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The micro-discharge effect limits the development of high-frequency microwave power components to miniaturization and integration. Therefore, it has become a focus of research to effectively suppress the micro-discharge effect, increase the micro-discharge threshold, and strengthen the environmental stability of high-frequency microwave devices. In this study, different elemental ratios of carbon (C)/silver (Ag)/titanium (Ti) composite films were obtained by multi-target magnetron co-sputtering technology and then systematically analyzed for micro-discharge effects. When the doping ratio of C/Ag/Ti was 3.538/1/0.013, the corresponding maximum secondary electron emission coefficient (δmax) decreased to 1.01 owing to the suppression of secondary electron emission by the increase in the content of sp2 hybrid bond. The micro-discharge threshold of Ku band waveguide filters coated with moderate C/Ag/Ti composite films showed an optimal performance of 10 000−12 500 W, which was increased by approximately 20 times. Moreover, the microstructure of the composite films exhibited higher density and flatness with a tiny increase in the titanium doping ratio, representing good environmental stability. Thus, the effective suppression of the secondary electron emission yield, significant improvement in the micro-discharge threshold, and enhancement of the environment stability of microwave components could be realized simultaneously by reasonably controlling the content of titanium in silver and titanium co-doped carbon-based composite films. [ABSTRACT FROM AUTHOR]

Secondary electron (SE) yield, δ , is a very sensitive surface property. The values of δ often are not consistent for even identical materials. The influence of surface changes on the SE yield was investigated experimentally in this article. Argon ion sputtering was used to remove the contamination from the surface. Surface composition was monitored by X-ray photoelectron spectroscopy (XPS) and surface topography was scanned by scanning electron microscope (SEM) and atomic force microscope (AFM) before and after every sputtering. It was found that argon sputtering can remove contamination and roughen the surface. An “equivalent work function” is presented in this thesis to establish the relationship between SE yield and surface properties. Argon ion sputtering of 1.5keV leads to a significant increase of so called “work function” (from 3.7 eV to 6.0 eV), and a decrease of SE yield (from 2.01 to 1.54). These results provided a new insight into the influence of surface changes on the SE emission. [ABSTRACT FROM AUTHOR]

Multipactor, a frequent detrimental effect in space high power systems, can degrade the performance of space microwave components or even cause devastation. Surface coatings with a low secondary electron yield (SEY) have been verified to mitigate multipactor efficiently, and some literature indicates that titanium nitride (TiN) coating is an excellent multipactor suppressor due to its recognized low SEY, whereas so far, the theoretical analysis for interpreting secondary electron emission (SEE) characteristics of TiN coatings is scarce. In this work, we experimentally and theoretically investigate the SEE characteristics of TiN coatings. We fabricate seven TiN coatings at different N2 concentrations by RF sputtering. The microscopic analysis indicates that the nanostructured TiN coatings are more likely to be formed at low N2 concentration, inversely, the compact TiN films are more likely to be formed at high N2 concentration. The SEE measurement shows that the nanostructured TiN coatings are more efficient to trap electrons than the compact TiN films do. Furthermore, via measuring resistivity, we find a novel regularity that the variation in true SEY largely depends on the resistivity for compact TiN films. Namely, the true SEY of compact TiN films linearly decreases as their resistivity exponentially declines. Then, we establish an equation to describe the true SEY as a function of resistivity via applying the semiconductor conductivity theory to Dionne's SEE model. The equation qualitatively interprets the experimental regularity. This work presents a probability to control the SEE level of TiN coatings by adjusting resistivity and is of significance to comprehend the SEE of semiconductors. [ABSTRACT FROM AUTHOR]

In satellite remote sensing (SRS), there is a demand for large-power microwave components. A Butler matrix is essential to a transmitting antenna array in SRS. This article illustrates the electrical and mechanical design, simulation, and test results of a large-power planar beamforming network for SRS at C-band. It is a 4 × 4 Butler matrix based on square coaxial lines. Short-ended stubs are used in the Butler matrix to broaden its bandwidth by 10%, support inner conductors, and enhance heat transfer in vacuum environments. The simulation results are consistent with the measured results. The reflection coefficient is less than −18 dB, and the isolation is more than 23 dB from 3.8 GHz to 4.2 GHz. The insertion losses are less than 0.6 dB, and the phase errors are better than ±6°. The measured peak microwave power of the proposed Butler matrix is 9 kW. Its size is 440 × 400 × 40 mm3. The proposed Butler matrix beamforming network can be applied to SRS systems. [ABSTRACT FROM AUTHOR]

