ENERGY CHARACTERISTICS OF A RECTANGULAR WAVEGUIDE T-JUNCTION INTERACTING WITH A MULTIELEMENT VIBRATOR-SLOT COUPLING STRUCTURE
S. L. Berdnik, V. A. Katrich, V. I. Kiyko, M. V. Nesterenko, Yu. M. Penkin
The study of peculiarity of influence of the impedance insertions on the electrodynamic characteristics of the rectangular waveguide junctions, which are widely used in the antenna-waveguide devices, is important for practical applications. A mathe-matical model for E-plane T-junction of rectangular waveguides with a three-element vibrator-slot coupling structure was built using approximate analytical solutions of equations for induced currents by a generalized method of electro-magneto-motive forces. The distinctive feature of the model is the usage of variable surface impedance along the monopole axes and constant impedance, distributed over the end wall of the lateral semi-infinite waveguide. Multiparameter energy characteristics of the junction in the single-mode waveguides are presented including the case of meta-material coating the end wall of the lateral waveguide. The possibility of efficient use of impedance coatings as control element for power division between the output waveguide junction arms is shown.
REFLECTION RESONANCES IN A RECTANGULAR WAVEGUIDE SECTION WITH A PAIR OF ANTIPODAL RECTANGULAR POSTS
L. P. Mospan, S. A. Prikolotin, А. А. Кirilenko
Intentional and controllable introduction of attenuation poles into the frequency responses of frequency-selective devices is in the great demand in the design of modern filters with complicated performance. Successful implementation of such an approach is possible using rectangular waveguide sections with metallic inserts. Here, the scattering characteristics of such sections with a pair of antipodal rectangular posts as waveguide units with rotational symmetry are studied. Comparative analysis with the characteristics of a section with a pair of unidirectional posts is performed. Spectral theory of open waveguide resonators is used in order to interpret the resonant phenomena. Within the frames of spectral theory the reflection resonances formed by such sections are the responses to the excitation of eigen oscillations of complex frequencies. It is shown that the spectral theory enables an order of magnitude more accurate (in comparison with the conventional modal analysis) evaluation for basic parameters of the resonance reflection, namely its frequency and the quality factor. The results obtained make preliminary synthesis of frequency selective devices based on such sections physically transparent and more accurate.
RADAR ELEVATION ANGLES MEASUREMENTS OF LOW-ALTITUDE TARGETS OVER THE SEA BY ROOT-MUSIC METHOD UNDER INTERFERENCE FROM MULTIPATH AND THERMAL NOISE ОF DIRECTION FINDER
Yu. A. Pedenko
The work is devoted to improvement of the accuracy of radar measurements of elevation angles of low-altitude targets above sea level when using the root-MUSIC, which is considered by experts as one of the means to solve this problem. Unlike previous studies, which take into account the multipath only, in this study the clutter is complicated by thermal noise of radar. This allows to evaluate the capabilities of the method and provide guidance on its application in the conditions close to reality. The study was carried out by computer simulation. It covered various sea states at which the conditions from specula to strong diffuse reflection were complied. In the simulation a wide range of signal/noise ratio was used. The main focus was the study of effects on measurement errors of a priori parameters of the method: the signal subspace dimension and the order of autocorrelation matrix of signals received by a multi-element antenna array. The recommendations of their choice, allowing to minimize the errors of elevation measurement in different conditions, have been developed. The results of the study extend the knowledge of how to improve the methods for measuring the target elevation angle above the sea.
RESEARCH ON THE UNDERLYING SURFACE BY RADIATION OF GLOBAL NAVIGATION SATELLITE SYSTEM
V. I. Lutsenko, D. O. Popov, I. V. Lutsenko
The investigation of the scattering signals features on the land surface can be used to study the physics of scattering processes, as well as for the establishment of multipath compensation methods for reducing positioning errors in global navigation satellite systems. The possibility of detecting the reflection areas on the underlying surface and estimating their parameters by using radiation of global navigation satellite systems is shown. The behavior of the signal levels for different satellites in urban areas is analyzed. The influence of the reflection area’s characteristics on the spectrum of the received radiations is considered; the method of determining their location is proposed.
