Showing papers in "IEEE Transactions on Electromagnetic Compatibility in 1981"

Absorbing Boundary Conditions for the Finite-Difference Approximation of the Time-Domain Electromagnetic-Field Equations

Abstract: When time-domain electromagnetic-field equations are solved using finite-difference techniques in unbounded space, there must be a method limiting the domain in which the field is computed. This is achieved by truncating the mesh and using absorbing boundary conditions at its artificial boundaries to simulate the unbounded surroundings. This paper presents highly absorbing boundary conditions for electromagnetic-field equations that can be used for both two-and three-dimensional configurations. Numerical results are given that clearly exhibit the accuracy and limits of applicability of highly absorbing boundary conditions. A simplified, but equally accurate, absorbing condition is derived for two- dimensional time-domain electromagnetic-field problems.

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

Abstract: 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.

Understanding Middleton's Canonical Formula for Class a Noise

Abstract: This paper develops an intuitive understanding of the meaning and implications of Middleton's canonical formula for Class A noise. The probability density function (pdf) for noise in decibels is derived, and each of the parameters has a clear physical meaning. The effects of parameter variation on the pdf are shown graphically. The canonical Class A formula predicts that the interdecile range of non- Gaussian noise (structured interference) is less than about 30 dB. A simple scenario that produces canonical Class A interference is described. The limited interdecile range of the interference forces the interfering sources in the simple scenario to be located within a limited range of distances. Thus the strictly canonical formula for Class A noise is inadequate for modeling many physical situations.

A Technique for Increasing the Resolution of Finite-Difference Solutions of the Maxwell Equation

Abstract: A two-step expansion technique has been developed for finite-difference codes that can increase the spectral resolution of such codes over selected subvolumes of the original problem space. The utility of this technique is demonstrated by predicting the responses arising from the coupling of an incident exterior field across an aperture in a hollow cylinder to an interior wire. Expansions on the order of fourfold or more are possible. The cost of such increased resolution is a second computer run, doubling the cost as opposed to a cost increase of a factor of 64 if the resolution equivalent to a fourfold expansion were sought from a single run. Possible applications extend to many diverse areas, but most importantly, interior coupling problems may be treated using this technique. For example, this technique may provide a useful method for estimating the responses of cables interior to an aircraft.

Low-Frequency Electromagnetic Penetration of Loaded Apertures

Abstract: Low-frequency (quasi-static) electromagnetic penetration of an aperture can be reduced by loading the aperture with a conductive film or a bonded-junction wire mesh. A quantitative analysis of this phenomenon is carried out in this paper for a loaded circular aperture in a perfectly conducting ground plane of infinite transverse extent. Contact resistance between the aperture loading and the rim is taken into account. The quasi-static magnetic-field problem and the electrostatic field problem from which the aperture polarizabilities and penetrant fluxes are determined are shown to reduce to the problem of solving a single Fredholm integral equation. Exact (numerical) and approximate (variational) solutions to this integral equation are obtained, and the latter are used to represent the polarizabilities and penetrant fluxes by simple analytical formulas and equivalent circuits. These representations are found to be quite accurate when the contact resistance is not too large

Emission Characteristics of Electrically Small Radiating Sources from Tests Inside a TEM Cell

Abstract: An electrically small radiating source of arbitrary nature may be modeled by an equivalent-dipole system consisting of three orthogonal electric dipoles and three orthogonal magnetic dipoles, each excited with arbitrary amplitude and phase. A method of determining the individual dipole moments and the cross-components of such a dipole system, by tests inside a transverse electromagnetic (TEM) cell, is presented along with some experimental results.

Numerical Determination of Induced Currents in Humans and Baboons Exposed to 60-Hz Electric Fields

Abstract: In order to extropolate 60-Hz electric-field effects on experimental animals (baboons) in terms of equivalent effects on man, scaling relations for the induced current densities have been developed by utilizing advanced computer-modeling techniques. Humans and baboons were modeled by a large number of small cubical blocks that were arranged to obtain the best possible fit to the contour of the object. Internal current densities for the models were calculated by the solution of an integral equation for the induced polarization at the center of each block.

The Polarizabilities of Electrically Small Apertures of Arbitrary Shape

Abstract: Numerical procedures, based on a method of moments approach, are given for computing the magnetic and electric polarizabilities of electrically small apertures of arbitrary shape. The magnetic polarizability density is determined through the use of pulse expansion functions defined over quadrilateral subdomains, while the electric polarizability density is obtained by using basis functions, each of which consists of a piecewise arrangement of simple linear functions defined over triangles and having an area coordinate representation. All the subdomains are generated automatically by applying either the Gordon-Hall or the Zienkiewicz-Phillips subdivision techniques. Computed results are obtained for several aperture shapes, including the circle and the ellipse. The calculations for the last two cases are in excellent agreement with the exact values.

