Broadband electromagnetic absorber with ferrite/ferrite hybridstructure

A new broadband electromagnetic absorber has been constructed by using the NiZn/NiZn ferrite hybrid structure and analysed using the FEM (finite element method). The structure is only 55.5 mm high, and has a reflection loss of <-20 dB in the frequency range 30 MHz-3 GHz. These characteristics are superior to those of conventional absorbers which have been used in anechoic chambers     

Electromagnetic wave absorbing characteristics of Ni-Zn ferritegrid absorber

The reflection loss of Ni-Zn ferrite grid absorber is studied in the low frequency limit which the period of the array is small compared with wavelength. The relative equivalent complex permeability and permittivity with air volume fraction is obtained using the Hashin-Shtrikman (1962) upper-bound formula. The impedance matching conditions for maximum electromagnetic wave absorption are obtained by the “contour map method.” Two impedance matching thicknesses and frequencies are compared with theoretical matching relationships derived under the limiting case of impedance matching formula. As the air volume fraction increases, the first matching frequency, f_m1 remains nearly constant, while the second one, f_m2 decreases and approaches f_m1. Therefore, the absorption band of a ferrite grid absorber is broader than that of the single layered ferrite plate absorber     

Millimeter wave dielectric loaded exponentially tapered slot antenna array using substrate integrated waveguide for gigabit wireless communications

A new and upcoming application is the use of 60 GHz antennas for high date rate point-to-point connections to serve Gigabit(Gi-Fi)w ireless communications.The design of M illimeter w ave(M m W)antennas has to cope w ith the unadorned influences of manufacturing tolerances and losses at 60 GHz.In this paper,the concept of Substrate Integrated Waveguide(SIW)and Exponentially Tapered Slot(ETS)antenna w ere used together to design a high gain,efficient planar dielectric loaded antenna for M m W Gi-Fi w ireless communications at 60 GHz.The SIW is used to feed the antenna and a dielectric is utilized in front of the antenna to increase the gain.The dielectric loaded ETS antenna and compact SIW feed w ere fabricated on a single substrate,resulting in low cost and easy fabrication.The antenna w ith elliptical shaped dielectric loaded w as fabricated using printed circuit board process.The measured gain of the single element antenna is 10.2 dB,w hile the radiation efficiency of 96.84%is obtained at 60 GHz.The Y-junction SIW pow er divider is used to form a 1×4 array structure.M easured gain of the 1×4 array antenna is 13.3 dB,w hile the measured radiation pattern and gain are almost constant w ithin the w ide bandw idth of the antenna.     

An exponentially tapered transmission line antenna

The analysis and design of an exponentially tapered transmission line antenna is presented. The exponentially tapered transmission line is designed to operate such that it has radiator characteristics at high frequency and serves as a matching section at low frequency. The NEC-2 is used to model the antenna at frequencies ranging from 500 MHz to 1 GHz to obtain the input impedance and the desired radiation pattern     

Transparent wave absorber using resistive film

The authors have succeeded in manufacturing a transparent wave absorber consisting of a spacer and two transparent resistive sheets for operation at V-band. Measured frequency characteristics of the reflection loss indicate that a peak absorption of 35-38 dB is attained at a target frequency of 60 GHz     

Three-layer wave absorber using common building material for wireless LAN

A wave absorber with three layers using only common building material for wireless LAN is introduced. The design method is shown, and a suitable structure by fibre reinforced cement board is presented. Based on this, the validity of the experimental absorber produced by this method is confirmed by comparison with calculated results.     

A wide-band low-shape-factor amplifier module using an acoustic surface- wave bandpass filter

An amplifier module using a novel surface-wave bandpass filter for a spread spectrum communication receiver has been designed to realize wide-band low-shape-factor requirements. This module with a center frequency of 168 MHz has a midband gain of 6 dB, a 7.1 percent fractional bandwidth (3-dB bandwidth of 12 MHz), and an extremely low-shape factor of 1.32 to 1 (ratio of 3 to 40-dB bandwidth). Excellent agreement is cited between the theoretical frequency and impulse responses of the surface-wave bandpass filter and its measured performance.     

Fundamental investigation on a weakly magnetized ferrite absorber

Investigated are the matching characteristics of a magnetized ferrite absorber, which applies a weakly static magnetic field H_dc perpendicular to the sintered ferrite surface. Applying a static magnetic field to the ferrite enables the matching thickness of the absorber to be reduced from 8 mm in the absence of H_dc to 3 mm under 750 gauss. The matching frequency can also be changed broadly from 0.1 to 0.9 GHz by controlling ferrite thickness and H_dc, simultaneously. These are well explained in terns of an nonsaturated permeability rather than tensor permeability. A thin magnetized ferrite absorber is realized using a ferrite with a large value of imaginary part of permeability when real part takes the value near 1.0. Matching frequency characteristics, whether broad or narrow, correlates closely with the slant of the curve for real part of permeability taking the value near 1.0 in the present frequency     

Electromagnetic wave diffraction using a finite volume method

The authors describe a finite volume time domain (FVTD) method for the resolution of electromagnetic diffraction by `complex' structures. Results obtained for an aircraft by this technique which allow a conformal meshing are compared with results from a classical FDTD code     

Electromagnetic scattering by an exponentially inhomogeneous plasma sphere

The mathematical analysis of electromagnetic wave scattering by radially inhomogeneous spherical objects is treated. Numerical integration of the differential equations for the separated radial wave functions has been carried out for the case of a plasma with an exponential electron density gradient, Parametric calculations of bistatic scattering have given many interesting results. The range of validity of the Born approximation has been demonstrated by comparing it with computed results.     

