Depolarization of 19-GHz signals

Path depolarization is a significant consideration in the design of dual-polarized, frequency reuse communications systems. The present paper reports long-term, continuous measurements of the depolarization of 19-GHz orthogonal linear polarized beacon signals from the Comstar D-1, D-2, and D-3 satellites. Both cross-polarization discrimination (XPD) and cross-polarization isolation (XPI) were measured for vertically and horizontally polarized signals under clear skies and under the influence of rain. XPD for vertically polarized signals is found to be slightly better than XPI at higher rain rates, while XPI is better than XPD in horizontal polarization. Analysis of ice depolarization events reveals variations in XPI and XPD of 5-7 dB from clear sky conditions, with XPI estimated as 2-5 dB lower than XPD. Comparison of the present data with the CCIR formula (1982) and a modification thereof (Chu, 1982) has identified certain weaknesses in the model.