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In the field of electronic communication warfare, accurately predicting the range and intensity of shortwave interference signals presents a significant challenge due to the complex interplay between the ionospheric parameters and the electromagnetic environment. To address this challenge, we designed a novel tool to assess the interference impact area of shortwave interference signals in a dynamically changing ionospheric environment. Considering sophisticated ionospheric radio wave propagation models and innovative spatial grid methods, this tool finishes the comprehensive spatial distribution of the interference impact area and delivers grid-based insights into the interference intensity. Furthermore, the test verification of the tool demonstrated a mean error of 8.42 dB between the measured and simulated results, underscoring the efficacy and reliability of this tool. This pioneering work is poised to make substantial contributions to the field of communication electronic warfare and holds significant promise for guiding the development of interference countermeasures. [ABSTRACT FROM AUTHOR]

The characteristics of a polarized radio wave detected by an antenna onboard a spacecraft depend on the relative positions of the transmitting source and the spacecraft, the orientation of the satellite antenna with respect to the wave propagation direction, the electric field of the incident wave, and the properties of the medium traversed by the wave. Precise knowledge of the radio wave propagation direction and the receiver antenna orientation is needed for resolving the received signal properties. In this work, the focus is on the coordinated experiments between the Radio Receiver Instrument (RRI) on Swarm-E and the Natural Resources Canada Ottawa transmitter (45.4°N, 75.6°W). Three experiments, in which the RRI boresight was along the ram (13 December 2017), nadir (20 December 2017) and slew-to-target (21 December 2017) directions were selected for detailed investigations and comparisons. The deviation of the RRI boresight direction from the propagation direction of the wave vector was up to 10° in the slewed pass and varied between 0° and 180° in the two other passes. The effects of the antenna pointing direction were pronounced in the observed powers on each dipole and affected the observed (apparent) polarization characteristics. The observations were not sufficient for describing the polarization state of the original signal during one third of the RRI-ram experiment when only one dipole was receiving the signal with optimal geometry. The methods developed lay the foundation for mitigating the attitude effects to determine the true polarization characteristics of the radio wave. [ABSTRACT FROM AUTHOR]

A low-profile slant ±45° polarized antenna for a 4G/5G base station with a dominant path wave propagation model (DPM) is reported in this paper. For dual-polarization and wide impedance bandwidth, the two dipole radiators are crisscrossed and a square metallic ring is integrated with the dipole arms and screwed with the four shorting vias. The antenna operates in Band 40/41/42/43 with strong isolation and low ECC (Envelop Correlation Coefficient). Fabricated antenna results show that the predicted wideband antenna has 13.38% bandwidth in 4G, which is Band 40/41, and 29.33% bandwidth in 5G sub-6 GHz Band 42/43. The antenna has a consistent radiation pattern, a 40 dB XPD (Cross Pol Discrimination), and a beam width of 69.5° ±1.5° in the entire frequency band. Three base station sites were explored to deploy the radiation pattern of a dual-polarized antenna in the 3D EM (Electromagnetic Analysis) tool. To evaluate signal quality, strength, radio network planning, and wave propagation analysis by analyzing antenna performance in real-time scenarios with 64 and 256 QAM (Quadrature Amplitude Modulation) techniques. For the proposed four-stream MIMO (Multiple-Input-Multiple-Output) antenna arrangement at deployed cell sites for 4G/5G base station applications, the maximum downlink and uplink data rates are 3.826/2.8 Mbps and 1044/800 Mbps respectively. [ABSTRACT FROM AUTHOR]

This paper focuses on the decomposition of different modes of Loran-C resultant waves, including ground waves and onehop/two-hop sky waves, propagating in the Earth-ionosphere waveguide obtained from direct finite-difference time-domain (FDTD) modeling in the presence of the natural magnetic field. After providing the FDTD iterative formulas for the ionosphere affected by the natural magnetic field, the Loran-C resultant waves propagating in the anisotropic Earth-ionosphere waveguide are estimated using the FDTD algorithm. In both the daytime and nighttime ionosphere models, different orientations of the natural magnetic field are taken into account. The arrival times of the different propagation modes for the resultant waves were then determined using a multipath time-delay estimation method. With the above delays, the amplitudes of the different modes are acquired by solving overdetermined equations. Finally, the decomposition results are compared with those obtained in the absence of the natural magnetic field. The numerical experimental results indicate that, with a radiation power of 1 kW and a natural magnetic field of 0.5 Gs, the influence of the direction of the natural magnetic field on the field strength of one-hop sky waves is significant when the propagation distance of LF radio waves is less than 1000 km. Radio waves have multipath effects such as convergence, divergence, and diffraction due to the curvature of the Earth and the ionosphere. This results in significant interference phenomena when the propagation distance of two-hop sky waves is greater than 500 km. [ABSTRACT FROM AUTHOR]

Modern standards of digital terrestrial broadcasting allow for more efficient use of the frequency resource, they provide multimedia, scalability and flexibility of the network, support for wireless receivers, local channels, and different time modes of content delivery. Digitalization of the existing network reduces energy consumption by times by television transmitters, positively affecting the environment, which corresponds to the current trends of reducing the carbon footprint including the consequences of the introduction of modern radio broadcasting technologies. The purpose of the present work is to calculate the signals of the radio relay station of a digital terrestrial television broadcasting network for the modernization of the network in the Naryn region of the Kyrgyz Republic. The method of predicting the propagation of radio waves based on statistical analysis and experimental data, and methods of determining electromagnetic compatibility in the design of digital terrestrial television broadcasting networks are used for calculations. Calculations of the service area of digital television transmitters; calculation of energy indices of useful and interfering signals, minimum median field strength of radio relay station Ala-Myshyk, efficiency of radiated power, interpolation of field strength as a function of distance for the lower and upper frequencies are made. Recommendations on the application of the method of propagation prediction in determining the full-service area of digital television transmitters considering the terrain are given. The technical and economic indicators are calculated: the number of equipment for the stations of the modernized network is determined, the total cost of acquisition, transportation and installation of new equipment, and the annual consumption of electricity consumed by digital television transmitters is calculated. The result and methodology of calculations were applied to other stations of the network in Naryn oblast of Kyrgyzstan for its modernization and they can be used for cases of modernization of the broadcasting network in mountainous areas. [ABSTRACT FROM AUTHOR]

Modeling radio signal propagation remains one of the most critical tasks in the planning of wireless communication systems, including wireless sensor networks (WSN). Despite the existence of a considerable number of propagation models, the studies aimed at characterizing the attenuation in the wireless channel are still numerous and relevant. These studies are used in the design and planning of wireless networks deployed in various environments, including those with abundant vegetation. This paper analyzes the performance of three vegetation propagation models, ITU-R, FITU-R, and COST-235, and compares them with path loss measurements conducted in a cassava field in Sincelejo, Colombia. Additionally, we applied four machine learning techniques: linear regression (LR), k-nearest neighbors (K-NN), support vector machine (SVM), and random forest (RF), aiming to enhance prediction accuracy levels. The results show that vegetation models based on traditional approaches are not able to adequately characterize attenuation, while models obtained by machine learning using RF, K-NN, and SVM can predict path loss in cassava with RMSE and MAE values below 5 dB. [ABSTRACT FROM AUTHOR]