Wide band electromagnetic wave absorber with thin magnetic layers

This paper presents the design and the trially made examples of the wideband thin electromagnetic absorber with multiple layers of magnetic materials, which will be useful for the walls in houses and office buildings for protection from thee radiated waves from wireless LANs and electronic equipment.. We achieved an absorbing performance of more than 80% at 1.9 GHz, 2.45 GHz and 19 GHz by using a 0.5 mm layer of the epoxy resin containing a carbonyl iron powder and another 2.5 mm layer of epoxy resin containing a ferrite powder     

太赫兹宽频带准全向平板超材料吸波体的设计

在太赫兹波段设计了一种宽频带准全向的平板超材料吸波体.仿真结果表明,该吸波体在4.36～4.91THz之间具有极化不敏感和宽入射角的强吸收.提取的等效阻抗实部表明,可以通过调节超材料的电磁响应造成吸波体一侧与自由空间近似阻抗匹配、另一侧与自由空间阻抗不匹配,从而在吸收频带内同时实现反射率和传输率最小、吸收率最大.仿真的...     

Millimeter wave ferrite circulators and rotators

In this paper the exact analysis on the waveguide junction circulator and Faraday rotator are presented in detail. The correctness of analysis is demonstrated by its successful prediction about the performance of the devices. Many calculation results are presented by comparing with the experimental results. The approaches of expanding bandwidth of devices at W band are stated.     

Electromagnetic wave effects on microwave transistors using afull-wave time-domain model

A detailed full-wave time-domain simulation model for the analysis of electromagnetic effects on the behavior of the submicrometer-gate field-effect transistor (FET's) is presented. The full wave simulation model couples a three-dimensional (3-D) time-domain solution of Maxwell's equations to the active device model. The active device model is based on the moments of the Boltzmann's transport equation obtained by integration over the momentum space. The coupling between the two models is established by using fields obtained from the solution of Maxwell's equations in the active device model to calculate the current densities inside the device. These current densities are used to update the electric and magnetic fields. Numerical results are generated using the coupled model to investigate the effects of electron-wave interaction on the behavior of microwave FET's. The results show that the voltage gain increases along the device width. While the amplitude of the input-voltage wave decays along the device width, due to the electromagnetic energy loss to the conducting electrons, the amplitude of the output-voltage wave increases as more and more energy is transferred from the electrons to the propagating wave along the device width. The simulation confirms that there is an optimum device width for highest voltage gain for a given device structure. Fourier analysis is performed on the device output characteristics to obtain the gain-frequency and phase-frequency dependencies. The analysis shows a nonlinear energy build-up and wave dispersion at higher frequencies     

Conformal double exponentially tapered slot antenna (DETSA) on LCP for UWB applications

We discuss the use of a double exponentially tapered slot antenna (DETSA) fabricated on flexible liquid crystal polymer (LCP) as a candidate for ultrawideband (UWB) communications systems. The features of the antenna and the effect of the antenna on a transmitted pulse are investigated. Return loss and E and H plane radiation pattern measurements are presented in several frequencies covering the whole ultra wide band. The return loss remains below -10 dB and the shape of the radiation pattern remains fairly constant in the whole UWB range (3.1 to 10.6 GHz). The main lobe characteristic of the radiation pattern remains stable even when the antenna is significantly conformed. The major effect of the conformation is an increase in the cross polarization component amplitude. The system: transmitter DETSA-channel receiver DETSA is measured in frequency domain and shows that the antenna adds very little distortion on a transmitted pulse. The distortion remains small even when both transmitter and receiver antennas are folded, although it increases slightly.     

（英）钡铁氧体薄膜自偏置毫米波环行器设计与制备

基于厚度为10 μm的钡铁氧体薄膜设计,制备了共面波导结构的毫米波薄膜环行器.这种薄膜环行器不需要外加磁体,在34 GHz和37.6 GHz显示出环行特性,其非互易效应大于15 dB.结果表明,采用共面波导结构可以实现薄膜环行器.这种薄膜环行器具有和单片微波集成电路集成的潜在应用.     

Gyrotron travelling wave amplifier: III. A proposed wide-band fast wave amplifier

A simple scheme is proposed for the construction of a wide-band fast wave gyrotron travelling wave amplifier. The key features of this scheme include a contoured waveguide, a tapered magnetic field, and injection of input signals in opposite direction of the streaming electrons. Bandwidths at tens of percents, and gain at tens of decibals, are projected.     

Electromagnetic surface waves in a metallised ferrite slab

The propagation of electromagnetic surface waves in a metallised ferrite?dielectric sandwich is described. The computed dispersion curve is found to be critically dependent on the dielectric-slab thickness. The theoretical results are illustrated by measuring the direct and reverse r.f. transmission through a polycrystalline y.i.g. slab as functions of the frequency.     

On the electron flow movement in the decelerated wave field with exponentially positive-going amplitude

Initially homogeneous electron beam movement in longitudinal electric field of the decelerated electromagnetic wave is discussed. The wave amplitude exponentially increases along the electron’s trajectory. Comparison of solutions obtained numerically and analytically by disturbance method for small amplitude as a sixth approximation is made. It is shown that the approximate solution’s error is small when transit angle is small and the error starts catastrophically rising at some angle’s value. The problem is urgent for building the non-linear clinotron’s theory.