Space Traveling Wave Tube Research Articles

Multistage Depressed Collector With Novel Dual Aperture Electrodes for Space Traveling Wave Tubes

Multistage Depressed Collector With Novel Dual Aperture Electrodes for Space Traveling Wave Tubes

Thermal and Structural Analysis of a Fully Integrated Space Traveling Wave Tube

Thermal and Structural Analysis of a Fully Integrated Space Traveling Wave Tube

Thermal Design and Analysis of Radiation Shield Cooling Assembly for Efficient Heat Dissipation of Space Traveling-Wave Tube

Thermal Design and Analysis of Radiation Shield Cooling Assembly for Efficient Heat Dissipation of Space Traveling-Wave Tube

Multiobjective Design Optimization and Experimental Verification of a High-Performance 200-W Ku-Band CW Helix TWT

In this article, the interaction circuit, electron gun, and collector of a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ku</i> -band helix space traveling-wave tube (TWT) are optimized by using the multiobjective optimization design tools, which were developed by combining the nondominated sorting genetic algorithm II (NSGA-II) with the microwave tube simulator suite (MTSS). A prototype of the optimized TWT was then fabricated and tested at a beam voltage of 7.12 kV and a beam current of 90.14 mA. The testing results show that this tube is capable of providing over 200-W output power, over 54-dB gain, and over 69% overall efficiency within a 1-GHz bandwidth at the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ku</i> -band, with a good linearity performance. The optimization design process takes 49 h with the help of optimization design tools.

Design and Experimental Study of an E-Band CW Space TWT

This article presents a design and experimental study of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$</tex-math> </inline-formula> -band continuous wave (CW) space traveling wave tube (TWT) at 71–76 GHz. To ensure a high beam transmission, a double anode electron gun and periodic permanent magnetic (PPM) focusing system were designed, while linear tapered transition waveguides with diamond windows were used to form an energy coupling system as to increase output power. A four-stage depressed collector was also designed to improve overall efficiency. A prototype <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$</tex-math> </inline-formula> -band CW space TWT was then fabricated and tested at a relatively lowered beam voltage of 14.8 kV and beam current of 73 mA. The testing results show that this tube is capable of providing over 87-W output power, 41-dB gain, and overall efficiency of over 31%, within a bandwidth of 5 GHz at 71–76 GHz, with a maximum saturated output power of 110 W, a corresponding gain of 49 dB, and an overall efficiency of 37%. Given the relatively lowered operating voltage and current, it is believed the overall performance of this <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$</tex-math> </inline-formula> -band TWT exhibits a substantial improvement as compared to those of the reported similar tubes.

The Effects of γ-Radiation on the Physical and Electrical Properties of Silicone Encapsulation for Electronic Power Conditioners

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.

Micro Resistance Spot Welding Optimization for Ultra-Thin Mo-Re Sheet Used in TWT

<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$30~\mu $ </tex-math></inline-formula> m ultra-thin Mo-Re sheet had been joined by micro resistance spot welding (MRSW) and successfully applied to the low heating power cathode of traveling wave tube (TWT). The effects of different welding parameters, surface state and protection conditions on the joint’s appearance, micro-structure and lap shear strength (LSS) were analyzed in this paper. The results showed that a 63.5 N LSS of the MRSW joint was obtained under the following conditions: electrode force <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$F=9.0$ </tex-math></inline-formula> N, welding current <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I=1000\text{A}$ </tex-math></inline-formula> , ramping time <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$t_{1}=5$ </tex-math></inline-formula> ms, welding time <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$t_{2}=2$ </tex-math></inline-formula> ms and dip in the alcohol for protection. The fracture occurs in the heat affected zone (HAZ). Using metallurgical microscopy observed the nugget, metallurgical fusion could be found, the diameter of nugget was about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi 0.3$ </tex-math></inline-formula> mm, without gas pores. Scanning electron microscopy (SEM) was used to observe the fracture surface. It could be found some “whisker” shape diverged from the joint center to the surroundings in HAZ. The electrode tip was observed by energy dispersive spectroscopy (EDS) and optical profiler. It was found that the tip was uneven and adhered the base metal obviously after spark. Additional work about electrode sticking will be required. The thermal test data showed that the use of ultra-thin Mo-Re sheet can reduce a space TWT cathode heating power (CHP) by 0.57 W, which will effectively save satellite energy and improve the expected working life of vacuum electronic devices.

