This study proposes a method for suppressing the multipactor effect in high-power microwave devices for spacecraft applications by integrating dielectric materials. Electromagnetic fields are numerically analyzed using the CST Microwave Studio, while multipactor thresholds are accurately predicted via an in-house developed 3-D particle-in-cell (PIC) simulation code. A systematic investigation is conducted to examine how the geometric parameters and material properties of dielectric influence multipactor. Simulation results show that when the dielectric width matches that of a parallel-plate or rectangular waveguide, increasing both the thickness and relative permittivity enhances the amplitude of the radio frequency (RF) electric field, accompanied by a decrease in the multipactor threshold. Conversely, when the dielectric width is smaller than the waveguide, the RF electric field amplitude decreases, leading to an increase in the multipactor threshold. Notably, partially filled dielectric can reduce the RF electric field amplitude by up to 90%, and improve the threshold by as much as 40 times compared to unfilled dielectric. These findings provide critical design insights for high-power microwave components in space applications.

Surface charging and electrostatic discharge are prone to occur in space environments. Here, to evaluate the effect of surface charging on the dielectric of an electronic device, we take a microstrip antenna as an example to study its charge and discharge characteristics by modulating the surface total electron emission yield (TEEY). Through theoretical calculations, it is revealed that the secondary critical energy, EP2, significantly influences the surface potential. The surface negative potential may reach very high level when the difference between EP2 and the incident electron energy is large. To modulate TEEY, MgO and Al2O3 films were deposited on the surface of the original antenna. The results show that the EP2 value increased from 3 keV to 6.6 keV for the antenna coated with MgO, and 5.7 keV for the antenna coated with Al2O3. The discharging tests show that after 70 s irradiation with a 30 keV electron beam and 0.3 mu A beam current, the antennas coated with MgO and Al2O3 films did not exhibit any discharge phenomenon, indicating the discharge threshold was significantly improved. Additionally, the S-parameter tests indicate that the changes in S-parameters are minimal both after coating functional films and before and after irradiation.

With the phase-to-phase cross-correlation method, we analyzed the single pulses of PSR B0950+08 obtained at the Five-hundred-meter Aperture Spherical radio Telescope. The correlation map produced with the single pulses reveals a modulation of the correlation coefficients, which are between the intensities at different phases of the single pulses. The modulation varies by a period of two phase bins with 2048 bins over the whole pulse phase. Such a modulation is related to the microstructures of the single pulses and may ultimately imply that the Lorentz factors of the charged particles in the pulsar magnetosphere are highly similar along the line of sight trajectory. The modulation rule reverses after a constant phase separation of 191 . ° 43 . It also reverses around the peak phase of the mean pulse profile, implying that the Lorentz factors are different from the normal value around the reversal phase. According to the analyses with the correlation map, we propose that the bridge emission between the main pulse (MP) and its preceding interpulse (IP) is the overlap of the MP and the IP. For the “weak emission” trailing the MP, it is identified as an independent profile component. There are strong emissions from the IP but no giant pulse from the MP during this observation. The correlation between the IPs and the MPs is mainly dominated by the positive correlations between the subcomponents of the IP and one subcomponent of the MP, according to our analyses.

This study investigates a novel dynamic balance mechanism of multipactor effect in a dielectric-loaded parallel-plate waveguide. A self-developed one-dimensional electrostatic particle-in-cell code was employed, considering both radio frequency electric fields and surface charge fields resulting from accumulated charge on dielectric surface. The multipactor evolution was analyzed for three dielectric materials in both single-sided and double-sided dielectric-loaded configurations. Key parameters, including net emitted electron numbers, average secondary electron yield, and the proportion of single-sided and double-sided impacts on both the metal and dielectric surface were systematically examined. The results demonstrate that multipactor saturation occurs in the absence of space charge fields, with the operational voltage range of the single-sided dielectric-loaded model being narrower than that of the double-sided dielectric-loaded model. This suggests that the single-sided dielectric-loaded model is more effective in improving the multipactor threshold. When the first crossover point of the dielectric is below that of the metal, the operational voltage resides near the upper boundary of the multiplication region; conversely, when the dielectric's first crossover point exceeds the metal's, the voltage stabilizes near the mid-region. Notably, in the single-sided dielectric-loaded model, the average secondary electron yield trend on metallic and dielectric surfaces inversely correlates with the self-extinguishing case (without space charge fields) at low voltages. The proposed model exhibits enhanced computational efficiency and aligns with practical scenarios where surface charges dominate over space charges, such as multipactor processes on pre-charged dielectric surfaces.

