Showing papers on "Radio wave published in 1995"

The computer for the 21st century

Abstract: Specialized elements of hardware and software, connected by wires, radio waves and infrared, will soon be so ubiquitous that no-one will notice their presence

Electron Density Power Spectrum in the Local Interstellar Medium

Abstract: Interstellar scintillation (ISS), fluctuations in the amplitude and phase of radio waves caused by scattering in the interstellar medium, is important as a diagnostic of interstellar plasma turbulence. ISS is also of interest because it is noise for other radio astronomical observations. The unifying concern is the power spectrum of the interstellar electron density. Here we use ISS observations through the nearby (less than or approximately =1 kpc) (ISM) to estimate the spectrum. From measurements of angular broadening of pulsars and extragalactic sources, decorrelation bandwidth of pulsars, refractive steering of features in pulsar dynamic spectra, dispersion measured fluctuations of pulsars, and refractive scintillation index measurements, we construct a composite structure function that is approximately power law over 2 x 10(exp 6) m less than scale less than 10(exp 13) m. The data are consistent with the structure function having a logarithmic slope versus baseline less than 2; thus there is a meaningful connection between scales in the radiowave fluctuation field and the scales in the electron density field causing the scattering. The data give an upper limit to the inner scale, l(sub o) less than or approximately 10(exp 8) m and are consistent with much smaller values. We construct a composite electron density spectrum that is approximately power law over at least the approximately = 5 decade wavenumber range 10(exp -13)/m less than wavenumber less than 10(exp -8)/m and that may extend to higher wavenumbers. The average spectral index of electron density over this wavenumber range is approximately = 3.7, very close to the value expected for a Kolmogorov process. The outer scale size, L(sub o), must be greater than or approximately = 10(exp 13) m (determined from dispersion measure fluctuations). When the ISS data are combined with measurements of differential Faraday rotation angle, and gradients in the average electron density, constraints can be put on the spectrum at much smaller wave numbers. The composite spectrum is consistent with a Kolmogorov-like power law over a huge range (10 or more decades) of spatial wavenumber with an infrared outer scale L(sub o) greater than or approximately 10(exp 18)m. This power-law subrange-expressed as ratio of outer to inner scales-is comparable to or larger than that of other naturally occurring turbulent fluids, such as the oceans or the solar wind. We outline some of the theories for generating and maintaining such a spectrum over this huge wavenumber range.

Waves: The Radio and Plasma Wave Investigation on the Wind Spacecraft

Abstract: The WAVES investigation on the WIND spacecraft will provide comprehensive measurements of the radio and plasma wave phenomena which occur in Geospace. Analyses of these measurements, in coordination with the other onboard plasma, energetic particles, and field measurements will help us understand the kinetic processes that are important in the solar wind and in key boundary regions of the Geospace. These processes are then to be interpreted in conjunction with results from the other ISTP spacecraft in order to discern the measurements and parameters for mass, momentum, and energy flow throughout geospace. This investigation will also contribute to observations of radio waves emitted in regions where the solar wind is accelerated. The WAVES investigation comprises several innovations in this kind of instrumentation: among which the first use, to our knowledge, of neural networks in real-time on board a scientific spacecraft to analyze data and command observation modes, and the first use of a wavelet transform-like analysis in real time to perform a spectral analysis of a broad band signal.

Radiowave Propagation and Antennas for Personal Communications

Abstract: Introduction. Fixed-Site Antennas. The Radio Communication Channel. The Radio Frequency Spectrum. Communications Using Earth-Orbiting Satellites. Radiowave Propagation - Radio Test Sites. Radiowave Propagation - The Urban and Suburban Paths. Waves in Multipath Propagation. Receiver Sensitivity and Transmitted Fields. Simulated Human Body Devices. Loop, Dipole and Patch Antennas. A Radio Communication System. Appendices.

