Helix Traveling-wave Tube Research Articles

Impedance Matching Using Support Rod Rings in C-Band Helix TWT

A helical (Slow Wave Structure SWS) traveling wave tube (TWT) operating in the C bandwidth was designed using CST software. Based on modelling, TWT components were produced. Conductor support rod rings were used to matching the impedance line and provide ease of assembly. According to the modelling, the signal gain was determined as 30 dB. In addition, Time Domain Reflectometer (TDR) analyses were performed to observe the effect of mounting rings on impedance improvements with the help of software. As a result, it has been determined that the support rod rings, which have not been used before in C band helix TWT systems, positively affect the ease of assembly and impedance improvement.

Power characteristics of a high-performance helix traveling wave tube

Traveling Wave Tubes (TWT) are most widely used in civil, defense, and space applications as power amplifiers over a wide range of frequency. When a TWT works at a higher bandwidth, it suffers from nonlinearities, which affects the overall performance of the tube and hence the required results aren't achieved. So, optimization of a TWT is required, mainly in terms of its power characteristics. Power characteristics of the TWTs are specified in terms of output power at different input drive levels, AM/PM transfer and AM/PM conversions, input, and output back-off, gain at saturation, etc. Some of the linearity factors like 3rd order inter modulation product (IMP), and the 1 dB compression point are also optimized. An exhaustive study has been made to achieve the optimum performance of a 140W TWT in Ku-Band. The result has been validated by experimental results.

A simple and fast split-model optimization technique for RF couplers of helix traveling-wave tubes

A simple and fast split-model optimization technique for RF couplers of helix traveling-wave tubes

Design and Fabrication of E-Band Traveling Wave Tube for High Data Rate Wireless Links

<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{E}$</tex-math> </inline-formula> -band (71–76 and 81–86 GHz) is widely used for wireless point to point (PtP) links with a few gigabit/second data rate. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{E}$</tex-math> </inline-formula> -band front ends are powered by solid-state amplifiers with about 1-W output power per module. This level of output power limits range and spectral efficiency in rain condition and has to be compensated by high gain antennas or backup low-frequency links with reduced capacity. The availability of tens of watts of transmission power would allows higher spectral efficiency and long range, and the use of lower gain antennas for multibeam and area coverage. Millimeter wave traveling wave tubes (TWTs) are gaining interest due to their higher power, more than one order of magnitude, in comparison with solid-state devices. Helix TWTs, typically built at microwaves, are very arduous to fabricate due to the extremely small diameter of a helix at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{E}$</tex-math> </inline-formula> -band. This article reports the design and fabrication of the first ever <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{E}$</tex-math> </inline-formula> -band TWT based on a full metal slow wave structure (SWS), the double corrugated waveguide (DCW). The TWT is designed to provide about 70-W power and more than 35-dB gain in the 71–76-GHz band. A test TWT using a single section interaction structure is in the final assembly phase as proof of concept with about 2-W output power. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{E}$</tex-math> </inline-formula> -band TWT performance will open new perspectives in the availability of long range wireless links with multi-Gb/s data rate needed for enabling 5G and 6G new networks.

Performance Improvement of Helix Traveling- Wave Tubes Based on Multiobjective Optimization Technique

An optimization design tool for helix traveling-wave tubes (TWTs) is developed by combining the nondominated sorting genetic algorithm II (NSGA-II) and the beam–wave interaction simulator (BWIS), which can realize multiobjective optimization of various TWT figures of merit (FoMs). FoMs include the output power, gain, efficiency, and nonlinear distortion characteristics. This optimization design tool can automatically construct a Pareto-optimal solution set according to FoMs. Then, the final simulation design can be obtained by analyzing the output power variation over the operating band of the individuals in the optimized solution set. In order to ensure the comprehensiveness and accuracy of FoMs, a workflow is established in the optimization tool, which can simulate the physical process by transferring the data between different computing tasks automatically during the design of beam–wave interaction. Based on this design tool, the performance of an L-band helix TWT has been improved significantly. For the demonstrated interaction, the output power, phase distortion, interaction, and recovery efficiency are taken as objectives. After analyzing the output power variation over the operating band, the final parameter set is determined from the Pareto-optimal solution set.

