Alexander P. Stone

Ultra-Wideband, Short-Pulse Electromagnetics 2

PULSE GENERATION AND DETECTION: Semiconductor Switching: The Time Evolution of Photonic Crystal Bandgaps (K. Agi et al.). General: Ultrawideband Pulser Technology (D.M. Parkes). ANTENNAS: Impulse Radiating Antennas: Transient Fields of Rectangular Aperture Antennas (S.P. Sulkin). Reflector Impulse Radiating Antennas: Temporal and Spectral Radiation on Boresight of a Reflector Type of Impulse Radiating Antenna (IRA) (D.V. Giri, C.E. Baum). Lens Impulse Radiating Antennas and TEM Horns: Design of the Low-Frequency Compensation of an Extreme-Bandwidth TEM Horn and Lens IRA (M.H. Vogel). Arrays: Transient Arrays (C.E> Baum). General: Some Basic Properties of Antennas Associated with Ultra-wideband Radiation (S.N. Samaddar, E.L. Mokole). PULSE PROPOGATION AND GUIDEANCE: Transient Dielectric Coefficient and Conductance in Dielectric Media in Nonstationary Fields (A. Gutman). SCATTERING THEORY, COMPUTATION, AND MEASUREMENTS: Early Time Signature Analysis of Dielectric Targets Using UWB Radar (S. Cloude et al.). SIGNAL PROCESSING: Time-Frequency Analysis: Feature Extraction from Electromagnetic Backscattered Data Using Joint Time-Frequency Processing (L.C. Trintinalia, H. Ling). Spectral Techniques: The E-Pulse Technique for Dispersive Scatterers (S. Primak et al.). Probabilistic Considerations: Robust Target Identification Using a Generalized Likelihood Ratio Test (J.E. Mooney et al.). General: Error Correction in Transient Electromagnetic Field Measurements Using Deconvolution Techniques (J-Z. Bao et al.). BROADBAND ELECTRONIC SYSTEMS AND COMPONENTS: Systems and Components: Ultra-wideband Sources and Antennas: Present Technology, Future Challenges (W.D. Prather et al.). Ultra-Wideband Radars: Dense Media Penetrating Radar (K. Min, M. Willis, Jr.). Polarimetric Ultra-wideband Radars: Polarimetry in Ultra-wideband Interferometric SEnsing and Imaging (W-M. Boerner, J.S. Verdi). BURIED TARGETS: Analytic Methods for Pulsed Signal Interaction with Layered, Lossy Soil Environments and Buried Objects (L.B. Felsen). 41 additional articles. Index.

Transient Lenses for Transmission Systems and Antennas

In the design of waveguide transitions we desire to transmit a TEM wave, ideally with no reflection or distortion, from one transmission line to another. Such waveguide transition regions are usually referred to as EM lenses or more specifically, transient lenses. This goal is accomplished by specifying the lens geometry and constitutive parameters (i.e., the shape and medium of the EM lens). The physical properties of these lenses, given by the permeability μ and the permittivity ∈, may be a function of position, but we assume that these properties are frequency independent. The conductivity of the medium is taken to be zero, and cross sectional dimensions are large compared to the wavelengths at the high frequencies of interest. This is in contrast to a lens such as the Luneburg lens or Maxwell fish eye lens, both of which are based on a geometric optics approximation. The need for a low dispersion system also argues for TEM guiding structures. Since we may also wish to change the direction of propagation of a wave being transmitted from one region to another, we must also allow for distortion introduced at bends. While in many cases we can obtain exact solutions to the lens design problem, approximations are generally involved in the practical realizations of most EM lenses. For example, one may have to cut off lenses that are theoretically infinite in extent. Moreover, frequency independence may not be realized exactly. The exact solutions to design problems are usually obtained by one of two basic approaches [1], The first method is a differential-geometric approach, while the second method is a differential-impedance-matching and transit-time-conservation approach.

A Differential Geometric Approach to Electromagnetic Lens Design

Abstract : The problems investigated under this minigrant arose in the authors research on electromagnetic (EM) lens design. This research was concerned with an EM lens design technique developed by C.E. Baum for transitioning TEM waves between cylindrical and conical transmission lines.

A Prolate Spheroidal Uniform Isotropic Dielectric Lens Feeding A Circular Coax

ABSTRACT In launching the TEM mode on a coaxial circular cylindrical transmission line at high frequencies, one can use coaxial circular cones as a wave launcher. Characteristic impedances are matched at the boundary of the conical waveguide and the cylindrical waveguide, and in the usual lens sense rays on the conical structure travel with equal time to an aperture plane perpendicular to the axis of the system. To accomplish this the conical region is filled with a uniform, isotropic, dielectric with frequency-independent dielectric constant (lossless and dispersionless). While the lens is not perfect in that there are small reflections at the lens surface, the high-frequency performance can be quite good for a large range of lens parameters.

