Amplitude-phase Distribution Research Articles

AMPLITUDE-PHASE DISTRIBUTION MEASUREMENT PLANE DIMENSIONS INFLUENCE ON THE HOLOGRAPHIC METHOD ANTENNA ARRAY RADIATION PATTERN RECONSTRUCTION ERRORS

The article explores the holographic method of measuring the antenna pattern. A flat antenna array is used as the antenna under test, and a planar rectangular surface is used as the surface on which the amplitudephase distribution in the near field is measured. Using the example of a flat antenna array, we consider the influence of the size of the measurement surface of the amplitude-phase distribution of the field in a plane orthogonal to the reconstruction plane of the radiation pattern. Antenna emitters are excited with a combined amplitude distribution and linear phase distribution. The field in the longitudinal zone of the lattice is determined using the Kirchhoff integral. The reconstructed radiation patterns are estimated using the amplitude-phase distribution over the entire measurement plane in comparison with the array radiation pattern in the far zone. A numerical analysis of the influence on the errors in determining the parameters of the lattice radiation pattern using the holographic method is also carried out: the number of columns of the amplitude-phase distribution on the measurement plane, the position of this plane in three coordinates relative to the plane of the aperture of the lattice. It is shown that if the spacing of the points of measurement of the amplitude-phase distribution and the pitch of the lattice are equal, to restore the radiation pattern using the holographic method, it is sufficient to use one column of the amplitude-phase distribution on the measurement plane. This greatly simplifies and reduces the cost of the measurement process and the necessary equipment. Examples of determining errors in measuring the parameters of the antenna array when shifting the plane of measurement of the amplitude-phase distribution in three coordinates are given.

Исследование характеристик частичных разрядов в искусственных дефектах линий электропередачи

The article describes the study of the characteristics of partial discharges (PD) in various types of artificial defects in cable lines. A total of 13 types of insulation defects are considered. The PD measurements are carried out using a high AC voltage source and a commercial PD recorder. For each type of defect, diagrams of the amplitude-phase distribution of PD (APDPD), the average value of the apparent discharge, and the PD intensity are obtained. The results of the study show that most of the defects of insulators of overhead power lines have a relatively high intensity of partial discharges with a small average apparent charge. In the samples of cable lines, relatively high values of intensity and average apparent discharge are recorded in the presence of a defect in the end seal and a defect in the ground electrode in the form of a needle. The results obtained can be used in the development of devices for detecting defects, as well as for expanding the base of diagrams (APDPD)

Small size phase shifter on compact structures

This article is devoted to the description of a miniature phase shifter of the reflective type. Its dimensions were reduced with the help of compact structures – they were replaced by structures, both quarter-wave segments and plug-in plumes allowing changing the phase at the output. Phase shifters are used in phased array antennas to change the phase on the emitters and thus change the amplitude-phase distribution, which leads to a change in the radiation pattern. For a large number of emitters, a large number of phase shifters are required, which is why at low frequencies they can occupy a sufficiently large area. For this reason, it is possible to use compact structures that have identical characteristics with transmission lines in a certain frequency band. Such replacement allows saving the occupied area of the power supply circuit of the antenna array (material saving), but at the same time reduces the permissible power. The design of a phase shifter with a Central frequency of 2 GHz, whose area was reduced by 63% in relation to the typical implementation of the design, was investigated.

Investigation of characteristics of waveguide channels system formed in PDLC with inhomogeneity of the amplitude-phase distribution of forming field

This work presents the results of modeling the influence of amplitude, phase and amplitude-phase heterogeneities of the forming field on the spatial distribution of the refractive index profile and, accordingly, the mode composition of radiation capable of propagating in waveguides formed by the holographic method in the photopolymer-liquid crystalline compositions. The spatial distribution of the refractive index is found by solving the system of kinetic equations. The mode composition of the radiation is determined by solving the dispersion equation for TE-modes.

Binary multi-order diffraction optical elements with variable fill factor for the formation and detection of optical vortices of arbitrary order.

