An analysis of a circular aperture antenna covered with a dielectric hemi-spherical shell radome over ground plane

Electromagnetic fields radiated from an aperture antenna covered by dielectric hemi-spherical shell radome over the ground plane are formulated in a closed form in this paper. Alternative representation of dyadic Green´s functions for the regions separated by the spherical shell is given. By applying the principle of the scattering superposition and making use of the boundary conditions, the transmission and reflection coefficients of the Green´s functions are derived. The new dyadic form provides a straightforward way by which the general expression of the electric field can be reduced for free space and far-field region to that obtained by Balanis. Both the near-field and the Fraunhofer far-field including and excluding the effects of the the dielectric radome are obtained. The Balanis´ expression of the electric field is produced exactly by assuming the radome to be filled with air or letting the thickness of the radome be zero in our general expression. Numerical computation is also made to show the difference between the antenna patterns at the near-field and far-field regions and to demonstrate the effects of the dielectric radome on the radiation patterns.