In nature, most of the surfaces are rough and waveguide flanges are not exception. And these surfaces topography are of high importance in the response of the waveguide flanges connection system. These surfaces topography are usually described by statistical parameters. And statistical parameters depend strongly on the resolution of the roughness‐measuring instrument, and hence the values of statistical parameters are not unique for a surface. As a result, the predictions of passive intermodulation (PIM) level of microwave devices based on these statistical parameters also may not be unique to a pair of contacting surfaces. Fortunately, fractal method is independent on the resolution of the roughness‐measuring instrument. Therefore, the randomness of the rough surface is not affected by the differences in the model. Consequently, if PIM level of rectangular waveguide is predicted with fractal parameters, the predicted value will be unique. Based on this motivation, a new model is developed. In this model, the fractal method is used to characterize the surface topography of waveguide flanges. Then, the third order PIM level of a rectangular waveguide flange is predicted. The analytic results are verified by PIM test set‐up. This work is help to understand PIM phenomenon and design the low‐PIM waveguide. [ABSTRACT FROM AUTHOR]

The micro-discharge effect is a failure mechanism that often appeared in space microwave devices under vacuum conditions, such as RF (radio frequency) cavity, RF satellite missile, and antenna launching communication system. How to control micro-discharge effectively and simply has become a research hotspot. In this paper, we have prepared a series of doping silver (Ag)/carbon (C) composite films by double target magnetron sputtering technology and have significantly reduced the maximum secondary electron emission coefficient (δmax) from 2.522 to 1.04 when the doping ratio of Ag/C is 1.345. Theoretically, the continuous increase of sp2 hybrid bond content tuned by the existing Ag nanoparticles has a greater contribution to the conductivity and inhibition of secondary electron emission in the Ag/C composite films. Meanwhile, the gradually emerged "multi-trap" surface structure with the increase of Ag doping content has further increased the collision between excited secondary electrons and free electrons, achieving an obvious inhibition effect. The results demonstrate that secondary electron emission can be suppressed effectively by tuning the structural feature of two kinds of compounded materials with low δmax. It is of great significance in physical mechanism analysis and design of the new doping process. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The novel coronavirus pneumonia triggered by COVID-19 is now raging the whole world. As a rapid and reliable killing COVID-19 method in industry, electron beam irradiation can interact with virus molecules and destroy their activity. With the unexpected appearance and quickly spreading of the virus, it is urgently necessary to figure out the mechanism of electron beam irradiation on COVID-19. In this study, we establish a virus structure and molecule model based on the detected gene sequence of Wuhan patient, and calculate irradiated electron interaction with virus atoms via a Monte Carlo simulation that track each elastic and inelastic collision of all electrons. The characteristics of irradiation damage on COVID-19, atoms' ionizations and electron energy losses are calculated and analyzed with regions. We simulate the different situations of incident electron energy for evaluating the influence of incident energy on virus damage. It is found that under the major protecting of an envelope protein layer, the inner RNA suffers the minimal damage. The damage for a ∼100-nm-diameter virus molecule is not always enhanced by irradiation energy monotonicity, for COVID-19, the irradiation electron energy of the strongest energy loss damage is 2 keV. [ABSTRACT FROM AUTHOR]

The analytical description of dielectric multipactors requires an accurate physical model. In this article, a nonstationary statistical theory for the analysis of single-surface dielectric multipactors is established by defining an emission-to-emission transition rate and involving all the probability densities related to the emitted secondary electrons. Under the same conditions, the fluctuation of electrons in the evolution process of dielectric multipactors was calculated by the proposed theory and simulated by a commercial particle simulation tool developed based on the Monte Carlo analysis. The calculated results comply well with the simulated ones. Our results also indicated that to obtain an adequate accuracy, at least two random variables, the emission velocity and zenith angle, need to be considered. [ABSTRACT FROM AUTHOR]

The aim of this article is to establish a general and practical analytical model of the one-sided multipactor on a dielectric of a metal surface and analyze the resonant multipactor effect for the recent growing interest in spacecrafts. A theoretical multipactor model involving a normal static electric field, a radio frequency (RF) electric field with both tangential and normal components, and the influence of the desorption gas is proposed. The kinetic properties and the resonant condition of the electron are studied by analytical calculations. The results show that the transit time of the electron decreases with the increase in the normal static electric field and the pressure of the desorption gas. The emission phase of the electron is the paramount factor that has a direct influence on the occurrence of the resonant multipactor. If the resonant multipactor effect could appear, the emission phase of the electron should be larger than a critical phase, and the ratio between the amplitude of the normal component of the RF electric field and the normal static electric field should be larger than a specific value as well. [ABSTRACT FROM AUTHOR]

