Vol 27, No 2 (2024)
Articles
Solution of the internal and external problems of electrodynamics for a symmetrical vibrator with a reflector made of parallel straight conductors
Abstract
Background. The work is aimed at the development and research of rigorous methods for calculating multi-element emitting and re-emitting structures, consisting mainly of the same type of elements, as well as studying the physical processes occurring in them. An iterative approach to solving the internal problem is proposed, which allows minimizing the cost of computer time and computer memory.
Aim. In this work, using the proposed approach, we solve the internal and external problems of electrodynamics for a symmetrical vibrator with a reflector made of parallel straight conductors. The convergence of the iterative process is studied, the currents on the elements of the structure, its input resistance and radiation characteristics are calculated.
Methods. The research is based on a strict electrodynamic approach, within the framework of which, for the specified structure in the thin-wire approximation, an integral representation of the electromagnetic field is formed, which, when considered on the surface of conductors together with boundary conditions, is reduced to a system of Fredholm integral equations of the second kind, written relative to unknown current distributions on conductors (internal task). The solution of the internal problem within the framework of the method of moments is reduced to solving a SLAE with a block matrix.
Results. A mathematical model of a radiating structure is proposed, which is a symmetrical vibrator with a reflector made of parallel straight conductors. The internal and external problems of electrodynamics are formulated and solved for given parameter values. An effective algorithm for calculating the block matrix of SLAEs is proposed. Recommendations are given for the selection of systems of projection functions within the framework of the method of moments. The convergence of the iterative process for solving an internal problem of electrodynamics has been studied. The input resistance of the structure and the basic characteristics of its radiation are determined.
Conclusion. A rational choice of systems of projection functions, based on the properties of the structure and its constituent elements, makes it possible to significantly reduce the size of the SLAE matrix and, accordingly, reduce computational costs. Taking into account the properties of the structure and its constituent elements also makes it possible to construct effective algorithms for calculating the SLAE matrix. It is shown that the convergence of the iterative process may be absent near resonant frequencies, therefore, when solving the internal problem, a combined approach should be used, which involves the use of both rigorous and approximate methods for solving SLAEs. At non-resonant frequencies, the iterative approach demonstrates its effectiveness. It is concluded that for such structures it is advisable to distinguish between resonant and non-resonant operating modes. In the non-resonant mode, the current functions have a fairly smooth dependence on frequency; in the resonant mode, these dependences become quite sharp and difficult to predict. In this regard, the task of developing an iterative approach to solving the internal problem of electrodynamics in resonant operating modes seems relevant.
7-21
Influence of atmospheric wind on the propagation of radio waves
Abstract
Background. It is necessary to study the influence of the physical characteristics of the atmosphere, in particular, wind on atmospheric turbulence and, consequently, on the characteristics of the radio signal it is shown.
Aim. The dependence of the time-spectral function of the radio signal energy flux on the wind speed in the troposphere in the antenna plane is found.
Methods. A method of transition from the Cartesian coordinate system in the antenna plane to the polar coordinate system of wave numbers has been developed. Based on this method the relationship between the Fourier spectral function of the correlation moment and the representation of the Bessel function is found. For the Fourier spectral function of the correlation moment, the previously obtained solution of the differential equation for the fluctuations of the eikonal amplitude of electromagnetic wave in a turbulent atmosphere at the front of the electromagnetic wave at the coordinate of the receiving antenna is used. Using the inverse Fourier transform the relationship between the time-spectral function of the radio signal energy flux and the time-correlation function of this flux is found.
Results. Based on the study of the time-correlation function of the radio signal energy flow its relationship with the two-point correlation moment characterizing the fluctuations of the eikonal amplitude of the radio signal is found. To analyze the effect of wind, a turbulence model was used, reflecting the inertial turbulence interval, in which the energy flow from larger turbulent vortices to smaller vortices is determined by the viscous dissipation of the smallest vortices.
Conclusion. Numerical calculations have shown that such a wind in the antenna plane blows away turbulent vortices in this plane, bettering the quality of the received radio signal.
22-29
Modeling of electromagnetic wave reflection from wet soil taken into account of dispersion, heterogeneity and surface roughness
Abstract
Background. Taking into account temperature, soil composition, surface roughness and the dependence of effective dielectric constant on frequency allows a more accurate assessment of soil moisture and other important parameters, which can be used in various fields such as agriculture, geology, ecology and hydrology.
