Showing papers on "Radio wave published in 1999"

The computer for the 21st century

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

Propagation characteristics at 5 GHz in typical radio-LAN scenarios

Abstract: In order to characterize the radio channel in typical WLAN scenarios a wideband measurement campaign at 5 GHz has been carried through. Four offices and two large open space environments have been investigated. Impulse response shape and fading statistics have been analyzed. Moreover, the Doppler characteristics have been studied. It was found that the impulse responses basically had the shape of one exponentially decaying cluster. The measured Doppler spectra indicates a basically uniform distribution of radiowave direction of arrival. Measured RMS delay spreads were in the range 10-100 ns.

Penetration of Antarctic subglacial lakes by VHF electromagnetic pulses: Information on the depth and electrical conductivity of basal water bodies

Abstract: Owing to the high level of absorption of very high frequency radio waves in water, previous investigators of airborne radio echo sounding (RES) data from Antarctica have assumed that the depth of subglacial lakes cannot be measured directly by this method However, we have identified a number of RES returns from beneath the ice-water interface at the surface of eight subglacial lakes that we have interpreted as being reflected from the lake floor The returns allow us to measure the depth of subglacial lakes, since the velocity of radio waves in water (334 m μs−1) is relatively unaffected by electrical conductivity Attenuation of radio waves within water is controlled largely by its electrical conductivity Consequently, by examining the decay of the radio wave amplitude with depth we can gain information about the conductivity of subglacial water bodies Our results indicate that the minimum water depths of eight subglacial lakes vary between 8 and 21 m The lakes from which our depth measurements were taken are distributed widely around the ice sheet Thus it may be concluded for the first time that Antarctic subglacial water bodies are generally at least several meters in depth By examining the attenuation of radio waves through subglacial water, the electrical conductivity of the water is estimated to be extremely low (ie, fresh pure water)

First direct observations of the reduced striations at pump frequencies close to the electron gyroharmonics

Abstract: It is well known that the ionospheric plasma response to high-power HF radio waves changes dras- tically as the heater frequency approaches harmonics of the electron gyrofrequency. These include changes in the spectrum of the stimulated electromagnetic emission, reduction in the anomalous absorption of low-power diagnostic waves propagating through the heated vol- ume, and reduction in the large scale F-region heating. Theoretical models as well as previous experimental evidence point towards the absence of small-scale field- aligned plasma density irregularities at pump frequen- cies close to electron gyroharmonics as the main cause of these changes. Results presented in this paper are the first direct observations of the reduced striations at the 3rd gyroharmonic made by the CUTLASS radar. In addition, simultaneous EISCAT observations have revealed that the ''enhanced ion-line'' usually present in the EISCAT ion-line spectrum during the first few seconds after heater switch on, persisted at varying strengths while the heater was transmitting at frequen- cies close to the 3rd electron gyroharmonics.

Radar backscattering from artificial field-aligned irregularities

Abstract: In June of 1992 a NASA sounding rocket was fired into the Arecibo heater beam to provide in situ observations of artificially induced ionospheric irregularities. In this paper we provide a radar scattering calculation based on in situ data and compare the same with previous remote sensing experiments and with theory. The calculated backscatter cross section is in good agreement with prior observations over the Arecibo heater at 50 MHz. More important, when we scale the observed in situ power spectrum appropriately and compare it with multiradar cross-sectional results from the Platteville, Colorado experiments, we find a remarkably similar radar frequency dependence, albeit one shifted to smaller scales over the higher-latitude site. Even though the rms fluctuation level is almost the same over the Arecibo and Platteville heaters, the shift in scales toward smaller structures over Platteville explains the much larger VHF radar cross section measured there. Comparison of our waveform and its power spectrum with similar predictions from a recent theory shows excellent agreement for k values up to about 5 times the breakpoint in the spectrum of the theoretical prediction. Taken together, these results give very strong evidence for the production of needle-like solitary structures as the dominant final state when high-power radio waves reflect from a magnetized plasma. The organization of these structures by as yet unexplained processes may explain the scales between 10 m and 10 km which occur in the heated volume. Finally, the dominant needle-like field-aligned density depletions seem to support a second source of smaller-scale irregularities. This creates a second break in the power law slope from its one-dimensional value of k−4.3 predicted by theory to one more nearly characterized by k−3. The multiradar results from Platteville show a similar break, and we speculate that a density and/or temperature-gradient-driven instability such as the drift wave is operating.

