A bound on EMP coupling

A bound on the energy coupled to a load by means of an antenna or aperture subjected to a step function electromagnetic pulse (EMP) is given by the polarizabilities of the antenna or aperture. Examples of coupling bounds for a slender electric dipole antenna, a circular aperture, and a narrow slot aperture with depth are given. It is demonstrated, by use of the bound on the integral of the effective area over all frequencies, that the maximum energy absorbed by an object subjected to a step function EMP is bounded in terms of the static polarizabilities of the object. (The energy spectrum of the step function EMP bounds the spectrum of EMP described by the double exponential over all frequencies.) It is demonstrated that this bound can be used on apertures in infinite ground planes for which Babinet's principle fails to apply (apertures having depth and cavity backed apertures), where the requirement is simply to use the polarizabilities on the incident side of the aperture.<>     

双指数源激励下垂直电偶极子产生的极低频近场

针对雷电过程在地面产生的近区极低频电磁脉冲,推导出了双指数模型激励下垂直电偶极子产生的极低频电磁场的瞬态近似表达式.该方案基于Sommerfeld积分在准静态近似下求解,从频域出发,利用单位脉冲响应的近似结果与双指数模型激励源卷积计算的方法,通过傅里叶逆变换,得到了双指数源激励下的瞬态解析表达式,其可用于模拟雷电信号产...     

New sensors for measuring very short electromagnetic pulses

In order to detect very short electromagnetic pulses under 100 ps in width, a wide-band receiving antenna with a bandwidth from 0 to 14 GHz is needed. The usual short dipoles or monopoles do not provide both the required fidelity (bandwidth) and sensitivity. A novel type of electromagnetic pulse (EMP) sensor has been designed, analyzed, and tested. It is simple, inexpensive, and can detect the electromagnetic pulse with both high fidelity and high sensitivity. An approximate analysis is given for better understanding and optimum design of the proposed EMP antenna     

Plane wave coupling to multiple conductor transmission lines abovea lossy earth

The current induced on an infinite multiple conductor transmission line located above a lossy homogeneous medium due to a transient plane wave is discussed. An exact solution is formulated in the frequency domain using a spatial transform technique. The widely utilized quasi-TEM approximation is derived directly from the exact solution with emphasis on the physical consequences of the assumptions made. Both frequency domain and time domain numerical results are presented for typical transmission structures and documented electromagnetic pulse (EMP) excitations. Comparison of the quasi-TEM approximation to the exact solution is made in order to study the validity of its application in EMP coupling problems. The modeling of the EMP source as an incident plane wave is examined by comparing the induced current due to a dipole source with its steepest-descent contribution     

微型化光纤传输电磁脉冲传感器研究

研制了一套用于小空间电磁脉冲测试的光纤传输电磁脉冲电场传感器。通过电磁仿真软件CST2011,研究了天线结构对被测场影响,并讨论了天线结构、负载阻抗与响应带宽和灵敏度之间的关系,确定了主要设计参数。研制的微型化传感器采用屏蔽结构与偶极子天线的一体化设计,有效减小了天线与电光转换部分的体积和对被测场的扰动,适用于核电磁脉冲和雷电电磁脉冲的测量。传感器采用对称结构,满足自由空间场测量的需要,为电磁脉冲测量和电磁脉冲场标准装置的校准提供了新的手段。     

Radiating dipole antenna with tapered impedance loading

The far-field radiated waveform and field pattern from a thin dipole antenna in the transmission line approximation are considered when the antenna is driven by a voltage generator of waveformV_{0}u(t), whereu(t)is the unit step function. The antenna is loaded with a tapered form of loading and is permitted to include reactance as well as resistance. Analytical and numerical solutions for the far-field pattern and waveform are discussed. In particular, the effects of parallel resistive and inductive loading are presented.     