Transmission method for intra-pipe radio wave

Abstract: PURPOSE: To provide a method which can optionally select a reaching range of the radio wave and therefore can transmit the radio wave to only the pipe that is checked by changing the frequency to be sent into the pipe in response to the cut-off frequency of the pipe. CONSTITUTION: A robot 3 is provided with a self-traveling device having wheels and a device which photographs the inside of a gas pipe 5. The robot 3 is controlled by the radio wave sent from a ground check device 1 and sends back the photographed images onto the ground to display them on a monitor 6. The cut-off frequency of the transmitted radio wave is regulated by a specific expression and decided by the inner diameter of the pipe 5. The decided frequency is selected and such radio waves are applied to the ground control of the robot 3 and also to the transmission of images from the robot 3. Thus radio wave can be smoothly transmitted in the pipe 5 and the smooth communication is secured with the robot 3. On the other hand, the radio wave is not transmitted in a slender pipe 4 since the frequency of the radio wave transmitted in the pipe 5 is less than the cut-off frequency of the pipe 4. Therefore, the radio wave is never sent into a home, etc., from an end part of the pipe 4. COPYRIGHT: (C)1996,JPO

Electronic clinical thermometer

Abstract: PROBLEM TO BE SOLVED: To always secure a measurement posture without disturbing a subject or a measurer SOLUTION: An electronic clinical thermometer includes a measuring part 1 for measuring a temperature of a region to be measured for obtaining measured temperature data and a body 2 for displaying a temperature based on the measured temperature data Antennas 12, 23 are provided respectively on the measuring part 1 and the body 2 for performing wireless data communication between them, wherein start for measurement is instructed to the measuring part 1 on the body 2 by operating a key input part 25 (25a to 25d), while temperature measurement is performed in the measuring part 1 according to the instruction for starting measurement from the body 2 by radio waves, and the resulting measured temperature data is reported to the body 2 by radio waves

Radio data communication apparatus having a relay function and radio data communication method and system using the same

Abstract: In a radio data communication network where a plurality of radio data communication apparatuses mutually communicate information through frames carried by radio waves, a communication method using radio data communication apparatuses having a relay function is provided. When two radio data communication apparatuses cannot directly communicate with each other due to the limit of the radio wave range, another radio data communication apparatus serves as a relay station to relay frames between the two apparatuses, thus extending a communicable range.

An imaging riometer for ionospheric studies

Abstract: An imaging riometer for ionospheric studies (IRIS) is described. This phased-array system has been continuously operating in northern Finland since late 1994, and permits spatial observation of ionospheric absorption of radio waves over the surrounding area. The paper gives an introduction to the principles of riometry and ionospheric absorption; it describes the physical implementation of the system and presents some initial results. Consideration is also given to the effect of the absorption on radio links operating in the auroral regions, which can be severe.

Stationary striations developed in the ionospheric modification.

Abstract: A nonlinear theory determining the conditions of existence and the structure of the stationary striations generated in the ionospheric modifications by powerful radio waves is proposed The structure of the density depletions and its characteristic length, width, and depth are shown to be in agreement with observations A strong enhancement of the electron temperature inside the striations is predicted

Data carrier system

Abstract: A data carrier system allows data to be transmitted and received The data is transmitted using weak radio waves of suitable frequencies, such as frequencies in a high frequency band (HF) or a very high frequency band (VHF) The transmitters and receivers need not physically contact each other, be located in any particular position, or be oriented in any particular direction The data carrier system does not suffer deficiencies in electric power supply, and therefore there exists no need to exchange batteries Individual transmitters and receivers are positively discriminated one from another The receivers are in the form of a plurality of tags The transmitters are in the form of a plurality of reader-writers Both are controlled by microcomputers, and each tag is equipped with a secondary battery as the power source

Line-of-sight indoor radio communication using circular polarized waves

Abstract: This paper presents an anti-multipath fading scheme employing a circular polarized wave for line-of-sight (LOS) indoor radio communications. The circular polarized wave transmission/reception significantly mitigates the multipath fading caused by reflections from walls, ceiling, and floor since the energies of single-bounce reflected waves do not appear at the receiver, thereby resulting in significant amplitude fade and delay spread reduction. The received signal intensity variations and delay spread are investigated numerically using a 14-path propagation model and the usefulness is confirmed by comparing with a linear polarized wave transmission/reception under a same LOS condition.

