Abstract: We propose a modification of the known method used to synthesize frequency time radio images in non-radiating radars and based on minimization of the r.m.s. deviation of the observation data vector from its linear model with an additional limitation imposed on the L1 norm of the vector of the evaluated amplitudes of two-dimensional signal distribution in the range of delays and Doppler frequencies. The essence of the modification is that instead of solving the problem of conditional minimization at a full array in the “time delay—Doppler frequency shift” coordinates, this problem is solved sequentially for the zeroth and a preset frequency shift. In combination with additional computational tricks, the proposed modification allows one to increase the computational efficiency of image formation by three orders of magnitude. PubDate: 2015-11-21

Abstract: We develop a combined method for calculating the characteristics of the integrated lens antennas for millimeter-wave wireless local radio-communication systems on the basis of the geometrical and physical optics approximations. The method is based on the concepts of geometrical optics for calculating the electromagnetic-field distribution on the lens surface (with allowance for multiple internal re-reflections) and physical optics for determining the antenna-radiated fields in the Fraunhofer zone. Using the developed combined method, we study various integrated lens antennas on the basis of the data on the used-lens shape and material and the primary-feed radiation model, which is specified analytically or by computer simulation. Optimal values of the cylindrical-extension length, which ensure the maximum antenna directivity equal to 19.1 and 23.8 dBi for the greater and smaller lenses, respectively, are obtained for the hemispherical quartz-glass lenses having the cylindrical extensions with radii of 7.5 and 12.5 mm. In this case, the scanning-angle range of the considered antennas is greater than ±20° for an admissible 2-dB decrease in the directivity of the deflected beam. The calculation results obtained using the developed method are confirmed by the experimental studies performed for the prototypes of the integrated quartz-glass lens antennas within the framework of this research. PubDate: 2015-11-21

Abstract: We develop and test (in numerical simulation) methods of computer tomography of distributed under-surface inhomogeneities in the conductivity of a medium and for holography (i.e., reconstruction of the shape) of solid and uniformly composed subsurface objects in the context of the problems of multifrequency electromagnetic diagnostics of the Earth’s crust structure in the extremely and ultra low frequency bands. The methods are based on solution of the inverse scattering problem using the results provided by multifrequency measurements of the distribution of complex amplitudes of the electromagnetic field on the surface of the medium under consideration. PubDate: 2015-11-19

Abstract: We present the results of the first simultaneous ground-based microwave measurements of the middle-atmosphere ozone and temperature performed at the beginning of 2012 above Nizhny Novgorod (56 N, 44 E) during a sudden stratospheric warming. The detected features of the atmosphere dynamics are compared with satellite sounding data from an MLS instrument onboard the Aura satellite. PubDate: 2015-11-19

Abstract: We present the results of observations of the Doppler frequency shift for the radar radio signals of broadcast and exact-time RWM stations, which are scattered by small-scale artificial ionospheric irregularities. By the method described in our previous paper [1] and using the multifrequency HF Doppler radar, estimates were made for a three-dimensional vector of the drift velocity of irregularities. It is shown that the drift velocity of irregularities can vary considerably both in magnitude and direction for short periods of time. The velocity lies in a wide range of values, 20–270 m/s, but sometimes it exceeds 500–700 m/s. The most probable drift velocity ranges from 40 to 70 m/s. PubDate: 2015-11-19

Abstract: We present the first results of the joint Russian–Ukrainian experiments for recording of signals from the EKB radar of the Institute of Solar–Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences (Arti observatory of the Institute of Geophysics of the Ural Branch of the Russian Academy of Sciences, Sverdlovsk region, Russia) at a distance of over 1600 km by using a coherent receiving system and a high-gain phased array of the UTR-2 radio telescope (S.Ya. Braude Radioastronomical Observatory (RAO) of the Institute of Radio Astronomy of the Ukrainian National Academy of Sciences (IRA UNAS), Kharkov region, Ukraine). It is shown that two pulse sequences that are identical to the transmitted EKB radar signal, but arrive with different delays were observed at the reception point. The sequence which was received first corresponded to the direct-signal propagation along the great-circle arc. The second sequence was received with delays corresponding to a path length of 2800 to 3400 km and was the result of scattering of the transmitted radar signal by high-latitude ionospheric irregularities. The Doppler frequency shift of the scattered signal was range-dependent and varied from −3 to +4 Hz, which corresponded to the radial component of the ionospheric irregularity velocity from −43 to +58 m/s. To interpret the results of the experiments, we numerically simulated the signal propagation based on the actual ionospheric conditions at an appropriate time. Ionospheric characteristics were retrieved by the vertical ionospheric sounding technique, with the ionosonde located in close proximity to the EKB radar. Comparison between monostatic radar diagnostic results and bistatic sounding results has shown a good agreement of the retrieved parameters of the high-latitude ionospheric irregularities. PubDate: 2015-11-19