Inversion of precise true height electron density profile from the measured virtual heights by the Ionosonde is a quite challenging and ill‐posed problem. In this paper, we present a new method to compute the true height profiles from ionograms that relies on computing the propagation path of radio waves with time. This method does not use predefined polynomial functions to fit the vertical electron density distribution; hence, it is free from fitting errors. Instead, this method implements iterative corrections in the electron density gradient between the successive points and progressively reconstructs the true height profile. This Iterative Gradient Correction (IGC) method assures minimizing the error to below a tolerance limit at all sampled points on the ionogram. The true height profiles derived from this method exhibit better accuracy than those derived from the widely used POLynomial ANalysis, particularly, at cusp and F2‐peak regions. Further, the IGC method gives the best results at higher sampling resolutions of ionograms and is less sensitive to scaling errors. Plain Language Summary: The ionosphere is an ionized layer of Earth's upper atmosphere that reflects the incident HF (high frequency) radio waves back to the ground. This property of the ionosphere is used to establish radio communications over far distances beyond the horizon. Monitoring the electron density in the ionosphere is essential, as the changes in the ionospheric electron density distribution can significantly impact these communication systems. Ionosonde is one such classical instrument that is widely used to measure the vertical electron density distribution of the ionosphere. However, like any radar, Ionosonde assumes the radio waves travel with the speed of light, which is not true in the case of ionosphere. This assumption gives rise to higher estimates of reflection heights by the ionosphere known as virtual heights that are far from reality. In this paper, we present a new method that computes the actual path of radio waves with respect to time in the ionospheres and computes the true height electron density distribution from the measured virtual heights by the Ionosonde. This method, besides scientific research, would have potential applications in Skywave communications, over‐the‐horizon target detection and ranging applications. Key Points: A new method to derive the true height profiles from ionograms that relies on computing the propagation path of radio waves with timeProgressively constructs the true height profile by iteratively correcting the gradient between successive points until the error is <±1 kmThe Iterative Gradient Correction method gives more accurate results at the cusp and F2‐peak regions and is less sensitive to scaling errors compared to POLynomial ANalysis [ABSTRACT FROM AUTHOR]

The interplanetary magnetic field (IMF) significantly influences the global ionospheric electrodynamics, but it is still largely unknown the high‐ and low‐latitude ionospheric electrodynamical coupling under long‐duration northward IMF Bz (NBz) and By conditions. During the long‐duration NBz and duskward By conditions (Kp < 2, AE < 100 nT, SYM‐H > −25 nT) on 20 August 2014, six pairs of magnetometer data showed that daytime equatorial electrojet (EEJ) underwent strong decreases (reach up to 90%) at wide longitudes. Thermosphere‐ionosphere‐electrodynamics general circulation model (TIE‐GCM) captured well the decrease and the control simulations revealed that both effects of the NBz and By significantly change the plasma convection, Joule heating, and thermospheric winds at high latitudes; and penetration electric field (PEF) due to the NBz plays an important role in the decrease of the equatorial electric field. This study indicates the significant NBz effects on the equatorial ionospheric electrodynamics even during weak geomagnetic conditions, apart from the widely believed meteorological effects. Further study should be taken to disclose the relative contribution between geomagnetic and meteorological effects on the decrease of the equatorial electric field. Plain Language Summary: Interplanetary magnetic field significantly influences the global ionospheric electrodynamics, and the electric field plays essential roles in shaping the spatio‐temporal characteristics of ionospheric plasma, generating the ionospheric plasma instabilities, and influencing various applications related to the radio wave propagation. However, limited attention has been paid to the coupling of high‐ and low‐latitude ionospheric electrodynamics under the prolonged periods of northward IMF Bz (NBz) and By conditions. During the long‐duration NBz, duskward IMF By, and weak geomagnetic conditions (Kp < 2, AE < 100 nT, SYM‐H > −25 nT) on 20 August 2014, the daytime equatorial electrojet (EEJ) underwent strong decreases (reach up to 90%) at wide longitudes from 77°W to 39°E. Thermosphere‐ionosphere‐electrodynamics general circulation model (TIE‐GCM) effectively captured the decrease and the control simulations revealed that both effects of the NBz and By significantly change the plasma convection, Joule heating, and thermospheric winds at high latitudes; and penetration electric field due to the NBz plays an important role in the decrease of the equatorial electric field. This study highlights the significant NBz effects on the equatorial ionospheric electrodynamics even during weak geomagnetic conditions. This effect is different from the widely believed meteorological effects, which modulate the ionospheric dynamo by the lower atmospheric waves. Key Points: Thermosphere‐ionosphere‐electrodynamics general circulation model reproduces well the observed long‐duration decreases of equatorial electrojet at wide longitudes (∼120°) during the weak geomagnetic activityBoth effects of the interplanetary magnetic field (IMF) Bz and By significantly change the plasma convection, Joule heating, and thermospheric winds at high latitudesPenetration electric field due to IMF Bz is important to the decrease of the equatorial electric field [ABSTRACT FROM AUTHOR]

This paper presents the findings of radio wave characterization based on the measurement data at 5.8 GHz. The measurement data were collected by a testbed channel, which links with the following scenarios: a single tree, a row of trees, a row of trees and a road, a row of trees, a road, and a building. These experiments were conducted at University Teknologi Malaysia (UTM) Skudai, Johor to represent the suburban environment. The links consist of pairs of transmitting and receiving antennas that deploy the path of a line of sight (LOS) and non-line of sight (NLOS) radio propagation wave networks. Based on the measurement data analysis, the general issue concerning the statistical probability distribution and the characteristics of LOS and NLOS are examined and discussed. Note that 5.8 GHz technology can be used in both LOS and NLOS scenarios, but its performance varies based on the presence of obstacles and signal propagation characteristics. Other prominent experimental analysis methods, such as hypothesis testing and goodness of fit tests, are implemented to consolidate the findings. The analysis found that the empirical probability density function of LOS and NLOS channels follows Gaussian, Rayleigh, and Rician distribution. Predicting specific future technological developments, such as the availability of 5.8 GHz technology, is challenging because it depends on various factors, including research and development efforts, regulatory decisions, market demand, and technological advancements. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper studies the feasibility of a deep neural network (DNN) approach for bone fracture diagnosis based on the non-invasive propagation of radio frequency waves. In contrast to previous "semi-automated" techniques, where X-ray images were used as the network input, in this work, we use S-parameters profiles for DNN training to avoid labeling and data collection problems. Our designed network can simultaneously classify different complex fracture types (normal, transverse, oblique, and comminuted) and estimate the length of the cracks. The proposed system can be used as a portable device in ambulances, retirement houses, and low-income settings for fast preliminary diagnosis in emergency locations when expert radiologists are not available. Using accurate modeling of the human body as well as changing tissue diameters to emulate various anatomical regions, we have created our datasets. Our numerical results show that our design DNN is successfully trained without overfitting. Finally, for the validation of the numerical results, different sets of experiments have been done on the sheep femur bones covered by the liquid phantom. Experimental results demonstrate that fracture types can be correctly classified without using potentially harmful and ionizing X-rays. [ABSTRACT FROM AUTHOR]

