Fused couplers of arbitrary cross-section

Simple expressions are presented to describe fused couplers of arbitrary cross-section and arbitrary refractive-index profile height. The length for polarisation splitting can depend dramatically on cross-sectional shape. Four cross-sections are compared to illustrate the concepts.     

TE-wave scattering by a dielectric cylinder of arbitrary cross-section shape

The theory and equations are developed for the scattering pattern of a dielectric cylinder of infinite length and arbitrary cross-section shape. The harmonic incident wave is assumed to have its electric vector perpendicular to the axis of the cylinder, and the fields are assumed to have no variations along this axis. Although some investigators have approximated the field within the dielectric body by the incident field, a more accurate solution is obtained here by treating the field as an unknown function which is determined by solving a system of linear equations. Scattering patterns obtained by this method are presented for dielectric shells of circular and semicircular cross section, and for a thin plane dielectric slab of finite width. The results for the circular shell agree accurately with the exact classical solution. The effects of surface-wave excitation and mutual interaction among the various portions of the shell are included automatically in this solution.     

Mode dispersion for optical fibres of arbitrary cross-section

The recent theory of Snyder and Zheng derived for high-V fibres of arbitrary cross-section is shown to be surprisingly accurate, e.g. it is less than 5% in error for single-mode fibres at cutoff of the second mode. On the basis of their asymptotic expressions, together with our new numerical data, we derive simple empirical formulas with much higher accuracy than previously reported.     

NUMERICAL ANALYSIS OF TWO-DIMENSIONAL MULTI-OBJECT SCATTERING SYSTEMS WITH ARBITRARY STRUCTURE

A general analysis approach to multi-object(M-object)scattering systems of ar-bitrary structure is presented.Through the system scattering equation(SSE),the M-objectproblems are first transformed into a series of single-object(S-object)problems and then arethey solved,one-object by one-object,to determine the unknown coefficients of SSE.Finally theSSE is solved to yield the global solutions of original M-object problems.As to the solution ofS-object problems concerned,we use the global numerical boundary condition(GNBC)basedfinite element method(FEM)for complex scatterers,or the moment method(MM)for conduct-ing scatterers.For clarity we will confine ourself in two-dimensional(2-D)cases,and show somecalculation examples of M-object scattering systems for demonstration.     

Analyzing multilayer optical waveguides with a localized arbitrary nonlinear guiding film

We propose a general method for analyzing a multilayer optical waveguide with a localized arbitrary nonlinear guiding film. This method can also be used to predict the evolution of a wave propagating along the multibranch planar waveguide with a localized arbitrary nonlinear guiding film. The numerical results show that our analyses are correct.     

The optimum transient radiation from an arbitrary antenna

Bounds on the optimum transient radiation from an arbitrary antenna enclosed by a spherical surface of specified size are presented. The optimization criterion is either maximization of the radiated electric field amplitude at a specified time and far-zone position, or maximization of the radiated energy density in a specified time interval for a particular far-zone position. The latter optimization results in the prolate spheroidal wave functions. In both cases, the total energy radiated by the antenna is constrained to be 1 J, and the antenna excitation is assumed to be bandlimited. The performance of the optimum arbitrary antenna is compared to that of optimized practical antennas, such as dipoles and arrays of dipoles. The effect of a sidelobe constraint is also studied.     

飞行器蒙皮红外辐射特征的反向蒙特卡罗计算与分析方法

建立了飞行器蒙皮红外辐射特征计算的理论模型,较为完整地考虑了各种热源对蒙皮温度的作用,包括气动加热、发动机热部件以及各部分的传导、对流和辐射.利用反向蒙特卡罗(RMC)法,并结合表面的多重遮挡算法,计算了飞行器复杂几何外形之间的辐射特性,分析了飞行器表面在8～14 μm空间特定方向上的红外辐射特征.结果表明:飞行器马赫数是影响其8～14μm红外辐射特征的重要因素之一,在超音速飞行状态下,气动加热对红外辐射特征的影响比亚音速的大;减小蒙皮表面发射率降低了它的红外辐射强度.该方法可为飞行器表面红外辐射特征计算提供参考.     

Numerical simulation of the multilayer W-type optical fibers radiation mode structure

Numerical simulation of the properties of guided and leaky modes in W-type multilayer cylindrical optical fibers is performed. The dependences of the losses of leaky modes on the parameters of the W-type optical fiber are studied. It is shown that, for certain structures of the W-fiber, the leaky modes have substantial effect on the behavior of propagating radiation. It is shown that, when the mode structure of the radiation in W-type optical fibers is studied, both guided and leaky modes should be taken into account.     

Theory of line-source radiation from a metal-strip gratingdielectric-slab structure

This paper describes the fundamental theory of line source radiation from a source on a dielectric slab backed by a metal-strip grating. A continuous phased-array (CPA) method is applied to treat the analytic and numerical problems of antenna interaction with periodic structures. Both TE and TM mode cases for a one-dimensional strip grating are investigated. It is found that the strip grating on the dielectric surface may result in surface wave elimination and may also be used to support leaky waves. It is shown that high-efficiency and high-gain antennas on a dielectric substrate are possible with such metal-strip gratings     

Finite element analysis of weakly guiding fibers with arbitrary refractive-index distribution

It is shown, with numerical examples, that fundamental quantities that characterize the guided modes of an optical fiber, such as propagation constant, field pattern, fraction of power in the fiber core, group delay, and waveguide dispersion, can be easily and accurately computed by a simple finite element method that incorporates an efficient recurrence algorithm for modeling the infinite cladding of the fiber. With this method, propagation characteristics of single-mode fibers with different refractive-index distributions are calculated and compared.     

