Showing papers on "Radio wave published in 1973"

Attenuation and phase rotation of radio waves due to rain: Calculations at 19.3 and 34.8 GHz

Abstract: Computations are made of the forward- and back-scattering intensities of oblate spheroidal raindrops at 19.3 and 34.8 GHz, assuming plane waves at normal incidence to the drop axis. Two kinds of polarization are considered in the incident field: one is parallel to drop axis; the other is perpendicular. Numerical values of these basic scattering intensities are listed in tables. Forward-scattering intensities are then used for determining the effective propagation constants of rain-filled space. From these propagation constants, attenuations and phase rotations for parallel and perpendicular polarizations are computed for several rain rates. One significant conclusion is that the difference between phase rotations in the two polarizations at 19.3 GHz becomes very large as the rain rate increases, whereas that at 34.8 GHz is bounded in a very small range throughout all possible rain rates.

Radio Detection of Interstellar CH

Abstract: As recently as 1968 the only molecules known to exist in interstellar space were CH, CH+ and CN, identified by means of their absorption spectra superimposed on the optical spectra of bright stars, and OH which in its ground state emits at a radio wavelength of 18 cm. Since then there has been a remarkable series of discoveries of about twenty additional molecules emitting in the radio spectrum, some of them quite complex (CH3OH for example). But of the originally discovered ‘optical’ radicals, only CN, emitting at about 2.6 mm, has been detected at radio frequencies—in the Orion Nebula, in the HII region W51, and in the infrared object IRC+10216. The other radical, CH, has not been found, mainly because the radio frequencies of its ground state lambda doublet have not been found in the laboratory, and it has not been possible to compute them theoretically with sufficient accuracy. The first estimate of the (main line) frequency seems to have been made by Shklovsky1: 3,180±10 MHz.

Interstellar Radio Communication and the Frequency Selection Problem

Abstract: THE largest microwave radio telescope on Earth, at the Arecibo Observatory of the National Astronomy and Ionosphere Center, will soon have the capability of communicating with an identical radio telescope, if such exists, anywhere in the Galaxy. But such communication assumes some previous agreement between the transmitting and receiving civilizations, or mutual discovery of the chosen radio frequency, bandpass, information rate and each other's location.

Instrument panel radio antenna

Abstract: In an automotive vehicle including an instrument panel assembly located beneath a windshield opening enclosed by a conductive body structure which forms a radio wave shield, a conductor is supported by a nonconductive top portion of the instrument panel assembly for inductively collecting radio waves passing through the windshield opening from outside of the vehicle thereby to provide a broadband antenna for an AM/FM radio receiver mounted within the instrument panel assembly.

Radio interferometry depth sounding: part ii—experimental results

Abstract: In such highly resistive geologic environments as ice sheets, salt layers, and the moon’s surface, radio waves penetrate with little attenuation. The field strengths about a transmitting antenna placed on the surface of such an environment exhibit interference maxima and minima which are indicative of the in‐situ electrical properties and the presence of subsurface layering. Experimental results from an analog scale model and from field tests on two glaciers are interpreted on the basis of the theoretical results of Part I. If the upper layer is thick, the pattern is very simple and the dielectric constant of the layer can be easily determined. An upper bound on the loss tangent can be estimated. For thin layers, the depth can be determined if the loss tangent is less than about 0.10, and a crude estimate of scattering can be made.

Instrument panel radio antenna

Abstract: An instrument panel assembly located beneath the windshield opening of an automobile, including a metal conductor in the form of a metal coating sprayed onto a non-conductive top portion of a rigid insert within the instrument panel assembly for collecting radio waves directly through the windshield opening from outside the vehicle to thereby provide an antenna for a radio receiver

Ray‐tracing simulation of ionization trough effects upon radio waves

Abstract: The propagation of high frequency electromagnetic waves through an ionosphere perturbed by a gaussian electron density trough is investigated using a three-dimensional ray-tracing computer program. Ray trajectories are presented for a normalized model ionosphere with troughs of varying width, depth, and distance from the transmitter. Focussing and defocussing effects are demonstrated to occur under special circumstances. Particular emphasis is placed upon simulation of records from fixed- and swept-frequency sounding equipment. In particular, a moving trough is found to have unique Doppler signature which may be useful for ground-based observational work.

