Direction Finding Error Research Articles

STREAMLINING DIGITAL CORRELATION-INTERFEROMETRIC DIRECTION FINDING WITH SPATIAL ANALYTICAL SIGNAL

This study investigated a search-free digital method for radio direction-finding that utilizes spatial analytical signal reconstruction. The research focused on optimizing the method's accuracy for estimating the direction of a radio source. The analysis identified the separation distance and number of chosen antenna elements for signal reconstruction as the key parameters influencing accuracy. Analytical optimization and simulations were employed to determine the optimal values for these parameters. The research successfully modeled the impact of antenna element selection on direction-finding errors under specific signal-to-noise conditions. This model can be used to guide further development and optimization of this radio direction-finding method.

Investigation of the polarization difference of the EM wave of an airborne EW system in the mode of coherent interference

Problem statement. Coherent interference generated from two or more points makes it possible to change the amplitude-phase distribution of the emitted wave. The effect of such interference on monopulse direction finders, which are widely used in weapon control radars, leads to abnormal coordinate determination errors. In some cases, combined jamming methods, the detection of such a jammer is a difficult task. The implementation of a set of measures to protect our own weapon control radars from electronic jamming is a critically important task. It is important to study the errors that occur and to form signs based on which it is possible to select sources of coherent interference. Goal. Evaluation of errors occurring in a monopulse direction finding system and investigation of polarization difference arising from the formation of coherent interference. Results. An assessment of the effect of coherent interference on the direction finding system has been carried out. Based on the calculation, a conclusion was made about the occurrence of an angular direction finding error, which in the range of 2-7 GHz exceeds the accuracy of modern radars. An electrodynamic simulation of the field in the far zone was carried out with radiation of the EA–18G Growler in the microwave CAD. The analysis of the influence of airframe elements on the distribution of the directional pattern is carried out. An assessment of polarization difference in the formation of coherent interference by AN/ALQ-99 aircraft stations has been carried out. It was concluded that there were significant differences in polarization characteristics within two beamwidths for AN/ALQ–99F jammers. Practical significance. Electronic protection against coherent interference generated by an electronic warfare aircraft station is possible on the basis of polarization selection.

Систематические ошибки установки углового положения в матричных имитаторах радиоэлектронной обстановки

Estimates of the error in setting the angular position of the apparent center of radiation by a matrix simulator, which are, in fact, its systematic error, are considered. It is shown that the cause of the error is the replacement of the simulated point emitter by several points. Analytical relations have been obtained that allow calculating the magnitude of the systematic direction fin-ding error based on the characteristics of the matrix simulator and the radiation pattern of the receiving antenna operating with the matrix simulator of the radio engineering system. It is shown that the considered error is completely determined by the nonlinearity of the direction finding characteristic of the antenna. It is established that the error is most significant when simulating the apparent center of radiation outside the matrix. For the area inside the matrix, the dependences of the maximum error values and their angular positions on the shape of the antenna pattern and the specified position of the radiation point are obtained. The relations allowing to estimate errors depending on the ratio of the angular dimensions of the matrix, the width of the antenna radiation pattern and the coefficients of approximation of its radiation pattern are obtained. The reliability of the obtained results is confirmed by comparison with the results obtained by numerical simulation. The results of the work can be used to solve applied problems related to the development of matrix simulators and simulation complexes based on them, as well as to predict their accuracy characteristics.

Improving the accuracy of a digital spectral correlation-interferometric method of direction finding with analytical signal reconstruction for processing an incomplete spectrum of the signal