The paper investigates software solutions to simulate radio waves propagation in urban environment, specifically for the context of the Internet of Things (IoT). The purpose of the study is to provide a comprehensive guide for utilizing the Altair Feko software to obtain a detailed representation of the IoT network, its associated parameters and how they relate to the modeling of electromagnetic fields. It is beneficial to simulate the network during the design stage to obtain valuable data and make necessary adjustments. The key features of a Sigfox or other low power IoT network can be obtained by simulation, enabling an evaluation of the network design prior to its actual implementation. Given the growing demand for IoT devices and networks, researching the optimal design and performance of such networks is of great importance. This underscores the need for continuous exploration of effective methods to achieve efficient design and performance of IoT networks. [ABSTRACT FROM AUTHOR]

The Very Low Frequency (VLF) radio wave propagation characteristics play a very important role in understanding the behaviour of the D-region. The earth-ionosphere wave guide theory has been used to evaluate the reflection height of VLF radio waves using the electron density profiles obtained from the International Reference Ionosphere (IRI) 2012 and 2016 models. For calculating the conductivity parameter, two different collision frequency models have been used. The diurnal shift in reflection height of 16-kHz VLF waves is evaluated for the midpoint of Visakhapatnam-Rugby path using the two IRI models and the results are compared with those values derived from VLF phase measurements made at Visakhapatnam. The theoretically evaluated values using the FT-2001 option for the D-region electron density profile in the IRI-2012 and IRI–2016 models are in good agreement with those obtained from phase measurements, especially in summer. The day to night shift in reflection height obtained using exponential collision critical frequency model are in good agreement with those derived from VLF phase measurements. The diurnal shift in reflection height of VLF radio waves during winter months derived from IRI models are much lower than those obtained from measurements. [ABSTRACT FROM AUTHOR]

It has long been known that field-aligned irregularities within equatorial plasma bubbles (EPBs) can cause long-range propagation of radio waves in the VHF frequencies such as those used for TV broadcasting through the so-called forward scattering process. However, no attempt has been made to use such anomalous propagations of VHF radio waves for wide-area monitoring of EPBs. In this study, we investigated the feasibility of monitoring of EPBs using VHF radio waves used for aeronautical navigation systems such as VHF Omnidirectional radio Range (VOR). There are 370 VOR stations in the Eastern and Southeastern Asian region that can be potentially used as Tx stations for the observations of anomalous propagation. We have examined the forward scattering conditions of VHF waves using the magnetic field model and confirmed that it is possible to observe the EPB-related anomalous propagation if we set up Rx stations in Okinawa (Japan), Taiwan, and Thailand. During test observations conducted in Okinawa since 2021, no signal has been received that was clearly caused by anomalous propagation due to EPBs. This is simply because EPBs have not developed to high latitudes during the observation period due to the low solar activity. In March 2023, however, possible indications of EPB-related scattering were detected in Okinawa which implies the feasibility of observing EPBs with the current observation system. We plan to conduct pilot observations in Taiwan and Thailand in future to further evaluate the feasibility of this monitoring technique. [ABSTRACT FROM AUTHOR]

Currently in Ukraine, taking into account the development of the latest mobile Internet standards (3G/4G), it is possible to access the Internet even in remote places. There are no wired Internet due to the high cost of installation and maintenance. At the same time, a huge amount of equipment appeared on the market, which allows you to assemble systems for obtaining high-quality Internet over a wireless communication line. This refers to various types of antennas in the 900–2700MHz range, modems and routers with 3G/4G support. The locations of 3G/4G Internet base stations are in district centers predominantly. So, there is a situation that remote villages, settlements do not have the opportunity to get access to high-speed Internet. This especially harms the work of biological stations and rural medical clinics, which are spread over the territory of Ukraine and are often connected in a network. The purpose of the work is to describe briefly some practical results of our own development of providing high-quality mobile communication in some remote places of the territory of the state. To provide this service in remote areas of Ukraine, signal amplification is necessary. In addition, there is a problem with the propagation of radio waves over the rough terrains for the ultra short wave and microwave ranges. To solve this problem, it is proposed to use an external antenna with a high amplification factor, which will be installed at a height of at least 6 meters above the ground to reduce the impact of interference on the path of radio waves. [ABSTRACT FROM AUTHOR]

This article discusses several aspects related to modeling the impact of offshore wind farms on maritime radar systems operating in the X and S bands. The first part of the paper focuses on theoretical models and analyses, taking into account radio shadowing and false radar echoes. Additionally, the issue of spatial modeling of wind turbines, with diffraction phenomena considered, is reviewed with the help of suitable propagation models. By relaying on a software-based implementation of the proposed model, the authors carried out a detailed simulation of the impact of wind turbines on radar systems operating in the X and S bands. The results of these simulations are presented and discussed in the second part of the article.

In this paper, we examine the features of RSDN-20 signal propagation in a high-latitude Earth–ionosphere waveguide during solar proton events, using computational experiment methods. We have analyzed two proton ground-level enhancement (GLE) events of December 13, 2006 (GLE70) and September 10, 2017 (GLE72). Electron density profiles were constructed using the Global Dynamic Model of Ionosphere (GDMI) and the RUSCOSMICS model, developed at PGI. We present estimated phase and amplitude changes in RSDN-20 signals during precipitation of high-energy protons in the high-latitude region of the Earth–ionosphere waveguide. From the results of computational experiments and the analysis of the electromagnetic signal attenuation based on analytical Maxwell’s equation system solution in magnetized ionospheric plasma, we have found a pattern in the signal attenuation frequency dependence associated simultaneously with the signal reflection height, electron density profiles, and the collision frequency of electrons with neutral particles and ions. We discuss limitations of the computational experiment method and compare simulation results with data from Lovozero and Tuloma observatories.

Subject and Purpose. The article is devoted to the analysis of theoretically and experimentally obtained values of the specific effective sea-scattering surface in the region of super-high-frequencies (SHF). The study is reasoned by the need to know characteristics of the electromagnetic wave scattering from various objects at the modeling stage. The focus is on the choice of backscattering model with a methodology of specific effective scattering surface estimation that takes into account the shadowing effect of the sea surface under given conditions. Methods and Methodology. The study is based on mathematical modeling techniques and is accompanied by the comparison of the modeling results with experiment. Results. Proceeding from the simulation results with the effect of sea-surface shadowing taken into account and relying on the check of consistency with the measured data, a comparison analysis has been performed among theoretical models of specific effective sea-scattering surface calculation at low grazing angles. Conclusion. Analysis has been given to the specific effective sea-scattering surface obtained by the facet and two-scale models and to the values measured by experiment. Quantitative estimates of the specific effective scattering surface have been obtained with the shadowing effect of the sea surface taken into account. Analysis of the quantitative estimates has been carried out.

