bluuebunny/crossref_metadata_2025 huggingface dataset:
Precise time dissemination via OMA‐50 kHz
Authors: Buzek O. , Čermák J.
Published: February 2008

In August 1977 the Czechoslovak standard time and frequency station OMA‐50kHz began transmitting a new time code which has completed the original A1 format. The new code is formed by a sequence of phase‐reversed pulses identifying minutes and hours of Central European Time (CET). It is planned to extend the code further in the near future. This paper presents the new code and discusses its basic properties. As an example of a practical application an OMA‐controlled clock is described.
Nova satellite time experiment
Authors: Rueger L. J. , Bates A. G.
Published: February 2008

A time transfer experiment was carried out between the master clocks of the U.S. Naval Observatory and the U.S. National Bureau of Standards in Boulder, Colorado, using passively recovered Nova satellite time signals at each ground station. Timing correlation of the master clocks derived from the satellite signals agreed with comparisons made by Cs clock transfers within 50 ns.
Synchronization of atomic clocks through the ‘Symphonie’ satellite
Authors: Brunet M.
Published: February 2008

The intercomparison of time and frequency standards is restricted by the inadequacy of terrestrial radio time transfer links in terms either of accuracy or of geographical coverage. The use of artificial satellites can improve this situation. (Blair, 1974; Chi and Byron, 1975; Markowitz et al., 1966; Ramasastry et al., 1973; Saburi et al., 1976; Steele et al., 1964; Yamamoto et al., 1976). Two experiments are described in which the geostationary telecommunications satellite Symphonie is used. A two‐way simultaneous link is employed in order to eliminate the need to know the propagation delays. Details of a test carried out in December 1976 between Raisting (West Germany) and Pleumeur‐Bodou (France) are given. Also, preliminary details of the time transfer experiment between Pleumeur‐Bodou and Ottawa (Canada) are described.
NBS time to the Western Hemisphere by satellite
Authors: Hanson D. W. , Davis D. D. , Cateora J. V.
Published: February 2008

As a complement to the present time and frequency services of WWV, WWVH, and WWVB, the National Bureau of Standards (NBS) is now providing a satellite‐disseminated time code using the Geostationary Operational Environmental Satellites (Goes) of the National Oceanic and Atmospheric Administration (NOAA). The time code is referenced to the NBS time scale, giving coordinated universal time (UTC). In addition to the usual information of day of year, hours, minutes, seconds, and the UTl correction the time code contains the satellite's current position for use in path delay calculations. The time signals are relayed to the entire Western Hemisphere from two geostationary satellites on a full‐time basis except during brief periods of solar eclipses occurring during the vernal and autumnal equinoxes. The time code, originally intended for use by environmental monitoring platforms, is easily accessible by anyone using relatively simple, commercially available equipment. Physically small antennas (30 cm × 30 cm × 1cm) are typical. The generation, satellite relay, and recovery of these signals is discussed. Results obtained with commercial receiving equipment are included.
Remote atmospheric probing on a line‐of‐sight path, using spatial filter concepts: 1. Theory
Authors: Leuenberger K. , Lee R. W. , Waterman A. T.
Published: February 2008

A rigorous treatment is given to a spatial filtering method for remotely determining the transverse wind velocity and the atmospheric structure constant along a line‐of‐sight path, assuming a Kolmogorov spectrum of refractivity and weak scattering. The results are applicable from the millimeter‐wave range to the optical range for linear array configurations at either one end or both ends of the path. Various methods of signal detection are considered, such as coherent, quasi‐coherent (knowledge of relative phases), and incoherent. In order to determine the two parameters the integral for the time covariance or the spectrum of the wave fluctuations must be inverted. For simple arrangements of single elements or pairs of elements at the transmitting and receiving locations the inversion is ill conditioned and yields only three or four resolution cells along the path. A statement of the problem in spectral form for line apertures representing narrow bandpass‐type spatial filters leads to optimal orthogonality of the inversion problem. In the limiting case of ideally sharp spatial filters, the inversion is shown to degenerate into a simple one‐to‐one relationship between spectral measurements of the spatially filtered wave fluctuations and the values of the parameters at a specified location along the path. A subsequent paper will be devoted to an experimental application of the principle in the mm‐wave region.
Exact ray paths in a multisegment quasi‐parabolic ionosphere
Authors: Hill Jay Roderick
Published: February 2008

Exact ray paths are calculated in a multiple quasi‐parabolic layer ionosphere. Ray fans, displayed by using minicomputers and microcomputers, aid in real time propagation assessment systems. Equations for valley layers are derived by using an inverted quasi‐parabolic layer.
Wiener‐Hopf solution for the junction between a smooth and a corrugated cylindrical waveguide
Authors: Daniele V. G. , Montrosset I. , Zich R. S.
Published: February 2008

