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  Subjects -> ELECTRONICS (Total: 207 journals)
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Radiophysics and Quantum Electronics
Journal Prestige (SJR): 0.362
Citation Impact (citeScore): 1
Number of Followers: 2  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1573-9120 - ISSN (Online) 0033-8443
Published by Springer-Verlag Homepage  [2467 journals]
  • Coherence of Active Noise Interference in Radar Systems with Antenna
           Arrays

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      Abstract: We analyze the coherence degree of active noise interference in radar systems. The entropy of the distribution of eigenvalues of the interference correlation matrix is used as a quantitative measure of the coherence degree of interference. The main factors influencing the coherence of active noise interference are analyzed, namely, the interference spectrum width and the interferenceenvironment nonstationarity due to variation in the angular relations between the antenna-array beam and the interference source in the process of the radar observation. It is shown that the analysis of coherence of an active noise interference allows one to quantitatively estimate the notions of wideband and narrowband interference.
      PubDate: 2022-12-06
       
  • Reflected-Signal Simulator for Tests and Calibration of Synthetic-Aperture
           Radars

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      Abstract: Increasing requirements to modern synthetic-aperture radars leads to a complication of both the radars themselves and the tools for monitoring of the radar parameters. Reflected-signal simulator is designed to check through characteristics of such radars at various stages of the life cycle, starting with the development of components and including regular operation, using the same methods. We describe a device for converting the sounding signals of synthetic-aperture radars to simulated reflected ones. A distinctive feature of the presented device is the ability to simulate point and spatially distributed targets and an arbitrary target environment (a set of observation conditions) for test, calibration, and validation.
      PubDate: 2022-12-06
       
  • Theoretical Analysis of Radiation Properties of X-Ray Free-Electron Lasers

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      Abstract: We perform a comparative analysis of the radiation of X-ray free-electron lasers (FELs) LCLS, PAL-XFEL, SwissFEL, SACLA, FLASH2, and European XFEL, as well as the visible radiation of the LEUTL FEL. The spectral characteristics of the considered FELs with account of all the main losses due to the electron energy spread, diffraction, emittance, and the beam diameter are compared. The results of the theoretical studies agree well with the experimental data available for all the FELs under consideration. The possibility to use and amplify harmonics in X-ray FELs with an adjustable dipole parameter (SwissFEL, LCLS-II, SACLA, FLASH2, and European XFEL) is studied. The advantages of amplifying the self-seed radiation of HLSS harmonics are demonstrated, at which the FEL can be made shorter due to efficient bunching at the harmonic wavelengths in a buncher with a great dipole parameter k of the undulator. The possibility of forced bunching discontinuity between the LCLS-II undulators and its influence on the third harmonic amplification are studied theoretically. Comparative analysis of the parameters of radiation, electron beams, and undulators of the considered FELs in various operation regimes is performed.
      PubDate: 2022-12-06
       
  • Calculation of Noise at the Output of a Phased Antenna Array in a Randomly
           Inhomogeneous Waveguide

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      Abstract: We develop models of the formation of additive sea noise and surface reverberation at the output of a phased vertical antenna placed in a plane-layered waveguide with a two-dimensional variabledepth bottom. The study is performed within the framework of geometrical acoustics. The noise calculations are performed for various types of refractive waveguides under conditions of coastal waters. The results of the studies allow one to conclude that the maximum contribution is ensured by the shallow-water areas concentrated near the radiating and receiving antennas. The directions of the main lobes of the antenna patterns also play a significant role during the noise formation.
      PubDate: 2022-12-06
       
  • Scattering of an Electromagnetic Wave by a Structure Consisting of Several
           Perfectly Conducting and Dielectric Finite-Length Thin Cylinders

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      Abstract: We generalize a variant of the auxiliary-source method, which was proposed earlier for solving the problem of electromagnetic-wave scattering by a structure consisting of several dielectric finitelength thin cylinders to the case where, along with the dielectric thin cylinders, the structure contains several perfectly conducting thin cylinders. The specially developed computer code is briefly described. The results of calculating the scattering cross sections of certain particular structures are presented.
      PubDate: 2022-12-06
       
  • The Formation of Large-Scale Plasma Disturbances Upon HF Ionosphere
           Heating: Dependence of the Disturbance Parameters on the Frequency and
           Power of HF Radiation

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      Abstract: We study the dependence of the parameters of large-scale plasma inhomogeneities upon HF ionosphere heating on the frequency and power of HF radiation by using a modified SAMI2 model for numerical simulations. It is shown that the variation of the plasma density profile in the F region due to heating results in a strong dependence of plasma density disturbances on the frequency and power of HF radiation. We also analyze the effect of the Joule absorption in the lower ionosphere on the formation of large-scale inhomogeneities.
      PubDate: 2022-12-06
       
