bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of the transmission of electromagnetic waves down a mine hoist
Authors: Wait James R. , Hill David A.
Published: February 2008

Using an idealized coaxial model, we consider the transmission, in the frequency range from 20 to 1000 kHz, down a mine hoist shaft from a symmetric source at the surface. The shaft is circular in cross section and the metal hoist cable is represented by a concentric conductor. To facilitate the analysis, the source is idealized as a voltage‐excited annular slot in a circular ground plane that is located in the air‐earth interface. The earth itself is taken to be a homogeneous conducting half space. Using a modal type analysis, the total power supplied to the annular slot is calculated as the sum of the power delivered to the lower half space, the power dissipated at the air‐earth interface and the power radiated into the atmosphere. Using these results, the relative power transmitted down the shaft to a specified depth is estimated. The resulting transmission efficiency is found to be almost completely dependent on the attenuation characteristics of the dominant TEM mode in the shaft.
Multiple scattering effects on coherent bandwidth and pulse distortion of a wave propagating in a random distribution of particles
Authors: Ishimaru Akira , Hong S. T.
Published: February 2008

In this paper, integral and differential equations are derived for the two‐frequency mutual coherence function in a random distribution of stationary and moving particles. The differential equation is then solved for a plane wave case, and the coherent bandwidth is obtained for both the weak and strong fluctuation cases. Using the two‐frequency correlation function, the output pulse shape is calculated for different particle densities. When the optical distance is small compared with unity, the pulse shape is substantially unchanged, but a long tail develops. When the optical distance is large, the coherent bandwidth is reduced and considerable pulse spread and delay occur. Numerical calculations are given for a nanosecond optical pulse propagating through cloud. It is shown that in dense cloud (density 0.5×109m−3), the pulse delay and spread are 3 and 1.28 μsec respectively over a distance of 5 km. This agrees with available experimental data.
Geophysical investigations by scattered radio waves
Authors: Dieminger Walter
Published: February 2008

The application of scattered radio waves to geophysical investigations is reviewed. The occurrence of ground scatter depends on the smoothness of the reflecting layer and limits for the inhomogeneity may be given. Direct backscatter occurs from field‐aligned irregularities in the auroral belt and movements may be derived from Doppler shift. The location and temporal movement of the two predominant precipitation belts are observed. Meteor scatter is strongly aspect sensitive and is used for deriving physical properties of the meteorites. The analysis of scattering in transequatorial short wave propagation points to a gravity wave induced system of eastward travelling field‐aligned inhomogeneities. Incoherent scatter has proved a successful tool for investigating many important parameters of the ionosphere. Satellite scintillations are helpful in mapping the irregularities of the electron content. They may be used for determining the height of the irregularities by radio wave holography. Scattering of microwaves on the ground is becoming a useful tool for geoexploration. Scattering processes in the troposphere are dealt with in a paper by C. G. Little in this issue.
Radio communications from early days to satellites
Authors: Bargellini Pier L.
Published: February 2008

The successes of Marconi in establishing radio communications, first with LF and VLF, and later with HF waves, are interpreted in terms of the (range)(rate)1/2 relationship of space communications. The evolution of the technology from the late thirties to that associated with present‐day communications satellites characterized by high capacity and reliability is outlined.
Effects of the troposphere on the propagation time of microwave signals
Authors: Thompson M. C.
Published: February 2008

Technological developments in the microwave spectrum have made possible highly accurate radio systems for position determination. Most of these systems depend upon measurements of the signal transit time or of the differential transit time for different portions of the received wavefront. In practice, the performance of such systems when operating in the Earth's atmosphere is usually limited by the random signal velocity. This effect is a consequence of the variable density and water vapor distribution throughout the normal troposphere. Theoretical and experimental work has provided a useful degree of understanding of these tropospheric effects and some progress has been made in reducing them in certain applications.
Research on earth‐to‐space propagation of frequencies above 10 GHz
Authors: Carassa F.
Published: February 2008

The importance of using frequencies above 10 GHz in satellite communication systems arises partly from the saturation of the bands presently in use. In addition, above 10 GHz, frequency bands have been specifically assigned to satellite communication systems, allowing earth stations to be located more freely, particularly near or within the cities. Directive multibeam antennas are also more easily realizable on board the satellites. These advantages are of particular relevance for domestic satellites. On the other hand, the propagation of such frequencies is mainly affected by rain attenuation.
Structure and dynamics of ionization and auroral luminosity during the auroral events of March 16, 1972, near Chatanika, Alaska
Authors: Hunsucker R. D. , Romick G. J. , Ecklund W. L. , Greenwald R. A. , Balsley B. B. , Tsunoda R. T.
Published: February 2008