The frequency behavior of the transition from a smooth to a corrugated cylindrical waveguide follows from the analysis of the canonical problem of the junction between two guides with different surface admittances, one being infinite and the other anisotropic. The Wiener‐Hopf technique leads to an exact solution of this canonical problem and yields modal coupling coefficients expressed only in terms of the longitudinal wave numbers of the modes supported by each of the two guides. Typical numerical results are presented for a given value of the ratio between the inner and the outer radii of the corrugated guide.
Scan independent phased arrays
Authors: Munk B. A. , Kornbau T. W. , Fulton R. D.
Published: February 2008

This paper discusses a derivation of the scan impedance for a phased array consisting of arbitrarily oriented planar elements with arbitrary current distribution located in a general stratified media. It is shown that the scan impedance will remain scan independent if and only if the product of the element power pattern and the transformation function for the stratified dielectric media varies as the cosine to the scan angle. An entire class of scan independent phased arrays is defined in this fashion. As simple examples of this class, we discuss arrays of slots or dipoles bounded by a single dielectric slab with ϵ = 1.3. The scan impedance has VSWR < 1.5 for scan angles up to ±80° in both principal planes, and further improvements appear possible. These designs are quite different and superior to earlier phased array designs (Magill and Wheeler, 1966; Campbell and Popovich, 1972; Chen, 1973).
A probabilistic model for the initial peaks of ground wave atmospherics generated by lightning return strokes
Authors: Lefferts Robert E.
Published: February 2008

By using a previously developed statistical model of the lightning discharge the probability density function for the initial peaks of the ground wave electric field generated by the return strokes was developed. The variation of the probability density function with the distance to the source is expressed analytically for the range of approximately 25–500 km in which the ground wave predominates. Since the statistical simulation model can include the frequency response of the receiving circuitry, the model can be used to predict the performance of threshold sensitive devices which operate on the initial peaks of the electric field. An example is given which illustrates the application of the results to a device similar to a lightning flash counter. Although only the induction and radiation field components were included in this study, it should be possible to modify the results to include the electrostatic component which would then allow calculation of the effective range of lightning flash counters.
Electromagnetic scattering patterns from sinusoidal surfaces
Authors: Jordan A. K. , Lang R. H.
Published: February 2008

In this paper we present an analysis and calculation of scattering patterns from sinusoidal surfaces. An exact space harmonic representation is used for the field on the surface, and as a result, the calculation includes the effects of shadowing, diffraction, and multiple scattering. An asymptotic evaluation has been employed to obtain an exact expression for the scattering pattern as a product of the space harmonic scattering coefficients times the corresponding pattern functions. The formula obtained has been simplified for illuminated areas that are many wavelengths long and plotted for a variety of surface parameters. The present method for scattering pattern calculations can be considered to be complementary to methods using physical optics and point‐matching techniques. In addition to the scattering pattern calculations the exact Bragg backscattering amplitudes have been computed and compared with their Rayleigh approximations.
Modulation of short gravity‐capillary waves by longer‐scale periodic flows—A higher‐order theory
Authors: Valenzuela G. R. , Wright J. W.
Published: February 2008

A higher‐order perturbation theory for the modulation of short gravity waves by longer‐scale periodic flows is developed, starting with Boltzmann's transport equation and including the input from the wind, energy transfer by nonlinear resonant interactions, and dissipation. Specific results are given for a model dealing with the straining of short gravity waves coupled to ‘parasitic’ capillary waves by second‐order resonant interactions. The initial value problem yields a relaxation rate for the short gravity waves equal to their growth rate. The predicted phase of the short gravity waves in relation to the crest of the longer gravity waves with this relaxation rate is in better agreement with measurements. Explicit expressions are obtained for the second‐order results in terms of Uo/C (ratio of orbital to phase speed of the modulating wave). Numerical results are obtained for the reduction of the short gravity waves amplitude and for the modulation and phase of the backscattered power of microwave sensors probing this system of water waves. The second‐order results predict the reduction of the linear modulations, but the reduction is not large enough to match the measurements for Uo/C ratios larger than 0.1. Accordingly, perturbation solutions do not converge fast enough for the larger Uo/C ratios.
Statistical model of the D region
Authors: McNamara L. F.
Published: February 2008

A collection of some 700 experimental D‐region electron density profiles has been digitized and made easily computer accessible. By using these profiles the density at a given height has been determined and modeled as a function of solar zenith angle, sunspot number, latitude, season, and magnetic index. Expressions have been obtained for the density at heights from 55 to 90 km. It is found that the effects of the different parameters of the model vary with height. Magnetic effects, for example, are more important above 80 km, while latitude effects are most important at 60 km.
Near field and damping effects on the radiation of ion acoustic waves from antennas
Authors: Nakamura Y. , Nomura Y. , Lonngren K. E.
Published: February 2008

Radiation patterns of a longitudinal wave transmitted in a warm plasma from monopole antennas are numerically calculated taking wave damping and near field effects into consideration. Both a wire and a circular grid are examined. The patterns are measured experimentally for ion acoustic waves. Experimental results agree with the theoretical prediction. Both effects broaden the radiation patterns.
On the limitations of the concept of space frequency equivalence
Authors: MacPhie R. H.
Published: February 2008

