Electromagnetic missile launched from a uniform current sheet ofarbitrary shape

A time-domain method, referred to as the variable transformation method, is used to study the transient radiation field from a uniform current sheet of any shape. A uniform current sheet of arbitrary shape is found to be capable of launching an electromagnetic missile (EMM) over the area equal to that of the sheet. The authors first derive the time-domain expression of the transverse electric and magnetic field strength along the axis of a circular sheet. The EMM condition is then derived in the time-domain form. It is then proven that the EMM can exist over an area equal to that of the sheet in any shape     

General and sufficient electromagnetic missile condition

It is proven that an equiphase current sheet with arbitrary shape and arbitrary current distribution is capable of launching an electromagnetic missile (EMM) if certain conditions are satisfied. These conditions are found to correspond to the planewave front for the restricted set of early-time waveforms     

基于半导体激光器的脉冲整形技术

论述一种新的激光脉冲整形方法-利用任意形状的整形电脉冲直接驱动半导体激光器,产生与电脉冲形状一致的激光脉冲, 作为高功率激光装置的种子光源。使用GaAs 场效应管作为开关器件,使用超宽带脉冲触发场效应管产生整形电脉冲,引入阻抗渐变微带技术克服了触发脉冲损耗对级联场效应管数量限制,将整形电脉冲脉冲宽度扩展到10 ns。以整形电脉冲直接驱动半导体激光器,可产生脉宽为10 ns,时域调节精度为330 ps 的任意整形激光脉冲。     

Simultaneous Optical Spectral Shaping and Wavelength-to-Time Mapping for Photonic Microwave Arbitrary Waveform Generation

Photonic microwave arbitrary waveform generation (AWG) based on simultaneous optical spectral shaping and wavelength-to-time mapping in a single specially designed linearly chirped fiber Bragg grating (LCFBG) is proposed. In the proposed approach, the spectrum of a transform-limited ultrashort optical pulse is spectrally shaped, and at the same time is wavelength-to-time mapped by the LCFBG to generate a microwave pulse with a shape identical to that of the shaped optical spectrum. By designing the LCFBG to have an arbitrary reflection profile, a microwave arbitrary waveform is generated. A simple and effective technique to synthesize the LCFBG with an arbitrary reflection response is proposed. Since amplitude-only index modulation is required, the designed LCFBG can be easily fabricated. Two examples showing the generations of a chirped microwave pulse and an ultra-wideband monocycle pulse are experimentally demonstrated.      

探针馈电印刷线天线的矩量法分析——（Ⅱ）多臂天线

通过应用模式分解法,本文将单臂探针馈电印刷线天线的分析方法推广到具有旋转对称性的任意多臂探针馈电印刷线天线的分析计算。首先给出探针馈电N臂印刷线天线的电流积分方程、矩量方程及远区辐射场计算公式;通过一个中心馈电螺旋天线的分析计算验证方法和计算程序的正确性;设计出具有良好圆极化特性的开口双圆环印刷线天线;最后分析了一探针馈电四臂印刷螺旋天线的辐射特性。     

Arbitrary pulse shape synthesis via nonuniform transmission lines

A discrete inverse scattering technique is used to define the impedance profile for a nonuniform transmission line which reflects an arbitrary waveform. Initially charged nonuniform lines, switched out into a general load, can also be synthesized by this method, and are discussed. The direct or layer peeling algorithm is applied to generate profiles which are subsequently analyzed using the one-dimensional finite difference method and fabricated in stripline. Excitation for the nonuniform line is done by using a charged line connected to a photoconductive Si switch triggered by a mode-locked YLF laser. Several lines were fabricated relevant to amplitude modulation of the master oscillator laser pulse for fusion experiments. Using the layer peeling method, a complex high-voltage pulse shape for use in laser fusion experiments is synthesized to an extraordinary degree of precision. It is possible to generate any arbitrary pulse shape by reflecting a step pulse off a synthesized nonuniform transmission line provided the power spectrum of the reflected pulse does not exceed that of the input pulse at any frequency     

