Direction Finding Research Articles

Enhancing monitoring systems with interference-handling radio frequency direction finding: BMKG C-Band weather radar in West Kalimantan Indonesia case study

This study investigates the effectiveness of the interference-handling radio frequency direction finding (RFDF) monitoring system in detecting and localizing interference sources near the BMKG C-Band weather radar in West Kalimantan, Indonesia. We conducted field tests varying interference transmitter power levels (0-30 dBm) and distances (100, 500, and 1,000 m) from the radar. Results indicate the RFDF system's robust performance, consistently detecting interference within 5-20 minutes and accurately localizing sources with minimal deviation from actual positions. The findings confirm the system's superiority over traditional manual methods, offering a reliable solution for interference management in weather radar operations. However, limitations include controlled test conditions and a need for further exploration of the system's efficacy in diverse environmental settings. This research contributes to improving radar reliability and lays the groundwork for future studies to refine RFDF technology for broader meteorological applications.

Unambiguous subarray-based direction of arrival estimation by dual-polarized antenna

ABSTRACT Subarray-based direction of arrival (DOA) estimation usually suffers from direction finding ambiguity due to the large subarray spacing. In this paper, a dual-polarized microstrip element antenna is designed to construct a subarray. The elements in the subarray are set to different polarization then the full antenna array becomes a diversely polarized one, which is sensitive to polarization and can achieve unambiguous DOA estimation. The polarization controlling mode of the element is introduced in detail in this paper. Simulations are implemented using a twelve-elements uniform linear array (ULA) which is divided into different subarrays. A measurement is carried out using a sixteen-elements uniform planar array (UPA) with four subarrays. Both simulation and measurement results demonstrate the effectiveness of this method.

Avaliação tomográfica e radiográfica de estenose/colapso do brônquio principal esquerdo em cão da raça Pug

Stenosis/collapse of the bronchi is a condition of luminal narrowing, often associated with obstructive syndromes in brachycephalic dogs, with the pug being one of the most predisposed breeds. The most common clinical signs include dyspnea and chronic cough. Diagnosis can be achieved through bronchoscopy, radiography, and computed tomography. The described patient presented clinical signs such as nasal discharge and dyspnea. This study reports a case of stenosis/collapse of the left main bronchus, diagnosed using a combination of imaging techniques, radiography, computed tomography, highlighting the importance of a detailed evaluation of direct and indirect findings from theses imaging modalities to reach this diagnosis

Model-Driven Deep Neural Network for Enhancing Direction Finding with Commodity 5G gNodeB

Pervasive and high-accuracy positioning has become increasingly important as a fundamental enabler for intelligent connected devices in mobile networks. Nevertheless, current wireless networks heavily rely on pure model-driven techniques to achieve positioning functionality, often succumbing to performance deterioration due to hardware impairments in practical scenarios. Here we reformulate the direction finding or angle-of-arrival (AoA) estimation problem as an image recovery task of the spatial spectrum and propose a new model-driven deep neural network (MoD-DNN) framework. The proposed MoD-DNN scheme comprises three modules: a multi-task autoencoder-based beamformer, a coarray spectrum generation module, and a model-driven deep learning-based spatial spectrum reconstruction module. Our technique enables automatic calibration of angular-dependent phase error thereby enhancing the resilience of direction-finding precision against realistic system non-idealities. We validate the proposed scheme both using numerical simulations and field tests. The results show that the proposed MoD-DNN framework enables effective spectrum calibration and accurate AoA estimation. To the best of our knowledge, this study marks the first successful demonstration of hybrid data-and-model-driven direction finding utilizing readily available commodity 5G gNodeB.

Research on methods to enhance the survivability of AWACS with FDA against anti‐ARMs on a battlefield

AbstractThe Airborne Warning and Control System (AWACS) are pivotal assets in aerial operations, necessitating specialised protection measures, and serving as prime targets for enemy anti‐radiation missiles (ARMs). This paper explores approaches to enhance the battlefield survivability of frequency diverse array AWACS (FDA‐AWACS) by incorporating airborne radar technology onto the platform. The study commences by analysing the typical operational methods of anti‐radiation missiles. Following this, a deception model is formulated for the frequency diverse array (FDA) against the passive radar homing head of anti‐radiation missiles utilising the adjacent antenna single‐pulse amplitude‐comparison direction‐finding technique. Expanding on this groundwork, the research further assesses the deceptive impacts of FDA‐AWACS on direction finding cross‐location techniques. Simulation results validate that FDA‐AWACS can effectively counter the threat of anti‐radiation missiles by diminishing their direction‐finding and positioning systems.

