Showing papers on "Radio wave published in 1990"

Quasi-optical stripline devices

Abstract: Quasi-optical stripline devices for forming and controlling a beam of radio waves are described. The devices include a strip transmission line having a pair of mutually parallel flat outer conductors and a flat center conductor with a dielectric between them. The center conductor has a narrow channel region, a wide expansion region and a tapered region smoothly connecting the regions. A beam of radio waves propagates freely in the expansion region and can be controlled in a quasi-optical manner by the pattern of the center conductor. The quasi-optical nature facilitates easy visualization of the devices for easy design and manufacture.

A relaxation method for integral inversion applied to HF radar measurement of the ocean wave directional spectrum

Abstract: The Chahine-Twomey relaxation method for inversion of the atmospheric radiative transfer equation is extended to provide an inverse solution to Barrick's equation describing second order scatter of high frequency (HF) radio waves from the ocean surface. The success of the method is demonstrated here using synthesised radar Doppler spectra obtained by solving the direct problem with wave buoy directional spectrum measurements. Wave buoy measurements are limited in the range of directional characteristics that can be measured. The results presented here suggest that HF radar is capable of providing a more general measurement of the directional spectrum.

Lightning electromagnetic radiation field spectra in the interval from 0.2 to 20 MHz

Abstract: New Fourier transforms of wideband time-domain electric fields (E) produced by lightning (recorded at the Kennedy Space Center during the summers of 1985 and 1987) were recorded in such a way that several different events in each lightning flash could be captured. Average HF spectral amplitudes for first return strokes, stepped-leader steps, and 'characteristic pulses' are given for significantly more events, at closer ranges, and with better spectral resolution than in previous literature reports. The method of recording gives less bias toward the first large event in the flash and thus yields a large sample of a wide variety of lightning processes. As a result, reliable composite spectral amplitudes are obtained for a number of different processes in cloud-to-ground lightning over the frequency interval from 0.2 to 20 MHz.

Doppler spread measurements of indoor radio channel

Abstract: The temporal variations caused by human movement or human-induced motion of the communication equipment, on the otherwise static indoor radio channel, are measured. For the reported narrowband measurements, a maximum Doppler spread of 6.1 Hz and a maximum RMS Doppler bandwidth of 0.87 Hz are observed.

Radio wave propagation through rain forests of India

Abstract: A radio wave attenuation measurement survey program was undertaken for the tropical rain forests of India. Measurements were taken at frequencies from 50 to 800 MHz, for antenna heights from 1.5 to 16.5 m above the ground with both horizontally and vertically polarized emissions, and at various separation distances varying from 40 to 4000 m. There were 96 combinations of system parameters for each selected distance between transmitting and receiving locations. In addition to the copolar measurements, cross-polar measurements were carried out to study cross-polar phenomenon in the presence of vegetation. The results of the studies are discussed, covering scatter of the data, lack of homogeneity of the foliage, variation in foliage proximity of the antenna, scattering of radio waves, effect of antenna beamwidth, effect of changes in wind velocity, frequency and polarization dependence of the basic transmission loss, seasonal variation of the loss, effect of climate and type of vegetation, foliage loss, specific attenuation, and effect of increased antenna height in the forest. An empirical model derived from these measurements is proposed. >

VLF heating of the lower ionosphere

Abstract: A controlled wave-injection experiment with a 28.5 kHz transmitter having a radiated power of 100 kW has revealed evidence of ionospheric heating by the VLF waves. Calculations indicate that the observed effect can be attributed to the absorption of wave energy in the lower ionosphere, which is estimated to result in a 30% enhancement in the collision frequency at 85 km. This process also represents a new means of direct coupling of lightning energy to the lower ionosphere.

