Visnyk of V.N. Karazin Kharkiv National University, series “Radio Physics and Electronics”

Antenna structures based on combined slot-vibrator emitters with impedance passive elements

Berdnyk S. L. — 2025-12-30

Relevance. The research is aimed at solving current problems related to the construction of mathematical models, methods and algorithms for calculating complex multi-element radiating structures, antenna systems and arrays, determining the physical processes of electromagnetic field formation by new electrodynamic structures and developing an automated system for optimizing the characteristics of antenna system fields based on electrodynamic and mass-dimensional parameters with the possibility of adapted control.

Solving the problem of creating radiating structures and antenna systems for the formation of electromagnetic fields with specified electrodynamic characteristics, which are the basic structural elements of modern radio-electronic systems and form the basis for the creation of the latest in functional properties and technical characteristics of hardware complexes (location, communications, electronic reconnaissance, electronic warfare, etc.).

Objectives. Determination of the features of the formation of electromagnetic fields by radiating structures and antenna arrays with combined slot-vibrator radiating elements when using passive ideally conductive or impedance vibrators (dipoles) and the possibilities of controlling the electrodynamic parameters of slot-vibrator radiators and optimizing the electrodynamic, technical and mass-dimensional parameters of antennas and antenna arrays.

Materials and methods. To solve boundary value problems formulated in a strict electrodynamic formulation in the form of integro-differential equations and to study the electrodynamic characteristics of antennas and antenna arrays with combined slot-vibrator structures, methods of mathematical physics (integral equations, generalized methods of reduced electro-magnetomotive forces and magnetomotive forces with basis functions obtained using the asymptotic averaging method, Galerkin methods, Green's functions and eigenwaves) and computational mathematics were applied.

Results. Methods and algorithms for calculating the electrodynamic characteristics of electromagnetic fields formed by single combined slot and slot-vibrator radiating structures and multi-element antennas and arrays with combined radiating elements have been developed. The physical features of the formation of electromagnetic fields by radiating structures and antenna systems for various geometric and electrophysical parameters and topology of the constituent elements of the radiating aperture of the antenna array have been investigated and determined.

Conclusions. It has been determined that the use of waveguide-slot antennas and antenna arrays with combined slot-vibrator radiating structures in the microwave and EHF ranges allows for the realization of the necessary (optimized) electrodynamic and mass-dimensional parameters of antenna systems and arrays, which are promising for the creation of the latest radio-electronic systems and complexes, for practical purposes.

Analysis of disturbances in the high-latitude ionosphere during a multi-step magnetic storm on November 4-5, 2023 based on incoherent scattering radar data

L.F. Chernogor — 2025-12-30

Relevance. The ionosphere is a key radio channel for radio communications, navigation, radiolocation, remote sensing and radio astronomy. Its condition determines the quality of operation of ground and space technological systems. The most powerful disturbances in the parameters of the ionosphere are caused by solar storms. As a result, radio communications, radar and radio sounding of near-Earth and deep space may be disrupted or made impossible. The high-latitude ionosphere (above ±60°) is most sensitive to such influences, where magnetospheric convection, current amplification, Joule heating, and energetic particle precipitation simultaneously manifest themselves. Incoherent scattering radar makes it possible to study the temporal and spatial dynamics of key ionosphere parameters — electron and ion temperatures, electron concentration, plasma velocities, and ionic composition. Since changes in the state of the ionospheric channel can cause failures or make it impossible to conduct a radio communication session, the operation of radio navigation devices, and positioning using satellite navigation systems, a comprehensive study of such disturbances is relevant.

The aim of this work is to study the features of disturbances in the high-latitude ionosphere using incoherent scattering radar.

Methods and Methodology. According to measurements from the Poker Flat incoherent scattering radar (Alaska, USA) during a multi-step magnetic storm on November 4–5, 2023, a study was conducted and the parameters of high-latitude ionospheric disturbances in the Northern Hemisphere were established.

