bluuebunny/crossref_metadata_2025 huggingface dataset:
Generalized Scattering Matrix Equations for Waveguide Structures of Varying Surface Impedance Boundaries
Authors: Bahar E.
Published: November 2015

An infinite set of coupled first‐order differential equations is derived for the complex amplitude of the forward and backward waves in multimode waveguide structures of varying surface impedance boundaries. Using a quasi‐optical approach in the first analysis, the waveguide is considered to consist of an infinity of elementary waveguide sections, with an infinitesimal variation of the surface impedance between two such adjacent waveguides. The second analysis is an extension to the application of the generalized telegraphist's equations for nonuniform waveguides. The two methods are compared in general. Finally, waveguide structures with varying surface impedance boundaries and nonuniform cross sections are considered.
Atmospheric Attenuation at Millimeter Wavelengths
Authors: Wulfsberg Karl
Published: November 2015

Daily measurements of atmospheric attenuation at 15 and 35 GHz were made over a 6‐month period using the sum as a source. Curves showmg percentage time distributions at various zenith angles and attenuation as a function of zenith angle for various weather conditions are presented. Clear sky attenuations were found to be well correlated with absolute humidity. The effect of solar flux variations is discussed.
Diurnal Phase Change of VLF Signals Propagated Over Long Paths
Authors: Ries G.
Published: November 2015

Diurnal phase changes of VLF signals propagated over long paths (d > 5000 km) are discussed. Assuming the model of single‐mode propagation, the annual mean phase change corresponds to the value expected from the theory. The strong scatter of the individual values may possibly be explained by a nonnegligible second mode during nighttime propagation. In the interpretation of the diurnal phase changes of VLF signals propagated over arctic paths, the dependence of the ionization in the lower ionosphere on the solar zenith distance has to be considered.
Transient E‐Mode Propagation in a Plane‐Stratified Plasma
Authors: Hirsch Peter
Published: November 2015

When a harmonic steady state electromagnetic wave, polarized in the plane of incidence, propagates in a plane‐stratified isotropic plasma (regarded as a dielectric), the electric field is found to diverge at the level of plasma resonance. It is shown that this physical inconsistency can be removed by discarding the steady state assumption. In the transient case, the field remains finite, but the magnitude of the longitudinal component increases linearly with time, while that of the transverse component increases as the logarithm of the time.
Electromagnetic Scattering From Rough, Finitely Conducting Surfaces
Authors: Stogryn Alex
Published: November 2015

The problem of electromagnetic scattering from a statistically rough surface bounding a uniform, finitely conducting medium of infinite extent is treated in the Kirchhoff approximation. Both intensity and polarization of the scattered wave is considered. Explicit formulas are obtained for the special case of a normally distributed surface. Comparison is made with previous results obtained by other authors under the assumption of infinite conductivity.
A New Method of Obtaining an lonospheric Index of Solar Activity From the F2 Layer Critical Frequencies
Authors: Chun-ming Huang
Published: November 2015

A new method of obtaining an ionospheric index of solar activity, based on the monthly median foF2 at 4 hours of the day (0, 6, 12, and 18 local hours), is described. The index for each month of the year has beeh determined, together with regression coefficients of quadratic equations for every hour at several typical stations, by minimizing the standard percentage error of foF2 estimates. The index has favorable features: the standard deviation of index above and below its running average is smaller; the standard percentage deviation of residual of foF2 and the standard percentage deviation of total error in forecasts of foF2 are much smaller than those of the index obtained by the current method for calculating an ionospheric index of solar activity. Reasons for considering the new index a better approximation to an ideal solar index for the ionosphere are presented.
RF Admittance Measurements of a Slotted‐Sphere Antenna Immersed in a Plasma
Authors: Waletzko J. A. , Bekefi G.
Published: November 2015

The admittance of a slotted‐sphere antenna immersed in a tenuous plasma was measured at frequencies between 35 and 110 MHz in the region of resonance of the probe‐plasma system. A set of antennas with radii R between 0.8 and 3.2 cm was used. The electron density and temperature were varied thus allowing studies to be made over a range of the parameter R/LD from 6 to 30, where LD is the Debye length. The approximate theoretical model of Harp (1964) for the position of the resonance was compared with measurements and was found to be adequate for values of (R/LD) ≳ 15. The width of the resonance line Δ was essentially independent of gas pressure for pressures below 10−3 Torr but was found to be a strong function of R and LD. The empirical relation (Δ/ωp) ≃ 7.8 (LD/R)1.5 where ω/ωp is the plasma frequency, fits the observations. Some form of collisionless damping causes the observed line broadening.
VLF Attenuation Rates Deduced From Aircraft Observations Near the Antipode of NPM
Authors: Bickel John E.
Published: November 2015

