AXIALLY-SYMMETRIC ELECTROMAGNETIC EXCITATION OF METALLIC DISCCONICAL SCATTERER
D. B. Kuryliak, O. M. Sharabura
The finite bi-cone is the basic structure for disc-conical antennas analysis by the approximation techniques. Here the rigorous solution of the problem of axially-symmetric TM-wave diffraction by the open end of the bi-cone, which consists of finite and semi-infinite shoulders, is obtained. The structure is irradiated by the ring of the magnetic current. The mode matching method and analytical regularization technique are applied to obtain the problem solution. The transition from bi-conical scatterer with arbitrary angular parameters to the disc-cone antenna is analyzed. The dependences of the far-field pattern and the radiation resistance from the scatterer parameters are investigated. Comparisons of the numerical results with known particular cases are carried out. It is shown that the wide-band properties of the disc-cone antenna are improving with increasing of the disc radius and the width of the bi-conical region. The obtained results allow to carry out the rigorous analysis of the electrodynamics characteristics of disc-conical scatterers for a wide range of geometrical and frequency parameters.
INVESTIGATION OF COMBINED GRATINGS PROPERTIES IN DIFFRACTION RADIATION ANTENNAS
A. V. Hnatovskyi, S. A. Provalov
Research and development of diffraction radiation antennas is one of the promising areas of antenna technology in the millimeter-wave and submillimeter-wave regions. For the introduction of this class of antennas in the creation of devices and systems for various applications it is necessary to develop new techniques for formation of radiation pattern. This study is aimed at experimental validation of proposed method for obtaining special shape radiation pattern by combining the properties of direct and inclined combs. A comparison of radiation characteristics of straight and inclined gratings was made. The choice of inclined comb parameters was substantiated. The measured radiation pattern of antenna with combined comb confirm the correctness of the chosen approach. The obtained results are an essential complement to the known properties of antennas and justify their applicability in different complexes of surface overview.
ON THE POSSIBILITY OF THE ATMOSPHERE CONDITION DIAGNOSTIC WITH THE MULTIBEAM INTERFEROMETER
Y. Kornienko, V. Pugach, S. Skuratovskyi
The influence of the atmosphere on the results of astronomical observations from the Earth’s surface dramatically decreases the resolution of obtained images. Many methods of fight against it require the information on atmospheric distortions. Obtaining of such information in practical case is usually carried out by using special wave-front detectors that operate on the basis of the natural or laser reference star. But there is the method that allows obtaining information on phase distortions in the atmosphere directly during the process of the observation of any object with the multibeam interferometer. Averaged over subapertures phases are the side result of image forming with such instrument. By their interpolation the phase distortions distribution over the aperture may be recovered. It was shown that the reconstruction accuracy is acceptable while atmospheric inhomogeneities exceed the distance between subapertures. The dependences of reconstruction accuracy on peculiar inhomogeneities size and mean square deviation of phase distortions are presented. The research results may be useful for atmospheric researches, as well as for fight against its influence, for example, first order adaptive correction.
SPECTRA AND WAVEFORMS OF ELF PULSES IN THE EARTH-IONOSPHERE CAVITY WITH SMALL LOSSES
A. P. Nickolaenko
There is a certain gap in the literature on Schumann resonance. The theoretical prediction of the phenomenon was made in the framework of the Earth–ionosphere cavity formed by perfectly conducting walls. However, when modeling the experimentally observed resonance, the ground is always considered as a perfectly conducting, while the ionosphere has a finite conductivity. The present investigation fills in the gap mentioned. We demonstrate for the first time the spectra and the waveforms of pulses propagating in a cavity with the negligible losses. The problem is solved in the framework of the exponential vertical profile of air conductivity characterized by the single scale height. The spectra and waveforms are computed for a set of the source–observer distances. Deviations are addressed of the spectra in the idealistic resonator from those of the conventional ionosphere model. Direct time domain solutions are used in computations that show deviations of the propagation velocity relevant to finite conductivity of the ionosphere. The pulse amplitudes are shown at the source antipode and at the source point itself for the round-the-world wave. We demonstrate widening of the pulses in the course of propagation combined with the reduction of their amplitude. Amplitude of the round-the-world wave reduces to the value that excludes the “auto-triggering” of lightning strokes even in the idealistic cavity model with negligible losses.
