Satellite communication link budget: identify the incorrect statement about free-space path loss and antenna apertures Which of the following statements about link loss (free-space path loss plus antenna effects) in a satellite link is incorrect? Consider fixed geometry and line-of-sight conditions, with standard definitions of antenna effective aperture and gain.

Introduction / Context:
Satellite link budgets balance transmitted power, antenna gains, and propagation losses to predict received power. Understanding how free-space path loss varies with frequency, distance, and antenna aperture is fundamental to designing reliable satellite links.

Given Data / Assumptions:

• Line-of-sight space link (free-space propagation).
• Standard relationships: FSPL = (4 * pi * R * f / c)^2 in linear terms.
• Antenna effective aperture A_e relates to gain G via A_e = (G * lambda^2) / (4 * pi).

Concept / Approach:
In free space, path loss grows with frequency squared and distance squared. However, when physical antenna apertures are fixed, their gain increases with f^2 (since G ∝ A_phys * (4 * pi / lambda^2)), which can compensate the frequency dependence if apertures are constant. Confusion often arises between holding gain constant versus holding physical size constant.

Step-by-Step Solution:
FSPL (linear) = (4 * pi * R * f / c)^2 ⇒ increases as f^2 and R^2.Received power Pr ∝ Pt * Gt * Gr / FSPL.For fixed frequency, increasing A_e,t and A_e,r increases G and raises Pr, effectively reducing link loss.For fixed gains and f, Pr falls as 1/R^2; thus link loss grows as R^2.Therefore, any statement claiming link loss is inversely proportional to f^2 for fixed apertures is incorrect.

Verification / Alternative check:
Using the Friis equation in linear form, Pr = Pt * Gt * Gr * (lambda / (4 * pi * R))^2. Since lambda = c/f, higher f reduces (lambda)^2 term, lowering Pr if gains are held constant.

Why Other Options Are Wrong:
Option B: Correct: Pr grows with A_e,t * A_e,r at fixed f, so effective link loss falls.
Option C: Correct: Higher gain reduces required Pt for the same Pr.
Option D: Correct: FSPL grows as R^2.
Option E: Incorrect as a general rule; downlink loss is not inherently negligible and depends on EIRP, G/T, and frequency bands.

Common Pitfalls:
Mixing up fixed-aperture versus fixed-gain scenarios; forgetting that higher frequency also allows higher gain for a given physical size.

Final Answer:
For fixed antenna sizes (physical apertures), free-space path loss increases with frequency approximately as f^2, not decreases.