Airborne phase and amplitude records of the transmissions from NPM on 19.8 kHz were obtained near its antipode in July 1963. The data are used to deduce attenuation rates at VLF. The results are presented as curves of attenuation rate of the dominant waveguide mode versus geomagnetic bearing of propagation path as measured at the transmitter. Results are given for both daytime and nighttime propagation and are considered applicable for sea water paths at temperate latitudes.
Solar Flare Effects and VLF Radio Wave Observations of the Lower Ionosphere
Authors: Burgess B. , Jones T. B.
Published: November 2015

The observed changes of phase and signal amplitude of VLF radio waves, propagated over distances varying between 1,000 and 10,000 km, which accompany solar flares have been studied for the period 1961 to 1964. In general, the phase of the received signal advances and the signal amplitude increases during the onset of a solar flare. However, observations of the GBR transmissions at Rome (1,500‐km path) show that for this particular path the phase of the received signal retards in contrast to all other paths studied. Assuming that the conductivity of the lower ionosphere varies exponentially with height under both quiet and disturbed conditions, it is possible to evaluate the waveguide mode characteristics of VLF propagation over large distances. Using this theoretical approach it has been shown that the observations can only be interpreted if both the D region electron density profile is lowered and the gradient of ionization density increased. The magnitude of the flare‐produced changes in ionization density profiles of the lower ionosphere have been evaluated analytically from solar X‐ray data. These profile changes are consistent with the lowering of the D region and increase in ionization gradient that are required to explain the VLF radio wave observations.
Oblique Incidence Ionospheric Reflections of 100 kHz Pulses
Authors: Doherty Robert H.
Published: November 2015

The results of a 16‐month study of the phase and amplitude variations of 100‐kHz Loran‐C pulse signals between Attu and Sitkinak in the Aleutian Islands are presented. The data show changes in signal amplitude which occur at the same solar zenith angle throughout the year and phase changes which do not occur at the same solar zenith angle throughout the year. Signal amplitudes averaged 15 dB higher during the night than during the day. The shape of the measured diurnal phase and amplitude changes suppprts a two‐layer formation of the lower ionosphere, the lower layer primarily influencing the signal amplitude, and the other primarily influencing the signal phase. The data suggest that an amplitude change occurs at a solar zenith angle of 100°. This effect occurs while the sun's rays reaching the ionosphere are still penetrating the ozone layer.
A Note on the Reflection Coefficient of a Sharply Bounded Ionosphere for VLF Signals at the Magnetic Equator
Authors: de Lisle J. M.
Published: November 2015

Closed formulae for the reflection coefficients of a sharply bounded ionosphere for plane waves incident from any direction at the magnetic equator are derived.
Measured Amplitude Variations of the 19.8 kHz Field of NPM Near Its Antipode
Authors: Snyder F. P. , Bickel J. E.
Published: November 2015

Measurements of the field intensity of VLF transmissions from NPM at 19.8 kHz were made at four fixed ground sites located in Bechuanaland, Mrica, during July and August 1963. The sites were in the vicinity of the antipode of the transmitter in Hawaii. Each site employed both a vertical whip and a vertical, rotating loop antenna.

The data indicate that a standing‐wave interference pattern is present in the antipodal region most of the time. During local sunrise and sunset, such a pattern appears to be absent and the signal appears to be received primarily from one general direction. Oscillations of 1‐ to 2‐hr periods in the diurnal amplitude data are explained as being due to interference of signals arriving from various directions, with phase changes associated with changes of the terminator position along the paths.

The difference between east‐to‐west (E‐W) and west‐to‐east (W‐E) attenuation rates for the first waveguide mode is examined. A value of about 0.6 dBfMm is consistent with the observations.
General Mode Structure and Resonant Frequencies for Ferrite‐Loaded Circularly Cylindrical Cavity Resonators
Authors: Bolle Donald M.
Published: November 2015

Some particular solutions have been reported for the mode structure and eigenvalues of cavities partly filled with ferrite. Further results are presented for the general mode structure and eigenvalues for circularly cylindrical cavities partly or completely filled with ferrite magnetized in the axial direction. Numerical results and representations are given for some typical cases.
Electromagnetic Scattering by Thin Inhomogeneous Circular Cylinders
Authors: Taylor Clayborne D.
Published: November 2015

The general problem of electromagnetic wave scattering by thin inhomogeneous circular cylinders is completely formulated. An integral equation for the induced axial current distribution is derived and solved for an incident plane wave of arbitrary direction of propagation. A knowledge of this induced current allows the determination of the scattered fields as well as the scattering cross section.

