Direction Finding System Research Articles

Single Transmitter Direction Finding Using a Single Moving Omnidirectional Antenna

Traditional direction-finding systems are based on processing the outputs of multiple spatially separated antennas. The impinging signal Angle-of-Arrival (AOA) is estimated using the relative phase and amplitude of the multiple outputs that are sampled simultaneously. Here, we explore the potential of a single moving antenna to provide useful direction finding of a single transmitter. If the transmitted signal frequency is steady enough during the collection of data, a single antenna can be moved while tracking the phase changes to provide an Angle-of-Arrival measurement. The advantages of a single-antenna sensor include the sensor size, the lack of a need for multiple-receiver synchronization in time and frequency, the lack of mutual antenna coupling, and the cost of the system. However, a single-antenna sensor requires an accurate knowledge of its position during the data collection and it is challenged by transmitter phase instability, signal modulation, and transmitter movement during the measurement integration time. We analyze the performance of the proposed sensor, support the analysis with simulations and finally, present measurements performed by hardware configured to check the validity of the proposed single-antenna sensor.

The Source Structure Design of the Rotating Magnetic Beacon Based on Phase-Shift Direction Finding System.

Target azimuth information can help further improve the accuracy of magnetic orientation, but the current periodic magnetic field generated by the magnetic beacon is multivalued, so it is not suitable for azimuth measurement. According to the distribution of a rotating magnetic field and the phase angle measuring principle, we put forward a new magnetic source structure design of a multiple rotating permanent magnet array by adjusting the spacing d, the rotating speed ω and the initial rotation angle φ, and then verified the mathematical model using COMSOL simulation software. A triple structure was obtained by comparison (d3=3d1=3d2=43 m, d3=3d1=3d2=43 m, φ1=0, φ2=4π5 rad. φ3=π rad), which can produce a strong characteristic magnetic signal similar to a heart-shaped field pattern. Finally, a signal transceiver system was set up for the experiment. The experimental result shows that the waveform of the magnetic signal generated by the real beacon meets the requirement of having a unique maximum value and good directivity within a period, which proves the practical application effect of the structure.

An Efficient Solution of Phase Interferometry Ambiguity using Zero-Crossing Technique

Direction finding systems applying phase interferometer of long baseline gives high accuracy of the angle of arrival measurements; however, they are suffering from phase ambiguity and phase error due to antenna spacing greater than half wavelength of the intercepted signals. In this paper, the simple two-antenna interferometer system has been adopted with the zero-crossing technique used to solve the phase measurement ambiguities in the processing unit. The zeros-crossing of both channels (lead and lag) were extracted using electronic circuitry. A count gate was formed to count the zeros throughout the phase difference between the two channels. The ambiguity factor was taken to be half of the even count which will be added to the output of the phase comparator to estimate the total phase difference. Multisim software has been used to simulate the proposed processing unit and the ambiguity was calculated for different values of phase difference. Antenna spaces (D/λ) of (1/2, 1, 2, 4, 8, 12, 14, and 16) were applied to the system and the corresponding ambiguity factors have been measured to be (zero, 1, 2, 4, 8, 12, 14 and 16) respectively. Therefore for antenna spaces (D ≤ λ/2) there is no ambiguity. These simulated results show a coincidence with the theoretical values. The lead-lag channels were also solved without the need to add other antennas to the system since the first zero detected by either antenna refers to the lead channel. The proposed technique has advantages over others since it solves ambiguities on the basis of real-time processing without the need for complex, expensive, heavy, and slower response systems.

DOA Estimation Based on LSTM Neural Network with Uniform Linear Antenna Array

Radio Direction Finding system is a system that determines the direction or coordinates of radio signal sources. The main function of this system is to determine the direction of arrival (DOA) of an incident radio wave. DOA information plays an important role in array signal processing and has many applications in communications, radar, seismic survey... In this paper, with the simulated signal data set obtained at the linear antenna array (ULA), the Long Short-Term Memory (LSTM) network model is used to estimate the DOA. The performance of the method is evaluated based on the RMSE parameter and compared with MUSIC, DNN algorithms in different cases such as: deviation of incident angle of radiation sources, signal-to-noise ratio (SNR).