RADIANT SYSTEM BASED ON COLD PLASMA
V. V. Ovsyanikov
The actual problem of studying the basic properties and searching for methods of improving the plasma radiator array, which is similar to the array of metal or dielectric antennas, has been considered. This problem is not sufficiently covered in the well-known publications, however, the great interest of professionals to emitters based on cold plasma is due to the prospect of creating effective multi-beam scanning selective plasma reconfigurable systems or the plasma array of radiators (PAR). The article studies the main electrodynamics parameters of PAR in the microwave range, characterizing it on the one hand, as the load for the generator (receiver) of electromagnetic (EM) signal. On the other hand, PAR is tested as transmitter of EM energy from the point of view of its direction pattern (DP) and the main parameters of radiation of PAR. When scanning DP beam, impedance distortion of PAR transmitters and DP deformation are investigated. For comparison, similar studies were carried out for the same design and configuration of the pattern antenna (PA) of metal antennas. The studies have been carried out by PAR modeling and their parameters calculations on computer in software environment FEKO by integral equation method and method of moments for linear PAR from 4 emitters in the form of loop dielectric tubes filled with cold plasma under reduced pressure. When studying the self and mutual impedances of the PAR and metal PA in common mode for the distance between the transmitters 0.5λ0, where λ0 is the central wavelength of the test range, it has been determined that electromagnetic interference between antennas in PAR is less than in the metal antenna array, and when reducing the distance between transmitters grating with 0.5λ0 – 0.25λ0 the relative change in value of units of the input impedance of each radiator of PAR is twice less than for a lattice of aluminum, which allows to bring together the radiator of PAR without a substantial increase in interference between them. From comparison of DP of radiant systems of PAR and aluminum arrays while scanning, it is obvious that DP of PAR are less distorted than aluminum array. The obtained results can be used for calculations and design of plasma array of radiators.
PLASMA-BEAM SUPERHETERODYNE FREE ELECTRON LASER WITH H-UBITRON PUMP WITH NON-AXIAL INJECTION OF ELECTRON BEAM
A. V. Lysenko, G. A. Oleksiienko
A cubic-nonlinear theory of a plasma-beam superheterodyne free electron laser (PBSFEL) with H-ubitron pump and non-axial injection of electron beam has been constructed. In the investigated system the parametric resonance interaction between a space-charge wave and cyclotron wave is realized. The signal wave saturation levels have been determined. It has been found that the mode using a slow cyclotron wave has the highest saturation level among all possible operation modes of the PBSFEL with H-ubitron pump. The injection angle of the beam at which the electromagnetic signal gain is maximal has been determined. It has been shown that PBSFELs using slow cyclotron waves are able to create a powerful coherent electromagnetic radiation in the millimeter wavelength range.
P. P. Maksymov
Construction of powerful sources of electromagnetic oscillations of microwave range is an actual task for creating modern semiconductor devices. In this paper the creation of powerful sources of electromagnetic oscillations based on reverse-biased abrupt p–n-junctions of avalanche-generator diodes (AGD) with external signal has been theoretically grounded. Classification of modes of avalanche-generator diodes has been carried out. The choice of oscillations generation mode is determined by the parameters of AGD and input signal. It is shown that coherent, multifrequency and broadband oscillations are generated in AGD. Power and spectral descriptions of oscillations of AGD are presented. The research results are of interest for the developers of powerful diode generators with the required range, power and spectral characteristics.