For convenience the conductivity is only considered to vary axially. Numerical results are presented for the induced axial current and scattering cross section. An important application of this work is in missile vulnerability studies. To this end numerical results are presented for a missile having an ionized exhaust trail. The conductivity of the exhaust trail is considered to taper exponentially along its axis.
Scaling for Rotationally Symmetric Potential in Uniaxial Media
Authors: Eichmann George
Published: November 2015

In this article it is shown that a rotationally symmetric potential can be derived in a uniaxially anisotropic medium whose optical axis is parallel to the axis of symmetry of a rotational boundary. The medium can be homogeneous or piece‐wise homogeneous, i.e., stratified or inhomogeneous where the inhomogeneity is along the axis of symmetry. It is further shown that a scaled Neumann problem can be formulated. Scaling can be extended for proper complex anisotropies. As an example, the scattered field of a dipole above and alined with the axis of symmetry of a conducting prolate spheroid immersed in a uniaxially anisotropic, homogeneous medium whose optical axis is parallel to the axis of symmetry of the boundary, is discussed. A special case of this problem is the field of a dipole scattered by a conducting disc perpendicular to the dipole.
Aperture Fields in an Anisotropic Medium
Authors: Jull E. V.
Published: November 2015

An integral equation for the tangential electric field excited in a slit by an H‐polarized plane wave in a gyrotropic medium, such as a magnetized plasma, is solved for a wide slit by a modification of the Wiener‐Hopf technique. The slit edges are parallel to the gyrotropic axis and normal to the otherwise arbitrary direction of incidence. Calculations for normal incidence on a slit with ka = 4 and 8, where k is the propagation constant in the medium and 2a is the slit width, show that the field becomes less uniform in both amplitude and phase with increasing anisotropy, demonstrating that the uniform field assumption used by some workers is invalid with appreciable anisotropy. The asymptotic form of this solution agrees with that obtained by geometrical diffraction theory, verifying earlier work based on this approach and providing a simple expression for the aperture field in slits of more than about two wavelengths in the medium.
Propagation in Nonuniform Slightly Gyrotropic Media
Authors: Gross Stanley H.
Published: November 2015

A previous paper, part I, presented the basic theory of propagation in nonuniform gyrotropic media in terms of an E and H mode representation. The representation results in a type of coupling that is independent of the rate of variation in the medium and thereby permits the study of regions with strong inhomogeneities along the gyrotropic axis. The coupling between modes arises due to the deviation of the gyromagnetic parameter Y =ωc/ω from zero and infinite values.

Part I provided solutions for models with Y > 1. In this presentation, details will be given for the Y < 1 case which is pertinent for propagation in the ionosphere at medium and higher frequencies. An iterative expansion procedure is employed, as previously, and some general properties are deduced from the solutions. The analysis is applied to the evaluation of the far field radiated by an electric current element exterior to a parabolic electron density layer. These results are applicable to the study of propagation through an ionospheric layer or an ionospheric irregularity.
Full‐Wave Solutions in Terms of Coupled Vacuum Modes
Authors: Walsh Edward J.
Published: November 2015

Various definitions of wave modes can be used to decompose the field of electromagnetic waves in a stratified magnetoionic medium. Magnetoionic modes corresponding to a homogeneous medium of the local characteristics are a very common, though arbitrary choice. They are not necessarily practical for computation or interpretation in all situations.

This paper deals with Poeverlein's modes which have the characteristics of waves propagating in vacuum. His modes represent the waves that would be obtained in an extremely narrow vacuum gap introduced at the point under consideration. The formalism is demonstrated and compared with conventional coupled‐wave theory in the simple ease of vertical propagation in a horizontally stratified isotropic medium.

The numerical solution of the general vacuum‐mode wave equations is discussed for oblique incidence on a horizontally stratified, anisotropic medium with arbitrary orientation of the magnetic field. Particular attention is paid to the problem of numerical swamping. A method is developed for dealing with the swamping phenomenon, which emphasizes the physical aspects of this computational problem.2

Computations were made on a realistic ionospheric model at 16 kHz. The results obtained are compared with other authors results for the same profile.
Biorthogonal Expansions for the Linearized Anisotropic Multifluid Warm Plasma Equations
Authors: Sancer Maurice I.
Published: November 2015

A biorthogonality relation is presented between the eigenfunctions of the operator representing the linearized anisotropic multifluid description of a cylindrical warm plasma and the eigenfunctions of the corresponding adjoint operator. This biorthogonality relation is used to describe the solution to the plasma equations when the plasma is excited by general sources, as well as to decompose a known solution into the appropriate eigenfunction expansion.
On Digital Computer Solutions of Fredholm Integral Equations of the First and Second Kind Occurring in Antenna Theory
Authors: Harrison Charles W. , Taylor Clayborne D. , O'Donnell Edward E. , Aronson Eugene A.
Published: November 2015

An open‐ended iterative technique is presented for solving a Fredholm integral equation of the second kind having a singular kernel, using a digital computer. To ascertain the accuracy of the solution, the original equation is recast analytically into a Fredholm integral equation of the first kind. The unknown function is then obtained by expanding it into a series of orthogonal functions and determining the unknown coefficients by inverting the infinite matrix (truncated at the desired order) using machine methods. The numerical results obtained from the two procedures are in complete agreement. This implies that a definitive solution of the integral equation is obtained.