During the period 1000–1030 UT on March 16, 1972, a very dynamic auroral event occurred in the latitudinal region from College to Fort Yukon, Alaska. Simultaneous observations of this auroral event were made with an all‐sky camera, a geomagnetic meridian scanning photometer, an incoherent scatter radar, a three‐component magnetometer, a 30‐MHz riometer, and two VHF/UHF auroral radars. The basic purpose of this report is to illustrate the advantages of such coordinated measurements and the possibilities for future experiments. These preliminary results point out many relationships which, although not hitherto unknown, are important to the understanding of the auroral ionosphere. Paramount among these are (1) intense discrete auroral forms (> 25 kR in 4278 Å) are associated with enhanced E‐layer electron densities near 106 electrons/cm3; (2( the riometer data and the height of maximum Ne from the incoherent scatter radar suggest that few energetic (> 40 kev) particles were precipitating during this event; (3) enhanced regions of VHF backscatter seem to be associated with eastward and westward electrojet current systems but do not spatially correspond to the regions of high Ne or bright auroral forms; and (4) the collective data yield a description which indicates that this period is associated with the Harang discontinuity region of the auroral current systems.
TM waves in nonlinear self‐focusing media
Authors: Miyagi Mitsunobu , Nishida Shigeo
Published: February 2008

In this paper, properties of stationary waves of the transverse magnetic (TM) type which have two electric field components, i.e., axial and transverse ones, in a nonlinear self‐focusing medium are discussed. Waves of the TM type are categorized into a solitary wave and several types of waves oscillating in the transverse plane. Analytical expressions of oscillating waves are obtained by using an asymptotic expansion and its extension for the large nonlinearity as well as the small one of the medium. A solitary wave is also discussed numerically, and some differences between the solitary waves of TE and TM types are mentioned.
Antenna pattern corrections to microwave radiometer temperature calculations
Authors: Beck F. B.
Published: February 2008

Equations are presented which correct microwave radiometer temperature calculations for the averaging effect of the antenna pattern. Principal plane antenna patterns at 1.43, 4.0, and 7.5 GHz are used to determine the radiometer temperature of a saline water surface. The calculations, made as a function of frequency, polarization, and viewing angle, compare favorably with measured data. The results also show that excluding the measured antenna pattern from the calculations produces errors of the order of 10 or 20 K at a viewing angle of 70°. The low level (<−22 dB) cross‐polarization patterns of the above antennas are found to contribute insignificant changes (<0.5 K for the scope of this paper) in the calculated results. However, for demonstrational purposes, cross‐polarization patterns higher in magnitude (−16 dB) than those measured are included in the computations for comparison. The effects of water surface dielectric constant changes are also presented.
A Toeplitz matrix application: A dipole in a warm plasma
Authors: Lytle R. Jeffrey , Lager Darrel L.
Published: February 2008

A linear dipole antenna has an impedance matrix of Toeplitz form. The problem of an acoustically long cylindrical antenna in a warm plasma thus becomes numerically tractable. Both the electromagnetic and acoustic wavelengths are evident in the current distribution for acoustically long antennas. Relative accuracies of 10−11 were obtained for inversion of a 5000×5000 complex impedance matrix, including both electromagnetic and acoustic contributions. Antennas up to 500 acoustic wavelengths long are considered in numerical examples.
An interpretation of Bernstein wave interference patterns in a magnetoplasma
Authors: Bitoun Jacky
Published: February 2008

Bernstein wave interference patterns observed in an afterglow plasma are interpreted as being due only to electrostatic waves. Their effect is shown to be reduced to that of the two fields corresponding to the limit wave vectors of the undamped domain determined from the hot dispersion curves. The formulas obtained through this point of view yield the temperature of the medium and the theoretical amplitude of the field in agreement with the experimental signal envelopes.
Use of atmospheric emission to estimate refractive errors in a non‐horizontally stratified troposphere
Authors: Gallop M. A. , Telford L. E.
Published: February 2008

Tropospheric refraction introduces errors into radar and radio communication systems by causing radio waves to travel along a curved path and at a speed which changes with position. Common error correction techniques, such as making estimates of refractive effects from surface refractivity, rely implicitly on the assumption that the troposphere is horizontally stratified. This study demonstrates that such an assumption may be unwarranted especially at elevation angles below 10°, and that such reliance can lead to substantial errors. The end product of this research is a system which employs atmospheric emission measurements in addition to surface refractivity to estimate refractive bending and range error. This approach relies on the similar dependence of refraction and emission on atmospheric parameters to account for nonhorizontal stratification. Performance results establish that such a system need employ no more than one radiometer channel to provide potential error reduction of more than 40% over conventional approaches, along with a potentially automated, real‐time operational capability.
VLF propagation in the magnetosphere during sunrise and sunset hours
Authors: Walter F. , Scarabucci R. R.
Published: February 2008