A method of correlation-interferometric direction finding has been improved, which effectively solves the problem of radio direction finding of radio emission sources under conditions of exposure to one or two masking interference. The problem was solved using the selection of an unmasked fragment of the spatial spectrum of the signal and the reconstruction of the missing samples of its signal group. As a result of the synthesis of the proposed method, estimates of signal samples were obtained as exact solutions to the proposed energy balance equations. The resulting solutions provide a significant increase in the signal-to-interference ratio and, accordingly, direction-finding accuracy without increasing the number of reception channels of the antenna array. As a result of the simulation, the dependences of the standard deviation of the bearing estimate on the signal-to-noise ratio in the presence of interference were built. Under the influence of one or two masking interferences and a signal-to-interference ratio of 0 dB, the use of the known direction-finding method without interference selection produces an anomalously large direction-finding error of more than 0.42 degrees, which is practically independent of the signal-to-noise ratio. The direction-finding method with selection of spectral signal samples masked by interference reduces the direction-finding error to 0.22 degrees when exposed to one interference and to 0.3 degrees when exposed to two interferences. This is due to the presence of power losses of the usable signal during the selection of its samples masked by interference. The proposed method of direction finding with reconstruction of signal samples provides a significant gain in accuracy by 3–30 times compared to the method of selection of masked samples in the range of changes in the signal-to-noise ratio (–20.5) dB. The direction-finding error of the proposed method decreases with increasing signal/noise according to a hyperbolic dependence. It is advisable to use the proposed direction-finding method when masking no more than two samples of the signal group

Influence of radar direction finding errors
 of aerological radiosonds on the accuracy of wind sounding

Influence of radar direction finding errors
 of aerological radiosonds on the accuracy of wind sounding

Watson–Watt Direction Finding With Transfer Learning-Based Calibration

A compression of an entire 4-element Watson-Watt direction finding (DF) process, including calibration, into a single neural network based system is introduced. First, a Watson-Watt DF architecture is approximated using neural networks, assuming idealized patterns. Next, the transfer learning is applied on these patterns to demonstrate that the conventional, often costly look-up-table calibration can be replaced at low cost and overhead. Finally, several neural networks are trained, and their performance is analyzed as a function of what data is used in the transfer learning process, and where it was collected. The proposed DF and calibration procedure is implemented with a four element array to achieve reduction in the maximum and root mean square DF errors by about 45% and 39%, respectively.

Research into the Influence of Millimeter-Wave Antennas on Direction Finding Errors by Phase Method

Research into the Influence of Millimeter-Wave Antennas on Direction Finding Errors by Phase Method

Development features of small-sized phased antenna arrays of millimeter wave band

Recently, a need has arisen for small-sized Ka-band phased antenna arrays (PAA) with electric beam scanning. In the development and study of phased arrays with small apertures not exceeding several tens of wavelengths, significant limitations were found on the accuracy of beam setting accuracy when its scanning in a wide angular sector. This leads to an increase in direction finding errors when using such phased arrays as part of small-sized monopulse radars for target tracking. The aim of the article is to investigate the causes of occurrence of various factors that affect the accuracy of the beam setting accuracy in the feedthrough phased arrays with spatial excitation by monopulse feeds, and also to note ways to eliminate or minimize this effect. The analysis of the main factors affecting the accuracy of the beam setting accuracy in the phased arrays, associated with the control algorithms of the phase shifters of the phased arrays, caused by the peculiarities of the circuitry implementation of the beam handling system of the phased arrays, and also having an electrodynamic nature and taking into account the excitation of the receiving antenna array by a monopulse feed, the mutual influence of emitters and edge effects in the antenna array. Recommendations on eliminating or mitigating the influence of these factors are given.

A Compensation Method of Nonideal Modulation Pulse for Direction Finding With Time-Modulated Array

In this letter, a direction-finding compensation method of nonideal modulation pulse for direction finding with the time-modulated array is investigated. With the transmission signal's increasing bandwidth, the conventional rectangular pulse cannot effectively describe the practical modulation pulse envelope shape, which will introduce the direction-finding error caused by the different harmonic characteristics. For compensating the error, a modeling method for the practical modulation pulse envelope shape is investigated and its harmonic expression is also deduced. Compared with the direction-finding method considering the rectangular pulse, numerical simulation, and experiment results are provided to verify the effectiveness of the proposed compensation method.

