bluuebunny/crossref_metadata_2025 huggingface dataset:
Amplitude probability distributions and impulse amplitude distributions for impulsive noise: Atmospheric radio noise from a near thunderstorm and automotive radio noise from a roadway
Authors: Nakai Taketoshi
Published: February 2008

An attempt has been made to derive the envelope amplitude probability distributions (APD) for atmospheric radio noise near thunderstorms. Formulas for APD's have been derived based upon the model for atmospheric radio noise near thunderstorms: First, elementary formulas for APD's are derived for the case when impulsive noise sources are continuously distributed over a limited range. Next, by taking into account the characteristics of the return stroke and K change pulses, APD curves at VLF are calculated using these formulas for atmospheric radio noise near a thunderstorm. Good agreement is shown between the calculated and measured APD curves. Further calculations indicate that the changes of the measurement frequency, and of the shortest distance to a thunderstorm influence the characteristics of the APD's. At last, similar procedure in analysis is applied to derive APD's for automotive radio noise, and the resulting calculated APD curves are shown for (1) a single vehicle and (2) a large number of vehicles running on a roadway, respectively.
Simulation of ionograms obtained during the October 1979 Platteville Heater experiment
Authors: Buchau J. , McNamara L. F.
Published: February 2008

Oblique propagation traces observed by an airborne ionosonde at different ranges from the Platteville heater facility during a period of overdense heating have been simulated by using a representative ionospheric model and standard ray‐tracing techniques. The heater frequency used during the time discussed in this paper was 6.2 MHz, while f0 F2 was approximately 8 MHz. The plasma frequency of 6.2 MHz was deduced to occur at approximately 260‐km altitude. The simulated ionograms are found to reproduce accurately the main features of the observed ionograms, over a wide range of ionosonde to heater distances. Comparison of the simulated and observed ionograms indicates that the irregularities created by the heater existed at altitudes of 200 to at least 280 km, over an area of radius approximately 100 km.
Full wave solutions for electromagnetic scattering and depolarization in irregular stratified media
Authors: Bahar E.
Published: February 2008

Using the complete expansions of the fields and imposing the exact boundary conditions at the interfaces of an irregular stratified medium, Maxwell's equations are transformed into a rigorous set of coupled first‐order differential equations for the wave amplitudes. This full wave approach is applied to a large class of propagation problems. Since these solutions account for specular point as well as diffuse scattering in a unified self‐consistent manner, it is not necessary to apply a hybrid physical optics‐perturbation approach to problems of rough surface scattering. The full wave solutions satisfy realizability, duality and reciprocity relationships in electromagnetic theory. They are invariant to coordinate transformations.
VLF/LF mode conversion model calculations for air to air transmissions in the earth‐ionosphere waveguide
Authors: Pappert Richard A. , Ferguson Jerry A.
Published: February 2008

In previous works, two mode conversion models, based upon slab approximations, were presented for treating lateral inhomogeneity along the path of propagation in the earth‐ionosphere waveguide. One model (termed Full MC in this paper) requires full‐wave determination of a biorthogonal set of height gains as well as numerical evaluation of their associated integrals. In the other model (termed Fast MC in this paper) height gain functions are discarded above some height h in the guide and are approximated below height h by Airy functions. No adjoint waveguide is introduced, and the associated integrals are performed analytically. Results of the two models are compared in this paper for air to air transmissions in laterally inhomogeneous environments. Results for both the vertical and transverse electric field are given for source electric dipoles of arbitrary orientation. It is found that the Fast MC model gives excellent agreement with the Full MC results.
A construction of the fields radiated by z‐directed point sources of current in the presence of a cylindrically layered obstacle
Authors: Pearson L. W.
Published: February 2008

Expressions for the electric and magnetic vector potentials for z‐directed magnetic and electric current point sources are developed as spectral integrals over longitudinal and azimuthal wave numbers. The representations are valid outside the source region. The construction is systemized, with the aid of Mason's signal‐flow graphs, in order to facilitate numerical implementation. The azimuthal spectral integral form is chosen rather than the azimuthally periodic form so that computations may be carried out in the complex plane associated with angular wave number without recourse to the Watson transform. Some example calculations are provided to demonstrate the practicability of the method.
H I calibration measurements at Arecibo Observatory
Authors: Colgan Sean W. J. , Terzian Yervant
Published: February 2008

From an analysis of galactic H I spectra acquired over a period of seven months, we investigate the accuracy of H I profiles obtained with the dual circular feed at Arecibo Observatory. The H I stray radiation contribution is estimated from a comparison of H I spectra toward the moon with H I spectra in the same direction when the moon is absent. The profile areas of corrected H I spectra are accurate to 3%, while individual features are accurate to 15%. At velocities where the H I emission is less than 3 K, the observed stray radiation is less than 0.5 K.
Vector solution for the mean electromagnetic fields in a layer of random particles
Authors: Lang R. H. , Seker S. S. , LeVine D. M.
Published: February 2008

