Direction-finding Characteristics Research Articles

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.

Direction-finding characteristics forming for wideband multibeam reflector antennas

Direction-finding characteristics forming for wideband multibeam reflector antennas

Photodetector module of optoelectronic control systems for tracking the moving objects

An algorithm has been developed for modelling the signals of four-plane photodetector, when moving an axisymmetric light spot along its surface. The form of direction-finding characteristics of photodetector has been calculated for different schemes of illumination of sensitive surface of the detector, which are used in optoelectronic automatic control systems, in particular in the motion control systems for tracking moving objects. Some samples of specialized focusing microprism devices with the distribution of light spot in the focal plane as a central circle with a light ring at its periphery, which are made using diamond micro-cutting based on our simulation results, have been experimentally investigated.

Search for conditions for providing an unambiguous range of direction finding characteristics of an active phased array antenna using difference channels

Search for conditions for providing an unambiguous range of direction finding characteristics of an active phased array antenna using difference channels

Метод определения направления на цель цифровой антенной решеткой моноимпульсной радиолокационной станции

On the basis of the analysis of the errors of the monopulse method of direction finding of the target of a radar station with a digital antenna array, a group of errors associated with fluctuations of the equisignal direction when scanning the beam of the antenna system, as well as with the non-identical shape of the generated beams of the monopulse group, was separated into a special cluster. This circumstance is especially critical for large-aperture radars with phased array with electric scanning, where the number of formed receiving beams is significant, in addition, the coordinates of the target usually do not coincide with the coordinate planes along which the coordinates are measured. The nonlinearity of this problem requires unique approaches and solutions. The classical formulation of the problem is associated with obtaining an estimate of the radiation vector of the entire antenna array from the known measured vector of complex signals at the output of the antenna array at a fixed time. To solve this problem and determine the decision rule, a neural network approach was used, while the neural network was trained according to the criterion of the minimum of the selected objective function. The substantiation of increasing the accuracy of measurements of angular coordinates in monopulse systems with scanning digital phased antenna arrays based on the use of neural networks in the process of radar data processing without the formation of direction finding characteristics is given. The results of modeling the characteristics of the antenna array (using the example of a flat antenna array with a dimension of 30 by 30 emitters) under the conditions adopted in the model of the antenna array of assumptions when implementing the classical and original methods are shown using examples of the surfaces of the variances of errors in measuring angular coordinates by the monopulse method in a rectangular spatial domain, which showed reduction of error and expansion of the measurement area. In the future, the practical implementation of this approach is assumed using FPGA in the receiving paths of the frequency-dependent part of the radio direction finder.

Control of the operating range of the direction finding characteristics of the onboard phased array antenna by means of a compensation channel

Control of the operating range of the direction finding characteristics of the onboard phased array antenna by means of a compensation channel

ПОЗИЦІЙНО-ЧУТЛИВА МАТРИЦЯ ФОТОДЕТЕКТОРІВ ДЛЯ ОПТИЧНОГО КООРДИНАТОРА

New position-sensitive matrices for an optical coordinator and a method for determining the coordinates of a light spot for micromovements are presented, an analysis of the topologies and direction-finding characteristics of the proposed matrices is shown.

An aperture’s amplitude-phase distribution for forming frequency-independent direction-finding characteristics of a linear antenna arrays

The aperture’s amplitude-phase distribution of a linear antenna array, ensuring the formation of frequency-independent direction-finding characteristics in a wide frequency band, is considered. The basic regularities of the choice of the amplitude-phase distribution parameters of linear antenna arrays for the case of frequency independent amplitude distribution and frequency dependent phase distribution are investigated. Using the example of a 45-element linear array designed for operation in a frequency band with a relative overlap of 4:1, the influence of the amplitude and phase distribution’s parameters on the magnitude and deviation’s character of the direction-finding characteristics in the operating frequency band is investigated. It is shown that the introduction of a substantially decreasing amplitude distribution contributes to a decrease in the integral standard deviation of the direction-finding characteristics in the frequency band. The relationship between deviation of frequency dependence of the direction-finding characteristics of the array and variations in the frequency dependence of the phase distribution in the aperture is established. The analysis of the basic regularities of the formation of frequency-independent direction-finding characteristics of broadband antenna arrays has been carried out.

Research of influence a physical carrier on the characteristics for four-element circular antenna array

The main problem arising in the development of mobile-based antenna arrays is the problem of taking into account the influence of the carrier body on the characteristics of such an antenna array. Pilotless vehicle are one of the most popular directions of modern aviation development. It is aimed to consider a quite simple in design four-element annular antenna array and to analyze the influence on the bearing direction finding characteristics of such a mobile carrier which is a pilotless vehicle. Theoretical consideration of the carrier body effect on the bearing direction finding errors is usually reduced to the problem of electromagnetic waves diffraction on conducting objects. Comparison of some absolute bearing direction finding errors obtained by the phase correlation method for the cases of placing the antenna array in free space and on the array carrier is given. The results of the calculation of the root-mean-square values dependence on the frequency, averaged over all the analyzed angles of the radio wave direction of arrival, are presented. The dependences of the root-mean-square value on the azimuth angle of the radio wave direction of arrival for the cases of the antenna array placement on the carrier body and in the free space averaged for all the analyzed signal frequencies were calculated.

