bluuebunny/crossref_metadata_2025 huggingface dataset:
Wave Propagation in Plasmas With Very Strong Magnetic Field
Authors: Lee S. W. , Liang C. , Lo Y. T.
Published: November 2015

In the study of wave propagation in a warm magneto‐ionic plasma, the fluid equations are usually supplemented by the equation of state where the pressure is assumed to be isotropic. This model appears to be a good approximation only for a collision‐dominated regime. In this paper, the third moment equation derived from the Boltzmann‐Vlasov equation is used instead of the equation of state. By following the Chew‐Goldberger‐Low theory, the dispersion relation for plane wave propagation can be determined under the adiabatic condition, for strong magnetic field, and without assuming isotropic pressure. Discussions of propagation characteristics under a few special conditions are also included.
Comparison of Experiments on Duct Propagation Above the Sea With the Mode Theory of Booker and Walkinshaw
Authors: Jeske Helmut , Brocks Karl
Published: November 2015

Experiments on tropospheric duct propagation above the sea are discussed, especially in comparison with the mode theory of Booker and Walkinshaw. While the salient features.of ducting processes are well described by this theory, we find no quantitative agreement between the observed and the theoretically predicted field‐strength values. The main reason for this may be additional energy scatter in the maritime sublayer and at the irregularities of the upper and the lower boundary of the evaporation duct, which are not covered by theory.
Numerical Solution of Full‐Wave Equation With Mode Coupling
Authors: Inoue Yuji , Horowitz Samuel
Published: November 2015

A new method for the numerical solution of the wave equation governing the propagation of electromagnetic waves in a horizontally stratified, inhomogeneous, anisotropic medium is described. The wave equation is a homogeneous set of four linear differential equations of the first order. Four linearly independent solutions are derived.

The medium is divided into a number of thin horizontal subslabs. Within a subslab, the propagation coefficient matrix is assumed to vary linearly with respect to height. Under this assumption, the modification of solutions from one height to another is expressed in power‐series form, and the inhomogeneity effect in a subs lab is examined. This, together with the extraction of the phase memory integral from the solution, allows an increase in the integration step size by a factor of 10 over that traditionally used.

During an ordinary integration for an inhomogeneous medium a degradation occurs in the degree of linear independence among special solutions. This cause is analyzed. To obtain a complete set of special solutions with good linear independence, a technique is developed suitable for general application.

This method has been programmed for computer calculation. The resultant wave fields and wave polarizations for the independent modes are shown for a model ionosphere. The resultant wave is described as a “scrambling” of four characteristic waves. The “scrambling” state is illustrated at each height.
Resistance of a Short Antenna in a Warm Plasma
Authors: Kuehl H. H.
Published: November 2015

The input resistance of a short filamental antenna in a warm isotropic plasma is considered from the kinetic (Vlasov equation) rather than the hydrodynamic approach. The results of the two approaches are compared. It is shown that the transverse component of the resistance given by the kinetic approach agrees closely with that of the hydrodynamic approach except for frequencies below the plasma frequency. The longitudinal component of resistance agrees in the two approaches only at frequencies which are large compared with the plasma frequency.
A Further Explanation of the New Theory of Antenna Radiation With Particular Reference to Uniaxial Media
Authors: Lee K. S. H. , Papas C. H.
Published: November 2015

Some tutorial remarks on the new theory of antenna radiation are made. The theory is applied to the special case of an oscillating dipole in a uniaxial medium.
Impedance of an Insulated Linear Antenna Between Layers of Compressible Plasma
Authors: Galejs Janis
Published: November 2015

A flat strip antenna is embedded in a planar dielectric slab, which is surrounded on both sides by layers of compressible isotropic electron plasma. Several closed‐form expressions are obtained for the impedance with a sinusoidal current distribution along the antenna. The antenna impedance is computed numerically when considering the perturbations of the antenna current by surface waves. Except for thin plasma layers, the antenna impedance can be computed using the same current distribution as for a cold plasma. This supports the validity of earlier work which neglects the perturbation of the antenna current by plasma waves. However, it is essential to consider the finite transverse dimension of the antenna and the presence of an insulating layer or of an ion sheath.
Boundary Conditions for a Unique Solution to the Linearized Warm‐Plasma Equations
Authors: Sancer Maurice I.
Published: November 2015

A criterion is presented to decide whether a given set of boundary conditions guarantees a unique solution to the linearized warm‐plasma equations, and a set of boundary conditions is given which meets this criterion. The boundary conditions often employed when the plasma is contained in a perfectly conducting rigid cavity are shown to belong to this set. An absorptive boundary condition based on sheath considerations is also shown to belong to this set.
A Possible Mechanism for Excessive Mode Conversion in the Earth‐Ionosphere Waveguide
Authors: Wait James R.
Published: November 2015

The influence of a spatial periodic variation in the ionosphere's surface impedance is treated theoretically with regard to VLF propagation. It is indicated that substantial mode conversion may take place if the wavelength of the impedance variation is equal to the difference between the guide wavelengths of the two interacting modes.
Role of a Complex Ionic Composition in the Wind‐Shear Theory of Sporadic‐E Layers
Authors: Cuchet Laurent
Published: November 2015