High resolution observations of HF‐induced plasma waves in the ionosphere

Abstract: Langmuir oscillations excited by a powerful, high-frequency (HF) radio wave reflecting in the F-region have been studied in detail with the 430 MHz radar at Arecibo Observatory, Puerto Rico. Exceptionally good altitude and temporal resolution made it possible to closely examine transient plasma phenomena and allowed very weak plasma features to be seen in the ionosphere. The observations reveal an unexpected richness of complex plasma structure. Langmuir turbulence detected with the 430 MHz radar often occupies an extended altitude interval, particularly during the “plasma line overshoot” and at late times following HF turn-on. In the late time plasma environment, multiple layers of Langmuir turbulence are often observed. In general, important distinctions can be made between the excitation of Langmuir oscillations in a “cold” background ionosphere and in an ionosphere “preconditioned” by prior HF transmissions. The greatest differences are evident in the altitude and range extent of the backscatter measured immediately after HF turn-on.

Indoor wideband radiowave propagation measurements at 1.3 GHz and 4.0 GHz

Abstract: Measured impulse response estimates of radio channels have been used to determine time delay spread and path loss characteristics inside four buildings using different antenna heights at 1.3 GHz and 4.0 GHz. RMS delay spread values were found to be dependent on building and local topography, but generally independent of frequency and antenna height. Path loss values were found to be nearly independent of frequency.

Transponder for vehicle identification device

Abstract: The invention relates to a transponder for a vehicle identification device in which a radio wave including vehicle information returned from transponders provided in a vehicle is received by an interrogator. The vehicle transponder receives a query radio wave and uses a detection device to generate a previously memorized coded signal train in response to a received wave. The coded signal train varies an amount of bias voltage of the detection device so that a reflection coefficient of the detection device is varied to modulate the reflection wave of the query radio wave and the modulated wave is transmitted back to the interrogator.

Upper limit set for level of lightning activity on Titan

Abstract: Because optically thick cloud and haze layers prevent lightning detection at optical wavelength on Titan, a search was conducted for lightning-radiated signals (spherics) at radio wavelengths using the planetary radioastronomy instrument aboard Voyager 1. Given the maximum ionosphere density of about 3000/cu cm, lightning spherics should be detectable above an observing frequency of 500 kHz. Since no evidence for spherics is found, an upper limit to the total energy per flash in Titan lightning of about 10 to the 6th J, or about 1000 times weaker than that of typical terrestrial lightning, is inferred.

Attenuation and reflection of radio waves by a melting layer of precipitation

Abstract: Attenuation and reflection of a melting layer are calculated using a meteorological model. The model employs a new scheme for the calculation of the dielectric properties of melting ice particles with densities ranging from those of loose snow to hail, and a new scheme for calculating the melting rate is employed. The input parameters are derived from high resolution Doppler radar data and provide a data set for statistical analysis. Statistical relations were derived for attenuation in the melting layer based on measurements made with a surface rain gauge, a radar (with and without a polarisation facility), and a lower frequency satellite link. It was found that the specific attenuation of melting snow surpasses the value of rain because of the larger size and particle number density during melting, the attenuation within the melting layer increasing with its reflection. In stratiform precipitation, the attenuation in the melting layer is found to increase only slightly with frequency. The reflection in the melting layer decreases with the frequency of the radio waves in such a way that a bright band is only observed for frequencies below 20 GHz.

Stimulated scattering of large amplitude waves in the ionosphere: experimental results.

Abstract: A powerful high-frequency radio wave propagating through the ionospheric plasma acts as a pump and excites parametric and other nonlinear processes. These processes can be observed by using diagnostic Thomson scatter radars to probe the pump-enhanced plasma turbulence or by analysing the scattered pump wave directly. Such analyses performed at high and low latitudes (Tromso, Norway and Arecibo, Puerto Rico) have shown that the physics is extremely complicated and that old theory cannot satisfactorily explain all results. These experiments can shed new light on nonlinear plasma physics in general but may also provide means for diagnosing the near-Earth plasma and for testing theories of astrophysical plasma processes.

