Radio physics and electronics

3-15

Authors: N.P. Yeliseyeva, S.L. Berdnik, V.A. Katrich

Subject and Purpose. A resonant monopole of an electrical length 0.2 £ l / l £ 0.3 mounted on an infinite, perfectly conducting plane or on a rectangular, perfectly conducting screen is considered. The objective is to determine how the radiation resistance, surface impedance, and input impedance depend on the length and thickness of the resonant monopole and how the screen size affects the resonant characteristics and directive gain of the impedance monopole. Methods and methodology. A three-dimensional vector problem of the field diffraction of an impedance monopole mounted on a perfectly conducting rectangular screen is solved using the method of uniform geometrical theory of diffraction and adopting asymptotic expressions of the diffracted fields and electric currents of a thin impedance dipole located in the free space. Results. Taking into account diffraction effects at the edges of the square screen, the resonant values of the surface impedance of the monopoles and the corresponding radiation resistance and directive gain have been calculated subject to the condition that the electric field amplitude is at its maximum. It has been found that as the screen size exceeds the two wavelengths, the edge phenomena have little effect on the monopole resonant characteristics. The radiation resistance reaches its maximum when the side of the square screen is as long as L / l = 0.9…0.95. The first maximum of the directive gain occurs at L / l = 1.2…1.3. The obtained results have been verified with the aid of the computational electromagnetics software FEKO. Conclusion. A three-dimensional vector diffraction problem has been solved for an impedance monopole mounted on an ideally conducting, rectangular screen. Algorithms and computational programs have been developed to determine resonant characteristics and radiation patterns of the radiating system. By choosing an optimum screen size it is possible to increase the directive gain of an impedance monopole of the length l = 0,2l by 24% and the radiation resistance by 38% compared to the infinite screen.

26-33

Authors: A.S. Bryukhovetski, A.V. Vichkan’

Subject and Purpose. The wave field produced by a spatial-temporal distribution of sound sources in a uniform subsonic flow is theoretically studied in an effort to obtain an analytical dependence of the sound field on physical parameters. Method and Methodology. Cauchy problem for wave equation in a moving medium is solved using a spatial-waveguide Fourier expansion of the sound field. A Fourier representation of the Green's function of a point-like pulse sound source is constructed whose inverse transform allows us to obtain the Green's function spatial-temporary representation. Results. With the Green’s function obtained, the wave fields from arbitrarily shaped sources have been represented in the “wave potential” form, which is a convolution type integral of the density of spatial-temporal distribution of the sound sources and the Green’s function. Conclusion. The calculation results give a clear idea of the propagation of sound waves excited by a point-like pulse source in a uniform homogeneous flow. The wave front of the sound field represents a sphere whose center “drifts” from the source at a speed equal to the speed of the flow in its movement direction, and the radius of the sphere grows in the course of time at a speed equal to the speed of sound. The obtained Green’s function allows for the analytic continuation to the supersonic flow case that, in contrast to the subsonic case, satisfies the causality principle not in all unlimited space but only at the observation points within the Mach cone. The wave field from a monochromatic source is the limiting case of the rectangular pulse solution.

42-53

Authors: V. N. Derkach, E. A. Alekseev, R. V. Golovashchenko, Ye. M. Ostryzhnyi, A. A. Meshcheryakov, S. I. Tarapov

Subject and Purpose. The subject of the study is spectral and energy characteristics of whispering-gallery disk resonators made up of low-loss microwave dielectric and semiconductor materials, namely, gold-doped silicon Si:Au, Chemical Vapor Deposition (CVD) diamond, Arc Plasma Jet (APJ) diamond, and alumina ceramics Al2O3. On the basis of the temperature dependences of the microwave energy loss in the materials mentioned, we seek to classify the loss contributions among the electromagnetic energy absorption mechanisms and find physical parameters responsible for these mechanisms. Methods and Methodology. The loss values were experimentally obtained by the whispering-gallery disk resonator technique with the usage of a cryodielectrometer. A phenomenological simulation was performed to classify the loss contributions to the temperature dependence of electromagnetic energy absorption among the major loss mechanisms in the examined materials. Results. The experimental study results on the dielectric loss temperature dependence within 4.2...300 K have been presented and discussed for low-loss semiconductor and dielectric materials, including gold-doped silicon Si:Au, CVD-diamond, APJ-diamond, and alumina ceramics Al2O3 with reference to the frequency band 110...140 GHz. Certain design features have been suggested to use in the authors’ software-controlled measuring unit to provide the interchangeability of backward wave tubes (BWT) inside the cryodielectrometer and extend the merasuring bandwidth up to 34...144 GHz. The unit offers software-controlled frequency tuning with a spectral resolution of about 0.1 MHz. The loss contributions have been classified among the major loss mechanisms, and physical constitutive parameters responsible for these mechanisms have been determined. Conclusion. The temperature dependences of dielectric loss in low-absorption materials have been registered and analysed. The developed measuring unit has advantageous design features and provides, in addition, an independent controllable radiation source which can be included in a frequency synthesis system with phase-locked loop.