The role of a complex (positive) ion composition in the wind‐shear theory of sporadic‐E layers is investigated. The vertical drift velocIty used is the classical one derived from the “slab” approximation, and it is almost the same for all the different ions. In the new model, with a mixture of positive ions, the limitation of the maximum density of the layers by recombination is much less serious than it was in the old model with a smgle positive ion. Two special cases are studied: the first is concerned with meteoric ions, and it is shown that very thin rectangular layers may occur if the total amount of these ions is sufficient; the second case involves the ions NO+ and O+2, and in this case it appears that large amplifications of electron density at the layer maxima could easily be accompanied by relatively small reductions at the minima.
Ionospheric Electron‐Density ProfiJes With Continuous Gradients and Underlying Ionization Corrections. II. Formulation for a Digital Computer
Authors: Howe H. Herbert , McKinnis Dean E.
Published: November 2015

Details are given of a practical computer formulation of the solution to the ionogram real‐height problem developed at the Institute for Telecommunication Sciences and Aeronomy (ITSA) by A. K. Paul. The method can make full joint or independent use of the ordinary and extraordinary group‐height information available from modern high‐quality radio soundings of the ionosphere. It takes advantage of the strong dependence of group height on the vertical electron‐density gradient at the reflection level to provide a profile with continuous gradients; this is an important feature when applying profile data to radio ray tracing or certain aeronomical problems. Corrections for the “starting” and “valley” portions of the distribution (not directly observed on the soundings) are made by fitting simple models for these regions to portions of the ordinary and/or extraordinary echo data. The problem of numerical convergence of integrals involving the group refractive index infinity is solved by a new expression for the index in which the singular part can be integrated explicitly. The layer maximum is obtained by a parabolic extrapolation which maintains the continuity of gradient to the layer peak and which does not require an independent estimate of the critical frequency.
The Overlapping‐Polynomial Analysis of lonograms
Authors: Titheridge J. E.
Published: November 2015

A simple and more direct derivation of the equations used in the overlapping‐polynomial analysis of ionograms is given. A set of five simultaneous equations is obtained which define the five polynomial coefficients required at each frequency. The steps involved in programming a computer to calculate these coefficients and analyze a virtual‐height record are outlined. The calculation of the coefficients takes about 40 percent longer than the calculation of the coefficients for a lamination analysis using the same number of points. Since, however, the polynomial method requires only about one quarter as many points as a lamination analysis for a given accuracy, a considerable saving is achieved both in the time required for measuring the virtual heights and in the computer time required for calculating the coefficients and analyzing the records. A procedure for allowing for the presence of ionization below the nighttime F layer is also described; this includes corrections for both the low‐density ionization in the E region and the finite ionization gradient at the bottom of the F layer.
A Quick Model Method for Obtaining Real‐Height Parameters From Routine Ionospheric Data
Authors: Taieb C.
Published: November 2015

A method is presented by which profile parameters of the F region may be obtained from the ionogram measurements systematically collected and published by the world ionosonde network. The graphical procedures allow for the effect of the earth's magnetic field, and correct for underlying layers.
Scattering of Waves by a Medium with Strong Fluctuations of Refractive Index
Authors: Bassanini Piero , Cercignani Carlo , Sernagiotto Franco , Tironi Gino
Published: November 2015

The scattering of waves obeying the scalar wave equation is studied by a method which can be applied to large fluctuations of the refractive index. Besides the general theory, a detailed treatment of the scattering from a half‐space and from a slab is given. The results can be applied to circumstances under which the Born approximation fails. This situation seems to arise in connection with the electromagnetic scattering from wakes of supersonic reentry vehicles.
Electromagnetic Wave Scattering From a Cylinder Immersed in a Warm Plasma
Authors: Miller Edmund K.
Published: November 2015

The scattering of transverse electric (TE; Ez = 0) and transverse magnetic (TM; Hz = 0) plane waves from a perfectly conducting cylinder located in a warm (compressible) plasma is considered. Numerical values for the total primary cross sections (TE‐TE and TM‐TM scattering) are given. Results for the ratios of the total conversion cross sections (TE‐TM, TM‐TE, TE‐electrokinetic (EK) and TM‐EK scattering) to the corresponding primary cross section are also presented. The effect of varying the cylinder radius, plasma frequency, electron temperature, and angle of incidence are shown. A comparison is also made of results obtained from a vacuum‐sheath model with those due to a more realistic inhomogeneous sheath model. It is found that, except for near‐grazing angles of incidence for cylinder radii much fess dian the EM wavelength or the plasma frequency nearly equal to the incident wave frequency, the conversion cross sections are on the order of 10−2 or less of the primary cross sections. Thr primary cross sections are, at the same time, not appreciably affected by the sheath or nonzero temperature.
Scattering From Resonant Slots on a Semi‐Infinite Cone
Authors: M. A. Plonus , Goodrich R. F.
Published: November 2015