Совершенствование формы плоских антенных решеток для повышения точности радиолокации со сверхразрешением

A promising way to increase the bandwidth and noise immunity of modern wireless information transmission systems is the use of antenna arrays equipped with a digital signal processing unit, which include MIMO systems (Multiple Input Multiple Output), as well as adaptive (smart) antennas. The main advantage of this approach is the antenna’s spacing, which makes it possible to assess the angular coordinates of radio signals with further developing 
 a radiation pattern. Gaps in studying the influence of the lattice geometry together with various kinds of antenna elements are known to be one of the factors of inaccuracy of such systems. The work is aimed at obtaining the shape 
 of a planar antenna array with a higher direction finding accuracy. There is described an algorithm for calculating such an arrangement of antenna elements of flat antenna arrays, in which the standard deviation of the estimates of the angular coordinates of one and two radio signal sources is reduced. The proposed approach is based on the analysis 
 of the influence of antenna location on the variance of estimates described by the lower boundary of Kramer-Rao. This value shows the influence of the location of antenna elements on the accuracy of estimating the direction of arrival of a joint assessment with two signal sources. It has been shown that the accuracy of the direction-of-arrival non-joint estimation is determined as the sum of squared differences between all coordinates of omnidirectional elements along the X- and Y-axis if one signal arrives. If two signals arrive, the accuracy of the direction-of-arrival joint estimation depends on the sum of cosines having the argument with the difference between sensor coordinates and signals radius-vectors. The optimal location of the antenna elements using the obtained expressions can be calculated very easily to reduce the direction-finding errors near particular sectors. In order to confirm the proposed method, there were studied the antenna arrays built after minimizing the boundary of Kramer-Rao, where the target functions are the new expressions. It is found out that the new shapes of antenna arrays based on the analytical expressions have better direction-of-arrival accuracy in comparison with the circular ones.

Dir-MUSIC Algorithm for DOA Estimation of Partial Discharge Based on Signal Strength Represented by Antenna Gain Array Manifold.

Inspection robots are widely used in the field of smart grid monitoring in substations, and partial discharge (PD) is an important sign of the insulation state of equipment. PD direction of arrival (DOA) algorithms using conventional beam forming and time difference of arrival (TDOA) require large-scale antenna arrays and high computational complexity, making them difficult to implement on inspection robots. To address this problem, a novel directional multiple signal classification (Dir-MUSIC) algorithm for PD direction finding based on signal strength is proposed, and a miniaturized directional spiral antenna circular array is designed in this paper. First, the Dir-MUSIC algorithm is derived based on the array manifold characteristics. This method uses strength intensity information rather than the TDOA information, which could reduce the computational difficulty and the requirement of array size. Second, the effects of signal-to-noise ratio (SNR) and array manifold error on the performance of the algorithm are discussed through simulations in detail. Then, according to the positioning requirements, the antenna array and its arrangement are developed and optimized. Simulation results suggested that the algorithm has reliable direction-finding performance in the form of six elements. Finally, the effectiveness of the algorithm is tested by using the designed spiral circular array in real scenarios. The experimental results show that the PD direction-finding error is , which meets the need for partial discharge DOA estimation using inspection robots in substations.

An improved method of impact point positioning at sea based on Beidou and dual cross-array

Ocean acoustics is an important research topic in ocean engineering. Among them, the location of the impact point at sea is an important method to evaluate the firing accuracy of naval guns. Most of the traditional methods for locating the impact point at sea use the optical positioning principle, which is expensive and has a high false alarm rate. It is easy to be affected by natural conditions, such as marine visibility. Based on this, this paper proposes an improved location method of the impact point at sea based on the Beidou differential and acoustic array, which improves positioning accuracy greatly. First, through the simulation analysis of single array positioning error, this paper gives the basis of the positioning method, then deduces the positioning principle of this method in detail, and simulates and analyzes the positioning error of the double array. Finally, the simulation experiment of the voice signal is carried out to verify the positioning performance of the dual cross-array. The results show that the direction finding of the dual cross-array is very accurate, and the ranging error is relatively large. Among the five positioning points selected in this paper, the maximum relative direction-finding error is 0.33%, and the maximum relative ranging error is only about 1%, which is much better than the ranging performance of a single array. It has certain engineering application values and provides a certain reference for the design of the impact point positioning scheme at sea.

