Far field of dipole antenna on substrate

Dear COMSOL community

I try to model a nanodipole antenna on glass substrate , first I create a model for a nanodipole in air and the far field seems good to me ( the tours shape typical for dipole antenna ) , where the far field calculation is made by a surface surround the dipole and placed lamb/2 far away from the dipole.

Now I placed the dipole on the top of a glass substrate , while the far field domain this time will be half air and half substrate , unfortunately the shape of the far field seems to me incorrect , I read on the thread that the far field domain has to be homogeneous, but how to calculate the far field in the case of antenna placed on substrate

Thanks in advance

M.H.Elshorbagy

UCM , Spain