A Novel Helical Slow-Wave Structure of a TWT With Increased Number of Helix-Support Rods for the Suppression of BWO Caused by Thermal Deformation

Backward-wave oscillation (BWO) is one of the important factors affecting the output power and operating stability of helix traveling-wave tubes (TWTs). A novel helical slow-wave structure (SWS) with six helix-support rods at the end of SWS of TWT is proposed to suppress BWO caused by thermal deformation. An electrical–thermal–mechanical finite element coupling analysis model for the TWT is established. The simulation analysis shows that the maximum temperature at the end of the helix is reduced by 49 °C, the maximum thermal deformation is reduced by 56%, and the saturated output power at 11 GHz is increased from 464 to 519 W. The analysis confirms that the novel SWS can effectively suppress BWO caused by thermal deformation in a high-power TWT and improve the TWT’s output power and operating stability.

Q-Band Helix Traveling-Wave Tube With High Efficiency by Helix Pitch and Diameter Profiling for Potential Application in the Next Generation Wireless Communication System

Q-Band Helix Traveling-Wave Tube With High Efficiency by Helix Pitch and Diameter Profiling for Potential Application in the Next Generation Wireless Communication System

Design of a Ka-Band Traveling Wave Tube Using Low Turn-On Field Emission Electron Source Made by Carbon Nanotubes

This article designed a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i> -band traveling wave tube (TWT) with the single wall carbon nanotubes (SWCNTs) field emission cathode electron gun. The designed cold-cathode TWT was miniaturized and could instantly startup at room temperature because of the field emission cathode. First, SWCNT cathode was made by imprinting. The field emission measurement results showed that its turn-on field was as low as 0.57 MV/m, and the maximum emission current was about 10 mA. Then, a grid-controlled electron gun with planar field emission cathode was simulated based on the experiment results, which had low operation voltage of the electron gun and would prevent their grid mesh from burning. The optimized electron beam waist radius of the electron gun was 0.15 mm with the structure of the focusing magnetic field. According to experiment and simulation results, we preliminarily designed a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i> -band helix TWT with an average output power of 8.6 W and a gain of 24.6 dB at 28 GHz. The designed miniaturized TWT with a low-operation-voltage field emission cathode electron gun is expected to be used in low-power applications including 5G communication.

Drive-Induced Backward-Wave Oscillations in Helix Traveling-Wave Tubes—A Case Study

The output section of helix traveling-wave tubes (TWTs) usually features a tapered delay line to enhance the amplifier performance. This alters the phase velocity of the circuit waves, which, in particular, disturbs the narrowband synchronism between the backward wave (BW) and the electron beam. As a result, the excitation threshold of BW oscillations (BWOs) increases. Large-signal operation significantly alters beam-wave synchronism, as the electrons loose kinetic energy during the amplification process, i.e., toward the TWT output. As a result, beam and BW may interact over a larger distance, thus lowering the threshold for the onset of BWOs. These would thus be drive-induced in contrast to the zero-drive BWOs mentioned above. The following investigates the occurrence of such drive-induced BWOs as a case study of several different TWT models and proposes a theory for the large-signal instability. As the simulation process is quite involved and time-consuming, a heuristic approach for the fast prediction of the oscillation is presented as well.

Theory and Hot Test of High-Power Broadband Helix Traveling-Wave Tube Based on a Double-Graded Radius and Pitch Circuit

The classical Pierce’s 1-D small-signal theory of backward-wave gain, generalized to allow axially varying the double-graded radius and pitch circuit characteristics, is applied. Numerical calculations demonstrate that the double gradient circuit can effectively suppress the backward-wave oscillation (BWO). Furthermore, the hot test experiment is carried out to predict the performance of the tube. The hot test results show that this helix traveling-wave tube (TWT) based on the double-graded pitch and radius circuit has achieved over 5.06 kW of output power, and the corresponding device gain achieves more than 34.1 dB in the frequency range of 8–18 GHz.