Results. It was found that the largest disturbances were observed on the night of November 4–5 and in the second half of November 5 and were accompanied by extreme values of Ti up to (5–6)·10³ K, high velocities of E×B drift (>500 m/s), local disturbances of Te and a drop in O⁺/N₂. The effects of a qualitative change in the chemical composition of the ionospheric plasma and thermosphere (a change in the distribution of the O⁺/N₂ ratio values over height and a level height of about 0.5) played a key role in the formation of the negative phase of the ionospheric storm, especially on November 5–6, when Ne remained low at elevated temperatures and the preservation of convection. Recovery from these disturbances took at least two days: first, the electron concentration recovered (22:00 on November 6 - 8:00 on November 8), then the electron and ion temperatures and plasma drift velocities returned to background values, while enhanced convective processes at altitudes above
360 km persisted until the end of the observation period.

Analysis of noise immunity of a neural network system for recognizing subsurface objects

V.A. Plakhtii — 2025-12-30

Background: Subsurface sensing systems based on impulse electromagnetic waves are widely used for detecting hidden objects in soil. However, the performance of such systems significantly degrades in the presence of strong interference caused by external reflections and radio-frequency sources. The task of automated object recognition from ground-penetrating radar (GPR) signals using artificial neural networks (ANNs) is particularly challenging, since the noise robustness of such systems strongly depends on the selection of modeling parameters, input data formation, and training procedures.

Objective: To investigate and optimize the parameters of an ANN-based subsurface object detection system in order to improve its noise robustness by applying a parameter grid search algorithm.

Materials and Methods: A subsurface medium containing a hidden metallic object was irradiated with a plane impulse electromagnetic wave. The electrodynamic problem of wave propagation and scattering was solved numerically using the finite-difference time-domain (FDTD) method, taking into account the interaction between the electromagnetic field, soil, and the object. The input data for the neural network were formed from the time-domain responses of the received signals, as well as from additional information obtained using a discrete tomography approach and ray tracing. A grid search was employed to identify the optimal system configuration by analyzing the influence of input data type, number of field sensors, time window parameters, data augmentation techniques, and target encoding strategies. Noise robustness was evaluated using the F1-score and the threshold Gate SNR metric.

Results: The grid search analysis identified system configurations that provide the highest noise robustness for object recognition. It was shown that the selection of the time window is a critical factor significantly affecting the Gate SNR values. Training the neural network on noisy data was found to enhance its generalization capability and improve stability under noisy conditions. Furthermore, the encoding strategy for the absence-of-object class was demonstrated to have the strongest impact on system performance, enabling lower Gate SNR thresholds compared to other investigated parameters.

Conclusions: The application of the grid search algorithm enabled systematic optimization of the parameters of an ANN-based subsurface object recognition system. The obtained results confirm the effectiveness of combining physically motivated signal processing methods with machine learning techniques to improve the noise robustness of ground-penetrating radar systems. The proposed approach can serve as a basis for further development of automated GPR data analysis methods under real experimental conditions.

Spatial–phase dynamics of radially polarized terahertz vortex beams

A. V. Degtyarev — 2025-12-30

Актуальність. У роботі розглядається задача непараксіальної дифракції вихрових лазерних пучків терагерцового діапазону, збуджених радіально поляризованими TM_0m (m = 1, 2, 3) модами діелектричного хвилевідного резонатора. Вихрові пучки ТГц-лазерів мають значний потенціал для застосування в зображенні, спектроскопії, неруйнівній діагностиці, зондуванні матеріалів, та у високочастотних системах зв’язку. Дослідження особливостей формування просторової структури таких пучків після взаємодії зі спіральною фазовою пластиною є важливим для підвищення керованості ТГц-випромінювання.

Мета роботи — встановлення фізичних закономірностей непараксіальної дифракції радіально поляризованих пучків терагерцового лазера, сформованих TM_0m (m = 1, 2, 3) модами, після їх взаємодії зі спіральною фазовою пластиною з різними топологічними зарядами n.

Матеріали та методи. Для моделювання поширення пучків використано векторну теорію Релея–Зоммерфельда у непараксіальному наближенні. У початковій площині задавалися TM_0m моди порожнистого круглого діелектричного хвилеводу, а спіральна фазова пластина з довільним топологічним зарядом забезпечувала формування вихрової структури поля. Досліджувалися розподіли інтенсивності, фазові профілі та внесок окремих компонент електричного поля в сумарну потужність пучка.

