How does RF LOS differ from visual LOS?

How does RF LOS differ from visual LOS?

• A. RF LOS does not require line of sight.
• B. RF LOS is accompanied by a Fresnel zone, a series of concentric ellipsoid-shaped areas around the visual LOS path.
• C. RF LOS and visual LOS are identical concepts.
• D. RF LOS is only relevant for microwave frequencies.

Answer: (B)

Radio waves don’t travel as a single narrow line; they occupy a volume around the straight path between transmitter and receiver. This volume is described by the Fresnel zones, with the first Fresnel zone being the most important. Obstructions inside that zone cause diffraction, which can weaken or disrupt the signal even if the direct line of sight looks clear. Visual line of sight is simply whether the two points have an unobstructed straight path. RF line of sight, however, accounts for the space around that path—the Fresnel zone—because it directly affects signal quality. That’s why describing RF LOS as being accompanied by a Fresnel zone around the visual LOS path best captures how RF propagation works. If something intrudes into the first Fresnel zone, you can expect diffraction losses and degraded link performance.