With the continuous increase in power capacity of spacecraft radio frequency payloads, low-pressure discharge effects have become a significant factor threatening the safe operation of spacecraft payloads. Clarifying the low-pressure discharge effects and their plasma evolution mechanisms is of great importance for elucidating the underlying discharge processes and proposing effective preventive measures. Based on the characteristics of the actual operating environment of spacecraft microwave payloads, this paper proposes a global simulation model for low-pressure discharge plasma in humid air. The validity of the model was verified through online diagnostic experiments on low-pressure discharge plasma. Using the constructed global plasma model, the influence of key parameters such as pressure and humidity on electron and ion densities in the plasma was investigated, revealing the impact mechanisms of initial discharge conditions on plasma characteristics. The potential hazards of these factors to spacecraft microwave payloads were also discussed. This model provides a foundation for improving the accurate prediction of key parameters in low-pressure discharge.

The gas desorbed from the dielectric surface has a great influence on the characteristics of microwave breakdown on the vacuum side of the dielectric window. In this paper, the dielectric surface breakdown is described by using the electromagnetic particle-in-cell-Monte Carlo collision (PIC-MCC) model. The process of desorption of gas and its influence on the breakdown characteristics are studied. The simulation results show that, due to the accumulation of desorbed gas, the pressure near the dielectric surface increases in time, and the breakdown mechanism transitions from secondary electron multipactor to collision ionization. More and more electrons generated by collision ionization drift to the dielectric surface, so that the amplitude of self-organized normal electric field increases in time and sometimes points to the dielectric surface. Nevertheless, the number of secondary electrons emitted in each microwave cycle is approximately equal to the number of primary electrons. In the early and middle stages of breakdown, the attenuation of the microwave electric field near the dielectric surface is very small. However, the collision ionization causes a sharp increase in the number density of electrons, and the microwave electric field decays rapidly in the later stage of breakdown. Compared with the electromagnetic PIC-MCC simulation results, the mean energy and number of electrons obtained by the electrostatic PIC-MCC model are overestimated in the later stage of breakdown because it does not take into account the attenuation of microwave electric field. The pressure of the desorbed gas predicted by the electromagnetic PIC-MCC model is close to the measured value, when the number of gas atoms desorbed by an incident electron is taken as 0.4.

The inspiring technological progress and turbulent military reforms have made high-power microwave (HPM) weapons a hot issue in the world today. As a modern technology integrating soft and hard killing, HPM weapons have always been called a new method to change the rules of the world war. The microwave energy emitted by HPM weapons irradiates the target with extremely high intensity. The expected function of the command system cannot be realized normally. In recent years, HPM weapons have gradually extended from traditional land, sea, and air to space. The significance of developing HPM is self-evident. In this article, the classification and generation of HPM are briefly reviewed. Several ways to realize HPM detection in a strong electromagnetic environment are discussed. Finally, the development of HPM technology in the future is forecast according to related contents.

The common faults encountered during the operation and maintenance of the Fuxing train sets are summarized and classified into refrigeration faults, ventilation faults, control and power supply faults, and heating faults. Through the analysis of the composition and working principle of the air conditioning system of the train set, the causes of these failures are summarized, and corresponding treatment methods are proposed for different types of failures to provide important reference for the daily operation and maintenance of the air conditioning system of the Fuxing train set and emergency disposal.