Aim. In this work, we calculate the reflection of a linearly polarized electromagnetic wave from wet soil, taking into account such physical factors as heterogeneity of soil structure, surface roughness and dispersion.
Methods. Based on a heterogeneous mathematical model of wet soil, taking into account the dispersion of the dielectric constant of water and surface roughness, expressions are derived for the complex reflection coefficients of electromagnetic waves of vertical and horizontal polarization.
Results. The model of loose wet soil with the standard deviation of roughness on the surface was chosen as the object of study. An analysis of the frequency and angular characteristics of the modules of the reflection coefficients was carried out at a fixed level of soil moisture.
Conclusion. The data obtained as a result of the calculations is a valuable tool for further improving methods of remote sensing of the Earth and contributes to the development of new technologies for monitoring soil parameters using unmanned aerial vehicles, which opens up prospects for more accurate and efficient analysis of the state of land resources and ecosystems.
30-37
Double wavefront reversal during six-wave interaction on Kerr nonlinearity in a waveguide with infinitely conducting surfaces
Abstract
Background. Generation of a wave with a double reversed wavefront in multimode waveguides increases the efficiency of six-wave radiation converters and expands the possibilities of its use in adaptive optics problems and the conversion of complex spatially inhomogeneous waves.
Aim. The quality of double wavefront reversal during six-wave interaction in a waveguide with infinitely conducting surfaces with Kerr nonlinearity is analyzed for the ratio of the wave numbers of the pump waves equal to 2 and 0,5, and the condition that one of the pump waves excites the zero mode of the waveguide, and the amplitude distribution of the other pump wave excites the edges of the waveguide are described by a Gaussian function.
Methods. The influence of pump wave parameters on the half-width and contrast of the amplitude modulus of the object wave was studied using numerical methods. A wave from a point source located on the front face of the waveguide was used as a signal wave.
Results. The dependences of the half-width and contrast of the amplitude modulus of the object wave on the ratio between the width of the waveguide and the width of the Gaussian pump wave are obtained.
Conclusion. It is shown that the maximum change in the characteristics of a wave with a double reversed wavefront is observed when the width of the Gaussian pump waves changes in the range from 0,3 to 2 half-widths of the waveguide.
38-44
Formation of a panoramic image of the inner surface of the pipe
Abstract
Background. Visual non-destructive testing of the inner surface of pipes is an important aspect in their production and operation. A defect detected and corrected in a timely manner can significantly reduce the number of defects in production and prevent various emergency incidents during operation. Formation of a complete panoramic image of the inner surface of pipes suitable for quality analysis is an urgent and sought-after task that can be solved using computer vision systems.
Aim. This work is the research and development of television methods for forming a complete panoramic image of the inner surface of a pipe, which can be analyzed to search for defects.
Methods. To form a cylindrical panoramic image, mathematical models for the formation of an equidistant projection of spherical images obtained using a fisheye lens were used. For high-quality stitching of the resulting frames, digital image processing methods were used, including brightness and contrast transformations, and searching for special points using the MSER algorithm. Theoretical results are verified by full-scale modeling.
Results. The result of this work is an algorithm for stitching frames of a video sequence generated by a television camera with a fisheye optical system, uniformly moved along the longitudinal axis of the pipe, into a single panoramic image of the internal surface. Conclusion. The algorithm ensures the formation of a high-quality image of a full panorama of the inner surface of the pipes with the absence of brightness artifacts.
45-55
Parametrical synthesis of various radio devices with the set quantity of identical cascades of type «the nonlinear part – the resistive two-port network»
Abstract
Background. Presence of possibility of analytical definition of a part of parametres of various radio devices, optimum by criterion of maintenance of preset values of modules and phases of transfer functions on necessary quantity of frequencies, considerably reduces time of numerical optimisation of other part of parametres by criterion of formation demanded PFC and FFC in a strip of frequencies. Till now such problems dared concerning radio devices only with one cascade of type «a nonlinear part – the coordination the device» or «the coordination the device – a nonlinear part». In quality согласующего devices were used the jet, resistive, complex or mixed two-port networks. The problem of multicascade radio devices with jet two-port networks is solved also. Change of basis for the coordination two-port networks and a place of inclusion of a nonlinear part leads to change of area of a physical realizability.