The mean electromagnetic fields are found in a layer of randomly oriented particles lying over a half space. A matrix‐dyadic formulation of Maxwell's equations is employed in conjunction with the Foldy‐Lax approximation to obtain equations for the mean fields. A two variable perturbation procedure, valid in the limit of small fractional volume, is then used to derive uncoupled equations for the slowly varying amplitudes of the mean wave. These equations are solved to obtain explicit expressions for the mean electromagnetic fields in the slab region in the general case of arbitrarily oriented particles and arbitrary polarization of the incident radiation. The results include special cases previously treated in the literature on propagation through the atmosphere. Numerical examples are given for the application to remote sensing of vegetation.
The backscattered field of a thin wire loop for E polarization
Authors: Burns Joseph W. , Senior Thomas B. A.
Published: February 2008

For a thin wire loop illuminated by a plane electromagnetic wave, the backscattered field is determined when the incident electric vector is parallel to the plane of the loop. The complete second order GTD solution is obtained and found to be in excellent agreement with numerical data at angles close to normal incidence on the loop. At wide angles, however, a substantial disagreement exists, and an analysis of the data shows that the discrepancy is due to current waves circulating around the loop. The waves are similar to those previously found for H polarization, and using a simple model for the circulating current, the corresponding contribution to the backscattered field is determined. When this is added to the GTD solution, the resulting expression for the backscattered field is in good agreement with the numerical data for all angles of incidence and all loop diameters greater than a wavelength.
The minimum distance to the far field in a magnetized plasma
Authors: Rasmussen C. E. , Banks P. M. , Harker K. J.
Published: February 2008

The conditions necessary to determine the minimum distance to the far‐field zone are obtained for a finite source, emitting waves within an anisotropic medium. Although this distance is well known for free‐space applications, little information is available pertaining to the far‐field distance in an anisotropic medium such as a magnetized plasma. In this paper it is shown that the free‐space criteria are not applicable to anisotropic media and, in some instances, they fail dramatically. It is shown that the principal curvatures of the wave number surface are important in determining the far‐field distance. In an anisotropic medium, the principal curvatures depend upon the wave normal or propagation angle of the wave. Thus, the far‐field distance depends not only upon the wave‐length or magnitude of k, but also upon the direction of k as well. This implies that the far‐field distance is not a constant at a given wave frequency, but varies with the direction of the observer from the source. Furthermore, one or both of the principal curvatures can be zero in an anisotropic medium and for wave propagation associated with these points on the wave number surface, there is no solution to the wave equation which represents a wave‐amplitude dependence of 1/r.
Predicting the arrival of meteors useful for meteor burst communication
Authors: Weitzen Jay A.
Published: February 2008

Renewed interest in meteor scatter propagation for cummunication applications has created a need for better and more accurate techniques to investigate the complex relationship between the arrival rate of usable meteors and antenna patterns, link parameters, Faraday rotation loss and polarization. In past efforts, the complexity of the models predicting the arrival of meteors was limited by the cost of computing resources on large main‐frame computers. The rapid decrease in computing costs has allowed more advanced and computationally intensive modeling techniques to be applied to meteor burst modeling. This paper surveys the development of previous models and describes a new model which has been developed as a research tool to allow investigation of the relationship between the arrival rate of meteors and antenna patterns, Faraday rotation, polarization and link parameters. Preliminary results from the model are compared to data from several meteor links.
Scattering by a thick impedance half plane
Authors: Volakis John L.
Published: February 2008

In this paper we consider the scattering by a thick impedance half plane in the situation of a normally incident plane wave. The solution is based on the angular spectrum method in connection with the generalized scattering matrix formulation (GSMF) and as such it closely follows a parallel formulation applied recently in the diffraction analysis of the perfectly conducting thick half plane. Essentially, the angular spectrum method is first used to obtain the diffraction, coupling, reflection and radiation (or launching) coefficients relating to a pair of thin parallel impedance half planes which are then employed in the GSMF. The coefficients follow after an approximate solution of the resulting coupled dual integral equations which are derived in terms of the electric and magnetic current spectra. Several backscatter patterns are presented and compared with corresponding patterns based on the geometrical theory of diffraction (GTD) and a numerical model. It is found that a combination of the simple GTD solution and the present results give an acceptable solution for the diffraction by impedance half planes of almost any thickness.
F layer irregularity observations of the SAR arc event of March 5–6, 1981
Authors: Aarons Jules
Published: February 2008

