Ovsyannikova E. Electromagnetic fields in the near zone of aperture antennas

Dissertation study is devoted to the solution of the urgent scientific problem of electromagnetic field study in the near zone of arbitrary electric sizes aperture radiators. The study is destinated to the solution of an external vector problem of electrodynamics for electromagnetic waves radiation by aperture systems with an aperture of circular, square and rectangular shapes for arbitrary aperture electric dimensions and also for arbitrary polarization of the field in the aperture at an arbitrary distance from the radiator. In the case of low-directional antennas, the analysis showed: the aperture diameter being not more than 1–1.5 wavelengths, the amplitudes distribution of the electric and magnetic fields in the near zone of the circular and square apertures are almost identical. The distance of the far zone of this type of antennas is 1.5 wavelengths. If the aperture electrical dimensions increase, the spatial distributions of the fields in the near zone for the circular and square apertures are qualitatively close, but the quantitative data differ significantly. In this case, local flat inhomogeneous waves of electric and magnetic fields are excited in the near zone, and their average amplitudes are close to that of the fields in the middle of the cross irrespectively to the electrical dimensions of the antenna aperture, i.e. the searchlight beam. The searchlight beam means a set of parallel rays in the near zone of aperture antennas in the direction of radiation maximum, described by a flat local inhomogeneous travelling electromagnetic wave. Almost all the radiation power of the antenna is concentrated in the searchlight beam. The influence of the sizes and shapes of horn antenna aperture was theoretically investigated by means of the Kirchhoff method; this method was applied for constant or zero value amplitude distribution at the aperture edges and at different quadratic phase field distributions in the spatial distribution of the near and intermediate zones. The developed physical and mathematical model, algorithms and computational programs allow us to solve the problem of constructive synthesis of the radiating system with a close to constant spatial distribution of the amplitude and power of the electromagnetic field in the near and intermediate zones.