Physics of Wave Processes and Radio Systems

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.

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.

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.

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.

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.

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.