Electrodynamic analysis of a two-way helical antenna over flat perfectly conductive screen with rectilinear boundaries

The construction of mobile radio-electronic complexes includes the search for technical solutions for determining rational designs of antenna systems, which make it possible to ensure high reliability of transmitting and receiving information over radio channels with restrictions on weight and size characteristics of receiving-emitting structures. Indicators of spatial-frequency selectivity of the equipment should be determined when the effects of shielding sectors of working angles by carrier surfaces and distortions of antenna directional patterns due to diffraction of the electromagnetic field on carriers are manifested. In the interests of miniaturizing the size of external equipment, spiral antennas made using planar technology are effectively used in complexes. Their design parameters are determined based on analysis of interactions with directional properties using electro-dynamic models of receiving-emitting structures located near screens corresponding to fragments of carrier bodies. Effective methods of electro-dynamic analysis are based on setting boundary value problems based on the apparatus of integral equations, which are solved by numerical methods due to mathematical incorrectness. The purpose of the article is to study of the patterns of change in the directional pattern of a two-way spiral antenna with various parameters of its design and the size of the underlying ideally conductive flat screen. Using integral equations for equivalent axial currents of curvilinear ideal conductors in approximation of wire structure and surface currents of ideally conducting infinitely thin plate with rectilinear boundaries, electrodynamic analysis of a two-way spiral antenna over rectangular screen has been carried out. To take into account electromagnetic connections in the antenna and electromagnetic interaction with the screen through secondary radiation, when setting the boundary value, boundary conditions have been applied to the superposition of the electric fields of the spirals and the plate on the surfaces of these elements. Based on the results of the numerical solution of integral equations obtained in the form of sequences of piecewise constant basis functions with weight coefficients equal to values of complex amplitudes of currents at sampling points of spirals and the screen, directional patterns of the two-way spiral antenna have been found. Patterns of antenna directional properties change at various parameters of its design and dimensions of ideally conducting plate have been investigated. It has been shown that the presence of the underlying surface leads to an increase in the level of the side lobes of the antenna radiation pattern relative to values characteristic of free space, and in some cases – to the collapse of the main beam due to a violation of the amplitude-phase distribution of spiral currents corresponding to the traveling wave law. When using a screen of resonant electrical dimensions, the direction of signal transmission and reception is maintained, as when using an infinitely long ideally conductive surface. Leakage of currents beyond the edges of the screen and excitation of surface waves reflected from its edges leads to an increase in the intensity of secondary electromagnetic radiation, which causes deterioration of the directional properties of the antenna. Change of screen dimensions in resonance area of scattering of electromagnetic field facilitates transformation of directional pattern of spiral antenna in area of side lobes due to differences in ratios of polarization components of diffraction field. The elevation of the antenna has a significant impact on the spatial frequency selectivity of signal transmission and reception. At a certain distance to the screen, the decay of the main beam of the antenna pattern is observed due to a violation of the amplitude-phase distribution of currents corresponding to the traveling wave law. On the basis of electro-dynamic analysis of a two-way spiral antenna above an ideally conductive screen, relationships of its directional pattern with design parameters and dimensions of the bearing surface have been established. The obtained results make it possible to substantiate the technical appearance of the antenna in order to achieve indicators of spatial frequency selectivity of signal transmission and reception, according to the requirements that ensure the performance of the target functions of mobile electronic complexes.