The Effect of Thermal and Moisture Stress on Insulation Deterioration Law of Ionic Contaminated High-Voltage Printed Circuit Board of Electronic Power Conditioner

Since the electronic power conditioner (EPC) is a crucial part applied of a Space Travelling-wave Tube Amplifier (STWTA), the reliability issue must be considered. Of all the failure modes of an EPC, the insulation failure of an EPC in thermal and moist environments is the most serious, and needs special attention. By investigating the influence of contamination, humidity, and temperature on surface insulation resistance (SIR) and surface discharge, we focused on the determination of the insulation failure boundary in an EPC. Considering real working conditions, we used the typical circuit applied in the EPC as the test object. The insulation deterioration phenomenon under different thermal and moisture stress was studied. The results show that: (1) SIR of the samples did not change with contamination levels when the relative humidity (RH) was below 70%. When RH was higher than 75%, the SIR began to vary with temperature and ionic contaminant concentration. (2) Even if the samples were not contaminated (the ionic contamination concentration was less than 1.56 μg/cm2), the deterioration of the SIR still occurred at 85 °C/90% RH. (3) The insulation failure boundary caused by surface discharge, and the degree of electrical erosion were related to humidity, pollution, voltage and temperature. To improve the failure caused by insulation, encapsulation was used. Experiments showed that encapsulation is an effective protection method to prevent insulation deterioration.

In-Orbit Reliability Evaluation of Space TWTA Based on Copula Function and Bivariate Hybrid Stochastic Processes

Currently, it is still a challenge to study the degradation mechanisms of the space traveling wave tube amplifier (TWTA) with no failure and small sample tests. Given that the Copula functions are used to describe the correlation of multiple performance characteristics, this paper develops a bivariate hybrid stochastic degradation model to evaluate the in-orbit reliability of TWTA. Firstly, based on the impact analysis of the life of TWTA, helix current and anode voltage are selected as the performance degradation parameters. Secondly, stochastic processes with random effects based on the one-dimensional Wiener process and Gamma process are applied to describe the degradation of TWTA’s helix current and anode voltage, respectively, and the corresponding marginal distribution function is obtained. Then, the Copula function is utilized to describe the correlation between two different performance parameters of TWTA. Meanwhile, this paper also proposed a two-step method to estimate the reliability level of TWTA based on its in-orbit telemetry data through a two-step method, which contains a Markov Chain Monte Carlo (MCMC) algorithm and a maximum likelihood estimation (MLE) algorithm. Besides, the Bayes-Bootstrap sampling method is also used to improve the evaluation accuracy to overcome the defect of an in-orbit small sample of TWTA. Finally, a TWTA degradation case with a set of telemetry data is carried out, and the results show that the method proposed in this paper is more applicable and more accurate than other methods.

Experiment for Evaluating a K-Band Space TWT Electron Beam

The electron beam of a K-band space traveling-wave tube (TWT) has been investigated in a beam measurement system in this article. The primary beam emitted from a Pierce-type electron gun is scanned by a Faraday cup probe, and the beam current density distribution and envelope are determined. The spent beam is also diagnosed with a novel retarding field energy analyzer (RFEA) by using the monopulse measurement method, and a comparison of velocity distribution between the experimental result and simulation is presented.

Design of an Asymmetric Multistage Depressed Collector for K-Band 100W Traveling Wave Tube

Efficiency and back-streaming current are important indicators in a traveling wave tube (TWT). A new asymmetric multistage depressed collector (MDC) is needed when designing a K-band 100W space TWT for high collector efficiency and low back-streaming current. In the new collector, the second, third, and fourth electrodes are asymmetrically designed to form an asymmetric electric field, and the potential and geometry of the electrode are appropriately optimized. The simulation shows that when the electronic efficiency is 27.28%, the collector efficiency is 85.34% with zero back-streaming current.

Automatic test system of full electrical parameters for space traveling-wave tubes

In the development of space traveling wave tubes (TWTs), there have been many problems in testing their performance, such as too many test sections, complex operation processes, long test times and large amounts of test data. In this paper, an integrated test system for space TWTs is studied to achieve an accurate, fast and complete test of its full electrical parameters. The system can automatically switch the test instruments according to the tested contents, which eliminates the manual operation of setting the test bench and reduces personal error. Then, the one-button testing of full electrical parameters is realized by means of automatic test software of space TWTs, which greatly improves the test efficiency. Moreover, a standardized and scientific test data management system is established to ensure the integrity and objectivity of the test data. Finally, the testing accuracy and stability of the system are verified by data comparison.

