Lowering antenna gain, sidelobes growing, boresight errors and depolarization field of aperture antennas and antenna arrays caused by radomes are under consideration. Transmission and reflection of electromagnetic waves by sandwich type antenna radomes are analyzed. The Green's functions of layered structures and equivalent currents are used for electric field calculation. Reflection and transmission coefficients are calculated for different structures, incidence angles and polarization. A circular polarized wave transformation by a sandwich type antenna is discussed.