Fresnel Distance Calculator
Calculate Fresnel zone distance or radius for wireless communication links. Essential for signal clearance planning in WiFi, radio, and satellite communications.
Link Parameters
Wireless frequency (e.g., 2.4 GHz for WiFi)
Distance between transmitter and receiver
Fresnel Zone Radius
Enter frequency and distance to calculate the Fresnel zone radius
What Is Fresnel Distance?
When wireless signals travel between two points, they don't follow a straight line. Instead, they spread out in what's called the Fresnel zone - an elliptical area around the direct line of sight. The Fresnel distance or radius tells you how much clear space you need around that signal path.
If something blocks the Fresnel zone - like a tree, building, or even the ground - your signal gets weaker. Network engineers, WiFi installers, and radio operators all need to know about Fresnel zones to make sure their links work properly.
It's like having a clear tunnel for your signal, not just a straight line.
Fresnel Distance Formula
First Fresnel Zone Radius Formula
Fresnel Zone Radius (F₁) = √[(λ × d₁ × d₂) ÷ (d₁ + d₂)]
For equal distances from transmitter and receiver (d₁ = d₂ = d/2):
F₁ = √[(λ × d) ÷ 4]
Where:
- • λ (lambda): Wavelength = speed of light ÷ frequency
- • d₁, d₂: Distances from midpoint to transmitter/receiver
- • d: Total link distance
Example: 2.4 GHz over 1 km link
F₁ = √[(0.125 m × 1 km) ÷ 4] = 5.6 meters
Fresnel Zone Examples
Common Wireless Frequencies
| Frequency (GHz) | Distance (km) | Fresnel Radius (m) | Use Case |
|---|---|---|---|
| 2.4 | 1 | 5.6 | WiFi 2.4GHz |
| 5.8 | 2 | 4.8 | WiFi 5.8GHz |
| 1.0 | 3 | 12.3 | Radio links |
| 0.9 | 5 | 16.7 | Long-range radio |
Higher frequencies require smaller Fresnel zones. Longer distances need larger clearance areas.
Wireless Signal FAQs
How much Fresnel clearance do I need?
60% clearance is typically recommended. This means obstacles should not block more than 40% of the Fresnel zone radius.
Does ground affect Fresnel zones?
Yes, the ground can reflect signals or absorb them. Antennas should be high enough to clear ground-level Fresnel zones.
Why do higher frequencies need less clearance?
Higher frequencies have shorter wavelengths, so their Fresnel zones are smaller and less susceptible to obstacles.