An Optimum Sampling Procedure for Use with the Prony Method

Abstract: The ill-posed nature of identifying the poles of a transient response is discussed along with a sampling scheme for minimizing the effect of this ill-posedness. Two simulation examples are given. The results of the second example are compared to previously published results.

Computation of Crosstalk in a Multiconductor Transmission Line

Abstract: Closed-form solutions for the terminal currents of a multiconductor transmission line are obtained. The results allow a numerically efficient computation of the crosstalk associated with an (n + 1)-conductor line when a large number of frequencies are of interest and bypass the usual requirement for the repeated solution of n simultaneous equations at each frequency. The results show the effect of parasitic circuits in the line on the coupling between any two circuits. It is also shown that the usual low-frequency notion of superimposing inductive and capacitive coupling which has been used for lines with only two circuits is valid, for an electrically short line and a sufficiently low frequency, for a multiconductor line containing any number of coupled circuits. Some additional qualitative details concerning the crosstalk are evident in this formulation.

Radio Astronomy and Spectrum Management: The Impact of WARC-79

Abstract: As a valid use of the radio spectrum and an official radio service, radio astronomy was very much a part of the 1979 World Administrative Radio Conference (WARC-79). The allocation of frequency bands is vitally important for the sustained health of the science. WARC-79 provided first the impetus for astronomers, worldwide, to examine the allocation requirements of radio astronomy and then the opportunity to communicate those needs to the regulatory community. The characteristics of radio astronomy, the criteria for interference-free operation, possibilities for sharing with other radio services, and the need for frequency-band allocations are discussed because all bear directly on an evaluation of the Conference. The Final Acts of WARC-79 are examined from the viewpoint of their impact on radio astronomy.

Standing Waves and Notches in an EMP Simulator and Their Reduction

Abstract: The high standing-wave ratio in a model simulator in the midfrequency range defined by kh = 27?h/? ~ 2? (where h is the height of the parallel-plate region) is investigated experimentally. It is shown that the isolated deep minimum or "notch" is due to the mutual cancellation of the imaginary parts of the TM01 and TEM modes. The effects on the SWR and the deep minimum of changes in the magnitude and location of the terminating resistance are investigated. Also studied are the introduction of a bifurcating plate, resistive modal filters, and series aprons. It is shown that, with the proper adjustment of the last named, the "notch" can be eliminated and the SWR reduced to near two at discrete frequencies that span the entire midfrequency range. Since the low-frequency and high-frequency ranges already have low SWR's, the simulator has been made effective over the entire frequency band, in the sense that the SWR is low.

Synthetic-Aperture Radar Based on Nonsinusoidal Functions: IX -Array Beam Forming

Abstract: For sinusoidal waves with bandwidth zero, one obtains the classical formula ϵ = κNL = kc//spl conint/L for the resolution angle of a sensor array, where L is the length of the array, λ the wavelength, /spl conint/the frequency, and c the phase velocity of the wave, while κis a constant whose value is usually chosen to be 1. Waves with the time variation of a rectangular pulse of duration ▵T yield the resolution angle ϵ = 2Kc/▵/spl conint/ P/P /sub N/, where P/P/sub N/ is the signal-to-noise ratio and ▵/spl conint/ = 1/2▵T the nominal bandwidth of the pulse; the same result holds for coded pulse sequences, such as Barker codes or complementary codes, if the main lobe of their auto-correlation function has the shape of a triangle with rise time ▵T. Hence, the resolution angle e can be reduced by increasing the signal power, as well as by increasing the array length L or the bandwidth ▵f. For sinusoidal waves, an increase of the signal power brings no reduction of the resolution angle. The trade between signal power and frequency bandwidth is of interest whenever the attenuation increases rapidly with frequency, e.g., in high-resolution all-weather radar or in underwater acoustic beam forming.

Transmission-Line MNodeling of Shielded Wires for Crosstalk Prediction

Abstract: The adaptation of a transmission-line model to the prediction of crosstalk in shielded-wire circuits is presented. The incorporation of pigtail sections of the shielded cable into the transmission-line model is discussed, and the presence of the pigtail wires is shown to be important. Experimental results are presented which illustrate the prediction accuracy of the model.

