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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  [2469 journals]
  • Brightness Fluctuations of the Sunny-Path Image Depending on the Sharpness
           Setting of the Observation-System Lens

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      Abstract: We theoretically study the variation coefficient of the solar radiation reflected from a wavy sea surface as a function of the range to which the observation-system lens is focused. During the study, we revealed the possibility of existence of two different regimes of the received-signal fluctuations, namely, the single- and double-hump dependences of the variation coefficient on the lens-adjustment range. The effect of splitting one maximum of the variation-coefficient dependence on the range into two maxima is explained within the framework of simple optical models.
      PubDate: 2022-03-29
      DOI: 10.1007/s11141-022-10147-6
       
  • Using the Maximum-Likelihood Method for the Angular Resolution of the
           Signal Sources in Multibase Phase Direction Finders

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      Abstract: We show that the angular resolution of the signal sources in the phase direction finders with the antenna systems in the form of linear arrays of the weakly directional elements can be reached by determining the own set of full periods of the phase difference, which are lost during the measurements, for each source. It is established that the maximum-likelihood method, which has been developed for estimating the arrival of one signal, can be used for the angular resolution of the signal sources. We show the generality of the basis for the angular resolution using the maximum-likelihood method and the method of summation of cosine functions. The estimates of the accuracy of the received-signal direction finding are given.
      PubDate: 2022-03-29
      DOI: 10.1007/s11141-022-10152-9
       
  • Superdirective Acoustic Imaging with the Use of Flexible Microphone Arrays

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      Abstract: We consider the problem of spatial localization of a set of sound sources using flexible microphone antenna arrays. At the beginning, the problem of determining the coordinates of microphones through the use of calibration sources is solved. For this, we use optimization of the objective function, which is the norm of the difference between the measured and estimated delays in the arrival of calibration signals from sources to microphones, by unknown coordinates of the calibration sources and microphones. The results of simulation and experiment are presented, which show an acceptable efficiency of the proposed calibration technique. For acoustic imaging, MUSIC and the maximum likelihood signal classification method (MLSIC) were employed. The first method is widely known and was previously used to estimate the direction of arrival of plane waves. The second method was recently proposed and is based on the interference model, which includes M sources of a coherent field. The results of localization of acoustic sources were obtained using numerical simulation, as well as by an experiment in an anechoic chamber. It was shown that the MLSIC method has a better spatial resolution than the MUSIC method.
      PubDate: 2022-03-29
      DOI: 10.1007/s11141-022-10148-5
       
  • Synthesis of a Wideband Diplexer Based on Interdigital Resonators for the
           Antennas Of Mobile-Communication Base Stations

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      Abstract: We study theoretically and experimentally a new design of the diplexer for mobile-communication base stations, which is based on interdigital resonators. A high-performance diplexer for operation in the frequency ranges 690–862 MHz and 880–960 MHz has been developed and manufactured. The diplexer is synthesized on the basis of an efficient combined method including the use of the coupling matrix technique, solution of eigenvalue problems for single and coupled rod-type resonators, and electrodynamic simulation of filters and the diplexer. The proposed design has a high potential for realization of diplexers with wide, moderate, and narrow passbands in the mobile-communication frequency ranges.
      PubDate: 2022-03-29
      DOI: 10.1007/s11141-022-10150-x
       
  • Development and Experimental Study of a Pulsed Megawatt Gyroklystron
           Operating in the Long-Wavelength Part of the Millimeter-Wavelength Range
           at IAP RAS

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      Abstract: We have developed and studied experimentally a two-cavity gyroklystron operating at a frequency of 35 GHz and the cavity mode TE0 2 1 in a cryomagnet. The output radiation power achieved in the pulsed regime is 750 kW with an efficiency of 24%, a gain of 20 dB, and amplified-frequency bandwidth equal to 220 MHz (0.63%) at an accelerating beam voltage of 74 kV, a current of 42.5 A, and a pulse duration of 100 μs. An operating-frequency bandwidth equal to 310 MHz (0.89%) at a power level of 430 kW has been achieved in another variant of the gyroklystron. At fixed current and beam voltage, the limitation of the efficiency and the bandwidth of the operating frequencies is determined by self-excitation of parasitic oscillations in the output cavity at the TE2 2 1 mode. The limitation of the highest power of the output radiation at a level of 750 kW is related to the formation of a high-frequency discharge in the output cavity because of the deterioration of the vacuum in it as a result of heating the internal surface of the cavity due to ohmic losses. Strong influence of the axial distribution of the static magnetic field in the interaction space on the efficiency and the output radiation power is predicted theoretically and demonstrated experimentally. By finding an optimal longitudinal structure of the magnetic field using solenoids and magnetic shields, we have managed to increase the efficiency and the power of the gyroklystron in the experiment by 1.3 times compared to the case of a homogeneous distribution of the magnetic field.
      PubDate: 2022-03-29
      DOI: 10.1007/s11141-022-10149-4
       
