with numerical simulation. Secondly, the transmission characteristic of 60 periods FMMBFW is analyzed. Finally, the beam-wave interaction characteristic of 0.14 THz FMMBFW TWT is completed by numerical simulation and theoretical calculation. When the DC current is 12 mA and the applied voltage is 15.75 kV, the 3 dB bandwidth of 0.14 THz FMMBFW TWT is 25 GHz (128-153 GHz), the maximum gain is 33.61 dB and the maximum output power is 23 W. When the DC current is 30 mA and the voltage is 15.75 kV, the maximum gain is 38 dB and the maximum pulse output power is 63.1 W at 0.14 THz. Compared with the fundamental single-beam folded waveguide (FW) TWT under the same working condition, the 3 dB bandwidth is doubled, its output power is raised by a factor of 9.66 and the interaction efficiency is increased by 3.22 times. Based on the same gain, the length of FMMBFW TWT is just 52.6 mm while the length of single beam FW-TWT is 78.2 mm. The proposed method can increase effectively the current of FMMBFW TWT; and the interaction gain, efficiency, 3 dB bandwidth, output power can be improved. When the gain is the same, a shorted and compact FMMBFW TWT can be constucuted.

345 GHz微折叠波导慢波结构的粗糙度和加工垂直度

345 GHz微折叠波导慢波结构的粗糙度和加工垂直度

并行多注THz折叠波导行波管的理论分析与数值模拟

并行多注THz折叠波导行波管的理论分析与数值模拟

0.14THz行波管的设计与实验研究

The folded waveguide, the electron optical system, input and output windows of the 0.14 THz folded waveguide traveling-wave tubes were designed and simulated with the help of HFSS and CST. The beam wave interaction was also simulated. Research on development of 0.14 THz TWTs was done, including fabrication and welding of the folded waveguide slow wave structure and hot test experiment. In the condition of voltage 15.4 kV, the maximum saturated output power was 8.3 W and the output frequency was 140.8 GHz. The maximum gain was 28 dB and maximum power bandwidth was 2.9 GHz.

Investigation of W-band Diverse-shaped Groove-loaded Folded Waveguide Traveling-wave Tubes

该文提出了3种槽加载折叠波导行波管慢波结构：三角形、梯形和燕尾形槽加载折叠波导。分析比较了不同槽形状对慢波结构的色散特性和耦合阻抗的影响。利用粒子模拟的方法对W波段4种槽加载折叠波导行波管的非线性注-波互作用进行了研究；在相同的电子注参数和输入功率的条件下，对输出功率、电子效率和增益等参量进行了比较。在多种槽加载结构中，梯形槽加载折叠波导输出功率(255 W)和增益(37.1 dB)最大，电子效率最高(10.7%)；燕尾形槽加载折叠波导达到饱和所需要的互作用电路最短(64.2 mm)；三角形槽加载折叠波导的3 dB带宽最宽。

Nonlinear investigation of beam-wave interaction in double-groove loaded folded-waveguide traveling-wave tube

A W-band traveling-wave tube (TWT) with double-groove loaded folded waveguide structure (FWSWS) has been designed and numerically modelled. The nonlinear performance of such a TWT is investigated by a particle-in-cell code MAGIC3D. Simulation results indicate this TWT produces a saturated electromagnetic power of 170.2 W at 90 GHz, corresponding to 36.9 dB gain and 69.6 mm interaction distance. A comparison between the novel folded waveguide traveling-wave tube (FWTWT) and the conventional one is also carried out to verify the effect of groove loading on the large-signal performance of TWT. Within the same working conditions, the double groove-loaded FWTWT could obtain higher saturated output power and gain in a shorter interaction length. The maximum of output power and gain of this novel TWT is 58.6% and 10% higher than those of the conventional FWTWT, while the 3-dB bandwidth of TWT is reduced to 4 GHz. With the additional advantage of ease of fabrication based on micro-electro-mechanical systems (MEMS) technologies, the double-groove loaded FWSWS is suitable for a millimeter-wave TWT with high power capacity and gain.

Effects of Random Circuit Fabrication Errors on the Mean and Standard Deviation of Small Signal Gain and Phase of a Traveling Wave Tube

Random fabrication errors may have detrimental effects on the performance of traveling wave tubes (TWTs) of all types, especially in the sub-millimeter wavelength regime and beyond. Previous studies calculated the standard deviation of the small signal gain and the output phase of a TWT in the presence of small random, axially varying perturbations in the circuit phase velocity, assuming synchronous interaction and zero AC space charge effects. This paper relaxes the latter assumptions. In addition, we calculate the ensemble-average gain and the ensemble-average phase that result from random axial variations in the circuit phase velocity, using two analytic approaches. One is a perturbative approach including all three modes of the coupled beam-circuit equations. The other treats the evolution of only the dominant (exponentially growing) mode. The analytical results on the expected gain and phase compare favorably with results from numerical integrations of the governing equation in the absence of space charge, but are found to deviate from the numerical integrations with the inclusion of space charge effects. The effects of small pitch errors in a 210 GHz folded waveguide TWT are evaluated in an example.

