Multipath Fade Margin Calculator
Calculate required fade margin for microwave link reliability against multipath fading.
Typical Fade Margins by Path
| Path Length | 99.99% | 99.999% | Notes |
|---|---|---|---|
| 10 km | 20-25 dB | 30-35 dB | Short path |
| 30 km | 30-35 dB | 40-45 dB | Typical |
| 50 km | 35-42 dB | 45-50 dB | Long path |
| Over water | +5-10 dB | +5-10 dB | Additional margin |
Multipath Fading Theory
Vigants-Barnett Model
P_outage = C * f * d^3 * 10^(-FM/10)
FM = 10 * log10(C * f * d^3 / P_target)
Where f = frequency (GHz), d = distance (km), C = geoclimatic factor
FM = 10 * log10(C * f * d^3 / P_target)
Where f = frequency (GHz), d = distance (km), C = geoclimatic factor
Multipath fading occurs when signals arrive via multiple paths (reflections) and interfere. Deep fades require adequate margin for reliable links.
Design Guidelines
- Path diversity: Space/frequency diversity for critical links
- Over-water paths: Add 5-10 dB extra margin
- Tropical regions: Higher C factors needed
- Short paths: Less susceptible to multipath
- Higher frequencies: More fading, need more margin