Order of received power from a GEO communications satellite at the earth station A typical carrier power received at the input of a properly pointed earth-station receiver from a geostationary communications satellite is usually of the order of a few:

Introduction / Context:Despite large Effective Isotropic Radiated Power (EIRP) at the satellite and high-gain earth-station antennas, the enormous free-space path loss over ~36,000 km reduces received carrier power to very small levels.

Given Data / Assumptions:

• GEO range ~ 3.6 * 10^7 m.
• Ku/Ka-band links with high gains but large FSPL.
• Receiver input sees narrowband carrier powers on the order of 10^−12 to 10^−9 W, depending on system.

Concept / Approach:Friis transmission formula indicates Pr = Pt * Gt * Gr * (lambda / (4 * pi * R))^2. Even with large Gt and Gr, R is so large that Pr is in the pico- to nanowatt range. “A few picowatts” is a common order-of-magnitude description for many GEO downlinks.

Step-by-Step Solution:Estimate FSPL at, say, 12 GHz and R ≈ 36,000 km.Compute lambda = c/f ≈ 0.025 m; (lambda/(4piR))^2 ~ very small.Combine with typical EIRP and G/T to infer Pr ~ 10^−12…10^−9 W.

Verification / Alternative check:Link budget examples in textbooks yield received carrier powers typically in the picowatt to nanowatt range for GEO links.

Why Other Options Are Wrong:Milliwatts/Watts/Kilowatts are many orders of magnitude too large for post-FSPL carrier at LNB input under normal operation. Microjoules are energy units, not power.

Common Pitfalls:Confusing EIRP with received power; ignoring FSPL magnitude at GEO distances.

Final Answer:Picowatts