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 Subjects -> ELECTRONICS (Total: 135 journals)

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ISSN (Print) 1573-9120 - ISSN (Online) 0033-8443
• Maximum Likelihood Estimate of the Coordinates of Wideband Noise Sources in the Case of Unknown Spectral Densities of the Signal and the Noise
• Abstract: We propose a method of obtaining the maximum likelihood estimate of the coordinates (the bearing, in a special case) of a wideband Gaussian noise source in the presence of background interference which is uncorrelated at the elements of the antenna array. The method is adapted to unknown spectral densities of the noise and the signal produced by the source. The Cramer—Rao bound is constructed, which characterize the variance of the coordinate estimate. Empirical estimates of the variance are compared with the Cramer—Rao boundary and the empirical variance estimates by the method of numerical simulation in the case of routine summation of the power values in the frequency channels. It is shown that when the spectral densities of the noise and the signal differ considerably, the proposed method ensures a much better accuracy. It is also shows that the influence of weak correlation of the noise at the receiver elements is insignificant.
PubDate: 2013-10-24

• A Multipactor Discharge in Crossed Fields Under the Conditions of a Combination of Two Waves with Close Frequencies
• Abstract: We study the multipactor discharge in crossed fields, specifically, a microwave electric field and a quasistatic magnetic field. The multipactor occurs under the conditions of superposition of two microwave pulses with close frequencies, which correspond to the three-centimeter wavelength range. Experiments in the rectangular waveguide demonstrate that the multipactor develops and exists in a wide range of differences in the signal frequencies, which covers on interval of up to 700 MHz. The specific power absorbed in the discharge is equal to several kW/cm2, and the radiation is absorbed efficiently at both frequencies. When the signal power is initially insufficient to ensure the multipactor development, an additional signal at a close frequency allows one to switch the discharge, which absorbs microwaves efficiently, on and off. At a frequency difference of up to 40 MHz, the achieved switch-on time is about 100 ns. Switch-on of the second signal in the line with a resonator cavity, which has a frequency belonging to the cavity frequency band, also results in the discharge development and switches the cavity from the transition regime to the reflection regime.
PubDate: 2013-10-24

• Wave Diffraction on a Stripe Grating at a Boundary of a Layered Inhomogeneous Medium: Method of Analytic Regularization
• Abstract: In this work, we develop a novel numerical-analytic method for solving the problem of wave diffraction on a stripe array situated at a boundary of a layered inhomogeneous medium. A high-efficiency algorithm for calculation of the diffraction characteristics of such a structure in the case where a plane electromagnetic wave is incident on it obliquely has been developed. The operation of the algorithm is demonstrated by the example of the problem about diffraction of a plane E-polarized wave on certain layered inhomogeneous media, including plasma-like ones, with a stripe grating at one of its boundaries.
PubDate: 2013-10-24

• On the Mechanism of Energetic Electron Losses from the Magnetic Mirror Trap at the ECR Discharge Startup
• Abstract: In this work, we discuss experimental evidence for the existence of an effective mechanism of energetic-electron losses at the initial stage of the discharge during electron cyclotron resonance (of the ECR discharge) when the electron scattering to the loss cone is caused by the development of the electron cyclotron instabilities of a strongly nonequilibrium plasma. The spectral composition of the transient pulses of electromagnetic radiation is studied in a wide frequency range at the initial stage of the ECR discharge, when the hot-particle density exceeds that of cold particles. The observed electromagnetic-radiation bursts and synchronous energetic-electron precipitation from the trap can be related to the development of a cyclotron instability of the fast extraordinary wave in the rarefied plasma.
PubDate: 2013-10-24

• Relaxation Time of Artificial Periodic Irregularities of the Ionospheric Plasma and Diffusion in the Inhomogeneous Atmosphere
• Abstract: We consider diffusion of the ionospheric-plasma irregularities as applied to the problem of experimental determination of the lower-ionosphere parameters by artificial periodic irregularities of the electron number density. A rigorous solution to the problem of diffusion of one-dimensional plasma irregularities in a weakly ionized medium, whose diffusion coefficient exponentially decreases with the altitude, is obtained. The Green’s function for this problem is found. Three parameters are taken into account in the solution, namely, the size of the region occupied by the irregularities, the size of the irregularities, and a typical spatial scale of the e-fold decrease in the diffusion coefficient. Theoretical relaxation times of the irregularities as functions of these parameters are analyzed. Calculated relaxation times are compared with the times measured in the observation of the artificial periodic irregularities created by the SURA facility. Calculated relaxation times of these irregularities are in good agreement with the observed values.
PubDate: 2013-10-23

