Radio physics and electronics

15-21

Authors: G. Veselovska, G. Khlopov

Radar methods of investigation of clouds and precipitation are the most effective methods of remote sensing of the atmosphere. The advantages of radar techniques are the abilities to measure quickly the characteristics of precipitation over large areas. In the context of the turbulent medium the particles may be at a different angle relatively to the incident field, so in the paper there was an attempt to study the scattering indicatrix of snow crystals (dependence of the radar cross-section (RCS) on the incidence angle of the electromagnetic wave), which allowed to evaluate the variability of the RCS of snow crystals at the variations of the elevation angle of the radar antenna. For the numerical simulation of the scattering properties of the snow crystals we used two types of particles at various angles of observation, at that in the paper we consider two azimuthal angles of incidence of electromagnetic field in a wide frequency range.

28-35

Authors: Yu. O. Averkov, Yu. V. Prokopenko, V. M. Yakovenko

Nowadays a good deal of attention is focused on problems of generation of millimeter and submillimeter electromagnetic waves under the interaction of fluxes of charged particles with solids. However, today there is no consistent theoretical description of this type of effects. In this connection we present the detailed theoretical research on the instability effect of non-relativistic infinitely thin hollow electron beam which moves in vacuum above a dielectric (plasma) cylinder. The calculations have been performed in electrostatic approximation due to the non-relativistic velocity of the beam electrons. The cases where the dielectric permittivity is constant and depends on the frequency have been considered. The dispersion curves of exited modes have been constructed. The dependences of the increments (decrements) of the modes on the value of the bunch radius and on the azimuth mode index have been studied. It has been shown that for both the dielectric and plasma media the largest values of the increments (decrements) of the excited modes occur for zero value of the azimuth mode index. The maximum values of the increments (decrements) decrease with increasing the azimuth mode index. It has been established that the frequency dependence of the dielectric permittivity leads to the absolute instability. This instability exists in the corresponding finite interval of the longitudinal wave number.

45-52

Authors: Yu. S. Kovshov, S. A. Kishko , S. S. Ponomarenko, S. A. Vlasenko, Yu. S. Novikova-Korotun, V. V. Zavertanniy, A. N. Kuleshov

The development of compact oscillators of electromagnetic radiation capable of providing the output power higher than several Watt in millimeter and sub-millimeter ranges is an actual task for a large number of practical applications, in particular, to enhance the sensitivity of DNP NMR spectroscopy. The simulation of 130 GHz CW Clinotron was carried out on basis of experimental results of the earlier developed CW Clinotrons in 2mm wavelength range. Basing on the analysis of oscillator operation characteristics, the space charge dependence on frequency, Pierce parameter and the system electrical length were determined. The obtained results were used in the simulation of grating and in further simulation of operation parameters of clinotron tubes. Basing on simulation results, the clinotrons with homogeneous and four-stage grating were designed. The output power more than one Watt in CW clinotron with homogeneous grating in the frequency range 125…135 GHz was experimentally obtained. Start current and required focusing magnetic field were obtained in the experimental test in electromagnet. The experimental test also shows the close fit between simulation results and experimental data. The proposed methodic can be used in the simulation of CW clinotrons in both millimeter and sub-millimeter ranges.

59-65

Authors: K. A. Lukin, P. P. Maksymov

Design of sources of powerful electromagnetic oscillations in microwave and THz frequency bands is a challenge for radio-electronic engineers. Design of avalanche-generating diodes that generate two phase locked oscillations in microwave and THz ranges is considered in the paper. Summation of two generating oscillations with either close or different frequencies allows managing power and spectral characteristics of the output signal. The physical processes occurring in the avalanche-generating diodes on the basis of abrupt Si and GaAs p–n-junctions at the constant reverse biased voltage are investigated. The effect of the double splitting of the multiplication layer has been revealed. In the suggested avalanche-generating diodes, regular and chaotic self-oscillations of electrons and holes components of the output power are excited in p- and n-regions of the p–n-junction, respectively.

74-78

Authors: A. A. Barannik, S. A. Vitusevich, А. I. Gubin, I. A. Protsenko, N. T. Cherpak

Using WGM resonators allow achieving high accuracy in determining the substances permittivities due to the high Q-factor. The resonator with a microfluidic channel is promising for the study of small-volume liquids, which is especially important for bioliquids. In a Ka-band a sapphire resonator with microfluidic channel has been proposed as a measurement cell, but in the sub-THz range a quartz resonator has more suitable characteristics due to its high Q-factor. In the paper we propose a measurement cell for the determination of complex permittivity of liquids in sub-THz range on the basis of quasi-optical quartz resonator with a layer of plastic comprising a microfluidic channel. Experimental studies of the resonator structure are carried out and a model for numerical research in the software COMSOL Multiphysics is proposed. By means of c omparing the resonator frequencies and Q-factors values with the corresponding values obtained with the numerical model the correction of the model has been carried out for the water-filled microfluidic channel. It is shown that the model for numerical studies correctly describes the resonator structure. The values of the resonator frequency and Q-factor obtained experimentally and numerically, for the microfluidic channel filled with the substances with well-known complex permittivity (methanol, propanol, ethanol, acetone), are in good agreement, which indicates the possibility of using the resonator as a measurement cell allowing the research on small-liquid permittivity using the special calibration procedure.

87-92

Authors: R. I. Bilous, M. V. Vovnyuk, I. G. Skuratovskiy, O. I. Khazov, A. S. Shakhova

The rapid development of electronic technology is characterized by continuous expanding the potentials of new types of created elements, devices and systems that use porous plastics. Therefore, it is necessary to study the main electrophysical characteristics of these materials. The effective solution to this problem is impossible without the accurate determination of the dielectric constant (e ). This paper presents two methods of measuring the relative low e (1.02...1.1) of foams using a cylindrical waveguide-dielectric resonator on the evanescent waveguide. The measurements of the e were carried out for four types of foams in the frequency range 10...12 GHz and the estimation errors are presented. In the “direct” method the test material is used as a dielectric element of the resonator. In the “indirect” method the dielectric element is made from ftoroplast, and the test material filled the evanescent sections of the waveguide. The investigations have shown that the “indirect” method gives a decrease of the measurement error in 2.5–5 times compared to the “direct” one. But the “direct” method is easier and allows to measure any permittivities.