Line-of-sight indoor radio communication using circular polarized waves

Abstract: This paper presents an anti-multipath fading scheme employing a circular polarized wave for line-of-sight (LOS) indoor radio communications. The circular polarized wave transmission/reception significantly mitigates the multipath fading caused by reflections from walls, ceiling, and floor since the energies of single-bounce reflected waves do not appear at the receiver, thereby resulting in significant amplitude fade and delay spread reduction. The received signal intensity variations and delay spread are investigated numerically using a 14-path propagation model and the usefulness is confirmed by comparing with a linear polarized wave transmission/reception under a same LOS condition. >

Millimetric wavelengths radiowave propagation for line-of-sight indoor microcellular mobile communications

Abstract: Discusses millimeter waves for indoor microcellular communications. The results of propagation experiments conducted at 60.4 GHz (the oxygen absorption band) and 38.25 GHz to determine multipath characteristics in a number of indoor microcell channels employing omnidirectional antennas are presented. Cumulative distribution functions for received signal envelope, as well as corresponding power spectra are given. In addition, a comparison between the fading statistics measured at 60.4 GHz and 38.25 GHz under similar conditions is made. The change in multipath characteristics due to the presence of different building materials is also illustrated. A ray model is developed to represent indoor microcell propagation by considering a direct ray plus rays which have undergone single and double reflections from the walls. Specular floor-reflected and ceiling-reflected rays are included when the antennas radiation pattern does not preclude them. Using this simple model, the signal variations and the amplitude of reflected rays with respect to the line of sight (LOS) ray as functions of mobile receiver position are predicted and used to assist in interpreting experimental results. Theoretical results are found to be in good agreement with measured ones, with the model also being used to predict structure-induced root mean square (rms) delay spread along receiver routes in an indoor microcell environment. This parameter is a measure of multipath conditions in a mobile radio channel and is inversely proportional to the maximum usable data signalling rate of a channel. >

Power spectral lineshapes of microwave radiation backscattered from sea surfaces at small grazing angles

Abstract: Analysis of recent small-grazing-angle microwave backscattering data indicate that the Bragg mechanism alone cannot explain the experimental results. The authors investigate the issue of scattering mechanisms by studying the lineshapes of the backscattered microwave power spectra. It is found that spectral lineshapes can be decomposed into physically meaningful basis functions which are Gaussian, Lorentzian or Voigtian. Generally, the spectral component corresponding to the lower frequency peak in the power spectral density (PSD) of the vertical polarisation is well described by a Gaussian profile, while the spectral component due to the higher frequency peak in the horizontal polarisation PSD is well described by either a Lorentzian or a Voigtian profile, depending on the size of the radar footprint. These quantitative results provide compelling evidence that several entirely different mechanisms, corresponding to different surface features of the dynamic sea surface, are active in contributing to microwave backscattering returns. These mechanisms comprise: first, scattering from free Bragg waves, characterised by a Gaussian distribution in scatterer speeds and a Gaussian component in the PSD; secondly, scattering from sporadically appearing, fast moving, short lifetime, facet-like scatterers, characterised by an exponential distribution in scatterer lifetime and a Lorentzian component in the PSD; and finally, scattering from fast-to-intermediate speed bound-Bragg waves, or not-so-fast facets, characterised by a convolution of the Gaussian and Lorentzian processes, resulting in a Voigtian component in the PSD.

Ionospheric plasma response to HF radio waves operating at frequencies close to the third harmonic of the electron gyrofrequency

Abstract: Experimental results concerning European incoherent scatter observations of heater-induced electron temperature enhancements, anomalous absorption of low-power HF probe waves, and the spectrum of stimulated electromagnetic emission (SEE) in the sidebands of a high-power HF electromagnetic wave are presented. For the experiments reported in this paper, an O mode pump wave was transmitted vertically into the F region above Tromso, Norway, while the injected frequency was varied in small steps around the third harmonic of the electron gyrofrequency. Systematic variations with pump frequency were observed in the data obtained from all three diagnostics. Measurements of anomalous absorption, the downshifted maximum (DM) spectral feature, and heater-induced electron temperature enhancements all exhibited broad minima as the heater frequency approached the third harmonic of the electron gyrofrequency. In addition, the signal strength of the HF probe wave measured during heater off periods is also reduced at these and higher heater frequencies. The experimental findings suggest that at heater frequencies in the vicinity of the third gyroharmonic, small-scale field-aligned irregularities are not excited, whereas very small scale irregularities, of the order of a few electron cyclotron radii, which are responsible for the production of fast electrons, may be generated. The observed reduction in the diagnostic signal strength is then attributed to the ionized patches produced by these energetic electrons.

