Fresnel Zone Calculator

Calculate Fresnel zone radius at the midpoint of an RF line-of-sight link. Determine required clearance above obstructions for reliable microwave and WiFi links.

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Formula

r_n = \sqrt{\frac{n \lambda d_1 d_2}{d_1 + d_2}}

r_n — nth Fresnel zone radius (m)

n — Zone number

λ — Wavelength (m)

d1, d2 — Distances from endpoints to midpoint (m)

How It Works

The Fresnel zone represents an elliptical region around the optical path between a transmitter and receiver in wireless communications and radio wave propagation. It describes the area where reflected signals can interfere with the direct signal path, potentially causing signal degradation. The Fresnel zone calculation helps engineers determine the clearance needed to minimize signal obstruction and diffraction loss.

Worked Example

Problem: Calculate the first Fresnel zone radius for a wireless link at 2.4 GHz with a total path length of 10 km Solution: 1. Calculate wavelength: λ = c/f = (3 × 10^8) / (2.4 × 10^9) = 0.125 m 2. Total distance = 10 km, so d1 = d2 = 5 km 3. First Fresnel zone radius: r1 = √(λ·d/4) = √(0.125 × 10000 / 4) = 17.68 m

Practical Tips

✓Ensure at least 60% of the first Fresnel zone is clear of obstructions
✓Consider terrain profile when designing wireless links
✓Use higher frequencies for shorter wavelengths and smaller Fresnel zones

Common Mistakes

✗Neglecting Fresnel zone clearance in radio link design
✗Using incorrect wavelength calculation
✗Forgetting to account for terrain obstacles

Frequently Asked Questions

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