Due to its potential harm to space payload, microwave corona breakdown of microstrip circuits has attracted much attention. This work describes an efficient way to suppress corona breakdown. Since the corona breakdown threshold is determined by the highest electric field intensity at the surface of microstrip circuits, lacquer coating with a thickness of tens of microns is sprayed on top of microstrip circuits. The applied dielectric coating is used to move the discharge location away from the circuit’s surface, which is equivalent to reducing the highest electric field intensity on the interface of solid/air of the circuit and thus results in a higher breakdown threshold. Two designs of a classic coupled-line bandpass filter were used for verification. Corona experimental results at 2.5 GHz show that in the low-pressure range of interest (100 to 4500 Pa), a 5.3 dB improvement of the microwave corona breakdown threshold can be achieved for a filter with a narrowest gap of 0.2 mm, while its electrical performances like insertion loss and Q-factor are still acceptable. A threshold improvement prediction method is also presented and validated.

The secondary electron multipactor on the inner surface of the output window is one of the main factors limiting the power capacity of high power microwave. Therefore, it is of great significance to carry out relevant research. In this work, the process of secondary electron multipactor and the resulting loss of power are numerically simulated by using the electromagnetic particle model with one-dimensional spatial distribution and three-dimensional velocity distribution at the microwave frequency of 110 GHz. The influences of microwave electric field at the surface and dielectric material type on the power loss are studied. The simulation results show that the electron number density is higher than the critical cut-off number density after the secondary electron multipactor has reached the steady state, but the microwave electric field does not show obvious change. This is because the electrons in a very high electrostatic field are mainly concentrated in the domain of several micrometers near the dielectric surface, which is far less than the corresponding skin depth. The electron number density in the multipactor steady state increases with the microwave electric field increasing, but the ratio of the power loss to the microwave power at the surface increases slowly. After the multipactor reaches the steady state, the number density of electrons near the sapphire surface is the highest, followed by the number density near the crystal quartz surface, and the number density near the fused quartz surface is the lowest, so the corresponding power loss decreases successively. In order to verify the accuracy of the model, the simulated value of the multipactor threshold is compared with the experimental data, and the difference between them is discussed.

This article presents a study of the multipactor effect in a double-sided dielectric-loaded parallel-plate waveguide. To this end, a 1-D electrostatic particle-in-cell model is established, which considers the radio frequency electric fields, space charge fields, and surface charge fields generated by the accumulated charge on the dielectric surface. The dynamic evolution of multipactor breakdown for different operating voltages and dielectric materials with different secondary electron yield (SEY) properties is investigated by numerical calculation. The results obtained show that multipactor does occur self-extinguishing phenomenon due to the presence of the surface charge fields under certain circumstances in the double-sided dielectric-loaded parallel-plate waveguide. Moreover, a comparative study of multipactor between metal, single-sided, and double-sided dielectric-loaded parallel-plate waveguides is carried out. The simulation results show that the self-extinguishing time of the multipactor in the double-sided dielectric-loaded model is less than that in the single-sided dielectric-loaded model. Finally, a multipactor susceptibility diagram for the SEY curve of different bottom dielectric materials in the parallel-plate waveguide is constructed. The results show that the single-sided dielectric-loaded microwave components are more beneficial to suppress the multipactor effect. The results reported in this study can be used to guide the design of space high-power microwave components.

The third chapter of this book is Passive Intermodulation Analysis and Evaluation Techniques for Microwave Components, written by Rui Wang and Bai He. This chapter first introduces the concept and main difficulties of PIM numerical analysis. The nonlinear analysis methods used for the numerical analysis of PIM are introduced in detail. The methods and results of the multiphysics field coupling analysis of passive intermodulation for microwave components are described. On the basis of solving the multiscale electromagnetic calculation, the evaluation method of the passive intermodulation field-path combination analysis of microwave components is discussed, and the numerical analysis is carried out with the waveguide flange as an example. Finally, the multiscale equivalent analysis and cosimulation method of the mesh antenna are described.

