Comparison of measured cross-polarization isolation and discrimination for rain and ice on a 19-GHz space-earth path

Rain and ice in a radio path can couple power from a wave transmitted with a given polarization into the orthogonal polarization. At any point along a path, the ratio of the cross-polarized signal component to the copolarized signal component is defined as depolarization or as cross-polarization discrimination. Cross-polarization isolation is the ratio of the cross-polarized signal component from one transmitted polarization to the copolarized signal component for the orthogonal transmitted polarization. The two signal components that determine cross-polarization isolation are received on the same polarization. In contrast, the two signal components that determine cross-polarization discrimination are received on orthogonal polarizations. Conventional single-polarization propagation experiments can only measure cross-polarization discrimination. However, cross-polarization isolation is the quantity that limits the performance of dual-polarized communication systems. Simultaneous measurements of copolarized and cross-polarized signal components for two orthogonal linear polarizations were made at Crawford Hill, New Jersey, by using polarization-switched 19-GHz beacons on COMSTAR satellites. Data from this experiment are used to show that instantaneous values of cross-polarization discrimination and cross-polarization isolation are equal. This is the first known experimental demonstration of this equality for a space-earth propagation path.