Abstract: We study the diurnal dynamics of the broadband spectral maximum in the polarization parameter spectra of ULF background noise. According to the monitoring data of 2009–2012, changes in the diurnal dynamics of the broadband spectral maximum (BSM) were detected in the increasing solar activity period at the Novaya Zhizn’ midlatitude station. This effect manifests itself in sporadic variations in the center frequency and polarization parameter spectrum during the day. Analysis of ionosonde measurement data shows that such changes in the diurnal dynamics of the BSM are usually not related with the electron number density variations at the ionospheric F-layer maximum. It is found that numerical calculations of the background noise polarization parameter based on the IRI-2007 model cannot explain the sporadic change in the BSM in the polarization parameter spectra. PubDate: 2013-05-12
Abstract: We propose an algorithm for determining the PSK-signal type from a short sample under the conditions of absence of information on the center frequency and modulation rate. The algorithm is based on the analysis of averaged characteristics of the spectrum of a signal and its even powers. PubDate: 2013-05-12
Abstract: We present an approximate method of performing the Fourier transform of the data sampled in nonequidistant readouts. It is shown that the data can be recalculated as equidistant readouts by using a nonuniform convolution, i.e., convolution of a certain function whose form depends on the calculated element and the character of nonequidistance. Thus, this recalculation does not require calculation of the values of the initial data in intermediate readouts (unlike the linear approximation, spline, or other recalculations). Since the size of the kernel of this nonuniform convolution is about 9, the proposed method can be the basis for an efficient computational algorithm. Applicability of the proposed approach to spectral optical coherence tomography is demonstrated. PubDate: 2013-05-12
Abstract: We consider the problem of propagation of the radiation from a point unidirectional source in a scattering medium with a spatially inhomogeneous refractive index. A scheme for numerical solution of the radiative transfer equation with isolated singularities of forward and backward fluxes is proposed. It is demonstrated that analytical solution of the problem is possible in the small-angle approximation, within the framework of which the numerical calculations of the angular distribution of intensity are also performed with allowance for the variances of the scattered-radiation propagation path lengths. PubDate: 2013-05-12
Abstract: We study the dynamics of the formation of an intense magnetic flux tube (IMFT) from the background magnetic field by a converging plasma flow with nonlinear magnetic diffusion due to the Cowling conductivity. We confirm the formation of a stationary profile of the magnetic field that was obtained earlier and estimate its onset time. We also consider relaxation of the background field inhomogeneities in the course of their advection into the magnetic flux tube. In the case of nonzero projection of the electrical current on the magnetic field, we found a new mode of the field inhomogeneity relaxation in plasmas with a highly anisotropic resistivity tensor. In this mode, unlike the case of absence of currents along the magnetic flux tube axis, which was studied earlier, an impulsive component of the magnetic energy release is observed, and the magnetic field outside the impulsive component is nearly force-free. A qualitative description of this phenomenon is proposed, analytical estimates are given, and the results of numerical calculations are presented. PubDate: 2013-05-12
Abstract: We present the results of experimental study of the mechanisms of interaction of nonstationary electron beams with magnetized plasma under conditions where typical durations τ of electon bunches satisfy the relation f
LH ≪ 1/τ < f
c < f
p, where f
LH is the lower-hybrid frequency, f
c is the electron-cyclotron frequency, and f
p is the plasma frequency. It is demonstrated that the electromagnetic responses occurring in the magnetized plasma due to the intrusion of such beams are transported by whistler-mode waves. It is shown that these responses are of different nature. Namely, the transition radiation occurring in the vicinity of the point of injection of the pulsed beam into the plasma is a packet of quasi-longitudinal whistler-mode waves, while the electromagnetic response excited in a rarefied plasma is due to the Čerenkov resonance with the pulsed beam. PubDate: 2013-05-12
Abstract: We describe the properties of microwave slot radiators and antennas on their basis which form directional radiation for all-around or sector surveillance. Experimentally obtained radiation patterns and characteristics of such antennas at frequencies from 8 to 12 GHz are presented. PubDate: 2013-05-12