  • Screening of Quantum States of an Optical Field from a Resonant Perturbing
           Subsystem

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      Abstract: We predict theoretically the effect of screening the quantum states (including entangled ones) of an optical field from interaction with a resonant perturbing subsystem by means of coupling with other field modes in the ground (vacuum) state. It is shown that an ensemble of resonators with fields in the vacuum state is able to screen the quantum state of a group of excited resonators from interaction with a resonant two-level atom. The degree of modification of the initial quantum state is inversely proportional to the number of “screening” modes unexcited at the initial moment of time.
      PubDate: 2022-03-29
      DOI: 10.1007/s11141-022-10151-w
       
  • Model Waveforms of Slow-Tail Sferics

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      Abstract: We simulate numerically the propagation of slow-tail sferics, which occupy a wide frequency band from 1 Hz to 10 kHz, in the spherical Earth–ionosphere cavity. The TM wave generated by a vertical lightning discharge is considered. Classic engineering models of a lightning stroke are employed. The calculations use the Williams stroke model as the field source. We assume that the upper boundary of the cavity is an isotropic horizontally stratified ionosphere, and the conductivity of each layer depends on its altitude. The day and night-time models of the vertical conductivity profile, which were used for correct description of the global electromagnetic (Schumann) resonance, are employed. The frequency dependence of the complex propagation constants of the zero- and first-order modes was found by using the full-wave solution in the form of the Riccati equation. The roots of this equation are the eigenvalues of the problem, which are found by iterations. Complex spectra of vertical electric and horizontal magnetic fields are constructed in the form of a series of modes with known propagation constants. Various source-to-observer distances in the day and night-time cavities are considered. The Fourier transform is applied to the complex field spectra to find the waveforms of the sferics. The model data allowed us to obtain the calibration curves for estimating the source-to-observer distance from the delay between the ELF slow tail and the VLF precursor. It is shown that the calibration curves are coincident for the day and night-time propagation conditions.
      PubDate: 2021-11-01
       
  • X-Ray Emission from Utracool Stars

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      Abstract: We study two possibilities of the origin of quiescent X-ray emission from ultracool stars using the examples of brown dwarfs TVLM 513-46546 and VB 10: (a) radiation from hot coronas and (b) radiation from a system of magnetic loops filled with a sufficiently dense hot plasma heated due to the dissipation of electric currents flowing in the loops. The parameters of the corona, as well as the parameters of the loops and their number, which are necessary for the implementation of the observed X-ray emission measure, have been determined. For the studied brown dwarfs, the generation of X-rays by a set of hot loops is energetically more favorable than in the case of a hot corona, which was also confirmed by the results of the analysis of quiescent microwave radiation from the brown dwarf TVLM 513-46546.
      PubDate: 2021-11-01
       
  • Electrodynamic Analysis of Eigenmodes of Spheroidal Dielectric Resonators

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      Abstract: We perform electrodynamic analysis of electromagnetic modes in a set of spheroidal dielectric resonators. The dependences of eigenfrequencies on the size of the resonators are found for a set of 5, 6, 7, and 9 spheroidal dielectric resonators. The problem is modeled numerically, and the dependence of the frequencies of coupled modes on deformations of the resonators is studied. The results can be useful in radioelectronics and biomedical applications.
      PubDate: 2021-11-01
       
  • Determination of the Velocity Profiles of Longitudinal and Shear Waves on
           the Basis of Analysis of Seismic Noise