• Features of Propagation of the Acoustic-Gravity Waves Generated by High-Power Periodic Radiation
• Abstract: We present the results of the bandpass filtering of temporal variations of the Doppler frequency shift of radio signals from a vertical-sounding Doppler radar located near the city of Kharkov when the ionosphere was heated by high-power periodic (with 10 and 15-min periods) radiation from the Sura facility. The filtering was done in the ranges of periods that are close to the acoustic cutoff period and the Brunt—Väisälä period (4–6, 8–12, and 13–17 min). Oscillations with periods of 4–6 min and amplitudes of 50–100 mHz were not recorded in fact. Oscillations with periods of 8–12 and 13–17 min and amplitudes of 60–100 mHz were detected in almost all the sessions. In the former and the latter oscillations, the time of delay with respect to the heater switch-on was close to 100 min and about 40–50 min, respectively. These values correspond to group propagation velocities of about 160 and 320–400 m/s. The Doppler shift oscillations were caused by the acoustic-gravity waves which led to periodic variations in the electron number density with a relative amplitude of about 0.1–1.0%. It was demonstrated that the acoustic-gravity waves were not recorded when the effective power of the Sura facility was equal to 50 MW and they were confidently observed when the effective power was increased up to 130 MW. It is shown that the period of the wave processes was determined by the period of the heating–pause cycles, and the duration of the wave trains did not depend on the duration of the series of heating–pause cycles. The data suggest that the generation mechanism of recorded wave disturbances is different from the mechanism proposed in 1970–1990.
PubDate: 2013-10-23

• Evolution of the Spatial Parameters of a Light Pulse During Its Propagation in a Medium with Strongly Anisotropic Scattering
• Abstract: We obtain the equations for determining the spatial moments of the radial distribution of brightness in the pulsed radiation field of a point isotropic source and similar characteristics of the distribution of irradiance from a point unidirectional source on the assumption of strong anisotropy of the scattering indicatrix of a medium and the studied light field. The procedure of analytical solution of these equations is shown. Formulas for calculating the spatial parameters of the light pulse at a given time instant, i.e., the distance between the front edge and the barycenter of the pulse, as well as its characteristic length, are derived. It is shown how and under which conditions the time parameters of the pulse can be determined from its spatial parameters.
PubDate: 2013-10-01

• Resonant Conversion of the Point-Source Field to Multipole Radiation Using Ring Layer of the Overcritical Plasma
• Abstract: We study numerically the two-dimensional problem of excitation of a hollow round cylinder, which is made of a nonmagnetic material with μ = 1 and the negative dielectric permittivity ε < 0, by a filamentary source. It is found that when the relative dielectric permittivity is close to −1, high-Q resonances exist in hollow cylinders having electrically small diameters. We show that when the source of a cylindrical wave is located within the cavity, undirected radiation is converted at the resonance frequency into multipole radiation with a great number of identical lobes in the radiation pattern. The patterns of the near and far fields are calculated. The influence of the loss on the resonance properties is studied.
PubDate: 2013-10-01

• Diffraction of Cylindrical Waves by a Plane-Stratified Structure with a Cylindrical Inclusion
• Abstract: We consider the problem of radiation from an electric-current filament located near the surface of a multilayer plane dielectric structure with a cylindrical inclusion. It is assumed that the penetrable inclusion lies completely within one of the layers and its generatrices are parallel to the current filament. The solution is obtained using the modified zero-field method. The results of numerical simulation and their physical analysis are presented.
PubDate: 2013-10-01