Over several years, various observers have recorded irregularities in the F layer of the ionosphere at latitudes which were identified as the plasmapause region. During the stable auroral red arc of March 5–6, 1981, intense irregularities were recorded using amplitude fluctuations of satellite beacon signals. In the case of this SAR arc optical intensity was well correlated with irregularity intensity. The location of the small scale (∼1 km) irregularities was centered at plasmapause latitudes; scintillation levels tapered off in the same longitude sector at trough latitudes and were of lower than normal intensity and of different nature at auroral latitudes. Reported optical measurements indicated no visible aurora until areas four L shells poleward. Low energy (<12 eV) electron precipitation accompanied by elevated electron temperatures have been reported within the region covered by SAR arcs. High neutral gas temperatures have also been reported. Scintillation of moderate level is not uncommon for the plasmapause region. In March 1981, approximately 60% of the nights had scintillation levels > 6 dB at 137 MHz lasting over one hour. These irregularities, frequently of lower intensity than those accompanying the March 5–6 SAR arc, are probably initiated by low energy precipitation at these latitudes. However the role of convection is not as yet clear in this latitude region.
A data base approach to analysis of meteor burst data
Authors: Weitzen Jay A.
Published: February 2008

This paper describes an approach to the analysis of data from the U.S. Air Force high latitude meteor burst test bed in which a data base of key statistics is created from the raw data records. The data base approach reduces the storage, processing and analysis requirements while preserving the flexibility of analysis inherent in using raw data and can be used to analyze the propagation and communication properties of the high latitude meteor channel as a function of operating frequency, time of day, day, month, and propagation mechanism. Expert system techniques are incorporated in the software to automate various elements of the analysis procedure allowing a massive amount of data to be processed in a time‐ and cost‐efficient fashion. Examples of output from the data base are presented to show the power of the technique.
Secondary diffraction of a plane wave by a metallic wide strip residing on the plane interface of two dielectric media
Authors: Büyükaksoy A. , Uzgören G.
Published: February 2008

Secondary diffracted fields from a perfectly conducting strip residing on a planar interface separating two dissimilar dielectric media is obtained via the approximate solution of a modified Wiener‐Hopf equation. Ray optical interpretations are associated with secondary diffracted waves which result from the asymptotic analysis.
Scattering by a conducting plate with a randomly serrated edge
Authors: Eftimiu C. , Huddleston P. L.
Published: February 2008

The monostatic coherent response of a conducting plate with a randomly serrated edge is calculated by considering the serration to be a realization of a stochastic process. Results are given for both polarizations and various geometric and statistical parameters of the plate.
Space‐time fourth moment of waves propagating in random media
Authors: Frehlich R. G.
Published: February 2008

A series expression is developed for the space‐time fourth moment of a beamed field propagating through a rigid random medium that is moving relative to the transmitted field. Useful approximations for the space‐time correlation of intensity fluctuations are extracted as two special cases of the fourth moment series: a low spatial‐temporal‐frequency region and a high spatial‐temporal‐frequency region. The same statistics are also derived for the case of spatially incoherent sources. The parabolic wave equation, the Markov approximation, and Gaussian refractive index fluctuations are assumed. The results are derived using path integral methods.
A technique for computing the rate of change of electron density in the ionosphere
Authors: Schultz Abraham
Published: February 2008

A technique for computing the time rate of change of electron density for stratified ionospheres has been developed. The input is an initial estimate of the electron density profile and the Doppler shift at a number of frequencies in the HF band. The Doppler shift is expressed as a linear functional of the rate of change of electron density. Two techniques for inverting this linear functional to obtain the rate of change profile have been developed. Both techniques determine the values of a parametric representation of the rate of change profile that minimize the mean square error between observed and predicted Doppler shifts. One technique employs the Simplex search scheme and the second uses the method of overdetermined linear systems. It is shown that the methods converge using two test cases. A rate of change profile has been deduced from data produced by a broadband HF channel probe. There are two peaks of the profile curve in the E and F layers that occur near the two heights where the electron production rate is believed to peak. A local minimum near the peak in the F layer can be related to the formation of the F1 ledge. Applications of the rate of change profile to the study of ionospheric dynamics are discussed.
Dependence of radar parameters on polarization properties of rain for bistatic CW radar
Authors: Dibbern Jochen
Published: February 2008

The scattered electromagnetic field from a collection of raindrops is determined by the coherency matrix. To estimate the polarization of the scattered field from radar measurements a dual channel receiver is required. The echo powers in the main and orthogonal channels and the complex correlation between them are proportional to the elements of the coherency matrix. A generalized radar equation is given in matrix form for the bistatic polarization diversity radar and the dependence of radar parameters on various model assumptions, such as drop shape, drop size distribution and canting angle distribution is investigated. Calculated results at 33 GHz show that bistatic measurements with a scattering angle of 90°–100° at horizontal and vertical linear polarizations are especially suited to estimate the parameters of the drop size distribution, the mean canting angle and the canting angle distribution. The effect of rain occurring on the path between the transmitter, the rain target and the receiver is also considered.
Communication in a rough three‐layered conducting medium
Authors: Bishay Samira T.
Published: February 2008

