THE INFLUENCE OF STRIPE GEOMETRY OF HIGH SPEED EDGE EMITTING LEDS ON ITS NEAR-FIELD PROPERTIES

The method used for measuring the near-field intensity profiles,radiative intensity linewidth and equi-amplitude contour areas in the radiative region is introduced.For devices with different stripegeometries,the change of intensity width and area,near-field intensity patterns and light intensity topograph,as a function of inject current is analysed.     

Measurement of the Waveguide Near—field Optical Spot

The characteristic of near-field spots is analyzed.The size of the near field and the heat response time of the hybrid record medium to overcome super paramagnetic effect are calculated based on the heat transfer theory.A novel measuring method for the diameter of near-field recording spot is also presented.Since the grain of the recording media is tiny enough,near-field optical lithography can be accomplished with the aid of atomic force microscope(AFM).The diameter of near-field recording sopt can be obtained by specifically designed computer.So the relationship between the near-field recording spot diameter and the probe size of near-field recording system,the near field recording distance coupling between head and disc can be got.     

THE DESIGN OF THE SHIFTING SECTION OF AN INTENSIFIER SILICON TARGET PICK-UP TUBE

The principle for designing the shifting image section of an intensifier silicon target pick-up tubeis given.An electrostatic electron-optical system with a photocathode having an effective diameterof 40mm and a system magnification of 0.65 has been designed.Experiments show that when theelectron image of the photocathode is transferred to the silicon target,the geometric distortion is2%,and the field curvature is 2mm.The astigmatism is less than 0.32 mm at 80 percent of theviewing field and the resolution is over 50 lp/mm.It shows that the design of the electron-opticalsystem is good and reasonable.     

USE OF FINITE-DIFFERENCE TIME-DOMAIN METHOD FOR CALCULATING EM ABSORPTION IN LOSSY DIELECTRIC SCATTERER

The problem for calculating EM energy absorption by lossy dielectric scatterer ir-radiated by plane wave are discussed.The factors affecting the accuracy of computation arediscussed.The calculated results of EM energy absorption and its distribution in homogeneousand layered homogenous lossy dielectric spheres are presented,and a comparison of these resultswith analytical solution is given.The calculation is carried out for dielectric cylinder on conduct-ing ground as well,and the results are compared with the image theory.All the computationsshew that the finite-difference time-domain method can give satisfactory results.     

NUMERICAL SIMULATION OF TIME-DOMAIN EM SCATTERING BY SHALLOW SUBSURFACE OBJECTS

The time-domain ElectroMagnetic(EM) scattering by buried objects in dispersive media is calculated with FD-TD method. The FD-TD formula in Debye dispersive media (both the complex permeability and the complex permittivity are described by Debye equations) are deduced, and the absorbing boundary condition is given. The validity of FD-TD method in lossy media is verified through comparing the FD-TD's results and the other ones. The propagation of transient pulses in dispersive media is studied in detail. The scattering pulses and the wiggle traces for typical buried objects are given.     

THE RELATIONSHIP BETWEEN THE EM ENERGY ABSORPTION OF HUMAN BODY AND THE INCIDENT DIRECTION AND POLARIZATION OF PLANE WAVE

The problems of EM energy absorption of human body irradiated by plane wave arediscussed by the Finite-Difference Time-Domain(FD-TD)method.The local Specific AbsorptionRates(SARs),the whole-body average SARs and the layer average SARs for the inhomogeneousblock model of human body with different incident direction and different polarization of theincident waves are calculated.The results show that the appearance of maximum EM energyabsorption is not always at the situation of the front incidence and the local SARs are moreimportant for the interaction of the EM fields with human body.All results provide more infor-mation about the electromagnetic dosimetry for human body.     

APPLICATION OF THE PML ABSORBING BOUNDARY CONDITION TO FD-TD SIMULATION

The key problem of finite-difference time-domain (FD-TD) method is the skillful application of special conditions on the boundaries of the computational domain. A new technique named Perfectly Matched Layer(PML) yields a robust Absorbing Boundary Condition(ABC) independent of the angle of incidence and the frequency of outgoing waves. In this paper, the principle of the PML technique is briefly presented. Then some problems in the application and their settlements are discussed emphatically. Finally three numerical tests and a measured result are devoted to examine the accuracy and effectiveness of this approach.     

PERFORMANCE ANALYSIS OF THE MUSIC ALGORITHM IN THE PRESENCE OF AMPLITUDE AND PHASE ERROR

This paper presents the performance analysis of the MUSIC algorithm in the presence of channel amplitude and phase Error. Theoretical expression for the error of DOA estimating with MUSIC algorithm and Cramer-Rao bound are derived. It is compared with simulations performed for some representative cases. The results of theoretical expression and simulation show that existence of these errors will increase the error of DOA estimating and degrade its performance.     

THE SYSTEM COMPENSATION OF ISAR

A method for compensating the amplitude-phase distortion of ISAR system is de-scribed.This system compensation can be separated into two parts:the compensation of thesystem before the mixer and the compensation of the system after the mixer.The experimentalresults of the compensation in microwave dark room are given.It is shown that the methodpresented is effective.     

时域近场测量综述

介绍了时域近场测量的基本原理以及时域近远场变换的两种计算方案.比较了时域近场测量和频域近场测量,得到时域近场测量的优缺点及适用范围.并对直接时域计算方案和间接频域计算方案两种计算方法进行简单的比较,得到了两种计算方法各自的优缺点.     

