Radio physics and electronics

3-9

Authors: Yu.V. Svishchov

Subject and Purpose. The spectral characteristics (eigenfrequencies, eigenmodes, Q-factors) of a spherical particle with arbitrarily valued permittivity and permeability are considered to take a further look into some important features of their behavior. The real and imaginary parts of the material parameters of the particle can be both positive and negative. The emphasis is on magnetic type modes. Methods and Methodology. The spectral problem is solved using the electromagnetic field expansion in vector spherical wave functions. Results. The first eigenfrequencies of a spherical particle have been calculated depending on its relative permittivity e 1 and relative permeability m 1 whose real and imaginary parts can take both positive and negative values. The eigenmodes split into two, internal and external, eigenmode families. The internal eigenmodes bear an independent, associated with eigenmode structure labeling in each quadrant of the plane (m 1 , e 1). The external eigenmodes, on the contrary, have a uniform labeling throughout the whole (m 1 , e 1) plane and bear a structural resemblance to surface plasmon oscillations distributed in the vicinity of the particle surface or outside it. In the first quadrant of the plane (m 1 , e 1), the external eigenmodes repeatedly interact with the internal eigenmodes, leading to either mode hybridization or mode type exchange. In the third quadrant of the plane (m 1 , e 1), the external eigenmodes can interact with one another. The anomalous behavior of the spectral characteristics of a spherical particle corresponds to the already known phenomenon of wave mode coupling described in the scientific literature well enough. Conclusion. The performed study has revealed some new behavioral patterns as to the spectral characteristics of a spherical particle with arbitrarily valued permittivity and permeability

18-29

Authors: R.E. Pashchenko, V.K. Ivanov, D.O. Tsyupak

Subject and Purpose. Comparative analysis of the shapes of phase portraits of Doppler signals (DS) reflected from drone rotating rotors is given with regard to different time delays. The shapes of DS phase portraits are examined for various rotational velocities and numbers of the rotating rotors. Methods and Methodology. A method using phase portraits is suggested for analysis of Doppler signals reflected from drone rotating rotors. The method determines the number of the rotors and estimates their rotational velocities. Results. It has been found that the shape of the phase portrait of the baseline signal is practically independent of the time delay and can be described as an occasional movement of the image point following the phase trajectory in the center of the phase portrait. The appearance of characteristic regions on the periphery of the phase portrait allows separating baseline and sounding signals. It has been shown that the shape of the DS phase portrait of the rotating rotor during the flight movement of the drone depends on the time delay value. With a larger delay, phase portraits similar in shape appear at regular intervals equal to the Doppler signal period. With a larger rotational velocity of the rotor, the rate of similar phase portrait appearance diminishes. Conclusion. During the sounding of drone rotating rotors, the shapes of DS phase portraits depend on the value of time delay. With a larger number of rotors in the drone flight, the periodic change character as to the DS phase portrait shape remains unchanged. In this case, DS phase portrait shapes differ substantially for different numbers of drone rotors

38-53

Authors: M.V. Mil’cho, K. Ilyenko

Subject and Purpose. A special need for oscillators amenable to operation in the short-wave end of the submillimeter wave band sends us in search for new ways of their development. A proposal exists related to vacuum-tube frequency multipliers based on the backward-wave oscillator (BWO) or its variant, the clinotron. Sometimes a simultaneous excitation of two different-frequency oscillations is experimentally observed in ordinary millimeter wave clinotrons, orotrons and diffraction radiation oscillators. The aim of the present study is to examine whether those operational regimes can be implemented in the creation of electronic frequency multipliers in the submillimeter wave band. Methods and Methodology. The research method is a theoretical analysis of the process of simultaneous interaction of the electron beam with the electromagnetic fields of two modes in the BWO slow-wave structure. The aim is finding relationships to impose on the slow-wave structure parameters and the BWO operation figures and thus furnish a simultaneous excitation of the two modes. The obtained relationships are tested against published experimental results. Results. Two conditions of simultaneous mode excitations have been formulated, requiring (i) equal velocities of the operating spatial harmonics and (ii) their strict frequency multiplicity. Handy diagrams have been constructed, which made it possible to build frequency multiplication schemes with any multiplicity. The rigorous analytical method of comb dispersion calculation has been generalized to the higher passbands of large numbers. The calculation results have been compared with relevant experimental data, lending support to the validity of the obtained formulas to describe the frequency multiplication regime. Conclusion. A possibility has been theoretically shown of designing submillimeter vacuum-tube frequency multipliers upon clinotron-type oscillators with a single slow-wave structure. The regime of simultaneous generation of two given frequencies requires that the system dispersion in different passbands be controlled by moving a screen over the comb-type slow-wave structure.

