A novel, accurate load-pull setup allowing the characterization ofhighly mismatched power transistors

The measurement of highly mismatched power transistors has always been a difficult problem. A novel, active load-pull technique providing an attractive solution is proposed in this paper. It consists of using suitable mismatched sources to drive the device under test. By using the proposed measurement setup, an electronic simulation of highly reflective loads very close to the edge of the Smith chart can be achieved (reflection coefficients larger than 0.9). Furthermore, the magnitude and phase of the reflected power waves at the output of the transistor under test are accurately controlled so as not to damage the component. Some examples of load contour mappings are given. They demonstrate the promising capabilities offered by this improved large signal measurement tool     

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.     

A new technique for in-fixture calibration using standards ofconstant length

This paper presents a new technique for in-fixture calibration using standards of constant length. The technique uses a through line, reflective load, symmetric two-port at a reference position, and the same two-port at a different position, all produced on substrates of the same electrical properties and physical length. When compared with the through-reflect line (TRL) technique, this one eliminates the need for a length change during calibration and device measurements while retaining comparable accuracy. Moreover, in contrast with the line-network network (LNN) technique, it provides easy resolution of all error coefficients without ambiguities and does not require physical movement of a reference two-port, but reproduction of a reference two-port on microwave integrated circuit (MIC) substrates, which is easy to realize. All these features make the new technique useful for in-fixture measurements requiring a constant distance between input and output connections. The validity of the proposed technique is illustrated by experimental results     

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.     

A comparison of theoretical and empirical reflection coefficientsfor typical exterior wall surfaces in a mobile radio environment

This paper presents microwave reflection coefficient measurements at 1.9 GHz and 4.0 GHz for a variety of typical smooth and rough exterior building surfaces. The measured test surfaces include walls composed of limestone blocks, glass, and brick. Reflection coefficients were measured by resolving individual reflected signal components temporally and spatially, using a spread-spectrum sliding correlation system with directional antennas. Measured reflection coefficients are compared to theoretical Fresnel reflection coefficients, applying Gaussian rough surface scattering corrections where applicable. Comparisons of theoretical calculations and measured test cases reveal that Fresnel reflection coefficients adequately predict the reflective properties of the glass and brick wall surfaces. The rough limestone block wall reflection measurements are shown to be bounded by the predictions using the Fresnel reflection coefficients for a smooth surface and the modified reflection coefficients using the Gaussian rough surface correction factors. A simple, but effective, reflection model for rough surfaces is proposed, which is in good agreement with propagation measurements at 1.9 GHz and 4 GHz for both vertical and horizontal antenna polarizations. These reflection coefficient models can be directly applied to the estimation of multipath signal strength in ray tracing algorithms for propagation prediction     

Modelling and Measuring Reflection Due to Flat Dielectric Surfaces at 5.8 GHz

Indoor radio channel planning tools implement different models to simulate propagation mechanisms such as transmission or reflection. The specular reflection formulation is commonly used instead of more complete scattering models. This happens because its coding is less complicated and the software runs faster than when considering reflection in all directions, not yet specular. In this paper, results from measurements are presented, consisting of the effect of constructive walls on an oblique incident wave. These experimental outcomes are modelled by means reflection pattern computations. Physical optics scattering model is used in its classical formulation, and it is then modified to take into account antenna pattern effects in the measurements. The comparison between measurements and simulations is also presented, showing good agreement. Measurements show that low reflective walls produce reflections in several directions across the incidence region. In these situations, the use of algorithms that compute reflection pattern, instead of just specular reflection coefficients, will lead to better agreement with actual results     

A method to predict multipath effects on a line-of-sight link

A method that computes the quality of a digital microwave line-of-sight link affected by multipath propagation is presented. The use of a statistical propagation model and of the signature concept allows the propagation effects to be separated from the characteristics of the equipment. Since the variations of the statistical mode coefficients with respect to the characteristics of the link under consideration are not known, experimental results have been achieved using assumptions based on physical considerations. A single channel is considered and the same principles, although more speculative because of the lack of data, are applied to a diversity channel     

