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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.

This letter proposed a combined susceptibility diagram, applicable to investigating and differentiating the inherent mechanism of multipactor in dielectric-loaded microwave devices. This susceptibility diagram consists of average secondary emission yield on the dielectric surface and both the surfaces. Using this diagram, we predict the electron multiplication mechanism in the partially dielectric-loaded parallel-plate waveguide. It is found that the multipactor extinguishing only occurs for a low multipaction rate, while the saturation occurs for a higher multipaction rate. To verify its validity, the dynamic evolution of multipactor is investigated by electrostatic particle-in-cell. A good agreement between simulations and prediction results has been achieved. This susceptibility diagram thus constructed can provide a guidance to clearly identify the condition for multipactor extinguishing or saturation.

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.

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.

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.

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.

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 (

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.

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.

This paper presents a novel passive intermodulation (PIM) prediction method considering random contact behavior using a Monte Carlo method for a coaxial connector. A smart contact model for a contact unit at a microcosmic level is proposed. Using Monte Carlo approximation and micromeasurements, different random distributed contact samples for different contact components inside the coaxial connector are reconstructed. In the experiment, PIM on inner and outer conductor was tested and compared with predication. A good agreement proves the proposed PIM prediction method is efficient. Rather than generating a single PIM prediction value, this method will give a PIM confidence interval for all the potential PIM values considering the contact force statistical behavior. The work will help analyze fluctuated PIM on coaxial connectors and inspire a new method to predict PIM risk.

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.

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.

Reducing the secondary electron yield (SEY) of Ag-plated aluminum alloy is important for high-power microwave components. In this work, Cu doped carbon films are prepared and the secondary electron emission characteristics are studied systematically. The secondary electron coefficient δ max of carbon films increases with the Cu contents increasing at first, and then decreases to 1.53 at a high doping ratio of 0.645. From the viewpoint of surface structure, the higher the content of Cu is, the rougher the surface is, since more cluster particles appear on the surface due to the small solid solubility of Cu in the amorphous carbon network. However, from viewpoint of the electronic structure, the reduction of the sp2 hybrid bonds will increase the SEY effect as the content of Cu increases, due to the decreasing probability of collision with free electrons. Thus, the two mechanisms would compete and coexist to affect the SEY characteristics in Cu doped carbon films.

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 N2, O2, 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.

Passive intermodulation (PIM) measurement is necessary for microwave and antenna products to evaluate their PIM performance. To achieve stable low residual PIM level of measurement system and make accurate PIM test, a compact waveguide flange adapter is proposed based on gap waveguide, dielectric filled bed of nails is adopted to construct compact double-sided artificial magnetic conductor (AMC) structure. When the adapter is connected between standard waveguide flanges, double-sided contactless electromagnetic band gap (EBG) structure with air gap is formed inside the flange connection. Electromagnetic leakage is prevented by stop band of the EBG structure. Meanwhile, metallic contact nonlinearity is almost eliminated by the contactless structure, and PIM can be therefore suppressed. A Ku band prototype of the adapter is designed for a Ku band PIM measurement system. By using the adapter, the system’s residual PIM is significantly improved with a maximum improvement better than 30 dB, achieving a stable low level.

To reduce the size of traditional waveguide flange, a solution of pluggable flangeless waveguide connection is proposed. Artificial magnetic conductor (AMC) structure is designed surrounding the outer surface of a size-reduced end of a waveguide, called part-A. Another waveguide with stepped transition to an enlarged end is part-B, the inner surface of the enlarged end works as PEC surface. When Part-A is inserted into part-B, a tight flangeless waveguide connection is achieved under proper size conditions. Tiny air gap exists between the PEC and AMC surface, the electromagnetic leakage from the air gap is prevented by band gap of the EBG structure formed by PEC and AMC surface. A Ku-band prototype of the flangeless connection is designed and manufactured, the measured insertion and return loss are better than 0.06dB and 20dB respectively over 10GHz to 15GHz. The sectional size decreases by more than 70% comparing with traditional waveguide flange.

The “long-term” multicarrier multipactor that is supposed to be stimulated by lower-power electric fields potentially threatens the safety of spaceborne microwave devices. In this paper, the instantaneous fluctuations of space electrons between the successive envelope periods of multicarrier signals with different carrier configurations are investigated based on particle-in-cell (PIC) simulations. The “long-term” multipactor discharge (LMD) is observed in a coaxial waveguide device for all the four chosen carriers with a 10-MHz frequency gap. Based on the LMD threshold power for each carrier, the equivalent P20 power is obtained using the ESA's Multipactor Calculator (MC) for the in-phase circumstance. Using a well know test case with known single carrier breakdown threshold, multicarrier multipactor design based on the P20 only for in-phase distribution would be dangerous for five and six carrier sets, while over conservative for three and four carrier sets.

In spite of recent rapid development of flexible electronics, voltage-tunable spintronic structures and devices on flexible substrates have been rarely studied. Here, voltage control of magnetic anisotropy (VCMA) is demonstrated via ionic gel (IG) gating on flexible polyimide substrates with a circuit operating voltage of 1.8 V. A reversible, nonvolatile VCMA switching of 114 Oe is achieved in Pt/Fe/Pt multilayer, where the spatial magnetic anisotropy distribution is determined quantitatively by electron spin resonance technique. This IG gating process is repeatable as the substrates are under different bending conditions. The voltage modulation of magnetic anisotropy through IG gating with excellent flexibility proposes potential applications in low-power wearable spintronic devices.

Dielectric antenna with a smaller size and numerous advantage is hardly applied in spacecraft due to complicated charging effects under electrons irradiation in space. And it is also difficult for researchers to obtain radiation properties of dielectric antenna under electron beam irradiation in experiment. In this paper, we investigate dielectric properties and characteristics of radiation and transmission under charging effects due to electrons irradiation via a numerical simulation. For simulating electrons irradiation in space more realistically, the primary electron (PE) energy is set to be multienergentic basing on the Geostationary Earth Orbit. The scattering process between PE and material atom includes elastic and inelastic scattering, while the transport process of internal charges consists of drift, diffusion, trapping, and neutralization. Performing less power loss and higher radiant efficiency, dielectric resonator antenna (DRA) is selected as the applied research object under E-beam irradiation induced charging effects. It is found that the evolution of internal charges is dominated with accumulation first, and then act in a main form of transporting toward depth with an invariant peak. The dielectric constant increases under the force of internal built E-field in ranges of internal charges. Under the continuous E-beam irradiation, the S(1, 1) curve of DRA shifts toward low frequency, and its bandwidth becomes wider. The numerical simulation method and presented results in this paper can offer a comprehensive insight into researches and developments on dielectric antenna in space.

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.

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.

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.

Contact nonlinearity is one of the primary sources of passive intermodulation (PIM). Common methods to eliminate the contact nonlinearity are focused on improving the electrical contact. In this letter, the contactless waveguide flange (CWF) based on gap waveguide technology is first applied to solve the PIM problem caused by waveguide connection. A compact folded CWF is proposed for low-frequency applications. The artificial magnetic conductor plate, in the form of a bed of nails, is arranged surrounding the outer surface of the male flange, whereas a waveguide with broader hollow end serves as the female flange. The size of the proposed contactless flange is significantly reduced compared to its planer counterpart. An S-band prototype is designed, manufactured, and measured. Compared to traditional waveguide flange, the measured PIM level achieves a maximum improvement of 30 dB, which is almost unaffected by surface plating materials and connection pressure.