Direction of Arrival Estimation for Coherent Signals’ Method Based on LSTM Neural Network

Radio direction finding system is a system that determines the direction or coordinates of radio signal sources. The main function of this system is to determine the direction of arrival (DOA) of an incident radio wave. DOA information plays an important role in array signal processing and has many applications in communications, radar, seismic survey, etc. In this study, we propose a method to estimate the DOA by using the simulated signal dataset obtained at the linear antenna array (ULA) and the suitable Long Short-Term Memory (LSTM) network model. The performance of the method is evaluated based on the root mean square error (RMSE) parameter and then is compared with 2 other algorithms, multiple signal classification (MUSIC) and deep neural network (DNN) in different cases such as deviation of incoming signals, variation of signal-to-noise ratio (SNR), and coherent incoming signals. The obtained results have shown that the proposed method has significantly improved accuracy compared to other methods.

The deception effect of FDA counteracting amplitude-comparison monopulse reconnaissance

Conventional phased array radar can direct the high-gain beam, resulting in high visibility under the reconnaissance system and even direct exposure to the enemy. As an amplitude-based direction-finding system, the amplitude monopulse system can recognize the traditional radar signals. However, there are still some issues with the countermeasures of the monopulse system, so it is necessary to find better styles of jamming. Since the beam of the frequency diverse array (FDA) signal at a certain angle varies with the range, we studied the deception effect of the FDA against the amplitude-comparison monopulse direction-finding system. By analyzing the established FDA-based direction-of-arrival location deception model against the amplitude-comparison monopulse system, we found that the introduction of the frequency increment might cause the FDA signals to deceit the monopulse system in principle. Then, to indicate the superiority of our deception method, we obtain the instantaneous signal-to-noise ratio, Cramér–Rao lower bound, root-means-square error, and variation. Numerical simulation results demonstrate that the FDA can generate deceptive signals to counteract the amplitude-comparison monopulse direction-finding system.

Maximum Achievable Gain of Annular-Shaped Beams

The maximum achievable gain and the corresponding source distribution for an annular or “donut”-shaped beam produced by a circular aperture are studied. Expressing the source in terms of orthogonal basis functions and then applying Lagrange’s multiplier method, the optimum source distribution is determined. The residue calculus is then invoked for the closed-form expressions. Numerical results are shown and discussed. In applications such as direction finding and satellite tracking systems on moving vehicles, a high-gain annular beam is suitable for maintaining uninterrupted connectivity.

Direction Finding and Tracking using Single-Ring Circular Array Antenna and Space Division Table

Single-ring circular array antennas can be applied to direction finding systems in order to use nose-section in other purposes, and the interferometry is a proper direction finding method to those systems. We usually make the interferometer baseline long enough to achieve good angular accuracy. However, an interferometer with baseline longer than a half-wavelength has the ambiguity problem. In this paper, we present a novel method for solving the ambiguity problem in interferometry systems. This technique is based on the amplitude comparison method and the space division table, and it can place a target within the angular region in which the ambiguity problem does not occur by roughly estimating direction-of-arrival. The Monte Carlo simulation results show that proposed method can effectively remove the ambiguity problem in the system.

ОЦЕНКА ПАРАМЕТРОВ РАБОТОСПОСОБНОСТИ ГРОЗОПЕЛЕНГАЦИОННЫХ СИСТЕМ LS8000 И ENTLS В РЕГИОНЕ СЕВЕРНОГО КАВКАЗА

The results of a comparative analysis of data on lightning discharges obtained by lightning direction finding systems LS8000 (Vaisala, Finland) and ENTLS (Earth Networks Inc., USA) are presented. The consistency of the output data of the compared systems on the Cloud-to-Ground discharges was investigated. Observations were carried out by the High Mountain Geophysical Institute in the North Caucasus in 2019.

Interferometer direction‐finding system with time‐division multiplexing of spread spectrum signals

AbstractA single channel interferometer direction‐finding (DF) system is proposed in this article. The interferometer DF system adopts time‐division multiplexing to receive different antenna phase information, which can effectively eliminate the differences in time delay and channel gain due to different channels. In addition, the spread spectrum signal and integer ambiguity resolution algorithm are used to make the system suitable for low carrier‐to‐noise ratios (CNRs) and high‐frequency signals. The simulations show that the system can measure the angle with root mean square error accuracy at a CNR of 50 dB‐Hz.

Определение местоположения ИРИ с применением однопозиционного подвижного измерителя на основе разностно-дальномерного метода пеленгования

Determination of the location of radio-electronic means radiating into the air is one of the main tasks of radio control, and under conditions of a priori uncertainty about the parameters of radio emission sources, the highest accuracy of coordinate estimation has a time difference of arrival method. The paper proposes a new approach to determine the coordinates of radio emission sources using a single-position mobile meter based on the difference-distance direction finding. In contrast to the known ones, it allows reducing the number of measuring points of the difference-distance direction finding system without worsening the accuracy of estimating the coordinates of radio emission sources owing to using the moving meter and the method of maximum likelihood to calculate the coordinates in multiple measurements. The practical application of the developed approach is expedient in the development of radio control complexes and allows not to take into account the orientation of the meter on an unmanned aerial vehicle in space, as well as to increase the accuracy of radio emission source coordinates determination.