Continuous measurements of rainfall parameters are required for radio planning and flood management among others. However, due to the dearth of requisite infrastructure and expertise within the region, it is usually necessary to use satellite and reanalysis data. In this study, the performance of ECMWF ERA5 data in providing fall velocity (W) and liquid water content (LWC) estimates at different altitudes was compared with measurements from a ground-based Micro Rain Radar in a tropical location. Results obtained showed correlation values of 0.60–0.94 and 0.16–0.93 for fall velocity and liquid water content, respectively. The performance of ERA5 was found to decrease with altitude. In general, the results show the sufficient reliability of the ERA-5 reanalysis data for the two parameters on vertical scales. Therefore, it can be inferred that the ERA-5 data are reliable in estimating the average LWC and W, especially on a vertical scale for both hydrological and radio wave propagation studies. [ABSTRACT FROM AUTHOR]

This article discusses several aspects related to the modeling of the radio channel in the wind farm propagation environment. The first part of the article is filled with the analysis of the ITU-R BT.1893-1 model, which—as will be shown—is also applicable to systems operating in the VHF and UHF bands. The conducted measurement campaign makes it possible to model a radio channel for VHF operating systems in the wind farm propagation environment. Thanks to the obtained results, the authors propose the VHF radio channel model for that environment. Using the software implementation of this model, the authors carry out a detailed simulation analysis of the impact of wind turbines on radio systems operating in the VHF band. The main motivation for this work is the growing importance of the offshore wind energy in general, numerous investments in that area in Poland, and the lack of existing mathematical models regarding the wind farms' impact on the VHF systems. The VHF band is of special interest here, as this part of the spectrum is utilized by numerous marine administration and border protection radio systems, which can be adversely affected by the wind turbines (due to interference and/or radio shadowing). [ABSTRACT FROM AUTHOR]

Information about the main characteristics of sprites and related lightning discharges is given. Results are presented of the analysis of atmospherics recorded using the IZMIRAN mobile equipment at the expedition site near the Levaya Avacha River in September, October 2002 and in August, November 2004 on the Kamchatka Peninsula. The results of the analysis are given of electromagnetic emission from lightning discharges that occurred on the Kamchatka Peninsula in July and August 2017 that were recorded by the equipment of the Institute of Cosmophysical Research and Radio Wave Propagation, Far Eastern Branch, Russian Academy of Sciences at the Karymshina expedition site are presented. The percentage of positive lightning discharges on the western and southern coasts of the Kamchatka Peninsula, which can be associated with sprites has been estimated. [ABSTRACT FROM AUTHOR]

VHF and UHF are widely used frequency bands, and accurate path loss prediction in these bands is of great significance. In order to improve the prediction accuracy and stability of radio wave propagation, we propose a combined modeling method based on the entropy weight method. This method assigns appropriate weights to the predicted values of sub‐models using entropy, and calculates the final predicted value through weighted aggregation. To validate the feasibility of our proposed method, we conduct modeling using data from Denver, Colorado. We compare our method with the ITU‐R models and a model established using the coefficient of variation method. The results demonstrate that our proposed model outperforms the compared models. Specifically, the root‐mean‐square error (RMSE) of our proposed model is reduced by 5.94 and 5.51 dB compared to the ITU‐R P.1546 and 2001 models, respectively. Moreover, our proposed model exhibits better stability than the ITU‐R models. We also use the improvement percentage (γ) to evaluate the degree of improvement of our model over the sub‐models, which is 49.13% and 47.86% for the ITU‐R P.1546 and 2001 models, respectively. Additionally, by comparing the RMSE and absolute error, we find that the entropy weight‐based method outperforms the coefficient of variation‐based method. This research demonstrates the superiority of the entropy weight‐based modeling method, providing a valuable channel modeling approach for path loss prediction and supporting the regional assimilation of radio propagation prediction methods. Plain Language Summary: VHF and UHF are widely used in various wireless transmission systems. To improve the accuracy and stability of the path loss model in these frequency bands. We proposed an entropy weight‐based method for path loss predictions for terrestrial services in the VHF and UHF bands. And to prove the performance of the path loss model based on the entropy weight method. We compared the model with the ITU‐R P.1546 and 2001 models, which are the standard model in force. The result shows that the model is better than the ITU‐R P.1546 and 2001 models by comparing the root‐mean‐square error and absolute error. Furthermore, we compared the proposed method with other weighting methods, such as the coefficient of variation‐based method. The result also shows the superiority of the proposed method. Key Points: Proposed an entropy weight‐based method for path loss predictions for terrestrial services in the VHF and UHF bandsProved the model based on the entropy weight method is better than the current model by comparing it with the ITU‐R P.1546 and 2001 modelsProved the superiority of the proposed method by comparing it with the coefficient of the variation‐based method [ABSTRACT FROM AUTHOR]

The frequency dependence of transmitted information qualitative indicators is analyzed on the example of two meridional radio links: single-hop (~2600 km) and dominant two-hop (~5100 km) for basic modes of radio wave propagation in the ionosphere. It is shown that the presence of highly efficient receiving-transmitting antennas in a radio communication system leads to the need to take the existence of a priori energetically extremely weak modes into account in the problem of radio path specification statement. In this case, we consider those formed exclusively by the mechanism of radiation transfer along the upper-angles ray trajectories in the ionospheric propagation of radio waves. If the angles of departure and arrival for such modes and the directions of the main lobes of the antenna patterns at the end points of the radio path coincide, the signal-to-noise ratio for the wave field can reach the required threshold value and ensure the successful operation of the radio communication system. This may expand the upper frequency limit for the passage of radio waves in the transition regions of jump propagation of radio waves in the ionosphere; it should be taken into account in forecasting the operation of ionospheric radio links. [ABSTRACT FROM AUTHOR]

In this paper, we study the amplitude and phase characteristics of VLF signals of an anthropogenic origin during solar proton events using the methods of a computational experiment. We consider the events of October 30, 2003 and January 23, 2012. Electron density profiles are plotted using data from the VHF EISCAT incoherent scatter radar located in Tromsø, Norway. Based on the processed data of computational experiments, that under the conditions of solar proton events, mainly amplitude distortions of VLF signals were shown to be observed while there is a frequency dependence of the magnitude of distortions of the signals of the RSDN-20 long-range navigation radio system. The signal phases of the RSDN-20 system are less affected by weak solar proton events. The effect of the lower boundary of the Earth-ionosphere waveguide in the cases of propagation of signals from the RSDN-20 system over the surface of land and ocean during a solar proton event was studied. [ABSTRACT FROM AUTHOR]