Machine Learning-Driven Analysis of Heat Transfer in Chemically Reactive Fluid Flow Considering Soret-Dufour Effects

ObjectiveThe study investigates tangent hyperbolic nanofluid flow across an extended media, emphasizing magnetohydrodynamic influences, mixed convection, and nanoparticle transport with the help of an innovative and advanced technique. MethodologyIt employs a sophisticated Gaussian Neural Network and Hybrid Cuckoo Search to mimic complex fluid dynamics accurately, ensuring efficient computation and solution precision. By transforming the governing system of nonlinear partial differential equations into ordinary differential equations via similarity transformation, the methodology attains computational efficiency and solution precision. Core FindingsStatistical measures confirm the model's resilience, indicating absolute error variations from E−05 to E−12 and mean squared errors continuously between E−02 − E−07, highlighting the reliability of the model, while the Error in Nash-Sutcliffe Efficiency values fall within the interval E−05 − E−15. The Theil's Inequality Coefficient values lie in the range of E−01 − 10−07. Future Direction and ApplicationsThe findings underscore the model's capacity to improve thermal management, energy efficiency, and process dependability in sectors like chemical processing, environmental engineering, and sustainable energy production. This study positions the Gaussian Neural Networks framework as a robust computational instrument, providing a foundation for subsequent investigations into intricate geometries, multi-physics phenomena, and magnetohydrodynamic systems for novel technology applications.

Antiambiguity Direction Finding by Harmonics' Amplitudes With Two-Element Time-Modulated Array

Antiambiguity Direction Finding by Harmonics' Amplitudes With Two-Element Time-Modulated Array

МАТЕМАТИЧНА МОДЕЛЬ СИГНАЛУ ІЗ ЗАДАНИМИ ПОЛЯРИЗАЦІЙНИМИ ПАРАМЕТРАМИ В ОРТОГОНАЛЬНОМУ ПОЛЯРИЗАЦІЙНОМУ БАЗИСІ

The experience of combat operations in the context of the large-scale invasion of Ukraine by the russian federation shows that the current level of development of electronic weapons is characterised by a wide variety of types and types of electronic means, the use of multifunctional means with widely variable signal parameters and operating modes. For example, modern (state-of-the-art) ground, air and sea radar stations use deliberate changes in the frequency, time and polarisation parameters of emitted signals in different modes of operation, depending on the tasks and conditions of a complex electronic environment. The presence of differences in the polarisation parameters of signals objectively creates prerequisites for their consideration in processing in order to improve the detection, recognition and direction finding performance of radio monitoring systems in a complex electronic environment. The approach is based on the use of antennas with orthogonal polarisation antenna elements, which allows signals to be represented as polarisation vectors. During the processing, it is necessary to take into account the influence of the polarisation characteristics of the antenna system on the parameters of the polarisation vector (change of the polarisation basis), which is relevant since the signals are received by the antenna system from different angular directions. An important condition for obtaining objective results when studying the efficiency of polarisation processing algorithms is the use of a correct mathematical model of signals with given polarisation parameters in a certain orthogonal polarisation basis, as well as the use of signals from real radio equipment whose polarisation parameters can be determined in a polarisation basis other than the specified one. The article presents a mathematical model that allows expressing the field components through the parameters of the polarisation ellipse, and also gives expressions describing the relationship between polarisation vectors and their covariance matrices in different polarisation bases of the antenna system.

