RADIO PHYSICS AND RADIO ASTRONOMY
type: channel
description: The Journal “Radio Physics and Radio Astronomy” (RPRA) is a peer-reviewed quarterly scientific journal of the National Academy of Sciences of Ukraine. RPRA was established in 1995. State Registration Certificate for printing mass media is КВ №1231, 02.02.1995; re-registration: КВ 25208-15148 ПР from 20.07.2022 ISSN 2415-7007 (Online) ISSN 1027-9636 (Print) Abbreviated key title: Radio phys. radio astron. DOI: https://doi.org/10.15407/rpra URL: http://rpra-journal.org.uа Language of publishing: Ukrainian, English Founders: The National Academy of Sciences of Ukraine Institute of Radio Astronomy of the National Academy of Sciences of Ukraine O. Ya. Usikov Institute for Radiophysics and Electronics of the National Academy of Sciences of Ukraine Publisher: The NAS-Ukraine Academperiodyka Publishing House The NAS-Ukraine Academperiodyka Publishing House replicates the RPRA within the NAS-Ukraine Journal Support Program. RPRA publishes papers, brief information and letters to the editors relating to the modern problems of radio physics, radio astronomy and astrophysics, containing the results of fundamental and applied researches, description of research methods, hardware implementation and practical application, as well as current information such as comments, events, men of science. The RPRA is included into the List of scientific professional editions of Ukraine, approved by the Decree No. 582 of 24.04.2024 of the Ministry of Education and Science of Ukraine, in which the results of Ph.D. and Doctoral theses (in physics and mathematics) are recommended to be published. Current Issue Volume 30, No.4 (2025) CONTENT
publisher: Видавничий дім «Академперіодика»
language: en-US
publication name: RADIO PHYSICS AND RADIO ASTRONOMY
issn: 1027-9636
copyright: Since April 2018, all papers in RPRA are published under the terms of the Creative Commons Attribution 4.0 International (CC-BY) License with the authors retaining a copyright to their papers. This license permits anyone to copy, distribute, spread, and adapt the paper content, without obtaining permission from the author(s) or the Journal, provided the proper acknowledgement of the work used authorship and initial publication in this journal. Please see the full license terms and requirements at https://creativecommons.org/licenses/by/4.0/ The authors of the papers published prior to December 2018, have granted the Journal the right of the first publication and retain the copyright as the owners of the manuscript.
items: IMPACT OF THE NOVEMBER 3, 2013 SOLAR ECLIPSE ON THE STATE OF THE IONOSPHERE AS INVESTIGATED IN A RADIO ASTRONOMICAL TECHNIQUE
items: LARGE-SCALE DISTURBANCES IN THE TERRESTRIAL IONOSPHERE, WHICH ACCOMPANIED THE LAUNCHES AND FLIGHTS OF POWERFUL ROCKETS
items: OFF-AXIS TARGET ILLUMINATION IN RADAR OVER-SEA TRACKING USING AN ACTIVE PHASED ARRAY ANTENNA
items: A NEW METHOD FOR SIDELOBE SUPPRESSION IN THE AMBIGUITY FUNCTION OF SIGNALS MODULATED BY PSEUDO-RANDOM SEQUENCES
items: PASSIVE RADAR LOCATION OF A SURFACE TARGET CARRYING A ROTATING RADIATION ANTENNA
items: A FIBER-OPTIC HYDROACOUSTIC PRESSURE SENSOR BASED ON INTERMODE INTERFERENCE
items: AXIALLY SYMMETRIC MODES IN AN OPEN RESONATOR