The problem chosen for solution in this paper arises in connection with the determination of the current distribution along a perfectly conducting open‐ended cylindrical tube that is sufficiently thin so that the phase change of the plane wave exciting electromagnetic field across its diameter may be neglected. A solution for the current that converges is obtained because the structure is driven by the field along its entire length—not at some discrete point by a slice generator, as is the case in the usual theoretical model of the linear transmitting antenna. Curves for the current distribution along the structure for parallel incidence of the electric field are given. Also, the radar cross sections of several tubes for the same field orientation are determined.
Response of Transmission Lines in Proximity to a Cylindrical Scatterer
Authors: Harrison Charles W.
Published: November 2015

A wire is run very close to the surface of a highly conducting cylinder and parallel to its axis. The cylinder is longer and of much larger radius than the wire. Arbitrary values of impedance are connected between the ends of the wire and the cylinder. One objective of this study is to develop formulas for the currents in the load impedances when the transmission line formed by the wire and its image is driven by the nonuniform field consisting of the superposition of the incident plane‐wave field and the backscattered field from the cylinder.

A second objective is to obtain formulas for the load currents in the terminating impedances of a transmission‐line loop oriented parallel to and in the near‐zone field of the cylinder. Coupling to the image two‐wire line is taken into account.

Since the theory depends fundamentally on the field very close to an unloaded cylindrical receiving antenna of moderate diameter, a portion of the paper is devoted to a short‐cut procedure for obtaining expressions for this field which satisfy the boundary conditions.

A brief tabulation of integral values required in the theory is supplied.
Quasi‐Static Fields of Dipole Antennas Located Above the Earth's Surface
Authors: Bannister Peter R.
Published: November 2015

The electric and magnetic field components produced by vertical and horizontal dipole antennas (both electric and magnetic types) located at or above the surface of a semi‐infinite conducting medium are derived and presented for the quasi‐static range. The horizontal separation between the transmitting and receiving dipole antennas (ρ) is assumed to be much greater than their heights (h and z, respectively). These derivations are the result of applying the quasi‐static approximation to the basic Sommerfeld integrals, utilizing the reciprocity theorem and expanding the exponential term involving the antenna heights in a power series. When ρ is much greater than an earth skin depth (δ), δ ≪ δ, or h = z = o+, the formulas for the field‐component expressions reduce to previously derived results. Some numerical values for these expressions are also provided.
A Note on the Description of Dipole Fields
Authors: Gothard Nicholas
Published: November 2015

Spherical and cylindrical dipole fields and the equipotential lines orthogonal to the lines of flux are described here in terms of various parameters. Differential distances along and across the lines of flux are derived. The “breathing balloon” concept is introduced by using a method of increasing the shell parameter L by an increment ΔL. The different parameters describing the dipole field are given in a concise form.
Wave Propagation in a Random Medium With Parabolic Background
Authors: Liu C. H.
Published: November 2015

Wave propagation in a random medium with inhomogeneous background is studied. The medium is assumed to he charactenzed by a dielectric permittivity ε0(x)+ε1(x) where ε0(x) is a function of space and ε,(x) is a random function of position. With ionospheric propagation application in mind, the background medium is taken as an mhomogeneous plasma region with electron density varying as a function of z. A slab of random irregularities is assumed to be imbedded in the plasma. fluctuations and correlatiOn functions of spherical waves propagating through this medium are calculated using W.K.B. and pertubation techniques. They are compared with the results obtained for the case where the background medium is homogeneous. It is found that the corrections to the fluctuations due to the inhomogeneous background are maximum when the irregularity slab is at the peak of the electron density profile. From this result, it is believed that scintillations of radio signals from satellites are more easily observable when the irregularities are near the peak of the ionosphere electron density profile.
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 spedal issue on Electromagnetic Wave Propagation in Anisotropic Media should be regarded in this light.
Spectral Parameters of the VLF Radio Noise Observed as Functions of the Azimuth
Authors: Frisius J. , Heydt G.
Published: November 2015

The actions of a new atmospherics analyzer, which determines for every incoming atmospheric the apparent angle of arrival together with certain characteristics of the VLF spectrum, are briefly explained. Then the physical significance of the observable spectral quantities are considered by use of a simplified version of the VLF waveguide mode theory. Finally, spectral observations of a 4‐ week period are presented in such a way that the influence of daytime and azimuth are evident and comparison with theoretical propagation computations is enabled.
Radio Propagation Through New Guinea Rain Forest
Authors: Whale H. A.
Published: November 2015

Measured relative field‐strength curves for frequencies in the range 2–50 MHz are given for propagation of vertically polarized radio waves through New Guinea coastal rain forest (jungle). These indicate very high attenuation at the higher frequencies.
Ray‐Path Equations for an Ionized Layer With a Horizontal Gradient
Authors: Nielson Donald L.
Published: November 2015

Equations are derived for ray paths in a model ionosphere that has a horizontal gradient in electron density. The basic vertical profile is second order or parabolic, while the horizontal variation is either linear or parabolic. Group and phase‐path expressions are also derived. The equations have been used successfully in a ray‐tracing approach to HF propagation prediction.
Wavelength Dependence of Microwave Propagation Far Beyond the Radio Horizon
Authors: Eklund Folke , Wickerts Sture
Published: November 2015

The wavelength dependence of microwave propagation far beyond the radio horizon is studied experimentally and theoretically. The experiments made over a 259‐km path at 1000 MHz and 3000 MHz with scaled antennas give as a main result a wavelength dependence of actually received power relative to received power in free space ranging from λ−1 to λ−3. The exponent of the wavelength dependence is found to be correlated to the level of received signal power.

