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 31, No.1 (2026) CONTENT
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WAYS TO IMPROVE MEASUREMENT ACCURACY OF ATMOSPHERIC TRACE GAS PARAMETERS: HARDWARE AND DATA PROCESSING
Subject and Purpose. Analysis of ways to increase the accuracy of determining the parameters of the Earth’s atmosphere through the improvement of the ground-based spectral radiometric complex designed for monitoring carbon monoxide (CO) by millimeter radio wave radiation control, which was developed at the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine The purpose is achieved by reducing the measurement errors of the emission amplitude of the observed tracer gas through the operational determination of the absorption of radio waves in the troposphere. By performing a rapid calibration of the troposphere opacity and promptly accounting for changes in radio signal absorption, we increase the accuracy and reliability of measurements of atmospheric CO radio emission intensity. This method is suitable for any systems of this type. By studying the frequency stability of local oscillators of all stages of frequency conversion in the receiving system, the maximum error in measuring stratospheric wind speeds at altitudes from 20 to 80 kilometers was determined. Methods and Methodology. The improved CO-monitoring setup measures radiometric atmospheric profiles, from which a new data processing method introduced in the paper quickly derives the antenna scattering coefficient. Then, the tropospheric absorption of the radio signal is evaluated immediately during monitoring in near-real time. Results. The CO-monitoring spectroradiometric complex has been upgraded and improved, enabling the measurement of radiometric atmospheric profiles and providing a prompt, near-real-time determination of the antenna scattering coefficient (previously unavailable). It has been demonstrated that monitoring the antenna scattering coefficient enhances the determination accuracy of the CO emission line amplitude, thereby increasing the reliability and validity of the obtained results. The studies related to the modernization of the monitoring instrument helped us evaluate the accuracy of measuring stratospheric wind speeds. Conclusion. Practical work and evaluations have proved that measuring tropospheric opacity directly during observations is feasible and significantly increases the accuracy and reliability of the results. Keywords: millimeter waves, aeronomy, measurement accuracy Manuscript submitted 06.10.2025 Radio phys. radio astron. 2026, 31(1): 003-010 REFERENCES 1. Forkman, P., Christensen, O. M., Eriksson, P., Urban, J., & Funke, B., 2012. Six years of mesospheric CO estimated from ground-based frequency-switched microwave radiometry at 57º N compared with satellite instruments. Atmos. Meas. Tech., 5(11), pp. 2827—2841. 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GEOMAGNETIC NEAR FIELD DISTURBANCES AS GENERATED BY THE JANUARY 15, 2022 UNIQUE EXPLOSION OF THE TONGA VOLCANO
Subject and Purpose. The January 15, 2022 explosion of the Tonga volcano, unique in its power, led to significant disturbances of the Earth’s subsystems, including the lithosphere and the World Ocean — atmosphere — ionosphere — magnetosphere system, plus the geophysical fields like the baric, the electric and the magnetic. A task of great importance is a detailed study of disturbances in all the subsystems and of the fields involved, in particular, a further study of geomagnetic field component variations (and such of their derivatives) that appear to be generated in the near-field zone by the unique explosion of January 15, 2022. Methods and Methodology. To analyze temporal variations of the geomagnetic field, data records of its three spatial components have been used, specifically of the X, Y, and Z, and of their time derivatives Ẋ, Ẏ, and Ż , as recorded at geomagnetic observatories (stations) of the INTERMAGNET network during the explosion. The measurement error never exceeded 0.1 nT. The time resolution was 1 min. The records obtained on the quieter days of January 13, 2022 and January 17, 2022 have been chosen as reference data. Results. Some