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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.

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.

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.

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.

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.

In recent years, microwave ferrite devices such as circulators, isolators and phase shifters have also been widely used in microwave and radio frequency band. Secondary electron emission (SEE) yield is one of most important parameters for multipactor in high power ferrite device. In this paper, we are presenting a system to measure SEE yield of ferrite materials at primary energies of 30eV to 3keV. According to the measurement, the decrease of secondary electron current under constant primary electron irradiation is because of surface charging. In order to minimize the impact of the surface charging, the primary electron beam had a short pulse of length 10 microseconds with a pulse interval of 1 second to release the charges on the sample. The SEE yield increased with the primary energy for low energies, then went to the maximum value 2.5 at primary electron energy of 300eV, and finally decreased for high primary energies, which is in accordance with the universal curve of SEE yield.

A dual-port tunable intermodulation (IM) generator is reported. This IM generator employs a coupling network to distribute carrier waves and IM. The proposed coupling network is constructed by cascading four parallel-coupled directional couplers, while a Schottky diode is working as a tunable IM source. By adjusting the IM performance of diode using bias voltage and distributing IM along symmetrical IM paths, a pair of tunable IM signals is introduced into passive IM (PIM) test loop simultaneously, they can serve as bidirectional IM reference in dual-port PIM measurements. The provided IM3 can be tuned to be lower than −112 dBm at $2 \times 43$ dBm at either 710 or 2550 MHz, while their dynamic IM3 range can reach about 20 dB at $2 \times 43$ dBm. The work promotes the application of IM predistortion techniques and provides a solution to realize dual-port dynamic IM calibration in PIM test.

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 Ks 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.

A significant trouble in high power microwave (HPM) systems is multipactor discharge – an avalanche of electrons resulting from the secondary electron emission (SEE). It would cause serious problems and limits the attainable power. Nano fabrication techniques, such as sputtering, photolithography, etching and Graphene, are adopted to reduce the secondary electron yield (SEY) of a material to improve multipactor discharge threshold. It is clearly demonstrated that these fabrications can suppress the SEY efficiently. The influence of surface characteristic on SEY is discussed to find that increase porosity and aspect ratio will reduce SEY. These results provided a criterion to determine nanofabrication techniques for multipactor suppression.

In this paper, a theoretical model is proposed for the evaluation of effect of secondary electron density in multipaction on the electromagnetic characteristics of microwave device. Considering the distribution zone of space electron as a plasma medium, the electromagnetic characteristics of the microwave device are theoretically related to the secondary electron density in multipaction. The coaxial waveguide is simulated using the PIC tool to validate the proposed model. The reflection signal is significantly changed due to the grown of number of electrons, which provides a physical criterion for the multipaction threshold prediction.

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.

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.

Recently, there has been increasing interest on electron irradiation-induced secondary electron emission of dielectric materials because of its important role in many fields of applied physics. For example, secondary electron emission is a key issue in Satellite antenna electrostatic discharges, which pose grave threats to the stable running of many devices such as outside spacecraft. The secondary electron emission yield (SEY) is relatively easy to measure nowadays for conductors, but troublesome for dielectric materials because of charge accumulation. In order to solve the charging problem, the pulsed method is used to measure dielectric materials. The sample is bombarded with low-electron dose to avoid the space charge effects. The samples were irradiated with a single current pulse with a duration lower than 190 ns for each primary energy and a spot size of 1 cm2 and always low current to allowing a dose lower than 106 electrons/pulse. The SEY of dielectric materials including PMMA, Kapton, Nylon, Teflon and Polyethylence has been measured as a function of the primary energy, and we have obtained the total δ max (maximum SEY), E max , and E 1 (first cross-over energy for SEY = 1) parameters.

In this paper, we propose a stochastic approach for the analytical analysis of the multicarrier multipactor discharge occurring in high-power vacuum microwave devices, in which electric flelds are not homogeneously distributed. We indicate that the statistical behavior of large amount of secondary electrons in the process of a multipactor discharge can be well described by the probabilistic random walk and Levy walk theory. Based on the derived probability density of the lateral difiusion of secondary electrons in homogeneous flelds, the multicarrier multipaction in inhomogeneous flelds can be analytically computed with signiflcantly enhanced e-ciency. As a demonstration, the accumulation of secondary electrons of a multicarrier multipaction in a rectangular waveguide supporting TE10 mode is given. The theoretical results comply well with the results achieved by the time-consuming particle simulation, the slope difierence of which is less than 0.8%, while only costs one-order less computational time. To the best of our knowledge, this is the flrst time that the probability density of the lateral difiusion of secondary electrons during a multipaction is theoretically derived. This density depicts the physical picture of the statistical movement of secondary electrons during the process of a multicarrier multipactor, which can be widely used in the areas of high-power electronics and electromagnetism.