A 2-pixel heterodyne receiver working in the 173–205-GHz band is presented in this paper. This receiver prototype is mainly composed of two balanced Schottky-based quadrature mixers and an integrated local oscillator (LO) chain. Based on sub-harmonically pumped mixing and quadrature coupling schemes, the proposed receiver operates in double sideband (DSB) mode or single sideband (SSB) mode. With combination of an external intermediate frequency (IF) 3-dB quadrature hybrid, the receiver can furtherly operate in sideband separation (2SB) mode. E-plane Riblet short-slot couplers combined with probe transitions are firstly employed in the radio frequency (RF) and LO path to realize quadrature configuration simultaneously; detailed theoretical derivation on 2SB operation is also given. The 2-pixel receiver is fabricated and tested, the measured SSB conversion loss of each channel achieves 12–20 dB when pumped with 18 dBm of input power at Ku-band, and the imbalance of conversion loss is less than 2 dB between all the IF ports. The typical sideband rejection ratio (SRR) is 12–16 dB over the operation frequency band. The corresponding achievements are valuable in the follow-up focal plane array detection system. [ABSTRACT FROM AUTHOR]

The domain structure fundamentally determines the piezoelectric/ferroelectric performance of ferroelectric materials. To understand the correlation between macro-properties and microstructure, the evolution of domain structure should be clearly figured out. Here, the diffraction-plane-transformation (DPT) model is proposed for the domain evaluation in BS-PT piezoelectric ceramics of rhombohedral crystalline structure. The transformation between different crystal planes is accurately revealed by the DPT model. Then, non-180° domain reversal in rhombohedral 0.4BiScO3–0.6PbTiO3 piezoelectric ceramics (abbreviated as BS-PT) can be quantitatively estimated, whether in electric poling or thermal depoling processes. Experimentally, the correlations between piezoelectric coefficients, electromechanical coupling properties, and non-180° domain reversal percentage are investigated. It is proven that the DPT model provides an effective method for the non-180° domain estimation in rhombohedral crystalline ceramics. [ABSTRACT FROM AUTHOR]

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 (<103 Hz). The charging balance mode method in this study can also be appropriate to the analyses of altering irradiation parameters and materials intrinsic parameters. [ABSTRACT FROM AUTHOR]

In physics, the Brewster effect initially refers to a reflectionless transmission of a transverse-magnetic wave that impinges on an interface separating two different regular media at a particular angle, known as the Brewster angle. Nowadays, people have recognized that the Brewster effect can also be observed under transverse-electric incidences such as in magnetic media. However, all Brewster effects observed so far were associated with a unique incident angle. In this work, we demonstrate a Terahertz metasurface on which the Brewster effect can be observed at all angles of incidence. The underlying physics behind this all-angle Brewster effect is the dispersion engineered at each angle of incidence to strictly match the longitudinal wave impedance on both sides of the surface. Theoretical analysis, full-wave simulation, and experimental results are consistent with each other. The proposed approach is simple but robust and scalable to other frequencies, implying promising applications such as perfect polarizers and space phase shifters. [ABSTRACT FROM AUTHOR]

One problem with current 3D printed microwave components is that they usually have more surface roughness than components manufactured with traditional machining processes. To estimate the multipactor threshold of 3D printed microwave components, it is important to evaluate the total secondary electron yield (TSEY) of the random rough surface. In this work, taking copper as an example, we conduct TSEY simulations for random rough surfaces. First, we generate both isotropic and anisotropic Gaussian type random rough surfaces; then, the dependence of the TSEY on both the roughness and correlation length is studied using Monte-Carlo simulations. Results show that when the root-mean-square roughness increases from 0 to 30 μm, the maximum TSEY increases slowly at first and then decreases rapidly. In other words, roughness can also enhance and not just suppress the TSEY. The results can be interpreted as follows: for a relatively smooth/rough surface, the TSEY enhancement/suppression induced by oblique incidence/a shadowing effect plays a dominant role. Simulation results also show that correlation length has a notable effect on the TSEY. Furthermore, for anisotropic surfaces, the azimuthal angle also influences the TSEY. Compared with currently published work, we provide an optional evaluation method for the TSEY of random rough surfaces. The predictions in this work not only confirm existing observations (the TSEY suppression effect) but also present new predictions (the TSEY enhancement effect and the azimuthal angle effect). [ABSTRACT FROM AUTHOR]