Whistlers observed on records of the OGO‐4 satellite during the sunset/sunrise hours show evidence of both the proresonance (PR) and prolongitudinal (PL) mode of propagation. By tracingrays in a model magnetosphere suitable for these hours, the whistlers observed on these records are reproduced. The upper cutoff frequency presented in the walking trace whistlers appears naturally as a consequence of the inclusion of latitudinal gradients in the electron density model. A new whistler trace is predicted which appears as a consequence of the transition from the PR to the PL mode of propagation.
Low‐angle radiation from vertically polarized antennas over radially heterogeneous flat ground
Authors: Rafuse Robert P. , Ruze John
Published: February 2008

A theory is presented giving far‐field radiation patterns and surface‐wave behavior for vertically polarized antennas located at zero height over flat ground, with a surface impedance which can be discontinuous along a radius from the antenna. The theory is based on the radiation from the surface electric and magnetic currents as determined by the Sommerfeld attenuation function. Both sky‐wave and surface‐wave solutions are obtained simultaneously, with applications to ground screens, recovery phenomena, Fresnel zones, and similar engineering problems discussed with examples. In general, the results agree with those obtained using the compensation theorem.
Application of multivariate autoregressive spectrum estimation to ULF waves
Authors: Ioannidis George A.
Published: February 2008

The estimation of the power spectrum of a time series by fitting a finite autoregressive model to the data has recently found widespread application in the physical sciences. The extension of this method to the analysis of vector time series is presented here through its application to ULF waves observed in the magnetosphere by the ATS 6 synchronous satellite. Autoregressive spectral estimates of the power and cross‐power spectra of these waves are computed with computer programs developed by the author and are compared with the corresponding Blackman‐Tukey spectral estimates. The resulting spectral density matrices are then analyzed to determine the direction of propagation and polarization of the observed waves.
Reorganization of URSI
Authors: Johnson Francis S.
Published: February 2008

At the XVIIIth General Assembly in Lima,Peru, last August, a decision was made to redirectthe emphasis of the Union and to reorganize theCommission structure. This represents the culmina‐tion of efforts to correct the organizational problemsbrought about by the considerable activity withinURSI in the field of geophysics. At the XVIIthGeneral Assembly in Warsaw, Poland, in 1972,consideration was given to moving in the directionof a closer association with the International Asso‐ciation of Geomagnetism and Aeronomy (IAGA),a part of the International Union of Geodesy andGeophysics, in the expectation that this wouldprovide a single organizational home for interna‐tional interests in solar‐terrestrial physics. How‐ever, this move was resoundingly rejected by theURSI Council; clearly it was desired that URSIretain its separate identity and its emphasis on radioscience.
Optimum pulse reflection from the ionosphere
Authors: El‐Khamy Said E.
Published: February 2008

The synthesis of optimum signals for ionospheric reflection is treated in this paper. It is shown that these optimum signals, when incident on the ionosphere, result in reflected signals which are enhanced in magnitude and compressed in duration. The optimum band‐limited signals are found to have relatively complicated frequency and amplitude modulations. The reflection of linearly swept carrier pulses having gaussian envelopes that approximate the optimum signals is also considered, with the result that considerable compression is seen to occur for these signals. The ionosphere is modeled as an inhomogeneous ionized medium with a linear ionization density profile and a constant collision frequency.
On certain theories of multiple scattering in random media of discrete scatterers
Authors: Olsen R. L. , Kharadly M. M. Z. , Corr D. G.
Published: February 2008

The paper presents new information on the accuracy of the heuristic approximations in two important theories of multiple scattering in random media of discrete scatterers: Twersky's “freespace” and “two‐space scatterer” formalisms. Two complementary approaches, based primarily on a one‐dimensional model and the one‐dimensional forms of the theories, are used. For scatterer distributions of low average density, the “heuristic” asymptotic forms for the coherent field and the incoherent intensity are compared with asymptotic forms derived from a systematic analysis of the multiple scattering processes. For distributions of higher density, both in the average number of scatterers per wavelength and in the degree of packing of finite‐size scatterers, the analysis is carried out “experimentally” by means of a Monte Carlo computer simulation. Approximate series expressions based on the systematic approach are numerically evaluated along with the heuristic expressions. The comparison (for both forward‐ and back‐scattered field moments) is made for the worst‐case conditions of strong multiple scattering for which the theories have not previously been evaluated. Several significant conclusions are drawn which have certain practical implications: (a) in application of the theories to describe some of the scattering phenomena which occur in the troposphere, and (b) in the further evaluation of the theories using experiments on physical models.
Application of electroacoustic probe in the study of plasma density profiles and other parameters in cylindrical plasma clouds
Authors: Olin Jack G. , Chen Kun‐Mu
Published: February 2008

A new diagnostic method based on the excitation of thermal resonances using an electroacoustic probe has been developed to determine the electron density profile and other plasma parameters of a cylindrical warm plasma column. A coaxial electroacoustic probe is used to excite and detect the dipole and thermal resonances as the plasma density is varied. The electron density profile is expressed functionally in terms of unknown profile parameters. The profile and other parameters of the plasma column are then determined numerically based on some theoretical formulas and experimental results.
Attenuation diversity measurements at 20 and 30 GHz
Authors: Vogel W. J. , Straiton A. W. , Fannin B. M. , Wagner N. K.
Published: February 2008

