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Vol 70, No 8 (2025)
ELECTRODYNAMICS AND RADIO WAVE PROPAGATION
Focusing of high-frequency electromagnetic fields by local inhomogeneities of the ionospheric electron density
Abstract
A recently developed and published specific analytical approach to the description of the processes of high-frequency electromagnetic waves propagation in the regular spherically-layered background ionosphere has been generalized to the case when the presence of medium-scale three-dimensional inclusions into the background ionosphere is also adopted. These inclusions essentially change the total ray pattern of the wave field. The effect of the local inhomogeneities has been analytically described as an additional phase increment of each wave component, with the distortion of its ray path being taken into account. The results of computations are presented that manifest the wave field focusing effects as they depend on the characteristics of the ionospheric inhomogeneities.
Radiotehnika i èlektronika. 2025;70(8):709-718
709-718
About Propagation of Gaussian Electromagnetic Pulse in a Resonantly Absorbing Gas Medium
Abstract
Based on direct and without simplifying assumptions calculation of the Fourier integral, the analysis of the process of the passage of terahertz pulses with Gaussian envelope and amplitude spectrum belonging to the frequency interval occupied by the spectral line, through the layer of resonantly absorbing medium was made. The interaction of the medium and the pulse is described by Drude-Lorenz model. It is shown that with an increase in the optical depth of the medium layer, the current envelope of the radiation field recorded at the receiving end of the path is increasingly affected by the interference effect of harmonics of individual sections of the current pulse spectrum, which leads to its fundamental deformation, but not to its systematic shift towards negative time values. Analysis of the integral characteristics of the received radiation field also does not agree with the conclusions corresponding to the first approximation of the dispersion theory. Methods are proposed for eliminating oscillations of the envelope of the received pulse by shifting the carrier and changing the bandwidth of the receiving device.
Radiotehnika i èlektronika. 2025;70(8):719-729
719-729
Achieving Angular Super Resolution Based on the Separation Method
Abstract
A comprehensive method for increasing the resolution and accuracy of angular measurements by digital antenna arrays is proposed and substantiated. The problem of searching for coordinates of individual objects in the form of a group target, which are not resolved by direct observation, is considered. Mathematically, the problem is reduced to solving Fredholm integral equations of the first kind of convolution type with additional conditions. It is proposed to implement solutions with angular superresolution based on a new method based on excluding one of the components from the analyzed signal. The results of numerical experiments on a mathematical model are presented and analyzed.
Radiotehnika i èlektronika. 2025;70(8):730-736
730-736
СТАТИСТИЧЕСКАЯ РАДИОФИЗИКА
One approach to analyzing the development of the tropical hurricanes
Abstract
An approach to tropical cyclogenesis is considered, based on the idea of the transition from the stage of a sea storm to the stage of a hurricane as a process when heat release from the ocean to the atmosphere is not balanced by heat transfer from the atmosphere to the ocean, as a result of which a surge in vertical heat fluxes at the interface of these media can be expected. The results of testing this approach for a number of tropical hurricanes in the Gulf of Mexico and in the tropical Atlantic are presented based on data on latent and sensible heat fluxes at the ocean surface from the HOAPS satellite archive. The influence of blind spots formed as a result of the divergence of the scanning bands of the microwave radiometers of DMSP satellites on the representativeness of the HOAPS archive data in the studied areas is estimated.
Radiotehnika i èlektronika. 2025;70(8):737-742
737-742
THEORY AND METHODS OF SIGNAL PROCESSING
Optimal user grouping in PD-NOMA systems
Abstract
An algorithm for optimal user grouping in wireless communication systems using PD-NOMA (Power Domain Non-Orthogonal Multiple Access) technology is proposed. The algorithm aims to minimize inter-group interference and improve the system›s interference resistance. The application of the proposed approach enables a base station with four transmit antennas to serve up to eight users, which significantly exceeds the capabilities of traditional systems employing MIMO (Multiple-Input-Multiple-Output) technology. Compared to existing user grouping algorithms, the new algorithm provides an interference robustness gain of up to 2 dB.
Radiotehnika i èlektronika. 2025;70(8):743-752
743-752
Method for converting speech signal to improve speech intelligibility
Abstract
The task of improving the speech intelligibility in communication systems is considered. The acute problem of speaker voice recognition when using known methods for solving it is pointed out. To overcome this problem, new method for converting a speech signal is proposed. It based on an autoregressive model of the vocal tract and on the principle of frequency-selective amplification of the main formants. An example of the practical implementation of a new method based on the fast Fourier transform is considered. Estimates of computational costs and its performance are given. A full-scale experiment was set up and carried out. Based on its results, the positive effect achieved by applying the proposed method was established, namely: increasing the intelligibility of the speech of the control speaker while maintaining a sufficiently high degree of recognition of his voice. The results obtained are intended for use in the development of new and modernization of existing voice communication systems, including a mobile communication and VoIP-systems.
Radiotehnika i èlektronika. 2025;70(8):753-760
753-760
PHYSICAL PROCESSES IN ELECTRONIC DEVICES
(111)A-, (411)A-oriented substrates efficiency for low-temperature epitaxial growth of (In,Ga)As photoconductive structures used in terahertz pulses generation
Abstract
In this article we have summarized the results of our research carried out since 2016 and devoted to single-layer and multilayer (In,Ga)As structures epitaxially grown at low temperatures on (111)A-oriented GaAs and (411)-oriented InP substrates, and the generation of THz oscillations by irradiating femtosecond optical pulses directly to the surface of these films or to a gap of photoconductive antennas manufactured on the surface of the films. Each of the films, in terms of its crystalline structure and THz generation efficiency, was compared with a film of similar composition grown on a GaAs or InP substrate with a standard surface orientation (100). It has been shown that films grown at low temperature on non-standard (111)A, (411)A substrates are saturated with extended defects (twins, stacking faults, low-angle boundaries of mosaic blocks) and are partially or completely polycrystalline, but this is not an obstacle to more efficient generation of THz oscillations compared to similar films on standard substrates (100), which are less defective and provide significantly higher electron mobility.
Radiotehnika i èlektronika. 2025;70(8):761-779
761-779
Effect of an inviscid nonconducting liquid on the absorption of Lamb waves in piezoelectric plates
Abstract
The dependence of the Lamb wave attenuation due to radiation into an inviscid nonconducting liquid (radiation losses) on 1) the ratio of the phase velocities of the waves in the plate Vn and the liquid VL and on 2) the ratio of the vertical component of the surface displacement U3 to the horizontal U1 in the wave of the considered number n has been experimentally investigated. It is shown that the dominant value in the formation of radiation losses is U3/U1: for small U3/U1 1, the emission of Lamb waves into a liquid and the magnitude of radiation losses are small even at Vn VL, for large U3/U1 ≥ 1, radiation into a liquid and the magnitude of radiation losses are large and can reach values comparable to with those for surface acoustic waves in the same material (~5 dB/mm). The dependence of the Lamb wave attenuation on the ratio of the velocities Vn and VL is much weaker.
Radiotehnika i èlektronika. 2025;70(8):780-786
780-786