  • Correction to: Quasi-Optical Sub-Doppler Lamb-Dip Spectrometer

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      PubDate: 2022-11-02
      DOI: 10.1007/s11141-022-10195-y
       
  • Antireflection Coating of a Dielectric Plate in the Microwave Band Using
           Surface Machining

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      Abstract: We present the experimental results of measuring the reflection coefficient of a microwave output window made of radiation-modified fluoroplast (Raflon™) with antireflection coating made by using surface machining. The quarter-wave antireflection coating was created by drilling shallow holes in a high-density hexagonal pattern over the plate surface. The Maxwell Garnett formula was used to estimate the value of the effective dielectric permittivity of the periodic structure, since this formula is the most suitable for approximation of effective properties of cylindrically shaped inhomogeneities. The dielectric permittivity of such a structure in the transverse direction corresponds to the value optimal for increasing the window transparency in the specified frequency range. It is found experimentally that the reflection coefficient in the band 120–140 GHz does not exceed −20 dB. The obtained results are compared with the theoretical calculation and numerical analysis in the CST Studio Suite.
      PubDate: 2022-11-01
      DOI: 10.1007/s11141-022-10194-z
       
  • Development of a Polarization Jet and Plasma Drifts in the Ionospheric F
           Region

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      Abstract: We consider Doppler measurements at the Yakutsk subauroral ionospheric station in the periods of the formation and development of a polarization jet above the observing station. It is shown that the times at which the vertical and horizontal velocities of the plasma drift reach their maximum values may not coincide. Comparison of ground-based measurements when observing a polarization jet and calculation of the model of a high-latitude ionosphere demonstrate that the presence of mismatched peaks of the vertical and horizontal components of the plasma drift velocity at the altitudes of the F2 layer leads to different variations in the basic parameters of the layer. It was found that in some cases, before the formation of a polarization jet, an increase in the critical frequency of the F2 layer is observed. A decrease in the ion recombination rate due to an increase in the height of the layer maximum and, consequently, accumulation of ions at these altitudes, is a possible explanation for this behavior. Such an increase in the critical frequency of the F2 layer may be an additional signature of the development of a polarization jet above the observing station.
      PubDate: 2022-11-01
      DOI: 10.1007/s11141-022-10189-w
       
  • Simulation of Spatial Coherence of a Multimode Signal and Response of a
           Horizontal Antenna in a Randomly Inhomogeneous Oceanic Waveguide

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      Abstract: We present simulation results for the spatial-coherence function of a multimode acoustic signal from a remote source in the horizontal plane of a randomly inhomogeneous oceanic waveguide and the angular response of the phased antenna to such a signal to estimate quantitatively the influence of the basic physical factors of the signal-field formation at the antenna input. The simulation was performed in a wide parameter range on the basis of a sufficiently general heuristic model, according to which the signal is the superposition of a finite number of plane waves with random complex amplitudes. It is shown that the most important factors include the spectrum of the longitudinal wave numbers of the normal waveguide modes, the total number and the spectrum of the intensities of the signal modes, and the mutual correlations of the mode amplitudes. Depending on the type of the wave-number spectrum, the influence of the mode-intensity spectrum turns out to be significantly different, which is indicative of the important role of the deterministic properties of the waveguide in the formation of the coherence function and the coherence scale as well as the related distortions of the antenna response to the signal compared with the case of an unbounded space. The physical interpretation of the results, which allows one to make predictive estimates of the considered characteristics in the presence of a priori information on the above-mentioned factors of the received-signal propagation, is given.
      PubDate: 2022-10-27
      DOI: 10.1007/s11141-022-10192-1
       
  • On the Possibility of Dust Grain Destruction by the Coloumb Explosion in
           Protoplanetary Disks

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      Abstract: We consider the dust charging processes in protoplanetary disks. It is shown that in the atmosphere of a disk, grains can acquire anomalously high positive charges, which can lead to their destruction as a result of the Coulomb explosion. The charging is due to the combined effect of radiation from a protostar and of electron and ion currents from the surrounding plasma. For typical protoplanetary disk conditions, such a process turns out to be effective both for porous dust grains of micron sizes and for submicron crystalline grains. Critical charges that are necessary for the destruction of dust grains and the charges acquired by the particles are found for their different sizes and various parameters of the dusty plasmas. Critical grain sizes as functions of the distance to the host star are calculated. It is shown that the Coulomb explosion leads to the appearance of a cascade of crushing of large dust grains. The character of the dependence of crushing conditions on the dust particle radius can lead to the formation of a bimodal grain size distribution in some areas of protoplanetary disks. One fraction corresponds to large particles that are not subject to destruction and the other, to small particles of submicron size.
      PubDate: 2022-10-27
      DOI: 10.1007/s11141-022-10188-x
       
