Observations of cloud‐produced amplitude scintillation on 19‐ and 28‐GHz earth‐space paths

Abstract

The amplitudes of satellite signals sometimes scintillate ± several decibels when heavy cumulus clouds pass through the radio path on hot summer days. These scintillations have been measured on a 19‐GHz and 28‐GHz earth‐space path using 7‐m and 0.6‐m antennas at Crawford Hill, New Jersey. Scintillation intensity at 28 GHz is 1.2 times that at 19 GHz, consistent with the ƒ 7/12 frequency dependence produced by a thin turbulent layer. The scintillation process is polarization‐independent and has a low‐pass power spectrum with a cutoff frequency of about 0.3 Hz. Rain attenuation often accompanies the more intense scintillation. The mean duration of scintillation‐produced fades is short (about 1.3 s for fades greater than 1 dB), but over 1000 fades of over 1 dB at 28 GHz were observed in two summer months. Because of their weak frequency dependence these short but frequent events could produce repeated outages on 4‐ and 6‐GHz earth‐space links having low attenuation margins.