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

Abstract

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.