The aim of this paper is to establish a numerical simulation model for the multipactor effect in a partially dielectric-loaded parallel-plate waveguide, with a focus on the investigation of multipactor saturation mechanisms for different dielectric materials with different secondary emission yield (SEY) properties. An electrostatic method involving the radio-frequency fields, space charge fields, and the dynamics of charge accumulation on the dielectric surface and solutions for electrostatic fields are proposed. The evolution of the electron number, accumulated charge, and secondary electron multiplication rate for different input voltages and SEY properties of the dielectric materials are studied using numerical calculations. The results show that two physical multipactor phenomena occur in a dielectric-loaded parallel-plate waveguide: a self-sustaining phenomenon, which means that the electron population reaches a saturation level, and a self-extinguishing phenomenon. The latter can be divided into two cases: in one, the number of electrons undergoes a process of multiplication, saturation, and reduction, and in the other, the number of electrons disappears after their population reaches a maximum. Furthermore, a multipactor susceptibility diagram for SEY curves of different dielectric materials is constructed. The results show that the multipactor effect is suppressed when the maximum of the SEY curve is less than 1.3.

The interaction between high-power microwave and dielectric surface discharge in vacuum and low-pressure gas is investigated by using an electromagnetic particle-in-cell–Monte Carlo collision model. Maxwell equations are solved by the finite-difference time-domain method combined with the boundary condition between the total and scattered field. The simulation results show that the transmission power loss is small and mainly attributed to the absorption of surface discharge, when the secondary electron multipactor reaches a steady state in vacuum. The simulated value of transmission power loss in vacuum is in good agreement with the experimental data. At a low pressure, the multipactor is the main source of electrons in the initial stage of discharge. After the multipactor reaches a steady state, the ionization leads to a significant increase in the number density of plasma near the dielectric surface. The absorbed power of plasma is greater than the reflected power in the initial stage of discharge, but with the increase of time, the latter becomes larger and even close to the power of incident wave. As the pressure increases, the transmission power decays faster due to the increase of ionization rate. When the microwave field near the dielectric surface decays significantly at a low pressure, the steady state of multipactor disappears, and the peak of plasma number density is near the surface, but not closest to the surface.

This article concentrates on the high-power microwave (HPM) breakdown process and behaviors in air-filled rectangular waveguide under the external dc magnetic field. To solve the persuasive issue, a three-dimensional (3-D) multiphysics model coupling full-wave Maxwell's equations with plasma fluid equations is established and solved by the spectral-element time-domain (SETD) method. In our simulation, the Galerkin's method is employed for the space discretization and the central difference scheme is used for the temporal discretization during the SETD process. The numerical results reveal that the external dc magnetic field applied in breakdown volume can significantly enhance the breakdown threshold to suppress the HPM breakdown, which is beneficial for the propagation of HPM pulse in air-filled waveguide. Our research provides theoretical guidance for suppressing the impact of HPM breakdown for HPM devices protection.

Based on the rough surface topography with fractal parameters and the Monte–Carlo simulation method for secondary electron emission properties, we analyze the secondary electron yield (SEY) of a metal with rough surface topography. The results show that when the characteristic length scale of the surface, G, is larger than 1 × 10−7, the surface roughness increases with the increasing fractal dimension D. When the surface roughness becomes larger, it is difficult for entered electrons to escape surface. As a result, more electrons are collected and then SEY decreases. When G is less than 1 × 10−7, the effect of the surface topography can be ignored, and the SEY almost has no change as the dimension D increases. Then, the multipactor thresholds of a C-band rectangular impedance transfer and an ultrahigh-frequency-band coaxial impedance transfer are predicted by the relationship between the SEY and the fractal parameters. It is verified that for practical microwave devices, the larger the parameter G is, the higher the multipactor threshold is. Also, the larger the value of D, the higher the multipactor threshold.