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      Abstract: We consider a method for determining the velocity profiles of the longitudinal and shear waves on the basis of analysis of seismic noise. It is a result of improving the widely used method of passive tomography. The proposed method is based on the relation between the mutual spectrum of signals from the spaced receivers, which record two projections of the displacement vector, and the incomplete Green’s function, which corresponds to the response of the surface Rayleigh wave. Using this method, it is possible to determine the frequency dependence of both the phase velocity and ellipticity of the Rayleigh wave. In turn, the latter allows one to reconstruct the profiles of the longitudinal- and shear-wave velocities. In this work, we explain the fundamentals of the method within the framework of a simple model and propose its experimental evaluation. A comparison with the results of an independent measurement using a vibrator is given.
      PubDate: 2021-11-01
       
  • Simulation of Large-Scale Disturbances of the Near-Earth Plasma Affected
           by High-Power High-Frequency Radio Waves from the Sura Heating Facility

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      Abstract: We present the results of simulation of large-scale disturbances of the near-Earth plasma modified by high-power HF radio waves from the Sura heating facility. The numerical simulation was performed over the entire range of ionospheric altitudes, using an SAMI2 modified version for the input parameters corresponding to the in-situ measurements of the spatial structure of the disturbed region performed by the method of low-orbit radio tomography. The numerical simulation results conform to the radio tomography reconstruction data. The dynamics of the evolution and relaxation of large-scale temperature and plasma-density disturbances under the action of high-power HF radio waves from the Sura heater are studied on the basis of simulation data.
      PubDate: 2021-11-01
       
  • Comparison of Sources of Narrowband and Ultra-Wideband Electromagnetic
           Pulses in Terms of the Efficiency of their Impact on Electronic Tools

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      Abstract: We solve the problem of determination of the conditions under which the source of microwave pulses and the source of ultra-wideband electromagnetic pulses have an identical resulting impact in terms of energy on semiconductor elements of technical means without special receiving antennas. It is shown that sources of microwave pulses, whose carrier frequencies range from hundreds of megahertz to several gigahertz, reach the desired effect at lower energy costs. However, as the carrier frequency increases, their energy efficiency becomes lower, and ultra-wideband sources turn out to be more efficient in many practical cases.
      PubDate: 2021-11-01
       
  • “Cooling” of an Electron Bunch in the Regime of Sectioned Trapping of
           Electrons by the Excited Wave Fields

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      Abstract: We propose and describe a method to decrease the spread in the energies of relativistic electrons in their ensemble (bunch). The method is based on the passage by the beam of a sequence of amplifying sections, in which the process of the trapping and adiabatic deceleration of the particles by the wave field that they excite is realized. Within the framework of the simplest universal model of the electron-wave interaction in the amplifying sections, the basic regularities of multi-section cooling of an electron bunch are revealed.
      PubDate: 2021-11-01
       
  • Nonlinear Acoustic Effects in Polycrystalline Solids with
           Frequency-Dependent Saturation of Hysteresis Losses

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      Abstract: Based on the modification of the quasi-static Davidenkov hysteresis, we propose a dynamic equation of state for polycrystalline solids with frequency-dependent saturation of the amplitude-dependent internal friction effects. The nonlinear propagation of an initially harmonic longitudinal elastic wave in a rod made of such a material is studied by the perturbation method. Numerical and graphical analysis of the obtained solutions is carried out and the amplitude–frequency dependences of nonlinear effects are revealed.
      PubDate: 2021-10-01
       
  • Dynamics of the Electrical Structure of Cumulonimbus Clouds

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      Abstract: We present the data on the dynamics of the electric field strength and volume charge of two severe thunderstorms in different regions of the world, namely, in the North Caucasus (Russia) and in Beijing (China). The data were obtained as a result of modeling, using a numerical three-dimensional non-stationary model of convective clouds developed at the A. I. Voeikov Main GeophysicalObservatory. The modeling was based on rawinsonde data obtained during the modeled thunderstorm events. The spatial distribution of the electric field strength and space charge inside the cloud and in its vicinity was calculated. The multilayer charge structure of the cloud with thin layers of “shielding” charges is reproduced and the corresponding structure of the electric field strength is presented for each electrification stage. The dynamics features of the electrical structure of the studied cumulonimbus clouds are discussed. The case of modeling of a cloud with inverted polarity is considered. Verification of the numerical model based on empirical models of convective cloud electrification showed a satisfactory result.
      PubDate: 2021-10-01
       