Calculations are made of received signal power under the assumption that the tropospheric refractive index field of the common volume is of a turbulent structure, where the variations obey the −5/3 spectral law. There are also locally sharp boundaries within the common volume, which act as reflecting facets.

A meteorological reasoning leads to the conclusion that there is a connection between the intensity of the turbulence and the refractive index gradient through the reflecting facets. Based on this, we get a relation between the exponent of the wavelength dependence and the level of received signal power.

As a main result, reflections in the facets at 1000 MHz play a dominating role while at 3000 MHz, turbulent scatter is the most important propagation mechanism.

Finally, theoretical and experimental results are compared and a comparatively good agreement is found.
Horizon Focusing Effects Observed on Ionospherically Reflected Radio Waves
Authors: Humphrey L. C.
Published: November 2015

The focusing gain parameters associated with radio waves reflected obliquely from the ionosphere as derived theoretically are compared with experimental observations. The description of the field in the neighborhood of the caustic depends on the shape of the ionosphere with respect to the earth. For an ionosphere concentric with the earth and a surface location transmitter it is convenient to describe the focusing gain in terms of the evaluation angle of arrival. For a tilted ionosphere, or for an elevated transmitter in which the caustic is elevated above the earth's surface, it is convenient to describe the field as a function of the distance behind the cusp, and above the caustic surface.

Experimental observations indicate both situations may exist in nature. The concentric ionosphere is termed the normal situation, and a gain inversely proportional to the approximate cube of the elevation angle was indicated by the experimental data as opposed to a straight inverse relationship by geometric optics. The effect of a distorted ionosphere was evidenced by strong focusing gain at positive elevation angles. It is hypothesized that an increase in curvature of the ionosphere can result in the observed gains which would be consistent with the theory. The required curvature has been observed on other experimental programs.
Ray‐Tracing Synthesis of lonogram Observations of a Large Local Disturbance in the Ionosphere
Authors: Paul A. K. , Smith G. H. , Wright J. W.
Published: November 2015

A ray tracing program especially suited to propagation at nearly vertical incidence has been developed and used to synthesize sweep frequency ionograms for a severely perturbed ionosphere. The actual disturbance was produced by the release of 22 kg of SF6 near the F2 peak as one of a series of chemical releases from rockets. For the ray‐tracing study, the observed unperturbed electron density distribution was modified by a four parameter reduction function to simulate the disturbed region. By varying the parameters to obtain agreement between observed and calculated ionograms, the temporal and spatial progress of such an electron‐deficient region may be investigated. Typical ray paths, calculated without the geomagnetic field, are illustrated and the resulting synthesis is shown to agree qualitatively with the perturbation echoes observed on ionograms obtained after the SF6 release.
Electromagnetic Scattering by a Moving Conducting Sphere
Authors: Restrick Robert C.
Published: November 2015

A relativistically correct expression for the far zone electromagnetic field scattered by a perfectly conducting sphere, moving with constant velocity, through an incident plane wave is developed. It is seen that if the scattered field is expressed in a special “retarded” coordinate system, a result that is more tractible, allowing physical interpretation, is obtained. When the field is expressed in this way, the expected first‐order effects are manifest, yet the higher order effects are also present. This solution may be directly applied to the finite bodies with more complicated shapes than the sphere. For the case of the sphere it is found that the form of the scattered field allows the calculation of the scattering cross section, the total scattering cross section, and the rate of exchange of electromagnetic and mechanical energies.
Numerical Solutions of Electromagnetic Boundary Value Problems by Means of the Asymptotic Anticipation Method
Authors: Neureuther A. R. , Zaki K.
Published: November 2015

A method for improving the accuracy of approximate numerical solutions of doubly infinite sets of simultaneous linear algebraic equations is presented. The method is based on using prior information about the asymptotic behavior of the solution to anticipate the dominant contribution of the terms beyond the truncation limit imposed by the restriction of numerical solutions to finite matrix equations. Such information is shown to be available for the sets of equations which are frequently used in electromagnetic boundary value problems. The advantages and disadvantages of this method are discussed and then illustrated via results for the well‐known problem of scattering from a planar grating.
Characteristic Waves on an Infinite Cylindrical Antenna in a Plasma Medium
Authors: Miller Edmund K.
Published: November 2015