A narrow‐band correlation interferometer using directive (large) antennas is equivalent to a wideband correlation interferometer employing isotropic (small) antennas. This concept of space frequency equivalence, due to Kock and Stone, is reexamined and is shown to hold exactly only for the mean or expected values of the correlation interferometer outputs. If their variances are considered, the equivalence disappears, with the variance of the wideband system always equal to or greater than that of the narrow‐band system.
Descriptive summary: Radiofrequency radiation dosimetry handbook—Second edition
Authors: Durney C. H. , Johnson C. C. , Barber P. W. , Massoudi H. , Iskander M. F. , Allen S. J. , Mitchell J. C.
Published: February 2008

The second edition of the Radiofrequency Radiation Dosimetry Handbook extends the data contained in the first edition, which was published by the United States Air Force School of Aerospace Medicine in September 1976 [Johnson et al., 1976]. Several additional techniques have been used to extend the frequency range over which the specific absorption rate or mass‐normalized rate of energy absorption (SAR) is calculated for models of human beings and animals, which results in useful theoretical data over the frequency range 10 kHz to 100 GHz. Some information is also given about ground‐plane effects, experimental data found in the literature, and thermal effects of irradiation.
Perinatal exposure of rats to 2450‐MHz CW microwave radiation: Effects on lymphocytes
Authors: Smialowicz Ralph J. , Kinn James B. , Elder Joe A.
Published: February 2008

Groups of rats were exposed in utero from day six of gestation through 40 to 41 days of age for four hours a day in a temperature‐ and humidity‐controlled environment under far‐field conditions to 2450‐MHz (CW) in an electrically anechoic chamber. An equal number of sham‐exposed animals, maintained under the same environmental conditions, served as controls. Two experiments have been performed at this frequency at a power density of 5 mW cm−2. Specific absorption rates (SARs) for rats of different ages were determined by twin‐well calorimetry and were found to range from 0.7 to 4.7 mW g−1. Rats were weighed at selected intervals to determine if microwaves affect growth. At 20 to 21 and 40 to 41 days of age, rats were bled and complete blood‐cell counts were done. In addition, the in vitro blastogenic response of blood and lymph‐node lymphocytes were measured by 3H‐thymidine incorporation into DNA following stimulation of cells with T‐ and B‐lymphocyte mitogens. There were significant increases in the mitogen‐stimulated response of both T‐ and B‐lymphocytes from irradiated rats. There were no consistent changes, however, in peripheral blood‐cell counts after exposure at this frequency. These results indicate that long‐term exposure of rats in utero and through early life may result in increased response of lymphocytes to stimulation with mitogens in vitro.
Videotape observation of rats and mice during an exposure to 2450‐MHz microwave radiation
Authors: Gage Michael I. , Bertnan Ezra , Kinn James B.
Published: February 2008

Rats and mice were observed in a microwave field to see if they would take behavioral action to minimize absorption of microwave energy by altering their orientation with respect to the E field. Individual rats were housed either in a cylindrical or in a cuboidal container, and mice were housed in a cuboidal container. They were placed in an anechoic chamber at 22 or 28°C for a one‐hour pre‐exposure period. During the second hour, animals were exposed to 2450‐MHz CW microwaves under far‐field conditions at a power density of 15 mW cm−2. Videotape samples of their positions were taken during a two‐hour session. Six rats and six mice were observed at each level of temperature and were scored for orientation relative to the electric vector or to the magnetic vector of the microwave field. Results indicate that 2450‐MHz CW microwaves did not cause animals to alter their position from that adopted in response to environmental or caging conditions. The specific absorption rate (SAR) in rats was not dependent on their orientation in the field. The SAR in mice was dependent on their orientation in the field but their orientation did not show changes interpretable as attempts to reduce microwave absorption. Containers reduce the SAR and, depending on shape, may reduce the orientation‐dependence of the SAR.
The effect of psychoactive drugs on operant behavior induced by microwave radiation
Authors: Monahan John C. , Henton W. W.
Published: February 2008

A total of five male CF1 mice was trained to escape from or to avoid 2.45‐GHz CW microwave radiation by emitting an operant response. The response consisted of an animal's interruption of a light beam passing through a conditioning chamber. If an animal responded while microwaves were on, radiation was terminated and remained off for 12 seconds (an escape response). If an animal responded during the off period, each response (constituting avoidance) would reset a timer that delayed the onset of microwaves for another 12 seconds. All responses involved discriminated cueing by a 2900‐Hz sonic stimulus that was paired with microwave irradiation. Averaged dose rates were approximately 45 mW g−1, but the duration of irradiation varied with the subjects' escape‐avoidance behavior. When stable baselines of responding were established, each subject was tested following administration of each of three psychoactive compounds at varying dosages: chlordiazepoxide, d‐amphetamine, and chlorpromazine. Chlordiazepoxide resulted in a decreased percentage of avoidance responding coupled with an increased percentage of escape responding. A substantial increase in the animals' cumulative exposure to microwaves was also noted when they were dosed with this drug. The data based on administration of chlorpromazine and of d‐amphetamine were highly variable both within and among subjects.
Microwave radiation and dextroamphetamine: Evidence of combined effects on behavior of rats
Authors: Thomas John R. , Maitland Georgia
Published: February 2008

