SIRIO-OTS 12 GHz orbital diversity experiment at Fucino

When rain occurs at a site, orbital diversity (OD) may be an alternative diversity scheme for future satellite communications above 10 GHz. The SIRIO-OTS OD attenuation measurements at 12 GHz with an aperture angle of 27.8° at Fucino show that the statistical gain obtainable is 20-25% of the OTS attenuation in decibels (if OTS is assumed as the satellite of the normal mode and SIRIO as OD resource, or spare link), or 30-40% of the SIRIO attenuation (if SIRIO is assumed as the satellite of normal mode, and OTS as OD resource). At 12 GHz these percentages represent a gain of a few decibels but at higher frequencies, such as 20/30 GHz, the gain may be multiplied by 2.5 to 5, giving noticeable power reductions. The instantaneous gain is also analyzed. The fundamental aspects of balancing an unbalanced diversity configuration are shown by applying the theory to the unbalanced SIRIO-OTS OD. Fade durations of the joint link show the same characteristics as the single-path ones: few long fades and many short fades. More important, the intervals of time in which the resource is used are long; this fact is favorable to the diversity configuration since switchover inefficiency is lowered