The phenomenon of secondary electron emission is of considerable interest in areas such as particle accelerators and on-board radio frequency (RF) components. Total secondary electron yield (TSEY) is a parameter that is frequently used to describe the secondary electron emission capability of a material. It has been widely recognized that the TSEY vs. primary electron energy curve has a single-hump shape. However, the TSEY–energy curve with a double-hump shape was also observed experimentally—this anomaly still lacks explanation. In this work, we explain this anomaly with the help of a millimetre-scale (mm-scale) silver pillar array fabricated by three-dimensional (3D) printing technology. The TSEY–energy curve of this pillar array as well as its flat counterpart is obtained using sample current method. The measurement results show that for the considered primary electron energy (40–1500 eV), the pillar array can obviously suppress TSEY, and its TSEY–energy curve has an obvious double-hump shape. Through Monte Carlo simulations and electron beam spot size measurements, we successfully attribute the double-hump effect to the dependence of electron beam spot size on the primary electron energy. The observations of this work may be of help in determining the TSEY of roughened surface with characteristic surface structures comparable to electron beam spot size. It also experimentally confirms the TSEY suppression effect of pillar arrays.

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.

The secondary electron emission characteristics of the space metal material are the important parameters to determine the surface charge rate and charge balance potential of the spacecraft. And it is also an important basis for material selection, analysis and design of high power microwave components of space vehicle. In order to accurately measure the secondary electron emission characteristics of space metal materials, the Academy of Space Technology has been developing a secondary electron facility with good performance and mature technology. The multi-functional test-stand is designed and constructed to evaluate characteristics of secondary electron emission of metals in ultrahigh vacuum, such as its emission yield, its energy spectrum and XPS. At present, this facility allows working in a large energy range (between 20eV up to 30KeV), a large temperature range (down to 0°C and up to 400°C), a variety of radiation sources (electrons, photons and ions), and at high vacuum level (10−8Pa). This paper mainly introduces the measurement principles and structures of the secondary electron emission characteristics of the platform, and presents a series of typical test results on the basis of the principles and functions of the test.

Secondary electron yield suppression is of great importance for high power microwave components in satellite. Great efforts have been made to find an easy and effective way to suppress the secondary electron emission process. However, it's still a challenge. In this paper we report a new approach for secondary electron emission suppression which can realize reducing the secondary electron yield from 2.12 to 1.09. Compared with the traditional techniques, this approach makes use of graphene which is deposited by remote plasma enhanced chemical vapor deposition on the surface of the components to realize the suppression of the secondary emission. Raman spectroscopy was used to character the quality of graphene. The nano-membrane of grapheme further enhances the suppression effect and contributes little to the insertion loss of the surface. Our technique shows great potential in space applications.

It has been a big challenge that breakdown occurs due to multipactor in the high-power antenna system. A novel approach was proposed which introduced porous structure on the surface of microwave components to reduce the secondary emission yield and improve the multipactor threshold. In addition, the simulation method of multipactor was established for the analysis of microwave components with the porous surfaces, which demonstrate reduced secondary emission properties and hence the increased multipactor threshold. Secondary electron emission data of metal samples have been measured under different finishing conditions based on the biased current method. Simulation results of a microwave switch, which is an essential component of the transceiver antenna feed system, show great improvement of the multipactor threshold and match well with the experiment results.

Passive intermodulation (PIM) products are spurious frequency signals generated by nonlinear components and devices. It has an important impact on the performance of multi-carrier communication system in satellites. System performance can be severe degraded once the passive intermodulation products are also transmitted in the reception band.

It has been a big challenge that breakdown occurs due to multipactor in the high-power antenna system. When it occurs electrons deposit considerable energy in a tiny spot between metallic walls, leading to power dissipation, electrical performance degradation, surface damage and even ultimate device damages.

Large reflector antenna contains a large number of metal-insulator-metal (MIM) junctions. When illuminated by high-power microwave radiation, passive intermodulation (PIM) products may disturb satellite communication system. The general materials used for space-borne antenna are stainless steel coated with nickel, gold-plated tungsten wire, gold-plated molybdenum wire etc. This paper presents a new complex wire, produced by gold-plated molybdenum wire and polyimide fiber. Passive intermodulation risk can be reduced, due to the improvement of the thermal stability of the wire gauze. The test results show that the mechanical properties of the complex wire meet the requirement of mesh antenna.