Propagation of Surface Waves on a Buried Coaxial Cable with Periodic Slots

Abstract: Consider a coaxial cable with a periodic array of slots in the outer conductor. The cable is buried at a fixed depth below the surface of the earth as one component of an intruder detection system. In this paper, we use an eccentric cylindrical model of the air-earth interface to develop the theory for surface-wave propagation on the buried cable. Numerical results are included for the phase velocity and attenuation constant as functions of the various parameters.

Fundamental Limits for Radio Signals with Large Bandwidth

Abstract: Radio services have traditionally used narrow frequency bands individually assigned. More recently, the concept of sharing very wide frequency bands by several users has been advanced, and this opens the door for the use of much larger bandwidths than in the past. This paper investigates the limits imposed by nature on the bandwidth of line-of-sight radio services operating in the earth's atmosphere. Furthermore, it investigates the limits for time resolution of radio signals, as well as the related limit of the angular resolution of a line array of sensors that receive signals with large bandwidth, and compares it with the classical resolution angle that holds for sinusoidal signals with vanishing bandwidth. Finally, an example is given where the concept of a practically finite bandwidth of a signal reaches its limit, and a more rigorous specification of the signal is required.

A Broad-Band Isotropic Real-Time Electric-Field Sensor (BIRES) Using Resistively Loaded Dipoles

Abstract: A broad-band isotropic real-time electric-field sensor (BIRES) developed by the National Bureau of Standards (NBS) consits of three resistively loaded dipoles mounted orthogonally to each other. It has the capability of measuring a complete description of frequency, polarization, magnitude, and phase information of the incident eleoa i (EM) fild. The typical tangential sensitivity of the BIRES is 13 to 16 ?V/m with a usable dynamic range of 125 to 144 dB for various bandwidths in the frequency range of 10 MHz to 1 GHz. The isotropic response, isotropy, of the BIRES is obtained by calculating the magnitude of the incident electric field, and its variation is found to be le than ± 1 dB.

Synthetic-Aperture Radar Based on Nonsinusoidal Functions: X-Array Gain, Planar Arrays, Multiple Signals

Abstract: Beam forming based on a line array of sensors and radio signals with a triangular autocorrelation function was discussed in Part IX of this series. The resolution angle e was shown to vary like 1/?P/PN with the signal-to-noise ratio P/PN, which puts a premium on getting the best possible signal-to-noise ratio. This paper shows that the signal-to-noise ratio holding for one sensor can be replaced by the signal-to-noise ratio holding for the whole array, which usually is referred to as making use of the array gain. The result is generalized from the one-dimensional line array to the two-dimensional planar array. Furthermore, the method of beam forming is extended from signals returned by point-like scatterers or reflectors to structures composed of several point-like scatterers; the utilization of the array gain has not yet been investigated for this case.

Computational Experience with a Dual Backtrack Algorithm for Identifying Frequencies Likely to Create Intermodulation Problems

Abstract: This paper describes the results of a computational study using a particular enumeration procedure, called a backtrack algorithm, to find the lowest order of radio-frequency intermodulation. The average lowest order and its standard deviation, the average computer time and its standard deviation, along with other relevent statistics are obtained for a series of randomly generated problems with sets of five to 75 threat or source frequencies. Other parameters, such as the guard band, the maximum number of concurrent threats, and the size of the frequency band on the lowest order of intermodulation are varied during the computations. Statistics for these computer runs, along with those relating to terminating the algorithm when the lowest "acceptable" order is reached, are presented in some detail. Brief conclusions follow a listing of the results.

Average Walsh Power Spectrum for Periodic Signals

Abstract: A circular shift-invariant Walsh power spectrum for deterministic periodic sequences is defined. For a sequence with period N, the power spectrum is the average of the Walsh power spectra of all N possible distinct circular shifts. The Average Walsh Power Spectrum (AWPS) consists of (N/2) + 1 coefficients, each representing a distinct sequency. A fast transformation from the arithmetic autocorrelation function of a periodic sequence to its AWPS is presented.

Noise Analysis of Soft Errors in Combinational Digital Circuits Via Walsh Transforms

Abstract: The noise produced at the output of combinational logic circuits by individual gate failures is analyzed through the use of Walsh functions. Soft errors are modeled by allowing the output of each gate in a particular realization to fail temporarily, possibly introducing an error in the single binary output. The input variables also are allowed to be stochastically driven. The output probability of error contains the Walsh transform of an extended logic function and the Walsh characteristic functions of the input variables as well as the individual gate failure variables. These results are specialized to the case where the inputs are statistically independent of the soft errors. A discussion of the transform of the extended logic function is included.