Near-grazing illumination and shadowing of rough surfaces

Abstract: A simple and computationally efficient methodology is demonstrated for treating the interaction of radio waves near grazing above rough surfaces. We apply it to the sea from HF through the microwave. Results using actual finite seawater conductivity depart significantly from those of a perfectly conducting profile for vertical polarization; for horizontal polarization there is essentially no difference. Shadowing behind wave crests is surprisingly shallow for vertical polarization even when the occluded depth is tens of wavelengths. This methodology gives expressions for the effective surface impedance at grazing as modified by the roughness when height scales greatly exceed the radio wavelength, augmenting prior expressions valid at HF for the sea obtained from perturbation theory. These effective impedances can then be used in formulations for radiation and surface wave propagation/diffraction at and below the horizon.

Vehicle travel guide system

Abstract: PURPOSE: To reduce the number of magnetic markers laid on the road surface in a vehicle travel guide system using the magnetic markers. CONSTITUTION: Magnet nails 100 are buried into the roads as the magnetic markers. Furthermore, a radio wave tag 104 is buried. The radio wave tag 104 transmitted roads shape data of about 100m in the direction of travel. The power of the ratio tag 104 is supplied from the magnetic field generator 14 of a vehicle. The vehicle detects a relative change with the magnetic nail 100 by a magnetic sensor 16 and receives road shape data from the radio wave tag 104 by a radio wave reception device 15. A controller 28 decides steering quantity based on the relative change against the magnetic nail 100 and shape data, and supplies it to an actuator 18. Since shape data is transmitted by the radio wave tag 104, the number of the magnetic nails 100 can be reduced. A beacon may be used instead of the radio wave tag 104. COPYRIGHT: (C)1996,JPO

Theory and observations of coronal shock waves

Abstract: Coronal shock waves are generated by flares and/or coronal mass ejections. They manifest themselves in solar type II radio bursts. The observational features of these radio bursts and their relationship to coronal mass ejections and interplanetary shocks are briefly reviewed. Finally, the various theoretical models of solar type II radio bursts are presented and compared with the observations. All these models base on the production of highly energetic electrons by coronal shock waves since nonthermal radio radiation is generally assumed as being generated by suprathermal electrons. These high energy electrons excite Langmuir waves or upper hybrid waves, which convert into radio waves.

Traveling ionospheric disturbance diagnostics using HF signal trajectory parameter variations

Abstract: In the model of a perfectly reflecting surface the inverse problem of restoring dynamic and statistical parameters of traveling ionospheric disturbances (TIDs) from variations of angles of arrival and Doppler frequency shift of HF radio signals on one-hop oblique radio paths is solved. The technique for determining dispersion law, fluctuation spectrum, geometry, direction, and velocity of TID motion is described.

Attenuation and scintillation of radio waves in the Earth's atmosphere from radio occultation experiments on satellite-to-satellite links

Abstract: A theoretical analysis of refractive loss of radio waves by the Earth's atmosphere in radio occultation measurements along the satellite-to-satellite line for various altitude profiles of the refractive index is given. Experimental results for refractive loss on the orbital spacecraft - geostationary satellite link are presented. Theoretical calculations are compared with experimental data, and a conclusion is drawn that the signal amplitude during radio occultation is strongly dependent on the layered structure of the refractive index profile. Amplitude scintillations of centimeter (λ1 = 2 cm ) and decimeter (λ2 = 32 cm ) radio waves used in radio occultation experiments are described. Dependences of the rms value of the amplitude scintillations versus the minimum altitude of the ray line for the two above wavelength bands are presented. The frequency spectra of the log-amplitude scintillations are analyzed together with the dependence of the rms amplitude on the wavelength. Experimental data are compared to the theory of scintillations in a turbulent atmosphere, and the altitude model of the structure constant of refractivity fluctuations is determined.