Aim. Working out of algorithms of parametrical synthesis of radio devices with any quantity of identical and unequal cascades of type «a nonlinear part -the coordination the resistive two-port network» by criterion of maintenance of the set frequency characteristics. Nonlinear parts are presented in the form of a nonlinear element and parallel either consecutive on a current or pressure of a feedback.
Methods. The theory of two-port networks, matrix algebra, a decomposition method, a method of synthesis of actuation devices microwave, numerical methods of optimisation.
Results. In interests of achievement of the specified purpose systems of the algebraic equations are generated and solved. Models of optimum two-port networks in the form of mathematical expressions for definition of interrelations between elements of their classical matrix of transfer and for search of dependences of resistance of two-poles from frequency are received. It is shown, that at certain parities between quantity of cascades and values of resistance of a source of a signal and loading of the one-cascade radio device frequency characteristics of one-cascade and multicascade radio devices appear identical or similar. Such schemes are named by equivalent.
Conclusion. The comparative analysis of theoretical results (PFC and FFC radio devices, value of parametres), received by mathematical modelling in system MathCad, and the experimental results received by circuit engineering modelling in systems OrCad and MicroCap, shows their satisfactory coincidence.
56-68
On-board equipment testing procedure for the effects of electrostatic discharges
Abstract
Background. The relevance of the topic of this work is due to the need to improve the reliability and quality of the assessment of the stability of the onboard electronic equipment of spacecraft to electrostatic discharges.
Aim. Investigation of the possibilities of using the electron flux in vacuum as a test effect on the spacecraft’s on-board radioelectronic equipment in assessing its resistance to electrostatic discharges.
Methods. Field experiment, research laboratory tests, modeling, mock-up, expert assessments. The article considers the conditions for the existence of an electronic stream in the «electronic spotlight» and «scanning» modes. A mock-up of an electronic device, which was previously used for testing in the atmosphere of air, was used as a test object. It has been structurally modified taking into account the dimensions, wiring diagram, tooling and electrophysical characteristics of the vacuum chamber. The modified layout is a first-level module with antennas located inside the housing. During the experiment, a vacuum meter, a kilovoltmeter, a digital oscilloscope with a bandwidth of 500 MHz, a high-voltage cable, a two-wire line, a hermetic plate, and an electron gun were used. The required vacuum was created using an automated pumping system.
Results. The conditions for the existence of an electron flow in a vacuum chamber with a pressure of up to 10–7 mm Hg have been experimentally established. The results of research tests of the radioelectronic module in the «electronic searchlight» and «scanning» modes have been obtained. The main types of interference from the action of electrostatic discharges are investigated. The analysis of the waveforms was carried out. Based on these results, a methodology has been developed for testing the onboard equipment of spacecraft for the effects of electrostatic discharges. The proposed method provides testing at a level of operating discharge current up to 30 µA with particle energy from 5 to 50 keV.
Conclusion. The test procedure and the means of its implementation comply with the basic requirements of GOST «Resistance to electrostatic discharges» and can be used for ground tests of spacecraft onboard equipment at four degrees of rigidity.
69-76
Convergence region size research of television signal superposition iteration method for measurement machine vision system
Abstract
Background. Image processing is used in machine vision measurement systems, which are widely used in industrial applications. One of the important tasks in processing is image superposition. Registration methods must fulfill two basic requirements: satisfactory registration quality and practical processing time. One of the methods that meets these requirements is iterative superposition.
Aim. The aim is to study the size of the area (region of convergence) for the values of the parameters of the initial approximation, which ensures satisfactory superposition. The size of the region determines the performance of the iterative algorithm.
Methods. The size of the region of convergence was determined experimentally: correlation analysis and statistical simulation.
Results. Experiments have shown if a sampling step is no more than 1/10 of the size of the image fragment, then the probability of correct registration is almost equal to one. If this threshold is exceeded, then the probability decreases.
Conclusion. The size of the region of convergence of the iterative image registration method has been established. It is possible to design processing algorithms and predict processing time by obtaining results. The superposition method was introduced into a machine vision system to recognize contact wire clamps on the railway. Image superposition in this system is carried out in real time.
77-84
Coordinates estimation of the unmanned aerial vehicles by using distributed system of base stations
Abstract
Background. The different sensors and global navigation satellite system are used for positioning unmanned aerial vehicles. But in case of short-term signal loss and increasing positioning accuracy, additional methods for estimating coordinates are used.