The scattered field, when a plane wave is incident along the axis of a slotted, perfectly conducting, semi‐infinite cone, is obtained by a superposition of the scattered field from an unslotted cone and the radiation field from the slot on the cone. The slot is a finite, thin, circumferential slot backed by a cavity which is characterized by an admittance. The induced voltage is represented by a sinusoidal distribution. The amplitude of the induced voltage is then related to the incident field by expressing it in terms of the radiating and load admittances of the slot. Expressions for the radiation admittance and the scattered far fields are derived.
An Integral Equation Approach to Scattering From a Body of Finite Conductivity
Authors: Mitzner K. M.
Published: November 2015

The problem of scattering from a homogeneous body is formulated in terms of two coupled integral equations relating the effective electric and magnetic surface currents Ke and Km. The formulation chosen, in which each equation involves the constitutive parameters of only one medium, is especially suited to the case of a high conductivity scatterer. From the equation for the conducting medium, one can derive. under increasingly restrictive assumptions, first an explicit expression for Km in terms of Ke then a curvature‐dependent boundary condition relating the two currents, and finally the usual Leontovich boundary condition. Numerical results for scattering from circular cylinders of small radius show the advantage of the curvature‐dependent condition over the Leontovich condition.
Numerical Application of the Compensation Theorem to Mixed‐Path Propagation Problems
Authors: Christiansen Søren , Larsen Tove
Published: November 2015

The problem of the propagation of radio waves over territories consisting of mixed land and sea areas has to a great extent been treated by the compensation theorem. However, these investigations have been analytical and, therefore, limited to rather simple configurations. This paper investigates whether the compensation theorem could be used in a more direct numerical approach, whereby it becomes possible to treat arbitrary mixed‐path propagation problems. The method is checked by comparison with a simple problem for which an analytical solution is known.
The Illinois 400‐Foot Radio Telescope; Performance and Electronic Equipment
Authors: Yang K. S. , Swenson G. W.
Published: November 2015

The 400‐foot radio telescope of the University of Illinois Vermilion River Observatory, operating at 610 MHz, depends upon a complicated focal‐line antenna array for its steering in declination. In order to obtam an acceptable compronuse between bandwidth and economy, the transmission line system for this array is a compromise between the “branching” system and the “traveling‐wave” system. The transmission‐line arrangements are analyzed in detail. The intricacy of the transmission system results in low overall power efficiency of the radio telescope, but permits easy and accurate adjustment, of declinatlon. An approximately optimum compromise between “sensitivity” and “confusion” is achieved, notwithstanding the low efficiency. From astronomical measurements the effective area of the telescope is 2200 m2, its pointing accuracy is 2 minutes of arc, and its beamwidth is 15 mmutes of arc. Two companson‐type radiometers are operated in synchronism to utilize all of the operating time of the telescope. Minimum detectable signal level in a single observation is approximately 10−26 wm−2Hz−1.
Present Views on Electrodynamics of Moving Media
Authors: Tai C. T.
Published: November 2015

The recent formulations on electrodynamics of moving media proposed by some authors are reviewed. It is pointed out that all these apparently new formulations can be uncovered in the earlier work of Minkowski and Born. It is recommended that this classical work should be thoroughly covered in the curriculum of educational institutions offering graduate courses in electromagnetic field theory.
Modal Solution of a Point Source in a Strongly Focusing Medium
Authors: Kornhauser and A. D. Yaghjian E. T.
Published: November 2015

The ray solution for a point source located in a medium with varying propagation constant given by k(z) = h0 √sech2 αz β2 exhibits for β = 0 the interesting property of the focusing of all rays at periodic distances. The problem of finding the exact solution for the electromagnetic field reduces to that of finding Green's function to the scalar wave equation,

∇G + k20 (sech2 αz − β)G = (1/2πr)δ(r)δ(z − z0).

The eigenfunctions for this equation consist of a mixed spectrum, i.e., a continuous set of eigenfunctions plus a finite number of discrete eigenfunctions. The mixed spectrum is normalized and shown to form a complete set, in which the Green's function is expanded. Examination ofthe discrete spectrum in the far field reveals that all the lower order modes add in phase where ray theory predicts focusing. Integral approximations for the continuous spectrum show that it represents a nonpropagating, rapidly decaying field, which is negligible compared to the discrete spectrum, except in the region “close” to the point source.
Proof That a Phased‐Array Antenna Can Be Impedance Matched for All Scan Angles
Authors: Hannan Peter W.
Published: November 2015

It is known that the impedance match of a phased‐array antenna can be improved over a range of scan angles be connecting lossless Circuits between the transmission lines leading to the radiating elements. Now it is demonstrated that, by more complex interconnections in an infinite series perfect impedance match can theoretically be obtained for all scan angles. This is proven first for an infinite linear array, and then for an mfirute planar array having a square or triangular arrangement of the elements.
A Study of the Depolarization of Lunar Radar Echoes
Authors: Tor Hagfors
Published: November 2015