A Spatially Confined, Platform-Based HF Direction Finding Array

A spatially-confined, platform-based HF antenna array with enhanced bandwidth and direction-finding (DF) accuracy is presented. As the HF band is widely used in many important civilian and military applications, HF DF systems are of great interest in electronic warfare support applications. However, due to the large wavelength, practical DF arrays mounted on moving platforms tend to be electrically small, resulting in fundamental limitations on antenna bandwidth and DF accuracy. Furthermore, many applications require mounting the array at a single location on the platform due to limited space and mobility considerations. To alleviate these issues, we employ the platform as the major radiator by exciting several of its significant characteristic modes (CMs) using a spatially-confined antenna array. Specifically, we examined four DF array designs mounted on a representative, mid-size passenger airplane operating at 10 MHz in simulation, each of which is confined within a virtual sphere with a 3-m diameter. A scaled model of one design was fabricated and characterized. Cramer-Rao bounds and Monte-Carlo test results are also reported. Our results demonstrate that the proposed DF array can provide a 15% lower DoA estimation error than the theoretical limit of a standalone array possessing the same volume and having the same bandwidth.

Analysis of Group Delay and Phase Delay Algorithms for Short Baseline Interferometry

As a fast direction finding technology, interferometry has the advantages of simple algorithm and high sensitivity, so it is widely used in various direction finding systems. Short baseline interferometer Angle measurement is the basic principle of phase Angle measuring method, it is using the delay difference between different receiving station in the system to obtain the target azimuth information, has the advantage of high accuracy of Angle measuring, but interferometer is inevitable during the high frequency signal direction finding Angle measuring fuzzy problems exist, in order to solve this problem in general with phase delay method improve the interferometer Angle measurement accuracy, The group delay method is used to deblur. In this paper, group delay and phase delay algorithms are simulated and analyzed, and the simulation results prove the effectiveness of the proposed method.

Design and implementation of a low cost, high performance ionizing radiation source detection and source direction finding system

Design and implementation of a low cost, high performance ionizing radiation source detection and source direction finding system

Estimation of noise radiance point sources multichannel direction finding systems resolution by linear prediction method

The resolution of multichannel direction finding systems of independent noise radiance point sources is estimated quantitatively under a limited learning sample on the basis of a linear prediction methods “bank” and modified Capon algorithms.

Peculiarities of spectrum of electromagnetic signals induced by discharges from artificial thunderstorm cell

Results of an investigation of the peculiarities of a spectrum of the electromagnetic signals induced nearby discharges between an artificial thunderstorm cell and a ground have presented. It was experimentally found that the impulse current parameters and an intensity, form, spectral characteristics of the induced electromagnetic signals depend on a variant of a discharge formation from an artificial thunderstorm cell (upward discharge, downward discharge, or counterpart discharge). Significant difference of the wavelet spectrum characteristics of the electromagnetic signals registered by the antennas in the vicinity of discharge formation has been found for these three variants. Significant difference of the spectral characteristics of the electromagnetic signals induced on nearby antennas during the time of the first and subsequent current impulses of a discharge between an artificial thundercloud and a ground: in average, subsequent discharges have more less characteristic frequencies. Possible reasons of that differences have discussed in paper. Role of the powerful streamer discharges during the main stage formation in the appearance of the ultrahigh frequency range of the induced electromagnetic signals has considered. Some dependencies between the spectral characteristics of signals registered by antennas and the parameters of the current impulses for the different variants of the main stage of the discharge between the artificial thunderstorm cell and the ground have been established. The possibility of applying the results obtained for improving the operation of lightning direction finding systems is being considered.