66-79

Authors: A.O. Puzanov

Subject and Purpose. The present paper is concerned with the method of surface schooping of materials using high-frequency torch discharge (HFTD) and glycerol vapor as a base for dissolving activating additives to the working gas. To approach the problem, a steam generator is employed in an effort to improve the HFTD catalytic performance in the activation of surfaces and deposition of coatings on them. The purpose is to develop a design technique of a steam generator intended for making a proper gas environment in the HFTD burning area. The discussed design techniques seek to enhance efficiency of the self-contained steam generator with allowance for its small size compared to the wavelength. Methods and Methodology. The analysis of the glycerol vapor behavior in the HFTD plasma depends on the knowledge of glycerol molecule ionization potential in the electron impact case. To find out about the measure to which the glycerol vapor affects the HFTD current, a known calcium ionization potential is used as a defined point. The heating elements as part of the steam generator are designed in terms of thermal design methodology adopted in the electroheating machine making. The calculation formulas of the running time ratios of the steam generator with various heating elements and energy efficiencies have been obtained in terms of galvanic cell theory. Results. It has been shown that glycerol vapor itself cannot affect the HFTD current. For the HFTD excitation, the microwave region has been chosen. In cooperation with activating additives to the discharge plasma, this factor also adds to the HFTD current increase. Hence, the HFTD catalytic performance depends not only on the HFTD energy and its excitation field frequency but on the glycerol-dissolved additives as well. A special design has been developed for the heating element as part of a small-size steam generator. Reference tables have been composed, enabling one to pick up a prpoper diameter and number of parallel connected wires in the spiral coil. Conclusion. A good use of glycerol vapor as a base for vaporous fluxes and activating additives to the HFTD working gas has been shown. The developed design technique concerning the heating element of the steam generator optimizes its heating circuit. Specifically, it enhances the steam generation and reduces the power consumption of the steam generator running on the galvanic cell. Second, it makes it possible to use stainless-steel spiral heating coils in regime of automatic temperature control.

3-15

Authors: N.P. Yeliseyeva, S.L. Berdnik, V.A. Katrich

Subject and Purpose. A resonant monopole of an electrical length 0.2 £ l / l £ 0.3 mounted on an infinite, perfectly conducting plane or on a rectangular, perfectly conducting screen is considered. The objective is to determine how the radiation resistance, surface impedance, and input impedance depend on the length and thickness of the resonant monopole and how the screen size affects the resonant characteristics and directive gain of the impedance monopole. Methods and methodology. A three-dimensional vector problem of the field diffraction of an impedance monopole mounted on a perfectly conducting rectangular screen is solved using the method of uniform geometrical theory of diffraction and adopting asymptotic expressions of the diffracted fields and electric currents of a thin impedance dipole located in the free space. Results. Taking into account diffraction effects at the edges of the square screen, the resonant values of the surface impedance of the monopoles and the corresponding radiation resistance and directive gain have been calculated subject to the condition that the electric field amplitude is at its maximum. It has been found that as the screen size exceeds the two wavelengths, the edge phenomena have little effect on the monopole resonant characteristics. The radiation resistance reaches its maximum when the side of the square screen is as long as L / l = 0.9…0.95. The first maximum of the directive gain occurs at L / l = 1.2…1.3. The obtained results have been verified with the aid of the computational electromagnetics software FEKO. Conclusion. A three-dimensional vector diffraction problem has been solved for an impedance monopole mounted on an ideally conducting, rectangular screen. Algorithms and computational programs have been developed to determine resonant characteristics and radiation patterns of the radiating system. By choosing an optimum screen size it is possible to increase the directive gain of an impedance monopole of the length l = 0,2l by 24% and the radiation resistance by 38% compared to the infinite screen.