THREE-CHANNEL PHASE METERS BASED ON THE AD8302 AND FIELD PROGRAMMABLE GATE ARRAYS FOR HETERODYNE MILLIMETER WAVE INTERFEROMETER
A. V. Varavin, G. P. Ermak, A. S. Vasilev, A. S. Fateev, N. Varavin, F. Zacek, J. Zajac
The paper presents the results of research and development of two types of phase meters for heterodyne two-wave “unambiguous” interferometer designed to measure the plasma density in tokamak COMPASS. The aim of this work is the creation of a phase meter capable of measuring fast phase changes of each probing wave, and their phase difference. Plasma is probed by two microwave signals with different wavelengths propagating along identical paths to meet each other. Each analyzed signal acquires a certain phase shift φ1 and φ2, and the “unambiguous” interferometer determines the difference (φ1–φ2). The phase measurement is carried out by using three-channel phase meters: a phase meter based on the pairs of the AD8302 and a phase meter based on field programmable gate arrays (FPGA). The proposed circuit decisions and algorithms of signal processing allow to measure phases in the range 0…360° in real time.
Z. А. Maizelis
For detecting and establishing the nature of frequency noises in the oscillating system, it is very important to separate different types of noises. For determination of characteristics of the frequency noise it is necessary to study statistical properties not of actual coordinate and its derivative, but of complex coordinate of oscillator. Its moments do not depend on the amplitude noises that often can prevail in the system. The growing interest in noises of frequency is related to the fact that they determine the loss of coherence of vibrations in many systems, from the devices based on Josephson contacts, to the nanomechanical resonators. The knowledge of statistical characteristics of frequency noises inevitably present in the devices of information read-out in quantum computers will allow correct processing of the information in them. Here the influence of the telegraph unbalanced noise of frequency on properties of electromechanical resonator is studied. It is shown that the dependencies of the higher cumulants contain features, which allow to separate the effects related to the presence of noise of frequency. The results may be useful in the theory of nanomechanical resonators, in processing the data, obtained in the radio-technical devices and devices, based on Josephson contacts, in quantum computers, in the estimation of precision of atomic clock.
RECONSTRUCTION OF IMAGES WITH LARGE NON-UNIFORM INCREMENTS
S. I. Melnyk, S. S. Melnyk
In recent years, the range of tasks related to the study of structures image elements of which are beyond the resolution of matrix type sensors is becoming wider. Thus, the problem of their reconstruction by applying algorithmic and information image processing techniques is relevant. The problems emerging when observing objects whose dimensions do not exceed several pixels of matrix of recorders have been considered. It is shown that motion of the object relative to the matrix and the use of multiple consecutive frames allow to improve the fidelity of shape and true size of the object. This measurement information can be represented as integrals along the trajectories on a three-dimensional lattice of space-time pixels. The reconstruction of a heterogeneity function of pixels through the use of the controlled motion of the test object and methods of computer tomography. The possibility of determining the relative velocity of the object in each of the frames using the blind method has been shown. The algorithm of reconstructing images with large non-uniform increment during their arbitrary and controlled relative motion has been elaborated.
V. P. Ruban
The estimation of synchronization instability becomes actual in GPR due to the fact that this phenomenon affects the accuracy of recording and reproducing the received signal forms and, accordingly, the efficiency of use of digital signal processing algorithms. The existing method for estimation of jitter of the GPR receiver using errors of the converted signal amplitude is not universal and should be corrected for the case of converter with incomplete charging of the storage capacitor. Simulation of the stroboscopic conversion with instability of sampling interval for cases of full charging (when the evaluation method gives correct results) and incomplete charging of the storage capacitor has been done in this paper. The relationship between the forms of probabilistic distribution of jitter and errors of amplitude after stroboscopic conversion has been analyzed. The jitter values originally specified in the simulation and the ones calculated (reconstructed) by a known method also have been analyzed. According to the simulation results, the limits of applicability of this method were determined. It is shown that the direct application of the jitter evaluation method which is right for the converter with a full charging gives incorrect estimates for the one with incomplete charging of storage capacitor. Due to this, the signal amplitude recovery procedure which allows obtaining a correct estimate of the jitter of synchronization of GPR receivers operating in the mode of incomplete charge storage capacitor has been suggested.