The problem of communication in the sea has been considered as propagation of radio waves in three layered media (air, sea, ground). The variations which may occur in the shape of the upper and lower surfaces are considered. The effect of these variations is studied by using the perturbation method. The results obtained are compared with those mentioned elsewhere.
Some new aspects in the problem of waves and turbulence
Authors: Tatarskii V. I.
Published: February 2008

Two questions are discussed. The first is the effect of turbulence intermittency on wave propagation. Such effects as bursts of scattering intensity or a sudden improvement of the image quality in turbulent media are connected with the turbulence intermittency. The second one is the increase of mean backscattering from objects surrounded by the random medium with large‐scale inhomogeneities.
Leakage from various waveguides in millimeter wave circuits
Authors: Oliner Arthur A.
Published: February 2008

Most waveguides for millimeter wavelengths are partly or fully open, sometimes in view of their low‐loss design but usually because they are employed in integrated‐circuit fashion. The open nature of these waveguides can cause leakage that results in cross‐talk between neighboring components, in the lowering of circuit Q, or in the outright loss of power. Such leakage can be produced by several different basic mechanisms, including radiation from waveguide discontinuities into surface waves, space waves, or leaky below‐cutoff higher modes of the open waveguides themselves, or by continuous leakage along the length of the uniform waveguide, where the dominant or above‐cutoff higher mode itself is leaky. In addition, because of dimensional tolerance problems in the fabrication of open waveguides of small cross section, slight asymmetry can be introduced that causes a bound mode to leak. Examples are presented to illustrate each of the situations, although the limited space available does not permit the inclusion of analytical expressions for the leakage or numerical examples. Some interesting problems in electromagnetics arise in connection with some of these considerations.
Stochastic wave‐kinetic theory of radiative transfer in the presence of ionization
Authors: Besieris Ioannis M.
Published: February 2008

The stochastic wave‐kinetic theory at the level of the first‐order smoothing approximation is used to construct a radiative transfer equation for a simple model of a weakly inhomogeneous, weakly non‐stationary, and locally isotropic cold turbulent plasma. All the coefficients in the resulting equation are expressed systematically in terms of the electrodynamic and statistical properties of the medium without the usual recourse to phenomenological arguments.
Spectral‐ and spatial‐domain filtering and sampling approach to the numerical solution of electromagnetic scattering problems
Authors: van der Veeken R. W. C.
Published: February 2008

A new systematic approach is developed for the numerical treatment of electromagnetic scattering problems. It employs a filtering and sampling procedure that is applied, alternately, to the spectral domain and the spatial‐domain electromagnetic field representations. The resulting linear algebraic problem is solved by minimizing, iteratively, the root‐mean‐square value of the residual. Numerical results are obtained for the scattering by inhomogeneous, penetrable objects in one, two and three dimensions.
A uniform asymptotic expansion in the problem of half‐plane diffraction
Authors: Kupčák Dominik
Published: February 2008

Three terms in the uniform asymptotic expansion of the diffraction wave have been obtained directly from the nonuniform asymptotic expansion by an approximative method of formal summation. The accuracy of the order up to k−2 in the vicinity of geometrical shadow boundaries, and up to k−3 outside transition regions is ensured, k being the wave number. The first two terms coincide with the known UTD + MSD solution.
A modification event of the auroral E region as studied with EISCAT and other diagnostics
Authors: Schlegel K. , Rietveld M. , Maul A.
Published: February 2008

Highly enhanced backscattered power levels were measured with EISCAT during a modification experiment with a powerful HF heater. They occurred sporadically when the heater frequency was close to the local plasma frequency and very regularly during a time period when the heater frequency was definitely below the local plasma frequency (overdense heating). In this latter time interval the background electron density in the E region was enhanced due to particle precipitation. From the fact that the enhanced power levels were observed only with the Tromsø antenna looking along the magnetic field line and not with the remote antennas, it was concluded that the artificially created irregularities are pancake‐shaped, with the plane of the pancakes perpendicular to the magnetic field. Several processes which may be responsible for the excitation of these irregularities are discussed, and simultaneous results from other ground‐based experiments are presented.
Aperture efficiency enhancement in a Cassegrain system by means of a dielectric lens
Authors: Hudson Jerome A. , Plambeck Richard , Welch William J.
Published: February 2008

We have succeeded in boosting the overall aperture efficiency of a Cassegrain radio antenna by introducing a dielectric lens into the beam. The gain amounts to 0.7 dB, or about 17%, at millimeter wavelengths. The lens, of weak optical power, but strongly aspherical figure, is placed a short distance in front of the feed. It serves to redistribute the field in the aperture of the telescope, making the amplitude more uniform, with a sharp cutoff at the edge. The aberrations (defocusing and spherical) introduced by the lens are balanced by slightly displacing the secondary mirror. The lens can be adapted to many existing telescopes employing classical paraboloid‐hyperboloid optics, at minimal expense.
Boundary element method for dielectric resonators and waveguides
Authors: Collin R. E. , Ksienski D. A.
Published: February 2008

