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

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 ƒ7/12 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.