Time-domain equivalent edge currents for transient scattering

Time-domain equivalent edge currents (TD-EEC) are developed for the transient scattering analysis. The development is based an the Fourier inversion of frequency domain equivalent edge current expressions. The time-domain diffracted fields are expressed in terms of a contour integral along the diffracting edges for any arbitrary input pulse shape, thereby yielding finite results at the caustics of diffracted rays. The approach also eliminates the need for the evaluation of a convolution integral in the time domain geometrical theory of diffraction (GTD) analysis. The results are compared with the first order GTD results for the transient scattering analysis for a circular disk     

On the aperture and pattern space factors for rectangular and circular apertures

A consequence of a recently discovered edge condition for planar apertures is that all planar aperture distributions are separable physically into a product of an edge factor and an aperture space factor, analogous to the way in which the radiation pattern separates into a product of an element factor and a pattern space factor. An exact relationship between these aperture and pattern space factors for physically realizable vector fields is derived here for rectangular and for circular apertures. For rectangular apertures it leads to a two-dimensional set of doubly orthogonal functions that are characteristic of the aperture geometry. Characteristic functions for circular apertures, however, are shown to exist only if the vector fields are circularly symmetric, although for scalar fields they exist for completely arbitrary aperture distributions with arbitrary edge taper. For rectangular apertures the characteristic functions consist of products of spheroidal functions and for circular apertures they are obtained from a generalization of the spheroidal functions. Some of the properties of these generalized spheroidal functions are developed here.     

A critical analysis of linear inverse solutions to theneuroelectromagnetic inverse problem

This paper explores the possibilities of using linear inverse solutions to reconstruct arbitrary current distributions within the human brain. The authors formally prove that due to the underdetermined character of the problem, the only class of measurable current distributions that can be totally retrieved are those of minimal norm. The reconstruction of smooth or averaged versions of the currents is also explored. A solution that explicitly attempts to reconstruct averages of the current is proposed and compared with the minimum norm and the minimum Laplacian solution. In contrast to the majority of previous analysis carried out in the field, in the comparisons, the authors avoid the use of measures designed for the case of dipolar sources. To allow for the evaluation of distributed solutions in the case of arbitrary current distributions the authors use the concept of resolution kernels. Two summarizing measures, source identifiability and source visibility, are proposed and applied to the comparison. From this study can be concluded: (1) linear inverse solutions are unable to produce adequate estimates of arbitrary current distributions at many brain sites and (2) averages or smooth solutions are better than the minimum norm solution estimating the position of single point sources. However, they systematically underestimate their amplitude or strength especially for the deeper brain areas. Based on these result, it appears unlikely that a three-dimensional (3-D) tomography of the brain electromagnetic activity can be based on linear reconstruction methods without the use of a significant amount of a priori information     

Electromagnetic Backscattering Measurements by a Time-Separation Method

The object of this research is to investigate the feasibility of adapting the conventional pulsed radar technique for closerange back-scattering measurements for obstacles of arbitrary shape and small scattering cross sections. The time-separation or microwave-pulse method described in this paper differs essentially from all previously used laboratory methods in that the scattered field does not mix with the incident field at the detector and is separated from it in time. The essential experimental arrangement of this method is similar to that of the CW magic-T method except that a source generating very short pulses is used instead of CW. Preliminary experimental data for thin circular metallic disks show that the pulse method is a feasible one, since the measured results are in close agreement with the theoretical values. Accurate back-scattering measurements for obstacles of arbitrary shape and small scattering cross sections should be obtainable by this method provided a short microwave pulse of high power level is available.     

On the excitation of a circular loop antenna by travelling-and standing-wave current distributions

Presented here is an exact formulation of the electric and magnetic (EM) fields radiated by a circular loop antenna, assuming both travelling- and standing-wave current distributions. By using a differential current element positioned in an azimuthal direction as the starting point, the paper systematically develops the EM fields radiated by the circular loop via a vector potential theory. This approach leads to a general integral representation for the radiation characteristics of the loop antenna where we completely evaluate the resulting expressions, when the excitations of the loop assume travelling- and standing-wave distribution forms. In addition, this paper briefly examines a method to generate approximately such current distributions by coupling the loop to a two- or four-wire transmission line. Furthermore, the paper discusses a graphical representation of the current distribution plotted as a function of frequency or loop size. From the field expressions determined, we derive generalized closed-form results for some important design parameters for the loop antenna. These parameters include the radial component of the Poynting vector, the total power radiated by the loop, the directivity, the radiation resistance, and the effective area and height of the antenna. When we specialize to the important case of uniform current excitation, the exact values of the parameters deduced from the general expressions, are summarized and exhibited in a comprehensive table. This table facilitates the computations of these important physical parameters. Further analysis involving small argument and asymptotic approximations in the residts for the travelling-wave current excitation leads to closed-form expressions in terms of tabulated functions. Numerical results presented, include the fields radiated by the loop when the standing-wave current excitation admits a Fourier series representation. The present approach via potential theory reveals that the fields can be calculated in any arbitrary direction : this is consistent with a previous observation of Knudsen (1951, 1953) who employed a different approach.     

偏心环微带天线谐振特性的研究

本文用点匹配法分析了偏心环微带天线的谐振特性,所得公式可将圆形、同心圆环和偏心圆环微带天线作为特例来应用.对偏心圆环谐振波数的理论计算与实验测试的良好一致性表明,这种方法适用于分析任意形状微带天线的谐振特性.偏心圆环较之同心圆环有较宽的带宽.     

Simple bounds on modal propagation constant for arbitrarily shapedoptical fibres

The authors show that, when a fibre core cross-section is distorted from circular, the fundamental mode propagation constant β always decreases. To complement the upper bound on β thus obtained, a second approximation is given to β resulting in a simple lower bound and which only requires computation of a geometric shape factor and results for circular cross-sections. The results hold for arbitrary shape and grading     

The circular loop antenna multiloaded with positive and negative resistors

Studies are made of both the driving-point impedance and the amplitude and phase distributions of the current in a circular loop which is driven by an arbitrary number of delta-function generators and loaded with an arbitrary number of lumped impedances. The only restriction imposed in the present treatment is that the elements (either generator or load) are spaced at equal intervals of2pib/malong the circumference wheremis the total number of elements andbis the radius of the loop. The numerical calculations include loads with negative resistances in order to take account of loops loaded with an element like an Esaki tunnel diode, with proper precautions against both self-oscillation and switching effects. A study of such precautions is to be considered separately. The experimental results agree quite well with theory except for the larger values ofbeta b. The radiation patterns of the loop antennas withbeta b=1loaded with various resistors were also measured.     

基于环形统计量和支持向量机的CPM信号调制识别

频率成形脉冲是CPM信号调制相位的度量,也是信号解调必需的调制参数,包括脉冲形状和关联长度。本文提出一种基于环形统计量和支持向量机(Support Vector Machines, SVM)的CPM信号调制识别技术。首先将基带采样信号的瞬时频率看作环形分布的随机变量,计算瞬时频率的三角矩;然后提取其统计量作为分类特征;最后利用支持向量机,实现了不同频率成形脉冲CPM信号的识别。仿真结果表明,该方法可以实现在不同调制参数类型情况下任意脉冲成形CPM信号的识别。仿真结果中给出了包括多指数CPM信号在内的,不同频率成形脉冲CPM信号间的识别率。由于本文采用基于SVM的分类器,不依赖于信噪比条件,因此具有很高的分类性能和良好的稳健性。      

