What is a Fresnel zone?

A Fresnel zone is an ellipsoidal region around the direct line-of-sight path between two antennas. Obstructions inside this zone cause signal diffraction and reduce link quality. The 1st Fresnel zone is the most critical — 60% clearance of its radius is the minimum recommended.

Why does frequency affect the Fresnel zone size?

Lower frequencies have longer wavelengths, which create larger Fresnel zones. A 900 MHz link requires more vertical clearance than a 5.8 GHz link over the same distance.

What happens if the Fresnel zone is obstructed?

Obstructions inside the 1st Fresnel zone cause signal diffraction, increasing path loss. Full obstruction can add 20 dB or more of extra loss, severely degrading the link.

What is the formula used?

The nth Fresnel zone radius at a point is r = sqrt(n × λ × d1 × d2 / (d1 + d2)), where λ is the wavelength, d1 is the distance from antenna 1 to the point, and d2 is the distance from the point to antenna 2.

Should I calculate the midpoint or the obstruction point?

The Fresnel zone is largest at the midpoint of the path. If you have a known obstruction (building, ridge), enter its actual distance from one end to find the exact clearance needed at that location.

Fresnel Zone Calculator

Name: Fresnel Zone Calculator
Availability: InStock
Author: Nham Vu

Enter frequency and link distances to find the Fresnel zone radius at any point along a wireless path.

Link Parameters

Frequency

Total Path Length

Distance from Antenna 1 to Point (obstruction or midpoint)

Must be less than the total path length.

Fresnel Zone Number (n)

Clearance Guide

≥ 60% of r1 — minimum for reliable link

100% of r1 — fully clear, optimal performance

< 60% of r1 — significant diffraction loss expected

Summary

Enter frequency and link distances to find the Fresnel zone radius at any point along a wireless path.

How it works

Enter the radio link frequency in MHz or GHz.
Enter the total path length between the two antennas.
Enter the distance from one antenna to the obstruction point.
Select which Fresnel zone number to calculate (1st is most common).
Read the zone radius — antennas must clear this by at least 60% of the 1st zone radius.

Use cases

Planning point-to-point Wi-Fi or microwave backhaul links.
Determining minimum antenna height above terrain or obstacles.
Checking whether trees, buildings, or hills will impair a link.
Verifying clearance for licensed microwave or unlicensed 5 GHz links.
Teaching RF propagation concepts in networking courses.
Pre-survey analysis before deploying outdoor access points.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu