Ground-based Transmitters Research Articles

System for delivering radio interference transmitters to receiving devices of ground-based radio electronic means of satellite radio communication and radio navigation systems

Formulation of the problem. The method of delivering radio jamming transmitters to the area where a radio-electronic device is located, based on dropping transmitters from an unmanned aerial vehicle, is characterized by a number of disadvantages: high complexity of the equipment and, accordingly, the high cost of the UAV; low efficiency of radio interference transmitters in suppressing ground-based radio electronics of satellite radio communication and radio navigation systems. Purpose. Consider the possibility of increasing the efficiency of radio-electronic suppression of ground-based radio electronics of satellite radio communication and radio navigation systems by autonomous radio jamming transmitters delivered to the work area using UAVs, while reducing the complexity of the equipment and the cost of UAVs - carriers of radio jamming transmitters. Results. A delivery system for radio interference transmitters is proposed. The system uses an uncontrolled free aerostat (balloon) filled with gas as a UAV. The volume of gas depends on the given flight altitude. The balloon, together with the transmitter and battery, is launched from a starting position placed on the earth's surface, taking into account the known direction of the wind and the known location of the suppressed weapon. The balloon is delivered to the electronic jamming work zone by moving air masses. The calculations showed that the use of the proposed system provides a gain in the required transmitter EIRP of at least 7 dB compared to a ground-based transmitter. To suppress a Starlink user terminal at a range of up to 4 km, a transmitter with an EIRP of no more than 13 dBW (20 W) is required. Practical significance. The results obtained can be used to increase the efficiency of electronic jamming of ground-based satellite radio communication and radio navigation systems.

Collaborative trajectory planning and transmit resource scheduling for multiple target tracking in distributed radar network system with GTAR

A reasonable resource management strategy can maximize the sensing performance of radar network system via adaptively controlling the working parameters of interest. In this paper, a collaborative trajectory planning and transmit resource scheduling (CTPTRS) strategy for multiple target tracking (MTT) in distributed radar network system with ground-based transmitters and airborne receivers (GTAR) is proposed. Firstly, the CTPTRS for the distributed radar network with GTAR (DRN-GTAR) is formulated as a non-convex optimization problem. To be more precise, the transmit power with the bandwidth of each transmitter and the trajectory of each airborne front-receiver are controlled jointly and adaptively to maximize the MTT performance. Secondly, to tackle the non-convex optimization problem, an efficient two-stage solution technique integrated with the semi-definite programming (SDP), the Latin hypercube sampling-based stochastic simulation (LHS) and the improved particle swarm optimization-tabu search (IPSOTS) is proposed. Finally, simulation results demonstrate the effectiveness of the proposed CTPTRS strategy. Furthermore, in terms of the MTT performance, the proposed strategy owns superior performance compared with six other existing baseline strategies.

Spatial and Temporal Distribution of Northwest Cape Transmitter (19.8 kHz) Radio Signals Using Data Collected by the China Seismo-Electromagnetic Satellite

Very Low Frequency (VLF) waves radiated from ground-based transmitters are crucial for long-distance communication and underwater navigation. These waves can reflect between the Earth’s surface and the ionosphere for Earth–ionosphere waveguide propagation. Additionally, they can penetrate not only the ionosphere but also the magnetosphere, where they interact with high-energy particles in the radiation belt. Therefore, studying the spatial and temporal distribution of VLF radio signals holds significant importance. Such research enables us to understand the propagation characteristics of VLF signals, their interaction with radiation belt particles, and their response to space weather and lithospheric activity events. In this paper, we investigate the seasonal variations in the intensity of the Northwest Cape (NWC) transmitter (19.8 kHz) radio signals at satellite altitude and the displacement of the electric field’s peak center. Our analysis is based on the nightly China Seismo-Electromagnetic Satellite (CSES) data from 2019 to 2021. The results reveal the following: (1) There is no significant seasonal variation in the electric field strength within a small area (2.5° radius) around the NWC transmitter. However, a clear seasonal variation in the electric field strength is observed within a larger area (15° radius), with higher strength during winter compared with summer. (2) The power spectral density of the electric field remains constant within the peak central area (approximately 1~2° radius), but it decays with distance outside this region, showing a north–south asymmetry. Moreover, the decay rate of the radiation electric field is slower in the northern direction than in the southern direction. (3) The center of the electric field moves northward from summer to winter and southward from winter to summer. (4) In winter, VLF waves radiated by the NWC transmitter may predominantly propagate by being ducted toward the conjugate hemisphere.