  • The Partial-Region Method for Electrodynamic Calculation of Cylindrical
           Structures with Metal Radial T-Ridges and Inhomogeneous Dielectric Filling
           

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      Abstract: We solve the problem of electrodynamic analysis of the mode content in a circular waveguide with radial metal T-ridges and layered dielectric filling. Algorithms for calculation of cutoff wave numbers, components of the electromagnetic fields of the H and E waves, and the propagation constants of the hybrid HE and EH waves are developed with allowance for the features of the field behavior near a metal ring-shaped sector of finite thickness. The dependences of normalized cutoff wave numbers and propagation constants on the geometric sizes of the structure and its dielectric permittivity are studied. The electromagnetic field of the fundamental and higher modes of the H and E waves and hybrid modes is visualized.
      PubDate: 2021-10-01
       
  • A Set of Receiving Equipment for Detection of Collective Thomson
           Scattering Spectra at the Gas-Dynamic Trap (GDT) Facility

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      Abstract: We describe the set of receiving equipment, which was designed for the experiments on detection of the Thomson collective scattering spectra of high-power millimeter-wave radiation in a large-scale open magnetic trap “Gas Dynamic Trap (GDT)” performed at the G. I. Budker Institute for Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk, Russia). The set consists of two identical radiometers/spectrum analyzers with an analysis band of 54.47 ± 0.55 GHz and a sensitivity of no less than 0.080–0.025 eV, which ensure simultaneous measurements in two independent channels corresponding to different reception angles of the scattered radiation.
      PubDate: 2021-10-01
       
  • Verification of a New Model of the Irradiance Distribution from a
           Unidirectional Point Source in Water Using the Monte Carlo Method

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      Abstract: We study the spatio-angular structure of a nonstationary light field produced in seawater by a unidirectional point source. The calculation results obtained using an analytical model, which allows for the photon spread over the propagation paths, and the statistical simulation method are compared. It is shown that the analytical model provides a good description of the amplitude-frequency characteristics of irradiance in a wide range of variation in the essential parameters of the problem, namely, the distance from the source, the angle reckoned from the radiation axis, and the frequency. Disagreement of the results of the analytical model and statistical simulation is observed at high frequencies and long distances where the approximations used during the model development are inapplicable.
      PubDate: 2021-10-01
       
  • Conditions for Correct Measurements of the Laser-Beam Characteristics
           Based on Determination of Initial Moments of the Spatial Intensity
           Distribution

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      Abstract: In the work, we study the convergence conditions for initial moments of the spatial distribution of the laser-beam intensity. These moments serve as the basis for determining the beam characteristics (the width, the divergence angle, and the propagation ratio M2) when using modern standards such as the ISO 11146:2005 standard and the ISO 11146-2008 state standard of Russia. On the basis of the parabolic equation of quasioptics in the Fraunhofer approximation, it is shown that the existing method for measuring the above-mentioned parameters, which does not take into account the finite size of the radiation aperture, can lead to divergence of the measurement results. Special attention is paid to the fact that this can also take place for continuous intensity distributions and, therefore, the replacement of the finite aperture by the infinite one is inadmissible when determining the initial spatial moments in the general case. It is proved that to obtain correct results of the measurements of the second moments, the spatial distribution of the amplitude at the aperture edge should be equal to zero. An example confirming the presence of the problem and the basic conclusions of this work is considered.
      PubDate: 2021-10-01
       
  • Study of the Radiation Capability of a Perfectly Conducting Half-Plane
           Excited by a Slot Perpendicular to the Conductor Edge

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      Abstract: We solve the problem of excitation of an infinite, perfectly conducting half-plane by an external field in the slot line, which is perpendicular to the edge of the half-plane, and study its radiation field. Based on the fundamental relationships, the formulas relating the excitation field on the half-plane and the radiation field of the half-plane are obtained. The theoretical formulas are derived which describe the structure and features of the slot radiation field in the far zone for the main electrodynamic planes (E and H) and serve as the basis for the development of the mathematical models of sources based on variously configured planar symmetric slot lines. The influence of the Green’s function and location of an elementary region in the radiation aperture of the conducting half-plane on its radiation field is determined. For this case, the corresponding theoretical relationships are found and substantiated, and some special and limiting cases are considered.
      PubDate: 2021-10-01
       
 
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