A general mode‐matching or boundary element method is described for formulating the eigenvalue problem associated with dielectric resonators and waveguides. The method is based on the use of dyadic Green's functions for which various different forms can be chosen. These different choices and the resultant computational advantages are discussed. The method is applied to the problems of a cylindrical dielectric resonator and a rectangular dielectric waveguide. It is shown that very accurate values of the dominant mode eigenvalue can be obtained using only a few global basis functions.
A method of estimating horizontal vectors of ionospheric electric field deduced from HF Doppler data
Authors: Tsutsui M. , Ogawa T. , Kamide Y. , Kroehl H. W. , Hausman B. A.
Published: February 2008

A formulation providing time variations of the horizontal electric field in the ionosphere from HF Doppler data is presented. The relationship between the electric field and frequency deviations of ionospherically reflected HF radio waves has been extended from the theory given by Jacobs and Watanabe in 1966. In the present formula, the effect of electron decay due to attachment and/or recombination processes is taken into account for long‐lasting variations in the electric field. The developed formula can provide time variations of the horizontal field vector even from data observed at only one station. The formula has been applied to an isolated substorm event. In examining the validity of the deduced results, equivalent ionospheric current systems have been used. These have been deduced from worldwide magnetometer data. With these current systems, we can roughly estimate the horizontal electric field in the ionosphere under some assumptions. The time variation of the electric field deduced from the HF Doppler data agrees with that deduced from current systems and high latitude electrojet activity. The results indicate that the HF Doppler method is a sensitive and useful tool for estimating the electric field in the ionosphere.
High‐resolution HF time of arrival measurements (1981–1985)
Authors: Rose Robert B.
Published: February 2008

Between 1981 and 1985, absolute time of arrival (TOA) measurements were made on HF sky wave time standard signals at different frequencies. A total of 113 path months of TOA data were collected over a one‐hop path between Fort Collins, Colorado and San Diego, California. In addition, 15 path months of data were collected between Fort Collins and Oahu, Hawaii, and 12 path months were gathered on signals between Tokyo, Japan and Oahu. The data show a higher degree of ionospheric movement than had been expected by the experimenters. They also show a higher degree of stratification within layers than can normally be explained with simple models based on a single‐layer ionosphere.
Short‐term magnetic field alignment variations of equatorial ionospheric irregularities
Authors: Johnson Allen L.
Published: February 2008

The ionospheric irregularities that cause equatorial scintillation are elongated along the north‐south magnetic field lines. During a 1981 field campaign at Ascension Island, 250‐MHz receivers were spaced from 300 m to 1.6 km along the field lines, and the signals received from the Marisat satellite were cross correlated. Data collected during eight nights of fading showed a linear relationship between fading rate and cross correlation. The alignment of the antennas was adjusted to give a zero time lag between the widely spaced receivers with a measurement accuracy of 0.03 s. Since the average irregularity velocity was 125 m/s, this time accuracy translated to an angular measurement accuracy of 0.1°. During a 4‐hour period of nightly fading, occasional differences in time of arrival were noted that corresponded to a tilt in the north‐south alignment of ±1°. Data from several nights of fading were analyzed, and each night exhibited the same variance in the north‐south irregularity alignment. It is postulated that the shift in the measured peak correlation may have been caused by patches of irregularities at different altitudes where the magnetic field lines have a slightly different direction.
The profile algorithm for microwave delay estimation from water vapor radiometer data
Authors: Robinson Steven E.
Published: February 2008

A new algorithm has been developed for the estimation of tropospheric microwave path delays from water vapor radiometer (WVR) data, which does not require site and weather dependent empirical parameters to produce accuracy better than 0.3 cm of delay. Instead of taking the conventional linear approach, the new algorithm first uses the observables with an emission model to determine an approximate form of the vertical water vapor distribution, which is then explicitly integrated to estimate wet path delays in a second step. The intrinsic accuracy of this algorithm, excluding uncertainties caused by the radiometers and the emission model, has been examined for two channel WVR data using path delays and corresponding simulated observables computed from archived radiosonde data. It is found that annual rms errors for a wide range of sites average 0.18 cm in the absence of clouds, 0.22 cm in cloudy weather, and 0.19 cm overall. In clear weather, the new algorithm's accuracy is comparable to the best that can be obtained from conventional linear algorithms, while in cloudy weather it offers a 35% improvement.
A simplified approach to bistatic radar reflectivity computations
Authors: Tarducci D. , Tao S.
Published: February 2008

This paper presents some simplified expressions for the four components of bistatic radar reflectivity (i.e., bistatic scattering cross section per unit rain volume), which are based on the Mie scattering theory for spherical drops and the Marshall‐Palmer raindrop size distribution, and can be used at least in the frequency range from 10 to 30 GHz, at an average temperature of 10°C. The coefficients of these simplified expressions are then fitted in frequency by polynomial expansions which make it possible to extrapolate their values, with a good precision, at any frequency in the 10–30 GHz range. A check of the variability of reflectivity components with temperature has also been performed; variations appear to be less than 1 dB for temperature differences ranging from 10°C to 20°C.
Dynamics of three‐dimensional ionospheric plasma clouds
Authors: Zalesak S. T. , Drake J. F. , Huba J. D.
Published: February 2008

