Propagation and coordination facts for GEO links Which statement is incorrect regarding GEO satellite link behavior and orbital spacing?

Introduction / Context:
GEO link design must account for atmospheric path length, frequency-dependent attenuation, and orbital spacing to control interference. Recognizing realistic values prevents misconceptions in planning ground stations and coordination.

Given Data / Assumptions:

• Elevation angle affects slant path through atmosphere and rain cells.
• Higher frequencies (Ku/Ka) suffer more rain attenuation than C-band.
• GEO satellites are coordinated along the equatorial arc with typical spacing of a few degrees (often ~2°–3°), not 10°.

Concept / Approach:
Attenuation by hydrometeors roughly scales with path length and specific attenuation, which rises strongly with frequency. Spacing values reflect practical frequency reuse and antenna beamwidths; modern systems achieve close spacing well below 10° with adequate antenna sidelobe control.

Step-by-Step Solution:
Evaluate (a): Lower elevation → longer atmospheric path → more loss; qualitatively true.Evaluate (b): Ku (12/14 GHz) exceeds C-band in rain loss; true.Evaluate (c): Slant range does vary with look angle; true.Evaluate (d): “At least 10° apart” is outdated and incorrect for present coordination; typical separations are a few degrees.

Verification / Alternative check:
ITU coordination practices and satellite operator filings show numerous GEO slots separated by ~2°–3° with suitable earth-station antenna patterns.

Why Other Options Are Wrong:

• (a), (b), (c) are consistent with standard propagation/orbit facts.
• (e) “None of these” fails because (d) is indeed incorrect.

Common Pitfalls:

• Confusing “inversely with elevation angle” (dimensioned) with the correct geometric dependence on 1/sin(elevation); here the qualitative statement is acceptable.
• Assuming very large orbital spacing is still the norm.

Final Answer:
Current GEO satellites using 4/6 GHz are spaced at least 10° apart in the geostationary arc.