Recently, the equivalent slab thickness τ of the ionosphere has attracted great attention. This is due to its role in determining the critical frequency foF 2 from the data of the total electron content TEC, which is important in obtaining the characteristics of the high frequency HF radio waves propagation, especially during disturbances, when vertical sounding data may be absent. Currently, a global Neustrelitz equivalent Slab Thickness Model NSTM model has been developed, for the use of which it is sufficient to have 12 coefficients and an index of solar activity. On the other hand, empirical models, in particular the IRI-Plas model, in which TEC and the maximum density NmF 2 are calculated, are also global and can provide values of τ on a global scale. These models can complement each other, but both need to be testing. Preliminary comparison of the NSTM model with the NGM model whose values were calculated as the quotient of values TEC(NTCM-GL) and NmF2(NPDM) has shown better performance for the τ(NSTM) model. In this paper, τ is compared for the NSTM and IRI-Plas models using the Grahamstown station data for 2001–2010. It is shown that both models reflect the diurnal and seasonal variations of the observational τ. To quantify the correspondence between the model and observational values of τ, standard metrics were used: the mean absolute error (MAE), the root mean-square-error (RMSE), the normalized root-mean-square error (NRMSE). The MAE values were 87.6 km for the NSTM model and 64.7 km for the IRI-Plas model in 2001. The corresponding values in 2007 were 70.2 km and 58 km. The RMSE values were 109.1 km for the NSTM model and 80 km for the IRI-Plas model in 2001. For low solar activity conditions, the RMSE values are 87.0 km and 73.1 km (that is, the values for IRI-Plas are also smaller than for NSTM). The NRMSE values are 25.2 % and 18.4 %, respectively, under high solar activity, and 21.2 % and 18.0 % under low solar activity. The greatest RMSE of the model values concern morning and evening hours: they can reach 180 km for the NSTM model and 120 km for the IRI-Plas model. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents an experimental characterization of the proposed radio link model for an underground mine sensor network. Power efficiency and range are critical factors to consider when designing a wireless sensor network, particularly for low data rate applications where the goal is to have a long-lasting, low-maintenance network. A 'deploy and forget' strategy is desirable because it allows the network to operate autonomously without requiring frequent maintenance or intervention from network operators. DASH7 and IEEE 802.15.4f are both excellent choices for low-power, long-range wireless sensor networking applications. The proposed radio link model was developed and evaluated for 433 MHz DASH7 in underground mines, considering the practical electromagnetic properties of mine walls and the propagation medium, which helps in calculating accurate signal characteristics. Radio wave propagation is a critical factor that needs to be considered when designing a wireless sensor network for complex mine structures. The received signal strength indicator (RSSI) and packet error rate (PER) are two key parameters that are used to measure wave propagation and assess the quality of the radio link between sensor nodes. The radio link design has been optimized for complex mine structures by utilizing these parameters in a model, leading to improved performance and reliability. The measurements were carried out in the world's second largest salt mine at Khewra, Pakistan, with representative irregular mine structures. The RSSI and PER were measured at different node positions and with variable separation between the nodes. The proposed model allows for the easy placement of nodes on either the rooftop or near the side walls of the mine corridors, with an average variation of 6% in RSSI and 1.9% in PER. The proposed model was validated using off-the-shelf wizzi sensor nodes received from Wizzi Lab, France, and was programmed to measure RSSI and PER while operating under the 433 MHz DASH7 protocol. An agreement between modeled and measured parameters has been noted, making the proposed model a decent method for efficient node deployment in underground mine sensor networks. [ABSTRACT FROM AUTHOR]

Accurate radio wave prediction models are necessary for the innovation of mobile communication technology and the deployment of wireless sensor networks in railways. The parabolic wave equation (PWE) method is one commonly used method to predict the electromagnetic characteristic of long railway tunnels. However, the advent of novel antennas and technologies (e.g., beam steering, beamforming) has posed new challenges to PWE‐based models such as effective means of taking tilted beam patterns into account. This study addresses such a challenge by using tilted Gaussian beams to embed antennas with oriented patterns or tilted beam directions into PWE‐based models. The proposed approach does not reduce the simulation efficiency of PWE itself. The validity and practicability of the technique are demonstrated by comparing against ray‐tracing as well as experimental measurements in various tunnel environments. [ABSTRACT FROM AUTHOR]

Given the problem that the communication distance and quality of the vehicle-mounted ultrashort wave radio are affected by ground attachments and topography in the actual combat environment, a radio wave propagation prediction model of vehicle-mounted ultrashort wave radio is established based on ray tracing and machine learning. The integrated modeling of armored combat vehicle and vehicle antenna is established to obtain the antenna radiation pattern, and combined with electronic images, the radio wave propagation simulation model based on ray tracing technology is established. Based on the machine learning algorithm of the random forest and data results for the simulation model, the radio wave propagation prediction model based on the random forest was established. Compared with traditional classical radio wave propagation models such as the Egli and Okumura-Hata models, the radio wave propagation prediction model based on the random forest has higher accuracy. The root mean square error reaches 2.190 1 dB, and the coefficient of determination reaches 0.960 1. It can accurately predict radio wave propagation in the tactical communication environment. [ABSTRACT FROM AUTHOR]

Radio propagation in the millimeter wave and subterahertz domain is heavily affected by shadowing conditions. The communication link is blocked without any additional technical means being used. Coverage improvements can be provided by using reflectors, RIS arrays, and repeaters to direct radio waves around corners or obstacles. These concepts show different performance and complexity levels affecting their network deployment. This paper investigates the achievable radio range or the received power to compare specific deployment concepts under realistic propagation conditions. Overall, the repeater solution provides either the largest radio range or the lowest necessary total transmit power compared to reflectors or RIS arrays and, thereby, is the most sustainable approach. A RIS array requires an additional centralized signal processing capacity for calculating optimized RIS settings and results in the highest level of network deployment complexity. [ABSTRACT FROM AUTHOR]

The data transmission reliability is analyzed under conditions of log-normal amplitude fluctuations controlled by Fraunhofer diffraction in the data transmission line spacecraft–ground tracking station in the coherent method of signal reception in the millimeter range. The transmission channel is broken into two communication ways: deep space spacecraft–near-Earth spacecraft; near-Earth spacecraft–ground tracking station through the tropospheric channel. Optimum signal transmission frequencies in the tropospheric channel are separated by the error probability minimization criterion, and the feasibility of reaching high data transmission rates are analyzed. [ABSTRACT FROM AUTHOR]

Context. The circular polarization of radio waves is used in various electronic systems. This includes, for example, space communications stations, some radio relay communication systems, radar stations, data transmission systems and others. The characteristics of radio wave propagation are studied by using electromagnetic waves separated by circular orthogonal polarization in radiomonitoring and radiocontrol systems. Compared to other antenna types, circularly polarized antennas, such as rings, have superior design simplicity and excellent electrodynamics properties. Objective. The objective of this study is to analyse the characteristics and application of directional microstrip couplers for supplying power to ring antennas. Method. To better the performance of microstrip ring antennas, the reasons for their limited operating frequency range are analysed. These causes include the frequency-dependent parameters of the coupler, errors in calculating the directional coupler circuit, and radiation from asymmetric strip lines. To understand how supply lines, affect antenna characteristics, correlations between radiation fields determined in both its coordinate system and that of the primary axis are taken into account. Results. An analysis of the dependence graphs of the main characteristics of ring microstrip antennas with intricate power supply circuits for directional couplers and comparison with similar characteristics for simple circuits revealed that the shape of the radiation pattern in the higher radiation hemisphere became symmetrical about the axis, especially when symmetrically supplying the ring with branch-line couplers. The frequency band has also widened, at which there was an acceptable degree of deviation in the ellipticity coefficient from unity. Conclusions. The simulation results of microstrip ring antennas with power lines connected to directional couplers of different types showed that supplying the ring antenna with electricity via the directional coupler ensures circular polarization for the emitted electromagnetic waves. Additionally, the range of operating frequencies where there is only a small discrepancy in ellipticity coefficient remains at an acceptable level of –3 dB is quite broad. By utilizing directional branch-line couplers to power a ring antenna, it is possible to simultaneously emit both right and left circularly polarized waves with the same antenna. [ABSTRACT FROM AUTHOR]

The development of near-field magnetic systems and means of transmitting messages through media that significantly absorb the electromagnetic field is one of the topical areas of research in the field of wireless communication. These lossy media include water, soil, buildings. The attenuation of the magnetic field in conducting media increases with increasing frequency. To organize communication channels through a conductive medium such as sea water electromagnetic radiation of extremely low frequencies and ultra-low frequencies from 3 Hz to 300 Hz is used. Traditional communication methods due to electromagnetic radiation in that frequency ranges require large sizes of transmitting and receiving antennas. The near-field communication method makes possible significant reduction both the dimensions of receiving and emitting antennas and the transmitter power consumption. A significant limitation of near-field long-wave communication is the low bandwidth and small, up to tens of meters, communication range. The operating principle of the proposed communication system is based on the use of the magnetic component of an electromagnetic field. Transmitting element in proposed system is a solenoid with a magnetic core. Receiving magnetic field sensor is a magnet fixed on a torsion suspension. The magnet is combined with a mirror reflecting the laser beam. Rotation of the magnet under the action of an external magnetic field leads to a change in the angle of reflection of the laser beam from the mirror surface of the magnet. The reflected signal is recorded by a linear photodetector. The attenuation of the magnetic field during the transmission of radiation from a dielectric to a conducting medium was evaluated with the solution of Maxwell’s equations. A three-position binary phase shift keying and a modified three-position binary phase shift keying are developed and substantiated. The proposed solutions provide the opposite arrangement of signal symbols, high message information density, localization of the emitted signal energy in low-frequency region and an increase in communication range. Experiments had shown that usage of modified keying type shown an increase the communication range by 10 % with the same reliability of message delivery in comparison with three-position binary phase keying. The estimates of the weakening and attenuation of the magnetic field during propagation in layered media obtained from the simulation are confirmed by experimental measurements. The results of research could be used in solving problems of local deployment of secure near-field communication systems through media that absorb an electromagnetic field.