Method and apparatus for radio location

Abstract: This disclosure relates to multi-element antenna clusters or arrays for the reception and transmission of radio waves for direction-finding, navigation aid and emitter and/or receiver location purposes. In particular, it relates to arrangements of multiple antennas whereby the direction of propagation (arrival or departure) of a wavefront is determined from a combination of the amplitudes of phasor (or total individual antenna output) differences between pairs of antennas, said arrangements being along certain geometrical patterns, such as a circle, an ellipse, a polygon, an open straight line, etc., with at least one longest dimension measuring more than one wavelength of the incident or departing wave. Although described in terms of electromagnetic waves and hence antennas as receiving sensors or radiators, this invention in reality applies to any other form of propagating waveborne energy, such as acoustic, ultrasonic, seismic, etc.

Portable telephone set

Abstract: PURPOSE: To reduce the distortion of radiation pattern of an antenna and the reduction of its gain by fitting an antenna having the 1/4 wavelength of a transmitting/receiving radio wave under an enclosure when using the antenna, and separating the antenna from the head of a user. CONSTITUTION: In the case of speaking while holding an enclosure 1, an antenna 4 having the 1/4 wavelength of the transmitting/receiving radio wave is fitted while being protruded downward, and connected to a feeder line 5 from a transmitter/receiver 3 at an approach point 6 between the antenna 4 and a base plate 2 composed of a metal member. Therefore, the radiation part of the antenna 4 is separated from the head of the user in the case of speaking and as the result, the radiation pattern of the antenna 4 has a main beam slightly directed upward rather than a horizontal direction. Thus, it is possible to reduce the distortion of the radiation pattern of the antenna 4 to be measured in a free space or the reduction of gain caused by the absorption of a human body. COPYRIGHT: (C)1992,JPO&Japio

Observation of the Crab pulsar, PSR 0531 + 21, at 0. 2-6. 0 MeV with the Figaro II experiment

Abstract: Observations of the Crab pulsar (PSR 0531 + 21) in the energy range 0.2-6 MeV have been made with the balloon-borne Figaro II experiment. The gross appearance of the light curve is characterized by the well-known double-peak structure with a phase separation of 0.4. The data confirm that the second pulse is the dominant feature, and the interpulse region is more luminous than in other energy ranges. Above about 0.5 MeV, an extra structure was detected in the light curve, with two features at a phase lag of 0.4 as the main one. Phase-resolved spectroscopy indicates that the first peak spectrum is concave upward, and the second one is concave downward, while the averaged spectrum is well represented by a single power law with slope 2.2. The good timing accuracy of Figaro made it possible to measure a delay between gamma rays and radio waves of 300 + or - 70 microsec, that if produced by dispersion, implies a value of DM fitting very well the radio measurements 2 months before and after the observation. 29 refs.

Source region of the smooth high-frequency nightside Uranus kilometric radiation: A ray-tracing study

Abstract: This paper presents a plasma density model for the Uranus nightside at r less than 4.2 r(u), developed on the basis of radio wave observations of the Planetary Radio Astronomy instrument on board the Voyager 2 spacecraft and on cyclotron maser instability. The results provide an accurate description of the Uranus kilometric radiation (UKR) source region dependent on a minimum of assumptions, and indicate that the UKR source region is more extended in longitude than previosly determined.

Mobile communication equipment

Abstract: PURPOSE: To easily install a new base station and to use an additional frequency by enabling a base station to detect frequencies used in its surrounding area and to assign a frequency which is not used in the surrounding area or another frequency which does not cause interference even when the frequency is used to its own station. CONSTITUTION: The frequency monitoring section 11 of a base station 1-n monitors the frequency of the control channel used in the radio zone of its surrounding area. The controlling section 12 of the station 1-n detects frequencies used in the surrounding area from the output of the section 11 and, when unused frequencies exist in the surrounding area, sets one frequency selected output of the unused frequencies to a synthesizer 13 and instructs a transmitting/ receiving section 14 to transmit a test radio wave after selecting the frequency. In this case, the section 12 checks whether or not the test radio wave causes interference from the output of the section 11. When no interference occurs, the radio wave is used. When no unused radio wave exists or when interference occurs, the same control made after the detection of frequencies used in the surrounding area is repeated. COPYRIGHT: (C)1992,JPO&Japio