Combined effects of microwave radiation and dextroamphetamine were investigated in studies of six male albino rats that performed on a temporal reinforcement (DRL) schedule. During one‐hour sessions, only a response that was delayed by 18 s or more after a preceding response was reinforced by a food pellet. Thirteen weeks of pretraining on the schedule generated a low‐and‐steady rate of responding, with the largest proportion of responses occurring after the appropriate interval of time. Initially, a dose‐effect function was obtained in the absence of radiation for a range of doses of dextroamphetamine (0.25 to 5.0 mg kg−1). Smaller doses of the drug produced an increase in response rate with consequent reduction in frequency of reinforcement. Maximal rates of responding occurred at 1.0 to 2.0 mg kg−1. Yet higher doses of the drug produced a decline of rate, then complete cessation of responding. A dose‐effect function was then obtained for the same doses of the drug during three‐month regimens involving single or multiple exposures to radiation. In the single‐exposure condition, after the drug was administered to a subject, it was exposed for one‐half hour to 2.45‐GHz pulsed microwaves at an averaged power density of 1 mW cm−2 (2 μS pulses; 500 pulses s−1). The resulting whole‐body dose rate was near 200 μW g−1. In the multiple‐exposure condition, a subject was exposed daily to microwaves under the same field conditions, except on days when dextroamphetamine was administered and behavior was observed. Under both conditions of radiation, the dose‐effect function was displaced such that the maximal behavioral effect was obtained at doses lower than those without radiation.
Studies of the blood‐brain barrier: Preliminary findings and discussion
Authors: Frey Allan H.
Published: February 2008

The tasks I have been assigned as a discussant are, first, to discuss results of my current experimentation that extends my earlier blood‐brain barrier work as it bears upon the work presented by the panelists. Second, I am to comment on the work presented by the various panelists.

I will briefly sketch three of my current experiments. One concerns the effect of microwave energy on the blood‐vitreous barrier of the eye. Another is concerned with the possibility of passage of dye through the placental barrier to the fetus. The third is concerned with the possibility of low‐intensity microwave energy enhancing the passage of cancer chemotherapeutic substances through the blood‐brain barrier.
On the coaxial excitation of the modified Goubau line
Authors: Rao T. C. K. , Hamid M. A. K.
Published: February 2008

The problem of excitation of the modified Goubau line from a coaxial junction is analyzed using the Wiener‐Hopf technique and Fourier transforms in the axial direction. The analytical expressions reduce to those of Ledeboer in the absence of the air gap. The effects of the air gap in reducing the input reflection coefficient and in modifying such other parameters as the launching efficiency and propagation constants for different frequencies are illustrated with numerical examples.
Backscattered pulse shape due to small‐angle multiple scattering in random media
Authors: Ishimaru Akira , Painter Kirk J.
Published: February 2008

Numerical and analytical solutions for the backscattered pulse shape from a slab of random medium are given based on the cumulative forward‐scatter single‐backscatter (CFSB) approximation given by deWolf, assuming small angular‐spread and a narrow‐band incident pulse. The analytic solutions for asymptotic limits for extreme small‐angle scattering are also obtained. The results are applicable to both discrete media with large particles and continuous media with a large scale of turbulence.
The new multimode horn composed of a corrugated guide and a smooth‐walled guide with changing flare angles
Authors: Zhang Ri‐rong , Li Feng‐zhi
Published: February 2008

A new multimode horn composed of a corrugated guide and a smooth‐walled guide with changing flare angles has been achieved. It not only has good electrical performance for both bands (at 4 and 6 GHz) used in satellite communications, but it also has advantages in production and application to engineering because of the small dimension of its length and its very short corrugated section.
A coherent integrator‐decoder preprocessor for the SOUSY‐VHF‐Radar
Authors: Woodman R. F. , Kugel R. P. , Röttger J.
Published: February 2008

The 53.5‐MHz radar of the Max‐Planck‐Institut für Aeronomie (SOUSY‐VHF‐Radar) was specifically designed for the study of the dynamics of the troposphere, stratosphere, and mesosphere including turbulence and other small‐scale phenomena. Transmitter and receivers were designed for a pulse width and altitude resolution of the order of 75–150 m. Such high resolution corresponds to sampling rates of the order of 2 million complex samples per second. Maximum sensitivity calls for the use of coded pulse schemes (pulse compression). The digital decoding and processing requirements of such a high information rate are beyond the capabilities of a general purpose digital computer and demanded a special purpose preprocessor. A programable preprocessor was designed and built, and it is the subject of this paper. It can decode an arbitrary sequence and perform coherent integrations for as many as 1024 altitudes. The coherent integration reduces the data rate into the computer to reasonable values. Also, by performing the coherent integration before decoding (they are linear operations and can be permuted), the necessary decoding operations in the preprocessor are reduced by 2 orders of magnitude. The master controller for the device is programed by a 1024 4‐bit instruction PROM. There are 16 different instructions allowing the necessary flexibility for different code and sampling schemes. The transmitter and analog‐to‐digital converter are also controlled by the same device. Stratospheric and mesospheric echoes obtained with the help of this device are presented for illustration. The detection of layers as thin as 150 m or less at both stratospheric and mesospheric heights justified the efforts to achieve the maximum resolution possible.
FM‐CW radar sensing of the lower atmosphere
Authors: Noonkester V. R. , Richter J. H.
Published: February 2008