An Acoustic Sea Glider for Deep-Sea Noise Profiling Using an Acoustic Vector Sensor

Abstract An acoustic sea glider has been developed for ambient sea noise measurement and target detection through the deployment of an acoustic vector sensor (AVS). The glider was designed with three cabins connected in sequence and it can dive to depths exceeding 1200m. The AVS fixed on the glider measure acoustic pressure and particle velocities related to undersea noise, and the inner attitude sensors can effectively eliminate the estimation deviation of the direction of arrival. The inherent self-noises of the acoustic sea glider and AVS are presented respectively in respect to the Knudsen spectra of sea noise. Sea trial results indicate that the AVS could work well for undersea noise measurement when the glider is smooth sliding, and the target azimuth estimated by AVS after correction is remarkably consistent with the values measured by the GPS, and direction-finding errors are less than 10 degrees. The research in this paper shows that the acoustic sea glider is able to undertake tasks such as a wide range of underwater acoustic measurement and detection.

Aerial Locating Method Design for Civil Aviation RFI: UAV Monitoring Platform and Ground Terminal System

A key open question in the aerial locating method is ensure that parameters that identify the location of the radio frequency interference (RFI) are monitored, and to make sure that the locating algorithm is unbiased. Furthermore, the transmission of parameters to the ground for real-time analysis and display of the RFI location is important as it provides insight into the performance advantages of the aerial location method. The main contributions of the article are four points: the first is the introduction of the angle of arrival (AOA) algorithm to civil aviation RFI location, and the integration of algorithm characteristics with unmanned aerial vehicle (UAV) operations proposing an aerial monitoring method for civil aviation RFI. Simulation results show that the two-point cross-location method obtains effective information on the location parameters of the RFI. The second is to build a UAV monitoring platform, which is as light as possible to make sure the direction finding and digital transmission devices meet the airworthiness requirements, so that the UAV can complete the data acquisition task within a safety margin. Thirdly, a ground analysis system was designed to receive information on the UAV’s parameters, enabling software manipulation to ensure safe operation under non-visual conditions. In addition to this, the monitoring data is processed in real time and algorithms are used to resolve the location of interference sources and display them on a map. The fourth one is to verify the implementation of the aerial positioning method by setting up different test scenarios. Compared with portable direction-finding equipment and ground monitoring, the test results show that the UAV-based RFI monitoring method performances better in monitoring radius and positioning accuracy with a small direction-finding error, and the advantages of the ground analysis system are highly integrated and intuitive display.

Effect of Plasma Sheath Covering Spacecraft-Borne Array Antenna on Direction-of-Arrival Estimation

During the reentry process of a spacecraft, a plasma sheath will attenuate and distort the amplitude and phase of the transmitting electromagnetic (EM) waves, influencing signal reception and measurement accuracy of the direction of wave arrival of the spacecraft-borne array antenna, by which the spacecraft communication and guidance system may be affected. To solve this problem, based on the space distribution characteristics of plasma sheath flow field, an EM simulation model of an array antenna under plasma sheath is established, and EM simulations related to field propagation across plasma sheath and radome are performed. Then, the array signal model is constructed by extracting the field strength data at the array element. Several spatial spectrum estimation methods are conducted to calculate the direction of arrival of an EM wave incident on the array antenna. By comparing the direction of the incoming wave in free space with the estimated direction after propagating through the plasma sheath, the direction-finding error of the spacecraft-borne array under the plasma sheath is obtained, and the cause of the error is analyzed. With compensation information, the results of the proposed method can enable higher target-tracking accuracy for the spacecraft guidance system.