In this paper we will present the first fully three‐dimensional analytic study of plasma cloud dynamics, as well as computational results based upon a recently developed three‐dimensional electrostatic code. We derive a stability criterion for the large‐scale structuring of an ionospheric cloud based on a water bag model for the special case Lz = rc(σ‖/σ⊥)1/2 (here, Lz is the half length of the cloud along the magnetic field, rc is the radius of the cloud, and σ‖,⊥ are the parallel and perpendicular cloud conductivities, respectively). We also present preliminary numerical results of three‐dimensional plasma cloud behavior. We examine the self‐consistent pressure‐induced plasma flow that results from a realistic plasma cloud in a realistic atmosphere in two‐dimensional cylindrical geometry, and the evolution of fully three‐dimensional perturbations of such a cloud.
Physical interpretation of the full wave solutions for the electromagnetic fields scattered from irregular stratified media
Authors: Bahar Ezekiel
Published: February 2008

The full wave solutions for the vertically and horizontally polarized electromagnetic fields scattered by irregular stratified media are expressed in terms of double infinite sums. These full wave solutions satisfy the reciprocity relationships in electromagnetic theory. The physical interpretation of each term in the double infinite series provides insights into the nonspecular scattering phenomena for irregular stratified media. It is shown that n+1 different terms of the full wave expansion replace the single nth term of the corresponding geometric optics series. From scattering in the specular direction these n+1 terms become analytically indistinguishable, and the full wave solution reduces to the geometric optics solution. The full wave solutions are also consistent with Rice's perturbation solution for rough surface scattering in the low‐frequency limit. The physical interpretation of the full wave solutions which are based on complete spectral expansions of the fields could be used to construct solutions for the nonspecularly scattered fields in complex problems involving irregular stratified media.
Propagating ionospheric waves observed throughout east Asia during the WAGS October 1985 campaign
Authors: Walker G. O. , Wong Y. W. , Ma J. H. K. , Kikuchi T. , Nozaki K. , Huang Y. N. , Badillo V.
Published: February 2008

The propagation of acoustic gravity waves has been observed by an investigation of their effects upon the ionosphere over distances ranging up to 3400 km and extending from mid‐latitudes (45.4°N) to low latitudes (14.7°N) in east Asia. Recognizable wave structures were observed mainly on low sounding frequency, virtual height h'f and to a lesser extent f0F2 time variations, obtained from ionograms taken at 10 ionosonde stations, sounding at 5‐min intervals throughout the period October 15–19, 1985. Investigations were mainly confined to the nighttimes, since during the day large latitudinal gradients of ionization (associated mainly with the equatorial anomaly) together with movements of the equatorial anomaly crest obscured the observation of waves. In general, inferred propagation of the waves was southward, but three cases of northward propagation were observed, the former having a range of periods 40–210 min, while the latter were consistently about 70 min. The waves structures, mostly, differed depending upon whether they were located to the north or south of Yamagawa (31.2°N). There was some evidence of the predomination of longer‐period waves to the south, the shorter‐period waves observed to the north being apparently damped out in their propagation southward. The southward propagating waves exhibited upward energy propagation, while at Hong Kong (22.3°N) there was some evidence of downward phase propagation with a shift to lower periods at lower heights. It has not been possible to identify the origins of the detected waves, but it is clear that sources existed within and outside the latitude range covered by the ionosonde sounding stations (14.7°–45.4°N).
Interaction of electromagnetic waves in the ionosphere
Authors: Laxmi V. N. , Saha A. K.
Published: February 2008

Time evolution of filamentation of an electromagnetic wave in the F region of the ionosphere has been studied numerically. It is seen that a plane electromagnetic beam of uniform power flux becomes unstable and gets filamented in the presence of transverse density fluctuations caused by a high power electromagnetic Gaussian beam. The computations are performed using Gaussian beams of 10, 30 and 50 μw/m2 power flux, to produce the nonuniform plasma fluctuations in the medium. The intensity of the plane wave is, however, fixed at 30 μw/m2. The filamentation of the plane wave develops in the entire region of the 100 km altitude range between 200 and 300 km used in the computations. The amplitude of the filaments increases with height and the growth is more rapid than an exponential variation. The plasma imitates the wave structure and the fluctuations in the electron temperature and density are field aligned. The relative density fluctuations associated with filaments lie in the range 0.1 to 1.5% and depend on the intensity of the incident Gaussian beam.
The effect of spatial inhomogeneities on the elevation angle dependence of atmospheric thermal emission at millimetric wavelengths
Authors: Gibbins C. J. , Cherry S. M.
Published: February 2008