26-33

Authors: A.S. Bryukhovetski, A.V. Vichkan’

Subject and Purpose. The wave field produced by a spatial-temporal distribution of sound sources in a uniform subsonic flow is theoretically studied in an effort to obtain an analytical dependence of the sound field on physical parameters. Method and Methodology. Cauchy problem for wave equation in a moving medium is solved using a spatial-waveguide Fourier expansion of the sound field. A Fourier representation of the Green's function of a point-like pulse sound source is constructed whose inverse transform allows us to obtain the Green's function spatial-temporary representation. Results. With the Green’s function obtained, the wave fields from arbitrarily shaped sources have been represented in the “wave potential” form, which is a convolution type integral of the density of spatial-temporal distribution of the sound sources and the Green’s function. Conclusion. The calculation results give a clear idea of the propagation of sound waves excited by a point-like pulse source in a uniform homogeneous flow. The wave front of the sound field represents a sphere whose center “drifts” from the source at a speed equal to the speed of the flow in its movement direction, and the radius of the sphere grows in the course of time at a speed equal to the speed of sound. The obtained Green’s function allows for the analytic continuation to the supersonic flow case that, in contrast to the subsonic case, satisfies the causality principle not in all unlimited space but only at the observation points within the Mach cone. The wave field from a monochromatic source is the limiting case of the rectangular pulse solution.

42-53

Authors: V. N. Derkach, E. A. Alekseev, R. V. Golovashchenko, Ye. M. Ostryzhnyi, A. A. Meshcheryakov, S. I. Tarapov

Subject and Purpose. The subject of the study is spectral and energy characteristics of whispering-gallery disk resonators made up of low-loss microwave dielectric and semiconductor materials, namely, gold-doped silicon Si:Au, Chemical Vapor Deposition (CVD) diamond, Arc Plasma Jet (APJ) diamond, and alumina ceramics Al2O3. On the basis of the temperature dependences of the microwave energy loss in the materials mentioned, we seek to classify the loss contributions among the electromagnetic energy absorption mechanisms and find physical parameters responsible for these mechanisms. Methods and Methodology. The loss values were experimentally obtained by the whispering-gallery disk resonator technique with the usage of a cryodielectrometer. A phenomenological simulation was performed to classify the loss contributions to the temperature dependence of electromagnetic energy absorption among the major loss mechanisms in the examined materials. Results. The experimental study results on the dielectric loss temperature dependence within 4.2...300 K have been presented and discussed for low-loss semiconductor and dielectric materials, including gold-doped silicon Si:Au, CVD-diamond, APJ-diamond, and alumina ceramics Al2O3 with reference to the frequency band 110...140 GHz. Certain design features have been suggested to use in the authors’ software-controlled measuring unit to provide the interchangeability of backward wave tubes (BWT) inside the cryodielectrometer and extend the merasuring bandwidth up to 34...144 GHz. The unit offers software-controlled frequency tuning with a spectral resolution of about 0.1 MHz. The loss contributions have been classified among the major loss mechanisms, and physical constitutive parameters responsible for these mechanisms have been determined. Conclusion. The temperature dependences of dielectric loss in low-absorption materials have been registered and analysed. The developed measuring unit has advantageous design features and provides, in addition, an independent controllable radiation source which can be included in a frequency synthesis system with phase-locked loop.

60-67

Authors: Yu.V. Kornienko, I. Liashenko, V.V. Pugach, S.I. Skuratovskiy

Subject and Purpose. The influence of Earth’s atmosphere leads to significant distortion of object images obtained with Earth-based instruments. In this case, the distortion of the Fourier component phase plays a far more important role than the module distortion. The influence of Earth’s atmosphere on the Fourier component phase may be considered as a multiplicative noise in the frequency domain. For combatting this influence, we propose signal accumulation, implying that total phases rather than their main values, which are available for the direct measurements by experiment, should be accumulated. The features of the proposed total phase accumulation method are studied in the present paper. Methods and Methodology. The current studies depend on computer experiment and theoretical analysis of the obtained results. The performance efficiency of the total phase accumulation method is evaluated with the aid of the computer system of astronomical image modeling and processing developed in the O.Ya. Usikov IRE of NASU. Results. A relationship has been obtained between the error of image reconstruction by the total phase accumulation method and the number of the accumulated images in different observation conditions. The dependence has a non-monotonic behavior, which remains to be investigated. Conclusion. That the reconstruction error dependence in the total phase accumulation method has a minimum is important for the practical method application as there comes an accumulation point after which the reconstruction accuracy degrades. The location of that minimum depends on the atmospheric parameters, sending us in search of a criterion for choosing an optimal sequence length of image accumulation.