Modelling of electromagnetic wave propagation in telecommunications has evolved from empirical models to highly deterministic ray tracing and numerical methods. The extraordinary computational effort of these methods and their wave nature seem ideally suited to be approached by quantum algorithms. We first examine current progress by reviewing recent proposals in the field. We scrutinize potentially advantageous quantum architectures, ranging from mainstream gate-level computers and near-term, mid-scale noisy architectures with limited capabilities, to adiabatic and annealing approaches that are already in commercial use. We analyze the weaknesses and strengths of recent proposals. Beyond the core algorithm, mechanisms to bridge the quantum and classical worlds are of particular interest. Extremely diverse algorithm specifications, from those based on Hamiltonian simulations and emulation of variational optimization to the unconstrained binary formulation, are compared with the use of pure gate-level circuits and known quantum subroutines. We show that the graph Laplacian, given its ability to integrate boundary conditions, is uniquely suited for quantum propagation modelling algorithms rooted in differential numerical methods. Quantum computers could overcome the temporal and spatial limitations of classical methods for larger computational domains and, to some extent, address the problems of dispersion and stability in finite-difference approximations. The ability to express the solution of a problem as an eigenvalue problem turns out to be an advantage in the quantum world, where eigenvalues and eigenvectors are inextricably intertwined with quantum mechanics. In this paper, we identify the most promising techniques and scenarios that hold the greatest potential.

The prediction of radio signal transmission in tunnels is important for wireless communication link design as it enables the delivery of optimum power to the intended receiver inside the tunnel. Several techniques have been proposed to estimate path loss for wireless communication inside tunnels. The radio coverage range and where base stations need to be installed can be figured out with the help of propagation models. At the time of developing these models, modeling complexity and environmental attributes, such as the tunnel geometry and the electrical and magnetic properties of its walls and interior materials are considered. A limited amount of literature currently overviews how waves transmits through tunnels and how electromagnetic wave transmission has recently changed. This survey, which examines current advancements in the propagation of waves in tunnels, aims to address this gap. In this review, thirty wave propagation models were analyzed and grouped into distinct categories for the first time. The detailed specifications of each model were omitted to make the survey easy to comprehend. This comparative research will help service providers adopt an appropriate propagation model and plan efficient transmitter and receiver placement and link management for a specific tunnel environment.

In this paper, the urban signal propagation characteristics based on the location of blind sources are investigated. To address the issue of blind electromagnetic radiation sources in complex urban environments, intelligent methods for propagation channel path classification, and model determination are brought forth based on field test data. The intelligent classification method distinguishes between the Line-of-Sight (LoS) path channel and a direct path, the LoS multipath channel with a direct path and other multiple paths, and the Non-Line-of-Sight (NLoS) multipath channel without a direct path from the source to the test point. The modeling aspect determines the model type to which the received signal belongs based on the statistical model derived from the tested data of a specific source. A validation measurement system was constructed for the FM broadcasting band, and validation campaigns were conducted in the city of Wuhan. The process and analysis of the data using this method demonstrate the accurate distinction of the different propagation path channels and models and involve the construction of a statistical model for the FM band in Wuhan’s urban area.

The ionospheric F2 layer is the essential layer in the propagation of high-frequency radio waves, and the peak electron density height of the ionospheric F2 layer (hmF2) is one of the important parameters. To improve the predicted accuracy of hmF2 for further improving the ability of HF skywave propagation prediction and communication frequency selection, we present an interpretable long-term prediction model of hmF2 using the statistical machine learning (SML) method. Taking Moscow station as an example, this method has been tested using the ionospheric observation data from August 2011 to October 2016. Only by inputting sunspot number, month, and universal time into the proposed model can the predicted value of hmF2 be obtained for the corresponding time. Finally, we compare the predicted results of the proposed model with those of the International Reference Ionospheric (IRI) model to verify its stability and reliability. The result shows that, compared with the IRI model, the predicted average statistical RMSE decreased by 5.20 km, and RRMSE decreased by 1.78%. This method is expected to provide ionospheric parameter prediction accuracy on a global scale. [ABSTRACT FROM AUTHOR]

Radio wave propagation in an intra-vehicular (IV) environment is markedly different from other well-studied indoor scenarios, such as an office or a factory floor. While millimetre wave (mmWave)-based intra-vehicular communications promise large bandwidth and can achieve ultra-high data rates with lower latency, exploiting the advantages of mmWave communications largely relies on adequately characterising the propagation channel. Channel characterisation is most accurately done through an extensive channel sounding, but due to hardware and environmental constraints, it is impractical to test channel conditions for all possible transmitter and receiver locations. Artificial neural network (ANN)-based channel sounding can overcome this impediment by learning and estimating the channel parameters from the channel environment. We estimate the power delay profile in intra-vehicular public and private vehicle scenarios with a high accuracy using a simple feedforward multi-layer perception-based ANN model. Such artificially generated models can help extrapolate other relevant scenarios for which measurement data are unavailable. The proposed model efficiently matches the taped delay line samples obtained from real-world data, as shown by goodness-of-fit parameters and confusion matrices. [ABSTRACT FROM AUTHOR]

Radio astronomy uses radio telescopes to detect very faint emissions from celestial objects. However, human-made radio frequency interference (RFI) is currently a common problem faced by most terrestrial radio telescopes, and it is getting worse with the development of the economy and technology. Therefore, it is essential to monitor and evaluate interference during the planning, construction, and operation stages of the radio telescope and protect the quiet radio environment around the radio astronomical site. In this paper, we present a software for an RFI analysis of the radio environment around the telescope. In this software, information has been collected, including the location of the site; the technical specifications, such as aperture and the frequency range of the radio telescopes; and the terrain around the site. The software and its modules are composed of telescope, geographic, and meteorological databases, and analysis modules of terrestrial and space-based RFI. Combined with the propagation characteristics of radio waves, we can analyze and evaluate RFI on the ground and in space around the radio telescope. The feasibility of the software has been proved by the experimental implementation of the propagation properties and RFI source estimation. With this software, efficient technical support can be expected for protecting the radio environment around the telescope, as well as improving site selection for planned radio astronomical facilities. [ABSTRACT FROM AUTHOR]