OPTIMIZATION OF RADIO SYSTEM STRUCTURES FOR DIRECTION FINDING OF SIGNAL SOURCES WITH COMPLETELY KNOWN PARAMETERS

Context. Direction finders are critical components of radar and radio navigation systems, particularly when installed onboard UAVs. The increasing use of unmanned systems has heightened the need for precise direction finding and wide-angle unambiguous measurements. The primary challenge is to strike a balance between achieving high accuracy and maintaining a broad range of unambiguous measurement angles. Objective. To simultaneously enhance direction finding accuracy and expand the range of unambiguous measurement angles through the statistical synthesis of functionally deterministic signal processing methods in multichannel direction finders. Method. The approach is grounded in the statistical theory of optimization for radio remote sensing and radar systems. For the specific type of signals considered in this study, represented by functional-deterministic models, the likelihood function is constructed, and its maxima are determined for various configurations of multi-antenna direction finders. The statistical synthesis results are validated through simulation and in-situ experiments. Results. Theoretical analysis and simulation modeling confirm that in dual-antenna direction finders, there is a trade-off between high resolution and the range of unambiguous direction finding angles. An improved signal processing method is developed for a four-antenna direction finder, utilizing a pair of high-gain and a pair of low-gain antennas. To achieve the maximum possible bearing accuracy within the range of unambiguous direction finder measurements, a new signal processing method is synthesized for a sixelement radio receiver, combining the processing of signals in two amplitude direction finders and one phase direction finder. Conclusions. The proposed approach achieves an optimal balance between resolution and angle range, making it particularly suitable for onboard systems of unmanned aerial vehicles. Simulation results confirm the effectiveness of the proposed method, highlighting its potential for implementation in modern radio systems.

Устранение неоднозначности оценок направлений прихода широкополосных сигналов в многосигнальном режиме пеленгования

Direction finding of wideband signals overlapping in the spectral domain by a fixed antenna array requires the correction of steering vector ambiguity and phase differences corresponding to different spectral components. The spectral components of the same signal correspond to unequal values of the distance in wavelengths between the antennas in the array. A method of steering vector ambiguity correction suitable for subspace methods such as MUSIC and ESPRIT is proposed. The ambiguity in the presence of multiple signals is resolved by correcting phase diffe-rences between antennas for each spectral component, with preliminary correlation of the ambiguous steering vector with unambiguous ones obtained for the low-frequency range of the spectrum using maximum correlation. The corrected steering vector for each spectral component is obtained from the adjusted phase differences between the antennas and is used in the direction finding correlation algorithm to obtain unambiguous estimates of the directions of arrival of the wideband signals. Simulation results for direction finding of five sound wideband signals using a square internally filled antenna array consisting of 16 antennas, based on ESPRIT with the proposed method of ambiguity correction, are presented. The proposed method for correcting the steering vector ambiguity caused by different spectral components of wideband signals in the antenna array allows estimation of their directions of arrival, as is done for narrowband radio signals.

Ошибка установки углового положения радиолокационного объекта, замещаемого двухточечной моделью, при использовании антенны с разностной диаграммой направленности

The issues of estimating systematic errors in setting the angular position of the apparent radiation center of a radar object simulated by a two-point model when using antennas with difference radiation patterns are considered. The dependence of the angular error on the model parameters, such as the spacing of the emitters, the expected position of the apparent center of radiation and the coefficients of the antenna radiation pattern approximation, is established. The angular error of the bearing is determined by including it in the direction finding characteristic of the antenna as a correction to the angular position with further analytical expression. Calculations were performed for the sum and difference directional diagrams, on the basis of which the error values were compared. The ratio of the approximation coefficients for the sum and difference radiation patterns of the antenna is determined. The obtained analytical results can be used in solving applied problems related to the development of matrix simulators and forecasting the accuracy characteristics of simulation complexes.

Planetary Laser Interferometric Seismoacoustic Observatory

The paper describes a planetary laser interferometric seismoacoustic observatory consisting of six stationary unequal arm laser strainmeters. Based on the triangulation method, the fundamentals of direction finding of various infrasound disturbances at any planetary distance have been developed. The authors show that in addition to determining locations of the occurrence of the recorded disturbance, using data from spatially separated laser strainmeters, it is possible to determine the nature of these signals’ divergence and, also, the loss of their energy in the propagation medium. The creation of the planetary laser interferometric seismoacoustic observatory, consisting of five stationary single-coordinate laser strainmeters and one two-coordinate laser strainmeter, united into a single measuring network with an accurate time clock TRIMBLE 5700 that is capable of recording displacements on their bases with an accuracy of 10 pm in the frequency range from 0 (conventionally) to 1000 Hz and two auxiliary laser strainmeters, will allow us to determine, at any planetary distance, the primary source of deformation infrasound disturbances with primary amplitudes from 100 nm.