78-88

Authors: A.D. Yegorov, S.A. Yegorov, V.A. Yegorov, I.E. Sinelnikov

Subject and Purpose. The subject of the work is atomic emission spectral analysis of substances using the most affordable arc and spark sources widely accepted in both laboratory and industrial practice. The aim is to improve solution principles of some technical problems in the field of construction of power supplies of arc and spark discharges with predetermined properties and to study their parameters. Methods and Methodology. Traditional methods of producing spark and arc discharges are used. Several designs are proposed for discharge current and discharge gap breakdown power supplies, modeled using a computer program of circuit simulation and tested on the existing prototypes. The developed generator was put through tests and compared with a production analog of it in terms of statistical analysis of spectrum measurement results. Results. The microprocessor-controlled arc plasma generator "TsUG-2" has been developed and performed. The discharge current generation unit was constructed on the principle of digital-to-analog converter (DAC) with current summation. The discharge gap breakdown unit was performed on the semiconductor circuitry basis without any gas spark gaps. A unit was added for generating the initial pulse of discharge current, which made it possible to extend the spectrum excitation range, provide the sampling process control and improve the discharge combustion stability. A parameter control unit was developed to create and maintain the protective gas environment in the discharge chamber. The control over the operating modes of the generator and its synchronization with the spectrum recording equipment is exerted through an external interface. The manual control is carried out via a stand-alone control panel. The created generator "TsUG-2" produces discharge gap breakdown pulses of up to 12 kV amplitudes and arc pulses spanning a discharge current range as wide as 1...47 A. On them, additional current pulses of up to 150 A amplitudes can be superimposed, which significantly increases the rate of discharge current rise. The highest frequency of the discharge excitation pulses is 800 Hz. Comparison tests of the developed generator "TsUG-2" and a production generator "UGE-4" have been carried out. Conclusion. The measurement results show that the standard deviation (RMS) of the photometric data of plasma formations obtained from the developed arc plasma generator "TsUG-2" is, on the average, three times less than from a production generator "UGE-4.

3-8

Authors: N.N. Beletskii, S.A. Borysenko

Subject and Purpose. The effect of total electromagnetic wave tunneling through a three-layer structure containing a plasma-like negative-permittivity layer is important for both gaining a better insight into the high-frequency properties of layered solids and, hence, creating new types of high-frequency radio-physical devices. The main purpose is to study the influence the frequency dispersion of the negative-permittivity layer exerts on the electromagnetic wave tunneling through a three-layer structure with an asymmetric dielectric medium. Methods and Methodology. A new universal approach is used, based on introducing dimensionless frequencies and dimensionless layer thicknesses of a three-layer structure. It allows the frequency-dependent conditions of the effect of total electromagnetic wave tunneling to be examined for different frequency ranges and various three-layer structure parameters. Results. It has been shown that taking into account the frequency dispersion of the negative-permittivity layer makes it possible to observe the total tunneling of electromagnetic waves at different frequencies with an appropriate choice of the three-layer structure parameters. In various frequency ranges, the effect of two-frequency total tunneling of electromagnetic waves has been predicted. Conclusion. In the presence of a frequency dispersion of a negative-permittivity layer as part of a three-layer structure, the total electromagnetic wave tunneling conditions of this structure are softened and modified significantly. In this case, unique phenomena arise that can be used to create fundamentally new high-frequency devices in optics, radiophysics, and electronics.

22-28

Authors: V.A. Kabanov

Subject and Purpose. One of the relevant areas of remote sensing of the environment is the development of microwave methods of passive sensing of the atmosphere. The biggest challenge occurring in radiometric measurements is measuring system calibration. The reason lies in the lack of external calibration elements whose brightness temperatures are known with a high accuracy. The paper deals with the method for determining the sky brightness temperature by relative measurements at different elevation angles. The brightness temperatures refined in the way fit for radiometric system calibration. Methods and Methodology. Basically, the approach is governed by the dependence of the atmospheric brightness temperature on the elevation angle in terms of the plane-layered isothermal atmospheric model. The measurements rely on a three-centimeter radiometric system having a horn-reflector antenna combined with the MPL-1 weather radar, the entire range of elevation angles being accessible. Besides, a combined setup of two, 10 GHz and 36 GHz, radiometers is involved for measurements from a building window. Results. The previously proposed methodology for radiometric system calibration against the sky temperature obtained by relative measurements at different elevation angles has been analyzed and tested. The calibration possibility has been examined in the case that zenith measurements are unavailable. Conclusion. The proposed method for getting sky temperatures upon relative measurements at different elevation angles significantly increases accuracy of radiometric system calibration and extends a range of weather conditions admitting calibration of the kind. It has been shown that the radiometric system calibration against the sky temperature is possible even with zenith measurements excluded.