Remote sensing of the turbulence characteristics of a planetary atmosphere by radio occultation of a space probe.

Abstract: The purpose of this paper is to analyze the effects of small-scale turbulence on radio waves propagating through a planetary atmosphere. The analysis provides a technique for inferring the turbulence characteristics of a planetary atmosphere from the radio signals received from a spacecraft as it is occulted by the planet. The planetary turbulence is assumed to be localized and smoothly varying, with the structure constant varying exponentially with altitude. Rytov's method is used to derive the variance of log-amplitude and phase fluctuations of a wave propagating through the atmosphere.

Total Electron Content Studies of the Ionosphere

Abstract: : Radio waves that pass through the earth's ionosphere travel more slowly than their free space velocity due to the group path delay of the ionosphere. This group path delay, directly proportional to the total electron content of the ionosphere, can be an important source of error to VHF, UHF and L-band satellite detection radars and satellite navigation systems. In this report, the current state of knowledge of ionospheric total electron content is outlined, with special emphasis placed on the North Atlantic region of the world due to NATO special requirements of this region. A numerical model of total electron content, valid over the European continent under certain conditions, is presented for systems engineering use for an average background total electron content correction. Typical values of total electron content are also given at various locations in the high, middle, and equatorial latitudes. If the results presented here seem incomplete, it is only because the state of knowledge of the total electron content parameter is still incomplete. With more observational data being taken at many locations, an over-all satisfactory picture of the world-wide behavior of this important parameter is beginning to emerge.

The detection of clear air turbulence by radar

Abstract: Considers the relationship between clear air turbulence (CAT) and the associated scattering of radio waves, and shows that radar detection is possible using extremely sensitive microwave systems. Successful measurements with such radars support the view that CAT is due to Kelvin-Helmholtz instability which results from a breakdown of highly sheared airflow. Using current radar technology it would be possible to design a ground-based system capable of detecting virtually all CAT within 100 km which might affect an aircraft, but the expense of such a large installation would be high

Reflection and transmission of radio waves at a dielectric slab with variable permittivity

Abstract: Expressions for the reflection and the transmission power coefficients are derived for the case where a plane wave is obliquely incident on a dielectric slab in which the relative permittivity decreases symmetrically according to a 1/z^{2} law from a given maximum value at the plane of symmetry and tends towards unity at the two faces of the slab. The effect of the curvature and other parameters governing the inverse square profile on the transparency property of the material at radar frequencies has been studied within a large d/\lambda range where d is the half-slab thickness and \lambda the wavelength of the incident wave.

Synthesis radio telescope at westerbork - methods of polarization measurement

Abstract: From the formula for the generalized response of a correlation interferometer to an incident partially polarized radio wave, the forms for the four output channels from each interferometer in the Westerbork telescope are developed. Then, the means of instrument gain, phase, and polarization calibration are detailed and the solutions for the four Stokes parameters obtained. The advantages and disadvantages of the technique are briefly discussed. The Appendix contains a derivation of the basic initial formula. (auth)

Direct Measurement of the Refraction Spectrum of Ethanol at Submillimetre Wavelengths

Abstract: THE complex refractive indices of many of the primary alcohols are known at various frequencies in the radiowave and microwave regions from complex permittivity measurements1–4. At submillimetre wavelengths they are known only at a few discrete frequencies from measurements using restrahlen radiation5 or laser sources6. Measurements as a continuous function of frequency are desirable throughout ; here we describe progress at submillimetre wavelengths.

Physics and Chemistry of the Ionosphere

Abstract: The ionosphere is the part of the upper atmosphere where free electrons exist in sufficient concentrations to affect the propagation of radio waves. This paper introduces the science of the ionosphere and reviews the experimental techniques used in its study (Sections 1–3); the average behaviour of the ionosphere and some of its notable anomalies are described in Section 4. In the lower part of the ionosphere, between heights of about 60 and 250 km, the distribution of electrons is almost entirely governed by the production and recombination processes (Sections 5–7). The movement of ionization by winds, electric fields and diffusion produces some interesting phenomena at heights above 100 km, and mainly governs the electron distribution at heights above 250 km (Sections 8–10). Finally, ionospheric storms and other problems are touched upon in Sections 11–12.