FM‐CW radars have revealed many unique marine boundary layer echoes in great detail and permit new interpretations when they are operated simultaneously with other remote sensors. Three different subject areas and associated observations are presented. First, an FM‐CW radar can provide information on tropospheric radio propagation conditions through a refractive index profile updating procedure. Mesoscale variations in radio propagation conditions can be obtained when separated FM‐CW radars are operated simultaneously. Second, highly distinct radar echoes, created by wing tip vortices, have been observed at a commercial jet airport. Third, simultaneous observations with two FM‐CW radars can reveal important submesoscale features.
On the accuracy and interpretation of Dynasonde virtual height measurements
Authors: Wright J. W. , Paul A. K. , Pitteway M. L. V.
Published: February 2008

Accurate group height estimates can be performed using two independent methods in the Dynasonde. The conventional time of arrival (TOA) of the echo envelope is measured directly in 0.2‐km units, while echo phase values, measured to 4° over small (8 kHz) frequency intervals, permit application of the stationary phase principle. Both methods receive corrections in real time for echo amplitude variations. Comparisons of TOA and stationary‐phase measurements by several Dynasonde display formats suggest that dispersive effects can cause considerable group height errors by the TOA method, especially near penetration frequencies. This is confirmed by a computer simulation which yields the pulse envelope and gives information concerning the effect of dispersion on the echo phase.
Radio scintillations during occultations by turbulent planetary atmospheres
Authors: Woo Richard , Ishimaru Akira , Yang Fang‐Chou
Published: February 2008

The radio occultation experiment which uses the radio link between the earth and spacecraft passing behind planets has proven to be an important method for remote sensing turbulence in planetary atmospheres. In this paper we examine the effects of defocusing and anisotropic irregularities on the turbulence‐induced fluctuations of the radio occultation signal. We employ Rytov's method along with geometrical optics to study the frequency spectra and coherences of the log amplitude and phase fluctuations of spherical waves operating at one as well as two frequencies. Comparison with the Mariner 5 2.3‐GHz measurements shows good agreement with the theoretical results.
Measurement of the radiated fields of a buried antenna at VHF
Authors: Vaziri Faramaz , Huang S. C. F. , Long Stuart A. , Shen Liang C.
Published: February 2008

The electric field near the surface of the earth was measured in the vicinity of an eccentrically insulated, traveling wave antenna buried in the earth. All three mutually orthogonal components were measured as a function of both azimuthal angle and of radial range.
A D region mid‐ and high‐latitude approximation to the Sen‐Wyller refractive index equations
Authors: Flood W. A.
Published: February 2008

Approximate expressions for high‐frequency D region refractive indices at mid‐latitudes are developed from the exact Sen‐Wyller formula. The proposed approximations, suitable for use with partial reflection and wave interaction experiments, are significantly better than the use of the strictly longitudinal Sen‐Wyller approximations at mid‐latitude. It is suggested that this approximation be incorporated into D region partial reflection and wave interaction experiments.
Comparison of multifrequency equatorial scintillation: American and Pacific sectors
Authors: Livingston Robert C.
Published: February 2008

In this paper we examine the severity of radio wave amplitude scintillation measured at two stations near the equator but far separated in longitude: Kwajalein, Marshall Islands (167°E), and Ancon, Peru (−77°E). The data used are long‐term observations of the Defense Nuclear Agency (DNA) Wideband satellite signal intensity at VHF, UHF, and L band frequencies. The seasonal behavior of the scintillation at the two stations is similar; each shows a broad 8‐ to 9‐month disturbed season centered about local summer. There is short‐term variability in the scintillation occurrence statistics but no clear equinoctial maxima. Little difference is observed in the occurrence or severity of L band scintillation at the two stations, although a systematic difference in the frequency dependence of the scintillation produces significantly stronger VHF and UHF scintillation at Ancon. The VHF and UHF latitudinal distributions of scintillation are asymmetric about the geomagnetic equator at both stations.
Resonance cones in non‐Maxwellian plasmas
Authors: Singh Nagendra
Published: February 2008