The occurrence of passive intermodulation (PIM) is inevitable in high-power microwave devices. It interferes with wireless communication and radar systems, resulting in severe deterioration of receiving performance. So far, narrowband PIM analyzers have been realized for different business bands. However, they are incapable of testing wideband systems. To solve this problem, rack-mounted analyzers piled with multiple narrowband analyzers were implemented. While such solutions significantly increase the volume, cost, and power consumption, they cannot provide a wide, continuous bandwidth for PIM localizations. Aiming to solve this problem, we propose a novel solution for realizing ultrawideband PIM analyzers. Based on the principle of cooperative radio frequency and baseband (RF-BB) nulling, we demonstrate an experimental prototype working within a continuous frequency band covering three octaves, exhibiting promising potential in PIM testing applications. [ABSTRACT FROM AUTHOR]

Local oscillator (LO) sources with sufficient output power are indispensable modules in submillimeter wave heterodyne detectors. In this work, we report on the design and characterization of a ×6×2 frequency multiplier chain that covers 176-196 GHz band. The LO chain mainly includes a W-band active times-6 frequency multiplier, a commercial W-band isolator, a W-band power module, a W-band band-pass filter (BPF) and a varactor-based G-band power-combined frequency doubler. First of all, design and performance of the W-band sextupler (×6), power module and BPF are briefly introduced. This is followed by a detailed description of the G-band frequency doubler as the key content. The final stage doubler employs two 50 μm thick quartz circuits and two commercially available varactor diodes. A circuit scheme named power-combining frequency multiplication is used for the doubler design. This circuit scheme is able to double the power handling capability of the frequency multiplier compared to the un-combined one. Therefore, the final stage doubler can fully make use of the driving power delivered by the power module to increase the output power. Each module is fabricated and assembled, and the discrete modules and the cascaded chain are measured, respectively. At room temperature, when pumped with 0 dBm at Ku-band, the LO chain produces at least 12.5 dBm in the 172-196 GHz band with a measured peak power of 16 dBm at 178 GHz. This power level is sufficient to pump a 0.36 THz heterodyne detector and makes it possible to deploy multi-pixel heterodyne imaging arrays in this frequency range. [ABSTRACT FROM AUTHOR]

Terahertz technology is one of the research fronts in the microwave society. Among many technical challenges, achieving high-power terahertz radiation has been attracting many efforts. In this paper, we investigate the possibility of power synthesis at low-end frequencies of the terahertz gap based on discrete sources. We show that by applying precision digital phase control, such a power synthesis can be achieved, overcoming the difficulty of phase alignment at these frequencies. For demonstration, we implement a 110-GHz prototype system employing solid-state impact avalanche and transit time diodes. Using a simulation- and measurement-based design methodology, the impedance matching of the designed cavity is able to be simultaneously obtained at both the RF bias and the 110-GHz frequency without using any absorbing material. Detailed design, simulation, and measurement of the prototype are introduced and the experimental results comply well with analytical expectations. Analysis shows that with increased wide digital bit width, the proposed approach is able to provide sufficient phase control precision, making it possible to be used in the power synthesis applications at low terahertz frequencies. [ABSTRACT FROM AUTHOR]

As the core technology of high‐throughput satellite payloads, multibeam antennas have received high attention and rapid development in recent years. Because of the characteristics of high gain and high beam isolation, multiaperture multibeam antennas is an important technical approach to meet the high‐performance requirements of high‐throughput satellites. This article proposes a mathematical modeling method based on the mutual coupling parameters of the reflector. This method takes capacity requirements and satellite structure design boundary conditions as input condition, and adopts an adaptive evolutionary multiobjective optimization algorithm to perform joint optimization and solution of multiple parameters, which can complete the optimization efficiently. This method does not need to perform a large number of antenna parameter simulation, reduces the number of iterations and structural layout design, greatly reduces the design cost. This article takes the demand of the AP‐6D satellite as an example, applies the above method to the multibeam antenna design of the satellite, and completes the simulation verification, structural design, physical manufacturing, and various tests of the antenna to verify the correctness of the design method. [ABSTRACT FROM AUTHOR]