IMPACT OF THE NOVEMBER 3, 2013 SOLAR ECLIPSE ON THE STATE OF THE IONOSPHERE AS INVESTIGATED IN A RADIO ASTRONOMICAL TECHNIQUE
type: item
description: Subject and Purpose. This work examines eff ects of the November 3, 2013 solar eclipse, in particular the atypical increases in the level of radio interference and scintillations of the radio sources 3C 123 and Cas-A that were observed at 25 MHz. These phenomena might owe to the enhanced wave activity in the ionosphere during the eclipse and a reduced radio wave absorption. Methods and Methodology. The observations were conducted with the use of the low-frequency radio telescope URAN-4 (operative range 10—30 MHz). The observational data concerning radiation from cosmic radio sources and the accompanying interference are presented, for further analysis, in the form of time series. Wavelet analysis has been applied to the data arrays to identify the dominant periods of radio source scintillation. Results. A significant increase in interference intensity was observed on the day of the eclipse climax, as well as the next day. The radio source Cas-A exhibited quasi-periodic variations of intensity on a timescale of 3 to 7 minutes. The scintillation analysis performed for the source 3C 123 before and aft er the eclipse failed to provide conclusive evidence of eclipse-related effects. Conclusions. Despite the fact that the solar eclipse of November 3, 2013, was not optically visible in Ukraine (because the nearest visibility zone for the partial eclipse lay farther toward the South of the Crimea and further on toward Turkey), an anomalous rise in the level of interference was still recorded over the time window of observations from October 31 to November 7, 2013. No similar enhancements were observed either before or after the eclipse. This is likely the result of a combined effect involving reduced absorption in the ionospheric D-layer, the noticeable shift in the F-layer’s location (which leads to appearance of distant reflections), and appearance of active agents like TIDs. All of these together brought forth a sharp increase in interference levels at 25 MHz. Despite th…
creator: A. L. Sukharev
creator: M. I. Ryabov
creator: V. V. Galanin
creator: D. A. Zabora
rights: Copyright (c) 2025 RADIO PHYSICS AND RADIO ASTRONOMY
date: 2025-12-08
publication date: 2025-12-08
volume: 30
number: 4
starting page: 217
doi: 10.15407/rpra30.04.217

LARGE-SCALE DISTURBANCES IN THE TERRESTRIAL IONOSPHERE, WHICH ACCOMPANIED THE LAUNCHES AND FLIGHTS OF POWERFUL ROCKETS
type: item
description: Subject and Purpose. The ionosphere is the main channel for the propagation of radio waves. Its condition is determined bythe state of the atmospheric and space weathers, both of which depend on processes on the Sun, in the geospace, and in the Earth’s atmosphere. A serious impact on the state of the atmospheric and the space weather is produced by launches and flights of powerful rockets. The purpose of this paper is to present the results of observations and analyses of the disturbances in the ionosphere that accompanied launches and flights of heavy rockets from various cosmodromes around the world. Methods and Methodology. In order to monitor disturbances in the ionosphere, a vertical Doppler sounder was used. The radar is able to detect relative disturbances in the electron density about 10–3 to 10–2 per cent over oscillation periods of 102 to 103 s. The beat signal formed by the signal reflected from the ionosphere and the one from the local oscillator were subjected to spectral processing over time intervals of 1 min. Results. As follows from the observational data, the rocket launch from the Plesetsk cosmodrome (RF) was accompanied by an aperiodic disturbance of electron density, of duration about 20 minutes and speed of 1000 to 1140 m/s. The disturbance with a speed of 450 to 500 m/s was also aperiodic. A quasi-periodic disturbance with a period of 6 to 7 min and speed of 330 to 340 m/s was carried by a long-wave infrasound. The amplitude of the relative disturbance in electron density was δN≈ 1 percent. For atmospheric gravity waves with periods of 20 or 30 min the relative disturbance in electron density was δN≈ 6 to 14 per cent. At the start of the Proton M rocket, three groups of disturbances with speeds of 555, 240 and 170 m/s were observed. In their case, the estimate for δN is 1.5 to 3 per cent. During the rocket launch from the Wenchang (PRC) cosmodrome, three possible groups of disturbances were noted, with speeds of 560, 410 and 270 m/s. In the ca…
creator: L. F. Chernogor
rights: Copyright (c) 2025 RADIO PHYSICS AND RADIO ASTRONOMY
date: 2025-12-08
publication date: 2025-12-08
volume: 30
number: 4
starting page: 232
doi: 10.15407/rpra30.04.232

OFF-AXIS TARGET ILLUMINATION IN RADAR OVER-SEA TRACKING USING AN ACTIVE PHASED ARRAY ANTENNA
type: item
description: Subject and Purpose. Th is paper addresses the challenge of measuring the angular coordinates of over-sea low-altitude targets and strives to improve the measurement accuracy of radar systems that employ high-resolution algorithms implemented through active phased array antennas (APAAs). The primary purpose is to substantiate the eff ectiveness of off-axis target illumination in the context of sea clutter and multipath. Off-axis target illumination reduces the depth of the probing signal interference fading over the radar-to-target path. The investigated illumination method focuses on mitigating errors in target angle measurements by multi-channel methods based on high-resolution algorithms, such as root-MUSIC. One of the main spoilers of measurement accuracy when using those algorithms is the noise in the radar receiving channels. Off-axis target illumination helps avoid a deep fade of the signal, thereby enhancing the signal-to-noise ratio (SNR) in the receiving channels of APAA-equipped radar systems, which contributes to target tracking stability despite destructive multipath interference. Methods and Methodology. The study employs computer simulations within a multipath radio-wave propagation model for a rough sea surface, allowing for both specular and diffuse reflections. The power distribution of diffuse reflections and their mapping along the propagation path are evaluated using the empirical glistening-surface model, the most advanced to date. Results. Quantitative assessments of the effectiveness of off-axis target illumination have been obtained in the context of fading conditions produced by multipath radio wave propagation over the sea surface. The optimal illumination angles have been identified. They help avoid deep fades over a wide range of sea states. These optimal angles are confined within 0.6 to 0.75 of the beamwidth of the radiation pattern. The lower end of the indicated range refers to the diffuse sea clutter, and the upper end corresponds t…
creator: Yu. F. Logvinov
creator: Yu. O. Pedenko
creator: O. V. Bukin
rights: Copyright (c) 2025 RADIO PHYSICS AND RADIO ASTRONOMY
date: 2025-12-08
publication date: 2025-12-08
volume: 30
number: 4
starting page: 250
doi: 10.15407/rpra30.04.250