3D tomographic inversion for frequency semi-airborne EM under multinary constraints

The semi-airborne electromagnetic method (SAEM) has recently gained increased interest in geophysical exploration applications. For SAEM, ground-based transmitters are deployed within the area of interest or in its vicinity, and the induced magnetic is measured airborne. Because of the large footprint of extended transmitters, three-dimensional (3D) effects can have a significant impact on the gathered data and 3D modelling and inversion approaches must be employed for data analysis. Any 3D EM simulation is a resource-consuming task and efficient tools can therefore be useful to add data interpretation. In this study, 3D tomographic inversion of frequency-domain SAEM data was accomplished based on the integral equation (IE) method. The inversion was linearised by approximating the sensitivity matrix. We further employ the quasi-linear approximation to facilitate out quick forward modelling in the inversion which is tractable on field computers. While this approach sacrifices inversion accuracy for efficiency, we guide the inversion by introducing multinary constraints. These constraints impose a priori known conductivity values into the inversion process. Our results from synthetic and field data demonstrate the efficiency of our approach in achieving a coherent geophysical model that is consistent with geological data and findings from other geophysical techniques. This method provides a practical and capable solution for unveiling conductive 3D structures in the field.

Electromagnetic Field in the Upper Ionosphere Fromhorizontal ELF Ground-Based Transmitter of Finite Length

Electromagnetic Field in the Upper Ionosphere Fromhorizontal ELF Ground-Based Transmitter of Finite Length

атухание низкочастотных электромагнитных волн в нижней ионосфере земли под влиянием сильного локального возмущения в атмосфере.

The value and duration of attenuation of low frequency waves (1...10 kHz) in the presence of a strong local disturbance of the atmosphere have been estimated. Sources of significant local disturbances of the atmosphere are, for example, precipitation of energetic particles of radiation belts; electromagnetic pulses of lightning discharges; radiation of powerful low-frequency ground-based transmitters; invasion of large meteors. Strong local disturbances lead to an increase of ionization (concentration of free electrons) of the environment by several orders of magnitude in the region of space whose characteristic dimensions are comparable to the length of the wave (tens and hundreds of kilometers). As such a disturbance, we use the previously developed macroscopic model of an instantaneous, point release of a relatively large amount of energy in the atmosphere below the ionosphere. This model makes it possible to estimate the features of the propagation of low-frequency waves through the disturbed layer of the lower ionosphere by changing only two initial parameters: the disturbance energy and its initial height. It is shown that the attenuation value is almost independent of frequency and geo- and heliophysical conditions. For initial heights up to 50 km, the fading duration does not exceed ~ 2 min. With an increase of the initial altitude, the attenuation in the lower ionosphere becomes extremely large. However, for heights of 50 ... 70 km (depending on the value of energy), the horizontal size of the disturbance decreases significantly, which leads to a decrease in the fading time to tens of seconds for initial heights of more than 80 km.

Shared Operation of a Barrage Jammer and Reference Signal Sources for Determining Ground-Based Radio Transmitters Operating via Geostationary Relay Satellites