非均匀传输线综合的特征法

本文利用特征法对无耗非均匀传输线进行了综合。在二倍于传输线延时的时间范围内给定时域反射电压响应的ｍ个取样值，则非均匀传输线可由ｍ段长度不等、延时为相应时间取样间隔的均匀线近似，各均匀传输线段的特性阻抗唯一求出。     

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     

Use of Asymptotic Waveform Evaluation Technique in the Analysis of Multilayer Structures With Doubly Periodic Dielectric Gratings

The reflection and dispersion characteristics of multilayer structures that involve periodically implanted material blocks are obtained by using the MoM solution of the volume integral equation. The asymptotic waveform evaluation (AWE) technique is utilized to obtain a Pade approximation of the solution in terms of a parameter such as frequency or incident angle. The use of AWE technique enables a fast sweep with respect to the approximation parameter. Moreover, a robust method for extracting the dispersion characteristics of periodic structures via Pade approximation is proposed. The AWE procedure requires the calculation of high order derivatives of the complicated kernel function that consists of Green's functions for stratified medium. These derivatives are calculated by employing the automatic differentiation theory. The reflection coefficient, propagation constant and band diagram of the structure are obtained both via point-by-point simulations and through the use of AWE technique. It is observed that AWE technique increases the computational efficiency without losing accuracy.     

面向6G通信感知一体化的40～50 GHz毫米波信道反射和透射特性研究

为解决毫米波信道反射和透射特性测量数据不足、多层材料传播系数计算不准确和传播特性表征不明的问题,该文开展面向6G通信感知一体化(ISAC)的40～50 GHz毫米波信道反射和透射特性研究。首先,基于菲涅尔理论和射线弹跳追踪原理,提出一种室内多层建筑材料传播系数计算方法;然后,利用基于矢量网络分析仪的毫米波信道测量平台,开展40～50 GHz频率范围内多层木板和多层玻璃的反射和透射系数测量活动。结果表明,该方法与测量值间高度吻合,传播系数误差低于0.1,能够准确地刻画毫米波信道反射和透射特性变化规律。此外,研究还发现反射系数谐振特性和有效布儒斯特角特性依赖于电波极化、入射角和材料厚度。     

Terahertz characterisation of building materials

To obtain realistic models for propagation channels in future pico-cellular indoor terahertz communication systems it is necessary to know the reflective properties of building materials found in a typical office environment. The angular dependent reflection coefficients of different building materials were determined using terahertz time-domain spectroscopy in transmission geometry and Fresnel's equations. This approach is more efficient than a set of measurements in reflection geometry for different angles. Verification of the method with a set of such reflection measurements shows an excellent agreement.     

Calibration of Multiport Reflectometers by Means of Four Open/Short Circuits

This paper presents a simple method for calibrating any practical multiport reflectometer by means of four reflection standards with known complex reflection coefficients. It is shown that these four standards can be such that their reflection coefficient modulus = 1. Computer simulation proves that no singularity appears for both ideal and nonideal five- and six-port reflectometer in a wide range of phase distribution of reflection coefficients. A group of calibration results for a practical simple six-port is fisted to show this calibration procedure; by the use of these calibrated network parameters, some measurement results are presented and compared with the values obtained at the National Bureau of Standard, U.S.A. Both computer simulation and experimental results show that the numerical singularities which may be encountered in multiport calibration procedures are not an intrinsic properties of multiport but from related mathematical treatment.     