The radar backscattering characteristics of the lunar surface are examined in detail at a wavelength of 23 cm. The backscattered waves are studied both for circular and for linear polarization of the transmitted wave. Effects relating to the orientation of the local plane of incidence on the moon with respect to the polarization of transmitted or scattered waves are investigated. The experimental results appear to strongly support the hypothesis that the returns at oblique angles of incidence arise through single scattering from discrete objects, as opposed to the returns at near normal incidence which are dominated by quasi‐specular reflection.
Preface to Special Issue on the Propagation of Long Radio Waves
Authors: Crombie D. D.
Published: November 2015

The propagation of long radio waves is of great practical importance in the fields of reliable communication, long range navigation, the dissemination of standard frequency and time, and the detection of nuclear explosions. Long radio waves propagate in the waveguide formed by the earth and the lowest ionosphere. Thus observations of changes in propagation, both diurnally and during solar and geophysical disturbances, provide a useful means of studying the properties of the lower ionosphere.
Frequency Dependence of VLF Fading at Sunrise
Authors: Steele F. K. , Crombie D. D.
Published: November 2015

The sunrise variations of phase and amplitude of VLF signals received over a single long path, at frequencies between 9.2 and 26.1 kHz are interpreted as interference between waveguide modes. The deduced differences in phase velocity and attenuation rates of the first two modes are in accordance with theoretical calculations and with earlier observations in a more restricted frequency range.
Preface
Authors: Felsen Leopold B.
Published: November 2015

Since a good many of the papers published regularly in Radio Science deal with wave problems in magnetoplasmas, especially those of the ionospheric variety, the readership has constant access to information and techniques pertaining to electromagnetic wave propagation in anisotropic media. Nevertheless, it is appropriate at times to draw attention to work in a given subject area by a concentrated grouping of papers dealing with various facets. The present special issue on Electromagnetic Wave Propagation in Anisotropic Media should be regarded in this light.
Ray Optics for Radiation Problems in Anisotropic Regions With Boundaries
Authors: Bertoni H. L. , Hessel A.
Published: November 2015

Based on a rigorous integral representation, the far fields radiated by an electromagnetic point source in the presence of a planar interface between two arbitrary homogeneous, lossless, anisotropic half spaces are evaluated. An invariant ray‐optical interpretation is given to the stationary point contributions (direct, reflected, or transmitted rays) and to the branch curve contributions (lateral rays) to the asymptotic evaluation. The invariant form of the results highlights the local character of the ray‐optical fields and permits one to postulate a generalization of the ray‐optical method of analysis to the problem of reflection and transmission at a gently curved interface, which is generally not amenable to a rigorous analysis. Based on a rigorous integral representation, the far fields radiated by an electromagnetic point source in the presence of a planar interface between two arbitrary homogeneous, lossless, anisotropic half spaces are evaluated. An invariant ray‐optical interpretation is given to the stationary point contributions (direct, reflected, or transmitted rays) and to the branch curve contributions (lateral rays) to the asymptotic evaluation. The invariant form of the results highlights the local character of the ray‐optical fields and permits one to postulate a generalization of the ray‐optical method of analysis to the problem of reflection and transmission at a gently curved interface, which is generally not amenable to a rigorous analysis.
Transient Radiation of an Electric Dipole in a Uniaxially Anisotropic Plasma
Authors: Mittra S. W. Lee and R.
Published: November 2015

Transient radiation from an infinitesimal dipole in a uniaxial plasma medium is examined for the signal frequency Wo greater, as well as less than, the plasma frequency Wp. The propagation of the main signal is calculated along different angular directions as functions of radial distance and time. It is found that, as a consequence of the anisotropy of the medium, the geometry of the “wavefront” may deviate considerably from a spherical surface: For X=(ωp/ωo)2 < l. the signal travels further along the magnetic axis than in the direction transverse to this axis. A much more pronounced effect occurs for X > 1, as the “wavefront” becomes four leaved. These correspond to non‐overlapping regions where the signal is either strictly propagating or strictly evanescent. For a given time there is also a dark region separating these two where no signal has reached. Of particular interest is the result that the critical characteristic bicones where the fields become infinite in the steady‐state analysis always remain in the dark region. This dark region narrows to zero only in the limit of t → ∞. These results shed new light on the so‐called “infinity‐catastrophe” problem which has become a subject of much controversy in recent years. The results of the present study suggest the desirability of a more realistic model for the medium which will include finite losses.
Electromagnetic Plane Wave Scattering From a Plasma‐Coated Conducting Cylinder
Authors: Mayhan R. J. , Schultz F. V.
Published: November 2015

The problem of electromagnetic plane wave scattering from a plasma‐coated, conducting, circular cylinder is considered. Both the TE and TM modes of polarization (with respect to the cylinder axis) are used. Numerical results are given for the back‐scattering cross section per unit length of the cylinder for normal incidence with the TE mode of incidence. In addition to evaluating this cross section with the use of the general model of a compressible, anisotropic plasma. for the sheath, several simpler models are also used and evaluated numerically. When compressible models are used, two different boundary conditions, the rigid and the soft boundaries, are used at the plasma‐air interface. The results of these calculations are then compared. The results indicate that when the soft boundary is used, only a slight degree of coupling between the electromagnetic mode and the pressure mode is obtained. A much greater degree of coupling is obtained with the use of the rigid boundary.
Ionospheric Wave Theory Using Coupled Vacuum Modes
Authors: Poeverlein H.
Published: November 2015