DEDUCING THE WORLD THUNDERSTORM ACTIVITY FROM THE SCHUMANN RESONANCE RECORD (ONCE AGAIN ABOUT POINT SOURCE MODEL IN SCHUMANN RESONANCE STUDIES)
A. P. Nickolaenko
Application of the records of global electromagnetic (Schumann) resonance in the Earth–ionosphere cavity attracts the permanent attention, as it allows the assessment of the global characteristics of the lower ionosphere and the dynamics of planetary thunderstorms by using a single or a small number of observatories. Solutions of the inverse problem are based on different approaches. We use a simple model of a point source in the present study. The vertical profile of the atmosphere conductivity is described by the “knee” model. The source–observer distance and its variations were evaluated from the first Schumann resonance peak frequency observed in the horizontal components of the magnetic field, since this frequency is proportional to the distance from the source. After estimating the source range, one can obtain the seasonal changes in their intensity by using the observed energy of oscillations. We process a fragment of the records at the Ukrainian Antarctic station “Academician Vernadsky”. We show that the seasonal latitudinal drift of global thunderstorms is estimated by 20°, and annual changes in the level of global lightning activity reach the factor of 1.5. The unequal duration of the “electromagnetic seasons” is confirmed: the summer (the farthest northern position of global thunderstorms) lasts for 120 days, while the winter is about 60 days. The duration of spring is shorter than that of the fall. The estimates obtained reasonably agree with the Schumann resonance data, with the climatology data, and optical observations of lightning flashes from the Earth’s orbit. We also note that experimental results have an alternative interpretation, which implies the changes in the effective height of the lower ionosphere by a few kilometers. The most realistic mechanism of the observed changes must comprise both the latitudinal drift of global thunderstorms and the variations of the height of the ionosphere. Both the processes are caused by variations in the solar activity. It is also noted that the inter-annual trends in the resonance intensity might be linked to the trends in the surface temperature of the planet. Relevant estimate is given.
MULTIDIMENSIONAL CLASSIFICATION OF ACTIVE-PASSIVE REMOTE SENSING DATA FOR HAZARDOUS PROCESSES ON DRAINED SOILS MONITORING
D. M. Bychkov, V. K. Ivanov, V. N. Tsymbal, S. Ye. Yatsevich
The monitoring of dangerous processes such as over-moistening of drained boggy soils and spontaneous combustion of peat, which occur in Ukraine over large areas, is difficult without remote sensing systems utilizing. The methods of modern computer identification of hazardous processes according to the data of aerospace survey by active-passive remote sensing are needed for effective monitoring of vast area. The methods of three-dimensional clustering of data on consecutive day and night thermal-radar airborne sensing of overwet drained soil and subsurface self-heating of organic matter have been proposed and tested. The results of the three-dimensional clustering of data demonstrate the reliability of the separation of clusters and confident correlation for the selected area of obtained clusters with the results of expert assessments of initial data. For propagation techniques to other areas it is necessary to conduct working out using both remote and synchronous ground data over large areas.
ON INTERPRETATION OF SURFACE WAVE EXCITATION BY PRISM METHOD IN SLABS OF PLASMA-LIKE MEDIA
A. V. Maksimenko, G. I. Zaginaylov
Effect of attenuated total reflection (ATR) are widely used for studying properties of the dielectric and metal films, and for studying dispersion properties of surface waves (SW). However, the theory of ATR is usually based on idealized models that may lead to not quite correct interpretation of resonance effects occurring in the experiments. In the paper, well-known features of ATP in Krechnam geometry are interpreted on the basis of leaky (improper or nonspectral) SW. It is shown that the minimum of the reflection coefficient corresponds to the resonance with leaky SW. It is shifted with respect to the resonance with the usual spectral (proper) SW. The approximate analytic estimation of the shift is addressed. The absence of ATR in the lossless case is associated with the geometric idealizations of the problem, which can lead to the impossibility of the proper SW excitation. We also give a physical interpretation of the conditions under which the reflection coefficient vanishes. The results may be useful in studying the dispersion properties of PV and in developing methods for accurate measuring the reflection coefficients and determining the parameters of dielectric and metal films.
