Time domain analysis of transient propagation in inhomogeneous magnetized plasma using Z-transforms

The electromagnetic propagation through an inhomogeneous magnetized plasma slab is studied using the Z-transform formulation of the Finite-Difference Time-Domain（FDTD） method. The direction of electromagnetic propagation is parallel to the biasing magnetic filed. To validate the Z-transform algorithm, the reflection and transmission coefficients for the right-hand circularly polarized wave of the homogeneous magnetized plasma slab are computed by means of discrete Fourier transform. The comparison between the reflection and transmission coefficients of the homogeneous plasma slab and analytical values indicates that Z-transform algorithm is very accurate. When the plasma frequency varies according to the square root and parabolic relations, the reflection and transmission coefficients of the inhomogeneous magnetized plasma slab are computed.     

Power Reflection and Transmission Coefficients for Meander‐Line Polarizers with a Chiral Slab

This paper presents a theoretical investigation of power reflection and transmission coefficients for a meander‐line polarizer placed periodically on a chiral slab. It is assumed that a linearly polarized transverse magnetic wave is incident on a chiral slab from the air region. In the analysis, we derive the electric and magnetic fields in the modal form in the air and chiral regions. We obtain power reflection and transmission coefficients in a straightforward manner after matching the tangential components of the electric and magnetic fields at the boundaries. We present numerical results for the power reflection and transmission coefficients versus frequency and incident angle for different values of the chirality admittance. A meander‐line polarizer placed on a dielectric slab can convert a linearly polarized wave to a circularly polarized wave. The design parameters for a meander‐line polarizer are the dimensions of the meander‐line and the values of the dielectric slab. Replacing a dielectric slab with a chiral slab introduces a new independent parameter which controls the wave polarization.     

Rectangular Waveguide With Metallic Nanostructure Driven by Magnetic Field

The changes in the propagation constant of the TE₁₀ mode of a rectangular waveguide with a metallic nanostructure, occurring under an external magnetic field have been investigated. Expressions for complex reflection and transmission coefficients have been derived. The dependence of the reflection coefficient upon the intensity of the external magnetic field is analyzed. It is shown that the experimental values of the propagation constant or the reflection and transmission coefficients can be used to estimate the value of the microwave magnetoresistance of nanostructures. Experiments on the measurement of the reflection and transmission coefficients in a waveguide with an (Fe/Cr)n nanostructure have been performed in millimeter and centimeter wave bands.     

An optimization approach to the frequency-domain inverse problemfor a nonuniform LCRG transmission line

The inverse problem for a nonuniform LCRG transmission line is considered in the frequency domain. Imbedding equations for the reflection and transmission coefficients are derived through the concept of wave-splitting. An optimization approach is applied to reconstruct the line parameters as functions of the position using band-limited reflection and/or transmission data. Exact and explicit expressions for the gradients are derived, and the reconstruction algorithm (based upon a conjugate gradient method) is tested with both clean and noisy data, The problem of the nonuniqueness is also discussed     

Scattering and radiation from a slitted parallel-plate withrectangular grooves: TE-wave

TE-wave scattering and radiation from a slitted parallel-plate waveguide with rectangular grooves is considered. The Fourier transform and the mode matching are used to represent the scattered field in terms of the continuous and discrete modes. The simultaneous equations for the discrete modal coefficients are obtained by matching the boundary conditions. The fast-converging series solutions are presented to evaluate the far-zone radiation, reflection, and transmission coefficients. The numerical computations illustrate the angular behavior of far-zone radiation in terms of the slit size, groove size, and operating frequency. The antenna radiation pattern of the slitted parallel-plate is measured and compared with theory     

Simulation and properties of Erbium-Doped Distributed Bragg Reflectors (ED-DBRs) and Fiber Bragg Gratings (ED-FBGs)

The structure of an active Erbium-Doped Distributed Bragg Reflector (ED-DBR) and a Fiber Bragg Grating (ED-FBG) is simulated using a rigorous transmission line model and an approximate version of the coupled-mode theory, respectively. The basic calculation steps and assumptions of the proposed simulation models are described and the key parameters that determine the devices’ reflection characteristics are in detail discussed. By applying the proposed transmission line model, numerical results are provided for both spectral reflectivity and transparency response for an active-slab DBR with increased erbium-ion concentration. In addition, using coupled-mode theory for the simulation of the cylindrical geometry of the ED-FBG device, the pump power-dependent reflection and transmission coefficients are obtained and their potential use in active sensor applications are discussed.     

