en 5-Scattering and Propagation Scattering and Propagation Research Paper Research Paper The proposed theorem in this paper is indicative of a kind of duality in the propagation of waves in the dual media of and in the spherical structures. Independent of wave frequency, the number of layers, their thickness, and the type of polarization, this theorem holds true in case of any change in any of these conditions. Theorem: Consider a plane wave incident on a multilayered spherical structure. The core of structure may be PEC, metamaterial or dielectric. If we apply the interchange or for the constituting materials of the spherical structure and the surrounding medium the radar cross section of the structure will not change in any direction. Double Negative (DNG) Materials,Double Positive (DPS) Materials,Epsilon Negative (ENG) Materials,Metamaterials,Mu Negative (MNG) Materials,Radar Cross Section, 159 167 http://ijeee.iust.ac.ir/browse.php?a_code=A-10-866-3&slc_lang=en&sid=1 A. Abdolali abdolali@iust.ac.ir 180031947532846002912 180031947532846002912 Yes Iran University of Science and Technology, Electrical Engineering Department M. M Salary Mahdi_Salary2006@yahoo.com 180031947532846002913 180031947532846002913 No Iran University of Science and Technology, Electrical Engineering Department