An adaptive ferroelectric transformer—A solid-state analog memory device

A new solid-state adaptive (analog memory) device is described and demonstrated. The device is a flat-band electronic transformer with adaptable voltage gain; that is, the voltage gain-frequency transfer characteristic can be "set" to different values of attenuation by the application of an adapt signal and will retain that setting after the adapt signal has been removed. Ferroelectric materials are used as the dielectric in the transformer structure composed of two capacitors bonded together so that mechanical vibrations established in one (the input capacitor) are coupled to the other (the output capacitor). Converse and direct piezoelectric effects generate the mechanical vibrations and the output voltages, respectively. Ferroelectric effects in either capacitor provide the analog memory capabilities. Experimental adaptive transformers demonstrated are suitable for audio frequency operation. The voltage and current gain-frequency transfer characteristics are flat over the entire audio frequency range. Maximum gain is typically about -20 dB. Application of a voltage pulse (100 to 300 volts) of low energy (mJ) to either side of the transformer can adapt the gains to specific lower settings (between-20 and -60 dB) within an arbitrary switching time (roughly 10⁺³to 10^-4seconds) as determined by the pulse amplitude. Gain settings are electrically stable to within a few percent of the maximum gain for periods of at least one year, and possibly indefinitely, and can be reproduced by the same or an equivalent sequence of adapting pulses.     

A partitioned polynomial integration algorithm for failure probability evaluation

Devices and components are subjected to stresses of certain types which the device must withstand to maintain proper operation. The applied stress and the withstand capability of a device are typically random quantities with associated probability distributions which can have arbitrary shapes. Previous workers approximated these distributions by standard shapes, for example, normal or Weibull, to calculate the failure probability analytically. This letter avoids the approximation of distributions and presents an efficient algorithm which can handle any distribution shape with complete control of the computation accuracy.     

Minimizing pattern effects in semiconductor lasers at high rate pulse modulation

This paper deals with analytical and experimental work related to modulation of a semiconductor laser used in high bit rate communication. The approach is based upon minimizing the charge storage effect by a proper choice of the area of the modulating pulses and the bias current. The concept of using additional current pulses to probe for variations in electron density between pulses is investigated. The primary limitation on bit rate is found to be the ability to generate laser drive pulses free of ringing or similar transients. This and the 300 ps pulsewidth, an experimental constraint, limit the bit rate to about 1 Gbit/s. However, by using this approach it appears that bit rates considerably higher than 2 Gbits/s could be reached with sufficiently accurate control of drive pulse shape. It is found that the laser bias and the current pulse area had to be controlled within 1 percent and 10 percent, respectively.     

声光调Q DPL衍射效率延迟速率对脉冲特性的影响

对于大增益声光调Q的二极管端面泵浦固体激光器,衍射效率延迟速率对输出脉冲特性的影响不再像小增益系统那样可以忽略不计。主要讨论了衍射效率延迟速率对输出脉冲的建立时间以及脉冲形状的影响。首先根据实验测得的衍射效率延迟速率情况对输出脉冲的特性进行了模拟,然后模拟了常数衍射效率延迟速率变化对输出脉冲的特性的影响。实验结果表明,在一定范围内增大衍射延迟速率可以缩短脉冲建立时间,缩短脉冲宽度,增加峰值功率。因此,可以根据实际应用的需要选取符合要求的衍射延迟速率。     

The Theory of Characteristic Modes Revisited: A Contribution to the Design of Antennas for Modern Applications

The objective of this paper is to summarize the work that has been developed by the authors for the last several years, in order to demonstrate that the Theory of Characteristic Modes can be used to perform a systematic design of different types of antennas. Characteristic modes are real current modes that can be computed numerically for conducting bodies of arbitrary shape. Since characteristic modes form a set of orthogonal functions, they can be used to expand the total current on the surface of the body. However, this paper shows that what makes characteristic modes really attractive for antenna design is the physical insight they bring into the radiating phenomena taking place in the antenna. The resonance frequency of modes, as well as their radiating behavior, can be determined from the information provided by the eigenvalues associated with the characteristic modes. Moreover, by studying the current distribution of modes, an optimum feeding arrangement can be found in order to obtain the desired radiating behavior.