specific features have been identified of the near-field geomagnetic effects that accompanied the powerful explosion of the Tonga volcano. The activity led to generation of an aperiodic "bay-shaped" disturbance and a number of quasi-periodic magnetic disturbances. The "bay-shaped" synchronous disturbances in the field components X-, Y- and Z- measured at the West Samoa API station as 15 nT, 28 nT, and –13 nT, respectively, and lasted for 120 to 146 min. Their generation mechanism is associated with the formation of an ionospheric "hole" under the action of a blast wave. The time delay of the "bay-shaped" disturbances was close to 16 min. Among the quasiperiodic disturbances, the earlier ones observed at the API station demonstrated a 6 min delay time, being caused by an acoustic resonance of a 4.4 min period and a 2 nT amplitude in the field of a standing wave. In addition to the resonant oscillations, other groups of quasi-periodic disturbances were also observed, whose delay times increased gradually from 8.5 to 75 min. The apparent horizontal velocities in their case were 4.0, 1.5, 1.0, 0.5, 0.31, and 0.2 km/s. Such velocities corresponded to slow magnetohydrodynamic waves, blast waves, atmospheric gravity waves, Lamb’s wave or a tsunami. At greater separations from the volcano, the time delays of disturbances in each of those groups demonstrated a trend toward increasing, which suggests a volcanic origin of the magnetic disturbances under discussion. Conclusions. The geomagnetic field disturbances observed in the near-field zone (up to 103 km from the volcano) differed qualitatively and quantitatively from the disturbances at larger separations (3 to 5)·103 km Keywords: Tonga volcano, near-field zone, geomagnetic field, bay-like disturbance, quasi-stationary disturbance, time delay, apparent velocity, disturbance mechanism Manuscript submitted 26.01.2023 Radio phys. radio astron. 2026, 31(1): 011-025 REFERENCES 1. Adushkin, V.V., Rybnov, Y.S., and Spivak, A.A., 2022. Wave-Related, Electrical, and Magnetic Effects Due to the January 15, 2022 Catastrophic Eruption of Hunga Tonga–Hunga Ha’apai Volcano. J. Volcanolog. Seismol, 16(4), pp. 251—263. DOI:https://doi.org/10.1134/S0742046322040029 2. Astafyeva, E., Maletckii, B., Mikesell, T.D., Munaibari, E., Ravanelli, M., Coisson, P., Manta, F., and Rolland, L., 2022. The 15 January 2022 Hunga Tonga eruption history as inferred from ionospheric observations. Geophys. Res. 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Physical effects from the powerful Tonga volcanic eruption of January 15, 2022, in the Earth — atmosphere — ionosphere — magnetosphere system. J. Atmos. Terr. Phys., 253, id.106157. DOI: https://doi.org/10.1016/j.jastp.2023.106157 7. Poli, P., and Shapiro, N.M., 2022. Rapid Characterization of Large Volcanic Eruptions: Measuring the Impulse of the Hunga Tonga Ha’apai Explosion From Teleseismic Waves. Geophys. Res. Lett., 49(8), id. e2022GL098123. DOI:https://doi.org/10.1029/2022GL098123 8. Imamura, F., Suppasri, A., Arikawa, T., Koshimura, S., Satake, K., and Tanioka, Y., 2022. Preliminary Observations and Impact in Japan of the Tsunami Caused by the Tonga Volcanic Eruption on January 15, 2022. Pure Appl. Geophys., 179, pp. 1549—1560. DOI:https://doi.org/10.1007/s00024-022-03058-0 9. Kubota, T., Saito, T., and Nishida, K., 2022. Global fast-traveling tsunamis driven by atmospheric Lamb waves on the 2022 Tonga eruption. Science, 377(6601), pp. 91—94. 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Atmospheric waves and global seismoacoustic observations of the January 2022 Hunga eruption, Tonga. Science, 377(6601), pp. 95—100. DOI:https://doi.org/10.1126/science.abo7063 16. 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Supplementary Materials for Atmospheric waves and global seismoacoustic observations of the January 2022 Hunga eruption, Tonga. Science, 377(6601). DOI:https://doi.org/10.1126/science.abo7063 17. Otsuka, S., 2022. Visualizing Lamb waves from a volcanic eruption using meteorological satellite Himawari-8. Geophys. Res. Lett., 49(8), id. e2022GL098324. DOI:https://doi.org/10.1029/2022GL098324 18. Zhang, S.