• Kinetic Theory of Radiation from a Point Monochromatic Dipole Source in a Moving Magnetized Plasma
• Abstract: We consider the problem of radiation from a point monochromatic dipole source in the warm electron plasma which is moving with constant velocity along a strong magnetic field. The diagonal permittivity tensor calculated for the magnetized plasma with the Maxwell electron velocity distribution is used to describe the electromagnetic properties of the plasma. The dispersion relation is analyzed numerically and expressions for the field amplitudes in the wave zone are derived. The kinetic description is shown to be necessary for finding the amplitudes of waves whose phase velocities are close to the mean velocity of the plasma motion.
PubDate: 2013-10-01

• Chirp Ionosonde–Radiodirection Finder as a New Tool for Studying the Ionosphere and Radio-Wave Propagation
• Abstract: Hardware of a chirp ionosonde–radiodirection finder, which, along with the conventional parameters, measures angular frequency characteristics on oblique ionospheric sounding paths, is briefly described. The results of the experimental studies of propagation of radio waves on paths of different length and orientation in the natural and artificially disturbed ionosphere are presented. Capabilities of the ionosonde–radiodirection finder for over-the-horizon HF radio detection and ranging of the Earth’s ionosphere on a global scale are shown.
PubDate: 2013-10-01

• Features of the Wave Disturbances in the Ionosphere During Periodic Heating of the Plasma by the “Sura” Radiation
• Abstract: We present the results of observations of the Doppler-spectrum and Doppler-frequency shift variations of the ionosphere-reflected radio signals from a high-frequency vertical-sounding radar when the ionospheric plasma is affected by the high-power periodic radiation of the “Sura” heating facility. The distance from the heater to the Doppler radar is about 960 km. It has been confirmed that high-power radiation leads to the generation (amplification) of wave disturbances in the parameter range of internal gravity waves (periods 10–30 min and velocities 360–460 m/s). Soliton-like wave packets with a period of 10–15 min, a duration of 20–30 min, and a relative amplitude of electron-density perturbations from 3 to 8 % have been detected. The same parameter for other wave disturbances was 1–3 %. It has been confirmed that the generation efficiency of periodic disturbances in the parameter range of internal gravity waves depends significantly on the heater operation regime.
PubDate: 2013-10-01

• The short envelope soliton dynamics in inhomogeneous dispersive media with allowance for stimulated scattering by damped low-frequency waves
• Abstract: We consider the soliton dynamics in terms of the extended nonlinear Schrödinger equation taking into account the inhomogeneous linear second-order dispersion (SOD) and stimulated scattering by damped low-frequency waves (SSDW). It is shown that the wave number downshift due to SSDW is compensated by an upshift due to the SOD decrease on the spatial coordinate. A new class of stationary nonlinear localized solutions (solitons) arising as an equilibrium of SSDW and decreasing spatial SOD is found analytically within the framework of the extended inhomogeneous nonlinear Schrödinger equation. A regime of the dynamic equilibrium of SSDW and inhomogeneous dispersive medium with the soliton parameters periodically varied in time is found. Analytical and numerical results are in good agreement for this regime.
PubDate: 2013-09-29

• On the problem about determination of the sea wave period based on radio altimeter data
• Abstract: We consider the features of backscattering of electromagnetic microwaves during nadir sounding of the sea surface. Combined analysis of radar data and sea buoy information allowed us to refine the connection between the parameters of the waves and the reflected radar signal. It is shown that knowing of the wind velocity and the wave steepness or the slope variance of largescale waves is sufficient to calculate the cross section of the backscattering at a zero incidence angle. Several types of wave periods were used as quantitative characteristics of sea waves. It has been shown that the sea wave characteristics can be retrieved from radio altimeter data. The comparison of the retrieved and measured parameters confirmed the efficiency of the developed algorithms. One can state that the allowance for these data in numerical sea wave models will make it possible to improve the accuracy of numerical modeling of the wave environment. A nonmonotonic dependence of wave periods on the backscattering cross section has been found.
PubDate: 2013-09-29