The interpretation of some observations of radio waves scattered from the lower ionosphere

Abstract: Possible shapes and spatial scales of ionospheric irregularities in the lower ionosphere have been determined from analyses of two sets of radio wave back-scattering observations: measurements of the spatial scale of the ground pattern of the wave field back-scattered from altitudes near 95 km and measurements of the amount and angular distribution of power back-scattered from solitary horizontally-moving irregularities at altitudes near 75 km. At 95 km the irregularities are anisotropic, with larger horizontal than vertical dimensions. For an assumed Gaussian distribution of ionization, the inferred axial ratio (horizontal to vertical) is about three. It is tentatively concluded that the irregularities at 75 km are sharply bounded and are some kilometres in horizontal extent.

Guided propagation of radio waves

Abstract: So fa r a s the propagation of electromagnetic waves is concerned, an underground tunnel behaves like a pipe o r hollowed waveguide. Waves propagate in this tunnel with a low attenuation only if their frequency is higher thana so-called cr i t i cal frequency which depends on the shape and mostly on the cross -dimensions of the tunnel and which value is in the neighbourhood of several tenths of MHz.

Rf hazard detector

Abstract: A hand-held tester for determining whether an object that is being irradiated with radio frequency energy is at a dangerously high induced radio frequency voltage level. The tester has a high impedance probe, and when this probe is brought in contact with such an object, the radio frequency flow, which takes place through it and the tester, develops a signal which is compared to a reference voltage. When this voltage is exceeded by a predetermined amount, a warning light source is operated.

Some results of investigations of nonlinear phenomena in the F-layer of the ionosphere

Abstract: Translated from Zh. Eksp. Teor. Fiz., Pis'ma Red.; 18: No. 10, Results of experiments on the nonlinear action of powerful radio waves on the F- layer of the ionosphere are reported and discussed. (auth)

Phase Integrals and Coupling for Radio Waves in the Ionosphere

Abstract: The phase integral method, for radio waves vertically incident on a horizontally stratified ionosphere, involves a study of the behaviour of the refractive indices in the complex height plane. The two characteristic waves, ordinary and extraordinary, either both upgoing or both downgoing, are said to be critically coupled at certain points in the complex height plane, called coupling points, where the two refractive indices are equal. There are two principal coupling points, and previous authors have considered only the one that lies on the positive imaginary side of the real height axis when collisions are neglected. It is shown here that a full description of the coupling processes also requires the use of the other principal coupling point, which usually lies on the negative imaginary side of the real height axis. Phase integral formulae are derived which describe the changes in polarization, caused by coupling, for the two main ionospheric reflexions, for frequencies less than the gyrofrequency. These formulae are compared with results obtained by a full wave analysis and show good agreement.

Venus: radar determination of gravity potential.

Abstract: We describe a method for the determination of the gravity potential of Venus from multiple-frequency radar measurements. The method is based on the strong frequency dependence of the absorption of radio waves in Venus' atmosphere. Comparison of the differing radar reflection intensities at several frequencies yields the height of the surface relative to a reference pressure contour; combination with measurements of round-trip echo delays allows the pressure, and hence the gravity potential contour, to be mapped relative to the mean planet radius. Since calibration data from other frequencies are unavailable, the absorption-sensitive Haystack Observatory data have been analyzed under the assumption of uniform surface reflectivity to yield a gravity equipotential contour for the equatorial region and a tentative upper bound of .0006 on the fractional difference of Venus' principal equatorial moments of inertia.

