Crosspolarization

Cross-polarization refers to the component of an electromagnetic field that is polarized orthogonally to the intended polarization of a wave. This phenomenon can occur naturally when waves reflect or scatter, or it can be engineered in systems to carry additional information. In radio communications and radar, cross-polarization is usually regarded as a source of signal degradation because it reduces the power that is received in the intended polarization. The degree of isolation between co-polar and cross-polar channels is quantified by cross-polar discrimination (XPD) or cross-polar ratio (XPR) in decibels. Cross-polarization can be caused by reflections from surfaces with roughness, multipath propagation, Faraday rotation in magnetized media, or imperfections and leakage in antennas.

In remote sensing and radar, cross-polarization channels such as HV or VH are used in dual- or full-polarization systems. Cross-polar data reveal different scattering mechanisms and can help distinguish surface textures, vegetation structure, and man-made objects. In optical imaging, cross-polarization involves placing polarizers at 90 degrees to suppress specular reflections and enhance contrast for subsurface or stressed features.

In magnetic resonance, cross-polarization is a specialized technique used to transfer spin polarization from abundant nuclei (typically protons) to less sensitive nuclei to boost signal, a method widely used in solid-state NMR experiments.

Mitigation and utilization strategies include polarization diversity and MIMO in communications, polarimetric processing in radar, and careful antenna design to maximize XPD while exploiting cross-pol channels for sensing when beneficial.