Vol 25, No 2 (2022)

The article is devoted to numerical methods for solving the problem of diffraction of electromagnetic waves by conducting bodies. Two approaches to solving the problem are considered. The first one is based on the use of the thin-wire integral representation of the electromagnetic field (TP-method) for a grid model of the body surface. The second approach is associated with the use of the basis functions of Rao–Wilton–Glisson when solving a vector integral equation formulated with respect to the electric current density on the body surface (RWG-method). The diffraction of a plane linearly polarized electromagnetic wave by a sphere is considered as a test problem. The results of calculations of the normalized diagrams of the scattered field are presented. It is shown that there are practically no visual differences for the results obtained using both approaches. At the same time, it should be noted that the TP method is much simpler in numerical implementation than the RWG method.

In this work we calculated the reflection coefficients modules of a linear polarization plane electromagnetic wave depending on soil moisture with a relative complex dielectric constant described by the heterogeneous Maxwell Garnett and Bruggeman models. A comparison is made of the calculated dependences of reflection coefficients for incident E- and H-polarization waves on soil moisture according to the two proposed heterogeneous two-component models. The correctness of the applied models is shown within the soil moisture content up to 10 %. Within the limits of soil moisture change from 10 to 50 %, there are slight discrepancies in the calculation results for two heterogeneous models. The reflection level of an electromagnetic wave from the soil surface in the case of its H-polarization is less than in the case of E-polarization. With an increase in soil moisture, a monotonous increase in the reflection level is observed. The proposed heterogeneous models of wet soil and the calculation method can be used for remote radar sensing of the Earth’s surface in order to determine the moisture content in the rooted layer of the soil.

Introduction: the analysis of the known literature shows that the use of various types of matching quadripoles (reactive, resistive, complex, mixed) and the feedback circuit covering the non-linear element makes it possible to increase the area of physical feasibility of the given forms of frequency characteristics. The purpose of the work is to increase the area of physical feasibility of given forms of frequency responses by optimizing the parameters of matching mixed quadripoles and using an additional feedback circuit covering a nonlinear element and a mixed quadripole. One part of such quadripoles consists only of resistive elements, and the second – only of reactive elements. Materials and methods: theory of four-terminal networks, matrix algebra, decomposition method, method of synthesis of microwave control devices, circuit engineering method for analyzing the characteristics of radio devices. Results: Mathematical models of matching mixed quadripoles are obtained in the form of relationships between the elements of their transmission matrix and the dependences of the resistances of their two-terminals on frequency, which are optimal in terms of the criterion for providing specified forms of frequency characteristics. Conclusion: a comparative analysis of the theoretical results (frequency response and phase response of amplifiers) obtained by mathematical modeling in the MathCad system and experimental results obtained by circuit simulation in the OrCad and MicroCap systems shows their satisfactory agreement.

The article discusses ways of describing digital systems with various schemes, provides a comparative characteristic of these schemes, indicates the advantages and disadvantages of different schemes. The four schemes for constructing digital systems described in the article are equivalent, since with the same input signal, the output signal for all circuits will be the same, although different signals will circulate inside these circuits. To build adaptive digital systems, preference should be given to state-space circuits, since in them it is easier to adjust the parameters of the digital system. When choosing between serial and parallel circuits, preference should be given to the parallel circuit if the coefficients in it are valid. With complex coefficients, the implementation of the parallel scheme becomes more complicated, therefore, in this case, one should choose a sequential scheme in the state space, all the coefficients are real.

In the paper the digital beamforming is examined in azimuth and elevation, which allows more accurate formation of nulls and maximum of the radiation pattern. The minimum variance distortionless response beamformer, the sample matrix inversion algorithm using regularization, and the null steering algorithms at the output of cylindrical, hemispherical and planar lattices are considered. The ratio of the useful signal power to the active interference plus noise resulting power and the bit error ratio at the output of digital antenna arrays are estimated depending on the directivity of the antenna elements and the number of averaging samples. It has been established that a hemispherical antenna array can significantly increase the transmission reliability in comparison with the considered ones, which will reduce the computational load without using complicated diagramming algorithms.