In this study, we aim to analyze the electromagnetic interference (EMI) regarding the Five-hundred-meter Aperture Spherical radio Telescope (FAST) caused by base stations in the International Mobile Telecommunications-2000 (IMT-2000) frequency band. By analyzing the frequency bands used by the transmitting and receiving devices and the surrounding environmental parameters and utilizing an approach to predicting radio wave propagation loss that is based on deterministic methods, we conclude by comparing the predicted received power at the FAST with its interference protection threshold. Our analysis demonstrates that, currently, only 55.31% of IMT-2000 base stations in the FAST radio quiet zone (RQZ) meet the protection threshold. Additionally, this article verifies the applicability and accuracy of the radio wave propagation model used in the research based on field strength measurements. Overall, this study provides valuable insights for improving the electromagnetic environment surrounding FAST and reducing the EMI caused by mobile communication base stations. It also provides corresponding analysis methods and useful suggestions for analyzing electromagnetic radiation interference in other radio telescopes. [ABSTRACT FROM AUTHOR]

The interaction of the magnetospheric–ionospheric (MI) system surrounding the Earth with the environment (solar wind) occurs in the form of a series of transient processes at different scales. The largest of them, magnetic storms, are obviously triggered by disturbances in the solar wind (direct driving). The role of the internal dynamics of the MI system, which is caused to a large extent by the nonlinearity and temporal delays of the loading–unloading processes of energy and particle from the solar wind into the magnetosphere, becomes more significant at smaller scales (substorms, pseudobreakups, injections, and activations). A typical dynamic state of the MI system is characterized as self-organized criticality or turbulence, which are characterized by statistical scale invariance (scaling) in the fluctuation distributions of many characteristics. The dynamics of the MI system is projected into the region of the auroral oval, the very existence of which is due to this dynamics. The space–time structure of auroral disturbances largely reflects the structure of processes in the MI plasma. The description of this structure is important both for studying the fundamental study of plasma processes and for many topical applied problems related to the propagation of radio waves in the ionosphere and vital activity at high latitudes. The paper discusses approaches and developments for constructing a model of the space–time structure of the auroral oval, based on fractal and multifractal characteristics. [ABSTRACT FROM AUTHOR]

This paper elucidates the importance of creating backup communication channels in emergencies when access to cellular and satellite communication systems can be limited. The purpose of the study is to substantiate the use of LoRaWAN technology as a basis for building reliable backup communication facilities. A block diagram of the device has been proposed, which is used as an example for modeling the autonomy time of the device. It is shown that, depending on the mode of operation, this time ranges from 150 to 900 days. To estimate the radio accessibility zone of the device, the maximum transmission range was modeled using various models of radio wave propagation. The results of the investigations have shown that the developed emergency communication system based on the LoRaWAN protocol is effective and superior to other wireless communication technologies under certain conditions. [ABSTRACT FROM AUTHOR]

Dramatic irregularities in the plasma density of the ionosphere, first discovered by their effects on radio wave propagation in 1938, despite decades of investigation, still remain puzzling. Their deleterious effects on radio wave communication, satellite command and control, and GPS navigation strongly motivate better understanding of their nature. Many aspects of such irregularities are now understood, but the mechanism(s) of their formation and their detailed nature remain a topic of great interest. In this work, detailed time resolved measurements of lightning generated waves sometimes show dispersionless, strongly attenuated propagation with substantial propagation delays. These characteristics of the electromagnetic wave propagation in the hypothetical two‐phase bubble/non‐bubble lower ionosphere parallel the characteristics of acoustic wave propagation through two‐phase liquid/vapor foams. This motivates the suggestion that the bottomside layer of the ionosphere may sometimes be foamy. Plain Language Summary: Just as ocean waves breaking at the interface between sea and land produce copious bubbles and foam, recent satellite data suggests a similar phenomenon at the interface between neutral atmosphere and the charged plasma of the ionosphere. Lightning generated electromagnetic waves passing through the lower ionosphere observed by low altitude satellites are found to have the same characteristics as acoustic waves passing through foamy water. This hypothetical foam in the lower ionosphere apparently strongly absorbs some radio wave frequencies and seems to prevent most such waves from escaping the foam to pass through to the upper ionosphere. Key Points: Dispersionless, highly attenuated, lightning generated electromagnetic waves are observed in the lower ionosphereThe propagation of these electromagnetic waves has characteristics of acoustic wave propagation through two‐phase foamsSuch foamy plasma bubbles may cover approximately 85% of the bottomside of the equatorial nightside ionosphere [ABSTRACT FROM AUTHOR]

This paper represents observations on detection of Very High Frequency (VHF) anomalous propagation over the area of the Adriatic Sea. During the research campaign, a Software Defined Radio (SDR) Automatic Identification System (AIS) receiver was employed for collection of AIS data packets at a fixed location in the Northern Adriatic. Data were collected during the 24-h period (25 February 2023 15:32 LT to 26 February 2023 15:32 LT), providing information from 115 AIS targets, or 159 965 AIS packets with 54.3% Packet Error Rate (PER), respectively. Subsequent analysis and post-processing of successfully demodulated signals and decoded packets was presented further. In certain instances, the SDR AIS receiver detected, received and decoded data packets from AIS targets distant several orders of magnitude larger than the VHF nominal ranges. To determine the magnitude of line-of-sight and over-the-horizon radio waves propagation, the great circle distances between the SDR AIS receiver antenna and AIS packets' decoded positions were calculated, revealing hundreds of Nautical Miles (NM). Possible reasons for these occurrences, including tropospheric scattering, diffraction, ionospheric sporadic E layer and refraction were discussed and evaluated, in accordance, among others, with the previous research. By exclusion criteria and neglection of possible causes, it was concluded that the enhanced, over-the-horizon propagation of AIS signals occurred as a result of refraction effects, namely trapping/ducting, subrefraction and superrefraction. Data from nine World Meteorological Organization (WMO) radiosondes surrounding the greater reception area were collected for the same observation periods. Atmospheric profiles were created using Advanced Refractive Effects Prediction System (AREPS) program, and analysed for each individual station measurement. The results confirmed anomalous, over-the-horizon enhanced propagation and their probable origins, i.e., the occurrence of refractive conditions in the atmosphere over the Adriatic Sea area. These findings provide a solid foundation for further research in the area of propagation of VHF signals and their anomalous features caused by the atmospheric phenomenon effects. [ABSTRACT FROM AUTHOR]

A special analytical method is developed to describe the propagation of high-frequency electromagnetic waves emitted by a vertical point dipole from the surface of perfectly conducting Earth in a regular spherically layered background ionosphere. The basic representation of the wave field employs an integral over the set of wave components, each of which is related to a specific ray trajectory. Such an approach makes it possible to analytically take into account the effect of medium-scale 3D inclusions in the background ionosphere as an additional phase shift of the wave component with allowance for the distortion of its ray trajectory and to numerically calculate the effect of wave-field focusing. [ABSTRACT FROM AUTHOR]

The method of bicharacteristics is used to study the propagation of decameter radio waves in the ionosphere containing the E, F1, and F2 layers and a traveling ionospheric disturbance (TID) upon slightly oblique sounding with frequency-modulated signals. The propagation of both ordinary and extraordinary waves is considered, the ionograms are compared, and their relative shift is studied. The structure of ionograms in the vicinity of caustics, which appear at the reception point at frequencies reflected in the vicinity of the E layer and TID, is studied. The divergence of the ray flux at the point of radiation reception, which determines a decrease in the amplitude, is calculated. [ABSTRACT FROM AUTHOR]