Multiwavelength monitoring of the BL Lacertae object PKS 2155-304. 3: Ground-based observations in 1991 November

Abstract: We present ground-based observations of the BL Lac object PKS 2155-304 during 1991 November. These data were obtained as part of a large international campaign of observations spanning the electro-magnetic spectrum from the radio waves to the X-rays. The data presented here include radio and UBVRI fluxes, as well as optical polarimetry. The U to I data show the same behavior in all bands and that only upper limits to any lag can be deduced from the cross-correlation of the light curves. The spectral slope in the U-I domain remained constant on all epochs but 2. There is no correlation between changes in the spectral slope and large variations in the total or polarized flux. The radio flux variations did not follow the same pattern of variability as the optical and infrared fluxes. The polarized flux varied by a larger factor than the total flux. The variations of the polarized flux are poorly correlated with those of the total flux in the optical (and hence UV domain; see the accompanying paper by Edelson et al.) nor with those of the soft X-rays. We conclude that the variability of PKS 2155-304 in the optical and near-infrared spectral domains are easier to understand in the context of variable geometry or bulk Lorentz factor than of variable electron acceleration and cooling rates.

Ionospheric model validation at VLF and LF

Abstract: A reliable knowledge of radio signal amplitude and phase characteristics is required to design and maintain communications and navigational circuits at VLF and LF. The ability to accurately calculate signal levels as a function of frequency, position, and time is of considerable importance in achieving reliable assessment of communication coverage. Detailed computer models based on multiple mode waveguide theory have been developed. These models have been found to produce good comparisons between measurements and calculations of signal variations as a function of propagation distance. However, results can be very sensitive to the ionospheric inputs to these computer models. This paper has two purposes. The first is to present the results of a systematic comparison of a set of measurements of signal strength from various transmitters over a number of propagation paths using a simple model of the ionosphere. The variation of the parameters of this simple model with basic propagation parameters is examined. The second purpose is to examine the built-in version of this simple model of the ionosphere as implemented in the Long Wave Propagation Capability. This model is found to adequately represent a set of in-flight signal strength measurements. It is also clear that there is still room for improvements in this ionospheric model.

The Ionospheric Focused Heating Experiment

Abstract: The Ionospheric Focused Heating rocket was launched on May 30, 1992. The sounding rocket carried an instrument and chemical payload along a trajectory that crossed the intersection of the beams from the 430-MHz incoherent scatter radar and the 5.1-MHz high-power radio wave facility near Arecibo. The release of 30 kg of CF{sub 3}Br into the F region at 285 km altitude produced an ionospheric hole that acted like a convergent lens to focus the HF transmission. The power density inside the radio beam was raised by 12 dB immediately after the release. A wide range of new processes were recorded by in situ and ground-based instruments. Measurements by instruments flying through the modified ionosphere show small-scale microcavities (< 1 m) and downshifted electron plasma (Langmuir) waves inside the artificial cavity, electron density spikes at the edge of the cavity, and Langmuir waves coincident with ion gyroradius (4 m) cavities near the radio wave reflection altitude. The Arecibo incoherent scatter radar showed 20 dB or greater enhancements in ion acoustic and Langmuir wave turbulence after the 5.1-MHz radio beam was focused by the artificial lens. Enhancements in airglow from chemical reactions and, possibly, electron acceleration were recorded with optical instruments. Themore » Ionospheric Focused Heating experiment verified some of the preflight predictions and demonstrated the value of active experiments that combine high-power radio waves with chemical releases. 30 refs., 14 figs., 1 tab.« less

Computation of attenuation, phase rotation, and cross-polarization of radio waves due to rainfall in tropical regions

Abstract: Computation of attenuation, phase rotation, and cross-polarization of radio waves due to rain in tropical regions using finite element method is the subject of this work. Computations are made of the forward-scattering amplitudes of oblate spheroidal raindrops at 20 and 30 GHz, assuming plane waves at normal incidence to the raindrop axis. The forward-scattering amplitudes are employed to obtain the required attenuation, phase rotation, and cross-polarization using the rainfall rate data for Nigeria, a tropical African country. The results obtained in this work compare with those existing in the open literature. >