The results of data obtained at The University of Texas at Austin in conjunction with the ATS‐6 millimeter wave experiment are presented. Attenuation measurements at 30 GHz and sky noise data at 20 GHz were obtained for 93 days simultaneously at each of two sites separated by 11 km and for 314 days at one site. The ratio of the loss at 30 GHz to that at 20 GHz due to rain varied from about 2 to about 4 with a median value of 2.65. This value was used to estimate 30 GHz losses for the 38.6% of time during attenuation events for which the satellite link was not available. Space diversity reduced outage time for a system in Austin, Texas, with a 10 db fade margin at 30 GHz from 3.8 hours to 4.1 minutes for the 93 days. Extrapolated to a yearly base this corresponds to 15 hours and to 16 minutes, respectively. A plot of maximum observed cloud height against maximum hourly attenuation indicates that for a given attenuation level a lower limit is set for the maximum cloud height.
Observation of seasonal effects in traveling ionospheric disturbances by the directional deviation technique
Authors: Walton E. K. , Bailey A. D.
Published: February 2008

An experiment was performed during the years 1962 through 1964 in which direction of arrival data were collected on pulse signals received over a 450 km east‐west path. In order to determine the effect that traveling ionospheric disturbances (TIDs) had on these data, a “corrugation” model was proposed. The corrugation model assumes that TIDs can be treated as if they were moving cylindrical sinusoidal perturbations on the ionospheric eflecting surface. Lateral deviations in the experimental data of the type predicted by this model were found to be quite common. Variations in the detected TIDs as a function of time of year were found to be consistent with the “seasonal effect” studied by Munro in 1958, Jones in 1969, and Davies and Jones in 1971.
Lower ionosphere effects on the propagation of waves from an ELF/VLF source in the magnetosphere
Authors: DeWitt R. N. , Kelly Francis J. , Chayt Gerald A.
Published: February 2008

A modified form of the Smith‐Pitteway full‐wave program is used in conjunction with various lower ionospheric profiles to calculate the propagation characteristics of ELF/VLF waves from a source in the magnetosphere, through the ionosphere. Expressions are developed which give the ratio of the power transmitted into the earth's surface to the power incident on the top of the ionosphere, as a function of the number of wave‐hops in the earth‐ionosphere waveguide. This depends upon the wave polarization after each hop and a limiting polarization is found after several hops. Numerical evaluation of these expressions is presented and discussed.
Transmission of pulses into a dielectric of finite conductivity
Authors: Marx Egon
Published: February 2008

The components of a transmitted electromagnetic pulse into a conducting dielectric are determined for an arbitrary angle of incidence. Different components of the fields are found to change in distinct ways, and the resulting equations are applied to a double exponential pulse transmitted into the ground.
Numerical study of the effect of two‐dimensional conductors on the surface fields of a buried vertical magnetic dipole
Authors: Stoyer Charles H.
Published: February 2008

Using a finite‐difference method, the surface magnetic fields of a harmonic vertical magnetic dipole buried in a laterally inhomogeneous earth are computed. The geoelectric section consists of a homogeneous half space in which a cylindrical conductor of square cross section is embedded. Results are presented in terms of the magnetic field polarization ellipse parameters, with particular attention being paid to the ellipticities in the horizontal and vertical planes. These are shown by means of equicontour maps in the surface plane, and promise to be quite useful in the detection and mapping of subsurface conductivity zones. With reference to buried‐source location methods, it is shown that the source location error, as derived from the tilt angle of the vertical polarization ellipse (measured at the surface) is quite small. Finally, some suggestions are made on field procedures, which may enable on‐site corrections to apparent locations to be made without knowledge of the subsurface conductivity structure
The terminated insulated antenna
Authors: Lee Kuan‐Min , King Ronold W. P.
Published: February 2008

The center‐driven insulated antenna end‐loaded with a bare quarter‐wave section is investigated theoretically and experimentally. This antenna is analyzed in terms of the theory of the bare antenna and that of the completely insulated antenna in a relatively dense ambient medium. A simple transmission‐line‐like solution is obtained. Input admittances computed from the theoretical formula have been shown to agree well with measured results with air‐insulated monopoles in both salt and fresh water. For an electrically short antenna the magnitude of the current distributions for a terminated insulated antenna can be kept quite constant, while that of the completely insulated antenna with the same physical length is triangular. This feature of the electrically short antenna provides a more useful current distribution and driving‐point impedance. By adjusting the radius of the insulation, it is possible to match the characteristic impedance of the insulated antenna to the apparent input admittance of the monopole antenna to obtain a nearly pure traveling wave even for a longer insulated antenna.
Bayes classification of subsurface electromagnetic responses
Authors: Moore Dennis F. , Quincy Edmund A.
Published: February 2008