A NEW METHOD FOR SIDELOBE SUPPRESSION IN THE AMBIGUITY FUNCTION OF SIGNALS MODULATED BY PSEUDO-RANDOM SEQUENCES
type: item
description: Subject and Purpose. One of the main challenges in achieving high-accuracy radar target parameter determination and improving radar system noise immunity is the presence of sidelobes in the ambiguity function of the used signals, especially when these signals are periodic Pseudo-Random m-Sequences (PRS) of maximum length. In this work, a new method for completely suppressing ambiguity function sidelobes is developed through theoretical analysis with cross-correlation processing of PRS-modulated signals and a specially tailored reference signal. Methods and Methodology. The suggested approach to suppressing sidelobes of the PRS ambiguity function addresses cross-correlation processing of the received signals. These are PRS modulated using a reference signal tailored so that zero values of the sidelobes of the correlation function fall beyond the zone of high correlation in the signals. Results. The proposed method can completely suppress all ambiguity function sidelobes along the time delay axis for the PRS of maximum length. Compared to traditional processing, the sidelobe level along the Doppler shift axis of the carrier is slightly higher. However, this is so when the number of PRS elementary pulses is too small. As their quantity increases, the difference tends to be negligible. The signal-to-noise ratio at the correlator output and the range resolution performance have been estimated for both the proposed and traditional processing methods Conclusions. A new algorithm for PRS cross-correlation processing has been developed, accompanied by a straightforward method for tailoring a reference signal. The innovation enables sidelobe elimination regardless of the PRS length, while maintaining both range resolution and signal energy efficiency. It has been demonstrated that the signal-to-noise ratio at the correlator output remains unchanged compared to traditional processing. These points highlight a significant advantage over traditional methods. These methods often …
creator: K. O. Lukin
creator: V. M. Konovalov
creator: L. V. Yurchenko
rights: Copyright (c) 2025 RADIO PHYSICS AND RADIO ASTRONOMY
date: 2025-12-08
publication date: 2025-12-08
volume: 30
number: 4
starting page: 258
doi: 10.15407/rpra30.04.258

PASSIVE RADAR LOCATION OF A SURFACE TARGET CARRYING A ROTATING RADIATION ANTENNA
type: item
description: Subject and Purpose. The authors recently proposed a passive radar method for determining ranges and coordinates of surface targets using a single reference receiving point. The work is directed at further developing this method with a focus on scenarios where the surface target incorporates a radar with a rotating radiation antenna, such as a pulse omnidirectional radar. Methods and Methodology. The previously proposed passive radar method for determining the distance to a target is extended to the case where a surface object can have a rotating radiation antenna. Still, the method is based on using a radio buoy, which creates a supplementary radio wave propagation path. The receiving device is installed on the shore and detects two signals. One is the radio buoy signal travelling the supplementary propagation path. The other is the target direct signal travelling the primary path. The time delay between the two signal arrivals is measured, and the distance to the target is calculated using a specially developed algorithm. The system operation is analyzed and evaluated. Results. The previously proposed passive radar method for determining the target distance employs a radio buoy equipped with a transmitter and an amplifier-repeater. The method has been refined enough to range targets carrying rotating radiation antennas. As before, an additional radio wave propagation path from the target to the amplifier-repeater arises and is caught by the ground-based receiver on the shore. The task of determining the time delay between the radio beacon signal and the main signal from the target faces challenges associated with the movement of the target’s rotating antenna. The challenges can be effectively managed through a technique that is presented in the paper and expertly addresses the time delay between signals traveling along the primary and supplementary paths, as detailed in the paper. For practical implementation, the proposed principle of passive radar operation is s…
creator: I. M. Mytsenko
creator: O. M. Roenko
rights: Copyright (c) 2025 RADIO PHYSICS AND RADIO ASTRONOMY
date: 2025-12-08
publication date: 2025-12-08
volume: 30
number: 4
starting page: 268
doi: 10.15407/rpra30.04.268