In coupled‐mode theory the wave field in a stratified anisotropic medium appears decomposed into modes, which are coupled in accordance with a set of coupled wave equations. The modes can be defined in various ways. In the conventional formulation they correspond to waves in a homogeneous magnetoionic medium; the present theory uses modes of vacuum propagation characteristics. The coupled wave equations for these vacuum modes have a fairly simple form. The effect of the medium appears in the coupling matrix, whose elements contain a number of terms depending on the various parameters of the medium.

The coupled wave equations, originally obtained from a study of partial reflection at differential slabs of the medium, are now derived in two different ways, both rather direct. In one derivation the vector potential is split into ascending and descending parts. The other derivation adheres to the matrix formalism of the conventional coupling theory as far as possible, thus indicating the essential deviations from the conventional theory. The vertical energy flux densities of the modes are expressed in terms of the field quantities used.
Mode Matching Method for Anisotropic Guides
Authors: Mittra R. , Lee S. W.
Published: November 2015

The mode matching technique is employed frequently in formulating discontinuity problems in isotropic waveguides. An example of this procedure appears in the work of Hurd and Gruenberg who have solved the problem of a bifurcated waveguide. They derive two doubly infinite sets of equations by using the continuity of the interface electrical and magnetic fields, respectively. The final equation for the large waveguide mode coefficients is obtained by subsequent elimination of the unknown mode coefficients of the smaller guides from the first two sets. A key step in this two‐step method of formulation involves the Fourier analysis of the fields using orthogonal mode functions as the basis. In the anisotropic version of the same problem, which is considered in this paper, it is observed that the conventional procedure does not lead to a convenient form. This is a consequence of the fact that the anisotropic guide modes are no longer orthogonal. It is shown that by using biorthogonality relationships introduced by Bresler and others, it is possible to derive a set of equations in the desirable form for the anisotropic case as well.

An interesting observation about the procedure is that the matching of interface tangential electric and magnetic fields is carried out in a simultaneous manner, and hence, the final equations are obtained in a one‐step process as opposed to the two‐step procedure conventionally followed in the isotropic case. The paper discusses the solution of the infinite set of equations appropriate to the anisotropic case and compares it with the Wiener‐Hopf solution derived elsewhere.
Electromagnetic Whispering Gallery Modes in a Dielectric Rod
Authors: Wait James R.
Published: November 2015

It is shown that some of the general coupled electromagnetic modes in a large dielectric cylinder are of a whispering‐gallery type. These have the property that their energy is mainly confined to the region near the boundary. When the axial wave number h is greater than the external wave number k2, these modes are shown to be unattenuated. However, if h is less than k2 the modes are leaky. Approximate expressions are derived for the circumferential phase velocity of these spiraling‐type whispering gallery modes.
Interferometer Phase and Amplitude Measurements for Determining Coherence Ratio and Wavefront Correlation
Authors: Fremouw Edward J. , Lansinger John M.
Published: November 2015

Numerical results are presented which describe the statistics of scattered signals observed with an interferometer. The ratio of nonscattered to scattered flux and the wavefront autocorrelation are related to the distributions and average characteristics of real amplitude product and phase difference. It is shown how a combination of pure amplitude and phase‐dominated information can yield unique solutions for the two wavefront parameters without a priori information concerning them. The treatment is based on assumption of a randomly phased angular spectrum.
Electromagnetic Reflectivity of Nonuniform Jet Streams
Authors: Kritikos H. N. , Lee K. S. H. , Papas C. H.
Published: November 2015

The reflection coefficient of a plane monochromatic electromagnetic wave incident on an idealized laminar plane stratified jet stream is determined. This is accomplished by applying the principle of invariant imbedding to derive a differential equation for the reflection coeffictent. The differential equation which is of the Riccati type is solved approximately for the case of a jet stream With a parabolic velocity profile.
Propagation of Hydromagnetic Waves in Current‐Carrying Regions of the Ionosphere and Magnetosphere (Parallel Propagation)
Authors: Abbas M. , Poeverlein H.
Published: November 2015

Propagation of hydromagnetic waves in the presence of a constant current density is investigated. The theory is developed from macroscopic equations in which a constant current density is introduced by assuming streaming velocities of the electron and ion fluids. The general dispersion relation is derived, and approximate solutions of the dispersion relation are obtained for special situations.

