Abstract: We solve the problem of electrodynamic analysis of a complex waveguide resonance diaphragm with an aperture in the form of a rectangular window with two centrally symmetric L-shaped ridges. The properties of the diaphragm are studied on the basis of the analysis of the imaginary part of its normalized conductivity. Critical wave numbers and electromagnetic fields are calculated by the partial region technique allowing for the singularity of the electromagnetic field on metal ribs. It is shown that the imaginary part of the normalized conductivity of the diaphragm as a function of the frequency not only turns to zero, but also contains a discontinuity of the second kind, which corresponds to the parallel and series resonance. PubDate: 2015-12-05

Abstract: We consider the operation principle of a spectral-selective radiometer unit with a bandwidth of up to 1 GHz, which calculates the spectra of the signals received by the antenna in real time with the subsequent exclusion of spectral components at the radio-interference frequencies. The latter allows one to perform radiometric measurements in continuum when exposed to radio-frequency interference without using the filtering methods of its selection in the widedband radiometer receiving channel. Under the radio-interference action, the observation results confirm the high accuracy of the radiometric measurements in continuum, which were conducted using the radio telescopes of the “Kvazar-KVO” complex. PubDate: 2015-12-05

Abstract: We consider the problem of retrieval of the radiated acoustic signal parameters from the measured wave field in some cross section of the nonlinear medium. The possibilities of solving regular and statistical inverse problems are discussed on the basis of the solution of the Burgers equation for zero and infinitesimal viscosities. PubDate: 2015-12-05

Abstract: We propose a new model of a compact intracloud discharge considered as the result of interaction between two (or more) bipolar streamer structures formed in a strong large-scale electric field of a thundercloud. The model assumes two stages of the compact discharge development. At the preliminary stage, two or more bipolar streamer structures appear successively in the thundercloud in the region of a strong electric field (at the boundaries between the regions of the main positive and the main negative electric charges or between the main positive charge region and the top negative screening layer). The time of development of such structures is determined by the characteristics of the conducting channels that form them and can reach tens of milliseconds. Spatiotemporal synchronization of the bipolar streamer structures is provided by the altitude modulation of the electric field, which, in particular, can originate from a large-scale turbulence of the cloud medium or the stream instability. It is shown that a single bipolar streamer structure accumulates significant electric charges of different signs at its ends as it develops. The start of the main stage of a compact intracloud discharge corresponds to the occurrence of the conducting channel (breakdown of the gap) between the mature streamer structures. The electric charge accumulated at the adjacent ends of the structures at this stage is neutralized over a time much shorter than the duration of the preliminary stage. The parameters of the current pulse are in good agreement with the estimates of the current of a compact intracloud discharge which were obtained in the transmission-line approximation. PubDate: 2015-12-05

Abstract: We study nonlinear beams of electromagnetic waves in vacuum. Within the lowest approximation, their structure is determined by the cubic self-focusing nonlinearity, which manifests itself with the maximum intensity in the presence of counterpropagating waves. It is shown that the fields in the beams have no singularities if their power is less than the critical power of the self-focusing. The dependences of the eigenfrequencies of the modes of the quasioptical resonator on the beam power are found. The structure of the fields of these modes corresponds to self-similar wave beams. PubDate: 2015-12-05

Abstract: A method for estimating the characteristics of the delayed coupling between the oscillatory systems, which is based on the empirical simulation of the phase dynamics with allowance for the phase-noise correlatedness, is proposed. The method efficiency is illustrated FOR the standard stochastic and chaotic oscillators in numerical experiments. Using this method for analyzing climatic time series, we confirm the presence of the delayed influence of the El Niño Southern oscillation on the North Atlantic Oscillation. PubDate: 2015-12-05

Abstract: We describe multitip field emitters with protective coatings, which were developed in Peter the Great St. Petersburg Polytechnic University. The coatings ensure long-term operation of the emitters under high currents and technical vacuum. Innovative multi-layer emitters composed of contacting nanolayers of materials with different work functions are presented as well. The possibility by using the developed emitters in high-voltage electronic devices is demonstrated. PubDate: 2015-12-05

Abstract: We consider the problem of determining the type of modulation of radio signals with the a priori unknown parameters. A new criterion for distinguishing between the frequency-shift keyed and phase-shift keyed signals is proposed. Replacing the conventional criterion by the proposed one allows one to improve the interference immunity of many existing algorithms for determining the modulation type. PubDate: 2015-12-05

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: 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