Generalized TEM, E, and H Modes

Previous papers have considered transient lenses for propagating TEM modes without dispersion. This paper considers the properties of E and H modes in such lenses. The presence of longitudinal field components brings in additional constraints on the allowable coordinate systems, limiting the cases of transient lenses supporting E and H modes to a subset of those supporting TEM modes.

Unipolarized Generalized Inhomogeneous TEM Plane Waves in Differential Geometric Lens Synthesis

Previous results have shown that one can have a generalized Transverse Electromagnetic (TEM) plane wave propagating in the u3 direction in u1, u2, u3 orthogonal curvilinary coordinates. The formal fields are functions of u1 and u2 only and have components in both these directions. The medium is inhomogeneous but isotropic, with formal propagation speed (with respect to the u3 coordinate) a function of only u3. In this case the u3 surfaces can only be planes or spheres. The case of constant φ surfaces for u3 gave a class of TEM waves propagating in the φPrevious results have shown that one can have a generalized Transverse Electromagnetic (TEM) plane wave propagating in the u3 direction in u1, u2, u3 orthogonal curvilinary coordinates. The formal fields are functions of u1 and u2 only and have components in both these directions. The medium is inhomogeneous but isotropic, with formal propagation speed (with respect to the u3 coordinate) a function of only u3. In this case the u3 surfaces can only be planes or spheres. The case of constant φ surfaces for u3 gave a class of TEM waves propagating in the φ

Electromagnetic Lens Design

In this paper we consider the design of transition regions (EM transient lenses) which serve to transmit waves, ideally with no reflection or distortion, from one transmission line to another. The design is accomplished by specifying the shape and medium of the lens region. The physical properties of these lenses, given by the permeability and permittivity, may vary from point to point, but we assume zero conductivity and frequency independence of the media parameters. The distortionless requirement dictates that wavelengths, at the high frequencies of interest, be small compared to the cross section dimensions. Since we may wish to change the direction of propagation of a wave being transmitted from one region to another, allowance must be made for distortion introduced at bends. Examples of EM transition regions include converging, diverging, and bending lens linking cylindrical and conical geometries. Solutions to design problems, which may be exact or approximate, are usually obtained by one of two general methods. One method is differential-impedance matching and transit-time conservation, while the other method is a differential geometric approach. An approach through approximations can also be employed. These transient lens have applications in the design of IRAs (Impulse Radiating Antennas).

Synthesis of purely dielectric transient lenses

It is shown that the generalized form of a TEM plane wave involving inhomogeneous constitutive parameters can be used for the formal fields for synthesizing lens designs based on differential-geometric scaling. This will allow one to have purely dielectric lenses (with free space permeability), and will provide an extra degree of freedom in lens design. It is also shown that guided TEM waves can be propagated in inhomogeneous isotropic media with permittivity proportional to /spl Psi//sup -2/, where /spl Psi/ is the cylindrical radius. Also, very general conductor cross sections can be specified, which allows for the construction of dispersionless bends in high-voltage transmission systems in which the pulse rise time is small compared to transit times across the transmission line (e.g. coax) cross section, a matter of importance for applications in high-power pulse generation and antenna design and for low-loss transmission lines.

Coplanar Conical Plates in a Uniform Dielectric Lens with Matching Conical Plates for Feeding a Paraboloidal Reflector

One form of an impulse radiating antenna (IRA) consists of a paraboloidal reflector fed by conical transmission lines that propagate a spherical TEM wave, which originates from the focal point of the reflector. A diagram which depicts such an IRA is shown schematically in Figure 1. The design considerations of a uniform dielectric lens useful in launching a spherical TEM wave onto such a paraboloidal reflector have been investigated in earlier work1, 2, 3, and the geometrical parameters for the lens design are indicated in Figure 2. The lens design in essence consists of specifying certain parameters. These include the cylindrical radius, h, of the outermost ray which intercepts the reflector, the relative permittivity e r of the lens medium, and the angle, θ r (out), from the apex of the conical transmission line (focal point) to the edge of the reflector. This angle is determined by the reflector geometry through the ratio F/D, where F is the focal distance from the center of the reflector and D is the reflector diameter. We also need to specify the angle θ r (in) made by the line inside the lens with respect to the directions of launch.

An Anisotropic Lens for Launching TEM Waves on a Conducting Circular Conical System

Abstract : A differential impedance and transit-time matching approach is used in the design of an anisotropic lens for launching TEM waves from a small source, through the lens, and onto a conducting circular conical system. This approach leads to a system of ordinary differential equations which may be solved exactly to obtain the lens parameters. An approximate solution, which would be applicable to a design procedure, is also given. (Author)