Tower mounted transmission lines are exposed to weather, and will degrade over time.
Without FDR techniques, the “Fix after Failure” philosophy becomes the only alternative.
Sunlight exposure can change the dielectric properties of the antenna housing, causing the antenna bandwidth to drift.
Antennas and transmission lines used on-board ships and aircraft may be degraded due to salt water corrosion.
The attenuation per foot or meter for the cable is also required in order to compensate for the attenuation versus distance.
Likewise the cutoff frequency and waveguide loss are required for DTF, measurements of waveguide transmission lines.