In this paper we consider the calculation of binary diffraction optical elements (DOEs) for the formation and detection of optical vortices of arbitrary order. The synthesis of binary DOEs is based on a combination of the method of carrier spatial frequencies and binary coding with a variable fill factor. Unlike various methods of multiplication, the method of carrier spatial frequencies is characterized by great flexibility and versatility. It allows us to not only form the given field distributions in arbitrary diffraction orders, but also to give them arbitrary weight ratio (energy distribution in orders). As a rule, such universality leads to the need to form a complex amplitude-phase distribution in the input plane. To avoid this, in this paper it is proposed to use binary coding with a variable level. The effect of such coding is studied in detail both theoretically and numerically. It is shown that the level variation makes it possible to change the set of the observed diffraction orders. The positions and orders of the optical vortices formed are uniquely determined by the values of the carrying spatial frequencies and the topological charges of the vortices in the basic order. The results can be useful in optical communications.

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.

Synthesis of Controlled Zeros in the Radiation Pattern of a Plane Phased Array Antenna Using Partial Patterns

A method for synthesis of controlled zeros in the radiation pattern along the jamming direction is proposed for a plane phased array antenna. To solve the problem, it is suffice to calculate the amplitude–phase distribution for only one row (column) of antenna elements located on the array at the mesh points of rectangular or hexagonal cells.

Hyperspectral Holography of the Demodex Mite in the Near Infrared Range

The possibility of analyzing the structure and the developmental stage of small parasites as exemplified by Demodex mites is considered. The analysis is based on the method of hyperspectral holography in the near infrared region. It is shown that the optical density of the mite structure can be registered in the wavelength range ≥0.7 μm. The amplitude–phase distribution of the structure in the short wavelength spectral region is obtained. Registration of the amplitude–phase information in the shorter wavelength range is complicated by the diffuse structure of the integument, which leads to image speckling.

Амплитудно-фазовое распределение для формирования частотно-независимых диаграмм направленности линейных антенных решеток.

Амплитудно-фазовое распределение для формирования частотно-независимых диаграмм направленности линейных антенных решеток.

PATTERN ANALYSIS OF THE RECEIVING-TRANSMITTING CIRCULAR ARRAY WITH LOW SIDE LOBE LEVEL

Context. A particular advantage of uniform circular arrays is the possibility of scanning the beam within 360° in azimuth withoutdistorting the characteristics of the directivity pattern only by changing the amplitude-phase distribution of the current on its elements.This feature, combined with modern beamforming techniques and digital methods of beamforming opens the prospect of usingcircular arrays in surveillance radars for military and civil purposes instead of antenna systems with mechanical rotation.Objective. Investigation of the possibility of reducing the sidelobe level of a uniform circular transmit-receive array using known amplitude distributions used for linear arrays.Methods. For the study, a phase-mode excitation technique is used in which an arbitrary excitation function of a uniform circular array is represented as a sum of phase excitation components (modes), and the circular array antenna pattern is a superposition of patterns produced by individual phase excitation modes. This technique makes it possible to apply for circular arrays the methods used to pattern synthesis and reduce the side lobe level in linear arrays due to the use of a special transformation matrix.Results. An imitation mathematical model of a discrete uniform circular array has been developed that provides an opportunity to study the efficiency of using amplitude distributions, known for linear arrays, to reduce its side lobe level.Conclusions. The computational experiments have confirmed the possibility of using the phase-mode excitation technique for a pattern synthesis with low sidelobe level in the uniform circular transmits-receive array. A variant of the practical application of the Dolph-Chebyshev amplitude distribution for the synthesis of a circular array pattern is shown.

Fault-tolerant active phased array antenna with neural network

A model and architecture for an active phased array antenna with a neural network control unit has been developed, which provides correction of the amplitude-phase distribution depending on the quality of work of individual array modules. The possibility of adapting the system to failures of individual modules is shown.

Evaluating Cramer-Rao Bound for Conformal Antenna Arrays with Directional Emitters for Doa-Estimation