38-45

Authors: T.V. Kalmykova, S.I. Tarapov, A.S. Vakula, S.V. Gorobets, O.Yu. Gorobets, Yu.I. Gorobets, M.A. Bulaevskaya, K.A. Getmanenko

Subject and Purpose. Synthesis of biological sorbents has become one of the ways to solve the problem of environment contamination with heavy metals. Today, studying properties of biosorbents with injection of magnetic nanoparticles is important. Thus, injection of magnetic nanoparticles of magnetite (Fe3O4) improves absorption properties of biosorbents. The subject of the present work is magnetic resonance properties of nanoparticles inside biosorbents, such as macromycetes like Pleurotus ostreatus. The purpose is to examine these magnetic resonance properties and analyze the state of magnetite nanoparticles inside Pleurotus ostreatus. Methods and Methodology. The X-band Electron Spin Resonance (ESR) method is employed to register ferromagnetic resonance (FMR) spectra at T = 294 K. TEM-images of magnetic nanoparticles are made in the transmission electron microscope. Mathematical modeling for the properties of the arising clusters of magnetic Fe3O4 nanoparticles inside macromycetes Pleurotus ostreatus is performed using a phenomenological model upon the well-known Kittel equation. A model enhancement is proposed in the case of interacting nanoparticles inside an ellipsoidal magnetic cluster. Results. It has been shown that Fe3O4 nanoparticles are well absorbed by macromycetes and gather into structural clusters regardless of the concentration of magnetic nanoparticles injected. These magnetic clusters of magnetic nanoparticles have ellipsoidal shapes with an aspect ratio of 3:1:1. The developed mathematical model makes it possible to obtain dimensions of magnetic clusters from the FMR spectra and evaluate their shape and mutual magnetic interaction. The mathematical modeling results are in good agreement with TEM-images of these clusters inside Pleurotus ostreatus. As a result of modeling are in good agreement with the TEM-images of these clusters inside Pleurotus ostreatus. Conclusion. The presented results will contribute to the development of non-destructive testing of the state of biological sorbents using magnetic resonance radio spectroscopy methods.

54-63

Authors: A.V. Degtyarev, M.M. Dubinin, V.A. Maslov, V.S. Senyuta

Subject and Purpose. In this paper, spatial power characteristics of laser beams with inhomogeneous spatial polarization are theoretically investigated depending on whether they have moderate or sharp focusing. The spotlight of the numerical simulation of laser beam focusing in the terahertz range is on the laser waveguide dielectric resonator modes coincident with waveguide eigenmodes. Symmetric and asymmetric modes with both spatially inhomogeneous azimuthal and radial polarizations and homogeneous linear polarization of the field are considered. Methods and Methodology. The study of the electric field components of laser radiation beams in their free space propagation employs Rayleigh-Sommerfeld integrals in nonparaxial approximation. The focusing lens action on the laser radiation is considered using the amplitude-phase correction function. The total intensity distributions of the resonator modes and their particular field components in the lens focal area are examined. Results. Wave beams with inhomogeneous spatial polarization of radiation are needed for meeting important fundamental and applied problems concerning terahertz electromagnetic wave interaction with matter and including diagnostics of material surface, thin films and biological objects, design and development of terahertz systems of information transmission and processing, terahertz communication systems, achievement of subwave resolution in terahertz tomography, etc. The literature on pulsed radiation beam focusing in the terahertz region is available, which cannot be said about continuous radiation beam focusing, data on the subject being practically absent. In the present work, physical features of moderate and sharp focusing of laser beams have been theoretically studied in the case of their excitation by modes of the resonator with a circular dielectric waveguide with different spatial polarizations of the field. The obtained results give a more in-depth view of the focusing features of terahertz laser beams. Conclusions. Physical features have been established for spatial power characteristics of radiation beams with different spatial polarizations of the field in the case of the excitation by modes of the laser cavity upon a circular dielectric waveguide in the terahertz range and with the regimes of moderate and sharp beam focusing in the free space considered.