Introduction. There are incidences of jamming the users of satellite communication systems, who apply e.g. geostationary relay satellites, and the illegal use of such satellite resources. These actions can be both intentional and unintentional, and, among other things, be caused by non-compliance with electromagnetic compatibility standards on part of other users of satellite communication systems. For a prompt and high -quality response of radio monitoring services and satellite operators to these illegal actions, it seems urgent to develop methods for accurate determination of the geolocation of radio emission sources.Aim. To develop a method for improving the accuracy of determining the coordinates of ground-based radio emission sources operating via geostationary relay satellites based on shared operation of a barrage jammer and reference signal sources.Materials and methods. The research was conducted using the statistical theory of radio engineering systems, the theory of digital signal processing and the method of simulation.Results. A method was developed for improving the geolocation accuracy of ground-based radio emission sources operating via geostationary relay satellites based on shared operation of a barrage jammer and reference signal sources. A method for resolving ambiguity regarding the true correlation peak of a reference source signal using a signal from a barrage jammer was described. An expression was obtained for the probability of a correct solution when resolving such ambiguity. As a result, the estimates of geolocation accuracy obtained using the developed method were compared with those obtained by a conventional method relying on the usage of 3 different reference stations.Conclusions. The method proposed in this paper makes it possible to achieve a relatively high accuracy when determining the geolocation of ground-based radio emission sources in the Earth’s regions of interest, at the same time as involving no organizational and financial costs for the installation of a large number of reference stations.

A land-based HF transmitter for ionospheric propagation studies using SuperDARN radars

Purpose The purpose of this paper is to design, build and test a low power high frequency (HF) transmitter that can be received by the Super Dual Auroral Radar Network (SuperDARN) radar installed at SANAE IV, the 4th South African National Antarctic Expedition Station. It is proposed that it may be possible to do propagation studies using the radar and the fixed frequency, ground-based HF transmitter beacon. Interpretation of the measurements can be used to study the ionosphere, especially Travelling Ionospheric Disturbances, which are signatures of atmospheric gravity waves. Design/methodology/approach In the absence of the actual deployment of the HF transmitter beacon in Antarctica, extensive simulations have been done to evaluate the expected performance of the transmitter in relation to the SuperDARN. A field trial has been executed between Hermanus (34.4241° S, 19.2247° E) and Pretoria (34.0558° S, 18.4589° E) in South Africa. In future, the beacon will be placed at the South Pole with its antenna radiating towards SANAE IV. Findings The HF transmitter conforms to the power and frequency stability requirements both during propagation tests conducted between Hermanus and Pretoria, as well as when the device was exposed to temperatures that ranged from +40°C to −45°C in a thermal chamber. Propagation in Antarctica is expected to differ from the field tests conducted due to the differences in density and dynamics of the polar ionosphere, compared to the mid-latitude ionosphere. Originality/value Space weather research, including forecasting atmospheric gravity waves and determining the expected electron density profile of the ionosphere, is of great scientific interest. The data received from the HF beacon can be used to study and characterize the ionosphere of the region between the South Pole and SANAE IV. Parameters of the ionosphere, such as electron density, geomagnetic storm effects, ionospheric motions and sky wave propagation paths will be better understood from analysing the signal received from this transmitter after it has been reflected and refracted by the ionosphere.

Indoor precise point positioning with pseudolites using estimated time biases iPPP and iPPP-RTK

The global navigation satellite system (GNSS) provides outstanding positioning services for outdoor activities with sufficient accuracies, but it has poor indoor performance. Indeed, indoor positioning is also expected to achieve the outdoor positioning level to cater to an even higher volume of user demands. A pseudolite (PL), also called a pseudosatellite, is a ground-based positioning system that offers flexible deployment and accurate “orbits”. The PL system can carry on the role of the GNSS to provide precise positioning for indoor users. The clock differences originating from ground-based transmitters cause unsynchronized timing issues and impede attempts to fix the integer ambiguity. Numerous studies have been conducted with an emphasis on time synchronization to obtain this ambiguity-fixed solution by employing multiple transceivers in transmitter-receiver combinations for self-calibration inside a regional network of the ground-based system. However, this process requires a large investment and complicates the positioning owing to its intricate implementation. Actually, time synchronization can easily be achieved with a transmitter-only PL system at a low cost once the clock bias between transmitters is properly handled. Thus, we propose and present indoor precise point positioning (iPPP) and indoor PPP-real-time kinematic (iPPP-RTK) to handle the PL clock bias efficiently. Experiments demonstrate that the transmitter-only PL system can be time-synchronized without high cost or complicated operations and that centimeter level indoor precise positioning can be reliably achieved with our proposed methods.