Radio frequency identification transponder having a reflector

Abstract: An improved radio frequency transponder has a reflector to increase its operative range. A system of one or more reflectors is operatively associated with a transponder and may be formed out of any sort of radio frequency reflective material. The reflector system can enhance reception or transmission of radio waves by or from the transponder. The reflector system may also be used to provide for selective coupling of the radio frequency transponder with a base station, user- or vehicle-supported reader, or the like based on relative orientation. In addition, the reflector system may be used to selectively reflect particular radio waves.

Radar apparatus for vehicle

Abstract: A radar apparatus of the present invention is a radar apparatus for detecting an object around a vehicle, which comprises a transmitter section for radiating a frequency-modulated, transmitted wave a receiver section for receiving a radio wave re-radiated from an object exposed to the transmitted wave and mixing the radio wave received with part of the transmitted wave to obtain beat signals, and a signal processing section for analyzing frequencies of the beat signals to detect the object around the vehicle. This radar apparatus is arranged to set a first threshold value and a second threshold value higher than the first threshold value as to signal levels of a frequency spectrum of the beat signals. The signal processing section is arranged to detect the object around the vehicle, using a beat frequency of a signal level over the second threshold value, and to compare the frequency spectrum with the first threshold value in a predetermined frequency range to determine whether there is dirt on the transmitter section or on the receiver section.

Patch antenna apparatus with improved projection area

Abstract: A patch antenna apparatus with a simple structure can obtain an improved desired projection area in accordance with a projection space. The patch has a dielectric substrate with a grounding conductor on its bottom surface. On the dielectric substrate is formed at least one conductor patch having a first feeding point for producing resonance in parallel to the X-axis at a predetermined resonance frequency and a second feeding point for producing resonance in parallel to the Y-axis at the resonance frequency. A controller for a power distributing and combining circuit controls each of radio signals of the resonance frequency fed to the first and second feeding points so as to change at least one of the amplitude and phase thereof. When the radio signals of the resonance frequency are fed to the first and second feeding points, the patch antenna apparatus projects radio waves including two linear polarizations which are parallel to the X and Y axes and which cross each other to be perpendicular to each other in a projection directional pattern corresponding to the control for the radio signals by the controller of the power distributing and combining circuit.

Letter to the Editor : First direct observations of the reduced striations at pump frequencies close to the electron gyroharmonics

Abstract: . It is well known that the ionospheric plasma response to high-power HF radio waves changes drastically as the heater frequency approaches harmonics of the electron gyrofrequency. These include changes in the spectrum of the stimulated electromagnetic emission, reduction in the anomalous absorption of low-power diagnostic waves propagating through the heated volume, and reduction in the large scale F-region heating. Theoretical models as well as previous experimental evidence point towards the absence of small-scale field-aligned plasma density irregularities at pump frequencies close to electron gyroharmonics as the main cause of these changes. Results presented in this paper are the first direct observations of the reduced striations at the 3rd gyroharmonic made by the CUTLASS radar. In addition, simultaneous EISCAT observations have revealed that the "enhanced ion-line" usually present in the EISCAT ion-line spectrum during the first few seconds after heater switch on, persisted at varying strengths while the heater was transmitting at frequencies close to the 3rd electron gyroharmonics. Key words. Ionosphere (active experiments; ionospheric irregularities) · Radio science (ionospheric physics)

