Showing papers on "Near and far field published in 1969"
TL;DR: In this article, the scattering of a time-harmonic, linearly polarized plane electromagnetic wave by a cylinder uniformly moving along its axis is discussed, and explicit forms are provided for first-order velocity effects.
Abstract: The scattering of a time-harmonic, linearly polarized plane electromagnetic wave by a cylinder uniformly moving along its axis is discussed. The formalism is relativistically exact, and explicit forms are provided for first-order velocity effects. Consideration is given to both a cylinder moving in free space, using the procedure suggested by Einstein, and two refractive media; it is veritied that the first case is a special case of the second one. Thin scatterers are considered and it is shown that no first-order velocity effects are present. For a moving medium, having in its rest frame the same constitutive parameters as the surrounding medium, it is shown that the velocity-independent part vanishes, but scattered fields of the first order in the velocity are still present. Moreover, these waves appear with the opposite polarization (compared to the incident wave).
48 citations
TL;DR: In this paper, the problem of determining an infinity of Fourier components by expanding each function of θ into a Fourier series is transformed into determining the diflerence current, making possible the determination of the inside and the outside total current.
Abstract: An electromagnetic plane wave in either E or H polarization is normally incident on a cylinder which is assumed to be an infinitely thin‐walled, perfectly conducting, circular tube of finite length with complete generality both in radius and length. For either polarization both axial and transverse currents are induced. The problem is transformed into determining an infinity of Fourier components by expanding each function of θ into a Fourier series. For each Fourier component a pair of integral equations for the total currents is obtained. These are decoupled in a special sense permitting the transverse total current to be obtained first, followed by the axial total current. The diflerence current is then defined and expressed in terms of the total current, making possible the determination of the inside and the outside total current. These are experimentally measurab e quantities. The theoretical formulas for the scattered fields, the far field patterns, and the scattering cross sections are also derived in terms of the total current. Finally, sample results, both theoretical and experimental, are included.
29 citations
TL;DR: In this article, the theory of a quantized Dirac field interacting with a classical electromagnetic field is considered and the resulting q • number problem is reduced to a closely related c • number.
Abstract: The theory of a quantized Dirac field interacting with a classical electromagnetic field is considered. The resulting q‐number problem is reduced to a closely related c‐number problem. The theory is then shown to be without divergences. The interpolating field is shown to exist and is local. Also, the S matrix is shown to be unitary.
25 citations
TL;DR: In this paper, a comparative study of several numerical quadrature techniques is presented, and the superiority of a variable interval-width technique based on Romberg's method is demonstrated for an integral typical of those which arise in scattering and radiation from thin-wire structures.
Abstract: The numerical evaluation of an integral is a frequently encountered problem in electromagnetic theory. This is particularly the case when the current distribution or near field of a scatterer or antenna is required, in which case the far-field approximation cannot be employed. A comparative study of several numerical quadrature techniques is presented. The superiority of a variable interval-width technique based on Romberg's method will be demonstrated for an integral typical of those which arise in scattering and radiation from thin-wire structures.
22 citations
TL;DR: Results have been presented for the far field intensity distribution in the diffraction images and the general triangular wave response of the system.
Abstract: Imagery of a general periodic triangular wave object formed by an aberration-free narrow rectangular aperture (slit) with tapered illumination, has been investigated. The system is assumed to be operating in incoherent light. Results have been presented for the far field intensity distribution in the diffraction images and the general triangular wave response of the system. An object function which gives a wave response nearly similar to that of sine wave has been pointed out.
21 citations
Patent•
08 Aug 1969
TL;DR: In this paper, a probe having a pair of thin film thermocouples positioned in quadrature functions as both an antenna and detector, and this voltage is then used to drive a meter element and display a quantity directly readable as radiofrequency power.
Abstract: A probe having a pair of thin film thermocouples positioned in quadrature functions as both an antenna and detector. The thermocouple elements develop a voltage commensurate with the radiofrequency power of the impinging field and this voltage is then used to drive a meter element and display a quantity directly readable as radiofrequency power.
21 citations
18 citations
01 Nov 1969
TL;DR: In this paper, a numerical technique is described for solving the problem of electromagnetic scattering from perfectly conducting bodies, illustrated by considering the two-dimensional problem of TM scattering from perfect electric conducting cylinders.
Abstract: A numerical technique is described for solving the problem of electromagnetic scattering from perfectly conducting bodies The approach is illustrated by considering the two-dimensional problem of TM scattering from perfect electric conducting cylinders The problem is formulated as a matrix equation involving the Fourier coefficients of the far-field pattern as unknowns, and an analytic continuation procedure is used to extend the far-field representation into the near field in order to apply boundary conditions The calculated far-field pattern for plane wave scattering from a square cylinder is given as an example
TL;DR: In this paper, the electromagnetic radiation from an aperture on a conducting cylinder coated with a moving isotropic plasma sheath is considered, and the radiation patterns as functions of sheath velocity and plasma frequency for the circumferential slot and axial slot apertures are presented.
Abstract: The electromagnetic radiation from an aperture on a conducting cylinder coated with a moving isotropic plasma sheath is considered. Numerical results are presented to illustrate the radiation patterns as functions of sheath velocity and plasma frequency for the circumferential slot and axial slot apertures. It is found for the circumferential slot aperture that the radiation is enhanced in the direction of sheath motion when the plasma is overdense and that relatively little change occurs when the sheath is underdense. For the axial slot, it is found that an electromagnetic field is radiated whose polarization is normal to that of the field radiated under stationary conditions, in addition to a field of the usual polarization. Significant alterations of radiation patterns from their form when the sheath is stationary can occur at relatively small velocities if the wave frequency is near the plasma frequency.