Abstract: We present a statistical model of the mixture of background noise and spectrally lumped interference. Such a mixture is realized in the case of wideband reception of a high-frequency signal with chirp modulation over the entire decameter-wave range. The types of the probability distributions statistically describing the random noise and interference, as well as their sum in the time and frequency domains, are established. The level of lumped interference with respect to noise is estimated using the signal-envelope parameters and a method of the useful-signal isolation in the power spectrum on the basis of describing the noise and interference sum by the Weibull distribution is proposed. PubDate: 2015-11-19

Abstract: We model numerically propagation of a stationary ionization wave oppositely to an incident plane electromagnetic wave within the frameworks of the simplest model which allows for gas ionization by an electron impact, attachment of electrons to neutral molecules, and plasma diffusion. The calculations are performed within the approximation of the self-consistent field allowing for the reflection of the electromagnetic wave from the plasma. The characteristics of ionization waves are found in a wide range of such parameters as the gas type, gas pressure, and frequency and amplitude of the incident electromagnetic wave. PubDate: 2015-10-29

Abstract: We develop the maximum-likelihood algorithm for detecting a radio signal with an arbitrary envelope shape, which is observed against the background of additive Gaussian white noise. The signal duration, amplitude, and initial phase are unknown. The developed algorithm is analyzed on the assumption of sufficiently large signal-to-noise ratios. Asymptotic expressions for the detection-error probabilities are obtained. The developed-algorithm efficiency is checked by computer simulation and the applicability range of the obtained asymptotic expressions for the algorithm characteristics is determined. PubDate: 2015-10-29

Abstract: We propose a method for calculation of the charge distribution along a short (on the wavelength scale) cylindrical antenna in an anisotropic medium and the impedance of the antenna. The method is based on the solution of the corresponding integral equation by using a “thin” antenna approximation for different angles of antenna orientation relative to the anisotropy axes of the medium. The calculation results coincide with the results obtained earlier by other methods if the antenna axis is not too close to the direction of the asymptote of an open wave-vector surface. The case where the antenna is oriented along this asymptote, in the vicinity of which the angular dependence of the real and imaginary parts of the impedance changes abruptly, is considered in detail. PubDate: 2015-10-29

Abstract: In this theoretical paper, we propose a method for measuring the temperature profile in the active topsoil of the Arctic tundra using observations of the brightness temperature for two different polarizations of the radiation at frequencies of 1.4, 6.93, 7.3, and 10.7 GHz. A multifrequency physical model of microwave emission of bare soil, a dielectric model of the Arctic tundra soil, and temperature profiles, which were measured in the active topsoil at the Toolik field station on the Alaska North Slope, were used to calculate the observed values of the brightness temperature. Temperature profiles were retrieved from the observed values of the brightness temperature in the approximation of a piecewise-linear profile of topsoil temperature during 2010–2011. Correlation analysis of the temperature profiles measured at the Toolik station and retrieved from the radiometric data has shown that in winter the error of measurement of the soil temperature at depths of 0.6 and 16.0 cm in terms of the variance (correlation coefficient) does not exceed 2.3 (0.98) and 7.2 (0.62°C), respectively. In summer, the error of measurement of the soil temperature using the radiometric method is two times less than in winter. PubDate: 2015-10-29