Repeater device for converting radio lan cross channel and radio terminal device

Abstract: PROBLEM TO BE SOLVED: To expand communication area using a relay system, capable of easily constructing a transmission and reception area between an access point and a radio terminal in a radio LAN where a plurality of channels are used. SOLUTION: A crossbar switch 81 is sent to frequency converting parts 41 to 44 of a set channel, converted into the frequency band of each channel and sent to amplifiers 21 to 24. Before that level detector 31 to 34 detect whether the channel is in a transmission state, and when the channel is in the transmission state, a control signals is sent continuously to switches 61 to 64, and the switches 61 to 64 go into 'OFF' state to stop receiving the channel. Thus, the intra-station loop of radio waves is eliminated. COPYRIGHT: (C)2001,JPO

On kinetic effects in the ionospheric f-region modified by powerful radio waves

Abstract: We consider effects related to acceleration of electrons by high-frequency plasma turbulence in the ionospheric F-region modified by powerful radio waves. The threshold of avalanche growth of the number of accelerated particles due to additional ionization is determined for pump-wave frequencies far from the multiple cyclotron resonance. The steady-state density of the accelerated electrons is found for the above pump-frequency values taking into account both turbulent trapping in the accelerating layer due to scattering of plasma waves and the return of electrons to this layer due to collisions. If the pump wave frequency is close to the multiple cyclotron resonance, fast electron distribution with significant transverse anisotropy is formed. Relaxation of this distribution due to collisions with charged particles outside the accelerating layer leads to the appearance of a maximum over transverse velocities in the tail of the distribution function. We propose a generation mechanism for the broad upshifted maximum feature in the spectrum of stimulated electromagnetic emission, which is related to the cyclotron instability of the accelerated electrons. The instability occurs in the double-resonance region in which the pump frequency is close to both the upper-hybrid and multiple-cyclotron frequency.

Communication system between road and vehicle

Abstract: Road transmission antennas (4a, 4b) are arranged along the road, and the road transmission antennas (4a, 4b) radiate radio waves of the same frequency and the same contents in the same cell (E). On-board devices (3) that receive the radio waves radiated from the road transmission antennas (4a, 4b) are adapted for directional diversity reception. Even if a small car enters a shadow region caused by large car, a communication between the small car and the road may not be interrupted.

Apparatus and method for location-dependent setting of air interface parameters of a mobile radio device

Abstract: The present invention provides a radio communication apparatus capable of automatically setting a frequency band, a transmission power and the like in accordance with radio wave specifications of an area where it is used. A positional information detecting section (31) receives a radio wave from a GPS satellite through an antenna (33) and inputs the radio wave to a GPS receiving section (34). The GPS receiving section (34) despreads and demodulates the spectrum-spread signal transmitted from the GPS satellite, and transmits the demodulated signal to a positioning section (35). The positioning section (35) extracts the information about a current position where the radio communication apparatus from the demodulated signal, and outputs the information to a CPU (37) of a specification controlling section (32) as information about a position where the radio communication apparatus is to be used. In accordance with the positional information transmitted from the positioning section (35), the CPU (37) makes access to a memory (36), reads radio wave specifications corresponding to the area from the memory (36), controls oscillation frequencies of oscillator (23, 29) and controls gains of amplifiers (24, 27) to control the power.

High-impedance electromagnetic surfaces with forbidden bands at radio and microwave frequencies

Abstract: A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped circuit elements, and distributed in a 2D lattice. Although it is made of continuous metal, and conducts DC currents, it does not conduct AC currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves. Furthermore, image currents induced in the surface are not phase reversed as they are on a flat metal surface.

CDMA receiving method and circuit

Abstract: A receiving method at a mobile terminal comprising performing communication by a code division multiple access (CDMA) using a spectrum diffusion, executing an arrival radio wave search for detecting radio waves from transmission lines with different delay times and synthesizing receiving signals from radio waves from different transmission lines using a rake synthesis, wherein, when a detected receiving status of a receiving signal satisfies a preset condition, a range of delay times for executing an arrival radio wave search is changed. For example, when a phasing pitch is used as a variation of a received electric field, a reciprocal of a phasing pitch is compared with a preset threshold value or a moving speed of a mobile terminal calculated from a phasing pitch is compared with the threshold value and, if the threshold value is smaller, a peak search is performed only in the vicinity of the peak determined by the previous search.

