The design point: Fresnel zones are ellipsoidal regions around a line-of-sight radio path where obstruction changes phase and can reinforce or cancel the received field; the first zone is most important for clearance.
Why the complete system matters
Its radius grows near the path midpoint and with wavelength and distance. A visually unobstructed straight line can still lose signal if terrain or structures intrude deeply into the first zone.
The assumption that breaks it
Treating line of sight as a zero-width ray leads to optimistic VHF/UHF and microwave links, while demanding 100 percent clearance may be impractical.
Build or deploy it correctly
Calculate the first-zone profile for the exact frequency and endpoints, include Earth curvature and terrain, aim for the required percentage clearance, and verify with path measurements.
Configuration boundary
Use the exact product guide, electrical topology, geometry, materials, loading, feed, return path, support, and environment. Mechanical fit or a visually similar arrangement does not establish electrical equivalence.
