Carl E. Baum

The singularity expansion method and its application to target identification

The singularity expansion method (SEM) for quantifying the transient electromagnetic (EM) scattering from targets illuminated by pulsed EM radiation is reviewed. SEM representations for both induced currents and scattered fields are presented. Natural-resonance-based target identification schemes, based upon the SEM, are described. Various techniques for the extraction of natural-resonance modes from measured transient response waveforms are reviewed. Particular attention is given to the aspect-independent (extinction) E-pulse and (single-mode) S-pulse discriminant waveforms which, when convolved with the late-time pulse response of a matched target, produce null or mono-mode responses, respectively, through natural-mode annihilation. Extensive experiment results for practical target models are included to validate the E-pulse target discrimination technique. Finally, anticipated future extensions and areas requiring additional research are identified. >

Transient electromagnetic fields

Propagation and diffraction of transient fields in non-dispersive and dispersive media.- Integral equation methods for transient scattering.- The singularity expansion method.- Radiation and reception of transients by linear antennas.- A pulsed dipole in the earth.

Emerging technology for transient and broad-band analysis and synthesis of antennas and scatterers

Due to some applied problems of recent interest significant effort has been devoted to developing the technology of the transient and broad-band electromagnetic response of various objects such as antennas and scatterers as well as the production mechanisms for such transient fields. This paper addresses the various types of approaches which have been used for understandiag such transient/broad-band properties. While initially various approaches aid in analysis of such fields, in some cases other properties of the approaches lead to more powerful results such as synthesis of transient/broad-band properties.

Impulse Radiating Antennas

A number of applications require radiation of a short pulse of electromagnetic energy out to large distances. These applications include target discrimination in a cluttered environment (e.g., looking over the ocean), aircraft identification by taking a “FDR” of its major scattering centers, and target location through foliage. The Impulse Radiating Antenna (IRA) has generated widespread interest for its ability to radiate a broadband pulse. The purpose of this paper is to summarize recent work on Impulse Radiating Antennas.

From the electromagnetic pulse to high-power electromagnetics

Since the 1960s significant effort has gone into developing requisite technology for the nuclear electromagnetic pulse (EMP). In the late 1970s several important summary documents were published. The author updates this information to the present. It is noted that EMP has affected a set of related areas which can be collectively referred to as high-power electromagnetics (HPE). This includes direct-strike lightning, high-power microwaves (HPM), and some aspects of transient radar. >

Analytic Return-Stroke Transmission-Line Model

ABSTRACT The transmission-line model previously developed for the leader stroke is applied to the return-stroke of a lightning channel. The charge stored in the corona is converted into current, by a discharge wave. The dependence of propagation velocity on coronal charge and radius leads to front steepening and the development of a jump discontinuity or electromagnetic shock in a finite time.

Application of Modal Analysis to Braided-Shield Cables

Transmission-line equations are derived for a braidedshield cable by modal analysis. The parameters of the braided shield appear in the coefficients as well as in the source terms of the equations. The source terms also depend on the currents and charges on the outer surface of the shield with all the shields apertures shortcircuited.

The Measurement of Lightning Environmental Parameters Related to Interaction with Electronic Systems

The measurement of electromagnetic fields and related quantities in a lightning environment is a challenging problem, especially at high frequencies and/or in the immediate vicinity of the lightning arcs and corona. This paper reviews the techniques for accomplishing such measurements in these regimes with examples. These sensors are often the same as for the nuclear electromagnetic pulse (EMP), but significant differences also appear.

Scanning and impedance properties of TEM horn arrays for transient radiation

A general concept for ultrawide-band array design using interconnected transverse electromagnetic (TEM) horns is described. At high frequencies (wavelength small compared to unit cell dimensions), the mutual coupling between elements is small and, consequently, the input impedance depends only on the lattice dimensions and not on either scan angle or frequency. At low frequencies (wavelength large compared to unit cell dimensions), the mutual coupling is purposefully made large, by interconnecting the elements to maximize the low-frequency performance. This paper presents the results of analyses using a periodic hybrid finite-element approach to calculate input impedance and scanning performance of generic TEM horn arrays. The limiting case, the planar bicone, is shown to have the frequency-independent property of a self-complementary antenna, making it a useful case for establishing the effects of feed region geometry. Although it radiates bidirectionally, it has the interesting property that its broadside-scan frequency response in the array environment is absolutely flat up to the grating lobe onset limit. A TEM horn array is more unidirectional, but as a consequence suffers both oscillatory variations in the input impedance with frequency and increased limits on minimum achievable rise time.

Exploiting early time response using the fractional Fourier transform for analyzing transient radar returns

This paper presents a new technique for estimating parameters of damped sinusoids and impulse-like responses utilizing both early and late time transient scattering responses. Transient scattering responses are composed of damped sinusoids at late times and impulse-like components at early times. Due to the impulse-like components, it is difficult to extract meaningful damped sinusoids when analyzing the complete data set. In this paper, the entire time-domain response is used to extract the signal parameters of interest utilizing both the early and late times. The fractional Fourier transform (FrFT), especially the half Fourier transform (HFT), is used to analyze the data for parameter identification. Impulse or Gaussian-like pulses can be easily separated from the late time damped exponentials in the HFT domain, as they have similar functional representations. In addition, the damped exponentials have a turn on time which needs to be solved for. Results from two examples show that the new technique is applicable for signals that are composed of damped exponentials with a turn-on time and short pulse-like components.