Radio wave emissions due to gravitational radiation

Abstract: We consider the interaction of a weak gravitational wave with electromagnetic fields in a thin plasma on a Minkowski background spacetime using the 1+3 orthonormal frame formalism. Because gravitational and electromagnetic waves satisfy the same dispersion relation, electromagnetic waves can be effectively generated as a result of this interaction. In the case of the interaction with a static magnetic field, the amplitude of the electromagnetic waves depends on the size of the excitation region in which the magnetic field is contained. It is argued that due to the presence of a plasma this process can also lead to the generation of higher harmonics of the original mode. Estimates are given for this effect in the case of a binary pulsar and a cold electron plasma. It is found that the emmited radiation will lie in the radio frequency band. We also speculate on the possible relevance of this process on situations in cosmology, in particular whether this could be used to constrain primordial magnetic fields.

Receiver of tire inflation pressure monitor

Abstract: A tire inflation pressure monitor includes wheel transmitters and a receiver The wheel transmitters transmit tire inflation pressure data by radio waves, and the receiver receives the data from the transmitters The receiver includes reception antennas for receiving radio waves from the transmitters and a receiver unit for processing the received data The reception antennas include external reception antennas, which are separated from the receiver unit, and at least one internal reception antenna, which is located in the receiver unit The number of the external reception antennas is less than that of the transmitters by one As a result, the receiver is simplified without reducing its performance Also, a loop antenna, which is used as a reception antenna to induce voltage by the magnetic field component of radio waves, improves the efficiency of the receiver

Weather band radio and method of tuning same

Abstract: A mobile weather band radio and method of tuning the radio to select a signal channel based on geographic position. The radio has a weather band tuner adjustable for a plurality of radio wave signal channels. A position indicative receiver is provided for receiving position indicative signals and determining a current position of the radio. A controller automatically tunes the tuner to a select signal channel based on the determined geographic region.

Comparative study of lateral profile knife-edge diffraction and ray tracing technique using GTD in urban environment

Abstract: In an urban environment, radio wave interaction with buildings may affect considerably the propagation of radio waves, mainly because of multipath, diffraction, and shadowing effects. This paper outlines the effect of two-dimensional (2-D) (vertical and lateral) diffraction and compares a Fresnel-Kirchhoff scalar approach to a vectorial geometrical theory of diffraction (GTD) approach applied to a four-ray system. The former can be considered as a generalization of conventional knife-edge diffraction theory while the latter (GTD) is useful in the context of ray tracing. A very good agreement between the Fresnel-Kirchhoff and GTD results is found within the limits of validity of both methods. Moreover, it is shown that conventional knife-edge diffraction theory can largely overestimate attenuation (10-15 dB) behind tall buildings in the center of a city environment. Different frequency bands have been tested for the sake of comparison, and emphasis has been put on the radio communications frequency bands used for the global system for mobile communications (GSM) and DCS/DECT systems at 900 and 1800 MHz.

Mobile terminal, method for controlling game and computer readable recording medium

Abstract: PROBLEM TO BE SOLVED: To vary progress of a game carried out by a mobile terminal according to the present location of the mobile terminal. SOLUTION: A portable telephone set receives a control signal radio- transmitted from a base station controlling a radio area in which the portable telephone set is presently located among multiple base stations, and detects the radio wave reception intensity of a radio signal. Then, the detected radio wave reception intensity of the radio signal is stored in a storage area. This detection of the radio wave reception intensity of the radio signal is performed one by one during waiting and the radio wave reception intensity of the newest radio signal is stored in the storage area. Then, an enemy character to fight with, an item to be generated and the branching of a game scenario are controlled according to the value of the radio wave reception intensities stored in the storage area in the advancing process of the game (step S205 to S213). COPYRIGHT: (C)2002,JPO

ELF emission generated by the HAARP HF-heater using varying frequency and polarization