Properties of resonance cones in non‐Maxwellian plasmas are examined and compared with those in Maxwellian plasmas. The dispersion relations and the potential of a point charge in a current‐carrying non‐Maxwellian plasma with a beamlike or a long flat tail of the electron distribution functions are investigated with the approximation of a large magnetostatic field. In the case of a beam, when the beam velocity is well above the thermal velocities of the beam and bulk electrons, the Cerenkov instability occurs. In this case the wave number spectrum k∥ > ω/νb becomes unstable, where νb is the beam velocity, ω is the frequency, and k∥ is the wave number parallel to the magnetic field. The Cerenkov instability causes strong radiation near a conical surface called the Cerenkov cone. When νb is not very large, the Cerenkov cone angle is found to be considerably smaller than the resonance cone angle, thus there are two distinct angles corresponding to the Cerenkov and resonance cones, where the radiation peaks. The Cerenkov cone peak grows with increasing distance from the source, while the resonance cone peak decays. For the situations when the resonance cone peak is not affected by the Cerenkov instability, we have compared the angular shifts of the resonance cone peaks caused by the same current in Maxwellian and non‐Maxwellian plasmas. This comparison throws light on the resonance cone technique for measuring magnetic field‐aligned currents in plasmas. It is found that a long flat tail to the bulk electron distribution function gives a characteristic split to the resonance cone peak in the downstream of the electron flow, an observation of this split can be used as an indication of the existence of the long tail.
On the theory of pulse wave propagation in media of discrete random scatterers
Authors: Ito Shigeo
Published: February 2008

The pulse wave propagation is theoretically investigated in a particular case of a medium of discrete random scatterers. As the basic equation the ordinary space‐time transport equation is used under the forward scattering approximation and is solved by means of the eigenfunction method developed in a recent paper. One of the major results is that an explicit expression of pulse intensity is analytically obtained for the realistic scattering amplitude, valid when the size of scatterers is sufficiently large in comparison with the wavelength. The dependence of pulse width broadening on the particle characteristic is also clarified for the case of large optical distances and is compared with that of previous literature. By the same techniques the temporal angular broadening of pulse wave is evaluated in order to find the conditions of applicability of the present method.
A second‐order renormalization theory for cross‐polarized backscatter from a half space random medium
Authors: Tan H. S. , Fung A. K. , Eom H.
Published: February 2008

A second‐order renormalization theory is formulated to calculate the cross‐polarized backscattering cross sections from an isotropic half space random medium whose permittivity fluctuations are characterized by center‐valued Gaussian statistics. The results show that the second‐order theory predicts a significant level of depolarized backscatter, in contrast to the first‐order theory, which has been shown to contain no depolarized backscatter except from anisotropy effects in the medium.
Comparison of two leading uniform theories of edge diffraction with the exact uniform asymptotic solution
Authors: Boersma J. , Rahmat‐Samii Y.
Published: February 2008

The diffraction of an arbitrary cylindrical wave by a half‐plane has been treated by Rahmat‐Samii and Mittra who used a spectral domain approach. In this paper, their exact solution for the total field is expressed in terms of a new integral representation. For large wave number k, two rigorous procedures are described for the exact uniform asymptotic expansion of the total field solution. The uniform expansions obtained are valid in the entire space, including transition regions around the shadow boundaries. The final results are compared with the formulations of two leading uniform theories of edge diffraction, namely, the uniform asymptotic theory and the uniform theory of diffraction. Some unique observations and conclusions are made in relating the two theories.
A study of the joint statistics of rain depolarization and attenuation applied to the prediction of radio link performance
Authors: Kanellopoulos J. D. , Clarke R. H.
Published: February 2008

A theoretical formula is derived for the joint statistics of cross‐polarization discrimination (XPD) and rain attenuation for a microwave link. This formula is then applied to the prediction of the distribution of XPD conditional on the copolar rain attenuation and also to the prediction of the distribution of XPD during a rain fade. Application is also made to the estimation of outage time of a dual‐polarization communication system. Theoretical results are compared with experimental data from the eastern USA and southern England, and the agreement has been found to be quite good.
A simple model of the effects of the mid‐latitude total ion trough in the bottomside F layer on HF radiowave propagation
Authors: Lockwood Michael
Published: February 2008

Observations of the amplitudes and Doppler shifts of received HF radio waves are compared with model predictions made using a two‐dimensional ray‐tracing program. The signals are propagated over a sub‐auroral path, which is shown to lie along the latitudes of the mid‐latitude trough at times of low geomagnetic activity. Generalizing the predictions to include a simple model of the trough in the density and height of the F2 peak enables the explanation of the anomalous observed diurnal variations. The behavior of received amplitude, Doppler shift, and signal‐to‐noise ratio as a function of the Kp index value, the time of day, and the season (in 17 months of continuous recording) is found to agree closely with that predicted using the statistical position of the trough as deduced from 8 years of Alouette satellite soundings. The variation in the times of the observation of large signal amplitudes with the Kp value and the complete absence of such amplitudes when it exceeds 2.75 are two features that implicate the trough in these effects.
On the multiple scattering of VHF/UHF waves in the equatorial ionosphere
Authors: Vats Hari Om
Published: February 2008

