Single-horn reflectometry for in situ dielectric measurements atmicrowave frequencies

The ability of single-horn reflectometry to determine reflectivity and, hence, calculate dielectric properties using plane-wave interpretation theory, has been investigated experimentally. The horn is part of a portable field unit operating at X-band and was placed above various natural materials. Good results were obtained for water and saline ice, which were flat and lossy, but not for an electrically thick sheet of fresh lake ice, for which reflectivity at the bottom interface was strong     

Bias dependence of the MODFET intrinsic model elements values atmicrowave frequencies

S-parameters of MODFETs were measured versus bias instead of frequency with a special feature of the HP8510 network analyzer. Figure of merit plots, f_T, and f_max, were quickly generated from the bias sweeps of S-parameters, and optimum bias points were easily found. The intrinsic device elements of MODFETs were calculated after de-embedding the measurements from the device parasitics. The technique is demonstrated with a 0.15-μm pseudomorphic MODFET with an f_T of 150 GHz. The usefulness of the technique for understanding the operation of the MODFETs is discussed. With this technique a bias scan of an intrinsic element value can be measured and plotted in 13 s     

Scattering cross-section of an inhomogeneous plasma cylinder

Scattering of em waves by the plasma cylinder is of significance in radar target detection, plasma diagnosis, etc. This paper discusses the general method tocalculate the scattering cross-section of em waves from a plasma cylinder which is radially inhomogeneous and infinitely long. Numerical results are also provided for several plasma density profiles. The effect of the electron density distribution on the scattering cross-section is investigated.     

Scattering response of a bianisotropic cylinder with electrically small cross-section

EM scattering response of an infinitely long bianisotropic cylinder with electrically small cross-section suspended in free space is presented. Formulation of this problem is based on the coupled integral equation method with the long wavelength approximation. Reduced expressions for the scattering of plane waves, both E-wave and H-wave types, are obtained. It is revealed that for certain polarization matrices determined by the constitutive parameters of the scatterer, cross-polarization and/or co-polarization phenomena may occur, respectively.     

Scattering from graded cylindrical media

The transmission line approach is used to describe scattering from a circular cylinder coated with a nonuniform dielectric. Rather simple techniques can be used for obtaining the solution in terms of surface admittance of the inner cylinder. An equivalent circuit for the sheath is a by-product of this approach. Numerical results include graphs of the effect of corrugations on the inner cylinder.     

A radar cross-section model for power lines at millimeter-wave frequencies

The knowledge of radar backscatter characteristics of high-voltage power lines is of great importance in the development of a millimeter-wave wire detection system. In this paper, a very high-frequency technique based on an iterative physical optics approach is developed for predicting polarimetric radar backscattering behavior of power lines of arbitrary strand arrangement. In the proposed scattering model the induced surface current is obtained using the tangent plane approximation in an iterative manner where the first-order current, obtained from the incident wave, is used as the source for the second-order current and so on. The approximation is valid for frequencies where the cable strand diameter is on the order of or larger than the wavelength. It is shown that the copolarized backscatter is dominated by the contribution from the first-order PO currents, whereas the cross-polarized backscatter is generated by the second- and higher order PO currents. Using this model, the effects of radar antenna footprint, surface irregularities, and cable sag (when suspended between towers) on radar backscatter are studied. To verify the validity of the proposed model, theoretical results are compared at 94 GHz with experimental results and are found to be in good agreement.     

Scattering from plane layered media

The problem of scattering from plane layered media, arbitrarily terminated, is studied. Use is made of the Marcuvitz-Schwinger formulation and of a Riccati differential equation (RDE). A method for obtaining approximate solutions of the RDE in some limiting cases is developed. The solutions are compared to those obtainable through different approaches, as well as, in some particular cases, to exact results. Possibilities of application to the design of broad-band matching junctions or terminations are illustrated.     

开口腔体的雷达散射截面计算方法

本文采用边界积分－模式混合法结合网络级联技术计算了开口腔体的电磁散射问题，计算结果与已知结果吻合良好。     

Active load technique for load-pull characterisation at microwave frequencies

The letter describes a load-pulling method that allows an extension of the two-signal approach to applications where the output frequency spectrum is different from the input one, as in the case of power devices operating with multicarrier input signals.     

Calculation of extinction cross-section of single vegetation elements placed in open resonator

The results of calculation of extinction cross — section for bodies of various shapes and electrical constants placed in open resonator are presented. Theoretical model for such structure was developed. It allowed to calculate transfer ratio, Q-factor and another characteristics of the resonator with sample. The results presented can be used for investigation of extinction cross — section for vegetation elements in millimeter wave band using open resonator.     

Experimental investigation of extinction cross-section of single vegetation elements using open resonator

The experimental results of investigation of the total cross — section of scattering and absorption (extinction cross — section) σ_t of stalks and strip leaves of grass in millimeter waves range are presented. The investigation was carried out using open quasioptical resonator with spherical mirrors. Measirements were carried out as by absolute method as using the relative method. Experimental results obtained by two different methods showed that in spite of some data differences obtained by absolute and relative methods the latter may be used for estimation of the extinction cross — section σ_t of vegetation elements.     