Statistical classification of geoelectromagnetic responses containing additive gaussian noise is considered. The classification is performed with minimum average probability of error criterion of goodness. The Bayes receiver structure for classifying three different but equally likely geoelectromagnetic responses is presented. Since each geophysical model is assumed to have one unknown parameter, the three hypotheses are composite and the received signals are treated as random. The composite hypotheses are developed in terms of frequency‐domain model responses. The three conductive models selected for this research are a half space, a sheet, and a two‐layer earth. Geoelectromagnetic responses are found to yield strongly correlated signals with correlation coefficients typically of 0.9999. The receiver performance in terms of average probability of error is compared with (1) a system having known and equally correlated signals (ρ = 0.9999), and (2) a system having known orthogonal signals. These comparisons illustrate the degradation of performance resulting from the random and correlated nature of geoelectromagnetic responses.
Input impedance of a short dipole antenna in a warm anisotropic plasma, 1, Kinetic theory
Authors: Nakatani D. T. , Kuehl H. H.
Published: February 2008

A theory is presented for the input impedance of a short, cylindrical dipole antenna immersed in a warm anisotropic plasma which is described by the kinetic theory (Boltzmann equation). The plasma is assumed to be homogeneous with collisions included. The input impedance is based on the induced EMF technique and a quasistatic approximation. The dipole is assumed to have a triangular current distribution along its axis. For a dipole oriented parallel to the static magnetic field, the input impedance is derived as a one‐dimensional integral suitable for numerical integration. Under certain conditions, this integral can be evaluated giving analytical formulas valid near the second and third electron cyclotron harmonics. The results show new contributions to the input impedance due to the excitation of cyclotron harmonic waves which propagate near the harmonics of the electron cyclotron frequency. These harmonic effects are not predicted by either the cold or hydrodynamic theories.
Some uses of the Huygens' obliquity factor
Authors: Lewin L.
Published: February 2008

It is shown how the effect of the mounting surface for a flush‐mounted aperture antenna can be considered as a modification of the Huygens' obliquity factor, which represents the pattern of the radiation of an element of the aperture. The same method, in conjunction with Babinet's principle, applied to a small slit, gives the corresponding element pattern for an elementary dipole and lends credence to the method even when applied to very small apertures. An application is made to a solid‐state laser configuration, and a result obtained by a more involved method is shown to correspond to the obliquity factor for an air‐dielectric interface. A correction to the formula is also found, and an (apparently new) expression is found for the obliquity factor when there is a change of medium at the aperture.
Reflection and transmission of electromagnetic waves by a semi‐infinite uniaxial plasma moving perpendicular to the plane of incidence
Authors: Ohkubo Motoaki
Published: February 2008

The reflection and transmission properties of electromagnetic waves by a semi‐infinite uniaxial plasma moving perpendicular to the plane of incidence are investigated theoretically for the incident H and E plane wave. In this case, the plasma becomes anisotropic, and electromagnetic field components of the transmitted wave should be hybrid modes. Thus it is shown that the behavior of the power reflection coefficient is remarkably different from that of a stationary one.
Wavenumber‐bandwidth‐limited near fields
Authors: Brown Alexander C.
Published: February 2008

Antenna near fields can be accurately computed by the plane wave spectrum (PWS) method. The PWS is directly related to the far field at infinity. That is, at infinity, only a single plane wave contributes to the field. At the close‐in distance of just a few wavelengths away from the antenna, integration is performed over all visible wavenumbers and some evanescent wavenumbers. Close (less than a wavelength) to the antenna, integration is performed over all wavenumber space. In between these two extreme distances from the antenna, there is shown to be a finite‐sized subregion of all wavenumber space that contains all significant contributions to the field. That is, near fields are shown to be wavenumber‐bandwidth‐limited. Exploiting this fact, a technique of computing near fields could be created which is faster than both the aperture method and the original PWS method, once a suitable method is developed for determining the wavenumber bandwidth of near fields.
Surface currents and charges on an electrically thick conducting tube in an E‐polarized, normally incident, plane‐wave field, 1, Theory
Authors: King R. W. P. , Sandler B. , Wu T. T. , Burton R. W. , Kao C. C. , Shen L. C.
Published: February 2008

The theoretical determination of the distributions of surface densities of current and charge induced on an electrically thick, infinitely thin‐walled, perfectly conducting, tubular cylinder by an incident, E‐polarized plane electromagnetic wave is reviewed. The theory is applied to a cylinder with ka = 1 and kh = 3π/2 where a is the radius, h the half‐length, and k the wavenumber. Extensive graphs of the axial and transverse distributions of the surface density of current and of the surface density of charge are presented. An analytical representation of these in terms of forced and resonant transverse Fourier components is described and used to interpret the properties displayed in the graphs.
Polarization‐related parameters for rain: Measurements obtained by radar
Authors: McCormick G. C. , Hendry A.
Published: February 2008