Analysis of the earth's surface influence on the accuracy of non directional beacon in mountain terrain

This paper deals with the measuring and checking of the Non Directional Beacon using flying laboratory AeroLab 1 at University of Zilina. It is based on the most simple radio navigation concept: a ground-based radio transmitter (the NDB) sends an omnidirectional signal that an aircraft loop antenna receives. Our practical measurement shows that the NDB satisfies ICAO standards and can be used in industrial part of urban area and is functional in spite of the interference. The paper concentrates on the measuring of the Non Directional Beacon (NDB) which is installed close to industrial part of the city. The ADF/NDB navigation system is one of the oldest air navigation system still in use today. One of the paper's goals is to familiarize the aviation public with the practical measurement of this urban area phenomenon in terms of flight safety, which is common in mountainous nations such as Slovakia. The article's other purpose is to educate professionals in the area about this occurrence in terms of its nature as a physical rule, in order to develop solutions to improve the navigation system's measurement accuracy.

Scattering effect of very low frequency transmitter signals on energetic electrons in Earth’s inner belt and slot region

Whistler mode very low frequency (VLF) waves from man-made ground-based transmitters in a frequency range of 10–30 kHz are mainly used for submarine communication, and they propagate primarily in the Earth-lower ionosphere waveguide and part of their energy can leak into the inner magnetosphere, leading the energetic electrons in inner radiation belt and slot region to precipitate into atmosphere and then affect the energetic electron dynamics in the near-Earth space. The scattering effects of artificial VLF signals from NWC, NAA and DHO38 transmitters on energetic electrons in Earth’s inner belt and slot region are investigated in detail in this work. Based on the quasi-linear theory and the Full Diffusion Code, we calculate the bounce-average pitch angle diffusion coefficients induced by NWC, NAA and DHO38 VLF transmitter signals, for which the resonance harmonics |<i>N</i>| ≤ 10 are considered, respectively. We further implement the one-dimensional Fokker-Planck diffusion simulations by using the available pitch angle diffusion rates to model the dynamic evolutions of energetic electrons caused by the scattering of the VLF transmitter signals in the inner belt and slot region in 200 d. The simulation results indicate that the NWC VLF transmitter signals are dominant in scattering ~100 keV electrons with pitch angles less than 60° at <i>L</i> ≤ 1.8, and the mainly scattered electron energy values increase with <i>L</i>-shell decreasing , from <i>L</i> = 1.8 to <i>L </i>= 1.5, the mainly scattered electron energy increases from 90–120 keV to 550–650 keV. The NAA and DHO38 VLF transmitter signals are important in scattering < 20 keV electrons with pitch angles less than 70° at higher <i>L</i>-shells (2.2 ≤ <i>L</i> ≤ 2.7), from <i>L</i> = 2.2 to <i>L</i> = 2.7, the mainly scattered electron energy decreases from 10–20 keV to several keV. The VLF transmitter signals are found to have a slight influence on the loss of energetic electrons with pitch angles larger than 80°.

Investigation of Precursors in VLF Subionospheric Signals Related to Strong Earthquakes (M > 7) in Western China and Possible Explanations

Earthquakes may disturb the lower ionosphere through various coupling mechanisms during their seismogenic and coseismic periods. The VLF signal radiated from ground-based transmitters is affected when it passes near the disturbed region above the seismogenic area, and this anomaly can be recorded by ground-based VLF receivers. In this paper, the seismic anomalies before two strong earthquakes (M > 7) that occurred in western China were detected using the ground-based observation of VLF signal; the possible reasons for the anomalies were discussed using full wave simulation. The amplitude of the VLF signals observed by the link between NOV, KHA transmitter, and VLF receivers at Ya’an and Tonghai show obvious anomaly by nighttime fluctuation analysis. The simulated results demonstrate that the anomalies could have been induced by ascending/descending of the bottom height of the ionosphere, caused by depletion/increase in D region electron density. The simulated result also illustrates that terminator time shift could have been induced by descending of the bottom boundary of the ionosphere, which is due to modal interference between different wave modes.