Techniques for the Measurement of Complex Microwave Conductivity and the Associated Errors

Complex microwave conductivity of 9 /spl Omega/ /spl dot/ cm p-type silicon samples has been measured using conventional reflection and transmission bridges to examine their relative advantages and disadvantages. An attempt has been made to improve the reflection results from an analysis of the parameters of a circle diagram for reflection coefficient obtained on using a variable reactive termination after the semiconductor-filled waveguide section. In conformity with the calculated accuracy attainable from different types of measurement under the actual experimental condition, using commercial standards, the dielectric constant for the sample was found to be scattered over a region of /spl plusmn/0.4. It has been concluded that because of lack of accuracy in commercial standards for attenuation and phase shift, the potential accuracy of the conventional microwave methods falls too short of its mark to make any detinite conclusion about the effective mass of carriers in semiconductors at room temperatures.     

Time-domain reflective beam propagation method

A time-domain reflective beam propagation method (TD-RBPM) is presented for the analysis of optical pulse propagation and reflection in waveguide structures with multiple discontinuities. By utilizing an implicit scheme, the method allows relatively large time steps and, therefore, is highly efficient. The accuracy of the method is verified by simulating a time-domain Gaussian pulse reflected and transmitted from a multiple period grating and a four-layer antireflection coating structure.     

Calibration procedures with series impedances and unknown linessimplify on-wafer measurements

Procedures to calibrate network analyzers using unknown calibration lines and series impedances are presented. These LZY and LZN self-calibration procedures are specifically suited for measurements on planar and integrated circuits. By means of the self-calibration algorithm, the propagation constant of the line standards and the quantities of the reflection standards Y and N are determined. The LZN procedure requires three two-port standards, whereas the LZY procedure deals with two standards only. The fact that it is neither necessary nor advisable to know all standards completely allows the realization of the planar calibration standards in an easy way. Both self-calibration procedures according to the seven-term model are based on closed mathematical solutions so that the accuracies are good, as demonstrated by measurement results     

ELECTROMAGNETIC WAVE PROPAGATION IN MAGNETIC MULTILAYERS-NON-RECIPROCAL REFLECTIONS''''

A theory of EM wave propagation through magnetic multilayers and superlattices is presented based on the propagation matrix of a magnetic film. By using the P matrix, the transmission and reflection coefficients of layered magnetic media, including: (l)semi-infinite magnetic surfaces, (2) magnetic multilayers, (3) semi-infinite magnetic superlattices are obtained. The numerical results show that the EM modes of a magnetic layer system is excited and manifested as the sharp dips in the S-polarized reflection and the dispersion curves of the magnetic polaritons can be measured by a method similar to the attenuated total reflection (ATR) technique.     

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     

Propagation constant and the velocity of the coherent wave in adense strongly scattering medium

Frequency- and time-domain experiments are conducted to study the effective propagation constant of the coherent wave in a dense strongly scattering medium. A wide-band microwave signal (10-40 GHz) is propagated through randomly distributed glass spheres with a 5.73 mm average diameter and separated into incoherent and coherent fields. The real and imaginary parts of the propagation constant are obtained from the coherent field. The narrow size distribution of the particles enables the authors to study scattering from the Rayleigh region through the Mie resonance scattering region. The results of the experiments are compared to independent scattering, effective-field approximation (Foldy's), and the higher order quasi-crystalline approximation (QCA) using Mie scattering coefficients and the Percus-Yevick approximation for the pair-distribution function. The phase and group velocities of the coherent wave are obtained from the effective propagation constant and compared with theory. In addition, the velocity of the coherent wave in random media is measured using the time-domain technique. It is shown that the velocity of the coherent wave in random media is neither phase nor group velocity     

Assessment of Rational Approximations for Square Root Operator in Bidirectional Beam Propagation Method

Accurate rational approximations to the square root operators are crucial for the bidirectional beam propagation method in simulation of strongly reflective structures. An assessment and comparison of various commonly used rational approximations is performed for both transverse electric (TE) and transverse magnetic (TM) waves. The range of validity and level of accuracy for the different approximations are studied by investigating the structures with varying reflection intensities. Guidelines for accurately modeling of evanescent and propagating modes are provided.