The special cases of this paper refer to a propagation vector in the direction of the magnetic field (“parallel propagation”). In parallel propagation, a transverse current density leaves the propagation vector unaffected, but causes a longitudinal electric field component and a consequent change of the ray direction. With the propagation vector and the current density in the magnetic field direction the effect of currents is significant when J0/H0 is of the order of k ≃ ω/Va (with H0 = B0/µ0 and Va as the Alfvém velocity). When the quantity J0/H0 is larger than the wave number k, the current densities lead to a nonconvective instability. A numerical evaluation demonstrates the effect that currents in the ionosphere and magnetosphere may have on the waves.
The Behavior of the First Normal Modes and the Lateral Wave in a Weak Dielectric Layer
Authors: Nicolis John S. , Hoodbhoy Samir
Published: November 2015

This note deals with some calculations involving the characteristics of the first normal modes and the lateral wave in a homogeneous straight dielectric slab bounded by free space on the one side and a perfect conductor on the other. Both the transmitter and receiver (isotropic radiators) are placed within the slab, d(Km) apart. The varying parameter is where k is the wave number, h is the width of the slab, and Δn = n − 1 ≪ 1 is the deviation of the refractive index of the slab from the free space. The layer is, therefore, considered a “weak” one which makes the obtained numerical results applicable particularly to some types of low level just above the sea surface tropospheric waveguides supporting microwave propagation.
Ray Tracing in the lonosphere
Authors: Kelso John M
Published: November 2015

The problems of tracing rays in the ionosphere for radio propagation, primarily for high frequencies (3 to 30 MHz) and above, are discussed. The limitations on “classical” geometrical optics are described, and their applications to ionospheric problems are indicated.

Some “simplified” processes of ray tracing, which apply well at the earth's surface, but not in the ionosphere itself, are first presented. Next, ray‐tracing methods which apply in an isotropic ionosphere, when the effects of the earth's magnetic field is negligible, are discussed. The results are then extended to more general cases of an isotropic medium, and, finally, to an anisotropic medium (such as the ionosphere in the presence of the earth's magnetic field).

Certain special problems which must be considered in ray‐tracing studies are described next; and, finally, a few of the important areas for the application of ray tracing are noted.
Scattering and Absorption by Short, Thin Metallic Filaments
Authors: Garbacz R. J. , Thiele G. A.
Published: November 2015

There has arisen recently some interest in absorptive obstacles possessing low scattering cross sections. One such obstacle is the very thin, short metallic filament which can absorb, typically, 20 to 30 dB more energy than it scatters. To calculate simply and quickly the broadside backscattering and absorption cross sections versus conductivity of such filaments and to explain their nature, a Thevenin equivalent circuit is postulated which yields reasonably accurate results under suitable restrictions on filament size. The cross sections so derived are checked by an independent computer calculation based on the point matching technique.
Scattering of Electromagnetic Waves From a Tilted Slightly Rough Surface
Authors: Valenzuela G. R.
Published: November 2015

The interaction of a plane wave and a slightly rough surface tilted away from a reference plane is investigated. Expressions for the scattered fields are obtained to second order for a perfectly conducting and a dielectric surface. In the limiting case of no tilt the fields agree with those of Rice. When the normal to the surface is rotated about the intersection between the incidence plane and the reference plane, the treatment yields important polarization effects and gives explicitly as a function of the tilt which irregularities on the surface contribute to the scattered power.

Numerical results are obtained to investigate the relative magnitudes of the terms contributing to the cross sections.
Calculation of Phase Errors in the Frequency Components of a (VLF) Pulse Using Measured Noise Amplitude Distributions
Authors: Lewis E. A. , Ganio A.
Published: November 2015

The theoretical relation between the amplitude distribution of noise and the resulting distribution of phase error in a sinusoid is developed for all values of the parameters. It is shown that the rms phase error can be determined directly from the noise amplitude distribution. The method is illustrated using experimental samples of atmospheric noise amplitude distributions observed in a particular receiving system for VLF timing pulses. For amplitudes well above manmade interference the atmospheric noise in these samples closely follows a 2¾‐power law.
Bearing Deviation in HF Transionospheric Propagation. I. Exact Computations for Some Ionospheric Models With No Magnetic Field
Authors: Narayana Rao N.
Published: November 2015

Expressions are derived for the exact computation of bearing deviation and other high frequency radio ray‐path parameters in a model ionosphere with no magnetic field, but with electron density varying in three dimensions. The three‐dimensional variation is simulated by assuming a spherically symmetric ionospheric model, but with its center of curvature displaced from the center of the earth and by launching the ray out of the plane containing the transmitter and the two centers of curvature. Some numerical results for the ray‐path parameters are presented for tile quasi‐parabolic and quasi‐linear models. Applications of the exact solutions are considered in a companion paper.
Fluctuations of a Gaussian Light Beam Propagating Through a Random Medium
Authors: Kinoshita Yasuaki , Suzuki Michio , Matsumoto Tadashi
Published: November 2015

Distributions of the log‐amplitude and phase fluctuations of a Gaussian light beam propagating through a randomly inhomogenous medium are studied by the evaluation of their mean square values. By means of the adequate focusing system (the optical transmitting antenna) of an aperture size large compared with the medium turbulence scale, log‐amplitude fluctuations are greatly reduced slightly behind the focal point of the focusing system. The reduced fluctuation is strongly dependent upon the focal length, when the focal length is short.
Observation of Wind‐Produced Doppler Shifts in Tropospheric Scatter Propagation
Authors: Birkemeier W. P. , Merrill H. S. , Sargeant D. H. , Thomson D. W. , Beamer C. M. , Bergemann G. T.
Published: November 2015