Optimum load for a linear antenna fed by a short duration pulse

An analysis is described to calculate the optimum load which maximizes the radiated electromagnetic field from a linear dipole antenna fed by a very short pulse. For each frequency in the band, the analysis is carried out by solving Pocklington's equation via a Galerkin moment method, together with a variational technique. A constraint on the energy of the radiated signal is used as an isoperimetric condition, so that the solution is physically realizable. The optimum solution is also compared with the response of an unloaded antenna.     

Finite-Difference Analysis of EMP Coupling to Thin Struts and Wires

This paper describes the implementation of the thin-strut formalism in the 3-D EMP time-domain finite-difference code THREDE. The thin-strut formalism permits inclusion of arbitrary fine wires in THREDE without imposing any corresponding demand to reduce the cell size to the wire size. The keystone of this technique is the so-called in-cell inductance-the inductance per unit length a thin wire would have with respect to an enclosing conductor half a cell removed. THREDE results using this formalism are compared with analytic EMP solutions for a linear dipole antenna and a loop antenna. Errors are around 10 percent for the loop and 7 percent for the dipole. The 10-percent loop error could probably be improved; the 7-percent dipole error seems to be fundamental to the basic THREDE approximations.     

电磁脉冲下通信偶极天线的时域响应快速计算

针对电磁脉冲作用下通信系统受扰的场路结合计算过程较为复杂的问题,提出了基于等效电路的偶极子天线端口时域响应的计算方法.通过分别建立天线的等效电路模型以及电磁脉冲照射下的等效干扰源模型,快速求解天线端口的时域电流响应.选取电磁辐照条件下两个不同尺寸的偶极子天线进行验证,并与采用全波电磁数值软件计算的结果进行了对比.结果表明：提出的等效电路方法不仅速度快而且元件参数易调整,等效电路模型还可以直接应用于通信系统内部电路的电磁受扰评估计算.     

Transient radiation from a linear antenna with nonreflecting resistive loading

The transient waveforms radiated by step voltage or Gaussian pulse excited resistively loaded linear antennas are investigated by numerical means. Current distributions on the harmonically excited antenna are obtained as functions of frequency and for different values of the loading. The transfer functions of the antenna and the spectral densities of the radiated waveforms are obtained as functions of frequency and the loading and for different directions in space. The time dependent radiated waveforms produced by the antenna are obtained by using the fast Fourier inversion technique. The effects of the various antenna parameters on the radiated waveforms are also investigated. Some of the results are compared with available approximate analytical results.     

Transient response of coupled linear dipole antennas

Transient responses of coupled linear dipole antennas are measured for a basic understanding of coupling in the time domain. A very short pulse for excitation is used and it is shown that the measured data represent the quasi-impulse responses. For further investigation and comparison with the measured data, a simple formula of the impulse response of this configuration is derived by using the transmission line approximation. They suggest that the tips and feed points of each antenna have a significant role in the electromagnetic coupling.     

Impedance of a short dipole antenna in a cold plasma

This paper presents the analysis of the impedance of a short dipole antenna in a cold plasma using a quasi-static approach. Two radically different current distributions on the antenna are considered and their influences on the antenna impedance are studied. These distributions include a one-dimensional (1-D) triangular distribution and a three-dimensional (3-D) exponential current distribution. Balmain (1964) analytically solved the first problem. Staras (1964) proposed the second one. In this paper, we offer an analytical solution for the second one as proposed by Staras. We compare both distributions and find that impedances resulting from them are remarkably close. We conclude that the impedance of a short antenna, as derived using the quasi-static approximation, is insensitive to the choice of current distribution. Therefore, any of these two theories can be used when analyzing data from an impedance probe immersed in a space plasma     

Multipath performance of adaptive antennas with multipleinterferers and correlated fadings