-R., Vierinen, J., Aa, E., Goncharenko, L.P., Erickson, P.J., Rideout, W., Coster, A.J., and Spicher, A., 2022. 2022 Tonga Volcanic Eruption Induced Global Propagation of Ionospheric Disturbances via Lamb Waves. Front. Astron. Space Sci., 9, id. 871275. DOI:https://doi.org/10.3389/fspas.2022.871275 19. Chernogor, L.F., and Shevelev, M.B., 2024. A statistical study of the explosive waves launched by the Tonga super-volcano on January 15, 2022. Space Sci. & Technol., 30(1), pp. 66—79 (in Ukrainian). DOI: https://doi.org/10.15407/knit2024.01.066 20. Aa, E., Zhang, S.-R., Erickson, P.J., Vierinen, J., Coster, A.J., Goncharenko, L.P., Spicher, A., and Rideout, W., 2022. Significant Ionospheric Hole and Equatorial Plasma Bubbles Aft er the 2022 Tonga Volcano Eruption. Geophys. Res. Lett., 20(7), id. e2022SW003101. DOI:https://doi.org/10.1029/2022SW003101 21. Harding, B.J., Wu, Y.-J.J., Alken, P., Yamazaki, Y., Triplett, C.C., Immel, T.J., Gasque, L.C., Mende, S.B., and Xiong, C., 2022. Impacts of the January 2022 Tonga Volcanic Eruption on the Ionospheric Dynamo: ICON-MIGHTI and Swarm Observations of Extreme Neutral Winds and Currents. Geophys. Res. Lett., 49(9)id. e2022GL098577. DOI:https://doi.org/10.1029/2022GL098577 22. Le, G., Liu, G., Yizengaw, E., and Englert, C.R., 2022. Intense equatorial electrojet and counter electrojet caused by the 15 January 2022 Tonga volcanic eruption: Space- and ground-based observations. Geophys. Res. Lett., 49(11), id. e2022GL099002. DOI:https://doi.org/10.1029/2022GL099002 23. Themens, D.R., Watson, C., Žagar, N., Vasylkevych, S., Elvidge, S., McCaffrey, A., Prikryl, P., Reid, B., Wood, A., Jayachandran, P.T., 2022. Global propagation of ionospheric disturbances associated with the 2022 Tonga volcanic eruption. Geophys. Res. Lett., 49(7), id. e2022GL098158. DOI:https://doi.org/10.1029/2022GL098158 24. Chernogor, L.F., 2023. Ionospheric total electron content variations caused by the Tonga volcano explosion of January 15, 2022. Space Sci. & Technol., 29(3), pp. 67—87 (in Ukrainian). DOI:https://doi.org/10.15407/knit2023.03.067 25. Chernogor, L.F., and Mylovanov, Y.B., 2023. Electron Density Reduction Caused by the Tonga Volcano Eruption on January 15, 2022. Kinematics and Physics of Celestial Bodies, 39(4), pp. 204—216 (in Ukrainian). DOI:https://doi.org/10.3103/S0884591323040037 26. Iyemori, T., Nishioka, M., Otsuka, Y., and Shinbori, A., 2022. A confirmation of vertical acoustic resonance and fieldaligned current eneration just after the 2022 Hunga Tonga Hunga Ha’apai volcanic eruption. Earth Planets Space, 74, id. 103. DOI:https://doi.org/10.1186/s40623-022-01653-y 27. Schnepf, N.R., Minami, T., Toh, H., and Nair, M.C., 2022. Magnetic Signatures of the 15 January 2022 Hunga Tonga–Hunga Ha’apai Volcanic Eruption. Geophys. Res. Lett., 49(10), id. e2022GL098454. DOI:https://doi.org/10.1029/2022GL098454 28. Soares, G., Yamazaki, Y., and Matzka, J., 2022. Localized geomagnetic disturbance due to ionospheric response to the Hunga Tonga eruption on January 15, 2022. Geophys. Res. Lett. DOI:https://doi.org/10.1002/essoar.10510482.1 29. Yamazaki, Y., Soares, G., and Matzka, J., 2022. Geomagnetic Detection of the Atmospheric Acoustic Resonance at 3.8 mHz During the Hunga Tonga Eruption Event on 15 January 2022. J. Geophys. Res.: Space Phys., 127(7), id. e2022JA030540. DOI:https://doi.org/10.1029/2022JA030540 30. Chernogor, L.F., 2023. Global variations in the geomagnetic field caused by the explosion of the volcano Tonga on January 15, 2022. Space Sci. & Technol., 29(4), pp. 78—105 (in Ukrainian). DOI:https://doi.org/10.15407/knit2023.04.078 31. Chernogor, L.F., and Holub, M. Yu., 2023. Bay-shaped variations in the geomagnetic field that accompanied the catastrophic explosion of the Tonga volcano on January 15, 2022. Kinematics and Physics of Celestial Bodies, 39(5), pp. 247—260. DOI:https://doi.org/10.3103/S0884591323050033 32. Sorokin, V.M., and Fedorovich, G.V., 1982. The physics of slow MHD waves in the ionospheric plasma. Moscow: Energoatomizdat. 33. Chernogor, L.F., Blaunstein, N., 2013. Radiophysical and Geomagnetic Eff ects of Rocket Burn and Launch in the Near-the-Earth Environment. Boca Raton, London, New York: CRC Press. Taylor & Francis Group.
