Measurement of Polarization Statistics of Signals Received Over a Short Range HF Path

A study was performed to measure variations in the polarization characteristics of an HF signal received over a short range ionospheric path. This paper describes a limited number of experiments using signals from Station WWV to determine the statistical nature of the polarization ellipse at the receiving site, Hathaway Hill, near Rochester, N. Y. The approach employed was to regard the elliptically polarized wave as the resultant of two linearly polarized waves of the same frequency and to measure the amplitude and phase of these two components by employing orthogonally oriented receiving dipoles and associated devices to provide continuous recordings of the variables. Three types of data were recorded during a one week field test period, and samples of each type were reduced and analyzed. The data compiled showed that the received signal exhibits Rayleigh fading characteristics with a mean fading rate of approximately 0.15 fades per second. The envelopes of the received components exhibit a high correlation in the morning hours, considerably less correlation in the afternoon, and a high correlation in the evening characterized by a substantial offset in time between the fading of the two components which is often periodic. The envelope of the cross correlation function indicates that the conditions causing the disturbance are changing slowly on a minute-to-minute basis, although complete polarization rotation appears to take about 5 to 10 seconds and is characterized by both phase and amplitude changes of the component waves. It appears that the milder perturbations of relative phase are confined within limits of approximately
\pm90\deg
, and severe perturbations are characterized by a rapid monotonic change in the relative phase of the components of 2π.