СИНТЕЗ ДОПЛЕРОГРАМ КВАЗІВЕРТИКАЛЬНОГО ЗОНДУВАННЯ ІОНОСФЕРИ ДОПЛЕРІВСЬКИМ ВЧ РАДАРОМ ІЗ РОЗНЕСЕНИМ ПРИЙМАННЯМ

Purpose: The ionospheric channel is widely used for the communication, radio navigation, radar, direction finding, radio astronomy, and remote radio probing systems. The radio channel parameters are characterized by nonstationarity due to the dynamic processes in the ionosphere, and therefore their study is one of the topical problems of space radio physics and earth-space radio physics of geospace. This work aims at presenting the results of synthesis of temporal variations in the Doppler spectra obtained by the Doppler probing of the ionosphere at vertical and quasi-vertical incidence. Design/methotology/approach: One of the most effective methods of ionosphere research is the Doppler sounding technique. It has a high time resolution (about 10 s), a Doppler shift resolution (0.01–0.1 Hz), and the accuracy of Doppler shift measurements (~0.01 Hz) that permits monitoring the variations in the ionospheric electron density (10–4–10–3) or the study of the ionospheric plasma motion with the speed of 0.1-1 m/s and greater. The solution of the inverse radio physical problem, consisting in determination of the ionosphere parameters, often means solving the direct radio physical problem. In the Doppler sounding technique, it belongs with the construction of variations in Doppler spectra and comparing them with the Doppler spectra measurements. Findings: For the radio wave ordinary component, three echoes being produced by three rays are observed. Influence of the geomagnetic fi eld and large horizontal gradients in the electron density of δ≥10 % give rise to complex ray structures with caustic surfaces. The ionospheric disturbances traveling along the magnetic meridian form the skip zones. The longitudinal and transverse displacement of the ray reflection point attains a few tens of kilometers along the vil. Haidary to vil. Hrakove quasi-vertical radiowave propagation path, for which the great circle range is 50 km. For the vertical incidence, the signal azimuth at the receiver coincides with the traveling ionospheric disturbance azimuth. The synthesis of temporal variations in the HF Doppler spectra has been made and compared with the temporal variations in the Doppler spectra recorded with the V. N. Karazin Kharkiv National University radar. The estimate of δ=15 % obtained confirms the existence of large horizontal gradients in electron density. Conclusions: Temporal variations in Doppler spectra and in azimuth have been calculated for the vertical and quasi-vertical incidence with allowance for large horizontal gradients of the electron density caused by traveling ionospheric disturbances. Key words: ionosphere, Doppler sounding at oblique incidence, synthesis of temporal variations in HF Doppler spectra, traveling ionospheric disturbances, electron density

A Simple Printed Cross-Dipole Antenna with Modified Feeding Structure and Dual-Layer Printed Reflector for Direction Finding Systems.

In this paper, a simple printed cross-dipole (PCD) antenna to achieve a right-hand circular polarization (RHCP) at the L/S-band for direction finding (DF) systems is presented. The radiating part of the antenna consists of two printed dipoles that interlock with each other and are mounted orthogonally on a dual-layer printed reflector. To connect the feedlines of the dipole elements to the antenna’s feed network, which is located on the backside of the reflector, a through-hole signal via (THSV) is employed as the signal interconnection instead of the mainstream approach of using coaxial bead conductor. This feeding technique provides a degree of freedom to control the impedance of the signal path between the feedlines and the feed network in the numerical simulation for improved matching conditions. The proposed THSV extending through the dual-layer printed reflector is more reliable, durable, and mechanically robust to stabilize the matching conditions of the fabricated antenna in contrast to the coaxial-based approach that is more susceptible to impedance mismatch due to solder fatigue. Thus, the proposed PCD antenna offers advantages of broadband, flexible impedance matching, and fabrication ease. The antenna exhibits an impedance bandwidth (IBW) of 59% (1.59–2.93 GHz), a 3-dB axial ratio bandwidth (ARBW) of 57% (1.5–2.7 GHz), and a peak of 7.5 dB within the operating frequency band.

Acoustic threat detection and direction finding system

In this paper, an acoustic threat detection system is investigated as preliminary study of one of the anti-terrorism systems. The proposed system is a prototype of acoustic threats detection, classification, and direction finding system. For this purpose, an experiment is performed to test the capability of a proposed warning system to perform the task accurately. The direction of the sound source is determined by means of two microphones. The angle to the acoustic threat is calculated based on time difference of arrival (TDOA). The limitations of the system are discussed and some possible solutions are introduced to improve the performance of the system.

Analysis of the spatial-temporal distribution of lightning discharges in the North Caucasus

The organization of lightning protection measures is based on information about the nature of the distribution of lightning discharges, their number and the current value in the region of the location of the protection objects. Therefore, the most relevant direction of the study is to clarify the existing recommendations in the field of lightning protection. In the article, based on the data of long-term measurements of the LS 8000 lightning direction finding system located in the North Caucasus, the analysis of the registration of lightning parameters is carried out. The revealed regularities of the distribution of lightning discharges over the territory in different periods of the year are the basis for the approximation equations developed by the authors, which are used to describe the space-time density of lightning. Maps of the distribution of the number of lightning discharges per square kilometer obtained from the initial data and constructed according to the developed equations are presented, and the relevance of the results obtained is evaluated.