  • Experimental Determination of Aerosol Particle Sizes Using Supercontinuum
           Radiation and Estimation of the Directional Pattern of Radiation from the
           Filamentation Region of Femtosecond Pulses

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      Abstract: According to the results of studying the interaction of high-power femtosecond pulsed radiation from a titanium–sapphire laser with the aerosol particles of an aqueous solution of NaCl, we estimate the directional pattern of Na emission from the filamentation region. It has been found that this directional pattern is characterized by minima in angular directions of 0° and 180° and a maximum in an angular direction between 20° and 160°. Based on the results of recording of supercontinuum radiation formed in the air and scattered by aerosol particles, the features of the aerosol particle size distribution have been determined. Gradient optimization methods using graphic processors were employed to speed up calculations. The neural network was used as an optimization method.
      PubDate: 2022-10-27
      DOI: 10.1007/s11141-022-10190-3
       
  • Influence of a Reactive Power on the Dynamics of an Ensemble of
           Oscillators Simulated by the Phase Equations with Inertia

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      Abstract: We study the simplest artificial model of a power-network operation. The original model has a ring topology consisting of locally coupled power generators alternating with power consumers. Each node of the network is represented as a phase oscillator such as the Kuramoto oscillator with inertia. The network dynamics equations are transformed in accordance with the method of effective network model proposed in [1] and are numerically studied. The purpose of the work is to analyze the possible regimes of the nonuniform-network behavior in the presence of a reactive power in the system. We also study the joint influence of the reactive power and nonlinear dissipation of oscillators. The coefficient of inertia, which is the same for all oscillators, and the reactive power of one of the oscillators are considered as the network control parameters. The regime maps on the plane of control parameters, which were obtained for constant and nonlinear dissipation of the oscillators, are compared. The results show that the reactive power complicates the network behavior and reduces the phase-locked region. On the contrary, the nonlinear dissipation has a positive effect, leading to synchronization of the network oscillators even in the presence of a reactive power.
      PubDate: 2022-10-27
      DOI: 10.1007/s11141-022-10193-0
       
  • Self-Action of Ultrashort Pulses in the Self-Similar Regime

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      Abstract: We study the specific features of the evolution of spatially confined pulses with a finite amplitude and a duration of several periods of wave field oscillations both analytically and numerically. The initial equation, which describes propagation of a reflectionless ultrashort pulse, is transformed to a nonautonomous modified Korteveg-de-Vries equation after passing over to self-similar variables. In this simpler equation for the self-similar function, the dynamics of the internal structure of the wave field is determined by the competition of “dispersion” and cubic nonlinearity only. The evolution of pulses in the directions of the increasing and decreasing nonlinearity is separately considered. Numerical simulation of the problem has demonstrated that: i) the energy center of the wave packet moves nonuniformly along the propagation path, ii) a dispersion shock wave consisting of a set of solitons is excited in the rear part of a pulse propagating in the direction of increasing nonlinearity in the process of the dispersion spreading, and iii) the evolution of the pulses propagating in the direction of decreasing nonlinearity is also accompanied by excitation of a breather soliton.
      PubDate: 2022-10-27
      DOI: 10.1007/s11141-022-10191-2
       
  • Use of Carbon-Based Composite Materials with Anisotropic Conductivity for
           Creating Microwave Antennas

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      Abstract: We develop and test engineering solutions aimed at creating antenna devices made of carbonbased composite materials and operated in various intervals of the microwave range. The main electromagnetic characteristics of the antennas in this range are computer simulated and studied experimentally. The influence of the anisotropy of the material conductivity on the parameters of horn antennas is studied. Feasibility of using materials with anisotropic conductivity for creating antenna devices with given radio-frequency characteristics is demonstrated.
      PubDate: 2022-10-08
      DOI: 10.1007/s11141-022-10186-z
       
  • Microwave and Lidar Measurements of Ozone and Temperature Variations
           during Stratospheric Warmings of 2012–2015

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      Abstract: We present the results of joint observations of ozone and temperature in the middle atmosphere above Tomsk in December–January 2012–2013 and in December–February 2014–2015 during stratospheric warmings. The results of simultaneous microwave observations of ozone in Peterhof (60° N, 30° E) and Tomsk (56° N, 85° E) in the winter of 2013–2014 are also given. Ground-based microwave radiometry and laser diagnostics were used in the observations. Microwave radiometry and lidar technology allow us to study ozone and temperature variations during large-scale wave disturbances in the middle atmosphere such as stratospheric warming.
      PubDate: 2022-10-07
      DOI: 10.1007/s11141-022-10182-3
       