Averages and distributions of the rain parameters, cancellation and degree of orientation, are presented. The quantities were determined from observations of power and correlation with a polarization diversity radar using circular polarization at 16.5 GHz during the period 1971–1974. Data are given for a related quantity, “maximum cancellation.” The fact that this quantity is not invariant with range is shown to be evidence for the occurrence of incoherent transmission processes at 16.5 GHz.
The bicoaxial leaky line and its applications to underground radio communication
Authors: Martin D. J. R.
Published: February 2008

The bicoaxial leaky line comprises two separate leaky cables spaced closely parallel so that the two outer braids or conductors form a bifilar transmission line. The type of construction was developed first as a research tool in the study of mode‐conversion processes in leaky coaxial cables and to test previously developed theories; the single‐wire modes of the two constituent cables combine to form a bifilar mode which can be more accurately predicted and measured. As well as serving this purpose, the new cable lends itself to a new configuration of leaky cable radio communication system in which line repeaters are bridged between the constituent coaxial cables in alternate directions instead of being connected simply in series; midspan filters ensure system stability. Such a system provides duplex communication from a unified base station using simple one‐way repeaters and is particularly adaptable to spurs and branching. The inherent “tailback” feature also provides a particularly consistent level of coupled signal through the system. The overall system of bicoaxial cable and line repeaters will accommodate several separate radio channels simultaneously and thus constitutes a bidirectional “communications highway” for mining use.
The physical significance of the correlation ellipse in ionospheric drift analysis
Authors: Briggs B. H.
Published: February 2008

It is argued that the conventional interpretation of the correlation ellipse in ionospheric drift analysis is correct, and that this ellipse provides a useful description of the spatial properties of the amplitude pattern over the ground.
Absorption of an electromagnetic wave in a dense plasma
Authors: Brysk Henry
Published: February 2008

It is demonstrated that the local absorption of an electromagnetic wave incident normally on a plasma can be obtained accurately by the geometrical optics approximation even in a region including the critical density provided that the electron density variation is moderate. The deviation from the WKB result with increasing density gradient is mapped out numerically for a linear profile in both the (isothermal well‐ionized) plasma and the (constant collision frequency) ionosphere models; implications for a more general distribution are discussed.
The eccentrically located wire in a cylindrical cavity in a conducting medium and the limit of a planar boundary
Authors: Wait James R.
Published: February 2008

Propagation along a thin wire located in an air‐filled tunnel is considered in the limiting case where the tunnel radius becomes indefinitely large but the distance of the wire to the tunnel wall remains finite. It is found that the results are consistent with the corresponding analysis for a thin wire located over a plane homogeneous earth.
A Martian entry propagation study
Authors: Nordgard John D.
Published: February 2008

The interaction of an electromagnetic wave with the shock‐induced plasma flow field generated around a blunt body capsule as it encounters the planetary atmosphere of Mars is examined. From two preliminary engineering models of the Martian atmosphere and the estimated entry‐trajectory characteristics of the capsule, it appears that the communication links to and from the capsule may be blacked out during entry because of a high free‐electron concentration in the wake region of the capsule. In the worst case of a frozen flow field behind a normal bow shock in local thermodynamic equilibrium, estimates of the free‐electron concentration in the wake region indicate peak values between 7.9 × 1010 e−/cc and 7.7 × 1011 e−/cc. Both of these values are above the critical electron concentration of 6.53 × 1010 e−/cc for the S‐band direct transmission link to Earth, and 1.80 × 109 e−/cc for the indirect UHF transmission link through a relay bus. Also, atmospheric reflection and refraction of the telemetry signals are considered near blackout. The reflection and refraction coefficients are shown to satisfy Riccati equations, which are solved numerically to yield the desired coefficients. Estimates of the reflection and refraction coefficients for several possible electron concentration and collision frequency combinations are cited for linear and exponential plasma wake distributions.
Optimization methods for arbitrarily oriented arrays of antennas in any environment
Authors: Sarkar Tapan K. , Strait Bradley J.
Published: February 2008

Formulas convenient for the optimization of various performance indices are discussed. Typical indices that have been optimized, both with and without constraints, are directivity, power gain, quality factor, and main beam radiation efficiency.
Shadow‐mapping to study attenuation by rain on satellite microwave links
Authors: Marshall J. Stewart , Cherna Eva
Published: February 2008

A technique has been developed for generating “shadow maps” (the shadow that an array of showers would cast on the earth's surface) in the microwave radiation from a hypothetical source in a geostationary satellite at specified azimuth and altitude. The input data for this technique are weather‐radar records on digital magnetic tape. To describe and demonstrate the technique and its intended use, this paper contains just one shadow map at high resolution (approaching that of the radar record), one sequence of maps at a lower resolution covering the three hours of one storm‐array passage, and an analysis of the effect that one passage would have had on an earth station and on various path‐diversity pairs. We hope to generate high‐resolution maps for a whole season (summer 1976) and to use them to catalogue and compare the various storm‐array passages that would have a significant effect on slant‐path microwave links.
Simultaneous 1.5‐ and 4‐GHz ionospheric scintillation measurement
Authors: Taur R. R.
Published: February 2008