Significant and consistent deviations from the “secant θ” law describing the elevation angle dependence of atmospheric thermal emission have been observed in radiometric measurements at millimeter wavelengths, which did not occur when observations were made at different azimuthal angles. The presence of a source of water beneath the radiometer beam suggested the possibility of additional, localized, “plumes” of water vapor. This paper considers the effect of such plumes on elevation angle scanning radiometers and suggests a possible method for remote sensing of water vapor plumes.
A space domain integral equation approach in the analysis of dielectric‐covered slots
Authors: Katehi Pisti B.
Published: February 2008

Coupling through dielectric‐covered slots is becoming a very important excitation mechanism for antennas and arrays in microwave and millimeter wave frequencies. The characteristics of these antennas can be analyzed by solving appropriate integral equations. A space domain method of moments applied for solving these equations may complicate the existing Sommerfeld integrals even more. In this paper a combination of analytical and numerical techniques has been developed which reduces the complexity of the integrals and improves efficiency and accuracy in their computation.
Medium scale structure of the F region
Authors: Paul Adolf K.
Published: February 2008

Data collected during 1980/1981 at Brighton, Colorado show clearly that the F region variations are undersampled in space and time by standard recording procedures. Fast temporal changes, with periods as short as 10 min are directly observable if ionograms are taken in rapid sequences of at least 12 ionograms per hour. In order to obtain a correct spatial sampling, the distances between observing stations should not be much larger than 100 km. This conclusion is derived from the temporal variations of F layer parameters assuming a propagation velocity typical for acoustic gravity waves. Some direct estimates of a spatial structure scale can be obtained from angle of arrival measurements. Comparison of ƒ0F2 and M U F(3000) indicate that the main effect of gravity waves on the F region structure is the variation of the height of the layer and to a lesser degree a variation of the maximum electron density.
Off‐axis performance of shaped antennas at millimeter wavelengths
Authors: Hudson Jerome A.
Published: February 2008

Antennas which have been shaped for optimal aperture efficiency will not give sharp off‐axis images. This is true for even quite small fields of view. The shaping to match feed horn illumination is at fault here; it leads inevitably to severe coma and curvature of the field. The analysis presented here is based upon geometrical optical computations.
Secondary diffraction of plane waves by an impedance strip
Authors: Büyükaksoy Alinur , Serbest A. Hamit , Uzgören Gökhan
Published: February 2008

In this paper, uniform asymptotic expressions are derived for the doubly diffracted fields associated with an impedance strip under plane wave illumination. It is shown that the result Senior (1979) obtained by doubling the secondary diffracted field across the upper face of the strip to take into account the contribution of the lower face seems to be unjustifiable because of the nature of the boundary condition. The analysis is performed through a new spectral method in which the Fourier integral representation of the primary diffracted wave by one of the edges is considered as the incident wave for the half plane terminating at the other edge where the secondary diffraction will occur. The surface wave contributions are also included in a uniform manner.
Ultrasonic diffraction of microwaves in magnetized ferrite
Authors: Mueller R. S.
Published: February 2008

A description of the phenomena of ultrasonic diffraction of electromagnetic microwaves in a transversely magnetized ferrite slab is accomplished by the partial wave approach. Starting with the Lorentz‐Lorenz law, the strength of the scattering is shown to be due to the change in the permittivity of an yttrium‐iron garnet (YIG) ferrite at frequencies in the X band and above. When traveling sound waves act like a phase grating, the normal type of ultrasonic microwave diffraction occurs. The spacing and intensities of the orders of spectra are given by the Raman‐Nath theory. Since the direction of magnetization is perpendicular to the direction of propagation, there are H and E waves that may propagate independently through the ferrite. Each wave has its own wavelength and direction of propagation. Two sets of upper and lower sidebands appear as right and left spectra to the primary H and E waves with equal intensity for the same order. Time variations of the refraction index are obtained by propagating ultrasonic energy as standing waves in a ferrite diffraction cell. The density variations associated with this sound wave result in a bending of a narrow microwave beam. For plane acoustic waves the horizontal beam deflection traces a vertical linear path.
Edge wave vertex and edge diffraction
Authors: Ivrissimtzis L. P. , Marhefka R. J.
Published: February 2008

An approximation for the diffraction of an edge wave by the vertex and edges of a conducting trihedron is developed. The edge wave is produced by an electric dipole source located in the vicinity of one of the edges and sufficiently far from the tip of the vertex. The radiation integral of the currents that would be induced over an infinite wedge, which is then truncated, is evaluated asymptotically yielding an endpoint effect. The effect of a fringe current component, excited by the terminating edges, is introduced subsequently. The approximation shows good agreement with method of moments computations and measured data for several flat plate structures.
Surface impedance of transversely moving microwave ferrite
Authors: Mueller R. S.
Published: February 2008