Abstract: In different fields of physical research, we often meet the problem of distinguishing between bidirectional and unidirectional couplings of oscillatory systems, i.e., mutual influence and one-way influence, on the basis of the observed time series. In this work, it is shown that a widely used approach, based on the calculation of prediction errors of empirical models (Granger causality), may give spurious conclusions on bidirectional coupling if a sampling interval exceeds a certain intrinsic time scale of the studied systems. Taking this effect into account, we propose and illustrate by standard examples a statistical test which allows one to reveal bidirectional coupling with specified confidence probability. PubDate: 2013-05-12
Abstract: We experimentally study the propagation of surface plasmons on a metal foil containing subwavelength structures in the terahertz frequency range. Additional measurements of the transmission spectra through the same structures allowed us to determine the effective dielectric function of the structured layer for the two directions of wave propagation, along and across the film surface. It was shown for the first time that even a thin two-dimensional film of metal with slits may reduce the surface plasmon velocity and enhance the spatial localization of the plasmon field at the surface. PubDate: 2013-05-12
Abstract: We use the self-generation method to study conductivity and temperature of the martensitic transition in the films of Ni52Mn24Ga24 and Ni49.5Mn28Ga22.5. The scheme of self-oscillator construction on the martensitic transition in a Ni49.5Mn28Ga22.5 film is described, and the influence of the magnetic field on the operation of such a generator is studied. PubDate: 2013-02-01
Abstract: We consider an adaptive antenna array (AAA) with the maximum signal-to-noise ratio (SNR) at the output. The antenna configuration is assumed to be arbitrary. A rigorous analytical solution for the optimal weight vector of the AAA is obtained if the input process is defined by the noise correlation matrix and the useful-signal vector. On the basis of this solution, the regularized estimate of the weight vector is derived by using a limited number of input noise samples, which can be either greater or smaller than the number of array elements. Computer simulation results of adaptive signal processing indicate small losses in the SNR compared with the optimal SNR value. It is shown that the computing complexity of the proposed estimate is proportional to the number of noise samples, the number of external noise sources, and the squared number of array elements. PubDate: 2013-02-01
Abstract: We consider specific features of the antipodal propagation of decameter radio waves based on long-range radio-path measurement data. The measurements were carried out at frequencies of 10 and 15 MHz onboard a research vessel when it crossed the antipodal region of the RID universal-time station located near the city of Irkutsk. Reduced multipath-effect band, increased level of received signals in the antipodal region, and details of diurnal variations of the signal amplitude are discussed. PubDate: 2013-02-01
Abstract: We propose a criterion for estimating the experimentally obtained time series for stationarity. The criterion makes it possible to automatically choose in real time the corresponding process of further processing and analyzing the recorded information and, correspondingly, improve reliability of the spectral estimates of a signal. The step-by-step estimation algorithm is presented. PubDate: 2013-02-01
Abstract: We analyze the operation of an oceanographic cross-track interferometric synthetic aperture radar and present estimates of the signal-to-noise ratio in the obtained interferograms. It is shown that after filtering additive phase noise, the interferograms allow one to restore the profile of a sufficiently large-scale part of water-surface roughness. The criterion of large-scale roughness is determined mainly by the ratio R/V of the oblique distance R to the velocity V of a carrier of the interferometric synthetic aperture radar, as well as by the character and propagation direction of the surface roughness. PubDate: 2013-02-01
Abstract: We propose an approach to recover the carrier frequency of phase-shift-keying (PSK) signals on the basis of digital adaptive filtering. The structures of the frequency-recovery schemes in the cases of 2-PSK and 4-PSK signals as well as the universal scheme are presented. The results of studying of the dependence of the scheme synchronization rate on the initial frequency mismatch and the signal-to-noise ratio as well as the results for interference immunity study of the schemes in the problem demodulation of PSK-signals are reported. Comparison with the classical counterparts is performed. PubDate: 2013-02-01