Результати. Встановлено, що поперечна структура вихрових пучків, збуджених TM_0mмодами, визначається топологічним зарядом спіральної фазової пластини: при n = 0 та n = 2 формується кільцева інтенсивність, тоді як при n = 1 максимум поля розташовується на осі. Використання спіральної фазової пластини призводить до появи азимутальної компоненти поля, внесок якої у повну потужність є незначним. Максимальні значення інтенсивності відповідають топологічному заряду n = 1, тоді як при n = 2 ці значення зменшуються. Фазові розподіли мають однопелюсткову структуру для n = 1 та двопелюсткову для n = 2.

Висновки. Теоретично встановлено фізичні закономірності просторово-енергетичних характеристик вихрових лазерних пучків терагерцового діапазону, збуджених радіально поляризованими модами TM_0m діелектричного хвилевідного резонатора при їх поширенні у вільному просторі. Визначено особливості внеску окремих компонент електричного поля у сумарну потужність випромінювання та встановлено характерні закономірності зміни інтенсивності та фазових структур для різних порядків мод та зарядів n.

Planar hybrid heterostructures on the monolayer – GaN system

O. V. Botsula — 2025-12-30

Background. Graphene-like two-dimensional (2D) materials as promising for creating the future element base of electronics are considered. Interactions between layers of two-dimensional materials are not limited by chemical bonding and matching of the interfacial lattice. It is permitted to form heterojunctions both from different 2D materials and hybrid 2D/3D heterojunctions, having many unique characteristics and opportunities for application. One of the actual tasks is to study 2D/3D heterojunctions, and possibility of their usage as elements of electronic devices to improve or change their properties.

The aim of the work. The aim of study is to determine characteristics of planar diodes based on bulk materials (GaN), in which monolayers act as structural elements forming a 2D/3D heterojunction with a diode channel.

Techniques and Methodology. Mathematical simulation of charge transfer processes is carried out applying a two-dimensional model of a planar diode by using Ensemble Monte Carlo technique. Since the main mechanism of charge carrier redistribution between regions of different sizes was considered to be transitions involving phonons, a channel based on molybdenum dichalcogenide (MoS2), which forms a heterojunction with GaN - diode channel, was analyzed. The peculiarities of the space charge regions formation near 2D/3D - heteroboundaries are analyzed. Static characteristics of diodes were determined.

Results Charge carriers distributions in the diode channel according to the ratio of the impurity concentration in the monolayer and the channel were obtained in the course of the research. Influence of the monolayer on average concentration of electrons in the channel was studied. Dependences of current on applied voltage in a diode with a monolayer is obtained. A significant effect on charge transfer processes in the diode channel was established which can be achieved when the doping level of the GaN-based channel does not exceed 4·10²² m^-3.

Conclusions: The main factors affecting on the total current of a planar diode with a 3D/2D heterojunction are the parameters of the bulk part of the diode, the channel width and the doping level leading to the appearance of depleted GaN layer bordering the monolayer.

Characteristics of noise diodes with a graded-gap cathode accounting for self-heating effects

V. O. Zozulia — 2025-12-30

Background. There are a number of limitations to obtaining the generation of electromagnetic oscillations at high frequencies and for functional application of solid-state electronic devices. Physical limitations, and the inertia of key processes to be determinate its operation, are often an obstacle to achieving the appropriate operating frequency or the desired functionality. The use of graded materials and their successful integration into in a device structure, such as bipolar heterotransistors or intervalley electron transfer diodes, can often ensure the obtaining of appropriate characteristics. The application of graded materials allows us to improve the frequency characteristics of devices. It is relevant for the creation of active elements intended for the generation of complex noise signals.

Purpose of Work. The aim of the work is the development of a GaN-based active element with an InGaN-based graded gap mesa structure, and evaluation of their characterization.

Techniques and Methodology. To simulate the operation of the diode and obtain its characteristics, the Ensemble Monte Carlo method was applied. It involved into a procedure for determining of temperature distribution and took into account the thermal properties of the contact regions (cathode, anode and substrate).

Results. A GaN-based active element for a wide frequency range is proposed. The diode structure consists of a conductive channel with a cathode mesa structure based on a graded-gap InGaN layer and two ohmic contacts to the cathode and anode. The direct current diode characteristics are obtained. The conditions to obtaining of the required electric field distribution in the diode cathode are examined

Conclusions: The characteristics of a GaN-based active element with graded InGaN mesa structures at the cathode were obtained by using Monte Carlo simulation. Electric field stabilization and impact ionization can be obtained in the structure was shown. The structure may be used for wide frequency noise generation.