Vol 68, No 1 (2023)

The problem of scattering of a plane electromagnetic wave by a 2D periodic structure formed by absorbing spherical radially inhomogeneous dielectric elements is considered. The elements have the type of electromagnetic black holes located on a semi-infinite substrate. The numerical algorithm of the solution is developed. The algorithm is based on the hybrid projection method and takes into account the peculiarities of the black hole construction. The algorithm is generalized to the case, when black holes are situated on a
perfectly conducting screen. New expressions for calculating the power absorbed by the structure elements are derived. The numerical results characterizing the efficiency of the structure absorption are presented.

A possibility of the ionosonde coverage expansion due to applying navigation satellite systems for supplying with the reliable short-wave radio communication acting along extended radio paths including multihop radio paths. It is shown on the basis of processing experimental data that the functionality increase of the vertical sounding ionosonde can be provided using the hardware-software ionospheric sounding complex that uses data of navigation satellites. The application of this complex in the place, where the vertical sounding ionosonde is located, allows to obtain the detailed picture of the electron concentration distribution not only far from the ionosonde but also inside the sounding region itself, along the trajectories that all points located under the ionosphere follow and that cross the responsibility zone of the vertical sounding station. It is shown that it is possible to create the dense network of the ionospheric control on the basis of vertical sounding stations distributed over a territory and hardware-software complexes.

Based on the calculation of the Fourier integral directly and without simplifying assumptions, the analysis of the process of passage of terahertz pulses with a hat-shaped envelope and Van Bladel envelope through a layer of a resonant-absorbing medium described by the Drude–Lorentz model is carried out. It is
shown that until the end of the time interval prescribed by the Maxwell equations, there is no radiation at the exit from the layer, i.e., the Fourier integral does not contain the effect of “superluminal” propagation of an
electromagnetic pulse through a resonantly absorbing medium. An alternative interpretation of the shift to the beginning of the pulse of the envelope maximum emerging from the radiation layer at small optical depths
(~1) of the layer at the resonant frequency of the medium is proposed.

A leaky-wave bifocal linear array focused in the Fresnel zone is considered. The structural parameters provide perfect focusing of the field at two points corresponding to two different frequencies. An approximate theory of antenna arrays is used to analyze the bifocal array, to study the shape of the frequency scanning arc, and to determine the field distribution in the focal spot. An electrodynamic simulation is performed for a strip array with slotted radiators. The scattering parameters of the array and its radiation characteristics
are presented. The design features of a strip antenna that suppress the effect of normal are discussed. The results of an experimental study of a strip bifocal array are presented. The possibility of implementation of a symmetrical scanning arc and a relatively low level of optical aberrations is shown.

The results of study on determining the height of the snow cover on a site with a relatively flat terrain using a laser rangefinder are presented. Data on the thickness of the snow cover was determined from the dependence of the difference in distances from the reflection point to the rangefinder with and without snow cover in the winter–spring period. The modeling of the determination of the thickness of the snow cover was carried out under the assumption of small irregularities of the measured surface. It is shown that the simulation data may differ from the experimental results up to ~200 mm even on relatively flat areas with a slope of less than 1°, which in some cases is insufficient to predict the impact of snow on snow-covered objects. Comparison
with other methods for measuring the depth of snow cover is carried out. Possible applications of the technique used in problems of monitoring and remote sensing are discussed.

The paper presents methods for describing distortions of signals during their propagation in transionospheric transmission lines, which cause inter-symbol and inter-channel interferences. A technique for estimating the statistical characteristics of the interference noise has been developed and their estimation for digital phase-shift keyed signals is carried out by simulating transionospheric lines. The probabilistic characteristics and asymptotic probabilities of erroneous reception of the considered signals with an increase in their frequency band are estimated using the calculated statistical characteristics for the lines of the P range.

The effect of high-order uniaxial anisotropy on the nature of orientational transition of magnetizationis considered. In the geometry of normal magnetization of the medium with respect to the anisotropy axis, the energy density and the equilibrium position of magnetization are obtained depending on the magnitude of the applied field. The orientation of magnetization is considered for anisotropy from the second to the eighth even orders only. As an example, the simultaneous presence of anisotropy of the second and fourth
orders is considered. For this case, an algebraic equation of the third degree is obtained for the analysis of which the Cardano discriminant is used. It is shown that in the case of a negative value of the discriminant, the dependence of the magnetization orientation on the field has a hysteresis character.

A 1D model of a finite-length spin chain with the Dzyaloshinskii–Moriya interaction is considered. An algorithm for simulation of the problem is developed, and calculations that demonstrate the existence of discrete magnetic breathers of various types in the phase of forced ferromagnetism of a chiral helimagnet are presented. It is shown that the analysis with allowance for the Dzyaloshinskii–Moriya interaction yields a decrease in the amplitude of discrete magnetic breathers.

The paper presents a generalized technique for calculating a passive current-controlled frequency mixer at an arbitrary intermediate frequency, taking into account the complex input impedance of the current source and output load. The results of simulation in the Micro-Cap environment and comparison with the
calculation are presented. The frequency dependences of the transfer impedance are considered.