Space-Frequency Processing Methods for Satellite Navigation Signals

Relevance. Quite low power of the global satellite navigation systems’ useful informational signals near the Earth surface along with an ongoing noticeable increase of the number of easily available and efficient portable means of blocking wideband energetic interference radiation make the problem of radionavigational satellite devices antijamming capabilities improvement especially relevant both from practical and scientific points of view. Therefore, the goal of this research was to increase the antijamming capabilities of the global satellite navigation systems via processing of the corresponding receiving apparatus’ input signals by special spatial filters. To achieve the work goal the scientific task of researching on the antijamming capability improvement in radionavigational devices by means of space-frequency signal processing was solved. The methods used. During the research, different spatial signal processing algorithms were considered, among them both the ones functioning without any information about interference situation, external with respect to the receiving radionavigational system, and the ones using the knowledge about the number and relative disposition of the jamming sources. Additionally different methods of interference sources number and angular directions finding were studied, as well as modern cost function optimization algorithms which are used for signal sources’ location determination. Scientific novelty of this work consists of usage of new algorithms that implement separate signal processing stages and that provide necessary information to the filtering algorithms during the problem solution, as well as of combining known methods with new approaches to their design. The results. During the scientific task solution, the performance quality metrics comparison was carried out for all the considered algorithms via the computer modeling method that employed recordings of real satellite navigational signals with addition of varying number of uncorrelated energetic interferences sources. As a result of modeling, the performance quality measure values were obtained for all the investigated algorithms and the comparative analysis thereof was conducted, at the end whereof the methods with the best characteristics were picked out. The significance of the work results consists of possibility of using the considered algorithms in real antijamming satellite navigation devices design.

High sensitivity multi‐channel digital receiver for wideband very weak signal direction‐finding classified by machine learning

AbstractFor weak signal detection with direction‐finding (DF), this article presents a new receiver design approach that combines our accumulatively increasing receiver sensitivity (AIRS) signal detection algorithm with the compressive‐sensing (CS)‐based DF‐array/algorithm. The former uses the concept of timeslot (TS)‐based signal threshold detection, whereas the latter employs a frequency‐independent array with randomly located elements, whose bandwidth (BW) largely determines the DF‐array BW. To estimate the direction of a signal, the AIRS algorithm generates the array steering vectors in each TS when the amplitude of any frequency bins exceeds the predetermined threshold of the TS. The aim of this paper is to demonstrate the ability of the new receiver to detect low probability of intercept radar signals with high DF accuracy, fine frequency resolution, and good time‐of‐arrival measurement resolution. To discriminate accurate emitter directions from many false estimations created by the DF‐array in very low signal‐to‐noise ratio environments, K‐means clustering was also applied. In a scenario, the frequency modulated signals from several 165‐mW X‐band radars were in the field of view of a 6‐element DF‐array. Simulation results show that the receiver can accurately estimate all the emitters' directions with root mean squared error of less than 1°, when the separation between the DF‐array and radars is about 100 km.

Mathematical model of single-channel signal search with two degrees of detection in radio frequency monitoring of mobile telecommunication systems

Today, technical means of radio interception, monitoring and direction finding in mobile radio communication networks are implemented in the form of software and hardware complexes, the most important performance indicators of which are considered to be speed, detection accuracy and probability of recognition of mobile radio communication means with their information content. At the same time, these issues still remain problematic and require further development of methods and techniques for searching and detecting signals of mobile radio communications in both frequency and time environments of telecommunication channels and their information processing.The authors propose a mathematical model for searching for mobile radio signals in the frequency-time domain with two degrees of detection. The description of the mathematical model for determining the spectral components of signals in the frequency and time domains is carried out using the basic provisions of the theory of directed probability graphs, geometric probabilities with its well-known problem of meeting in a given time interval and the theoretical foundations of statistical information processing.It is shown that the application of the mathematical model of single-channel search for signals of mobile radio communications with two degrees of detection in the frequency-time domain in practice will make it possible to determine the quality of the radio monitoring process and increase the efficiency of evaluating the spectral components of radio signals in terms of speed, detection accuracy and probability of recognition of mobile radio communications with further determination of their information content.

Reanalysis on Performance of Microwave Phase Detector for Multisignals.