Dispersion properties and beam excitation of symmetric slow waves in helix traveling wave tubes in the presence of plasma

The propagation of the hybrid slow waves in the new helix traveling wave tube, including a dielectric rod, gas plasma layer, and helix sheath is examined. It is assumed that the plasma is strongly magnetized. The dispersion relation of symmetric hybrid slow waves in this waveguide is obtained. It is shown that the frequency increases by increasing the axial wavenumber and the group velocity of slow waves reduces with increasing the dielectric constant. Moreover, by injecting the electron beam in the vacuum area in the waveguide, the symmetric hybrid slow waves are excited and the influence of various parameters on the growth rate of these waves is examined. Furthermore, therequired parameters such as plasma frequency, dielectric constant, and other geometric parameters for waveguide fabrication are expressed. According to this configuration, the allowed region for the operation of this waveguide and its growth rate and other results are obtained.

Time simulation of the nonlinear wave–particle interaction in meters-long traveling-wave tubes

We propose a multi-particle self-consistent Hamiltonian (derived from an N-body description) that is applicable for periodic structures, such as traveling-wave tubes (TWTs), gyrotrons, free-electron lasers, or particle accelerators. We build a one-dimension symplectic multi-particle algorithm to simulate the nonlinear wave–particle interaction in the time domain occurring in an experimental 3-m-long helix TWT. Our algorithm is efficient thanks to a drastic reduction model. A 3D helix version of our reduction model is provided. Finally, we establish an explicit expression of the electromagnetic power in the time domain and in non-monochromatic (non-“continuous waveform”) regime.

Design of Magnetic Focusing system for a Compact Ka band Helix TWT

In this paper we discuss the design of Magnetic focusing system (MFS) for a compact helix travelling wave tube (TWT) operating in Ka-band. Issues related to the design of the magnetic focusing system have been discussed in detail along with practical measurement results. The key design parameters considered for this TWT are: the cathode voltage is around 9.3kV, beam current is 200mA and total length of the tube not more than 6 inch with minimal weight.

Accurate and Efficient Thermal Analysis of Slow Wave Structures for Helix Traveling-Wave Tubes by Finite-Element Method

In slow wave structures (SWSs) for helix traveling-wave tubes, both thermal conductivities (TCs) of materials and thermal contact resistances (TCRs) are temperature-dependent, which have a great influence on the heat dissipation of helix SWSs. This article presents an accurate and efficient thermal analysis method of helix SWSs by finite-element method (FEM). In this method, a novel contact boundary condition (CBC) approach is proposed. This CBC approach can easily integrate various TCR models to simulate temperature-dependent TCRs accurately and conveniently. Specially for double nonlinearities arising from temperature-dependent TCs and TCRs within helix SWSs, a fast nonlinear solver named FMONS is also proposed to significantly improve the efficiency of the thermal simulation for helix SWSs. Based on this method, we further developed a 3-D thermal design tool for helix SWSs called TS2. Different from all the present FEM codes, for example, ANSYS, our TS2 can directly model temperature-dependent TCRs. By simulating various helix SWSs including a global model of the entire helix SWS, it is found that our TS2 has very high accuracy and efficiency in the thermal analysis of helix SWSs, which would be very useful for the design of high-power helix traveling-wave tubes.

Design of coaxial and waveguide couplers for helix TWT

Abstract In this paper, two types of coaxial coupler and waveguide coupler for different frequency helix traveling wave tubes (TWTs) are designed, fabricated and cold tested. The coaxial coupler includes of window ceramic and RF transformer section. At present multi-section impedance transformer design approach is used for wideband helix TWTs. In any helix TWT, impedance of the source is transformed to the characteristic impedance of helix. This is done by the quarter-wavelength (λ/4) impedance transformation approach. The simulated results of different types of couplers are carried out by HFSS and CST microwave studio software and compare with experimental results. Three-dimensional electromagnetic field simulators allowing the any geometry with port excitations it is possible to model the complex coaxial and waveguide type couplers with helix SWS assembly and predict its desired return loss performances.