DATA ACQUISITION AND MULTITHREAD PROCESSING IN STEPPED-FREQUENCY NOISE GROUND-BASED SAR FOR 2D REAL-TIME IMAGING
Subject and Purpose. In the paper, the real-time operation of the data acquisition (DAQ) system for stepped-frequency noise ground-based Synthetic Aperture Radar (SAR) is described with an emphasis on DAQ system characteristics and software in an effort to elaborate a real-time operation algorithm on this basis. Methods and Methodology. The real-time operation algorithm outlined in the paper uses Fourier analysis to process input signals acquired with the SAR receiver. The algorithm utilizes multithreading technology to achieve the required real-time performance. The validity of the proposed algorithm is evaluated against conventional signal processing algorithms and techniques using MATLAB packages for numerical analysis and graphic visualization. The experimental investigation of the proposed real-time operation algorithm as part of the software for the developed stepped-frequency noise ground-based SAR was conducted indoors via preliminary laboratory tests. Results. An algorithm for real-time data acquisition and radar imaging has been developed. Its implementation in the software for stepped-frequency noise ground-based SAR enhances the performance of the data acquisition and processing system. A comparative analysis has been performed, showing that the results obtained in the context of the proposed real-time signal-processing program align with reconstructions by standard signal-processing simulation techniques. Measurements performed with the DAQ system as part of the developed stepped-frequency noise ground-based SAR validate our approach and its particular implementation. The observations suggest good target visibility. The target resolution in range and azimuth provided by a 32-element antenna array exceeds that of the 16-antenna configuration. The multithreading approach essentially reduces software runtime. As a result, making a single radar image takes about 10 milliseconds. Conclusions. It has been shown that the developed data acquisition and processing system integrated into stepped-frequency noise ground-based SAR lends itself well to real-time radar imaging. Keywords: stepped-frequency noise ground-based SAR, 2D imaging, data acquisition Manuscript submitted 20.02.2025 Radio phys. radio astron. 2026, 31(1): 026-034 REFERENCES 1. Batool, S., Frezza, F., Mangini, F., Simeoni, P., 2020. Introduction to Radar Scattering Application in Remote Sensing and Diagnostics: Review. Atmosphere, 11(5), 517. DOI: https://doi.org/10.3390/atmos11050517 2. Moreira, A., Prats-Iraola, P., Younis, M., Krieger, G., Hajnsek, I., Papathanassiou, K.P., 2013. A tutorial on synthetic aperture radar. IEEE Geosci. Remote Sens. Mag., 1(1), pp. 6—43. DOI: https://doi.org/10.1109/MGRS.2013.2248301 3. Park, S., Kim, Y, Lee, K., Smith, A.H., Dietz, J.E., Matson, E.T., 2020. Accessible Real-Time Surveillance Radar System for Object Detection. Sensors, 20(8), 18 pp. DOI: https://doi.org/10.3390/s20082215 4. Cumming, I.G., Wong, F.H., 2005. Digital Processing of Synthetic Aperture Radar Data: Algorithms and Implementation. Norwood, MA: Artech House. 5. Woodhouse, I., 2006. Introduction to Microwave Remote Sensing. Boca Raton, FL: CRC Press. 6. Oliver, C., Quegan, S., 2004. Understanding Synthetic Aperture Radar Images. Herndon, VA: SciTech Publishing. 