The secondary electron emission (SEE) characteristics of materials is one of the issues of interest for microwave components used in space, as it has a decisive effect on the multipactor. In the presented work, the SEE characteristics of gold and silver plating widely used in microwave components is systematically investigated as a function of atmospheric exposure time for up to 400 days. The secondary electron yield (SEY) and the first energy crossover point (E 1) increase and decrease non-monotonically with exposure time for gold plating, whereas they decrease and increase non-monotonically for silver plating, respectively. The results of surface characteristics test and analysis indicate that after exposure to the atmosphere, the surface of gold plating has an adsorption layer consisting of C and O elements, which leads to an increase in SEY, while the surface of silver plating becomes rough and a microporous structure is formed on it due to natural chemical reaction, which results in a decrease in SEY. In addition, the analysis results of parallel plate model show that the multipactor voltage is reduced by up to 3 dB for gold plating and increased by up to 3 dB for silver plating after prolonged exposure to the atmosphere. • Secondary electron yield of gold plating increases non-monotonically with exposure time. • Secondary electron yield of silver plating decreases non-monotonically with exposure time. • Variation of secondary electron emission characteristics greatly affects the multipactor voltage. [ABSTRACT FROM AUTHOR]

A new electromagnetic band gap (EBG) structure based on the soft and hard surfaces for gap waveguide (GW) technology is introduced in this article. The proposed EBG structure consists of a soft surface and a hard surface in parallel with a gap between them, where the ridges/corrugations of the two surfaces are perpendicular to each other or with an angle near 90°. Compared with the contactless bed of nails EBG, the most widely used EBG structure in GW technology, the structural strength of the new EBG structure is increased significantly, which makes it very suited for high-frequency applications. Another advantage is that with the varying of the angle between the ridges/corrugations of the two surfaces, the stopband shifts in a wide frequency band, which makes the stopband tunable after the EBG is fabricated. The stopband performance of the proposed EBG is investigated. Straight and bended groove GWs (GGW) employing this new EBG are designed, manufactured and tested. The isolation performance with different columns of ridges/corrugations is also tested. The measured results show the proposed GGWs have excellent transmission performance. [ABSTRACT FROM AUTHOR]

It is known that an appropriate surface structure can suppress the secondary electron emission as a result of the receded multipactor in a spacecraft microwave component. On the other hand, the multiplier effect caused by electron re-entrance in ordinary surface structures can degrade the suppression of secondary electron emission. The present paper concerns our proposition of a new type of two-level nested microtrap structure surface able to effectively inhibit the generation of the secondary electrons inside the trap structure to achieve better suppression of the total secondary electron emission on the surface. The surface of a two-level nested microtrap array structure was obtained by lithography, stripping, dry etching, and Ag sputtering. Experimental tests were conducted on the two proposed nested structures with different sizes. The test results show that inhibition effects of the two structures have been improved by 100% and 144% compared with those of the traditional single-hole trap structure. The secondary electron yield on the bottom surface of the rough nested trap due to Ag sputtering is higher than that of the ideal regular structure simulated by Monte Carlo. In addition, the larger depth-to-width ratio of the nested trap can inhibit the multi-generation multiplication of electrons in the trap more effectively and further improve the inhibition effect on secondary electrons. For an impedance transformer, the proposed two size nested structure surface can increase the multipactor power threshold by about 346% and 386%. This method plus the nested microtrap structure can achieve a better secondary electron emission suppression effect and further improve the multipactor threshold of space microwave components. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper proposes a theoretical model for the single-surface multipactor on a dielectric. We consider the combined effects of the normal cumulative electric field, the normal and tangential radio frequency (RF) electric fields, as well as the tangential external direct current (DC) magnetic field and study the suppression effect of the tangential external DC magnetic field on the resonant multipactor. Kinetic properties of the electron and the resonant multipactor condition with no tangential external DC magnetic field are derived by analytical calculations. The flight time of the electron is analyzed profoundly by considering different values of the electron's initial energy, the amplitude ratio between the normal cumulative electric field and the normal RF electric field, and the tangential external DC magnetic field. Our results demonstrate that the tangential external DC magnetic field can decrease the flight time, and hence, the resonant multipactor can be suppressed or mitigated effectively by the tangential external DC magnetic field. The flight time of the electron shows a decreasing trend as the electron's initial energy increases, and the amplitude ratio between the normal cumulative electric field and the normal RF electric field decreases. The suppression effect of the tangential external DC magnetic field on the resonant multipactor can be much stronger when the amplitude ratio between the normal cumulative electric field and the normal RF electric field becomes larger. The resonant multipactor suppressing is also relevant to the amplitude ratio and the initial phase difference between the tangential and normal RF electric fields. [ABSTRACT FROM AUTHOR]