An application of FDTD in studying the end effects of slotline andcoplanar waveguide with anisotropic substrates

In this paper, the finite-difference time-domain (FDTD) method is applied in conjunction with the generalized pencil of function (GPOF) technique to evaluate the reflection coefficient from shorted slotlines and coplanar waveguides (CPW) on anisotropic substrates, and to extract the propagation constant along the line from these data. For each frequency, the field solutions at different locations are processed by using the GPOF technique to extract two complex exponents that correspond to the forward and backward traveling waves, which provide all the information about the reflection coefficient and the dispersion characteristic of the transmission line. The advantage of combining the GPOF technique with the FDTD method is that the reflection coefficients can be obtained with a single run. Recognizing that there is a dearth of results for the reflection coefficients of slotline and CPW-line discontinuities with anisotropic substrates, the present problem is also solved by using the spectral-domain method for the purpose of validation, and the two results are found to compare quite well with each other. For further validation, the FDTD and GPOF solutions are derived for isotropic substrates, and are compared with the published theoretical and experimental results     

A Precise and Sensitive X-Band Reflecto"meter" Providing Automatic Full-Band Display of Reflection Coefficient

A simple waveguide system has been made for the instantaneous measurement of the magnitude of the reflection coefficient as a function of frequency for the 8.2-12.4 Gc band. Reflection coefficients in the range 1 to 0.001 can be measured on linear scales; above 0.01 the error is less than /spl plusmn/3 per cent, below 0.01 it is estimated to be in the order of /spl plusmn/5 per cent. By using a long line between the unknown impedance and the two wall-current detectors, which act as measuring probes, an audio-frequency voltage has been obtained which is linearly proportional to the amplitude of the unknown reflection coefficient. A third wall-current detector is used as a leveler. The principle is quite simple and can easily be applied for other frequencies or transmission lines.     

Automatic measurement of complex dielectric constant and permeability at microwave frequencies

With the advent of the computer and automatic test equipment, new techniques for measuring complex dielectric constant (ε) and permeability (µ) can be considered. Such a technique is described where a system is employed that automatically measures the complex reflection and transmission coefficients that result when a sample of material is inserted in waveguide or a TEM transmission line. Measurement results of ε and µ for two common materials are presented.     

Identification of cascaded microwave circuits with moderatereflections using reflection and transmission measurements

A method for identifying the component values of a cascaded microwave circuit with the aid of the time-domain reflection and transmission coefficients is presented. The model proposed is composed of commensurate nondispersive transmission lines separated by either lumped series or shunt resistances. The line delays are equal to the sampling interval. The algorithm takes into account the third-order multiple reflections, thus allowing identification of circuits with moderate internal reflections (reflection coefficient smaller than about 0.2). The method can be applied to the modeling of connectors, discontinuities, transitions, jigs, and even impedance transformers. A numerical example is given to demonstrate the ability of the algorithm     

Maximizing the channel capacity of multicarrier transmission bysuitable adaptation of the time-domain equalizer

An adaptation algorithm for determining the time-domain equalizer coefficients is described that maximizes the total channel capacity for all carriers of a multitone (discrete multitone) transmission. It takes into account the crosstalk noise environment and the interblock interference as a common disturbance. Furthermore, the leakage effect of the discrete Fourier transform (fast Fourier transform) is considered, too. Including this into the algorithm for the equalizer coefficients leads to a notable improvement in the signal-to-noise ratio, especially at lower frequencies for a typical asymmetrical digital subscriber line application     

An Impedance Transformation Method for Finding the Load Impedance of a Two-Port Network

An unknown load impedance terminating a lossy two-port junction can be calculated if the input impedance and junction parameters are known. It is to be shown that there exists a linear relationship, dependent upon two calibration constants, between the input reflection coefficient and a modified reflection coefficient of the load. Applying the linear transformation to the junction input impedance permits evaluation of the unknown load impedance. Calibration is accomplished by terminating the transmission line in at least three different reactance and measuring the corresponding input reflection coefficients. These data plot into the usual circular configuration on a Smith chart from which the necessary calibration data is obtained. When several load reactances are used, the calibration accuracy can be considerably increased, since the averaging advantage of plotting a mean straight line is utilized. Furthermore, once the junction has been calibrated, its equivalent T-network impedances and scattering coefficients may be found.     

Measurement of the high-frequency giant magnetoresistance of nanostructures in the traveling-wave mode

The change that occurs under the action of an external magnetic field in the propagation constant of the H ₁₀ mode of a rectangular waveguide containing a metallic nanostructure is investigated. Expressions for the complex reflection and transmission coefficients are derived. The dependence of the reflection coefficient on the intensity of the external magnetic field is analyzed. It is shown that experimental values of the propagation constant or the reflection and transmission coefficients can be used for estimation of the value of the microwave magnetoresistance of nanostructures. Experiments on the measurement of the reflection and transmission coefficients in a waveguide with an (Fe/Cr)_n nanostructure are performed in the millimeter and centimeter wave bands.     