A Passive Location Method Based on Virtual Time Reversal of Cross Antenna Sensor Array and Tikhonov Regularized TLS

The multi-station direction finding and cross positioning method is often used in three-dimensional passive detection system when the measurement information only has DOA estimation value. However, the essence of this algorithm is to linearize the nonlinear problem, which is very vulnerable to the influence of direction finding error. In order to solve the above problem, the anti-interference virtual time reversal (VTR) algorithm combined with Tikhonov regularization total least squares (TLS) are for passive location. A multi-station passive location model is built and the cross antenna sensor array is used to receive signals. According to the established array model, the coordinate transformation formula of the observation station is derived and the coordinate formula of each array element is obtained by the transformation matrix, then the signal receiving model is established. The coordinates of virtual points are transformed for DOA estimation which accomplished by VTR, then the direction lines obtained. The results of the VTR direction finding are transformed into new space angles and the observation equations of the space angles are constructed. In order to overcome the influence of noise on the positioning solution, Tikhonov regularized TLS method is used to solve the equations for obtaining target position. The simulation results show that the algorithm can achieve high-resolution DOA estimation of the target at low SNR and the positioning errors under different number of observation stations are analyzed. The positioning accuracy has better performance compared with the unimproved least square method.

Efficiency of rejection of abnormal measurements of the phase difference in the survey location finder when receiving signals of the scanning radio-frequency source under the rough terrain

The paper presents the results of a study on rejecting anomalously large direction-finding errors from the results of instantaneous measurements of the ratio of the amplitudes of the output signals of the receiving antennas. Bearing rejection algorithms are based on theoretical dependences obtained for the normal model of fluctuations of the quadrature components of the output signals of the receiving antennas. The efficiency of algorithm rejection is determined by the terrain of open and semi-enclosed routes and may reach 54 percent.

Ship Detection and Direction Finding Based on Time-Frequency Analysis for Compact HF Radar

Ship detection at the sea surface is important for improving human marine activities. Most existing ship detection methods for high-frequency surface wave radar (HFSWR) are based on peak and constant false alarm rate (CFAR) detection and require a coherent integration time (CIT) of several minutes. However, in such a long period, the target may not be stationary. To account for the nonstationary property, a time-frequency analysis (TFA)-based ship detection and direction finding (DF) method is proposed for HFSWR. Target ridges on the TF representation (TFR) of the echo data are detected first. Next, array snapshots are formed by sampling the extracted ridges and are used to estimate the direction of arrival (DOA). The processing results of the radar data collected at Dongshan, Fujian Province, China, show that the proposed method outperforms the CFAR method with both increased detection rates and decreased DF errors, especially under relatively low signal-to-noise ratio (SNR) scenarios.

Error Estimation of Direction Finding and Determining Coordinates of Signal Source Using Combined Hydroacoustic Receivers

The paper deals with the possibility of direction finding and determining the coordinates of a source of acoustic signal emitted by a surface or underwater vehicle in the subsonic frequency range. For this purpose combined hydroacoustic receivers are used. During the first experiment, the estimates of the systematic component of direction finding error were obtained when the source emitted a tone or polyharmonic signal, and the direction finding results were averaged over a set of frequencies. The obtained results were used in the second experiment for estimating the error in determining the coordinates of the polyharmonic signal emitter consisting of three combined receivers (CR) which form the navigation base distributed in the horizontal plane.

Погрешности измерения угловой координаты протяженных целей моноимпульсным методом в зоне Френеля линейной антенной решетки

Introduction. The basic theoretical information on measuring systems in radar is presented, an analysis is performed to determine the errors of direction finders, and calculation expressions are found to determine the magnitude of the direction-finding errors by a single-pulse method in the Fresnel zone of a linear receiver antenna array caused by the combined action of the internal noise of the radio direction finder receiver and the angular noise of extended reflective interference. Purpose of the study. To consider the influence on the magnitude of the errors of direction finding together of the levels of the side lobes of both the differential and total directivity characteristics of the receiving antenna of the radio direction finder in the Fresnel zone. Materials and methods. Approaches for determining the magnitude of direction-finding errors are a generalization to the Fresnel zone of the known result of calculating the error during operation of a monopulse direction finder in the far zone of the receiving antenna. Results. The influence of the angular size and the distance size of a multi-point reflector on the magnitude of direction-finding errors by a single-pulse method in the Fresnel zone of a receiving linear antenna array of a radio angular system is investigated. Conclusion. Theoretical methods of measurement in radar are considered and it is shown that expanding the functionality to ensure high accuracy of measuring an information parameter will improve the accuracy of determining errors in direction finding systems.