An analysis of the current on an infinite cylindrical dipole antenna immersed in a lossy plasma medium that may, in the general case, be both compressible and anisotropic, is discussed. The antenna current, for the isotropic, incompressible plasma with no sheath present is evanescent along the antenna axis for frequencies (f) less than the electron plasma frequency (fp). When f > fp, the current is axially propagating with a wave number whose real component Kzr is given by , where KE0 is the free‐space electromagnetic wave number. Addition of a static magnetic field parallel to the antenna axis opens up a region of propagating antenna current below the electron cyclotron frequency (fh) with , so that the region of evanescent current is reduced to . A further decrease in the region of evanescent current behavior to approximately (fh + 9ft)/10 < f < ft is effected by plasma compressibility or a vacuum sheath. At the same time, the value of in the latter case may exceed KE0 by two or three orders of magnitude in the range (fh + ft)/2 ≲ f < ft so that the electrical wavelength of a finite antenna in the plasma would be a more sensitive function of frequency than for the free‐space medium.
Ray‐Tracing Simulation of HF Radio Measurements of Large Traveling Ionospheric Disturbances
Authors: Detert David G.
Published: November 2015

A two‐dimensional Snell's law digital computer ray‐tracing program is used to simulate the effects of large traveling ionospheric disturbances on oblique‐incidence HF radio transmissions. Two path lengths are considered: 452 km and 3000 km. The phase path, group path, received elevation angle‐of‐arrival and Doppler‐shift variations produced by the passage of representative disturbance models through the transmission paths are calculated. The relationship between the measured variations and certain disturbance parameters is discussed. Comparisons between the simulated results and experimental data appearing elsewhere in the literature are made.
Interpretation of Anomalous Oblique Incidence Sweep‐Frequency Records Using Ray Tracing
Authors: Kopka Helmut , Möller Hans G.
Published: November 2015

Oblique sweep‐frequency ionospheric sounding experiments indicate that the propagation is affected by a horizontal variation of the electron density. To gain insight into the importance of these effects, ray‐tracing experiments were carried out. Examples show the influence of the horizontal variation of the electron density. Variations of the critical frequency as well as variations of the layer height are considered.
Exact Ray Computations in a Tilted Ionosphere With No Magnetic Field
Authors: Folkestad K.
Published: November 2015

A set of formulas is derived giving exact expressions for group paths and ground distances to the impact points for rays propagated in an ionosphere eccentric to the earth. The eccentricity is measured in terms of a displacement, D. between the center of curvature and the center of the earth. Curves displaying layer tilts and layer height variations as functions of D are presented. Some sample results obtained with a “quasi‐parabolic” electron density model are given.
An Analysis of the Vector Kirchhoff Equations and the Associated Boundary‐Line Charge
Authors: Sancer Maurice I.
Published: November 2015

The vector Kirchhoff equations are derived by the systematic use of the free‐space dyadic Green's function and the appropriate Green's theorem. As is generally the case, the derivation is valid only if the surfaces over which the integrations are to be performed are closed surfaces or infinite surfaces that can be closed at infinity. The approximations used in conjunction with Kirchhoff's equations can lead to integrations over portions of the closed surfaces and these portions are open surfaces. When the approximations are discontinuous and the resulting integrations are over open surfaces, the Kirchhoff equations derived in this paper intrinsically include the boundary‐line charge contributions. It is not necessary to addend integrals to equations resulting from a mathematical analysis of Maxwell's equations in order to include the boundary‐line charge contributions.
Ionospheric Diagnostics Using Resonances of an Electric Dipole Impedance
Authors: Blair W. E.
Published: November 2015

A technique of using the driving‐point impedance of an electric antenna in the ionosphere to diagnose the ionospheric plasma is presented. Specifically, the locations of the resonances in the driving‐point impedance of a center‐fed cylindrical electric dipole imbedded in the ionosphere are analyzed. The ionospheric model is a lossy, anisotropic, homogeneous neutral plasma containing various ionic constituents. It is found that there are zeros in the reactance at the upper and lower hybrid frequencies and poles at the electron and ion gyrofrequencies. These critical frequencies are independent of antenna length and orientation (parallel or perpendicular to the earth's magnetic field) to the first‐order approximation. It is shown that pole‐zero frequencies could be used to determine the earth's magnetic field strength, electron density, and ion masses and densities at any point in the ionosphere at which the impedance was measured. Consequently, this technique offers the possibility of measuring several ionospheric plasma characteristics with one instrument aboard rockets and satellites.
On the Theory of Radiation From an Annular Slot in a Compressible Plasma
Authors: Yeh Y. S. , Wait James R.
Published: November 2015

Radiation from a circular‐slot antenna in a warm plasma is treated as a boundary‐value problem. The slot is excited symmetrically by a coaxial waveguide which has an infinite flange. The waveguide aperture and the flange are separated from the plasma by a dielectric coating. An exact formulation is given for the fields produced in the plasma region in terms of the aperture field at the open end of the waveguide. An asymptotic evaluation of the integrals shows that, in addition to space wave radiation, a surface wave is excited by virtue of the finite temperature of the plasma. Also, waveguide‐type modes in the dielectric layer are excited and they are attenuated even in the absence of ohmic or collision losses. Finally, a variational formula is obtained for the terminal admittance of the coaxial line.
Leaky‐Wave Beams of Multiply Layered Plasma Media
Authors: Harris J. H.
Published: November 2015