Persistent average frequency shifts obtained from phase data have been consistently observed on a 230‐km closed‐loop troposcatter circuit when the antennas were synchronously pointed off the great‐circle azimuth. The magnitude of the “Doppler shift” systematically increases with the antenna pointing angle from the great circle. The sign of the Doppler shift reverses across the great circle and depends upon the direction of the crosspath wind simultaneously observed in the lower common volume. Average Doppler shift data are presented for several fixed‐antenna‐offset and antenna‐beam‐swinging experiments conducted under varied meteorological conditions. Observations are interpreted in terms of atmospheric “scatterers” drifting across the path at the average crosspath wind speed. A model based on phase geometry is derived for the average Doppler shift and for Doppler spectra in terms of the crosspath wind velocity, antenna patterns and propagation mechanism.

It is concluded that Doppler frequencies observed with a bistatic transhorizon microwave system depend primarily upon crosspath wind speed and the prevailing atmospheric structure. Crosspath motions thus appear to be an effective source of interference fading in tropospheric transhorizon propagation.
An Investigation of Boundary Theories for the Resonance Probe
Authors: Kostelnicek R. J.
Published: November 2015

A formula for the admittance of a spherical probe in a warm collisional homogeneous plasma is derived using a step ion sheath with complete electron reflection at the sheath‐plasma interface. The resulting equations for the perturbations in sheath voltage and number density at the interface are related to the resonance probe phenomenon. Laboratory measurements displayed the effect of sheath thickness on the resonance probe characteristic. The rigid boundary theory is experimentally shown to break down at sheath collapse, comparing a suitable absorptive boundary theory with the experiment.
Hydromagnetic Wave Instabilities in a Nonneutral Plasma‐Beam System
Authors: Kimura I. , Matsumoto H.
Published: November 2015

Hydromagnetic wave instabilities excited by an electron or ion beam passing through the magnetospheric plasma are investigated especially for the case when the wave frequency ω and wave number k are small and an excess charge remains in the medium. It is found that the electron excess beam causes instability in the Alfvén mode wave and the positive excess charge beam does so in the modified Alfvén mode wave. The frequency of the instabilities is roughly proportional to the excess charge density and to the ion gyrofrequency. The physical picture of this instability is given in terms of wave‐wave interaction. The major morphological features of the pc‐5 micropulsation can be interpreted by this instability, if there exists an excess charge beam of electrons or ions in the magnetosphere.
Linear Array Synthesis for the Best Mean‐Square Approximation of Radiation Patterns
Authors: Butler J. K.
Published: November 2015

A theory of synthesizing linear antenna arrays for the best mean‐square approximation of given radiation patterns is presented in this paper. Element currents and spacings are allowed to vary to achieve the best approximation. Approximations of the given patterns are also made by synthesizing the optimum uniformly spaced arrays. For a given number of elements the non uniformly spaced arrays give better mean‐square approximations than uniformly spaced arrays. The characteristic vector approach is employed for finding the optimum element excitations and spacings.
Synthesis of Concentric Ring Antenna Arrays Yielding Approximately Equal Side Lobes
Authors: Ma M. T. , Walters Lillie C.
Published: November 2015

Based on the Haar's theorem, known in the general approximation theory, a method of synthesizing an optimum concentric ring array is presented. The far field pattern function of such an array is first formulated in terms of the zeroth‐order first kind Bessel function. A numerical approach is used for obtaining a solution approximating any specified radiation pattern according to the “minimax”
rather than the ordinary least‐mean‐square error criterion. With respect to a prespecified array size, the solution obtained has the following properties: (1) the maximum deviation between the synthesized and desired patterns is minimized, (2) the side lobes are approximately equal in level if the specified pattern is a Gaussian function, (3) a maximum directive gain can be realized, (4) a minimum number of elements required to achieve such a performance can be determined, and (5) the solution is unique under certain conditions. The theory and method to be presented are valid for arrays consisting of either isotropic sources or physical directional elements.
The Array as a Space‐Time Information Transducer
Authors: Ksienski A. A.
Published: November 2015

An antenna is considered as a space‐time sampling system whose function is to abstract from the incoming signals the information required for a particular system objective. Examples of such array designs are described for communication and radar objectives. A self‐phased array is described that optimizes the reception of communications signals. An optimum radar array processing is shown to provide a significant resolution improvement over the conventional array.
Fully Developed Turbulent Irregularities in the Ionosphere Due to Cross‐Field Plasma Instability
Authors: Sato Tetsuya , Tsuda Takao , Maeda Ken‐ichi
Published: November 2015

Diffuse nonblanketing type sporadic E layers of midlatitudes are considered in the light of recent
plasma instability theory. Some irrelularities observed in the E region do not seem to be associated
with the wind‐shear mechanism. Computer study of nonlinear cross‐field instability strongly suggests
that this instability is responsible for irregularity formation in the E region of midlatitudes.
General Solution to the Problem of Reflection and Transmission by a Moving Dielectric Medium
Authors: Shiozawa T. , Hazama K.
Published: November 2015

The present paper describes a general problem of reflection and transmission of a plane electromagnetic wave at the interface between a stationary dielectric medium and a dielectric medium moving in an arbitrary direction parallel to the interface. Either case of an incident E or H plane wave is treated.