Passive Intermodulation (PIM) becomes a serious electromagnetic interference due to the development of high-sensitivity microwave communication systems, especially large deployable mesh antennas. In this paper, a 3D geometrical model which can describe the precise metal-metal contact is established. The metal-metal contact is described by a nonlinear equivalent circuit which is regarded as PIM source. Then the contact current is scattered to far-field, and PIM value of one meter quadrate mesh sample is evaluated, which agrees with the experiment result.

Surface morphology is one of the main factor affecting the secondary electron (SE) emission from a rough metal surface. To overcome the limitation of only using the roughness to reveal the SE emission properties of a rough surface morphology, the fluctuation correlation length, which represents the spatial frequency of surface fluctuation, is thus introduced. In addition, the effects of the rough surface morphology on SE emission properties from the metal surface, which considers both the surface roughness and the fluctuation correlation length, are examined in this work. On the basis of the mechanism of electron interaction with morphology including the shading, multigeneration, and oblique effects, the SE emission properties versus the rough surface morphology, primary electron energy, and incident angle can be reasonably explained. The results further reveal the effect of surface morphology on SE emission, which gives a comprehensive insight into the control of SE emission properties using surface morphology.

In this letter, a tunable microstrip bandpass filter (BPF) with two independently adjustable transmission zeros (TZs) is reported. By introducing two microwave varactors to tune the TZs, the center frequency and the bandwidth of the BPF can be separately adjusted within a broad tuning range by varying the dc bias voltages applied to the varactors. Theoretical analysis and design approach are described. The experimental result of a demonstrative BPF shows that a less than 4 dB insertion loss, a relative bandwidth of 9% and a center frequency tunable from 1.4 to 2 GHz are obtained. The measured performance of the fabricated filter shows good agreement with the proposed theory.

A method for the improvement multipactor discharge of microwave components is described in this paper. It is a kind of surface treatments with regular micor-porous structure by the photolithography technique or irregular micro-porous structure by chemical etching process on silver plated coatings. Their influences of the micro-porous structure for secondary emission are compared. A C-band impedance transformer is used to valid multipactor discharge level by three-dimensional simulations and experimental results. Results show that this method can improve greatly the multipactor discharge of microwave components in theory and experiments.

A three-dimensional numerical simulation method of multipactor in open-structured high-power microwave systems is presented in this work. This method considering the perfect absorption of electrons at open boundaries, the commonly used absorption method with perfect-matched layers in electro-magnetic simulations has been modified and an improved absorbing boundary has been established which avoids the instability of computation. Together with the electromagnetic Particle-In-Cell technologies and the secondary electron emission models, the high-diffusion effect and the nonlinear dynamics of electrons in multipactor phenomena are intuitively investigated for the first time in open structures. As an illustration, the simulation results of a spiral antenna are provided, which reveals the transient evolution of electron accumulation in this typical open structure. By analyzing the tendency of the evolution, the multipactor threshold of the antenna has been successfully estimated.

Multipaction, caused by the secondary electron emission phenomenon, has been a challenge in space applications due to the resulting degradation of system performance as well as the reduction in the service life of high power components. In this paper we report a novel approach to realize an effective increase in the multipaction threshold by employing micro-porous surfaces. Two micro-porous structures, i.e., a regular micro-porous array fabricated by photolithography pattern processing and an irregular micro-porous array fabricated by a direct chemical etching technique, are proposed for suppressing the secondary electron yield (SEY) and multipaction in components, and the benefits are validated both theoretically and experimentally. These surface processing technologies are compatible with the metal plating process, and offer substantial flexibility and accuracy in topology design. The suppression effect is quantified for the first time through the proper fitting of the surface morphology and the corresponding secondary emission properties. Insertion losses when using these structures decrease dramatically compared with regular millimeter-scale structures on high power dielectric windows. SEY tests on samples show that the maximum yield of Ag-plated samples is reduced from 2.17 to 1.58 for directly chemical etched samples. Multipaction testing of actual C-band impedance transformers shows that the discharge thresholds of the processed components increase from 2100 W to 5500 W for photolithography pattern processing and 7200 W for direct chemical etching, respectively. Insertion losses increase from 0.13 dB to only 0.15 dB for both surface treatments in the transmission band. The experimental results agree well with the simulation results, which offers great potential in the quantitative anti-multipaction design of high power microwave components for space applications.

In this paper, the four-beam antenna made of anisotropic metamaterial is investigated. Based on the dispersion relationship of anisotropic metamaterial, we give a detailed instruction on the design of multi-beam antenna using metamaterials with proper permittivity and permeability. The radiation property and gain pattern are experimentally obtained based on an experimentally fabricated four-beam antenna, further verifying the effectiveness of design approach. This new design provides an alternative way to design the multi-beam antennas.

