Distance Ratio Squared describes the energy coupling into a building as distance changes.

• A. Increases with distance
• B. Decreases with the square of the distance
• C. Remains constant
• D. Increases with distance squared

Answer: (B)

Distance affects how energy from a transmitter reaches a building through the inverse-square law: the power density of the radiated energy falls off with the square of the distance. As energy spreads over a larger spherical surface with increasing distance, the amount available to couple into the building’s aperture decreases proportionally to 1/d^2. That means if you move the source twice as far away, the energy that actually couples into the building drops to one-quarter; three times farther gives one-ninth, and so on. This basic relationship holds in open, unobstructed space in the far field, with real-world factors like reflections or antenna gains adjusting absolute levels but not the fundamental d^2 scaling.