The very low-frequency transmitter radio wave anomalies related to the 2010 Ms 7.1 Yushu earthquake observed by the DEMETER satellite and the possible mechanism

Abstract. Earthquakes may disturb the lower ionosphere through various coupling mechanisms during the seismogenic and coseismic periods. The VLF (very low-frequency) signal radiated from ground-based transmitters will be affected when it penetrates the disturbed ionosphere above the epicenter area, and this anomaly can be recorded by low-Earth orbit satellites under certain conditions. In this paper, the temporal and spatial variation of the signal-to-noise ratio (SNR) of the VLF transmitter signal in the ionosphere over the epicenter of 2010 Yushu Ms 7.1 earthquake in China is analyzed using DEMETER (Detection of Electro-Magnetic Emission Transmitted from Earthquake Regions) satellite observation. The results show that SNR over the epicenter of the Yushu earthquake especially in the southwestern region decreased (or dropped) before the main shock, and a GPS–TEC (Global Positioning System; total electron content) anomaly accompanied, which implies that the decrease in SNR might be caused by the enhancement of TEC. A full-wave method is used to study the mechanism of the change in SNR before the earthquake. The simulated results show SNR does not always decrease before an earthquake. When the electron density in the lower ionosphere increases by 3 times, the electric field will decrease about 2 dB, indicating that the disturbed-electric-field decrease of 20 % compared with the original electric field and vice versa. It can be concluded that the variation of electron density before earthquakes may be one of the important factors influencing the variation of SNR.

COBIS: Opportunistic C-Band Bistatic SAR Differential Interferometry

Monitoring large built structures, landslides, volcanoes, or glaciers implies relative height measurements and line-of-sight (LOS) displacement measurements, which are typically performed with monostatic spaceborne synthetic aperture radar (SAR) sensors. In this case, for each satellite that illuminates a given location, we can usually exploit only the information available from one ascending/descending orbit, and if the satellite uses multiple subswaths, the information is obtained only from one subswath per orbit. A bistatic configuration with spaceborne transmitter and fixed ground-based (GB) receiver opens the possibility to exploit the information available from more than one orbit and one subswath per orbit. Additionally, such a configuration offers new perspectives for target tracking and characterization (e.g., multiple LOSs and bistatic scattering signatures). This article presents an opportunistic C-band bistatic SAR differential interferometry architecture that uses a multichannel GB stationary receiver and a separate transmitter, which can be either the Sentinel-1A/B satellite, used opportunistically, or a specially designed GB sliding transmitter. The combination of the operation modes based on spaceborne and GB transmitter allows monitoring a small critical area of interest with many acquisitions triggered by the GB transmitter and surveying of the whole surrounding area with a small number of acquisitions corresponding to the satellites passes. The hardware platforms are presented along with the bistatic interferometric processing flow, and the potential of the proposed architecture is assessed in the context of monitoring large built structures.

Modeling of the Dynamics of Radio Wave Reflection and Absorption in a Smoothly Ionomogeneous Plasma with Electromagnetically Driven Strong Langmuir Turbulence

This work was initiated by experiments on studying the self-action of radio waves incident on the ionosphere from a ground-based transmitter at the stage of electromagnetic excitation of Langmuir turbulence (Langmuir effect). The emphasis is on the impact of “self-consistent” collisionless absorption of radio waves by the Langmuir turbulence, which develops when the incident-wave field swells in the resonant region of a smoothly inhomogeneous plasma, on the dynamics of the radio wave reflection. Electrodynamic characteristics of the nonlinear-plasma layer, which has a linear unperturbed profile of the plasma density, with different features of the absorption development are obtained for a high intensity of the incident radiation. Calculations of “soft” and “hard” regimes of the absorption occurrence, as well as hysteresis modes in which the damping switch-on and off thresholds differ several times, are carried out. The algorithms we devised and the results of the study can serve as the basis for a more adequate and more detailed numerical simulation for interpretation of the experimental data obtained at the stage of the Langmuir effect in the ionosphere.

Analysis of the possibilities to determine lunar soil characteristics with the help of bistatic radar

An opportunity of determining the lunar soil characteristics via bistatic radar involving high-power ground-based transmitters operating in meter and decameter wave ranges and receivers located aboard Moon satellite is analyzed. Direct and inverse problems concerning stratified soil sounding to a large depth, as well as algorithms for determining the regolith layer thickness, permittivity, radio wave absorption, and regolith and bedrock densities, are examined.