Nighttime radio wave scintillation at equatorial stations in Indian and American zones

Abstract: This paper reports studies of VHF radio wave scintillations during the nighttime in the Indian zone and compares the results with the corresponding data from the American sector. The seasonal variation of scintillations in the Indian sector showed maxima during equinoxes, compared to a single maxima during the December solistices in the American sector. Indian stations showed a very large decrease in scintillation activity with decreasing solar activity, compared to a very low dependence of scintillations on solar activity in the American sector. The geomagnetic disturbances tend to reduce the occurrence of scintillations more significantly in the Indian than American sector.

Comparison of a diffraction based radiowave propagation model with measurements

Abstract: A comparison between a theoretical diffraction based radio propagation model and measured path loss data for flat terrain in New Zealand in terms of variation in path length, frequency and environment is described. Results of measured town planning data for the model are also given.

What is happening at the center of our Galaxy

Abstract: Recent discoveries and new technologies have made it possible at last to study the center of our own galaxy in some detail. These developments include improved techniques for collecting analyzing astronomical radio waves and infrared radiation as well as space flights above the earth's atmosphere, which have made possible the detection of energetic X-ray and gamma-ray radiation emanating from the center of the galaxy. All these types of waves--radio, infrared, X-ray and gamma-ray--are similar to visible light in that they are all forms of electromagnetic radiation and differ only in their wavelengths and energy levels. Unlike light, however, they can penetrate interstellar clouds of dust with some ease and hence provide a window into the structure and dynamics of the galactic center. Each wavelength region probes different aspects of the physical properties there; for example, X rays are emitted by very hot gas, whereas much infrared radiation is emitted by interstellar dust grains and cooler gases. Studies at these various wavelengths have produced a wealth of information about and new understanding of the central part of our galaxy. They have also raised a host of new puzzles. This mysterious region contains antimatter, radioactive clouds, veiled sources of intense radiation, swirlingmore » gas and dust and an unseen object with a tremendous gravitational pull--perhaps a massive black hole.« less

Statistical AR models for the frequency selective indoor radio channel

Abstract: A statistical model of the indoor radio channel is proposed that is derived from a second order autoregressive process representation of the channel frequency response. The accuracy of the statistical model is examined by comparing the cumulative distribution functions of the RMS delay spread and the 3dB width of the frequency correlation function computed from the regenerated data with that of the measurements performed in two indoor radio propagation studies in the 0.9–1.1 GHz band.

Interplanetary particle beams

Abstract: The purpose of this paper is to review the observations of particle beams of the kind that are frequently observed in the interplanetary medium, usually but not always accompanying a solar flare. Most frequent are beams of electrons. They are generally associated with radio bursts of type III and only sometimes with flares and X-ray bursts. The properties of these electron beams have been well studied using quasi-linear and nonlinear theory, in situ observations of electrons and of plasma waves, and remote observations of radio waves Thanks to the interaction between theory and observation, the decade of the 1980s has been one of great progress in understanding the main features of these beams and their associated plasma waves and radio bursts. However, uncertainties remain in terms of (1) whether fine scale features, filamentary structures or wave condensations, occur together with the beams, (2) whether quasi-linear or nonlinear wave emission is the dominant process, and (3) if wave condensations are important, what is the mechanism of conversion of some Langmuir wave energy into radio emission.