1维光子晶体中TM波的传输公式及其辨析

为了得到1维光子晶体中TM波的传输公式,采用传输矩阵的方法和电磁波的边界条件,推导出TM波在介质层中的特征矩阵及其反射系数和透射系数公式。结果表明,用TE波反射系数和透射系数公式做代换的方法不能得到正确的TM波的反射系数和透射系数公式;对推导出TM波的反射系数和透射系数公式进行了分析,由TM波的反射系数和透射系数公式得出的光强透射率和反射率满足能量守恒;并且推出的TM波反射系数公式不仅能够反映反射波与入射波的数量关系,且能够反映反射波与入射波的位相关系。这些结果对研究1维光子晶体中TM波的传输性质是有帮助的。     

An accurate measurement technique for line properties, junctioneffects, and dielectric and magnetic material parameters

Transmission/reflection coefficients of unknown transmission lines are analyzed. The characteristic impedance, the propagation constant, and the parameters of the junctions at the connections with the measurement setup can be calculated if the coefficients of three different lengths of the line being investigated are measured. Therefore it is called the L³ method (line/line/line). Transmission data suffice for the determination of only the propagation constant. They are used in the case of material parameter measurements with loaded lines. Dielectric and magnetic properties of the filling material are calculated using the set of transverse resonance equations     

A new boundary description in two-dimensional TLM models ofmicrowave circuits

A boundary representation for the two-dimensional transmission line matrix (TLM) method of numerical analysis is described. In conventional TLM simulations, boundary conditions are realized by introducing the appropriate impulse reflection coefficients halfway between two nodes. Since the total field quantities are only defined on the nodes, their values at the boundary are not directly available from TLM solutions. The TLM procedure is modified so that boundaries can be placed across the nodes. The boundary conditions in TLM can then be formulated in terms of the field boundary conditions derived from Maxwell's equations rather than in terms of impulse reflection coefficients. The essential differences between the conventional TLM and the proposed procedure are presented. Examples are given for several typical problems, and the results obtained with the two methods are compared. These are found to be in excellent agreement     

Monolithic IMPATT oscillator characterization

Two methods were developed to characterize the monolithic IMPATT resonator used in the design of the millimeter-wave oscillators. Although they are only good for discrete frequency points, the accuracy is much better than the method of de-embedding. The transmission resonance method can also be applied to other circuitry with high reflection coefficients, such as the matching circuit of a narrowband power FET, or HBT. The varactor method is very handy for in situ measurements. The drawback is that it is destructive and the accuracy deteriorates when the loss is high (a small arc). The experimental results are valuable for monolithic IMPATT oscillator design     

Reflection and transmission of electromagnetic waves normally incident on a plasma slab moving uniformly along a magnetostatic field

Power reflection and transmission coefficients are found for linearly and circularly polarized plane electromagnetic waves, normally incident on a plasma slab, moving uniformly along a magnetostatic field, normal to the slab boundaries. The solution is found by applying the boundary conditions in the rest frame, and then using relativistic transformations for the fields and the plasma parameters to find the reflection and transmission coefficients observed in the laboratory frame. The results for the circularly polarized incident waves are found in closed form. Numerical results are presented for linearly polarized incident waves. It is found that with an increase in the magnetostatic field, the absolute maximum of the reflection coefficient increases at different velocities. An increase in the magnetostatic field makes the slab more transparent at velocities for which the transmission coefficient with no magnetostatic field is very small. A dielectric-like behavior is observed for large magnetostatic fields. The sum of the power reflection and power transmission coefficients is found to be no longer equal to unity for velocity different from zero.     

L波段掺铒光纤放大器的增益平坦滤波器设计

EDFA的增益平坦化是WDM系统中的重要问题．用成本低、插损小的光纤光栅实现该功能是一项有吸引力的方案，采用剥层法设计了基于啁啾光栅的增益平坦滤波器。基于时间因果律的剥层算法将光纤光栅看成一个分离的模型，由一系列长度为△的复反射器所组成，每个反射器的后端耦合系数都可由它的前端耦合系数递归地求出，从而能快速、精确地反演出光栅的耦合系数函数。啁啾光栅的目标反射谱由理想的增益平坦滤波器透射谱获得，利用与反射谱群时延有关的常数α可控制光栅的长度，α取值为0．0024cm。时，对应的光栅长度为3．5cm。用剥层法反演出耦合系数函数后，又通过解Riccati方程模拟了合成光栅的透射谱。数值模拟结果显示理想透射谱与合成光栅透射谱之间的峰峰值误差小于0．1dB．并且在工作带宽范围内，透射谱群时延的变化量小于0．6ps，表明该滤波器对系统没有额外的色散影响。