Radio physics and electronics

15-32

Authors: I. Ivanchenko, N. Popenko, M. Khruslov, R. Chernobrovkin, S. Radionov, V. Pishchikov

Subject and purpose. This article is devoted to the review of the original works of the authors on studying the effective small-sized individual radiators of various types using near-field technology. Methods and methodology. The research algorithm consists in carrying out numerical modeling of the proposed antenna designs using software packages, creating the appropriate physical prototypes and comparing the results of numerical and direct experiments of such radiator characteristics as bandwidth, radiation pattern, gain and ellipticity. At the same time, a detailed analysis of the spatial near-field distributions gives the necessary information for further optimization of the antennas and obtaining their optimal characteristics. Results. The characteristics of various modifications of monopole, disk, aperture, microstrip and spiral antennas with record characteristics are systematized and analyzed, and the possibility of their use in a compact mobile microwave direction finder and nonlinear locator is also shown. The results of studying the diffraction coupling of individual aperture radiators with the involvement of developed methods of measuring the spatial near-field distributions were used to create a laboratory model of an antenna array. Conclusions. A review of the results of studying the small-sized microwave antennas of various types over the past decade is given. We demonstrate the efficiency of using information on the spatial near-field distributions in the inductive and wave regions of the radiating apertures during the elaboration and subsequent optimization of the main characteristics of both individual original radiators and antenna arrays based on them.

49-56

Authors: M.M. Solovan, P.D. Maryanchuk

Subject and purpose. The subject of research is the electrical and photoelectric properties of the МoN/n-Si heterostructure fabricated for the first time by means of the deposition of thin film of molybdenum nitride (n-type conductivity) by the reactive magnetron sputtering onto single crystal substrates of n-type Si. The purpose of the work is to fabricate the photosensitive MoN/n-Si surface-barrier structures, determine the barrier parameters and dominant mechanisms of current transfer through the obtained heterostructure at direct and reverse biases, investigate the photoelectric properties and causes of losses of photogenerated charge carriers in the obtained heterostructures. Method and methodology. Direct and reverse volt-ampere characteristics of the MoN/n-Si heterostructure were measured at various temperatures, as well as when irradiated with white light with an intensity of Popt= 80 mW/cm2 and three lasers with λ = 405, 646, 780 nm with intensity Iopt = 5 mW cm-2. Results. The obtained heterojunctions with the height of potential barrier φ0 = eVbi = 0.37 еV have pronounced rectifying properties. The dominant current transport mechanisms through the heterojunction under investigation were determined: at forward bias, volt-ampere characteristics are well described within the generation-recombination and tunneling-recombination models with the participation of surface states, and аt reverse bias, they are described within the tunnel model. Conclusion. It was established that when illuminated with white light with the intensity of Popt = 80 mW/cm2, the reverse current Ilight increases compared with its value in the dark Idark by more than an order of magnitude due to the separation of photogenerated electron-hole pairs. The photosensitivity of this heterostructure to monochromatic illumination by lasers with electromagnetic wavelengths λ = 405, 646, 780 nm and intensity Iopt = 5 mW cm-2 is shown. The results obtained allow us to c

68-77

Authors: S.A. Vlasenko, A.V. Degtyarev, M.M. Dubinin, V.A. Maslov

Subject and ppurpose. In this paper, the spatial-energy characteristics of laser beams with inhomogeneous spatial polarization with their moderate and sharp focusing are theoretically investigated. In the numerical simulation of focusing of wave laser beams in the terahertz range, laser resonator modes based on a circular metal waveguide were used as the radiation under study. These modes coincide with the proper types of oscillations of such a waveguide. For the calculation, we selected symmetric and asymmetric modes with azimuthal, radial, and complex spatial polarization of the field. Methods and methodology. In the study of the propagation of the components of the electric field of laser radiation in free space, Rayleigh-Sommerfeld integrals were used in the nonparaxial approximation. The effect of the focusing lens on the radiation under study was taken into account using the function of amplitude-phase correction. The transverse distributions of the total field intensity and its individual components of the studied resonant modes in the region of the minimum size of the focal spot of focused radiation beams were studied. Results. Wave beams with inhomogeneous spatial polarization of radiation are necessary for solving important fundamental and applied problems. These tasks are associated with the interaction of electromagnetic waves of the terahertz range with matter. For example, diagnostics of the surface of materials, thin films, biological objects, THz transmission systems and information processing, the achievement of subwave resolution THz tomography, terahertz communication systems, etc. The results of studies of focusing features in the terahertz range are practically absent. A theoretical study was made of the physical features of moderate and sharp focusing of laser beams of radiation excited by the modes of a resonator with a circular metal waveguide with different spatial polarization of the field. The results obtained extend knowledge of the focusing features of terahertz laser beams. Conclusions. The physical features of the spatial-energy characteristics are established with moderate and sharp focusing in free space of radiation beams with different spatial polarization of the field. These beams were excited by laser resonator modes based on a circular metal waveguide in the terahertz range.