A theoretical study was made of the surface impedance Z for an electromagnetic transverse magnetic wave from free space on a magnetized ferrite surface moving normal to the plane of incidence. It was found convenient to decompose the surface impedance into two transfer impedances, Z1 and Z2, which relate the hybrid reflected amplitudes to the amplitude of the incident wave. The surface impedance does not vary much with respect to the angle of incidence, so only the case of normal incidence (θi = 0°) was evaluated. Resonant poles at ƒc, [ƒc(ƒc + ƒm)]1/2, and ƒc + ƒm dominate the frequency characteristics of Z1 and Z2. The frequencies ƒc andƒm are the precessional frequency and magnetization frequency, respectively.
Multiple scattering effects on the transmission and reflection of millimeter pulse waves in rain
Authors: Oguchi Tomohiro , Ito Shigeo
Published: February 2008

Numerical solutions of the vector two‐frequency radiative transfer equation are obtained to investigate the effects of multiple scattering on pulse propagation in rain. Only the case of circularly polarized incident wave is treated. First, the shape and magnitude of transmitted incoherent pulses in co‐ and cross‐polarized channels are compared with those of the incident pulses, and the effect of multiple scattering on communication quality is discussed. Next, the shape and magnitude of the reflected pulses in the main polarization channel are compared with those calculated by the conventional radar equation, and the difference of the two results is examined. In backward scattering, the radar returns of spherical raindrops in the cross‐polarized channel given by the multiple scattering calculations are often comparable to those obtained by the first‐order calculations for Pruppacher‐Pitter‐shaped distorted raindrops. The multiple scattering effect on the polarimetric interpretation of cross‐polarized radar returns from distorted raindrops is discussed.
The ionosphere as a focusing lens: A case study involving simultaneous type III solar radio storm measurements from the ISIS 1 and 2 and ISEE 3 satellites
Authors: James H. G. , Benson R. F. , Fainberg J. , Stone R. G.
Published: February 2008

For several decades ionospheric focusing has been suggested as a means of improving antenna resolution at frequencies less than about 10 MHz for the observations of spatial features of the cosmic noise background as well as the spectra of discrete radio sources. In this paper the possibility of using terrestrial ionospheric focusing to improve the directivity of electric dipoles on space missions has been investigated by comparing simultaneous observations of a solar radio storm by the ISIS 1 and ISIS 2 spacecraft, in near Earth orbit, and the ISEE 3 spacecraft located beyond the magnetosphere. To this end, a three‐dimensional ray tracing in a spherically stratified ionosphere has been carried out for conditions appropriate to the observations by the ISIS spacecraft of a solar radio storm in September 1983. This procedure allows Poynting flux spectral densities measured on ISIS to be converted to spectral densities well outside the ionosphere where they can be compared directly with simultaneous observations on ISEE 3. The results demonstrate good agreement over their common observing frequency range (1–2 MHz). Furthermore, since ISIS covers higher frequencies than ISEE 3, the spectrum of the solar radio storm was extended to 4 MHz.
A phased‐array radiowave imager for studies of cosmic noise absorption
Authors: Detrick D. L. , Rosenberg T. J.
Published: February 2008

Most measurements of cosmic radio noise absorption in the polar regions have been made with riometers using broad‐beam (∼60 deg) antennas. Only limited information about the spatial structure and dynamics of the aurora can be obtained by this means. Recent trends in riometry have emphasized the use of multiple narrow‐beam antennas operated in a fixed beam or one‐dimensional scanning mode to examine smaller ionospheric regions. A further step in this direction has been the development of the imaging riometer for ionospheric studies (IRIS). This instrument provides a two‐dimensional image of regions of enhanced cosmic noise absorption at 38.2 MHz with a spatial resolution as small as 20 km and time resolution of 1 s. The IRIS antenna is a 64‐element dipole array, phased to produce 49 independent beams viewing an ionospheric area about 200 km square at 90 km altitude. One IRIS instrument has been operating at the South Pole station since January, 1988; a second instrument was recently installed at Sondre Stromfjord, Greenland. This paper presents a technical description of the IRIS system. The response of the IRIS to a sun‐aligned absorption arc is illustrated and compared with that of a broad‐beam riometer. An intense, localized structure that developed within the arc was observed by IRIS to propagate in the magnetic poleward direction with a speed of 1 km/s.
An induction gradiometer for conductivity contrast detection: Experimental development
Authors: Mariani David R.
Published: February 2008

A gradiometric induction sensor has been developed as a sensitive indicator of spatial electrical conductivity gradients. Utilizing a configuration of three antennas in a single, monolithic metal slot, its design is simple and compact. Its feasibility as a geometry indicator for use in oil wells drilled with oil base mud has been demonstrated by a series of laboratory experiments which simulated many borehole and logging conditions. Response to real and synthetic rock arrays, resolution, standoff sensitivity, and response to dipping geologic beds are among the issues quantified by the experiments. In addition, some useful models are presented as an aid in conceptualizing the principles behind the operation of the sensor.