Shielding of ELF Magnetic-Dipole Fields by Ferromagnetic Cylindrical Shells

Abstract: The shielding effectiveness of ferromagnetic cylindrical shells against static and extremely low-frequency ( ELF) magneticdipole fields has been measured and calculated under various conditions. The theory is specifically developed for initially non-uniform electromagnetic fields (no restriction on the dipole-shield separation distance). In addition, the theory takes into account the finite length of the shield where necessary. Satisfactory agreement between theory and experiment is obtained over the range of parameters tested. The results presented here agree in the uniform-electromagnetic-field limit with those derived previously by King for infinite cylinders.

Real-Time Hadamard Transform Coding for TV Signals

Abstract: Analog and digital schemes for implementing the onedimensional Hadamard transform in real time for TV signals has been proposed. Within practical limitations, hardware has been developed and tested according to the scheme. The evaluation of the hardware has been carried out using a real image. Furthermore, bandwidthreduction experiments are conducted for various bit rates. Analog and digital transform coding schemes are compared for prominent performance parameters. It is demonstrated that good broadcast and video-phone quality pictures can be obtained using the first four coefficients, and the first two coefficients, respectively.

Remarks on Anti-RFI Fences

Abstract: In anti-RFI applications such as shielding two radars from one another, the protection obtained from a fence may be significantly less than the diffraction loss introduced by the fence. The effect can be alleviated by using an inner and an outer fence. This tandem design is also advantageous for anticlutter fences, because a given diffraction loss can be obtained with smaller and less costly structures. If the diffraction loss is to be augmented by an edge treatment, the tandem design makes possible the equivalent of stagger tuning.

Experimental Characterization of Partially Degenerate Three-Conductor Transmission Lines in the Time Domain

Abstract: In a recent paper [1], a method for the time-domain characterization of lossless multiconductor transmission lines with cross sectionally inhomogeneous dielectrics was presented. This method is limited to lines with completely nondegenerate propagation; i.e., all the modes have distinct propagation velocities. In this paper, a method is presented for the characterization of lossless partially degenerate three-conductor lines, together with experimental data. The results are in good agreement with independent frequency-domain measurements.

Spectrum Allocations above 40 GHz

Abstract: The 1979 World Administrative Radio Conference (WARC-79) significantly revised the International Table of Frequency Allocations above 40 GHz to reflect a high level of interest and activity in this portion of the spectrum. The new Table of Allocations was created with the objectives of stimulating development of this spectrum resource by providing guidance and protection to users and of providing each potential user bands in all parts of the spectrum suitable to his charter. Thus propagation phenomena played a major role in defining the new table-as did the desire of some Administrations to add services such as Fixed and Mobile. This paper discusses the approach used in creating the new table, summarizes the allocations, discusses some bands of special interest, indicates how future refinement of the table will likely occur, and addresses the challenge presented to the frequency manager by this part of the spectrum.

Walsh Series Expansions of Probability Distributions

Abstract: This paper discusses the representation of probability distribution functions by Walsh series expansions. Generally, such expansions may be employed for the representation of multivariate distributions. However, we confine attention here to univariate and bivariate distributions. The resulting expansions are consequently utilized in the derivation of useful expressions for the moments of corresponding probability distributions. Applications of Walsh expansions of probability distributions are further illustrated by computing output moments for some general classes of nonlinear systems.

Statistics of Electromagnetic Noise Due to High-Voltage Power Lines

Abstract: The impulsive noise caused by a 275-kV transmission line has been measured at 80, 150, and 480 MHz and the results are presented in the form of graphs of the amplitude probability distribution (APD), average level crossing rate, and pulse width (PWD) and pulse-interval distributions (PID's). It is concluded that the noise decreases as the monitoring frequency increases and as the moniitoring antenna is moved away from directly beneath the line. The character of the noise also changes, noise bursts being much less apparent at higher frequencies.

A Model for Assessing the Impact of an Impulsive Noise Process on Land-Mobile Communication

Abstract: This paper develops a statistical model with which the impact of a given noise random process upon a land-mobile communication system (LMCS) can be assessed. This model is useful for computing an upper bound for the fraction of communication-system messages which are affected by any given EMI at any given interference level. Applications of the model include, for example, bounding the interference effects on land-mobile communication of the EMI produced by arbitrary electrical apparatus.

On the Forcing Functions for Externally Excited Transmission Lines

Abstract: This note addresses the issues raised by Frankel in a recent correspondence [1]. Examples are worked out to show the utility of the new theory developed in [2].