Analysis of simultaneously recorded 1.5‐ and 4‐GHz scintillations at Tangua, Brazil, has shown that the scintillation index varies approximately as the wavelength between 1.5 and 4 GHz under weak scattering conditions. The amplitude distributions, especially those of the 1.5‐GHz data, are somewhat irregular in shape and cannot be represented by a simple mathematical expression. The power spectra of the amplitude fluctuations on a log‐log plot show a slope of −3 and have low wave number rolloffs near 10−2 m−1. This paper discusses some possible implications of these findings. Half of the 4‐GHz power spectra show the minima which are predicted by the thin‐screen weak scattering theory. The l/e falloff of the autocorrelation corresponds to irregularities between 100 and 200 m. The cross correlation between the 1.5‐ and 4‐GHz scintillations is about 0.3.
A radar study of attenuation on terrestrial microwave links
Authors: Kilambi A. , Marshall J. S.
Published: February 2008

A hypothetical array of terrestrial microwave links has been designed at radar ranges 36 to 110 km and all azimuths, such that useful attenuation statistics can be derived from the weather‐radar record on digital tape of the few hours' passage of one storm system across the array. These statistics cannot be used as the basis for design in the way that the data for a whole season might be used, but one can compare one storm with another, and hope to relate attenuation to meteorological aspects of the storm. From one case of a line of intense storms it has been found that: (i) Total duration of attenuation in excess of A decreased approximately exponentially with increasing A for a given link length, and for a given value of A increased approximately linearly with link length, at any rate up to 48 km. (ii) Durations varied with link direction, but less than ±20%. (iii) Individual fades of attenuation in excess of A were more numerous but more brief for links perpendicular to the direction of motion of the precipitation pattern than for those parallel. (iv) “Synthetic links” based on raingauge data have statistics like links parallel to the direction of pattern motion. Thus they are representative of links generally for “total duration” statistics (see i) where direction is unimportant (see ii) but not for individual‐fade duration and frequency (see iii). These findings for one storm passage were confirmed by two others: a less intense line and a case of widely scattered light showers.
Effect of source bandwidth and receiver response time on the scintillation index in random media
Authors: Fante Ronald L.
Published: February 2008

We have studied how the scintillation index is affected by the source bandwidth, the response time of the measuring instruments and the properties of the random medium. It is found that large‐bandwidth sources lead to a scintillation index other than unity in very strong turbulence.
Incoherent scatter radar observations during August 4–7, 1972
Authors: Wedde T. , Doupnik J. R. , Banks P. M. , Park R. J. , Siren J. C.
Published: February 2008

The incoherent scatter radar installation at Chatanika, Alaska (Λ = 65°) has been used to investigate ionospheric conductivities, electric fields, and electron densities during the extraordinarily large magnetospheric disturbances of August 4–7, 1972. It is found that following two sudden commencements which occurred on August 4 while Chatanika was in the afternoon sector, the polar cusp moved equatorwards to the latitude of Chatanika. The usual midnight sector discontinuity of the ionospheric electric field was probably encountered around 2100–2130 MLT on all four days studied, although on August 4, the discontinuity may have been encountered as late as 0100 MLT and on August 6, as early as 1900 MLT. Heating of the neutral atmosphere by precipitating energetic particles and Joule dissipation varied considerably throughout the period of observation, at times reaching 200 ergs cm−2S−1. With regard to the electric field, unusually large values were not seen during the storm period. In the local evening sector, for example, the northward component of the field reached only 60 mV m−1. During the times near local noon, the electric field reached some 50 mV m−1 in association with an encounter of the polar cusp. Examination of the height‐integrated Pedersen and Hall conductivities shows the presence of a periodic variation with conductivity maxima being spaced roughly one hour apart throughout most of the period of observation. To a large extent it appears that at Chatanika the exceptional nature of this storm period was associated solely with a greatly enlarged and thickened auroral oval since neither the conductivities nor the electric field strength were unusually large.
Multifrequency studies of ionospheric scintillations
Authors: Umeki R. , Liu C. H. , Yeh K. C.
Published: February 2008

Simultaneous scintillation data from the ATS‐6 Radio Beacon Experiments for signals at 40, 140, and 360 MHz offer the opportunity to study the frequency dependence of the scintillation phenomenon. Using these data variations of the spectral index, correlation coefficient, and the correlation interval are investigated. It is found that for weak scintillations, the spectral indices lie between 1.5 and 1.7. When the scintillation is strong, the spectral indices vary from about 1.4 to 0.7. The correlation coefficients are found to decrease for increasing scintillation level. The interesting behavior of the correlation intervals as functions of signal frequency is also discussed. The observational results are compared with theoretical predictions.
Computational study of long‐range high‐frequency ionospheric ducting
Authors: Toman Kurt , Miller David C.
Published: February 2008