RADIO SOURCE DIRECTION FINDING IN WIDE FREQUENCY BAND USING CIRCULAR ANTENNA ARRAY

For the VHF broadband direction finder, coherent and incoherent direction finding algorithms for switched and non-switched connection of the antenna array (AR) to receiving device in single-signal and multi-signal direction finding modes are developed and investigated.Their synthesis is based on the methods of space-time theory of radio systems. Numerical calculation of the direction finding characteristics of the algorithms for different number of antenna array elements determines the operating range upper limiting frequency, in which this configuration provides single-value estimates of the azimuth and elevation angle. Statistical simulation modeling shows that for an odd number of antennas, the antenna array amplitudephase response is unique in a wider frequency band than for an even number of antennas. Due to this MUSIC based property applied in the space of antenna array elements, direction finding algorithm is developed for wide frequency band with several signals overlapping in frequency, with switched and non-switched AR connection to a radio receiver. It is shown that the use of ESPRIT and MUSIC methods in free-space diagram does not allow for direction finding in a wide frequency band with the antenna array fixed configuration. The results of the field studies of the developed algorithms are presented for the single-signal and multi-signal modes of operation, software and hardware implemented in the VHF radio direction finder. A comparative analysis of the developed algorithms with the known APs with fixed configuration is performed. It is shown that with the same AR configuration, it is the direction finding algorithm that determines the frequency range in which the direction finding is unique.

Применение потенциалов Дебая для расчета первичного поля в изотропной упругой среде, возбуждаемой вертикальным источником

An analytical solution of the problem of exciting an isotropic elastic medium by a vertical point source is proposed. This problem is a model one and is also a part of the solution of other model problems such as wave excitation in a plane-layered medium. The solution is based on the method of Debye potentials, which is widely used in solving various problems of electrodynamics. The range of these problems includes radiation from an antenna of a fairly arbitrary kind over a plane-layered dielectric medium, consideration of the effect an intricate fairing of an aircraft has on the operation of the radar station antenna system (the effect on the antenna pattern and the direction-finding characteristics of the system as a whole), designing slit radiators with a feeding resonator, and radiation from horn and waveguide antennas into a magnetodielectric semi-space. In many cases, it is possible to obtain an analytical solution of the problem; if an analytical solution is not available, numerical methods developed using the Debye potentials are effective from the computational point of view. The significance of an analytical solution lies in the simplicity and clarity of the interpretation and understanding of the wave propagation processes in contrast to a numerical solution. However, the fundamental difference between the problems of exciting elastic bodies from electrodynamic ones is in that two types of waves, namely, transverse and longitudinal ones, propagate in elastic media. This feature substantially complicates both the analytical solution and the elastic wave propagation process in comparison with electromagnetic waves. In view of this specific feature, a technique for calculating the excitation of an isotropic elastic medium using the apparatus of Debye potentials is proposed. It is shown that the displacement field of an isotropic elastic medium excited by a vertical source is represented as the sum of longitudinal and transverse wave fields, and symmetrically in the plane perpendicular to the source axis. Simple analytic expressions for calculating the displacement field at an arbitrary point in space are obtained. The results of calculations using analytical formulas are compared with the data of numerical modeling in the COMSOL Multiphysics 3.5a computer program. In view of the fact that the COMSOL Multiphysics 3.5a computer program is intended for calculating structures with finite dimensions, an original model of unlimited elastic medium in the form of a large-radius sphere (around 20 wavelengths) with radially-symmetrical absorption was developed.

Direction finding characteristic of an “antenna – radome” system and ways of increasing direction finding accuracy for radiolocation objects

In the work we provide a theoretical verification for various techniques of increasing direction finding accuracy of on-board radio systems equipped with “antenna – radome” systems, based on representing a direction finding characteristic of an “antenna – radome” system as a power series. Moreover, we describe design principles and flowcharts of direction finders ensuring a multiple increase in detection accuracy. Consequently, we analyse direction finding errors, and supply our research with the results of investigating a device implementing the techniques suggested.

Method of estimation of appear direction of unknown shape signals

It is proposed a new method of build of direction-finding characteristic of antenna array to detect the direction of the signal source in condition of unknown signal shape. A comparative analysis of proposed method is carried out with numerical simulation.

Model of a persistent photodetector for analyzing the threshold sensitivity in the problem of detection of a moving point object

A model of the direction-finding characteristic of a moving point object for a persistent photodetector is proposed. The model ensures the calculation of the direction-finding characteristic as a function of photodetector parameters and object velocity, which form the basis for calculating the probability of detection of moving point objects. Results of numerical experiments are reported.

Correction of the amplitude-phase distribution of electromagnetic field in the context of wireless direction finding problem

A technique for correcting the amplitude-phase distribution of the aperture field in the antenna array has been investigated. The optimal number of points for placing the reference oscillator was determined. The specified number provides for achieving the efficiency of superresolution algorithms. A correction technique based on presenting the antenna array in the form of large-radius array consisting of ideal noninteracting elements was proposed. This technique involves the use of only one reference point. Using the MUSIC method, as an example, the direction finding characteristics were calculated for the techniques under consideration.

Energy-calibration methods for multichannel scanning optoelectronic devices

This paper discusses high-efficiency methods for energy calibration of multichannel scanning optoelectronic devices, including a method of measuring the probability characteristics of the threshold sensitivity, taking into account the direction-finding characteristic of the device. A comparative analysis of the described methods is carried out, using the results of the experimental studies.

Portable Instrument for Locating Noise Sources in Mechanical Equipment

A portable direction finder utilizing correlation techniques was developed for locating noise sources in mechanical equipment. A description of this instrument and some test results are given. The test results include studies of the direction finding characteristics of the apparatus and a simple method of determining wave fronts.