Abstract: We present first observations of the ELF emission generated by the modulated ionospheric HF-heating using the HAARP facility We focus primarily on the dependence of the polarization and of the amplitude of the ELF wave upon the frequency and polarization of the heating radio wave A simple 1D computational model of the ELF generation based on the earlier developed model of a horizontal magnetic dipole caused by the HF ionospheric heating [1] is presented The model develops a qualitative understanding of the changes in the ELF amplitude and polarization due to variations of the heating frequency The obtained results imply that polarization of the ELF emission generated by the ionospheric HF-heating can be controlled by changing the frequency or polarization of the radio wave

Influence of small-scale irregularities on the features of the overshoot effect in the temporal evolution of stimulated electromagnetic emission. Part I. Development stage

Abstract: We present the results of experimental studies of the evolution of stimulated electromagnetic emission of the ionosphere (SEE) under the F-layer modification by powerful HF radio waves in a broad range of the pump wave frequencies. We compare the parameters of the overshoot effect in SEE evolution to the observations of anomalous attenuation and field-aligned scattering of radio waves. We show the overshoot effect to result from the anomalous attenuation under scattering at artificial small-scale ionospheric irregularities. We found the characteristic time scales of the overshoot effect development to decrease and its value to increase as the pump wave frequency decreases from 6 to 4 MHz; this is attributed to the observed increase of the irregularities amplitude at scales\(l \bot \sim 3 - 10m\) m.

Behaviour of scattering from a rough surface at small grazing angles

Abstract: The particular problem of wave scattering at low grazing angles is of great interest because of its importance for the long-distance propagation of radio waves along the Earth's surface, radar observation of near surface objects, as well as solving many other fundamental and applied problems of remote sensing. One of the main questions is: how do the scattering amplitude and specific cross section behave for extremely small grazing angles? We consider the process of wave scattering by a statistically rough surface with the Neumann boundary condition. This model corresponds to sound scattering from a perfectly ‘hard’ surface (for example, the interface between air and the sea surface) or ‘vertically’ polarized electromagnetic waves scattered by a perfectly conducting one-dimensional (i.e. cylindrical) surface when the magnetic field vector is directed along the generating line of this cylindrical surface. We assume that the surface roughness is sufficiently small (in the sense of the Rayleigh para...

Letter to the editor CUTLASS observations of a high-m ULF wave and its consequences for the DOPE HF Doppler sounder

Abstract: . The CUTLASS (Co-operative UK Twin Located Auroral Sounding System) Finland HF radar, whilst operating in a high spatial and temporal resolution mode, has measured the ionospheric signature of a naturally occurring ULF wave in scatter artificially generated by the Tromsu Heater. The wave had a period of 100 s and exhibited curved phase fronts across the heated volume (about 180 km along a single radar beam). Spatial information provided by CUTLASS has enabled an m-number for the wave of about 38 to be determined. This high-m wave was not detected by the IMAGE (International Monitor for Auroral Geomagnetic Efects) network of ground magnetometers, as expected for a wave of a small spatial scale size. These observations over the first independent confirmation of the existence of the ground uncorrelated ULF wave signatures previously reported in measurements recorded from an HF Doppler sounder located in the vicinity of Tromso. These results both demonstrate a new capability for geophysical exploration from the combined CUTLASS-EISCAT ionospheric Heater experiment, and provide a verification of the HF Doppler technique for the investigation of small scale ULF waves. Key words. Ionosphere (ionosphere – magnetosphere interactions) . Magnetospheric physics (magnetosphere – ionosphere interactions; MHD waves and instabilities)

NICMOS and VLBA observations of the gravitational lens system B1933+503

Abstract: NICMOS observations of the complex gravitational lens system B1933+503 reveal infrared counterparts to two of the inverted-spectrum radio images. The infrared images have arc-like structures. The corresponding radio images are also detected in a VLBA map made at 1.7 GHz with a resolution of 6 mas. We fail to detect two of the four inverted radio spectrum components with the VLBA even though they are clearly visible in a MERLIN map at the same frequency at a different epoch. The absence of these two components could be due to rapid variability on a time-scale less than the time delay, or to broadening of the images during propagation of the radio waves through the ISM of the lensing galaxy. The degree of scatter-broadening must be sufficient that the missing images fall below the surface brightness detectability threshold of the VLBA observations. The variability explanation is the least plausible. The failure to detect the same two images with NICMOS is probably due to extinction in the ISM of the lensing galaxy.