7. Tomiyasu, K., 1978. Tutorial review of synthetic-aperture radar (SAR) with applications to imaging of the ocean surface. Proc. IEEE, 66(5), pp. 563—583. DOI: https://doi.org/10.1109/PROC.1978.10961 8. Henderson, F., Lewis, A., 1998. Manual of Remote Sensing: Principles and Applications of Imaging Radar. New York: Wiley. 9. Curlander, J.C., McDonough, R. N., 1991. Synthetic Aperture Radar: Systems and Signal Processing. New York: Wiley. 10. Lukin, K.A., 2001. Noise Radar Technology. Telecommunications and Radio Engineering, 55(12), pp. 8—16. DOI: https://doi.org/10.1615/TelecomRadEng.v55.i12.20 11. Vyplavin, P., Melnikova, E., Lukin, S., 2010. Real-time signal processing in noise radar. In: Proc. 11th Int. Radar Symposium (IRS-2010). Vilnius, Lithuania, 16—18 June 2010, pp. 1–3. 12. Lukin, K.A., Moreira, J.R., Vyplavin, P.L., Lukin, S.K., Zemlyaniy, O.V., 2013. FPGA based soft ware defined noise radar. Appl. Radio Electron., 12(1), pp. 89—94. 13. Lukin, S., Zemlyaniy, O., Palamarchuk, V., Tatyanko, D., Lukin, K., Pascazio, V., 2018. Methods for Generation of Probing Signals in Software Defined Noise Radar. In: Proc. 2018. 19th Int. Radar Symp. (IRS). Bonn, 2018, pp. 1—9. DOI: https://doi.org/10.23919/IRS.2018.8448097 14. Lukin, K., Palamarchuk, V., Zemlyanyi, O., Tatyanko, D., Zaets, N., Shelekhov, O., Lukin, S., Jarabo Amores, P., and Rosa Zurera, M., 2023. Ku-Band (sub-THz) Demonstrator of Microwave Video Camera. URSI Radio Sci. Lett., 4, pp. 59—63. DOI: https://doi.org/10.46620/22-0059 15. ICP DAS CO., LTD, 2024. PCIe-8622 ICP DAS Data Sheet [pdf]. Available at: https://www.icpdas.com/web/product/ download/pc_boards/document/data_sheet/PCIe-8622_en.pdf 16. ICP DAS CO., LTD, 2015. PCIe-862x Series User Manual [pdf]. Available at: https://www.icpdas.com/web/product/download/pc_boards/document/manual/pcie-862x_user_User_Manual_v10_en.pdf 17. Lyons, R.G., 2011. Understanding Digital Signal Processing. 3rd ed. Prentice Hall. Upper Saddle River, NJ. 18. Soumekh, M., 1999. Synthetic Aperture Radar Signal Processing: with MATLAB Algorithms. State University of New York, Buffalo, John Wiley & Sons, Inc., ISBN: 0-471-29706-2. 19. MATLAB SAR Toolbox. Available at: https://github.com/ngageoint/MATLAB_SAR
TERRESTRIAL INVESTIGATION OF THE LOW-FREQUENCY SENSITIVITY OF A RADIO ASTRONOMICAL ANTENNA PROPOSED FOR LUNAR FAR-SIDE OBSERVATIONS OF COSMIC RADIO EMISSIONS
Subject and Purpose. Theoretical and experimental studies of an active antenna element, seen as a part of the future low-frequency radio telescope for an observatory on the lunar far-side. The project is focused on design simplification. The objective of the research is to provide for a high fl uctuational sensitivity of the telescope while minimizing antenna’s mass and dimensions, thereby facilitating its delivery and deployment on the lunar surface. Methods and Methodology. To develop an antenna element up-scaled from the GURT prototype for 4...40 MHz, it was proposed to exclude the three-meter vertical support, using the arms of the crossed dipoles as load-bearing elements. Effectiveness was evaluated through estimating the antenna’s sensitivity, specifi cally by applying the criterion which proceeds from estimates of excess of the external over the internal noise temperature. Terrestrial experiments used short-wave radio noise as a virtual "free generator", which allowed determining characteristics