The Secondary Electron Yield (SEY) is one of the key factors of multipactor, which remains a serious potential risk for high power vacuum applications. In this paper, the SEY and electron dynamics at different porous medium interfaces have been analyzed numerically for multipactor simulation and suppression. Due to the existence of an RF field, accumulated charge field, and external bias magnetic field, the previous electron trajectory tracking method in porous metal surfaces is not applicable. The real electromagnetic field distributions in porous medium, including metal and dielectric, are obtained theoretically and numerically for the calculation of electron motion. Based on the Monte Carlo simulation method, a novel numerical algorithm is proposed for the SEY calculation in porous medium. Simulation results show that SEYs of the porous dielectric perforated with cylindrical pores are correctly calculated and match well with experiments. It is demonstrated that the SEY at the porous interface is not only determined by electron motions but is also affected by the geometry structures of micro-pores. Different from the metal surface, the SEY at the porous dielectric interface increases when the width-to-depth ratio of micro-pores is greater than 1. The SEY reduces only since the depth of micro-pores is larger than lateral dimensions. As the depth gets much larger than the width, the "electron trapping" effect becomes remarkable and the SEY reduces considerably, which is promising for multipactor-free design in high power applications. [ABSTRACT FROM AUTHOR]

A new kind of contactless electromagnetic bandgap (EBG) structure in the form of interdigital-pin bed of nails is introduced for the first time in this paper. It consists of two metal plates with interdigital-pin bed of nails face to face with each other, where each pin is surrounded by four pins on the other plate. The working mechanism of the interdigital-pin contactless EBG structure is suppressing the modes supported by the parallel plate waveguide (PPW) by loading interdigital pins inside the PPW. The advantage of the interdigital-pin lattice is there is a significant pin gap increase. This lattice makes the minimum pin gap that could be processed by the machining center, after assembling, reduced from the diameter of the milling clutter to its radius. It provides a way to process EBG structures at higher frequency band with the same milling cutter. The cases the pins allocated between the two plates in a random manner are also studied. Compared to its traditional counterpart, the stopband is stable with a small variation. A W-band groove gap waveguide (GGW) prototype with interdigital-pins and a Ka-band GGW with randomly allocated pins are designed, manufactured, and tested. The measured results agree well with the simulation. [ABSTRACT FROM AUTHOR]

The underlying mechanisms of multipactor between dielectric and metal and the discharge threshold of practical dielectric components have been investigated numerically and experimentally in this paper. The reduction in secondary electron yield (SEY) and the change in surface condition are achieved using the microstructure processing technology on both of ferrite dielectric and metal. Combined with the electromagnetic particle-in-cell method, the SEY model fit with the experimental data is utilized to simulate multipactor in three groups of ferrite circulators with different surface conditions. Simulation and experimental results demonstrate that the multipactor threshold of the circulator is increased by a factor of 2 through the SEY reduction on the ferrite and is increased by a factor of more than 8, from 380 W to more than 3400 W, through the SEY reduction on both of the ferrite and the metal. Different multipactor discharge mechanisms, including two-side multipactor with positive charge accumulation, singe-side multipactor with negative charge accumulation, and multipactor suppression effect, exist in circulators with the same physical structure and different surface conditions. [ABSTRACT FROM AUTHOR]

Many radio frequency measurement systems require multicarrier signals with coherent phases between carriers with different frequencies. A typical example is the signal generator which is used in multicarrier multipactor (MM) testing systems. In this paper, we propose a new approach for the generation of coherent multicarrier signals based on a state-of-the-art phase-locked loops technique. Different from existing systems that rely on a heavy use of commercial microwave instruments, this generator can be implemented with on-shelf chips and devices. As an example, an ultrahigh frequency band generator is implemented and how to implement the in-system calibration of this generator in an experimental multipactor testing system is demonstrated. Based on the proposed approach, performing a quantitative experimental research on MM becomes affordable for an ordinary microwave laboratory, which may promote the in-depth experimental study in this area. It can also be used in a wide range of applications such as MIMO and phased array systems. [ABSTRACT FROM AUTHOR]