Dynamic properties of ionospheric plasma turbulence driven by high-power high-frequency radiowaves

A review is given of the current state-of-the-art of experimental studies and the theoretical understanding of nonlinear phenomena that occur in the ionospheric F-layer irradiated by high-power high-frequency ground-based transmitters. The main focus is on the dynamic features of high-frequency turbulence (plasma waves) and low-frequency turbulence (density irregularities of various scales) that have been studied in experiments at the Sura and HAARP heating facilities operated in temporal and frequency regimes specially designed with consideration of the characteristic properties of nonlinear processes in the perturbed ionosphere using modern radio receivers and optical instruments. Experimental results are compared with theoretical turbulence models for a magnetized collisional plasma in a high-frequency electromagnetic field, allowing the identification of the processes responsible for the observed features of artificial ionospheric turbulence.

Station-keeping of a high-altitude balloon with electric propulsion and wireless power transmission: A concept study

A stable, ultra long-duration high-altitude balloon (HAB) platform which can maintain stationary position would represent a new paradigm for telecommunications and high-altitude observation and transmission services, with greatly reduced cost and complexity compared to existing technologies including satellites, telecom towers, and unmanned aerial vehicles (UAVs). This contribution proposes a lightweight superpressure balloon platform for deployment to an altitude of 25km. Electrohydrodynamic (EHD) thrusters are presented to maintain position by overcoming stratospheric winds. Critical to maintaining position is a continual supply of electrical power to operate the on-board propulsion system. One viable solution is to deliver power wirelessly to a high-altitude craft from a ground-based transmitter. Microwave energy, not heavily attenuated by the atmosphere, can be provided remotely from a ground-based generator (magnetron, klystron, etc.) and steered electrically with an antenna array (phased array) at a designated frequency (such as 2.45 or 5.8GHz). A rectifying antenna (“rectenna”) on the bottom of the balloon converts waves into direct current for on-board use. Preliminary mission architecture, energy requirements, and safety concerns for a proposed system are presented along with recommended future work.

DGNSS 위치정확도 향상을 위한 PRC 보정정보 모델링에 관한 연구

We studied on pseudo-range correction(PRC) modeling in order to improve differential GNSS(DGNSS) accuracy. The PRC is the range correction information that provides improved location accuracy using DGNSS technique. The digital correction signal is typically broadcast over ground-based transmitters. Sometimes the degradation of the positioning accuracy caused by the loss of PRC signals, radio interference, etc. To prevent the degradation, in this paper, we have designed a PRC model through polynomial curve fitting and evaluated this model. We compared two quantities, estimations of PRC using model parameters and observations from the reference station. In the case of GPS, the average is 0.1m and RMSE is 1.3m. Most of GPS satellites have a bias error of less than and a RMSE within 3.0m. In the case of GLONASS, the average and the RMSE are 0.2m and 2.6m, respectively. Most of satellites have less than for a bias error and less than 3.0m for RMSE. These results show that the estimated value calculated by the model can be used effectively to maintain the accuracy of the user's location. However;it is needed for further work relating to the big difference between the two values at low elevation.

Unexpected Very Low Frequency (VLF) Radio Events Recorded by the Ionospheric Satellite DEMETER

DEMETER was a low Earth orbiting microsatellite in operation between July 2004 and December 2010. Its scientific objective was the study of ionospheric perturbations in relation to seismic activity and man-made activities. Its payload was designed to measure electromagnetic waves over a large frequency range as well as ionospheric plasma parameters (electron and ion densities, fluxes of energetic charged particles). This paper will show both expected and unusual events recorded by the satellite when it was in operation. These latter events have been selected from the DEMETER database because they are rare or even have never been observed before, because they have a very high intensity, or because they are related to abnormalities of the experiments under particular plasma conditions. Some events are related to man-made radio waves emitted by VLF ground-based transmitters or power line harmonic radiation. Natural waves, such as atypical quasi-periodic emissions or uncommon whistlers, are also shown.