Time-dependent nonlinear theory and numerical simulation of folded waveguide traveling wave tubes

In this paper, a time-dependent nonlinear theory including the generalized time-dependent radiofrequency (RF) field equations is presented to simulate the beam and wave interaction (BWI) of folded waveguide (FWG) traveling wave tubes (TWTs). The analytical RF fields in FWG TWTs are replaced by digitized RF field profiles obtained from electromagnetic simulations. A W-band FWG TWT is studied by using a self-consistent one-dimensional code based on the theory. The numerical results show good predictions when compared with the experimental tests.

W波段折叠波导行波管振荡抑制

W波段折叠波导行波管振荡抑制

A novel 140-GHz sheet-beam folded-waveguide traveling-wave tube

A novel folded-wave guide (FWG) slow-wave structure (SWS) with sheet-beam tunnel is presented for the high-power and considerable bandwidth in terahertz (THz) wave band. Its electromagnetic characteristics and nonlinear interaction between the electron beam and the electromagnetic field were investigated. A novel input and output coupler was proposed that could produce good input and output matches. The particle-in-cell simulation results revealed that the tube can be expected to produce over 100 W of average power in the range from 141 to 146 GHz, assuming an RF input signal with an average power of 45 mW. Compared with the conventional folded-waveguide traveling-wave tube (FWGTWT) at 140 GHz, the novel FWGTWT had a 48% higher output power, and the novel FWGTWT can operate at same frequency band with larger dimensional parameters. Meanwhile, the novel FWG was also much shorter than the normal FWG with good performance at the working frequencies. It, therefore, will favor the miniaturized design of a high-power terahertz wave band traveling-wave tubes (TWT).

A research of W-band folded waveguide traveling wave tube with elliptical sheet electron beam

Folded waveguide (FWG) traveling wave tube (TWT), which shows advantages in high power capacity, moderate bandwidth, and low-cost fabrication, has become the focus of vacuum electronics recently. Sheet electron beam devices are better suited for producing radiation sources with large power in millimeter wave spectrum due to their characteristics of relatively low space charge fields and large transport current. A FWG TWT with elliptical sheet beam working in W-band is presented in this paper, with the analysis of its dispersion characteristics, coupling impedance, transmission properties, and interaction characteristics. A comparison is also made with the traditional FWG TWT. Simulation results lead to the conclusion that the FWG TWT with elliptical sheet beam investigated in this paper can make full use of relatively large electric fields and thus generate large output power with the same electric current density.

Effects of Multiple Internal Reflections on the Small-Signal Gain and Phase of a TWT

We formulate and solve a set of equations that model the effects of reflections from an arbitrary number of circuit discontinuities in a traveling-wave tube (TWT) operating under small-signal conditions. Applying this model to a case in which the discontinuities represent a series of small random pitch variations due to fabrication errors in a helix TWT, we find that reflections may significantly increase the statistical effects on the gain and output phase first reported in the work of Pengvanich In another example, we report on a study of the effects of many small pitch errors on gain ripple in a 220-GHz folded waveguide TWT.

Theory and simulation of the folded waveguide traveling-wave tube working in low voltage with changed period and big size

The folded waveguide traveling-wave tube which works at 3 mm band and above the band is limited to machining accuracy and power capacity. So a slow-wave folded waveguide structure which has a finite number of cycles and whose period can be changed nonasymptotically is proposed. Firstly, the theory for effectively increasing the high-order space harmonic coupling impedance of the structure is given. And the expressions for dispersion and coupling impedance are derived. Then through the simulation, a set of optimized design parameters is achieved. Thus the operating point of the traveling-wave tube is determined. Finally, it is simulated by MAFIA. And an effective gain is obtained. The traveling-wave tube which works at low voltage, relatively large size and relatively large period, is designed.

A wave-beam interaction theory for folded-waveguide traveling wave tubes

Based on velocity-modulating model, a nonlinear wave-beam interaction theory for folded-waveguide traveling wave tubes is developed. In this theory, the continuing beam is treated as discrete macro-particles with different initial phases. Then beam-wave interaction and energy exchange are analyzed at each crossing point between beam-tunnel and wave-tunnel. Compared with PIC result, the error of output power predicted by this model is within 10%, and the error of saturated length is within 15%. The results of this model are significant for designing folded-waveguide traveling wave tubes.

140 GHz多束折叠波导行波管仿真分析

140 GHz多束折叠波导行波管仿真分析

V波段大功率带状注曲折波导行波管

V波段大功率带状注曲折波导行波管

A Tapered Ridge-loaded Folded Waveguide Slow-wave Structure for Millimeter-wave Traveling-wave Tube

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.

Investigation on a W Band Ridge-Loaded Folded Waveguide TWT

A W-band ridge-loaded folded waveguide traveling-wave tube (FWTWT) is modeled, and the nonlinear interaction between the electron beam and the electromagnetic field is investigated by utilizing a 3-D particle-in-cell (PIC) code, MAGIC. The process of beam–wave interaction for millimeter wave TWT is presented, including the longitudinal momentum of the electron, the averaged radiation power, and the influence of input power on output power. Compared with the conventional FWTWT at 95 GHz, the ridge-loaded FWTWT obtains a 29.3% higher output power and shortens 31.7% interaction distance. The radiation power and the gain of TWT are raised up in most of the working band covering from 85 to 97 GHz, indicating effectual enhancement of beam–wave interaction by loading ridge. Furthermore, the novel FWTWT works in 7-GHz bandwidth with output power varying only 1 dB throughout the band.