Portable radio telephoney set and its system

Abstract: PURPOSE: To display information relating to a current location and an object on a map with a portable radio telephoney set by allowing a reception base station receiving a radio wave to specify the transmission position of the portable radio telephone set and sending map information including the transmission position to a caller in a radio wave. CONSTITUTION: When a receiver inquires of this system about a transmission position at a point A by a portable radio telephoney set, a mobile communication controller MSC selects an on-ground reception base station having a strongest reception radio wave among on-ground reception base station groups CS1-CS5, retrieves local map information including the on-ground reception base station CS2 in huge map information of a map information film LR relating to the on-ground reception base station CS2 and position or reception enable area information of the on-ground reception base station CS2 to a portable radio telephoney set of the caller via the on-ground reception base station CS2 together with the local map information in a radio wave. The caller receives a radio wave from the on-ground reception base station CS2 by a portable radio telephoney set PS and the local map and the position or reception enable area of the on-ground reception base station CS2 on a picture display element D. COPYRIGHT: (C)1992,JPO&Japio

A comparison of H-alpha intensity and radio wave scattering on eight low-latitude lines of sight

Abstract: Radio scattering and H-alpha measurements for eight sources in Cygnus are compared. The diameter of the radio scattering disk at 1 GHz is found to be correlated with emission measure as determined from the H-alpha measurements, and that strong radio scattering characterized by a diameter of about 30 milliarcsec is produced in regions with emission measures of about 100/cm exp 6 pc or less. The slope of diameter-emission measure correlation is steeper than would be the case if all lines of sight were characterized by the same turbulent outer scale and modulation index. It is suggested that the lines of sight to unscattered or lightly scattered sources traverse only a diffuse medium which is revealed by H-alpha observations at high latitudes. Heavily scattered sources are viewed through an additional component of interstellar H II which has turbulence with different properties.

Echo power loss with RASS (radio acoustic sounding system) due to defocusing effects by distorted acoustic wave front

Abstract: We have calculated the intensity of RASS (radio acoustic sounding system) echoes scattered by refractive index fluctuations produced by acoustic waves. Because of temperature changes in the atmosphere, the sound speed decreases in the troposphere and the shape of the acoustic wave front becomes elliptical. When the shape of acoustic wave fronts is significantly distorted from a sphere, the backscattered radio wave does not focus on the radar. Consequently, the spot size of the RASS echo becomes large, and the peak intensity of the RASS echoes decreases. We numerically estimated the echo power loss due to defocusing effects for an atmosphere whose sound speed decreased linearly with altitude. The loss was found to be a function of the range, radar beam width, radar wavelength, and degree of distortion of the acoustic wave front. When the temperature gradient is 5° C/km, the echo power loss at a range of 10 km for 50- and 500-MHz radars becomes as large as 0.5 and 16 dB for radar beam width of 2.0°, and 7.0 dB and 19.0 dB for a 5.0° width, respectively.

Can ionospheric refraction and oblique reflection explain the Canadian 50 MHz IGY radio aurora observations

Abstract: Uspensky and Williams (1988) have recently suggested that the aspect sensitivity of the radio aurora is universally near 10 dB/deg. They have further suggested that the Canadian measurement of 1-2 dB/deg at 48 MHz can be understood by correctly accounting for E region ionospheric refraction and oblique reflecton in the case of equatorward directed radio waves. This hypothesis has an attractive simplicity. Moorcroft (1989) has subsequently proposed refraction by tilted layers to explain a number of puzzling features of Canadian Bistatic Aurroral Radar System (BARS) data. The authors haqve therefore made an examination of the ionospheric conditions necessary to enable refraction/reflection to explain the Canadian International Geophysical Year (IGY) observations and have compared them with those expected in the E region ionosphere. It is established that refraction in extended and uniform E region plasma layers is insufficient to explain these observations using the Uspensky and WIlliams hypothesis. On the other hand, it may be possible that oblique reflection in a thin, dense, and localized sporatic E structure is sufficient to support the hypothesis. More information about these strucutres is required before a definitive conclusion can be drawn. The properites necessary for these structures to be consistent with an universal aspectmore » sensitivity of about 10 dB/deg are presented.« less