Design and Performance of a High-Efficiency 120-W Q-Band Space Helix TWT

$Q$ -band traveling-wave tubes (TWTs) with high efficiency and high power will be needed for high-data rate broadband communications in next-generation satellite communication systems. According to the key technical problems and difficulties in the development of $Q$ -band helix TWTs, this article presents a design strategy for high-efficiency and high-power $Q$ -band TWTs. A $Q$ -band helix TWT was successfully manufactured on the basis of this strategy, and the test results indicate that the $Q$ -band helix TWT can operate at up to 120-W continuous-wave output power and with 49.9% minimum overall efficiency over 41.5–45.5 GHz. The group delay and the saturated gain fluctuation of the $Q$ -band TWT over the operating band are only 0.268 nspp and 2.19 dBpp, respectively. The present design strategy is also expected to be applicable to other highly efficient space TWTs, such as $V$ -band space TWTs.

PSO-Algorithm-Based Optimal Design of LCLC Resonant Converters for Space Travelling-Wave Tube Amplifiers Applications

Due to the advantages of zero-voltage-switching (ZVS) and zero-current-switching (ZCS), LCLC resonant converters are universally applied in two-stage electronic power conditioners (EPCs) of space travelling-wave tube amplifiers (TWTAs). In two-stage EPCs, as the output voltage is regulated by the first stage, the main functions of LCLC resonant converters are to boost the input voltage, provide galvanic isolation, and maintain high efficiency. However, the total power loss of an LCLC resonant converter is very challenging because of the multiple resonant components and their mutual couplings. In order to solve this problem, in this paper, a PSO (Particle Swarm Optimization)-algorithm-based, efficiency-oriented optimal design method of an LCLC resonant converter is proposed. Based on an analysis of working principles, the total power loss (with consideration of all the power losses, including the driving loss and the conduction loss of the main switches), transformer loss, and power loss of the rectifiers is calculated. After that, the total power loss is appointed as the objective function of the PSO algorithm, where the optimal circuit parameters are derived to minimize the total power loss. After the optimal circuit parameters are obtained, an LCLC resonant converter with the desired parameters is built. Finally, the proposed PSO-algorithm-based, efficiency-oriented optimal design method is validated by an example.

An Efficiency-Oriented Two-Stage Optimal Design Methodology of High-Frequency LCLC Resonant Converters for Space Travelling-Wave Tube Amplifier Applications

The high-frequency LCLC resonant converters are widely used in the two-stage power converter as a dc transformer for the space travelling-wave tube amplifier applications. In the two-stage power converter, since the output voltage is controlled by a preregulator, which is the first stage, the main functions of the high-frequency LCLC resonant converter, which serves as the second stage, are to boost the input voltage and to provide galvanic isolation while keeping high efficiency. As boosting the input voltage and providing galvanic isolation can be achieved by the transformer, achieving high efficiency is most challenging. Previous studies on the LCLC resonant converter mainly focus on reducing the switching loss. However, in addition to the switching loss, the total power loss of the LCLC resonant converter contains driving and conduction loss of the main switches; core loss, copper loss, and dielectric loss of the transformer; and the conduction loss of the rectifiers. As a result, low switching loss cannot guarantee the high efficiency of the LCLC resonant converter. To solve this problem, in this paper, an efficiency-oriented two-stage optimal design methodology of the LCLC resonant converters is proposed. In the first stage, the optimal parameters of the LCLC resonant converter, which aims at minimizing the total power loss of the converter, are found from the proposed genetic algorithm + particle swarm optimization algorithm. After that, in the second stage, a single-layer partially interleaved transformer structure is proposed to realize the optimal parameters. After the transformer design is finished, the optimal LCLC resonant converter is built. The proposed efficiency-oriented two-stage optimal design method and the transformer structure are validated by simulations and experiments.