The radiation patterns of antennas in the presence of plasma media may exhibit large narrow beams that are due to leakage of trapped energy. The nature of these beams is discussed, and such characteristics as spatial dependence, magnitude, and power content are determined.
Electric and Magnetic Fields Near a Long Horizontal Line Source Above the Ground
Authors: Bannister Peter R.
Published: November 2015

The electric and magnetic field components near an elevated horizontal line source are derived and compared with the components calculated from image theory. When the measurement distance is much less than an earth skin depth, the results obtained by image theory are in good agreement with the author's derivations.
A Note on the Millimeter and Submillimeter Wave Dielectric Constant and Loss Tangent Value of Some Common Materials
Authors: Breeden K. H. , Sheppard A. P.
Published: November 2015

A tabulation of relative dielectric constant and loss tangent is presented for a number of common materials. Measurements were made by using an interference spectrometer to measure insertion loss and phase shift of dielectric samples.
A Numerical Study of VLF Mode Structure and Polarization Below an Anisotropic Ionosphere
Authors: Pappert Richard A.
Published: November 2015

The cylindrical waveguide problem with a diffuse, anisotropic upper boundary is rigorously formulated using a conformal transformation. This will allow us to demonstrate the adequacy of an ad hoc method used in a previous paper for simultaneously treating earth curvature and ionospheric
effects.

Weakly attenuated components of the mode spectrum associated with easterly propagation below a highly anisotropic ionosphere are developed numerically in the frequency range from 10–30 kHz. Also, the field strength distributions in the guide are presented. It is shown that modes of the earth detached variety, unlike the usual quasi‐TM or quasi‐TE modes, can contain comparable amounts of vertical and horizontal polarization. The numerical results also suggest that at the high end of the frequency spectrum considered, modes which are principally TE may be of importance in the mode sum.
Propagation in a Superrefractive Troposphere With a Nontrapping Surface Layer
Authors: Gerks Irvin H.
Published: November 2015

An extension of an earlier treatment to the case of a surface superrefractive layer is presented. An essentially exact solution for the eigenvalues is obtained, and graphical results obtained from a computer are presented. The enhanced effect of a shallow superrefractive layer at shorter wavelengths is illustrated. The solution for the case of a surface duct will be presented in a later article.
Surface Waves and Mode Selection on Multielement Spiral Antennas
Authors: Ru‐Shao Cheo B. , Rumsey V. H.
Published: November 2015

The solution of Maxwell's equations for the idealized sheet of spiral antennas has been extended to a cos nφ input excitation. At large distances the current density is the combination of a circularly polarized surface wave that vanes as exp (−jnφ) and the frequency independent current distribution previouslr worked out. The frequency independent component is almost entirely in the exp (jnφ) mode. Half the input power goes into the exp (jnφ) radiation pattern, and almost half goes into the surface wave. This explains the remarkable mode selection properties of multielement spiral antennas that were observed a few years ago.
Parametric Properties of Dielectric Slabs With Large Permittivity Modulation
Authors: Holberg D. E. , Kunz K. S.
Published: November 2015

Plane‐wave solutions in a permittivity‐modulated dielectric slab, bordering on each side on an infinite half‐space of constant permittivity, are found both analytically and numerically. The permittivity moduiation assumed, namely ∊(t) = ∊/(1 − 2p cos 2Ωt), permits expressing the time dependence of the waves in terms of Mathieu functions and deriving the wave characteristics from the known properties of Mathieu functions. Exponentially growing waves may be spontaneously generated in the slab if the modulation index 2p and the slab width are sufficiently large. In the analytical approach, existence of increasing waves and their rate of growth is determined by attempting to attain field continuity at the interfaces by a superposition of Mathieu functions. For the case when the modulation index and the slab width are too small to support growing waves, a method is sketched for calculating the complete frequency spectrum of the response of the slab to a normally incident plane wave. The numerical approach involves use of partial difference equations and matching their solutions at the interfaces. Good agreement between analytical and numerical field solutions is demonstrated.
Relativistic Magnetoionic Theory for Drifting Plasma
Authors: Unz H.
Published: November 2015

The relativistic magnetoionic theory for drifting plasma for arbitrary directions and large drift velocities is discussed and the general refractive index equation for the relativistic case is derived by using Lorentz transformation of the Booker quartic equation. Particular cases are found to agree with previous results.
Radiation Conductance of an Axial Slot on a Dielectric Coated Cylinder
Authors: Knop Charles M. , Gylys V.
Published: November 2015

An expression is derived for the radiation conductance of an axial slot on a dielectric coated metal cylinder, using the work of Wait in conjunction with Parseval's theorem in mode space. The condition for no axial surface waves to exist is stated, and computations for the radiation conductance are then made, for a Teflon dielectric coating of various thicknesses, none of which support axial surface waves. The computations reveal that the radiation conductance increases with both the coating thickness and frequency, for the range of parameters considered.
A Note on the Groundwave Phase Velocity Over a Plane Earth
Authors: Segal B.
Published: November 2015

