Vol 26, No 4 (2023)

Background. Polaritons attract the attention of researchers and engineers with their unique properties and promising applications in the field of micro- and nanoelectronics. Such applications could include devices such as transistors or even polaritons lasers, as have been reported in the scientific literature.

Aim. The work analyzes the frequency reflection spectra upon excitation of polaritons, and also considers the change in the polarization ellipse upon reflection of circularly polarized light from an anisotropic crystal.

Methods. Based on the wave equation in an anisotropic medium, a dispersion equation for polaritons is derived. To calculate energy reflection coefficients using the characteristic matrix method.

Results. An aluminum nitride AlN crystal was chosen as the object of analysis. It is shown that the use of circularly polarized incident radiation makes it possible, using an anisotropic crystal, to change the nature of polarization from circular to almost linear polarization.

Conclusion. The found dependence of the polarization of reflected light can be used in electronic devices based on polaritons.

Background. The use of methods for researching and designing stable nonlinear dynamic systems by constructing the frequency characteristics of the loop gain of the negative feedback of a pulsed voltage converter through time characteristics obtained by numerical methods for solving nonlinear differential equations that describe electromagnetic processes in the converter takes a lot of time and has low accuracy in calculating optimal modes, when you need to calculate hundreds of options.

Aim. Therefore, it seems necessary to further develop the theory of stability of modulation-type pulse voltage converters using frequency stability criteria, Lyapunov functions, amplitude and phase frequency characteristics of the converter loop gain.

Methods. Stability in the «small» is solved using linearized models, which are constructed using the so-called first Lyapunov method - the «first approximation» method. The second method for studying the stability of nonlinear dynamic systems is the harmonic linearization method, when the nonlinear element is replaced by a harmonically linearized link with a transmission coefficient only for the first harmonic.

Results. The Lyapunov function for a pulse voltage converter with nonlinear relay-type elements was found. Conclusion. The results obtained in the work make it possible to simplify the design of Lyapunov-stable pulse voltage converters through the use of the method of amplitude-frequency characteristics used for stationary linear systems.

Background. There is a growing need for active sensory diagnostics of partial HF channels to provide frequency support to quasi-zenith HF radio links in varying signal propagation conditions. Enhancing the efficiency of active sensor algorithms, particularly by reducing emission time, is topical. To address this, a transition from sequential to parallel (simultaneous) diagnostics is proposed. Another significant challenge in HF communication is narrowband interference, and overcoming this issue involves the method of passive sensory diagnostics. This method assesses the availability of partial channels by analyzing the spectral density of interference power within them.

Aim. The goal of this study is to develop algorithms and software tools that implement spectral monitoring and parallel sensing of partial channels for sensory diagnostics of ionospheric channels in quasi-zenith HF communication.

Methods. The proposed approach involves integrating dynamic diagnostic methods into the development of intelligent sensors for ionospheric HF radio links, along with the creation of data analysis methods. Specialized computer software is employed to address the defined tasks. Experimental studies are conducted using the developed devices, which include intelligent active and passive radio sensors for HF radio links, to assess the load on HF communication channels.

Results. A sensor for orthogonal quasi-zenith ionospheric radio channels has been created, incorporating algorithms for synthesizing a group pulse with orthogonal subcarriers while minimizing the peak factor. Additionally, algorithms for separating subcarriers and calculating the correlation function at the reception have been developed. The sensor employs the OFDM-BPSK signal modulation method, enabling operation in simultaneous-sequential sounding mode across the potential frequency range for communication. This led to an 8-fold reduction in the total signal emission time.

Conclusion. The scientific results obtained have broad practical applications, particularly in enhancing the efficiency of wideband HF communication systems using spread spectrum signals.

Background. Antenna arrays are widely used in various fields of radio engineering, such as radio and telecommunications, satellite communication systems, etc. One of the important characteristics of an antenna array is its radiation pattern. The estimation of impedance matrices, scattering matrices, and partial radiation patterns is usually performed based on the results of numerical electrodynamic modelling. In the case of a large number of antenna elements, such modelling and optimization of the array requires significant time.

Aim. To investigate the mutual coupling between dual- polarised antenna elements included in a linear antenna array.

Methods. Modelling of antenna arrays based on cross-dipole elements was performed using methods of electrodynamic modelling software. The study of the mutual coupling of antenna elements in the antenna array and verification of the developed mathematical model were carried out by numerical methods.

Results. A physical interpretation of that there is no almost interaction between the elements operating in orthogonal polarizations, and the coefficients of mutual coupling decrease with increasing distance between antenna elements is given. Proposed a simplified model of mutual coupling, which reduces the computational complexity of the problem of determining the mutual coupling matrices.

Conclusion. It is developed a mathematical technique that allows to calculate the characteristics of antenna arrays with a large number of antenna elements, meanwhile electrodynamic modelling is carried out only for an isolated antenna element and a two-element array.

Background. The disadvantage of spectrally efficient signals with frequency multiplexing is the occurrence of intersymbol interference, which is further aggravated when these signals propagate in frequency selective channels.

Aim. The possibility and effectiveness of using neural network approaches for channel equalization and signal detection in communication systems using SEFDM signals has been assessed.

Methods. A receiver structure for SEFDM systems based on a deep complex-valued convolutional neural network is proposed, which allows recovering bits from the temporal representation of the signal without using the fractional Fourier transform and inverting the cross-correlation matrix between frequency subcarriers. A two-stage network training scheme has been developed. Based on simulation modeling, a comparative analysis of the noise immunity of SEFDM systems was carried out both in a channel with white Gaussian noise and in a channel with Rayleigh fading, using classical and neural network receivers.

Results. It is shown that there is no loss of noise immunity in channels with additive white Gaussian noise and an increase in noise immunity of the system up to 2 dB in the channel specified by the extended automotive model (3GPP-EVA).

Conclusion. The effectiveness of using deep neural complex-valued convolutional networks as receivers for spectrally efficient communication systems, as well as their advantage over classical ones, is shown.

Keywords – SEFDM; deep complex-valued convolutional neural network; turbocoding.