Simulation of Drive-Induced Oscillations in Helix Traveling-Wave Tubes

Drive-induced oscillations (DIOs) in helix traveling-wave tubes (TWTs) may occur during large-signal amplifier operation. As the kinetic beam energy is reduced, the beam-wave synchronism possibly shifts into the π-point, thus enabling simultaneous interaction with the forward and the backward circuit mode. There, asymmetries in the beam-wave interaction region introduce an additional coupling mechanism and lower the oscillation threshold compared with backward-wave oscillations (BWOs). Consequently, DIOs are likely to arise. In addition even without asymmetries, drive-induced BWOs are observed. A hybrid timeand frequency-domain simulation approach is presented and applied to analyze this phenomenon in a helix TWT. In addition, an effective suppression technique is proposed.

Carbon Nano Tubes: Synthesis and Characterization for Microwave Applications

Attenuators are used to suppress the reflections in the helix traveling wave tubes and these attenuators are normally fabricated with the coating of some lossy material on the helix support rods. Carbon is the most commonly used attenuator material for the microwave applications and is usually deposited by pyrolytic or sputtering methods. However, other materials like iron and nickel are also used sometime for the attenuation applications. Helix is usually supported by the rods of some ceramic material like APBN (Anisotropic Pyrolytically Deposited Boron Nitride) or Alumina etc. Attenuator materials are deposited on these support rods to absorb the reflections. In order to look forward to new methods of deposition as well new attenuator materials, Carbon nanotubes have been proposed as another alternative attenuator material. Multi-Wall Cabon Nano-Tubes have been grown on the rectangular alumina substrate using the chemical vapour deposition method. Microwave attenuation/loss has been measured on these samples with X-band microwave frequencies. Specific experimental set-up has been designed for the measurement. The work is centered toward making good quality novel attenuators for the microwave applications and particularly the TWT.

A Novel Method for Backward Wave Cancellation of Traveling Wave Tube Amplifier Using Ferrite Material

This article presents a novel dielectric support for RF circuits of helix traveling wave tubes (TWTs) for the backward wave cancellation. RF circuit comprised two sections: the first section is a conventional dielectric material and the second section is a ferrite rod which replaces the dielectric support. Considering nonreciprocal electromagnetic property of ferrites, the proposed solution acts as a one-way tunable bandstop filter which only affects the propagating waves in one direction. By tuning this filter in the backward wave frequency, the backward wave can be suppressed without any effect on the forward wave. The electromagnetic characteristics and hot test behavior of ferrite-added slow wave structure (SWS) are observed through the numerical simulations. The proposed structure successfully damps the backward wave oscillation and higher gain is achieved in comparison with conventional TWTs.

Technology, Assembly, and Test of a W-Band Traveling Wave Tube for New 5G High-Capacity Networks

The folded waveguide (FWG) traveling wave tube (TWT) developed in the frame of the Horizon 2020 TWEETHER project for enabling a novel ${W}$ -band (92–95 GHz) high capacity wireless network for 5G is presented. The FWG TWT was designed by particle-in-cell (PIC) simulations. The technology and the results in terms of measured RF losses and beam transmission from the realized beam tester are presented. Amplification on the first TWT breadboard has been observed but with a poor multireflection pattern resulting from spurious burrs inside the FWG. It indicates, however, that the FWG technology offers great manufacturing simplification compared to conventional helix TWTs, thus enabling a low-cost device with large series production suitable for the wide market of wireless communications.

Multiple-GPU-Based Simulation of Ka-Band Helix Traveling Wave Tube

The finite-difference time-domain (FDTD) algorithm and the particle-in-cell (PIC) method-based simulation are classic approaches to design and optimize the helix traveling wave tubes (TWTs). In this article, a multiple-graphics processing unit (GPU)-based 3-D-FDTD-PIC parallel program is developed to complete the full-wave simulation of a Ka -band helix TWT in the time domain. The specific parallel simulation scheme is given. The code based on compute unified device architecture (CUDA) and message passing interface (MPI) can run on a scalable heterogeneous cluster consisting of multiple CPUs and GPUs, substantially improving the simulation speed and shortening the development period of TWTs. In this article, the specific parameters of the experimental TWT are given. The simulation results are found basically consistent with the measured values and theoretical analysis, verifying the correctness of this code. Moreover, this program can realistically restore the physical processes occurring in the tube in a short period of time, which means it can be applied as an efficient simulation tool for further research of TWTs or even other microwave power devices based on beam–wave interaction.