Influence of a saltwater film on a radio-transparent dome on the amplitude-phase distribution of a millimeter-range antenna

Abstract

Transition of communication systems installed on naval ships to the millimeter range requires an analysis of the effect of the saltwater film formed on the radio-transparent dome (RTD) on the radiotechnical characteristics of the mirror antenna. The latter are determined by the amplitude-phase distribution in the antenna aperture, so the topic of research is relevant. The objective of the article is to analyze the effect of the salt-water film on the surface of a marine mounted RTD, as well as the effect of millimeter wavelength antenna placement inside the RTD on the distortion of the field generated in the outer region. It has been shown that when installing millimeter-wave range antennas on a naval ship under a radio-transparent dome it is necessary to consider the distortions introduced by the water film on the dome surface into the generated amplitude-phase distribution when calculating the radio technical characteristics. We do so because most of the known methods for calculating the directivity characteristics of mirror antennas are based on the known amplitude-phase distribution in the antenna aperture. In the paper, the influence of the spherical dome wall and the saltwater film on the amplitude-phase distribution is taken into account as follows. Distortions in the amplitude distribution are caused by energy losses of the electromagnetic wave due to the passage of the curved dielectric wall at different angles. Phase distribution losses are due to the phase shift from the original phase as the dome wall is passed through at different angles. The angles of radio wave entry into the dome wall depend on the location of the antenna inside the radio-transparent dome. The electrical parameters of the saltwater film are determined using the well-known ITU methodology, while its thickness is found using the Gibbs formula, assuming that sea spray is similar to the intensity of drizzle rain. The studies have been conducted for the highest stiffness mode. Studies for a single-mirror antenna with a parabolic reflector 5.4 m in diameter and a radio-transparent dome 18 m in diameter showed that the water film influence is manifested in the phase front distortion, as well as a symmetry violation of the generated amplitude distribution. The degree of water salinity is manifested mainly in the distortion of the phase distribution. This is due to the fact that the electrical parameters of salt and fresh water do not differ much. The detected distortions are stronger for the horizontally polarized waves and in the case when the antenna swing center is offset with respect to the dome symmetry line. The detected patterns allow to give a scientific justification for the choice of the amplitude-phase distribution of the mirror antenna when installing it inside the RTD on the naval ship.