In this paper, based on peculiar electromagnetic characteristics of metamaterials, peculiar properties of ridge waveguide with substrates of metamaterials with zero index of refraction are analyzed. These results provide some interested insights for potential applications.

Multipactor breakdown is a serious risk in all types of high power microwave components for satellite applications. In order to suppress multipactor, a new surface treatment with low secondary electron emission yield (SEY) is developed. The silver substrate is etched by ion beam to form micro porous, then several nanometers thick amorphous carbon coating is sputtered. The SEY of both new treated surface and silver substrate are measured. The maximum SEY of treated surface is reduced by 37.1 percent compared to untreated silver substrate. Using measured SEY, the numerical simulation of multipactor threshold is calculated in Full-wave Electromagnetic Simulation Tool. The simulation result shows that the multipactor threshold of treated surface is higher than silver coating.

The conductor loss of the waveguide with rough surface is discussed in this paper. The surface morphology is characterized by roughness root-mean-square (rms), and the effect of roughness on the propagation properties equivalent to the conductivity of the conductor. Results for attenuation constant of S-band and Ku-band rectangular waveguide using the rapid estimation show that this method avoids the complex modeling process and greatly reduces the time to calculate the conductor losses when compared to numerical methods, thus it is more convenient for the engineering applications.

The C-band impedance transformer is designed using a synthesis tool FEST3D(Full-wave Electromagnetic Simulation Tool) and fabricated with good electrical performances, the central frequency is 3.95GHz, the bandwidth is 500MHz, the return loss is less than −15dB, the insert loss is less than 0.3dB. Experimental results agree well with the simulation results.

Numerical studies of low pressure discharge in the cavity component, such as impedance transformer, are discussed in this paper. The basic physics behind such a phenomenon also have been described. In the S-band impedance transformer low pressure discharge effect will take place in the pressure range of 3–8mBar. In addition, the influence of the temperature for the breakdown threshold is slight.

A theoretical model is presented for calculation of passive intermodulation(PIM) in waveguide junctions. First, the Weibull distribution, instead of Gaussian distribution, is used to simulate the roughness of interconnecting waveguide surfaces because of its capability of characterizing the rough surfaces with asymmetric distribution of asperity heights. And then, based on (1)the assumption that the only passive intermodulation source is the tunnel current flowing through the insulator film on the metal surfaces of the flanges, (2)the equivalent circuit model derived from the contact rough surfaces model, (3)the Fourier Transformation method, the passive intermodulation products of some orders have been calculated. The calculation results are in qualitative agreement with previous research and this justified its application in engineering.

In this paper, the radiation of an omni-directional line source placed in a uniaxial metamaterial slab is experimentally presented. The anisotropic slab made of metallic symmetrical rings with dispersive permeability is investigated both theoretically and experimentally. For low value of the permeability, a directive radiation at the broadside of the slab can be obtained. Due to the excitation of the leaky wave mode supported by this structure, the emitted electromagnetic wave transmits at a greater angle from the normal of the slab as the value of permeability increases along with the frequency. Thus a rainbow-like radiation will be formed since waves of different frequencies will deflect into different directions.

In this paper, we discuss the peculiar radar cross section properties of metamaterials with negative permittivity, and the connections between the radar cross section, the polarizability and the permittivity of metamaterials are investigated, respectively. These results have shown that the polarizability and radar cross section of the spherical object made of metamaterials whose permittivity is less than - 2 are much larger than conventional materials.

In this paper, based on peculiar electromagnetic characteristics of metamaterials, peculiar radar cross section properties of metamaterials with zero index of refraction are discussed. These results provide some interested insights for potential applications in radar.

Wavelet support vector machines (WSVM) using the Mexican Hat wavelet kernel has been used for nonlinear system identification successfully, but its universal approximation property has never been proved in theory. Based on the Stone-Weierstrass theorem, the universal approximation property of the WSVM to arbitrary functions on a compact set is proved with arbitrary accuracy. These simulations show that WSVM is very effective in nonlinear system identification, and can deduce the noise of the system, so WSVM has great potential applications in function estimation, nonlinear system identification, signal processing and control

Artificially designed transformation medium offers great opportunity to control the field distributions inside a waveguide. By rigorously solving Maxwell’s equations in cylindrical and rectangular waveguides, we show that filling waveguides with properly designed transformation medium with a space gradient can reduce the electric field at boundary to zero. Full-wave finite element modeling is also performed to confirm this point. This property can be used to reduce the probability of multipactor discharge at the surface of conductor inside a waveguide.