Introduction. The direction-of-arrival estimation of signal sources is of serious research interest in various fields. As an example, the coordinate information in three-dimensional space can be used for spatial diversity and filtering to increase concurrent users. The influence of the directivity coefficient of a separate antenna element on the accuracy of determining the angular coordinates of radio sources of circular, cubic and spherical antenna arrays consisting of directional radiating elements that have found the widest application in modern wireless communication technologies is investigated. Theoretical results. For the correct functioning of advanced radio direction-finding algorithms along with the antenna arrays under consideration the accurate expressions describing the amplitude-phase distribution of the electromagnetic field of the arrays have been derived, so-called steering vectors. The Cramer-Rao lower bound for estimating errors and accuracy of direction-of-arrival estimation is discussed for a number planar waves arriving on an antenna array consisting of directional elements. Experimental results. A theoretical study of the operation of these antenna arrays using the Cramer-Rao lower bound was carried out, as well as computer simulations with the implementation of the MUSIC superresolution method. The influence of the directivity factor of the individual antenna element on the accuracy of the direction-of-arrival estimation of the radio emission sources by using the circular (cylindrical), cubic and spherical antenna arrays consisting of the directional antenna elements was investigated. The limits of the change of the coefficient of directional action of a separate element, at which the maximum accuracy of an estimation of angular coordinates is achieved, is determined. It is shown that further increasing the directivity factor of each antenna element makes the mean square error in the determination of the coordinates of the signals increase as well. The estimation of the resolution of conformal antenna arrays is carried out depending on the directional factor of each antenna coefficient. It is found that the best configuration is spherical. Conclusions. Thus, a comprehensive statistical analysis of radio direction finding with the azimuth and elevation for the conformal antennas depending on the directivity of the antenna elements constituting them was implemented. With an increase in the gain of individual antennas, the accuracy of direction finding can vary significantly depending on the azimuthal position of the signal and an acceptable choice of directional coefficient is four to six.

Focused antennas for diagnostics of spacecraft antenna systems

The use of a focused radiating system principle opens up additional possibilities for solving a number of technological problems in the development and testing of spacecraft antenna systems. This paper presents the basic properties of antennas focused in the near radiated-field zone and the indicated applications. The paper deals with the tasks of diagnostics of the amplitude-phase distributions of antennas, materials of space antenna construction, cable lines.

Calibration of Phase Shifters on Basis of Vector-Sum Signals

Attenuators and phase shifters which are the circuits for amplitude-phase distribution control are key elements of antenna arrays. Dispersion of technology parameters results in deviation of the characteristics of integral circuits from rated values that requires application of the techniques for this effect compensation. In this paper there are considered the methods for development and calibration of the circuits in a basis of vector-sum signals allowing to modify both amplitude and phase of input high-frequency signal. It is proposed the method of calibration on a basis of interpolation of measured dependences of absolute value and phase of transfer factor on controlling voltage. Application of proposed method for calibration of vector phase shifter with operating frequency band 2.8–3.2 GHz fabricated with 0.18 mm CMOS allows to provide mean square deviation of phase error is not greater than 0.9°. At that amount of required measurements is 20 times decreased comparing known approach on a basis of measurement of all amplitude-phase states.

ВОССТАНОВЛЕНИЕ КОГЕРЕНТНЫХ ИЗОБРАЖЕНИЙ ПОВЕРХНОСТЕЙ В ЗОНЕ ФРЕНЕЛЯ МЕТОДАМИ МНОГОКАНАЛЬНОЙ ОБРАБОТКИ СИГНАЛОВ

The generalized structure of the electromagnetic field in the registration area is considered in the case of the solution of problems of remote sensing of the underlying surfaces. Examples of the existing radar and optical coherent devices are given. Analytical expressions for the electromagnetic field in the reception area when sounding is carried out in a near-field Fresnel region, in the assumption that the size of the field of registration and radiation is considerably less than a distance between them, are concretized. It is shown the main operations that are necessary for the recovery of coherent images in a near-field Fresnel region by the methods of multichannel signal processing. Research shows that as the amplitude-phase distribution of the registration field is necessary to choose the classical basic function of Fresnel transformation with the reversed sign in the exponent power. Formally, in an infinite range, the Fresnel transform is invertible, i.e. in the ideal case, the function can be completely restored. However physically to Fresnel's region satisfies area with finite sizes. From the analysis of the obtained operations over the received field, it follows that the radar or optical system forms an estimate of the coherent image in the form of a convolution of a true image of the underlying surface with an ambiguity function. Generally, this function contains two multipliers, one of which determines the resolution of recovery of the coherent image. In that specific case, when the linear sizes of the field of registration go to infinity, ambiguity function takes a form of delta function and the required image can be restored without distortions. It is offered to determine resolution by the width between first zeros of ambiguity function. For rectangular area ambiguity function has the form of two sinc functions which width is directly proportional to wavelength, to the height of sounding and is inversely proportional to the linear sizes of receiving area on the corresponding coordinates. Finally, it is mentioned that for the higher-quality coherent imaging with good resolution by the same receiving area it is necessary to perform scanning and movement in space