Equations are derived for the phase velocity of an electromagnetic groundwave propagating over a plane earth having a constant surface impedance. The equations are found to differ in essence from one previously derived by King and Schlak (1967). As a result of the interpretation made here, it is concluded that the local phase velocity over a highly inductive surface exceeds the velocity of light in free space under certain conditions. For strongly capacitive surfaces, the phase velocity is expected to exceed the velocity in free space at all distances. (At the end of this Note, R. J. King and G. A. Schlak provide a reply to the criticisms. Ed.)
Equally Spaced Spherical Arrays
Authors: Chan Andrew K. , Ishimaru Akira , Sigelmann Rubens A.
Published: November 2015

A method is described analyzing the radiation characteristics of a spherical array by means of the Poisson sum technique. The elements are arranged as a series of circular arrays of different radii on a spherical surface. The main beam behaves as (sin u)/u. A method of estimating other side‐lobe characteristics is also described; numerical examples are given.
Random Periodic Arrays
Authors: Lo Y. T.
Published: November 2015

Recent theoretical and experimental works on large arrays showed important advantages of random spacings over conventional uniform spacings. In that design, however, the elements can be anywhere in the aperture; as a result, the element distribution becomes completely chaotic, an undesirable practice. In this paper, another approach is investigated, which allows a random selection of elements over a uniform grid system in the aperture, thereby giving rise to an array with random periodic pattern function. Probabilistic properties of these arrays are analyzed in detail and several Monte Carlo experiments are used to verify the theory.
Density Tapering of Circular Aperture Array Antennas
Authors: Redlien Henry W.
Published: November 2015

The evaluation of the performance of density‐tapered arrays may be made in simple terms and based on the simple concept of dividing the total input power into a “design” component and a “hash” component of radiation. The design component is the nominal directive radiation pattern that would result from the continuous aperture excitation of the array; the hash component is the wide‐angle radiation that results from the gaps in the aperture excitation required in density tapering.

The parameters evaluated include antenna gain, number of active and inactive (dummy) elements, and the level of hash radiation. Density tapering is compared with amplitude tapering, and formulas are summarized for convenient reference. Examples of particular low side‐lobe taper functions have been computed, and the results are tabulated.
Spacing Perturbation Techniques for Array Optimization
Authors: Tseng F. I. , Cheng David K.
Published: November 2015

A spacing perturbation technique is developed for the maximization of the directive gain or the signal‐to‐noise ratio of a linear array of identical elements. The initial array can be of uniform or nonuniform spacings with any given excitation amplitude and phase distribution. After an optimum set of spacings is obtained by perturbation, the excitation amplitudes and phases can be adjusted for further improvement in the performance index of interest. The optimum spacings can be recalculated and the cycle of iteration repeated if desired. The spacing perturbation technique is based on a new optimization theorem; there is no need to solve nonlinear equations or to rely on a trial‐and‐error procedure. Illustrative examples are given for both broadside and endfire operations. Typical radiation patterns are plotted that bring out a number of interesting features of the optimization process.
On the Mismatch of Electronically Steerable Phased‐Array Antennas
Authors: Varon D. , Zysman G. I.
Published: November 2015

The problem of matching an infinite, electronically steerable array is considered here. We show that for an array with smooth boundaries, a perfect match over a continuous scanning range implies a nonphysical field in the array‐space interface. Thus, although an array match can be considerably improved, a perfect match over a continuous scanning range cannot be obtained in general.
Aperture Synthesis in Radar Astronomy and Some Applications to Lunar and Planetary Studies
Authors: Hagfors T. , Nanni B. , Stone K.
Published: November 2015

The fading of a radar return from a planetary surface can be interpreted as a drift of a random diffraction pattern over the receiving antenna. Measurement of the signal autocorrelation function can, therefore, be interpreted as a spatial correlation (visibility) along the direction of drift. With two spaced antennas the cross‐correlation of the received signals with variable time shifts is shown to lead to a variable effective baseline. It therefore takes only a one‐dimensional array of receiving antennas to completely cover the two‐dimensional correlation plane. Aperture synthesis technique as discussed is applied to the mapping of the lunar surface at 23 cm.
Identification of a New Type of Mode Conversion Interference in VLF Propagation
Authors: Kaiser A. B.
Published: November 2015

The sunrise and sunset interference patterns observed in VLF propagation over long paths are
largely consistent with the model of mode conversion interference proposed by Crombie, which considers
both the first and second modes in the nighttime portion of the path, but only the first mode in
the daytime portion. Several authors, however, have reported anomalies during the first part of the
sunrise transition. Except for effects produced by a direct second mode, these anomalies may be
explained by a model of mode conversion interference which involves first and second mode propagation
along the daytime portion of the path, and first mode propagation along the nighttime portion.