  • Capability of Bistatic Radar Systems to Solve the Problem of Detection of
           Potentially Hazardous Celestial Objects

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      Abstract: We analyze the capabilities of bistatic multipositional facilities with correlation signal processing for the purposes of enhancing significantly the efficiency of radar systems in detecting celestial objects which are potentially hazardous for the Earth, specifically, asteroids, comets, and large fragments of space debris. In particular, we consider radar systems using the forward scatter radar method, which is based on a significant increase in the bistatic efficient reflective area of the target independently of its shape and material in the case of forward scattering of the probing signal. The possibility to use natural radio sources as probing emitters is considered. The efficiency of two variants of ground-based space radar for both detection of celestial objects and monitoring of space hazards is estimated for further promising research developments.
      PubDate: 2022-10-07
      DOI: 10.1007/s11141-022-10187-y
       
  • Quasi-Optical Sub-Doppler Lamb-Dip Spectrometer

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      Abstract: We describe a new sub-Doppler spectrometer with an enlarged gas cell, which was created at the IAP RAS for high-precision laboratory measurements of molecular transitions at millimeter and submillimeter wavelengths in the interests of radio astronomy. By using a larger diameter with a shortened cell length, a calibrated attenuator for radiation power adjustment, and synthesizers with lower phase noise, it was possible to eliminate a number of shortcomings of the previous spectrometer and not only to measure with high accuracy the transition frequencies of a number of molecules taking into account hyperfine splitting, but also to study their shifts due to both pressure and radiation power. In particular, information about precise frequencies will be used to examine the inner dynamics in the star-forming regions, and also to search for variations of fundamental constants. The principle of frequency-independent cell-aperture irradiation was employed when the optical scheme of the spectrometer was designed. The examples show Lamb-dip measurements of the hyperfine structure in the CH3CN and HNCO molecular lines.
      PubDate: 2022-10-07
      DOI: 10.1007/s11141-022-10185-0
       
  • Determination of Integrated Water Vapor and Liquid Water Contents from the
           Measurements of Microwave Atmospheric Radiation

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      Abstract: We present an overview of the results of our studies in the field of using the radiothermal-detection method for determining the integrated water vapor content in the atmosphere and the integrated liquid water content in the clouds, as well as a general overview of modern achievements in this field. The possibilities of determining the atmospheric integrated water vapor content and the integrated liquid water content of the clouds are shown for particular examples using the ground-based measurements of the microwave atmospheric radiation simultaneously at the frequencies 22.235 and 36.000 GHz (near the water-vapor absorption line). The possibility is shown of detecting the regions of high content of liquid water in an upper overcooled part of the powerful convective clouds and using the microwave measurements for predicting dangerous weather events including thunderstorms. The prospects of using the radiothermal-detection method in meteorology on the basis of the radiophysical complex of Lehtusi Geophysical Observatory are discussed in relation to improving the technology of regional very short-term forecast (with a lead time of 2–12 h) of dangerous phenomena caused by the development of clouds and precipitation.
      PubDate: 2022-10-07
      DOI: 10.1007/s11141-022-10183-2
       
  • Dust Temperature Profiles in Dense Cores Related to the High-Mass
           Star-Forming Regions

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      Abstract: We obtained continuum maps at a wavelength of 350 μm for eight gas–dust clouds from the southern hemisphere using the APEX-12m telescope. The clouds are related to the regions of the formation of high-mass stars and star clusters and have dense cores. The core sizes estimated at half the maximum intensity at a wavelength of 350 μm are 0.1–0.2 pc. The core masses and gas mean densities lie in the ranges 20–1000 Mʘ and (0.3–7.3)·106 cm−3, respectively. A comparison of the obtained data at a wavelength of 350 μm with observation data of the same objects at a wavelength of 1.2 mm was carried out. From the intensity ratios at two wavelengths reduced to one angular resolution, the spatial distributions of the average dust temperature on the line of sight are calculated. Dust temperature maps in most objects correlate with intensity distributions at a wavelength of 350 μm. A decrease in the dust temperature with distance from the center is detected in most cores. The obtained dust temperature profiles in most cases turned out to be close to linear ones. Using a simple spherically symmetric model of a dust cloud, it is shown that temperature profiles close to the observed ones can be obtained under the assumption of the presence of an internal source by varying the density profile parameters and specifying a powerlaw index β of the dust emissivity dependence on frequency as a constant. It is shown that the dust temperature estimates strongly depend on the chosen value of β. It is considered how possible variations of β in the cloud can affect the results obtained.
      PubDate: 2022-10-07
      DOI: 10.1007/s11141-022-10184-1
       
 
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