74-81

Authors: O.V. Holovan, V.M. Kharchenko

Subject and Purpose. The paper presents a technology of constructing a promising meteor-burst communication system (MBCS) with code division multiplexing. It increases the bandwidth and improves the noise immunity and covert operation of the system. Methods and Methodology. The proposed technology is based on software-defined radio (SDR) and provides MBCS adaptation to the environment conditions by means of software parameter control of the signals and their transfer protocols. It includes a technique of forming a large ensemble of signals with a direct sequence spread spectrum and improved auto- and cross-correlation properties, involves the optimal reception and matched digital filtering of large-base signals. In order to improve the noise immunity, the narrow-band interference rejection in the signal spectrum is proposed and is jointly software installed with the matched filtering. The detection and synchronization techniques effectively working in the non-Gaussian and non-stationary interference conditions gained consideration. Results. A method of forming a large ensemble of direct sequence spread spectrum signals with improved auto- and cross-correlation properties has been software implemented using a pseudorandom permutation of codeword elements of a maximum-length register code. Designed with the use of fast Fourier transforms, algorithms of digital matched filtering and interference rejection as applied to large-base signals have been implemented via field-programmable gate arrays (FPGA). A method of detection and synchronization of large-base signals has been proposed and software implemented on the FPGA basis. Conclusion. The proposed algorithms and their implementation methods make it possible to increase the bandwidth, improve noise immunity and enhance covert operation of the meteor-burst communication system with code division multiplexing.

3-10

Authors: L.P. Mospan, А.А. Kirilenko, D.Yu. Kulik, S.О. Steshenko

Subject and Purpose. Peculiarities of the electromagnetic wave scattering at screens perforated by U-shaped slots are the subject of the paper. Numerical modeling of frequency-selective surfaces with frequency characteristics given and research into the possibilities of the performance control of the screens by complicating their elementary cell geometry are the purposes of the paper. Method and Methodology. The numerical modeling is performed upon the MWD3 software package developed in the laboratory of computational electromagnetics of the IRE NASU. Based on the scattering mode technique and the mode-matching technique taking into account the electromagnetic field behavior near the edges, this software package enables calculations of scattering characteristics of both compound waveguides and gratings with piece-wise boundaries. Results. A virtual waveguide was incorporated into the MWD3 projection schemes, extending capabilities of the MWD3 software and making it possible to treat the frequency-selective surfaces with piece-wise boundaries without adding new building blocks. Numerical modeling of perforated screens with U-shaped slots was carried out. Conclusion. Configurations of single and double metal screens and, also, a compound grating formed by two screens separated by a dielectric layer were calculated in full agreement with the given task. The perforated screens provide essential reflectivity decrease at low frequencies and, also, a low insertion loss level in the given millimeter wave region. The obtained results can be of interest for specialists in antenna-feeder engineering and for MWD3 software users.

21-27

Authors: D.M. Bychkov, V.K. Ivanov, A.Ya. Matveev, V.N. Tsymbal, S.E. Yatsevich

Subject and purpose. The purpose of this work is to study the effect of wind on the anomalous scattering of radio waves during aeolian processes of sand and dust transporting. Мethods and methodology. The article analyzes the spatial variations of the near-surface wind and their effect on the characteristics of anomalously narrowly directed radio wave backscattering according to the long-term studies of desert regions of Al-Jouf, Akshar and Trarza in Mauritania by Envisat-1 satellite SAR. Results. Analysis of SAR data indicates that intensity of radio wave scattering on the leeward slopes of sand ridges is more than 12...15 dB higher than the one from the slopes located in the "wind shadow" zone, which indicates the direct influence of the surface wind on the back scattering of radio waves during aeolian sand and dust transportation. The dependences of changes in the backscattering coefficient s 0 on the angle of local irradiation q along sections of fragments of homogeneous sections of the surface radar images are obtained. Conclusion. SAR data indicate that the spatial distribution of the maximum intensity values of anomalously narrowly directed backscattering of radio waves corresponds to the spatial distribution of the near-surface wind. The intensity of backscattering of radio waves, starting at a speed of 2 m/s and higher, steadily depends on the wind speed.