of the antenna over a wide frequency range. This method enabled evaluating the antenna’s operation under actual interference conditions governed by the state of ionospheric layers D and F2. Results. Numerical analysis and measurements showed that the proposed design, devoid of the support rack, does not significantly degrade the antenna’s sensitivity, allowing efficient reception in the 7...40 MHz range. Experiments also demonstrated possibility of operation below 7 MHz, although terrestrial effectiveness is limited by local radio interference. Under lunar conditions, where such interference is absent, additional prospects for efficient observations are open. The data confirm the antenna’s ability to follow the impact of geophysical phenomena on ionospheric parameters. Conclusions. The results confirm effectiveness of the simplified active antenna design and suitability for lunar missions. The antenna can be employed for monitoring solar radiation and studying space radio sources in the terrestrial environment. Removal of the mast has made the modification more compact than the GURT prototype, which is critical for space transportation. Keywords: active antenna, ionosphere, F2 layer, the Moon, radio astronomical observations Manuscript submitted 23.12.2025 Radio phys. radio astron. 2026, 31(1): 035-050 REFERENCES 1. Lin, Y., Yang, W., and Zhang, H., 2021. Return to the Moon: New perspectives on lunar exploration. Innov., 2(1), 100063. DOI:https://doi.org/10.1016/j.xinn.2020.100063 2. Burns, J.O., 2021. Transformative science from the lunar farside: observations of the dark ages and exoplanetary systems at low radio frequencies. Philos. Trans. R. Soc. A: Math. Phys. Eng. Sci., 379(2188), 20190564. DOI:https://doi.org/10.1098/rsta.2019.0564 3. 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Kyiv, Ukraine: Naukova Dumka (in Ukrainian). 10. Tokarsky, P.L., Konovalenko, A.A., Yerin, S.N., and Bubnov, I.N., 2019. An Active Antenna Subarray for the Low-Frequency Radio Telescope GURT — Part I: Design and Theoretical Model. IEEE Trans. Antennas Propag., 67(12), pp. 7304—7311. DOI: https://doi.org/10.1109/TAP.2019.2927841 11. Azami, M., Aubin-Fournier, P.-L., Hojjati, M., and Skonieczny, K., 2025. Additive Manufacturing of PEEK/Lunar Regolith Composites for Sustainable Lunar Manufacturing. arXiv preprint. arXiv:2508.00894. 12. HPL Machining, 2025. Does NASA Use Carbon Fiber? [online] Available at: https://hplmachining.com/uk/blog/does-nasa-use-carbon-fiber/ (Accessed: 18 Oct 2025). 13. Vecchio, A., Brinkerink, C., Karapakula, S., Klein-Wolt, M., Falcke, H., Boonstra, A.J., Bentum, M., Ruiter, M., Rotteveel, J., Bertels, E., Ping, J., and Chen, L., 2022. The Netherlands-China Low-frequency explorer (NCLE), 2022. In: Proc. 3rd URSI AT-AP-RASC. Gran Canaria, Spain, 29 May — 3 June 2022. 14. Karapakula, S., Brinkerink, C., Vecchio, A., Pourshaghaghi, H.R., Dolron, P., Jordans, R., Bertels, E., Aalbers, G., Ruiter, M., Boonstra, A.J., Bentum, M., Prinsloo, D., Arts, M., Bast, J., Damstra, S., van Duin, A., Ebbendorf, N., van der Marel, H., Morawietz, J., Witvers, R., Poiesz, W., van Dongen, R., Cecconi, B., Zarka, P., Dekkali, M., Chen, L., Wang, M., Zhang, M., Huang, M., Yan, Y., Dong, L., Tan, B., Zhang, L., Xiong, L., Sun, J., Zhang, H., Ping, J., Wolt, M.K., and Falcke, H., 2024. Architecture Design and Ground Performance of Netherlands-China