60-67

Authors: Yu.V. Kornienko, I. Liashenko, V.V. Pugach, S.I. Skuratovskiy

Subject and Purpose. The influence of Earth’s atmosphere leads to significant distortion of object images obtained with Earth-based instruments. In this case, the distortion of the Fourier component phase plays a far more important role than the module distortion. The influence of Earth’s atmosphere on the Fourier component phase may be considered as a multiplicative noise in the frequency domain. For combatting this influence, we propose signal accumulation, implying that total phases rather than their main values, which are available for the direct measurements by experiment, should be accumulated. The features of the proposed total phase accumulation method are studied in the present paper. Methods and Methodology. The current studies depend on computer experiment and theoretical analysis of the obtained results. The performance efficiency of the total phase accumulation method is evaluated with the aid of the computer system of astronomical image modeling and processing developed in the O.Ya. Usikov IRE of NASU. Results. A relationship has been obtained between the error of image reconstruction by the total phase accumulation method and the number of the accumulated images in different observation conditions. The dependence has a non-monotonic behavior, which remains to be investigated. Conclusion. That the reconstruction error dependence in the total phase accumulation method has a minimum is important for the practical method application as there comes an accumulation point after which the reconstruction accuracy degrades. The location of that minimum depends on the atmospheric parameters, sending us in search of a criterion for choosing an optimal sequence length of image accumulation.

78-88

Authors: A.D. Yegorov, S.A. Yegorov, V.A. Yegorov, I.E. Sinelnikov

Subject and Purpose. The subject of the work is atomic emission spectral analysis of substances using the most affordable arc and spark sources widely accepted in both laboratory and industrial practice. The aim is to improve solution principles of some technical problems in the field of construction of power supplies of arc and spark discharges with predetermined properties and to study their parameters. Methods and Methodology. Traditional methods of producing spark and arc discharges are used. Several designs are proposed for discharge current and discharge gap breakdown power supplies, modeled using a computer program of circuit simulation and tested on the existing prototypes. The developed generator was put through tests and compared with a production analog of it in terms of statistical analysis of spectrum measurement results. Results. The microprocessor-controlled arc plasma generator "TsUG-2" has been developed and performed. The discharge current generation unit was constructed on the principle of digital-to-analog converter (DAC) with current summation. The discharge gap breakdown unit was performed on the semiconductor circuitry basis without any gas spark gaps. A unit was added for generating the initial pulse of discharge current, which made it possible to extend the spectrum excitation range, provide the sampling process control and improve the discharge combustion stability. A parameter control unit was developed to create and maintain the protective gas environment in the discharge chamber. The control over the operating modes of the generator and its synchronization with the spectrum recording equipment is exerted through an external interface. The manual control is carried out via a stand-alone control panel. The created generator "TsUG-2" produces discharge gap breakdown pulses of up to 12 kV amplitudes and arc pulses spanning a discharge current range as wide as 1...47 A. On them, additional current pulses of up to 150 A amplitudes can be superimposed, which significantly increases the rate of discharge current rise. The highest frequency of the discharge excitation pulses is 800 Hz. Comparison tests of the developed generator "TsUG-2" and a production generator "UGE-4" have been carried out. Conclusion. The measurement results show that the standard deviation (RMS) of the photometric data of plasma formations obtained from the developed arc plasma generator "TsUG-2" is, on the average, three times less than from a production generator "UGE-4.