I. V. Linchevskyi
High efficiency of light modulators based on the Faraday effect can be achieved using a magneto optical crystals. Essentially new characteristics of such modulators can be prepared using magneto mechanical resonance in magneto optical crystals. However, the use of only one magneto optical crystal is not efficient enough. The paper discusses the features of the modulation of optical radiation due to the Faraday effect of the thickness of magneto mechanical excited vibrations in the composite structure of the substrate-magneto optical crystal-ferrite. The frequency dependence of the amplitude and the initial phase of the variable component of the Faraday effect was obtained. It is shown that when the magneto optical crystal is placed between substrate and magnet passive magnet strictive ferrite there is an additional enhancement of mechanical stress in the crystal under magneto-mechanical resonance. Additional increase of the variable component of the Faraday effect can reach up to 50 % compared with a single-layer structure. It is shown that for the considered type of modulator the initial phase delay of the variable component of the Faraday effect to the values of 30–60° at resonance is typical. The resonance dependence of the initial phase shift for the variable component of the Faraday effect is characterized by an absolute stability to the amplitude of the alternating magnetic field and is determined by the characteristics of magneto mechanical oscillations in the structure.
N. N. Beletskii, S. A. Borysenko, N. I. Gvozdev
The study of the defect periodic layered structures bordering upon plasma-like media has attracted interest recently. This is due to the fact that in such structures there are the surface and bulk electromagnetic waves interacting resonantly. The effect of resonant interaction in defect periodic layered structures is not sufficiently studied. In the paper the resonant interaction of surface and bulk TM-electromagnetic waves in the one-dimensional defect dielectric periodic layered structure placed in a parallel-plate waveguide is investigated on the basis of a numerical solution of the dispersion equation. The dispersion and energy properties of the plasma and bulk modes are studied in accordance with the location of the defect layer in the periodic structure. It is shown that the peculiarities of the resonant interaction of the plasma and bulk waves essentially depend on the geometric configuration of the defect periodic layered structure. The results of our investigations expand considerably notions about the nature of the resonant interaction of electromagnetic waves in defect periodic layered structures. They can be used in developing new models of radiophysical devices for the signal processing in microelectronics and photonics.
L. D. Lobzov, N. G. Shulika, V. F. Kovalenko, V. N. Belan, O. N. Shulika, A. P. Podolak, L. N. Makarova
Multipactor discharges, accompanied by electron reproduction of secondary electron emission (SEE) and reaching electron close of electrodes in linear ion accelerator (LINAC) are undesirable phenomena that must be removed. The closes are possible between the electrodes of its other areas. However, in the scientific literature there is no information on disruption of the accelerator characteristics, distorted by discharges in its different areas. In such cases, discharge areas outside the acceleration channel are identified and eliminated. If after that the electron closes of the electrodes in accelerating gaps still occur, they are eliminated by the known and available methods. In this study a modern accelerator excitation circuit, with two identical RF-sources with independent positive feedbacks is used. They work together on the same resonant load (primary or perturbed frequency) which allows to provide both sustainable RF excitation voltages and suppression of multipactor processes and discharges. In practice, this is confirmed by the fact that for small values of voltages and, consequently, on the leading and trailing edges of the current pulse of SEE, there is only the initiation of electron multiplication (multipactor splash). However, such a stable operation of the accelerator was disturbed by gross distortion of pulse voltages and currents of SEE. Examination of the internal structure showed that there are intense glow discharges in other areas of the accelerator – at the entrance and its periphery. At the entrance it is the calculated gap of length 1.353 cm with sections of parallel end surfaces of the first drift tubes. In the periphery it is a parasitic slot ~ 0.1...0.2 mm (at opening vacuum jacket), formed by the surface structure and the end of the copper plate (patch that closes the unnecessary through hole); the tin solder between them was partially sublimated. From the analysis of pulse distortion of control voltages and common currents of SEE, it became clear that the basic rules relevant to the research subject are observed. Visual display of the time luminosity of the discharge and a character of these distortions forms of voltages and currents electronic, allowed to characterize uniquely both discharges as the multipactor, which greatly facilitates their research and selection of methods for removal. Results of the investigations extend knowledge of the conditions of development and control of multipactor processes in high–Q (Q0 >> 1) resonator structures, which is essential for provision constancy in time characteristics of a linear ion accelerator.