• Blind synchronization of the OFDM signals in multipath channels on the basis of the time and frequency protection intervals
• Abstract: New methods of symbol-timing and carrier-frequency blind synchronization of an OFDM-signal receiver are developed and studied. They generalize the well-known methods which use either the protection interval in time in the cyclic prefix form or the protection interval with respect to frequency in the form of virtual subcarriers, and are based on their joint application. To reduce the computational complexity, approximate algorithms which are based on the approximation of the optimal rules, but, according to the study results, have almost the same characteristics of parameter-estimation accuracy and the reception bit-error-rate performance are proposed. It is shown that in terms of the parameter-estimation accuracy and the reception bit-error-rate performance, the proposed methods are superior to the well-known methods of synchronization by the cyclic prefix and the virtual subcarriers in the two-path Rayleigh-fading channel. For incoherent systems with the differential phase shift keying variants, using such methods makes it possible to rule out the necessity of accurate synchronization and, due to insignificant redundancy of the system band and the cyclic prefix length, closely approach the reception bit-error-rate performance for perfect synchronization.
PubDate: 2013-09-29

• A new method for acoustic characterization of particulate materials: preliminary results
• Abstract: We describe a new method of measuring acoustic properties of particulate (unconsolidated) materials and present preliminary results of its application to studying artificial granular media. The results demonstrate promising prospects for the new method. Earlier unknown features of a dynamic response of unconsolidated granular medium are revealed. Experimental observations of slow relaxation in such media are performed.
PubDate: 2013-09-29

• Influence Nonuniformity of the Atmospheric Water Vapor Field on the Phase Measurements of Radio Signals from Global Navigation Satellite Systems
PubDate: 2013-07-01

• Calculation of the Derivatives of the Ray Coordinates with Respect to the Initial Parameters in the Inhomogeneous Two-Dimensional Media
• Abstract: We consider the theory of numerical calculation of the fields in inhomogeneous two-dimensional media in the geometrical-optics approximation. Analytical formulas describing transformation of the matrix of the derivatives of the ray coordinates with respect to the initial parameters during the ray reflection from the curvilinear surfaces located in the medium are obtained. The numerically calculated derivatives are compared with those given by the obtained formulas. Asymptotic expressions for the amplitudes of the fields reflected from the large-curvature bodies are derived.
PubDate: 2013-07-01

• Study of characteristics of a short-range multistatic radar system for diagnostics of the dynamic processes
• Abstract: Based on the correlation and ranging methods, we developed an algorithm determining the coordinates of moving sources of wideband noise. The main advantage of this algorithm is the ability to eliminate the ambiguities of determining the target coordinates arising in the multistatic systems. To test the proposed algorithm, a laboratory passive multistatic radar system was designed and assembled. This paper describes the parameters of the experiment conducted using this system. The obtained results are discussed and analyzed.
PubDate: 2013-07-01

• Impedance of a Spacecraft-Borne Antenna in the Magnetospheric Plasma and Quasi-Equilibrium Noise EMF in the Lower-Hybrid Frequency Band
• Abstract: We present analytical and numerical estimations of the value and frequency dependence of the impedance and noise electromotive force (EMF) in the context of the conditions which correspond to the trajectories and parameters of the antennas borne by geophysical monitoring satellites. The estimations were obtained for two circular orbits at altitudes of 600 and 1200 km over the Earth’s surface in the frequency range from 20 to 120 kHz, which corresponded to the area of the lower-hybrid resonance, where a higher level of noise emissions is observed at the altitudes under consideration. It is shown that near the lower-hybrid resonance frequency, the real part of the antenna impedance is determined by the resonant “monopole” loss by radiation of quasipotential waves. In the nonresonant frequency band (at the frequencies below the frequency of the lowerhybrid resonance), the antenna reactance is determined by the transit loss, which is, however, low as compared with the resonant loss. When the noise was calculated, the medium was assumed to be a two-temperature plasma. The spectral density of the power of the noise EMF lies in the range $V_{\omega}^2\approx \left( {2-4} \right)\cdot {10^{-12 }}-{10^{-13 }}\;{V^2}\cdot H{z^{-1 }}$ and is determined mainly by suprathermal electrons. In the nonresonant frequency band, the efficient temperature of noise radiation is equal to the temperature of the “cold” plasma component, and the antenna reactance is determined by the transit loss, i.e., the level of the noise EMF is low as compared with the EMF in the resonant frequency band.
PubDate: 2013-07-01

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