We developed a framework merging unsupervised and supervised machine learning to classify lightning radio signals, and applied it to the possible detection of terrestrial gamma‐ray flashes (TGFs). Recent studies have established a tight connection between energetic in‐cloud pulses (EIPs, >150 kA) and a subset of TGFs, enabling continuous and large‐scale ground‐based TGF detection. However, even with a high peak current threshold, it is time‐consuming to manually search for EIPs in a background of many non‐EIP events, and it becomes even more difficult when a lower peak current threshold is used. Machine learning classifiers are an effective tool. Beginning with unsupervised learning, spectral clustering is performed on the low‐dimensional features extracted by an autoencoder from raw radio waveforms, showing that +EIPs naturally constitute a distinct class of waveform and 6%–7% of the total population. The clustering results are used to form a labeled data set (∼10,000 events) to further train supervised convolutional neural network (CNN) that targets for +EIPs. Our CNN models identify on average 95.2% of true +EIPs with accuracy up to 98.7%, representing a powerful tool for +EIP classification. The pretrained CNN classifier is further applied to identify lower peak current EIPs (LEIPs, >50 kA) from a larger data set (∼30,000 events). Among 10 LEIPs coincident with Fermi TGF observations, 2 previously reported TGFs and 2 unreported but suspected TGFs are found, while the majority are not associated with detectable TGFs. In addition, unsupervised clustering is found to reflect characteristics of the ionosphere reflection height and its effect on radio wave propagation. Plain Language Summary: In this study, we developed a machine learning‐based method to classify lightning radio signals. The method uses unsupervised and supervised machine learning to distinguish different types of signals with high accuracy. The focus of the study is to identify energetic in‐cloud pulses (EIPs) that are associated with a subset of lightning‐related terrestrial gamma‐ray flashes (TGFs). The method successfully identified 95.2% of true EIPs with up to 98.7% accuracy, and discovered new TGF events that were not previously reported. Additionally, the method revealed insights into the ionosphere and radio wave propagation. This method can be useful for studying lightning and other related phenomena. Key Points: A framework merging unsupervised clustering and supervised convolutional neural network (CNN) for lightning classification is developedClustering of positive polarity energetic lightning radio pulses (>150 kA) identifies three processes: +EIPs (6%–7%), +NBEs, and +CGsCNNs detect 95.2% of manually identified +EIPs with up to 98.7% accuracy, enabling studying EIP‐TGF link with lower peak current (>50 kA) [ABSTRACT FROM AUTHOR]

Conventional forecasting of high‐frequency (HF, 3–30 MHz) radio wave propagation is based on a combination of ionospheric and propagation models. However, at very high latitudes this approach is seriously undermined by the intrinsically dynamic ionospheric conditions regularly perturbed by energetic particle precipitations and strong electric fields. From this perspective, the multi‐year observations of HF propagation characteristics by Super Dual Auroral Radar Network (SuperDARN) radars across auroral and polar cap regions represent a unique opportunity for systematic validation of the conventional approach, as well as for creating an empirical propagation model directly from the radar observations. Qualitative identification and quantitative characterization of the propagation modes requires an accurate knowledge of the vertical angle of arrival (elevation angle) across the high‐latitude part of the radar network. This information has become available only in recent years, facilitated by the development of reliable data‐based calibration techniques for SuperDARN interferometry. We present the solar‐cycle/seasonal/diurnal climatology of HF propagation characteristics at very high latitudes derived from two‐frequency observations by the Rankin Inlet SuperDARN radar. Plain Language Summary: High‐frequency (HF, 3–30 MHz) radio waves are used for long‐distance communication, navigation and surveillance purposes, as they can propagate over the horizon due to consecutive reflections from the ionosphere and the ground surface. The conventional forecast of HF propagation at mid and low latitudes relies on ionospheric models that are used to derive HF propagation characteristics. However, this approach becomes less reliable at auroral and polar cap latitudes due to the intrinsically high variability of the high‐latitude ionosphere. In this work we lay an experimental foundation for an alternative propagation model based on direct observations of the HF propagation characteristics by Super Dual Auroral Radar Network (SuperDARN). This approach eliminates the necessity of using an ionospheric model by utilizing accurate SuperDARN angle‐of‐arrival information obtained for a full solar cycle. Key Points: Modeling high‐frequency (HF) propagation at very high latitudes is complicated by highly dynamic processes in the ionospheric plasmaSuperDARN represents a convenient tool for direct observations of HF propagation characteristicsSuperDARN interferometry data are utilized to build a climatological model of HF propagation [ABSTRACT FROM AUTHOR]

Using data from the Van Allen Probe and Swarm‐Bravo satellites, evidence for a persistent population of slow magnetosonic waves in the ionosphere is presented. Dispersion relations from two‐fluid analyses of waves in warm plasma are used to interpret and explicate these observations. These waves appear to be continuously present and globally distributed. Their amplitudes systematically decrease with increasing altitude. The amplitudes are also correlated with longitude in a manner consistent with the global distribution of lightning strikes. Evidence for narrow resonances in the Swarm data consistent with doppler shifted Schumann resonance frequencies is presented. In addition, nearly dispersionless fast magnetosonic waves are sometimes also seen. A new method for the analysis of these waves suggests they show the existence of "foamy" plasma bubble "roots" at the base of the ionosphere. Plain Language Summary: Using satellite data, just as the acoustic noise from distant lightning is heard to rumble, sometimes a considerable time later, for a much longer duration than the visible flashes, an even more greatly delayed and spread‐out series of plasma‐sound waves are found in the earth's ionosphere after every lightning bolt. The noise of these plasma‐sound waves comes in two forms. One set of plasma‐sound waves is slow and is found to be always present over the entire globe. Properly accounting for this noise in satellite electromagnetic field measurements could improve the quality of measurements of the earth's magnetic field from space, and lead to a better understanding of our earth's magnetic field and its ionosphere. A second set of plasma‐sound waves is fast, and more sporadic in appearance. These fast plasma‐sound waves are associated with plasma bubbles that can interfere with radio wave communications around the globe. Better understanding these fast waves and bubbles could possibly allow for better radio communication processes. Key Points: Globally distributed slow magnetosonic waves in the ionosphere have been found with amplitudes decreasing versus altitudeIt is suggested that these are produced by lightning generated waves impacting the Earth Ionosphere waveguide upper boundaryUnusual low dispersion whistlers suggest the existence of plasma depletion "roots" extending to the base of the ionosphere [ABSTRACT FROM AUTHOR]

In order to improve the identification effect of vehicle key performance parameters, this paper applies the PSO algorithm to the identification of vehicle key performance parameters and focuses on analyzing the parameters of the vehicle key performance parameter monitoring equipment and the propagation environment. The improvement of sensitivity of the monitoring receiver can effectively extend the coverage distance. NLOS is a ubiquitous transmission environment and changing NLOS to LOS propagation further extends the coverage distance. In order to ensure the communication quality of radio communication users, ensure that the service area covered by radio waves and the reliability of radio wave propagation, this paper calculates the propagation loss from the receiving antenna to the transmitting antenna in detail. The experimental results show that the identification method of vehicle key performance parameters based on PSO algorithm proposed in this paper can play an important role in the identification of vehicle key performance parameters. [ABSTRACT FROM AUTHOR]