I. P. Storozhenko, A. N. Yaroshenko, Yu. V. Arkusha
Graded-gap semiconductors can increase the efficiency and output power of Gunn generators. In InBN and GaBN compounds, unlike other ternary semiconductor nitrides, the energy gap between the valleys can be reduced to zero, which gives the opportunity to find the optimal distribution of the BN component in graded gap compounds for Gunn diodes. The paper presents the results of numerical experiments on the oscillation generation in the range of 0.03...0.7 THz using the n+–n–n+ Gunn diodes based on InBN and GaBN graded gap semiconductor compounds at different BN distribution. It is shown that the maximum efficiency and output power of generation occur at the maximal BN content near the cathode contact and a length of graded-gap layer of 0.6...0.8 µm. At optimal BN distribution graded-gap semiconductor InBN- and GaBN-Gunn diodes for efficiency and output power exceed GaN-, InN-diodes in 1.07¸3.44 times and AlGaN- and AlInN-diodes in 0.93¸1.69 times. Power consumption of graded-gap InBN- and GaBN-diodes is 11–19 % less than the power consumption of InN-, GaN- and AlInN-diodes. Findings of study extend the knowledge about the physical processes of carrier transfer in complex semiconductor structures and can be used for technological designing of new high-speed devices based on semiconductor nitrides.
V. P. Radionov, V. K. Kiseliov
In the mid part of the terahertz range of frequencies (~ 1 THz) gas-discharge lasers are among the most common and available generators. Alignment of the resonator mirrors is one of the most critical and complex operations that have to be performed while using such lasers. Development of laser resonators that do not require adjustment of the mirrors is an important task. A study of the conical mirrors with an apex angle of 90° was conducted. These mirrors are tested in a laser cavity. The tests were carried out in a gas-discharge HCN-laser at a wavelength of 337 microns (f = 0.89 THz). Experimental results have shown that such mirrors do not require precise alignment. This makes it possible to improve the stability of the radiation, to simplify the design of the laser and to reduce the complexity of its maintenance.
K. A. Vytovtov, A. D. Arkhipov
Controlled frequency-transmit filter with isolator properties for terahertz band is presented in this work. The filter is based on non-homogeneous anisotropic structure. For this purpose the frequency, axis orientation and field value dependences are investigated for layered anisotropic structures. On the basis of the obtained results a layered structure with arbitrary axis orientation and arbitrary wave incidence is proposed. Optimization problem is solved for the acceptable characteristics obtaining. The theme is important because of fast terahertz telecommunications development. Thereby, development of controlled devices and their minimization is important. The obtained results may be useful for modern telecommunication systems. Calculation methods are fully analytical and may be used in any frequency region. Monte-Carlo and Newton optimization methods were chosen because the frequency-orientation characteristics of reflection coefficient of anisotropic layered structure are a multiextremal function.
R. I. Bilous, A. P. Motornenko, I. G. Skuratovskiy, O. I. Khazov
The fundamental parameters of the resonator are the frequency and Q-factor. The drawback of the waveguide-dielectric resonator is the decrease of the Q-factor when the short-circuit plunger approaches the dielectric in the course of frequency tuning. In this paper the possibility of increase of eigen Q-factor of the waveguide-dielectric resonator tunable with the resonance short-circuit plunger has been investigated. The negative influence of the resonance short-circuit plunger on the H111 mode characteristics in the investigated resonator of the 3-cm band has been found out and studied. It was demonstrated how to eliminate this influence in order to obtain the measurement of eigen frequencies and Q-factors of the main mode in the waveguide-dielectric resonator corresponding to the computed data for all frequency tuning band. The results of the investigation extend the possibility of the practical use of this resonator.
G. V. Golubnicha, A. Ya. Kirichenko, E. V. Krivenko, V. I. Lutsenko
Each of the numerous dielectric methods has its limitations on use, namely, the aggregate state of the substance, the range of electromagnetic spectrum of used frequencies, the quantities of dielectric permittivity and electromagnetic losses in the substance, etc. In particular, the opportunities of express-methods of dielectrometry of liquid substances with high losses in the millimeter (mm) range of the electromagnetic spectrum are currently limited. New features in this area are opened when advancing the capillary-waveguide method to shorter wavelengths mm range and when using the proposed method of the vibrating string. It is shown that these methods allow to conduct the determination of the real component of the permittivity in the strongly absorbing liquids (weak aqueous solutions). As identification parameters in the capillary-waveguide method, the amplitude of measured resonance signal is selected, and in the method of the vibrating string the wavelength in the test liquid is selected (in this case, the water samples were taken from some sources of the Kharkov region). The high value of correlation of the identification parameters of these two methods, which confirms the efficiency and authenticity of the use of these express-methods for identification of liquids with high electromagnetic losses in mm wavelength range is set. It is shown that the proposed methods for rapid identification of weak aqueous solutions, for example, pharmacological preparations, wine materials, etc can be applied.