Low-Frequency Explorer. Radio Sci., 59(1), e2023RS007906. DOI: https://doi.org/10.1029/2023RS007906 15. Sridharan, T.K., Lehmensiek, R., Schwarz, S., and Marrone, D.P., 2025. Antenna Technology Readiness for the Black Hole Explorer (BHEX) Mission. arXiv preprint. arXiv:2504.15560. DOI: https://doi.org/10.1109/ICEAA65662.2025.11305888 16. Konovalenko, A.A., Falkovich, I.S., Kalinichenko, N.N., Gridin, A.A., Bubnov, I.N., Lecacheux, A., Rosolen, C., and Rucker, H.O., 2003. Thirty-Element Active Antenna Array as a Prototype of a Huge Low-Frequency Radio Telescope. Exp. Astron. 16(3), pp. 149—164. DOI:https://doi.org/10.1007/s10686-003-0030-8 17. Falkovich, I.S., Konovalenko, A.A., Gridin, A.A., Sodin, L.G., Bubnov, I.N., Kalinichenko, N.N., Rashkovskii, S.L., Mukha, D.V., and Tokarsky, P.L., 2011. Wide-band high linearity active dipole for low frequency radio astronomy. Exp. Astron., 32(2), pp. 127—145. DOI: https://doi.org/10.1007/s10686-011-9256-z 18. Hicks, B.C., Paravastu-Dalal, N., Stewart, K.P., Erickson, W.C., Ray, P.S., Kassim, N.E., Burns, S., Clarke, T., Schmitt, H., Craig, J., Hartman, J., and Weiler, K.W., 2012. A Wide-Band, Active Antenna System for Long Wavelength Radio Astronomy. Publ. Astron. Soc. Pac., 124(920), pp. 1090—1104. DOI: https://doi.org/10.1086/668121 19. ITU-R Recommendation P.372-16, 2022. Radio Noise [pdf]. International Telecommunication Union, Geneva. [online] Available at: https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.372-16-202208-S!!PDF-E.pdf 20. Ellingson, S.W., 2005. Antennas for the Next Generation of Low-Frequency Radio Telescopes. IEEE Trans. Antennas Propag., 53(8), pp. 2480—2489. DOI: https://doi.org/10.1109/TAP.2005.852281 21. Cane, H.V., 1979. Spectra of the non-thermal radio radiation from the galactic polar regions. Mon. Not. R. Astron. Soc. 189(3), pp. 465—478. DOI: https://doi.org/10.1093/mnras/189.3.465 22. Duric, N., Theodorou, A., Smith, K., Zouaoui, G., Harris, M., Junor, W., and Gaussiran, T., 2003. RFI report for the U.S. SouthWest. [online] Available at: ftp://gemini.haystack.edu/pub/lofar/siting_docs/SWUS_RFI.doc (Accessed: 11 July 2021). 23. Zakharenko, V., Konovalenko, A., Zarka, P., Ulyanov, O., Sidorchuk, M., Stepkin, S., Koliadin, V., Kalinichenko, N., Stanislavsky, A., Dorovskyy, V., Shepelev, V., Bubnov, I., Yerin, S., Melnik, V., Koval, A., Shevchuk, N., Vasylieva, I., Mylostna, K., Shevtsova, A., Skoryk, A., Kravtsov, I., Volvach, Y., Plakhov, M., Vasilenko, N., Vasylkivskyi, Y., Vavriv, D., Vinogradov, V., Kozhin, R., Kravtsov, A., Bulakh, E., Kuzin, A., Vasilyev, A., Ryabov, V., Reznichenko, A., Bortsov, V., Lisachenko, V., Kvasov, G., Mukha, D., Litvinenko, G., Brazhenko, A., Vashchishin, R., Pylaev, O., Koshovyy, V., Lozinsky, A., Ivantyshyn, O., Rucker, H.O., Panchenko, M., Fischer, G., Lecacheux, A., Denis, L., Coffre, A., and Grießmeier, J.-M., 2016. Digital Receivers for Low-Frequency Radio Telescopes UTR-2, URAN, GURT. J. Astron. Instrum., 5(4), 1641010. DOI: https://doi.org/10.1142/S2251171716410105 24. Braude, S.Y., Men, A.V., Sodin, L.G., 1978. Decameter wave radio telescope UTR-2. In: A.A. Pistolkors, ed. 1978. Antennas. Moscow: Svyaz’ Publ. 26, pp. 3—15. 25. Men, A.V., Sodin, L.G., Sharykin, N.K., Braude, Y.M., Melianovsky, P.A., Inyutin, G.A., Goncharov, N.Y., 1978. Design principles and characteristics of the UTR-2 radio telescope antennas. In: A.A. Pistolkors, ed. 1978. Antennas. Moscow: Svyaz’ Publ. 26, pp. 15—57. 