Using amplitude data of radio beacons at 40, 140, and 360 MHz from ATS 6 (phase II), an attempt has been made to study scattering of these waves in the equatorial ionosphere. A comparison of observed scintillation index S4 with the theoretical results of the multiple scattering approach and variation of autocorrelation time with the frequency indicates that this theory explains the results to a large extent. A comparison of power spectra of amplitude records with the ionograms of a nearby equatorial station has led to the following conclusions: The change from a weak scattering regime to a strong scattering regime is gradual and occurs because of the gradual decrease in the scale size of the irregularities (i.e., broadening of the spectra) and the gradual increase in the thickness of the irregular region.
Clear weather meteorological effects on propagation at frequencies above 1 GHz
Authors: Gossard E. E.
Published: February 2008

This paper reviews the various effects the clear atmosphere may have on the propagation of radio waves above 1 GHz. The role of the transfer processes at the lower boundary of the atmosphere in modifying the refractive index structure of air masses is reviewed, and some results of modification of refractive index and its structure constant by the lower boundary are shown. The formation of various classes of elevated layers is discussed and examples are shown of subsidence layer formation. The formation of refractive structures capping the convective boundary layer is discussed and examples of monsoonal refractive layers are shown. Examples of refractive index gradients and structure constant distributions in the neighborhood of frontal interfaces are also shown and discussed.
A review of transhorizon propagation phenomena
Authors: Crane Robert K.
Published: February 2008

Interference problems underlie the current interest in transhorizon propagation. In particular, statistics of the rare, high‐level fields are of interest. This paper reviews the propagation mechanisms which produce the high‐level fields and summarizes recent work in the modeling of the transhorizon propagation.
Field matching and singular integral equations
Authors: Lüneburg E.
Published: February 2008

A new approach to the solution of a class of diffraction problems for closed and open periodic structures is illustrated by means of the scattering of an incident modal field at the junction of a parallel‐plate waveguide with electric and magnetic walls. The formulation is in terms of field matching. The resulting singular integral equation is solved in closed form by reduction to a Hilbert problem. A comparison with the results of the residue‐calculus method of the mode‐matching technique is included.
Prediction and performance of radome‐covered reflector antennas
Authors: Clarricoats P. J. B. , Parini C. G. , Rizk M. S. A. S.
Published: February 2008

The return loss (reflection coefficient) of a paraboloidal reflector antenna covered by a paraboloidal radome is predicted using a physical‐optics method based on the power‐coupling theorem. An asymptotic form of the expression is found to be a good approximation. The performance of the antenna has been measured and results are in good agreement with those predicted theoretically. A method for reducing the return loss is investigated using a hemispherical iris‐loaded sandwich section at the center of the radome. An improvement in return loss of approximately 5 dB is observed over a useful frequency bandwidth. Contributions of the radome to the radiation pattern of the antenna have been identified and those near to boresight have been predicted. Computed values in that region agree well with measurements.
Wiener‐Hopf solution for the radiation from a cylindrical truncated waveguide with anisotropic boundary conditions on the walls
Authors: Daniele V. G. , Montrosset I. , Zich R. S.
Published: February 2008

The Wiener‐Hopf approach has been extended to the problem of the radiation by a cylindrical truncated waveguide with walls characterized by anisotropic boundary conditions on both the inner and the outer surface. When balanced hybrid mode conditions are assumed on both surfaces, two uncoupled scalar Wiener‐Hopf equations are determined. The factorization of the kernel can be accomplished through a numerical integration.
Scattering of surface waves on transverse discontinuities in planar dielectric waveguides
Authors: Gelin P. , Toutain S. , Citerne J.
Published: February 2008

The reflection, the transmission, and the scattering properties of transverse electric surface waves incident on single and multiple discontinuities in a dielectric slab waveguide are analyzed. Boundary conditions acting together with the orthogonality provide singular coupled integral equations on the discrete and continuous wave amplitudes at the discontinuities. This system of singular integral equations is solved by iteration via the conventional Neumann series which are found rapidly converging. Illustrative examples such as the step, the abruptly ended, and the air‐gap junctions are treated.
Complete orthogonal functions for strip conductor in stratified dielectrics
Authors: Liu Bing‐Hope
Published: February 2008

A new method for systematically constructing basis functions for two‐dimensional field problems containing a strip conductor buried in stratified dielectrics is proposed. By applying a simplifying averaging process to the associated static problem, the structure of the specific kernel or Green's function for the problem can be determined approximately. An integral form of continuity equation is derived; general sets of quasi‐eigenfunctions are established, which are orthogonal and complete in Hubert spaces L2(Ω, w). By substituting the specific information into the latter, the required quasi‐eigenfunctions for the problem can be obtained. Hence, with both the edge condition and the continuity equation being satisfied simultaneously and with the inhomogeneity of dielectric constants being taken into account, these resultant functions form a particularly suitable expansion basis for the series solution to such physical quantities as scalar potential, induced surface charge, and surface current.
New image representation for dipoles near a dissipative earth 2. Discrete plus continuous images
Authors: Mahmoud Samir F. , Metwally Ahmed D.
Published: February 2008