Abstract: In this series of papers, we propose a method for development of an approximate solution of the Maxwell equations in smoothly inhomogeneous anisotropic gyrotropic media with allowance for aberrations, spatial dispersion, and absorption. Evolution equations for wave beams are obtained, and a method for their numerical solution is developed. The relation of the quasi-optical evolution equation to the aberration-free equation for wave beams is shown, and a general solution to the latter equation is found. The applicability conditions for the aberration-free equation have been written explicitly. Methods of allowance for dissipative aberration effects within the framework of the nonaberrational approximation are described. PubDate: 2013-02-01
Abstract: Increasing the number of sea-wave parameters measured by radar methods raises the problem of calibration of new processing algorithms by using contact measurement data. A new instrument named an underwater acoustic wave gauge is proposed for the satellite experiments. A feature of the new instrument is the ability to measure exactly the sea roughness characteristics that affect the reflection of electromagnetic waves. Formulas for the Doppler spectrum of the reflected acoustic signal in the Kirchhoff method approximation with allowance for the different patterns of the receiving and emitting antennas are obtained. As a result, a new algorithm for measurement of all second-order statistical moments of sea waves by the modified acoustic wave gauge has been developed. The data obtained in the numerical experiment were processed by the new algorithm. The results confirmed the efficiency of the proposed algorithm and also demonstrated the inefficiency of the previous algorithm when a new configuration of the acoustic wave gauge was employed. PubDate: 2013-01-01
Abstract: We consider the problem of coordinated spatial signal processing at the base stations of modern high-throughput wireless cellular systems using orthogonal frequency division multiplexing (OFDM) and adaptive antenna arrays. In the existing OFDM systems with coordinated multi-point (CoMP) transmission, the user throughput gain is achieved via co-channel interference mitigation by means of coordinated transmit beamforming at the base stations. For such schemes, it is assumed that each base station transmitter is equipped with linear antenna array comprising a set of elements with the same vertical polarization. In this paper, a new approach to spatial coordination is studied using the joint coordination of the signal polarizations at the transmitting base stations whose antenna arrays are made of pairs of mutually orthogonal antenna elements. In this case, co-channel interference mitigation among the base stations is achieved via the adaptive choice of the signal polarization at each transmitting antenna array. An algorithm of coordinated spatial signal processing with polarization selection is proposed in this work and the system throughput is analyzed for the proposed CoMP scheme. PubDate: 2013-01-01
Abstract: The limits of applicability of the method of integral field representation as the double weighted Fourier transform (DWFT) are determined on the basis of an exact path representation for the Green function of the parabolic equation. The estimates we have obtained imply that the DWFT method takes into account the effects of diffraction by inhomogeneities with scales equal to or less than the radius of the first Fresnel zone of a plane wave and can be exploited to solve the inverse problems of retrieval of the inhomogeneous-medium parameters from the data measured in the source and receiver planes. PubDate: 2013-01-01
Abstract: We consider the development of an integrated lens antenna for LAN radio communication systems operated in the 60 GHz frequency band. The antenna is an extended hemispherical silicon lens. On its flat surface, a microstrip antenna element is located. The use of silicon, which has a dielectric permittivity ε = 11.7, as the lens material ensures the maximum range of scanning angles for the minimum axial size of the lens. The approximate analytical formulas, which are used for initial calculations of the lens parameters, allow one to evaluate the basic parameters of the lens antenna integrated with the microstrip antenna element. For further optimizing the parameters of the lens and the antenna element, 3D simulation of the electromagnetic-field distribution was performed. Based on its results, we have developed and manufactured extended hemispherical silicon lenses, which had radii of 6 and 12 mm. The planar microstrip antenna element was manufactured by the low temperature co-fired ceramics (LTCC) technology. The results of simulation and experimental studies of the manufactured prototypes demonstrate that the developed lens antennas has directivities of 17.6 and 23.1 dBi for lenses with radii of 6 and 12 mm, respectively. In this case, the maximum beam deflection angle is achieved, which is equal to 55°, while the permissible decrease in the directivity is no more than 6 dBi compared with the case of a non-deflected beam. The obtained results show that the developed integrated lens antennas can find applications in high-speed radio communication systems operated in the millimeter-wave range. PubDate: 2013-01-01
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