The article "The Definition of Cross Polarization" by Arthur C. Ludwig, published in the IEEE Transactions on Antennas and Propagation in 1973, discusses the various definitions of cross polarization used in the literature and proposes a standard definition. The author presents three alternative definitions and evaluates their applicability to different scenarios, such as describing secondary radiation patterns and source field distributions. The IEEE Standard definition, which is "the polarization orthogonal to a reference polarization," is considered adequate for circular polarization but requires further specification for linear or elliptical polarization. The article provides detailed mathematical derivations and comparisons to illustrate the advantages and disadvantages of each definition. Ludwig concludes that Definition 3, which is based on the standard measurement practice, is the best choice for describing antenna patterns, despite its imperfect relationship with the source current definition. The article also highlights the importance of accurate cross polarization measurements and the potential pitfalls of misalignment in such measurements.The article "The Definition of Cross Polarization" by Arthur C. Ludwig, published in the IEEE Transactions on Antennas and Propagation in 1973, discusses the various definitions of cross polarization used in the literature and proposes a standard definition. The author presents three alternative definitions and evaluates their applicability to different scenarios, such as describing secondary radiation patterns and source field distributions. The IEEE Standard definition, which is "the polarization orthogonal to a reference polarization," is considered adequate for circular polarization but requires further specification for linear or elliptical polarization. The article provides detailed mathematical derivations and comparisons to illustrate the advantages and disadvantages of each definition. Ludwig concludes that Definition 3, which is based on the standard measurement practice, is the best choice for describing antenna patterns, despite its imperfect relationship with the source current definition. The article also highlights the importance of accurate cross polarization measurements and the potential pitfalls of misalignment in such measurements.