Charging effects of dielectric due to space electron beam irradiation have a huge impact on spacecraft. To understand charging equilibrium characteristics of dielectric under electron beam irradiation, in this paper, we present a novel numerical simulation method for analyzing the secondary electron yield (SEY) based on a charging balance mode. We used the Mott scattering model and the Penn dielectric function (PDF) model to calculate the collisions between incident electrons and material the atoms of material. For internal charge transport, we considered the processes of drift, diffusion, trapping, and neutralization. These were calculated with a finite-difference time-domain (FDTD) method. Based on mechanisms of import-export dynamic charge evolution, charging balance can be categorized into three modes: SE mode, leakage (LE) mode, and cooperation (CO) mode (a combination of the two). In most situations, the SE mode corresponds to the surface charging state, while the LE mode always corresponds to deep charging states. Shortening the distance of free charge transport, a thinner sample is more likely to present as LE mode. Although the surface potential can be enhanced by monotonously increasing the thickness, the total internal charge quantity approaches a local maximum with thickness because of a charging balance mode transformation. In addition, with a larger average density of carriers in the LE mode, the material conductivity is enhanced and the dielectric loss tends to be larger at low frequencies (<10(3) Hz). The charging balance mode method in this study can also be appropriate to the analyses of altering irradiation parameters and materials intrinsic parameters.

Based on the theory of high frequency breakdown calculation, this paper studies the calculation method of ionization breakdown threshold of ridge waveguide filter under the action of RF field. By comparing with the experimental measurements, the accuracy of the theoretical analysis method of the ionization breakdown of the typical ridge waveguide filter structure is proved. At the same time, the low-pressure ionization breakdown thresholds of different air pressures, structural gaps and working frequencies were calculated, and the action law of each influencing factor was analyzed, and the relationship between breakdown position and electric field distribution was clarified.

Due to the poor conductivity of the dielectrics, if an electron collides with the dielectric material, a charge will be deposited on the surface as a consequence of the secondary electron emission. Thus, the multipactor process in dielectric-loaded microwave devices differs from those in metallic devices. The objective of this paper is to study the self- extinguishing physical mechanism of the multipactor in parallel-plate transmission lines partially filled with dielectric layers by particle-in-cell simulation. The self-consistent field generated by the electrons in the simulation is assumed to be neglected, since there do not exist too many electrons in the self-extinguishing process. To illustrate the self- extinguishing phenomenon in a dielectric-loaded waveguide device, the strength of electric field in the vacuum area needs to be the same as that in a metallic device. When the input power is slightly higher than the multipactor threshold, the self-extinguishing phenomenon occurs after the initial electron multiplication while the number of electrons increases exponentially with the simulation duration in metallic device. Based on this fact, the physical mechanism of self-extinguishing phenomenon is investigated in detail. By analyzing the temporal evolution of the electrons and the average secondary electron yield (SEY), it can be concluded that the self-extinguishing phenomenon is caused by the electrostatic field generated by the charges deposited on the surface of the dielectric. Moreover, the average SEY of the dielectric tends to be one or greater than one when the number of electrons drops to nearly zero. Hence, it is necessary to further analyze the ability to continue accumulating charges on the dielectric surface when extra electrons are injected into the simulation region at the instant when the number of electrons is close to zero. For the former case, the charges deposited on the dielectric surface remain steady all along, while the charges reach to a stable state eventually as the number of injected electrons increases for the latter one. Both of them mean that the average SEY of the dielectric surface will be unity in the end. Since the electrostatic field generated by the charge deposited on the dielectric surface can reduce the risk of occurrence of multipactor, the electret material could be used in the design of the dielectric-loaded microwave devices to improve the multipactor threshold.