Modern topics in microwave propagation and air-sea interaction : proceedings of the NATO Advanced Study Institute held at Sorrento, Italy, June 5-14, 1973

Abstract: Opening Session.- Introductory speech.- Welcome address.- Introductory lecture/Some aspects of modern radiometeorology.- I Group / Air-Sea Interaction and Ducting: Meteorological and Radiometeorological Aspects.- The physical processes of air-sea interactions: a review.- Present state of knowledge on evaporation from the sea and numerical analysis/forecasting of water vapor pressure in the surface layers of the air.- Preliminary observation of the evaporation duct in the I.M.S.T. air-sea wind tunnel.- The dynamics of water vapor flux in the marine boundary layer.- The structure of the atmospheric boundary layer at sea.- About the need of a standard technique to compute atmospheric refractive index from radiosonde data.- Determination of the wind stratification by scatter propagation methods on 7 and 16 GHz.- Turbulent transport and refractive index structure immediately above the air-sea interface.- II Group / Air-Sea Interaction and Ducting: Radiopropagation Aspects.- The structure of moisture and temperature profiles in the near-surface layers, their variability and effects on radar propagation as demonstrated with ray tracing techniques.- State and limits of prediction methods of radar wave propagation conditions over sea.- Characteristics and applications of line- of-sight duct propagation.- Propagation theory for the evaporation duct.- Oceanic duct and its effects on microwave propagation in the Mediterranean Sea.- Transmission of millimeter radio waves in over water ducts.- Diffraction of radio waves by terrain obstacles in radio ducts.- Interference lobes pattern connected to a ground based radar duct.- The Occurrence of very high field strengths at beyond the horizon propagation over sea in the frequency range 60-5000 MHZ.- III Group / Atmospheric Influence on Radio Propagation Above 10 GHz: Communication Aspects.- Communications requirements at frequencies above 10 GHz and their correlation with propagation aspects.- Aspects in using frequencies bands above 10 GHz for satellite communication systems.- IV Group / Atmospheric Influence on Radio Propagation Above 10 GHz: E.M. Propagation Phenomena and Results.- Attenuation by rainfall in the sub-millimetre wave region.- Recent studies of visibility and atmospheric attenuation at optical wavelengths.- Some recent lidar experiments on particle scattering in the lower troposphere.- Radiometry, the structure of atmospheric spectrum lines, and related experiments.- Depolarization phenomena on electromagnetic waves through rain.- Analysis of the influence of the various parameters on the attenuation-rain rate relation.- Quantitative analysis of precipitations through radar techniques.- Reports of Working Groups.- Group A: Some general comments on the exchange and stability processes in the surface layer.- Group B: Concerning evaporation and intermittency.

The influence of polarization on millimeter wave propagation through rain

Abstract: The influence of polarization on millimeter wave propagation is investigated from both an experimental and a theoretical viewpoint. First, previous theoretical and experimental work relating to the attenuation and depolarization of millimeter waves by rainfall is discussed. Considerable detail is included in the literature review. Next, a theoretical model is developed to predict the cross polarization level during rainfall from the path average rain rate and the scattered field from a single raindrop. Finally, data from the VPI and SU depolarization experiment are presented as verification of the new model, and a comparison is made with other theories and experiments. Aspects of the new model are: (1) spherical rather than plane waves are assumed, (2) the average drop diameter is used rather than a drop size distribution, and (3) it is simple enough so that the effect which changing one or more parameters has on the crosspolarization level is easily seen.

Ionospheric Observations using an Ultrasonic Image Forming Technique

Abstract: Large arrays of aerials are often used to obtain high angular resolution for observations in radio astronomy, ionospheric physics and for radar applications. The objective is to record the intensity of radio waves arriving from different directions. One approach is to scan a narrow beam produced by the whole array across the sky according to some type of raster pattern. But it has been realized for some time that if the amplitude and phase of the signals at each aerial are available for processing, then it is possible to obtain simultaneously the amplitude arriving from each direction. The processing may be carried out by analogue or digital methods. The digital approach is not always practicable because of the need to digitize a very large number of amplitudes and phases and because a computer of sufficient speed is often not available “on line” at the location of the aerial array. This is particularly important if the observations are required in “real time” and if rapid time variations are present. Here we confine the discussion to analogue methods.

Variable Control

Abstract: Radio emission from Sco XR-1 shown as synchroton radiation of relativistic electrons in low density region surrounding denser core producing X ray