A modified image theory for vertical magnetic and electric dipoles above a dissipative earth is presented. Namely, the Fresnel reflection coefficient for horizontally polarized waves is approximated by an exponential term plus a new term which extends the validity of the approximation to high values of the horizontal wave number. While the exponential term represents a single image inside the earth, the new added term represents a set of continuous distribution of images. A similar approximation is applied to the Fresnel reflection coefficient of the vertically polarized waves. These image representations are applied for the determination of input impedances of vertical magnetic and electric dipoles and horizontal large loops at a very low height above the earth. Excellent agreement with previous exact results is reported in all cases.
Electromagnetic wave scattering by spheroidal objects using a method of spin‐weighted harmonics
Authors: Futterman John A. H. , Matzner Richard A.
Published: February 2008

We describe a technique for calculating wave propagation adapted from the study of black hole perturbations in general relativity, and illustrate its use by treating the scattering of plane electromagnetic radiation by perfectly conducting oblate spheroids. The technique employs expansions in terms of orthogonal functions called spin‐weighted spheroidal harmonics. The advantages of the technique are that it suppresses the vectorial nature of the problem and allows for simple application of boundary conditions. A specialization to the spherical case is made in order to compare explicit analytical expressions to well‐known results.
Joint statistics analysis between rain depolarization and attenuation
Authors: Kanellopoulos J. D. , Kontonasios A. B.
Published: February 2008

A direct formulation of joint statistics between rain attenuation and cross‐polarization discrimination (XPD) is proposed. The results of this model agree well with existing experimental data concerning the performance of radio links, as well as with previous two‐dimensional normal approaches.
On junction of two semi‐infinite dielectric guides
Authors: Aoki Kazuo , Miyazaki Tetsuro , Uchida Kazunori , Shimada Yoshitaka
Published: February 2008

Reflection and excitation problems of circularly symmetric surface waves occurring at an abrupt discontinuity in a homogeneous core‐type optical fiber are analyzed using the Fourier transform and Wiener‐Hopf techniques. The frequency characteristics of reflection and transmission coefficients are revealed with numerical examples.
Analytical bending loss formula of optical fibers with field deformation
Authors: Sakai Jun‐ichi , Kimura Tatsuya
Published: February 2008

Bending losses in a radially inhomogeneous profile fiber were studied, taking into account bend‐induced field deformation to the first‐order perturbation. Analytical bending loss formulas are given for arbitrary mode numbers in step‐index fibers. Polarization degeneracy in bending loss still exists even when field deformation effects are taken into account. The bending loss in a step‐index single‐mode fiber increases by 36% at υ = 2.4 and ℜ = RΔ/a = 10 as compared with that without field deformation.
Zero total dispersion in single‐mode optical fibers over an extended spectral range
Authors: Okamoto K. , Miya T.
Published: February 2008

The waveguide and material dispersion are investigated for various silica‐based single‐mode optical fibers with arbitrary refractive‐index profiles. It is shown that in the case of the doubly clad optical fiber with an index difference between the core and the outer cladding Δ1 = 1.0% and that between the inner and the outer cladding Δ2 = −1.0%, where the diameter of the core 2a = 7.2 μm and the thickness of the inner cladding t = 1.1 μm, the total dispersion is reduced to within ±1 ps km−1 nm−1 over a wide spectral range of λ = 1.35–1.67 μm.
Numerical analysis of the discontinuities in slab dielectric waveguides
Authors: Hosono Toshio , Hinata Takashi , Inoue Akiya
Published: February 2008

We propose an approximate method, of general applicability, for analyzing the discontinuities in slab dielectric waveguides. The method is based on replacing the unbounded configuration by a corresponding periodic multilayer structure. Hence the entire spectrum becomes discrete, and this makes the problem easier. The characteristic equation for the modal solution in a periodical multilayer dielectric waveguide is expressed in a matrix form which can be readily solved with a computer. In order to solve the discontinuity problems of slab waveguides, we expressed the reflected and transmitted fields by truncated modal expansions. The unknown amplitudes of the reflected and transmitted modes are determined by the boundary conditions. Numerical results are graphically shown including the cases which have been difficult to analyze by other methods. The accuracy of our results is checked by evaluating the relative errors and comparing with other available results.
Intensity profiles of outgoing beams from tapered grating couplers
Authors: Miyanaga Shigeki , Asakura Toshimitsu
Published: February 2008

The intensity distribution of an outgoing beam from a linearly tapered grating coupler is studied on the basis of the first‐order perturbation theory by dividing the grating region into short subsections. The resultant intensity distribution of the outgoing beam is compared with that calculated by means of the step approximation in which the linearly tapered grating is assumed to consist of a sequence of uniform gratings with amplitudes varying stepwise from one grating to the next. This comparison verifies the validity of the step approximation for investigating the profile of the outgoing beam from the tapered grating coupler. With this verification for the step approximation, the beam profiles from tapered grating of various types are actually investigated by means of the step approximation. It is found that the beam profile of an outgoing beam can be further made to approach a Gaussian shape of the laser beam by using a tapered grating with a Gaussian shape instead of a linearly tapered grating.