Radio telephone system

Abstract: PROBLEM TO BE SOLVED: To provide a radio telephone system which can secure impedance matching between a transmitting circuit and an antenna by detecting an approaching a human body. SOLUTION: In this radio telephone system, an antenna 44 transmits the signals outputted from both transmitting and receiving circuits into the air, a human body detection part 63 detects the approaching human body and a communication control part 30 controls a variable impedance matching part 43 according to the detection result of the part 63 to secure impedance matching between a radio transmitting/receiving part 40 and the antenna 44. In such a constitution, the transmission power is sent from the part 40 to the antenna 44 with no attenuation and then radiated from the antenna 44 as the radio wave with high efficiency.

Anisotropy of ionospheric irregularities determined from the amplitude of satellite signals at a single receiver

Abstract: . A new method of determining the anisotropy parameters of small-scale irregularities in the ionospheric F region is presented and experimental results are shown. The method is based on observations of amplitude fluctuations of radio waves transmitted by satellites flying above the F region. In practice, Russian navigational satellites are used and both the amplitude and the phase of the received signal is measured on the ground level. The method determines both the field-aligned anisotropy and the field-perpendicular anisotropy and orientation of the spatial spectrum of the irregularities, assuming that the contours of constant power have an elliptic shape. A possibility of applying the method to amplitude tomography is also discussed. Using a chain of receivers on the ground level, one could locate the regions of small-scale irregularities as well as determine their relative intensities. Then the large-scale background structures could be mapped simultaneously by means of ordinary ray tomography using the phase observations, and therefore the relations of small-scale and large-scale structures could be investigated. Key words. Ionosphere (auroral ionosphere; ionospheric irregularities; instruments and techniques)

Base station communication device and method of power supplying to portable radio communication device

Abstract: PROBLEM TO BE SOLVED: To realize use of a sheet or a plurality of portable radio communication equipment by providing a resonance circuit with a resonance frequency controllable counterposed to a transceiving antenna of base station communication equipment, and supplying power to the portable radio communication equipment from the base station communication equipment through electromagnetic induction. SOLUTION: A noncontact IC card 18 of portable radio communication equipment is inserted to an opening part A of a base station communication device 10, the portable radio communication equipment communicates with the base station communication device 10 through the use of radio waves. In the case of a single sheet of the non-contact IC card, due to large deviation in resonance frequency, power transmitting efficiency from a reader/writer is deteriorated, to provide a possibility of insufficient communication range and card starting power. Here, a current flowing in a resonance frequency adjusting counterposed antenna 16 is monitored by a current inspection circuit, a control circuit adjusts the inductance or capacitance of a tuning circuit 17 to allow a maximum current to flow, the resonance frequency is set to an optimum value, and the power transmitting efficiency is optimized.

High resolution bistatic HF radar observations of ULF waves in artificially generated backscatter

Abstract: High resolution HF radar observations of ULF waves in the ionosphere are possible by artificially generating irregularities using the EISCAT heater at Tromso, Norway. The line-of-sight velocities from the CUTLASS radars have been combined for the first time to form bistatic flow vectors during a ULF wave, generating ionospheric electric field measurements with a higher accuracy than ever previously recorded by any instrument. A high-m wave observed in the ionosphere exhibits a frequency which is a harmonic of that of a low-m field line resonance which is observed simultaneously in the ionosphere and at the ground. The high-m pulsation resembles a class of particle driven wave previously recorded on VHF radars. These results are consistent with recent HF radar observations of small scale waves possessing similar characteristics to field line resonances and with the theory that the low-m wave may be driving the high-m wave through a non-linear Kelvin-Helmholtz instability.