TL;DR: In this paper, the focusing of radiating VLF sources immersed in a cold magnetoplasma was investigated for the case in which the focusing takes place along the static magnetic field direction.
Abstract: The focusing of waves from radiating VLF sources immersed in a cold magnetoplasma is investigated for the case in which the focusing takes place along the static magnetic field direction. The explicit form of tensor Green's function valid along the field line is derived for the far field, and the frequency ranges where focusing may be expected are specified. The theory is applied to calculate the power flux along the field line for an electric dipole and a magnetic loop with two orientations with respect to the static magnetic field.
TL;DR: In this article, a general formulation for the treatment of electromagnetic scattering from an arbitrary configuration of thin wires is presented, and a system of integral equations is derived for obtaining the currents in the wires.
Abstract: A general formulation is presented for the treatment of electromagnetic scattering from an arbitrary configuration of thin wires. A system of integral equations is derived for obtaining the currents in the wires.
01 Apr 1969
TL;DR: In this paper, a 3.57 km line-of-sight atmospheric path using a phase quadrature technique at 10.4 GHz, plus a combination of near-infrared and 23.8-GHz transmissometers operating in oxygen and water vapor absorption bands, respectively, is investigated.
Abstract: Simultaneous measurements have been made on a 3.57- km line-of-sight atmospheric path using a phase quadrature technique at 10.4 GHz, plus a combination of near-infrared and 23.8-GHz transmissometers operating in oxygen and water vapor absorption bands, respectively. The latter two systems provide the separate dry and wet terms of integrated radio refractivity for use in interpretation of the 10.4-GHz phase data. Direct measurement of the statistics of the phase quadrature components of the incoherent scattered field yields several incoherent field parameters not obtained before in line-of-sight experiments. The usefulness of these parameters for atmospheric characterization is being investigated. On this short path the incoherent field is primarily at phase quadrature to the coherent field, and this component is normally distributed, implying a predominantly near-field situation. The postulated decrease of the ratio of quadrature component variances, and of their cross correlation, with spectral frequency has been verified. The agreement noted between transmissometer data and 10.4-GHz phase data in the near field transfers to agreement with 10.4-GHz amplitude data in the far field. This difference, noted in a comparison of measurement spectra, is a helpful analytical tool in the characterization of the atmospheric turbulence wave number spectrum.
Journal Article•
01 Dec 1969
TL;DR: In this paper, the axial and transverse components of the outside total current for the case of E polarization have been measured for two finite tubes with ka = 1.895 and kh = 0.724\pi, both as a function of z or \theta.
Abstract: An experiment is designed to confirm a rigorous theory on the three-dimensional electromagnetic scattering from a circular tube of finite length. Both axial and transverse components of the outside total current for the case of E polarization have been measured for two finite tubes with ka = 1.895 and kh = 0.4827\pi and 0.724\pi , both as a function of z or \theta . Special care was taken to preserve the continuity of the transverse current after each change in the position of the probe. The measured results are in good agreement with the theoretically computed data. Theoretical curves for the corresponding infinite cylinder are also included to show the limitations of using them as approximations to the currents on finite cylinders.
31 Dec 1969
TL;DR: In this article, a model equation for the trajectory of a selected profile ray is described for thermal blooming of a laser beam, and the model equation is applied to an examination of optical focusing for increasing transmitted power density.
Abstract: : Thermal blooming of a laser beam is described by a model equation for the trajectory of a selected profile ray The model equation is applied to an examination of optical focusing for increasing transmitted power density It is shown that the model equation is asymptotic in the far field to the geometric far field solution based on Snell's law for a stratified medium (Author)
TL;DR: In this article, a theoretical investigation concerning scattering of a plane electromagnetic wave by a straight resistive wire of finite length in an isotropic homogeneous medium is reported, based on the travelling-wave solution obtained by repeated use of the Wiener-Hopf method.
Abstract: A theoretical investigation concerning scattering of a plane electromagnetic wave by a straight resistive wire of finite length in an isotropic homogeneous medium is reported. The work is based on the travelling-wave solution obtained by repeated use of the Wiener-Hopf method. Some numerical data for backscattering cross-section at broadside incidence are given.
TL;DR: In this article, an analogue model measurements of electromagnetic variations over an anisotropic conducting cube embedded in a conducting flat model earth in the near field of an oscillating sheet current, line current, vertical magnetic dipole, and a horizontal magnetic dipoles are presented.
Abstract: Analogue model measurements of electromagnetic variations over an anisotropic conducting cube embedded in a conducting flat model earth in the near field of an oscillating sheet current, line current, vertical magnetic dipole, and a horizontal magnetic dipole are presented. The Ex/Hy and Hz/Hy ratios are given as a function of frequency for several depths and orientations of the anisotropic cube and horizontal distances of the cube from the overhead field sources.
TL;DR: In this paper, a laboratory experiment has been conducted to test the theory of Hsieh relating to the effect of an electrostatic field on propagation of electromagnetic waves in an anisotropic plasma.
Abstract: A laboratory experiment has been conducted to test the theory of Hsieh relating to the effect of an electrostatic field on propagation of electromagnetic waves in an anisotropic plasma. Experiment does not support this theory.
TL;DR: Gyrosynchrotron from accelerated electron, discussing effects of cold and collisionless magnetoplasma on far field and frequency spectra as discussed by the authors, discussed the effects of magnetoplasmas on the Far Field and Frequency Spectra
Abstract: Gyrosynchrotron from accelerated electron, discussing effects of cold and collisionless magnetoplasma on far field and frequency spectra