For the incident E plane wave the reflected wave is generally no longer an E plane wave but a linear combination of E and H plane waves, and similarly the transmitted wave has not only an E‐wave component but also an H‐wave component. For the incident E plane wave, in addition, the E‐wave components of the reflected and transmitted waves carry a positive power, but the H‐wave component of the transmitted wave always carries a negative power while the power carried by the H‐wave component of the reflected wave is always positive. Although the power flow with regard to the H‐wave component of the transmitted wave is negative, the total power transmitted is always positive. A similar argument applies also to the case of an incident H plane wave. The phenomenon of total reflection is shown as modified in ait interesting manner by the motion of a medium.
Radiation From A Scattering Antenna Embedded in a Dissipative Half Space
Authors: Tuan H. S. , King Ronold W. P.
Published: November 2015

The radiation characteristics of a horizontal antenna embedded in a conducting half space and illuminated by a refracted electromagnetic wave are investigated. Asymptotic expressions of the far fields are given in two regions: the horizontal plane of the interface at large radial distances from the vertical axis and the upper hemisphere far from the origin. Due to the interference of the fields generated by the currents in different parts of the antenna, the groundwave and spacewave radiation patterns are different from those due to an infinitesimal horizontal dipole.
On the Scattering of Electromagnetic Waves From a Long Wire
Authors: Chen Chin‐Lin
Published: November 2015

A study is made of the scattering of a plane electromagnetic wave by a long and thin metallic wire in which the case of arbitrary incidence is considered. The Wiener‐Hopf technique is used to solve the integral equation. Explicit and rather simple expressions for the induced current, the far‐field pattern, and the backscattering cross sections are found; numerical results are presented. These results are in reasonable agreement with existing experimental data.
Coniugate Effects of Atmospherically Scattered Auroral Electrons
Authors: Rees M. H.
Published: November 2015

Calculations and experiments have shown that some fraction of an electron stream incident on a gas is scattered in the backward direction. Applied to the aurora we find that about 15 to 20 percent of the electron flux returns up the field lines. These electrons are transferred to the conjugate region via the lines of force, if these are continuous between hemispheres. Losses are negligible, but a small drift in longitude may be expected. The energy spectrum of the electrons becomes softer; however, a close correspondence in occurrence of aurora must prevail. Absence of aurora would be a clear indication that the phenomenon is not associated with closed magnetic shells.

A minor effect on the spectral character of the electrons scattered into the conjugate area is found, which could be associated with a difference in the model atmosphere and ionosphere.
Most Recent Studies of Low Latitude Effects Due to Conjugate Location Heating
Authors: Carlson H. C.
Published: November 2015

The present experimental evidence for the existence of a streaming of a photoelectron flux between magnetically conjugate hemispheres is reviewed. During local night but sunlit conjugate conditions, significant effects are observed on electron temperature, ionic composition, electron density distribution, the intensity of a weak plasma resonance line, and 6300‐Å airglow emissions, due to the conjugate photoelectron flux. The flux is viewed as important not only in its ionospheric and magnetospheric effects, but also as a tool to probe and study related phenomena.
Conjugate F‐Region Enhancement Related to the South Atlantic Magnetic Anomaly
Authors: Pike C. P. , Herman John R. , Gassmann G. J.
Published: November 2015

Airborne ionospheric measurements have been made during solar minimum years (1963‐1965) off the east coast of the United States from Boston to Puerto Rico, the area conjugate to the western slope of the South Atlantic magnetic anomaly. Vertical incidence ionosonde soundings were made on 17 flights under both day and night conditions, and were compared with ground‐based observations along the 75° W meridian. On several late afternoon and night flights, higher values of foF2 were observed over the North Atlantic Ocean compared with the same local time values observed by the ground stations. During the daytime, no such enhancements were found. To determine the east‐west extent of this anomaly, an additional analysis was made using published true‐height profile data (from White Sands, New Mexico, as well as from the east coast chain), which revealed that the east coast exhibits a significant enhancement of F‐region ionization when compared to White Sands and manifests seasonal and diurnal variations. Earlier reported measurements in the southern conjugate region indicated that there is an effect of dumping of trapped electrons, which is most pronounced in the F layer on the western slope of the magnetic anomaly between L = 1.75 and 3 during December and January. No significant D‐ or E‐region effects have been observed in both hemispheres as yet. Circumstantial evidence indicates that there are F‐region ionospheric effects in the Northern Hemisphere due to energetic electrons backscattered from the southern dumping region.