Microwave phase detectors (MPDs) are key components of instantaneous frequency measurement (IFM) receivers and phase interferometer direction finding (PIF-DF) receivers. In conventional analyses, there is seldom a major quantitative discussion of MPD characterization when multiple signals arrive at the same time, which is often the case in complex and noisy electromagnetic environments. We have reanalyzed the characteristics of MPDs with respect to filter effects acting on more than two RF signals and differential amplifiers, which are not considered in conventional analyses. First, a step-by-step mathematical model of the signal flow is developed, which creates a cross term between the two signals and naturally introduces intermodulation effects. Second, the new response characteristics of the MPD are evaluated by simulation. Finally, the intermodulation effects of zero-forcing and extreme-forcing were found simultaneously in the crosspoint frequency and near-frequency regions of multiple signals, which led to significant deviations and errors in the output of the MPD. This effect may have significant implications for IFM and PIF-DF receivers.

High-Altitude Discharges and Whistlers of Volcanic Thunderstorms

The results of the observations of atmospherics and whistlers initiated by high-altitude electrical discharges that occurred during the eruption of the Kamchatka volcanoes (Bezymianny and Shiveluch (Russia)) on 7 and 10 April 2023 are presented. Recording of atmospherics and associated whistlers was carried out by a VLF (very low frequencies) radio direction finder. Two-hop whistlers were identified by dispersion coefficient, which corresponded to the double passage of the signal from Kamchatka to Australia and back. The heights of the electric discharges were determined by means of interferograms of direct and reflected from the ionosphere radiofrequency atmospherics. The high-altitude distribution of an electric discharge is obtained, the penetration of which into the ionosphere is responsible for the generation of whistlers. The characteristics of volcanic electrical discharges and whistlers can be used to estimate the height of an explosive eruption.

SPECIFIED GLOBAL POINCARE–BENDIXSON ANNULUS WITH THE LIMIT CYCLE OF THE RAYLEIGH SYSTEM

In the work of A. Grin and K. Schneider [1] two algebraic transversal ovals, which form the Poincare–Bendixson annulus 𝐴(𝜆), are analytically constructed. This annulus contains the unique limit cycle of the Rayleigh equation ¨ 𝑥+𝜆( ˙ 𝑥2/3−1) ˙ 𝑥+𝑥 = 0 for all values of the parameter 𝜆 > 0. In the constructed annulus 𝐴(𝜆) inner boundary consists of zero-level set of the Dulac–Cherkas function and outer boundary represents the diffeomorphic image corresponding boundary of such an annulus for the van der Pol system. In this paper new methods of construction two Dulac–Cherkas functions are worked out. With help of these functions a better inner boundary of the Poincare–Bendixson annulus 𝐴(𝜆) depending on the parameter is found. Also, for the Rayleigh system, a procedure for direct finding a polynomial whose zero-level set contains a transversal oval used as the outer boundary 𝐴(𝜆) is proposed. Then we determine the interval for 𝜆 where the better outer boundary of the annulus is a closed contour, which composed from two arcs of the constructed oval and two arcs of non-closed curves belonging to zerolevel set of one from Dulac–Cherkas functions. Thus, finally the specified global Poincare–Bendixson annulus for the limit cycle of the Rayleigh system is presented.

Device‐Free Detection of Pedestrian and Movement Direction Using Bluetooth Direction Finding Function

From Bluetooth 5.1, a direction finding function has been added that allows the receiver to measure the angle of arrival (AoA) of the wireless signal from the sender. In this letter, we propose a method for detecting pedestrians and their movement direction passing between Bluetooth devices equipped with direction finding functions. As a result of the evaluation, pedestrians could be detected with higher accuracy (F‐score 0.929) by combining received signal strength indicator and AoA than when using each alone. In addition, the accuracy rate for estimating the movement direction using AoA was 0.704. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Применение критерия косинусного рассогласования при учёте наличия рэлеевского шума в задаче моноимпульсной пеленгации

The aim of the work is to develop a modified algorithm for passive monopulse direction finding and to estimate the precision of this algorithm. A non-zero average value of the amplitude error of the recorded signals is a feature of the input data for the problem of direction finding. It is proposed to estimate and take into account the average value of the amplitude error, while estimating bearing. The proposed solution is based on optimizing the cosine mismatch function between the measured and estimated amplitudes. To increase the computational efficiency of the method, a partial analytical optimization of the cosine mismatch by the average amplitude error was performed. The result of modeling shows that it is advisable to use the proposed mismatch function, when the signal-to-noise ratio is less than 15 dB. To improve performance the obtained analytical expression of the average amplitude error should be used. The proposed method makes it possible to provide a bearing error not exceeding ~ 0.1 of the beam width of the radiation pattern with a signal-to-noise ratio of ~ 6 dB.