26. Berngardt, O.I., St-Maurice, J.-P., Ruohoniemi, J.M., and Marchaudon, A., 2022. Seasonal and diurnal dynamics of radio noise for 8—20 MHz poleward-oriented mid-latitude radars. Radio Sci., 57, e2021RS007338. DOI: https://doi.org/10.1029/2021RS007338 27. Pederick, L.H., and Cervera, M.A., 2016. A directional HF noise model: Calibration and validation in the Australian region. Radio Sci., 51, pp. 25—39. DOI: https://doi.org/10.1002/2015RS005842 28. International Radio Consultative Committee, 1964. World Distribution and Characteristics of Atmospheric Radio Noise. Geneva: International Telecommunication Union. 322. 29. 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DOI: https://doi.org/10.15407/rpra21.02 33. Colonna, R., and Tramutoli, V.A., 2021. New model of solar illumination of Earth’s atmosphere during night-time. Earth, 2, pp. 191—207. DOI:https://doi.org/10.3390/earth2020012 34. Zawdie, K.A., Drob, D.P., Siskind, D.E., and Coker, C., 2017. Calculating the absorption of HF radio waves in the ionosphere. Radio Sci., 52, pp. 767—783. DOI: https://doi.org/10.1002/2017RS006256 35. Alsina-Pagès, R.M., Hervás, M., Altadill, D., Calduch, J., and Blanch, E., 2017. Vertical and oblique ionospheric soundings performance comparison over the 12,760 km transequatorial HF link between Antarctica and Spain. Radio Sci., 52, pp. 498—510. DOI:https://doi.org/10.1002/2016RS006232
AN OPEN RESONATOR WITH INTERNAL INHOMOGENEITIES
Subject and Purpose. Investigations on axially symmetric oscillations excited in a hemispherical open resonator (OR) are presented with a specific focus on the effects exerted by internal inhomogeneities in the OR structure. In this context, a waveguide section is inserted in the center of one of the OR mirrors, and the field distributions of axially symmetric oscillations and the OR oscillation spectrum selection are examined. The motivation behind this study is to minimize the geometric size of the inserted waveguide while still accommodating a small-diameter dielectric sample, thereby ensuring that the measurement results are as little affected by diffraction loss as possible. Methods and Methodology. The electric-field distribution of OR eigenoscillations is studied in the framework of quasi-optic methods of probe perturbations. The OR resonance characteristics and the physical phenomena occurring within the OR are examined using established and validated techniques to measure transmission coefficients along the EHF path. Results.It has been established that in a circular waveguide with radius ɑ = 0.6042w0 (w0 is the TEM00q mode field spot radius), the TE11 mode is excited with an efficiency of 0.8993 by the central spot of the TEM10q mode. The oscillation amplitude distribution was measured at a frequency of 74.98 GHz. The axial symmetry of the OR structure is broken, but axially symmetric oscillations are still excited due to the flat insert. The circular waveguide section provides angular selection of the oscillation spectrum. The loss introduced by this waveguide to the OR does not exceed −2 dB. Conclusions. A hemispherical open resonator incorporating specific inhomogeneities that facilitate axially symmetric OR oscillations has shown potential for measuring the electrophysical parameters of materials. 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