Passive intermodulation (PIM) potentially occurs in all high-power passive microwave devices. It can severely deteriorate the receiving performance of wireless communication and radar systems. To date, the simultaneous localization of multiple PIM sources in practical microwave devices is still a technical challenge. In this paper, we indicate that if a reference PIM source can be introduced into the standard PIM testing system, and the amplitude and frequency-dependent phase difference between the reference and the real PIM products can be used to construct a k-space multicarrier signal, PIM localization algorithms for both wideband and narrowband devices can be proposed based on the inverse k-space Fourier transform and inverse optimization of the partial multicarrier signal. Simulation and experimental results validate the effectiveness of the proposed approaches. These methods can solve the difficulty of multipoint PIM localization, and can be widely used in the design, production, testing, and troubleshooting of high-power microwave systems. [ABSTRACT FROM AUTHOR]

The newly discovered “long-term” multicarrier multipactors that can be induced by low-energy electric fields potentially threatens the reliability of spaceborne microwave systems. It also causes a new technical challenge to the prediction of the global occurrence threshold of multicarrier multipactors. In this paper, we propose efficient approaches to rapidly compute the fluctuation of space electrons in the evolving process of a multicarrier multipactor, based on which Monte Carlo approaches are developed to efficiently find the global “worst case” waveforms and the occurrence thresholds for both “single-event” and “long-term” multipactors. The proposed approaches can be used for wideband devices, providing an efficient integrated solution for the multicarrier multipactor analysis for practical high-power microwave devices with inhomogeneous field distribution. [ABSTRACT FROM PUBLISHER]

Passive intermodulation (PIM) is one of the major reliability problems in microwave communication systems. In this paper, the PIM interference generated by the metal–insulator–metal (MIM) contact nonlinearity was analytically modeled and experimentally verified. The pressure-dependent nonlinear $I$ – $V$ equations of the MIM contact were derived based on electrical contact theory and verified using a manufactured MIM contact structure. Then a point source model for the PIM product based on the metallic contact nonlinearity was proposed. The PIM product is mainly determined by the contact resistance, surface current density, and nonlinear current coefficient from the model, and in the small contact resistance region, the PIM level decreasing rates are 60, 60, and 20 dB/decade by decreasing the contact resistance, surface current density, and the nonlinear current coefficient, respectively. A designated PIM current source was utilized to verify the relationship. In the end, the PIM equation for the rectangular waveguide connection was derived based on the point source model. This model will provide guidance on low PIM system design. [ABSTRACT FROM PUBLISHER]

• Ordered monolayer silver nano-bowl coatings prepared by an electrodeposition method. • Coating structure modulated by altering the deposition time and template diameter. Multipactor leads to the unrepairable damage to high-power microwave devices in the satellite. Restraining the secondary electron yield (SEY) is an effective method to suppress the multipactor of microwave devices. In this work, silver nano-bowl coating was fabricated via electrodeposition in AgNO 3 electrolyte at room temperature on the surface of silver-plated aluminum alloy using the monolayer colloidal crystal of polystyrene (PS) spheres as templates. The scanning electron microscope images show that the surface structure of the silver-plated aluminum alloy sample could be modulated by altering the deposition time and adjusting the size of the PS spheres. And the pore diameter and the aspect ratio of the nano-bowl have a great influence on the SEY of the silver nano-bowl coating. When the size of the PS spheres is 2000 nm and the electrochemical deposition time is 90 min, the maximum value of SEY value of silver nano-bowl coating drastically decreases by 39.3% from 2.44 to 1.48, compared with that of the initial silver aluminum alloy samples. The silver nano-bowl coating shows great multipactor suppression for potential application in a satellite. [ABSTRACT FROM AUTHOR]

• The influence of adsorption of N 2 , O 2 , Ar and air for Ar ion sputtered Cu on the secondary electron emission were researched experimentally. • Different effects of heat treatment on between Ar ion sputtered sample and gas adsorption sample were confirmed. • The relative contents of C and O with different treatment were analyzed by in-situ XPS. • The relationship between the secondary electron yield and secondary electron spectrum was theoretical derivation and experimental validated. Secondary electron (SE) emission is a superficial physical phenomenon. The range of SEs excited in materials which are finally emitted from the surface is generally within a few tens of nanometers. SE emission from materials by electron irradiation has great dependence on surface quality, such as gas adsorption, oxidation, contamination, and morphology. In this paper, the influence of surface adsorption of N 2 , O 2 , Ar and air on SE yield (SEY) and the SE spectrum (SES) of copper was investigated by experiment. The measured SEY and SES were compared before and after the copper surface was sputtered by Ar ions. The results show that gas adsorption could increase SEY, and air adsorption lead to the maximum increase, Ar adsorption the minimum. Meanwhile, the relationship between the SES and the SEY was deduced and validated by the experiment. It was also found in the experiment that the Ar ion sputtering or heating alone can effectively reduce the SEY, while heating the sample after Ar ion sputtering increases SEY. The reasons for the variation of the SEYs with gas adsorption, sputtering and heating are preliminarily explained with the help of in-situ XPS. Accordingly, the research helps to further reveal the mechanism of SEE influenced by complex superficial factors. [ABSTRACT FROM AUTHOR]