Aim. The paper deals with positioning methods for unmanned aerial vehicles based on range estimation to base stations.
Methods. The positioning methods were investigated by mathematical modeling in Uma scenario.
Results. The methods of coordinate estimation of unmanned aerial vehicles was analyzed. The accuracy of measurements and computational complexity in an urban scenario with different numbers of base stations were investigated by mathematical model.
Conclusion. The analysis shown that the standard deviation of the coordinate estimation is about 1 m.
85-90
Antenna array of waveguide horns with an E-plane aperture, as well as horns with an aperture in the E- and H-planes
Abstract
Background. Currently, in connection with the conduct of a special military operation, the issue of the availability of inexpensive mobile terminals for high-speed satellite communications of domestic production is very relevant, as well as due to the large extent of the territories of our country, there are a number of areas where cellular communication is absent, for example, the Taiga, the Arctic, the territory of the Arctic Ocean, etc. Therefore, the only possible connection in these territories is satellite communication.
Aim. Development of a linear equidistant antenna array with equal amplitude and common-mode excitation for a mobile satellite communication terminal.
Methods. The antenna array was designed from the open ends of waveguides with a cross section of 19 × 11 mm with air filling. Adjacent pairs of radiating waveguides are powered by an E-planar divider: the waveguide is divided in half in height by a thin metal diaphragm, wave reflections from which are insignificant; further, in each half of the power divider, height-separated right and left turns and smooth transitions in the E-plane are implemented – an extension from 5,25 mm to 11 mm.
Results. An antenna array with a period of 19,5 mm has been developed. Overall dimensions: opening width – 624 mm, height – 12 mm, depth – 118 mm. A feature of the antenna array design is the use of smooth asymmetric transitions in the E-plane according to the exponential law; in the opening of the headlights, waveguide asymmetric horns alternate, with a period equal to 4 values of the width of the waveguides, taking into account the width of their narrow walls, expanding in the upper (2 adjacent radiators) and lower (next 2 radiators) directions.
Conclusion. The advantage of using an approach to the construction of linear antenna arrays powered by multichannel power dividers is the ability to minimize the depth of the antenna system. The main disadvantages are the constructive and technological complexity of power dividers and significant power losses with a large number of channels. Possible manufacturing technologies of the developed phased array: 1. Stamping of polystyrene of the inner part of the power divider and emitters. Next, polishing, copper spraying and electroplating with a layer of copper. 2. Printing on a 3D polystyrene printer, polishing, copper spraying and copper electroplating. 3. Manufacture of a power divider using SIW technology based on standard microwave laminates. The use of metallized through holes for matching power dividers. Antenna elements and coaxial waveguide junctions are made by stamping from polystyrene, or printing on a 3D printer from polystyrene, then polishing, spraying a layer of copper and electroplating with a layer of copper. 4. Metal stamping of the power divider, emitters and coaxial waveguide junctions (2 parts). The dielectric insert can be printed on a 3D printer made of polystyrene.
91-99
Estimation of the spatial resolution of a synthetic aperture radar antenna of the VHF frequency range placed on board an unmanned aerial vehicle along a real flight path
Abstract
Background. Currently, there is an intensive development of radar systems for remote sensing of the Earth, including those placed on unmanned aerial vehicles. Synthetic aperture radars are an effective means of round-the-clock and all-weather observation of objects on the Earth’s surface. Radars operating in the VHF range allow you to observe hidden and subsurface objects. The need for practical implementation of VHF band radar with synthesizing the aperture on board unmanned aerial vehicles requires additional research on the spatial resolution of radars, taking into account the unstable trajectory of the carrier.
Aim. The article considers the analysis of the influence of the flight path and its measurement errors on the quality of the radar image.
Methods. The research method provides an analysis of the shape of the radar uncertainty function with the synthesis of an aperture, which was built along a real trajectory using semi-natural mathematical modeling.
Results. As a result of the conducted research, it is shown that the quality of radar images is influenced not only by errors in the knowledge of motion parameters, but also by the very nature of the carrier’s movement and the duration of the flight.
Conclusion. Based on the results of field tests, it turned out to be possible to analyze these factors and determine the requirements for the UAV navigation system. Thus, the article shows the possibility of quality control of VHF band radar with synthesized aperture placed on board a UAV.
100-110
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