A FIBER-OPTIC HYDROACOUSTIC PRESSURE SENSOR BASED ON INTERMODE INTERFERENCE
type: item
description: Subject and Purpose. The use of the two-mode operation of an optical fi ber in fiber-optic sensors simplifies the interferometerdesign and enhances the reliability of sensing. Methods and Methodology. The mechanism behind the appearance of intermode phase shifts of the light modes Lp01 and Lp11 under various types of optical fiber deformation is examined. A mathematical model of a hydroacoustic sensor based on a two-mode optical fiber is proposed and experimentally validated. The intermode phase-acoustic sensitivity of the optical fiber to hydroacoustic pressure is evaluated for the Lp01 and Lp11 modes. A segment of a multimode optical fiber is fusion-spliced to the output of the two-mode fiber. This method creates conditions for the interference of the Lp01 and Lp11 modes and increases the modulation depth of the light flux at its output. Results. The heart of a hydroacoustic pressure-sensitive element in this research is an optical fiber with a core diameter of 18 μm and a numerical aperture of 0.0592. With the use of a 0.86 μm laser, propagation conditions are created for the two modes, Lp01 and Lp11 . The alteration of the mode content when a mode mixer is installed at the input of the optical fiber has been studied. For the fiber-optic sensor with a signal-to-noise ratio of 1:1 at the photodetector output and a frequency bandwidth of 100 Hz, the minimum detectable acoustic pressure inside the sensitive element is 55 Pa, and the intermode phase-acoustic sensitivity is 5.2*10-9 Pa. Conclusions. It has been shown that the two-mode operation of the optical fiber enables the development of interferometric fiber-optic sensors that are sensitive to mechanical deformations of the fiber. These sensors are characterized by a simpler design compared to traditional fiber-optic sensors based on Mach–Zehnder interferometers. It has been demonstratez that using a single-mode optical fiber with a reduced optical radiation wavelength ensures propagation conditions for the two l…
creator: I. V. Linchevskyi
creator: M. V. Chursanova
rights: Copyright (c) 2025 RADIO PHYSICS AND RADIO ASTRONOMY
date: 2025-12-08
publication date: 2025-12-08
volume: 30
number: 4
starting page: 276
doi: 10.15407/rpra30.04.276

AXIALLY SYMMETRIC MODES IN AN OPEN RESONATOR
type: item
description: Subject and Purpose. The behavior of axially symmetric oscillations in a hemispherical open resonator (OR) integrated into a waveguide transmission line and operating in pass-through mode is studied. The apertures of the OR mirrors are 60 mm. The radius of curvature of the spherical mirror is 85 mm. Two 3.6×0.17 mm slot coupling elements are positioned symmetrically about the OR axis and 13.2 mm away from it. The axially symmetric oscillations excited in a hemispherical OR by slotted coupling elements are analyzed with the view of characterizing dielectric materials using resonant methods in the EHF range. Methods and Methodology. Basic quasi-optical techniques are adopted. Namely, the electric-field structures of oscillation types are measured by the perturbation method. The resonant transmission coefficients of open oscillatory systems and the physical phenomena occurring within them are experimentally studied using standard microwave measurement techniques. Results. In the experimental study conducted at 70.622 GHz, OR oscillations with large transverse indices were identifi ed from amplitude distributions. The perturbation method was used with a 1 mm diameter probe. It has been shown that in non-axial OR excitation, axially symmetric oscillations, among others, are excited. Experimentally, a distinctive feature of those axially symmetric oscillations has been established, which is an area with zero electric-field intensity at the center of the cavity. For the investigated TEM*0,1,12 oscillation, this area is 6 mm in diameter. Conclusions. It has been demonstrated that an open resonator with axially symmetric oscillations is effective for measuring the electrophysical parameters of materials, including liquids. It has been established that the placement of a disk-shaped sample or a liquid-filled cuvette at the center of the flat mirror of a hemispherical OR not only does not disrupt the working oscillation but additionally contributes to the angular mode selectio…
creator: I. K. Kuzmychov
creator: O. S. Lukash
creator: O. B. Senkevych
creator: O. A. Voitovych
creator: T. M. Narytnyk
creator: G. I. Churyumov
rights: Copyright (c) 2025 RADIO PHYSICS AND RADIO ASTRONOMY
date: 2025-12-08
publication date: 2025-12-08
volume: 30
number: 4
starting page: 285
doi: 10.15407/rpra30.04.285