38-49

Authors: M.V. Balaban, Y.V. Goncharenko, V.M. Gorobets, O.L. Kovorotniy, F.V. Kivva, G. Farquharson

Subject and Purpose. The paper is concerned with Synthetic Aperture Radar (SAR) imaging and data processing and seeks to modify the conventional time-domain back projection algorithm (BPA) used for creating a SAR image. The modification consists in the radar squint-angle control at the stage of data processing. Methods and Methodology. Mathematical modeling methods are used. The modeling results are verified by reference to the experimental data. Results. A modification proposed for the back projection algorithm (BPA) enables fast-moving targets to be detected on a stationary image created by synthetic-aperture squint-angle side-looking radar. The back projection algorithm with the squint angle control was experimentally verified by a speedboat example to show that the SAR image has signatures of fast-moving targets which are not observed on the image formed by the classic back projection algorithm. Conclusion. The proposed modification of the back projection algorithm improves the detection probability of fast-moving targets on a SAR image and does it without any complication of the classic back projection algorithm or additional computing time.

60-69

Authors: Yu.O. Averkov, Yu.V. Prokopenko, V.M. Yakovenko

Subject and Purpose. The creation of millimeter and submillimeter electromagnetic wave generators is a promising direction in radio physics. These generators are demanded in medicine, biology, spectroscopy, broadband wireless communications and other branches of science and technology. One of the ways of millimeter and submillimeter wave generation is interaction between charged-particle beams and super-dimensional electrodynamic structures in multimode operation. In this regard, elementary physical mechanisms underlying this interaction invite further investigation. In the paper, the problem of spatial-surface eigenmode excitation is considered for a solid-state cylinder when a nonrelativistic electron moves in a vacuum over the surface of this cylinder and parallel to its axis. Because of the nonrelativistic character of the electron motion, the electron field and the radiation field in a vacuum are treated in the electrostatic approximation, while the fields inside the cylinder are calculated with the delay effect taken into account. Methods and Methodology. Maxwell’s equations in space-time field terms yield an analytical expression of the electron energy loss for the spatial-surface eigenmode excitation of a dielectric cylinder. This expression is numerically analyzed using the bisection method to find roots of the dispersion equation. Results. The analysis of the electron energy loss suggests that the E-type modes are the most efficiently excited. The electron energy loss for the E-mode excitation is approximately two orders higher than the loss for the excitation of H-modes with the same azimuthal and radial mode indices. The largest electron energy loss corresponds to the HE11 mode excitation. Conclusion. The performed study gives a deeper insight into the physical mechanism underlying the eigenmode excitation of a dielectric cylinder under the action of charged particles. The obtained results can be generalized to the case of a multijet electron beam used to generate whispering-gallery electromagnetic modes.

80-85

Authors: M.А. Miliaiev, S.V. Nedukh, S.I. Tarapov

Subject and Purpose. The paper presents the development and testing of a microwave splitter based on a planar hyperbolic metamaterial with a structural defect. The planar hyperbolic metamaterial is so constructed that a propagating electromagnetic (EM) wave is channeled in a certain direction depending on the metamaterial parameters. The wave splitting is possible where a part of the incident wave is reflected from a defect created inside the metamaterial. As the defect spatial orientation relative to the incident EM wave changes, the propagation direction of the reflected EM wave also changes. By this means the wave propagation control can be implemented in the considered splitter. Methods and Methodology. A defect in a planar hyperbolic metamaterial is created using the circuit theory that relates the material parameters to the equivalent unit-cell capacitances and inductances which, in turn, depend on the parameters of the microstrip line and capacitors. Thus, a change in any parameter of the circuit inside the unit cell changes its material parameters and makes a defect cell. In this work, a defect is created by changing the capacitance of the capacitors in a given set of elementary cells of a planar hyperbolic metamaterial, controlling thereby the size of the defect and its spatial location relative to the propagating wave. The numerical model of EM wave propagation inside a planar hyperbolic metamaterial with a defect is validated by experiment. In it, the field distribution over the metamaterial surface is obtained using the active probe method in the three cases: a defect-free metamaterial and two variants of defect orientation. To insert the electronic control, it is proposed to replace the elementary cell capacitors with varactors. Results. The obtained field distributions show that the defect partially reflects the incident EM wave channelized in the planar hyperbolic metamaterial. As the defect location angle changes, the wave reflection angle also changes. To make a defect unit cell, it will only suffice to change its capacity by 20% from the original, which is quite feasible in modern varactors. Conclusion. The performed studies have shown that the considered planar hyperbolic metamaterial with a structural defect is good for creating tunable electromagnetic wave splitters.