Approximate calculation of radiation from open-ended wide microstrip lines

Theoret ca results as given in the literature for the open-ended dielectrically loaded parallel-plate waveguide are used to calculate the input reflection coefficient of open-circuited wide microstrip lines. Numerical computations are in good agreement with measurements for a stripwidth/substrate-height ratio of greater than 3.     

Electromagnetic radiation from structures consisting of combinedbody of revolution and arbitrary surfaces

A formulation is developed to treat radiation from structures consisting of a body of revolution (BOR) in the presence of multiple arbitrarily shaped three-dimensional objects. An electric field integral equation is set up on the surface of the combined structure. The resulting integro-differential equation is solved using the method of moments. On the BOR, harmonic entire domain expansion functions are used for the circumferential dependence, while overlapping subdomain functions are used to model the axial curvature. The arbitrarily shaped portions of the structure are modeled using triangular surface patches. The resulting system matrix has a partial block diagonal nature, which provides a more economical solution for structures that have some rational symmetry. Numerical results are presented and compared to measurements of a unique cavity-backed patch fed antenna     

SOLUTION OF ARBITRARY CROSS-SECTION WAVEGUIDE USING METHOD OF EIGEN WEIGHTED BOUNDARY INTEGRAL EQUATION

Based on the second kind of Green's identity,a boundary integral equation forarbitrary cross-section waveguide is transformed to a system of linear homogeneous algebraicequations by means of expansion of boundary bases and by using the eigenfunctions of a fictitiousregular boundary as weighting functions,which corresponds to less algebraic equations than BEMand simpler coefficients than the modified BEM.The numerical results for some typical metallicwaveguides are given by using the method of eigen-weighted boundary integral equation,and theyare accurate enough with fast convergence.     

Approximate calculation methods for pulse radiation of a TEM-hornarray

Simple approximate calculation methods of pulse radiation by a TEM-horn array are suggested. The first one is based on substitution of the radiation field of each horn to a system of V-antennas; the currents in all of these are equivalent to a single horn current distribution. The second one is based on Huygens-Kirchhoff method applied for time domain. The experimental investigation of radiation field by the array and comparison with results calculated have been carried out     

Plasma channels formed by a set of filaments as a guiding system for microwave radiation

The possibility of formation of a virtual guiding system from a bunch of plasma channels of the filaments of femtosecond laser pulses for transmission of microwave radiation in air is considered. The effective conductivity and the skin depth of the laser plasma of such filaments are calculated for the microwave band. Optimum spatial configurations of plasma channels corresponding to a single-wire transmission line and a hollow cylindrical waveguide are proposed. Estimates of the energy loss of microwave radiation in plasma waveguides of various configurations are obtained.     

Full-wave solutions for the scattered radiation fields from rough surfaces with arbitrary slope and frequency

Full-wave solutions are derived for the scattered radiation fields from rough surfaces with arbitrary slope and electromagnetic parameters. These solutions bridge the wide gap that exists between the perturbational solutions for rough surfaces with small slopes and the quasi-optics solutions. Thus it is shown, for example, that for good conducting boundaries the backscattered fields, which are dependent on the polarization of the incident and scattered fields at low frequencies, become independent of polarization at optical frequencies. These solutions are consistent with reciprocity, energy conservation, and duality relations in electromagnetic theory. Since the full-wave solutions account for upward and downward scattering, shadowing and multiple scatter are considered. Applications to periodic structures and random rough surfaces are also presented.     

Exact derivation of the coupling coefficient in corrugatedwaveguides with arbitrary cross-section: application to optical fibers

Expressions for the coupling coefficient in corrugated waveguides with rectangular tooth shape are derived based on local mode expansion. The expressions are exact to first order in the tooth height (or index difference) for any waveguide cross-section. When applied to slab waveguides, the familiar expressions are obtained. Specializing to weakly guiding fibers, with step index profile, result in simple expressions in terms of the fiber parameters, which are compatible with the effective index method     

坦克排烟的红外辐射计算及热图像仿真

为研究坦克排烟的红外辐射特性,建立了坦克排烟热流场数值计算模型,对流场分布进行分析和计算,得到了排烟的温度场分布。使用谱带模型C-G近似法,计算出排烟的辐射亮度,并进行热图像仿真。通过CO₂辐射亮度的计算值与实测值比较表明:该模型和方法能够得到较为准确的结果,可应用于坦克排烟的红外热图像仿真。     

Methods of calculation of nonstationary nonharmonic fields in guiding electrodynamic structures

Methods of calculation of nonstationary nonharmonic electromagnetic fields excited by electron streams in guiding electrodynamic structures (ESs) of microwave devices are considered. The methods can be applied in first- and second-level spectral models. The proposed discrete approximation is based on decompositions of the field in normal or partial modes of ESs. The continuous approximation proposed is based on decomposition of the field in regular modes of ESs.