Generation and transmission of FM and π/4 DQPSK signals atmicrowave frequencies using harmonic generation and optoelectronicmixing in Mach-Zehnder modulators

A novel method of using the harmonic generation and optoelectronic mixing properties of Mach-Zehnder modulators to generate modulated subcarrier signals at high-order harmonics of the input signals is presented. The method permits the simultaneous transmission over optical fiber of a modulated and an unmodulated signal, both at high-order harmonic frequencies of the input signals, for the purpose of transmitting both a local oscillator tone and the modulated signal required at a base station for microcellular applications. We present the theory of operation and demonstrate the validity of the concept with a narrow band single-tone FM experiment as well as a 20-Mb/s π/4 DQPSK experiment     

Scattering by an inhomogeneous dielectric/ferrite cylinder ofarbitrary cross-section shape-oblique incidence case

A moment method (MM) solution is developed for the fields scattered by an inhomogeneous dielectric/ferrite cylinder of arbitrary cross-section. The incident field is assumed to be a plane wave of arbitrary polarization with oblique incidence with respect to the axis of the cylinder. The total electric and magnetic fields are the unknown quantities in two coupled equations from which a system of linear equations is obtained. Once the total electric and magnetic fields within the cylinder are computed, the scattered fields at any other point in space can be calculated. It is noted that for the case of oblique incidence, the scattered field has TE_z and TM_z polarized fields regardless of the polarization of the incident field. The echo widths of cylinders and shells of circular, semicircular, and rectangular cross section are calculated for TE_z and TM_z polarized incident fields. It is shown that the results obtained for dielectric/ferrite cylinders and shells of circular cross section with the solutions developed here agree very well with the corresponding exact eigenfunction solutions     

一种太赫兹频段粗糙凸体目标散射计算方法

太赫兹频段下目标散射特性计算需考虑目标表面的粗糙特性和目标材料参数。在对粗糙目标几何建模时,通常的精细面元剖分建模方法使得散射计算问题难以求解。提出确定性建模与统计性建模相结合的粗糙目标几何建模方法,并且基于全波法提出了一种太赫兹频段可计算任意材料、任意粗糙凸体目标散射场的计算方法。通过与通用电磁计算软件计算结果的比较验证了该方法的准确性。     

Comment: Scattering by infinite cylinders of arbitrary cross-section by the method of finite differences [and reply]

A finite-difference method of computing the field scattered by conducting cylinders of arbitrary cross-section has recently been proposed by Patwari and Davies. The advantage claimed for their method?essentially that it overcomes the fundamental objection to the Rayleigh method?is shown to be unjustified and the two methods are, in fact, shown to be identical.     

Scattering of electromagnetic waves by a metal lattice placed at the interface of two media

Simple formulas for determination of components of the scattering matrix of a plane electromagnetic wave incident along the normal onto a thin infinite 2D metal lattice with square windows placed at the interface of two media are derived for the first time. Frequency responses (FRs) of this structure calculated with the use of these formulas agree well with responses obtained by the numerical electromagnetic analysis of a 3D model in the case when the lattice period is less than one-half of the wavelength. The capability of efficient control of the FR of the analyzed structure by means of variation in the width of conductors and the lattice period enables application of this lattice for fabrication of a reflector with prescribed reflectivity. Such reflectors at interfaces of dielectric layers are required, for example, in the design of multilayer sufaces radio transparent in a specified frequency band or optical bandpass filters.     

传媒数字时代草木染的发展及在现代服饰文化中的应用

传媒数字化是传媒产业重要的发展趋势,是科学进步的结果,也是社会文明向前发展的标志。传媒数字化给中国传统文化传播带来了新的机遇与挑战,对传统文化的传承也带来了深远影响。目前,“草木染”成为生态服装设计发展的一个重要方向。因此,应扩大草木染在网络环境中的宣传,让其更多的应用在现代服饰中。     

Scattering of TM excitation by coupled and partially buried cylinders at the interface between two media

An analysis of scattering from coupled conducting cylinders near the planar interface between two semi-infinite, homogeneous halfspaces of different electromagnetic properties and from partially buried conducting cylinders is presented. The perfectly conducting cylinders of general cross sections are of infinite extent and the excitation is transverse magnetic to the cylinder axes. Coupled integral equations for the unknown current induced on the cylinders are derived and a numerical method for solving them is described. In addition, a simple technique is employed to determine the far-zone scattered field from knowledge of the cylinder current. Data displaying the distribution of the induced current and the scattered field patterns for cylinders of interest are presented and discussed.     

Parametric amplification in spatially extended media and application to the design of tuneable oscillators at optical frequencies

A theory of travelling- and backward-wave variable parameter amplification appropriate to the amplification of a light beam is developed. It is an extension of the theory of Tien and Suhl for one-dimensional propagation to the case in which the pump wave, signal wave and idler waves have different directions of propagation. The theory is then applied to the design of a tuneable oscillator at optical wavelengths. The device is tuned by changing the orientation of a parallel mirror system. It appears that currently available pulsed laser powers are sufficient to drive such devices and that a continuous tuning range over a three to one interval in frequency is possible.