Abstract: The method of calculating the total drift velocity vector of small-scale artificial ionospheric irregularities as measured by the effective Doppler frequency shift of aspect-scattered signals from several diagnostic illumination transmitters operated at different frequencies is discussed. The technique of adaptive simulation of decameter radio waves propagating in an inhomogeneous magnetized ionosphere with allowance for the aspect scattering effects due to small-scale field-aligned irregularities is developed. A multifrequency HF Doppler radar for simultaneous measurement of the Doppler spectra of radio signals at a set of frequencies is described. PubDate: 2015-10-29

Abstract: We estimate the ohmic losses in the case of scattering of a plane electromagnetic wave by a metal corrugated surface. Comparative analysis of the losses is performed for different regimes of wave incidence and scattering (self-collimation and different incidence angles), and their dependence on the amplitude and shape of the corrugation profile is studied. The study is based on numerical solving of the integral equation which describes the diffraction of a plane electromagnetic wave by a corrugated interface between two dielectrics. Metal is regarded as a dielectric with purely imaginary dielectric permittivity of a great value which is determined by metal conductivity. The waves with E polarization (i.e., the waves with the electric-field vector directed along the grooves), which are used in echelette gyrotron cavities, are studied in detail. PubDate: 2015-10-29

Abstract: We consider the issue of small observation samples in the problem of spectral analysis of the random time series. It is proposed to solve the considered problem using the information-theoretic approach and a new algorithm based on the principle of minimum divergence of the cognominal spectral estimates yielded by the results of several independent observations in the Kullback–Leibler information metric. An example of a practical realization of the algorithm is considered and its asymptotic properties are studied. PubDate: 2015-10-29

Abstract: We propose a new method for determining the wind-velocity vector above the ocean surface using the data of a polarimetric synthetic aperture radar. The preliminary calculations show that for wind waves, the location of the maximum in the radar image is unambiguously related to the wind velocity, whereas the wind direction is retrieved with an uncertainty of 180°, which is related to the central symmetry of the image spectrum. To eliminate the ambiguity when determining the wind direction, a criterion based on the information on the sign of the coefficient of correlation among the complex signals on the co- and cross polarizations is used. It is shown that using the polarimetric radar, it is theoretically possible to obtain information on both the wind velocity and direction without exact radar calibration. PubDate: 2015-09-26

Abstract: We present for the first time the experimental data on the frequency of ion–neutral collisions at the altitudes of the ionospheric E layer, which were obtained by the method of resonance scattering of the radio waves by artificial periodic irregularities of the ionospheric plasma. The measurements were carried out in different time periods from 1990 to 2012. Time and altitude dependences of the collision frequency are given. The dependence of the collision frequency on the solar and geomagnetic activity has been analyzed. PubDate: 2015-09-26

Abstract: We introduce the notion of a quasi-ellipsoidal three-dimensional optical pulse beam with a diffuse boundary and solve the problem about its propagation in free space. The quality of the diffracted pulse is characterized by two parameters responsible for distortions in the transverse intensity distribution and blurring of the entire pulse. Imposing constraints on these parameters, one can find the maximum distance which the pulse can propagate without critically strong distortions and, consequently, determine the required accuracy of the longitudinal positioning of the elements of the optical scheme which transmits the pulse. PubDate: 2015-09-26

Abstract: We have developed and tested experimentally a method for measuring optical wave fields, which is based on diffraction of the optical wave field at two complementary screens. An optical scheme of the experimental setup, which implements this method, has been developed, as well as the experimental procedure used to measure the phase of the optical wave field. The main parameters of the method, such as accuracy and spatial resolution, were studied experimentally. The developed optical scheme was calibrated, which allowed eliminating the systematic error of phase measurements introduced by the scheme elements. PubDate: 2015-09-26

Abstract: Using the process model, we describe the phase, amplitude, polarization, and spatial characteristics of the parametric scatterer. The mathematical model of the parametric scatterer, which is developed on the basis of its equivalent circuit, is also discussed. The relation between the parameters of the process and mathematical models of the parametric scatterer is shown. The transient processes during simultaneous action of the pump- and synchronization-signal radio pulses on the parametric scatterer are studied. We show that it is expedient to use the synchronization radio pulse at the reply-signal frequency not only for disambiguation of the initial phase of the reply signal, but also for quick excitation of the parametric circuit. PubDate: 2015-09-26