Correction of amplitude-phase field distribution at aperture of deformed large-aperture fixed phased array

On the basis of an analytical review of scientific and technical information sources dedicated to correction of errors in the gainphase distribution of the field on the aperture of the phased antenna array, such errors been caused by correlation of errors in phase quantization by discrete phase shifters, and also caused by disbursement of their characteristics and by failures in a part of the phased antenna array elements, an unresolved problem has been discovered. It is required to correct the amplitudephase distribution errors caused by deformation of the curtain of the large-aperture stationary phased antenna array and resulting in deviation of the radiating elements from their design parameters. A mathematical apparatus of the field distribution electronic correction is being developed together with an algorithm for controlling the radiation pattern of the phased antenna array. The effectiveness of the proposed method for correcting the array pattern distribution on the aperture of the deformed phased antenna array has been evaluated and an option for technical implementation thereof has been proposed.The relevance and novelty of the work is confirmed by the patent for the invention developed on the basis of the studies performed and by the certificate of state registration of the software, which was based upon in the processing of results of the measurements of the deformations in the curtain of the large-aperture phased antenna array.

APPLICATION OF STATISTICAL METHODS TO ASSESS THE METROLOGICAL CHARACTERISTICS OF RADIO-HOLOGRAPHIC MEASURING COMPLEXES

Practical application of the radio-holographic method for measuring the characteristics of antennas, especially when conducting acceptance testing of systems, requires an adequate assessment of the errors in the recovery of long-range characteristics. These errors appear to be a superposition composed of various sources, having different nature, different time characteristics and different degrees of influence on the final result. The purpose of this work was the development of a practical technique for determining the influence of random errors in measuring the amplitude-phase distribution of the field of the antenna required for the accuracy of restoring long-range characteristics (primarily the antenna pattern) of the antenna, the proposed technique being based only on processing the experimental results obtained with this measuring complex.A practical method for determining the influence of random errors in measuring the amplitude-phase distribution of the field of the antenna under study on the accuracy of restoring its long-range characteristics (primarily the directional pattern) on the basis of correlation and spectral analysis has been developed and experimentally confirmed. The main advantage of the developed method in comparison with the use of mathematical modeling is that the estimation of the accuracy of the reconstruction of the directivity diagrams is based on the results of processing experimental data obtained on a specific measuring complex and does not a priori impose any preliminary requirements on the statistical parameters of errors. The developed procedure for estimating the influence of random errors can be used to develop a methodology for metrological certification of measuring systems as measuring instruments.

On Calculation of the Amplitude–Phase Distribution of the Field Radiated from an Open End of a Rectangular Dielectric Waveguide

The problem of calculating the amplitude–phase distribution of the field radiated from an open end of a rectangular dielectric waveguide expanding along one of its sides (a plane dielectric horn) is considered. The problem of diffraction on the junction of a feed dielectric waveguide and the horn is solved by the domain decomposition method using a model in the form of a screened dielectric waveguide. The amplitude–phase distributions over the distance from the end of the radiator are studied. The possibility of using the screened model for solving the problem of radiation from the open end of a dielectric horn is shown.

Correction of the Measured Amplitude-Phase Field Distribution in the Near Field from the Directional Pattern of the Probe

A new method of correcting the amplitude-phase field distribution in the near field is proposed. The correction is made in accordance with the probe’s directional pattern. Unlike existing methods of correcting the restored directional pattern of the antenna under study in accordance with the probe directional pattern, this method can be applied to any scanning surface. It does not require numerical solution of integral expressions for each point. The effectiveness of the proposed method is shown using the example of the recovery of the directional patterns of horn and mirror antennas using a planar scanner.

Method of the Amplitude–Phase Synthesis of a Pareto-Optimal Planar Antenna Array

A method of the amplitude–phase multicriteria synthesis of a Pareto-optimal antenna array is proposed. The method is based on representation of the initial antenna array synthesis problem in the form of successively solved partial problems (subproblems) with small dimensionality. Each subproblem is reduced to determination of Pareto-optimal parameters of the amplitude–phase distribution of an additional beam added to the initial radiation pattern.