• Secondary electron yield of inert metals increases with exposure time. • Surface adsorption layer consisting of carbon and oxygen elements results in the increase. • A two-layers secondary electron yield model is established and parameters of adsorption layer are obtained. • The increase of secondary electron yield can significantly reduce the multipactor threshold. The secondary electron emission (SEE) property of materials is closely related to the multipactor, which is one of the potential risk factors affecting the reliability of high power microwave components for space application. In the presented work, the influence of atmospheric exposure on the secondary electron yield (SEY) of the inert metal is investigated. It is found that the SEY increases gradually with exposing time, and the increase in SEY results from the surface adsorption layer consisting of carbon and oxygen elements. A two-layers SEY model is established to explain this evolution and obtain the corresponding parameters of the adsorption layer. Simulation on a C band impedance transformer shows that 45 days of exposure will result in a 7.5 dB decrease of multipactor threshold. [ABSTRACT FROM AUTHOR]

• Surface engineered Ag/Al substrates by carbon coating for space microwave devices. • K s factor is extracted from the angular-dependent SEY coefficient measurement by using the Vaughan model. • Low-cost, easy-to-scale process is provided to reduce the SEY coefficient by 35%. High power microwave devices have been suffering from secondary electron yield (SEY), which occurs at the surface and leads to increases in energy dissipate and noise level in microwave cavities. The suppression of SEY in microwave materials is significant for space applications. In this work, we report a surface roughness evolution mechanism induced by carbon coating on a widely-used microwave cavity material Ag/Al. The competition between the preferred growth and the island growth modes leads to the roughness enhancement in the 60 nm carbon coated Ag/Al substrates. By extracting the smooth factor K s in Vaughan model from the angular dependent SEY measurement, we attribute the suppression of SEY to the intrinsic low SEY of the carbon film and the high surface roughness. Our work demonstrates a low-cost, easy-to-scale coating process to effectively prevent the formation of secondary electron avalanche in space borne microwave devices. [ABSTRACT FROM AUTHOR]

In this work, fluorocarbon film was deposited on silicon (P/100) substrate using polytetrafluoroethylene (PTFE) as target material at elevated sputtering temperature. Field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed to investigate the surface morphology as well as structural and chemical compositions of the deposited film. The surface energy, as well as the polar and dispersion components, were determined by water contact angle (WCA) measurement. The experimental results indicated that increasing sputtering temperature effectively led to higher deposition rate, surface roughness and WCA of the film. It was found that the elevated temperature contributed to increasing saturated components (e.g., C–F2 and C–F3) and decreasing unsaturated components (e.g., C–C and C–CF), thus enhancing the fluorine-to-carbon (F/C) ratio. The results are expected aid in tailoring the design of fluorocarbon films for physicochemical properties. [ABSTRACT FROM AUTHOR]

Porous Ag/TiO2/Au coatings with excellent multipactor suppression were prepared by fabrication of porous Ag surface through two-step wet chemical etching, synthesis of TiO2 coatings by electroless-plating-like solution deposition and deposition of Au coatings via electroless plating. Porous structure of Ag surface, TiO2 coatings on porous Ag surface and Au coatings on porous Ag/TiO2 surface were verified by field-emission scanning electron microscopy, the composition and crystal type of TiO2 coatings was characterized by X-ray photoelectron spectroscopy and X-ray diffraction. Secondary electron yield (SEY) measurement was used to monitor the SEY coefficient of the porous Ag coatings and Ag/TiO2/Au coatings. The as-obtained porous Ag coatings were proved exhibiting low SEY below 1.2, and the process was highly reproducible. In addition, the porous Ag/TiO2/Au coatings showed excellent multipactor suppression with the SEY 1.23 and good environmental stability. It is worth mentioning that the whole preparation process is simple and feasible, which would provide a promising application in RF devices. [ABSTRACT FROM AUTHOR]