Multipath fading at L band for low elevation angle, land mobile satellite scenarios

We characterize multipath fading at low elevation angles for unshadowed line-of-sight propagation over a land-mobile satellite link. Equipment aboard a van recorded a CW signal from INMARSAT's geostationary satellite MARECS-B2 while driving in the states of Utah, Nevada, Washington, and Oregon. Elevation angles ranged from 7/spl deg/ to 14/spl deg/. The van carried a tracking helix antenna with beamwidths in the principal planes of approximately /spl plusmn/18/spl deg/. Multipath fading was observed in flat and hilly terrain and is compared with an example of fading due to tree shadowing. The measurements demonstrate that multipath effects at low elevation angles may result in fades exceeding 7 dB for approximately 1% of the driving distance for a worst case scenario corresponding to driving in rolling, hilly terrain where the satellite is in front or behind of the vehicle. Fading in such a case is typically dominated by a single multipath reflection from a terrain feature. On the other hand, tree shadowing at low elevation (7/spl deg/) may result in fades which exceed 25 dB at the 1% level.>