Some Effects of Measurement Errors on Rain Depolarization Experiments

It is desirable to use two orthogonal polarizations to double the number of radio channels available in future 20- and 30-GHz satellite repeaters. Since rain-produced depolarization (cross-polarization coupling) is more severe for circular polarizations than for linear polarizations 1 oriented parallel to the raindrop axes (see Fig. 1), two properly oriented orthogonal (near vertical and horizontal) linear polarizations are the logical choice for such systems. The only measurements of rain-produced depolarization 1-4 above 10 GHz have been made on terrestrial propagation paths. Therefore, measurements of rain-produced depolarization for linearly polarized 20- and 30-GHz satellite signals oriented vertically (Y) and horizontally (H) and a few degrees either side of V and H are required to determine both the proper polarization orientation for future systems and the rainproduced depolarization at that orientation. 435 There will be considerable variation, however, in the polarization orientation of linearly polarized signals received at different measuring sites within the coverage area of 20- and 30-GHz area-coverage satellite beacons.5 For example, the polarization orientation will varyon the order of 40 degrees over the continental United States for a satellite in synchronous orbit. Thus, the orientation cannot be optimum at all receiving sites from the standpoint of collecting data for system design. Also, since the angular orientation of the raindrop axes with respect to V and H at a given site varies from storm to storm, 4 statistics of the polarization orientation that produces the minimum depolarization and of the minimum value of that depolarization are needed, as well as statistics of the depolarization for several fixed polarization orientations.