Sequential Offline-Online-Offline Measurement Approach for High-Frequency LCLC Resonant Converters in the TWTA Applications

The high-frequency LCLC resonant converter is one of the important parts of the two-stage power supply in the space travelling-wave tube amplifier application. Usually, the high-frequency LCLC resonant converter utilizes open-loop control and simultaneously sets its switching frequency and duty cycle to the required values to guarantee low cost and high power efficiency. However, the required switching frequency and duty cycle are determined by the transformer parasitic parameters. Therefore, how to measure the real transformer parasitic parameters under the real working conditions precisely becomes very important to the high-frequency LCLC resonant converter. The conventional way to measure the transformer parasitics is to employ an offline impedance analyzer. However, the transformer parasitics under real operating conditions may deviate from the offline measured results. The online measurement methods can obtain the real values when the high-frequency LCLC resonant converter is working, but these online approaches also mean additional cost and complex implementation requirement. To solve the above-mentioned problems, a sequential offline-online-offline (SO3) measurement method is proposed in this paper. With this SO3 measurement approach, all the real transformer parasitics can be easily obtained in a low cost and simple implementation way, which combines the advantages of both traditional offline and online measurement methods while removing their corresponding shortcomings. The proposed method is validated by the experiments.

Study the Mechanism and Suppression of AM/PM Conversion of Traveling-Wave Tubes Using Eulerian Hydrodynamic Analysis

In this paper, the fourth-order analytic solution of amplitude modulation to phase modulation (AM/PM) conversion is first derived from an Eulerian nonlinear analytic model. The analytic relationships between electron phases, detuning parameter b, and AM/PM conversion are also found. Then, the mechanism of AM/PM conversion is studied. It is found that the generation of the harmonics in the dc component of the electron phase in the nonlinear beam–wave interaction region is the main mechanism of AM/PM conversion. Next, a series of AM/PM conversion suppression schemes is discussed by using the mechanism. The Eulerian formations are validated by an in-house code based on the Lagrangian theory. Results show that the fourth-order analytic solution of normalized axial electric field and AM/PM conversion agree well with the Lagrangian theory in the nonlinear region. In addition, the suppression schemes are applied to a high-efficiency Ku-band space traveling-wave tube (TWT). The AM/PM conversion distortion is greatly reduced by approximately 50% with a slight drop of output power. We hope that our efforts will help the nonlinear design of TWT in the future.

Study of the Mechanism and Suppression of Group Delay Distortion of a Traveling-Wave Tube Using Eulerian Hydrodynamic Analysis

In this paper, a simplified Eulerian nonlinear beam-wave interaction (BWI) theory of a helix traveling-wave tube (TWT) is developed. Derived from this model, analytic solutions are first obtained by the method of successive approximation. Then, the linear analytic solution of group delay distortion (GDD) is obtained. Subsequently, the mechanism of group delay is studied. It is found that the main mechanism of GDD is the propagation time difference between the wave group and electron beam throughout the BWI region. Furthermore, a series of group delay suppression schemes is discussed by using the mechanism. Finally, the Eulerian formation and the suppression schemes are validated by an in-house code based on the Lagrangian theory. Results show that the analytic solutions of Eulerian model and GDD agree well with the Lagrangian theory in small-signal region. In addition, the suppression schemes are applied to a high-efficiency Ku-band space TWT. The GDD is greatly reduced by approximately 50% with a slightly drop of output power.

Development of 45W Q-band Space Qualified TWTs

Beijing Vacuum Electronics Research Institute (BVERI) has developed a series of Ka band space traveling wave tubes (TWTs) with saturation power of 12-100 W and efficiency of 55-63% for data transmission and communication for both conduction and radiation cooling. Recently Q-band space TWTs with conduction-cooled and space qualified are developed which are capable of delivering over 45W saturated RF power with overall efficiency exceeding 45%. This paper gives the main technical characteristics of Q-band space TWTs’ design, performances and qualification tests over 5.5 GHz bandwidth.

Simultaneous Suppression of IMD3 and IMD5 in Space TWT by IMD3 and 2HD Signal Injection

This paper presents a signal injection technology showing significant reductions in both 3rd-order and 5th-order intermodulation distortions (IMD3 and IMD5) in space traveling wave tube (STWT). By applying the IMD3 to the IMD5 ratio (TFR) as measures of location, the simultaneous suppressions of IMD3 and IMD5 in TWT are achieved by second harmonic distortion (2HD) and IMD3 injection. According to the research on theoretical analysis and computer simulation, the optimum amplitude and phase parameters of the injected signal for maximum simultaneous suppressions are obtained. Then an experiment system is established based on vector network analyzer, optimum TFR are 2.1 dB and 12.5 dB, respectively, by second harmonic and IM3 injection, and the output powers of IMD3 and IMD5 were decreased. TFR with IMD3 injection is smaller than that with second harmonic injection in STWT, and the experiment system is more straightforward and easy to operate. Thus, the IMD3 injection performs better than that of second harmonic injection to suppress IMD5s for the narrow-band STWT.