The propagation of high‐frequency (HF) signals over long distances by way of ionospheric channels is studied by computing ray trajectories in numerically specified ionospheres without magnetic field. Horizontal ionization gradients are introduced to provide favorable conditions for the injection of rays from the ground into elevated ionospheric ducts. Electron density height distributions with and without ionization valleys are considered. The ducting efficiency, expressed in terms of frequency‐and launch‐elevation‐angle interval for trapped rays, is controlled by negative horizontal ionization gradients for successful injection of rays and by the shape of the electron density height profile and its change with distance. Long‐range ionospheric ducting of HF rays does not require but is facilitated by the continued presence of an ionization valley in the plane of the ray trajectory.
Status of integrated optics and some unsolved problems
Authors: Whinnery J. R.
Published: February 2008

There have been recent dramatic advances in guided‐wave optical devices and although only a few functions have so far been integrated onto a single substrate, the individual devices are being applied and there is promise for integration in the future. The most dramatic advances have occurred with respect to semiconductor lasers, with GaAs and GaAlAs lasers now operating at room temperature with long life. A variety of techniques, including chemical etching, liquid‐phase epitaxy and ion implantation have been used for fabricating waveguides on these materials. Similar advances have been made with respect to guiding and electro‐optic effects on LiNbO3 and LiTaO3. Devices discussed in the paper include the guides themselves, junctions and bends, switches or modulators, the laser sources, and detectors. Many of the electromagnetic problems encountered in the analysis of these devices are inhomogeneous and anisotropic and some are nonlinear. Mode conversion is a common problem, and sensitivity to polarization must be kept in mind.
Resonant polarization conversion and beam shift in planar multilayered structures
Authors: Kitajima Hiroe , Hano Kazunori
Published: February 2008

For planar multilayered structures composed of thin‐film waveguides with anisotropic or gyrotropic media, resonant polarization conversion and anomalous lateral beam shift are considered. If an oblique gaussian beam is incident under the optimum condition, polarization of the field incident on the top region is almost completely converted to cross polarization; under the other condition, instead of the polarization conversion, the corresponding system produces a large beam shift—nearly twice the ordinary beam shift of a prism coupling structure. The interpretation of the physical mechanism for these phenomena is presented with numerical examples. New schemes for modulation and optical switching applications are proposed.
An investigation of temporal moments of stochastic waves
Authors: Yeh K. C. , Liu C. H.
Published: February 2008

It is proposed to describe the temporal characteristics of a wave propagating in a random medium in terms of its temporal moments. The first two moments are related to the mean arrival time and the mean pulse width. It is shown that the one‐position two‐frequency mutual coherence function enters in the formulation naturally. The form of the expression suggests expanding the mutual coherence function in a narrow‐band expansion whose coefficients can be solved exactly from the parabolic equation that takes into account all multiple scattering effects except the backscattering. A brief survey of the literature shows that the irregularity spectrum, under various conditions, has a power‐law dependence. In order to conform to this observation a Bessel function spectrum proposed by Shkarofsky is found convenient to use since it not only reduces to the desired power‐law form in the proper range of wavenumber space, but also has all the finite moments. Exact expressions for the mean arrival time and mean square pulse width are obtained; some numerical examples are given. Finally, the effect of noise on these moments is discussed.
Coupled horizontal‐wire antennas over a conducting or dielectric half space
Authors: Shen L. C. , Lee K.‐M. , King R. W. P.
Published: February 2008

The properties of two coupled horizontal‐wire antennas over a homogeneous isotropic halfspace are derived. The complex wave number, distribution of current, and admittance of the antennas are determined for symmetrical and antisymmetrical excitations. The wave number of the halfspace is assumed to be large in magnitude compared with that in air. The theory of the coupled horizontal‐wire antennas is extended to take account of radiation into the air and so enlarge its range of validity while preserving the transmission‐line form. This is accomplished by incorporating the effects of this radiation and of the capacitive end correction for the open end in a lumped terminal impedance which is conveniently represented by a complex terminal function. This function is determined from a least‐squares fit of the measured and the theoretical current distributions.
The comparison between radar‐ and radiometer‐derived rain attenuation for earth‐space links
Authors: Hodge D. B. , Austin G. L.
Published: February 2008

The object of this paper is to establish the accuracy with which radar reflectivity measurements may be used to determine rain attenuation on earth‐space propagation paths. This objective was accomplished by comparison of attenuation calculated from 3 GHz radar reflectivity data from the McGiIl Weather Radar and attenuation calculated by the Communications Research Centre from 13 GHz radiometric temperature data along earth‐space propagation paths. It was found that path attenuation may be simulated with good accuracy provided that care is taken with the calibration analysis. This approach then allows the study of attenuation statistics from radar data, greatly expanding the available data base for rain attenuation studies.