This paper presents an approximate analytical cumulative distribution function of the output signal-to-noise-plus-interference ratio (SINR) of an adaptive antenna operating in multipath environments with multiple interferers and correlated fadings. Previously, approximate analytical results were only available for the case of one interferer and independent fadings between antenna branches, whereas in other cases Monte Carlo simulations had to be used with many limitations including excessive computer time and inaccurate results for small probability levels. The distribution, expressed in terms of the mean eigenvalues of the system, is accurate in most cases investigated even though it is based on an approximation to the characteristic function of the output SINR. As a result, a closed-form expression of bit error rate (BER) for coherent phase-shift keying (PSK) has been derived based on this approximation     

Photonic systems for antenna applications

For well over a decade, research groups around the world have been investigating photonic devices for use in antenna, phased-array, and electromagnetic-field-sensor systems. Proposed applications include EMC monitoring, EMP measurements, anechoic-chamber calibration, novel antenna and array designs, remotely located antennas, and smart skins. Photonic antenna links allow immunity from electromagnetic interference, provide an extremely wide working bandwidth, and allow long cable runs with a minimum of loss. Developments in laser technology allow photonic-based links to have very low noise figures and high dynamic range. Opto-electronic devices are now being built in III-V semiconductors (GaAs, InP), which will ultimately lead to opto-electronic integration with MMIC devices. Photonic systems will revolutionize the way in which electromagnetic-measurement and antenna systems will be designed and built in the future. The paper presents an introduction to the types of photonic links and modulator systems available to the antenna engineer     

A phase shifter with one tunable component for a reflectarray antenna

The combination of a dipole and a tunable varactor forms a phase shifter with one tunable component that provides a phase shift over a wide range, from 00 to nearly 3600. The dipole, loaded with a tunable varactor, is used as a patch component of a low-profile reflectarray antenna. An economic assessment shows that the production price of the suggested phase shifter with one tunable component is more than 10 times smaller than the price of the traditional phase shifter, based on p-i-n diode components. The design of such a phase shifter is the goal of this paper. Simulations of the phase shift and loss of the reflected wave as a function of control voltage applied to the varactor were used, based on an analytical model verified by fullwave analysis. The results of simulations are in agreement with measurements. The fast and correct simulation of the reflection coefficient from the dipole loaded with the tunable varactor can be used for the design and optimization of a lowprofile steerable reflectarray antenna.     

阵列辐射瞬态电磁脉冲能量合成特性研究

根据单元天线辐射瞬态电磁脉冲轴线能量传输特性的解析解,提出了阵列辐射瞬态电磁脉冲的点源近似模型,给出阵列辐射瞬态电磁脉冲高效合成特性的物理实质。并采用阵列瞬态电磁脉冲产生系统,对高效合成特性进行实验验证。实验结果和采用点源近似模型计算结果都很好地证明了阵列瞬态电磁脉冲的高效合成特性。     

Near fields of wire antennas by matrix methods

The method of moments [1], [2] is applied to wire antenna near-field problems. Within the general method, two computational procedures are developed. Results of these are compared with those of certain approximate analytical techniques and also with those of other investigators. A treatment for junctions is outlined. Examples are included for a single dipole antenna, for linear arrays of dipoles and also for loop andT-junction radiators.     

Antenna patterns of nonsinusoidal waves with the time variation ofa Gaussian pulse

The development of antenna theory for nonsinusoidal electromagnetic waves has been based on the idealized rectangular pulse. In practice, an antenna that is designed to operate in the mode of an electric hertzian dipole would radiate a pulse that best approximates a Gaussian one when the driving current consists of a linear transient. The principle of radiation of nonsinusoidal electromagnetic waves with the time variation of Gaussian pulses is discussed. The properties of the Gaussian pulse are presented, i.e., the autocorrelation function, energy spectral density, and spectrum. Antenna patterns, such as peak-amplitude pattern, peak-power pattern, energy pattern, and slope pattern are derived for a Gaussian pulse received (or radiated) by a linear array antenna. Computer plots of the derived antenna patterns are presented that show a considerable improvement in the angular resolution capability over that of the antenna patterns that have been derived for a rectangular pulse