Planar near-field scanning in the time domain .2. Sampling theoremsand computation schemes

For part 1 see ibid. vol.47, no.9, p.1280 (1994). Two computation schemes for calculating the far-field pattern in the time domain from sampled near-field data are developed and applied. The sampled near-field data consists of the values of the field on the scan plane measured at discrete times and at discrete points on the scan plane. The first computation scheme is based on a frequency-domain near-field to far-field formula and applies frequency-domain sampling theorems to the computed frequency-domain near field. The second computation scheme is based on a time-domain near-field to far-field formula and computes the time-domain far field directly from the time-domain near field. A time-domain sampling theorem is derived to determine the spacing between sample points on the scan plane. The computer time for each of the two schemes is determined and numerical examples illustrate the use and the general properties of the schemes. For large antennas the frequency-domain computation scheme takes less time to compute the full far field than the time-domain computation scheme. However, the time-domain computation scheme is simpler, more direct, and easier to program. It is also found that planar time-domain near-field antenna measurements, unlike single-frequency near-field measurements, have the capability of eliminating the error caused by the finite scan plane, and thus can be applied to broadbeam antennas     

时域近场测量的间接频域算法和直接时域算法研究

时域近远场变换是时域近场天线测量的关键技术。本文对时域近远场变换的间接频域算法和直接时域算法进行了数值模拟和分析。针对开口矩形波导天线的时域近场测量 ,选取时空采样参数和内插公式 ,用两种算法计算时域远场方向图 ,分析周期性、时域混叠问题和扫描面截断效应 ,在相互比较和验证的基础上 ,指出两者的优、缺点及适用的情况。     

Formulation of spherical near-field scanning for electromagneticfields in the time domain

Spherical near-field scanning techniques are formulated for electromagnetic fields in the time domain so that a single set of time-domain near-field measurements yields the far field in the time domain or over a wide range of frequencies. Probe-corrected as well as nonprobe-corrected formulations are presented. For bandlimited time-domain fields, sampling theorems and computation schemes are derived that give the field outside the scan sphere in terms of sampled near-field data     

Formulation of probe-corrected planar near-field scanning in thetime domain

Probe-corrected planar near-field formulas in the time domain are derived for both acoustic and electromagnetic fields, so that a single set of near-field measurements in the time domain yields the fields of the test antenna directly in the time domain. The time-domain probe-corrected formulas are first derived by taking the inverse Fourier transform-of the corresponding frequency-domain formulas, and then by using a time-domain expansion for the fields of the test antenna and a time-domain receiving characteristic of the probe. Because these general formulas, which involve a double integral over the scan plane and an infinite time-convolution integral, are rather complicated, we consider a special probe whose output due to an incoming time domain plane wave is proportional to the time derivative of the field of that plane wave. For this special “D-dot probe”, the probe-corrected formulas simplify to give the time-domain far-held pattern as a double spatial integral of the time-domain output of the probe over the scan plane multiplied by the angular dependence of the inverse receiving characteristic of the probe. Time-domain reciprocity relations are derived for reciprocal probes, and their time-domain receiving characteristics are related to their far fields. Finally, a time-domain sampling theorem is derived and a numerical example illustrates the use of the time-domain probe-corrected formulas     

Computation of aperture antenna mutual coupling using FDTD andKirchhoff field transformation

A new method for computing the mutual coupling between aperture antennas using the finite-difference time-domain (FDTD) method together with the Kirchhoff near-field to near-field transformation is described. The method offers a reduction in computer storage, particularly for widely spaced antenna elements in an array     

超分辨近场结构中二元共晶合金掩膜的工作机制

超分辨近场结构(super-RENS)技术通过在传统光盘结构中插入掩膜结构而实现近场超分辨,是目前最具实用化前景的超高密度光存储技术之一,其中掩膜层的近场光学特性是决定其光存储性能的关键。利用三维时域有限差分法(3D-FDTD)对合金掩膜的近场光强分布进行了数值仿真和分析,提出二元共晶合金薄膜在激光作用下形成的规则微结构可能是以其作为掩膜层的超分辨近场结构光盘产生较高信噪比(SNR)的原因。     

Time-domain spherical near-field formulas in the case where theradial components of the electromagnetic field are measured

Spherical near-field formulas in the time-domain are derived so that the electromagnetic field outside a given scan sphere can be found from measurements of the radial electric and magnetic field components on that scan sphere     

Near-to-far-field transformation by a time-domain spherical-multipole analysis

The contribution deals with a new time-domain near-to-far-field (NFF) transformation which is particularly suited for the finite-difference time-domain (FDTD) method. The far field is derived from the tangential field components on a surface enclosing the scatterer by employing a time-domain spherical-multipole representation. The necessary time-domain convolution is performed as "on the fly," in parallel with the FDTD time-stepping algorithm. The efficiency of the method is improved by incorporating a temporal linear interpolation of the near-field data. With the once obtained multipole amplitudes an analytic series representation of the time-domain far field is achieved, which allows a physical interpretability of the result. Moreover, this expansion serves as an ideal basis for a systematic and efficient post processing. The proposed technique may also be useful for other numerical and for asymptotic methods.     

"时间窗"对天线时域平面近场测试结果的影响

天线时域近场测试技术是一种新兴的、测试宽带场和工作在窄脉冲激励下天线辐射场的高效的测试技术.因为它可以利用"时间窗"技术进行信号处理,使其相对频域测试具有独特的优势.本文在已建立的天线时域近场测试系统的基础上,从实验的角度,对"时间窗"参数在天线时域平面近场测试中的影响进行验证分析.举例了三个波段标准天线方向图的测试分析结果,并得出初步结论.