Current polarization impact on cross-polarization definitions for practical antenna elements

With the growing interest in polarization diversity in communications and radar systems, the use of Ludwig's second and third definitions have become controversial among scientists and antenna engineers. Therefore, this paper is an attempt to clarify some of the ambiguity and confusion caused by these definitions. A detailed comparison of Ludwig's 2nd and 3rd definitions of cross-polarization, as applied to linearly polarized antennas, was performed. The results show that, in the diagonal plane, Ludwig's 2nd definition leads to a lower cross-polarization level than the 3rd definition for x- or y-polarized current sources. For a Huygens source, by Ludwig's 3rd definition, the radiation pattern has a lower cross-polarization level than that obtained by Ludwig's 2nd definition.