Open AccessThe paper sets a task to design protection covers (PC) of large aperature antennas to be used in difficult climatic conditions of operation, wide range of temperatures or under specified requirements for the operation mode of equipment. Methods to analyse the influence of antenna covers and radomes on characteristics of antennas radiation vary depending on the electrical size and complexity of the PC structure. Both strict methods of the electrodynamic analysis, and quasioptical approximations can be applied.
The aim of research was to define the influence of thickness of a single-layer radome in the form of a cylindrical or spherical cover on radiation characteristics of the aperture antenna with antenna mouth of about several tens wavelengths in free space (λ). The second task was to establish the interrelation between the change of the directional pattern and shift of the antenna mouth with respect to the center of PC generatrix.
Influence of radome thickness was assessed according to several parameters such as amplitude of the field radiated in the axial direction, reduced to results of modeling antenna without PC; level of power radiated in the conic sector with angular half-aperture of 6 °; width of the main maximum at half power with regard to the case with no radome.
It is found that with increasing PC thickness there is growth of the principle pattern width at half power. Thus, it is defined that, qualitively, a difference in influence of the spherical radome and cylindrical one consists in reduction of radiation power in the axial direction, more distorted principle pattern shape, change of minor-lobe angle, and reduction of minor-lobe level. With increasing PC thickness the minor-lobe level for both cases becomes almost even, and the ratio of radiation level along the axis remains unchanged. It is shown that difference in the pattern shape gives fractions of percent for power with a shift along a system axis. Proceeding from initial simplifications, this fact can be easily explained that for the parallel output beams of an aperture, refraction conditions at the air-PC boundary with a shift of antenna mouth along the axis remain unchaged except for the beam cross section area of a display tube.