Fresnel Zone Calculator: Zone Radius and Clearance for a Radio or Microwave Link

How much clear space a radio link needs around the straight line.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Enter the frequency of the link.

Enter the distance from each end to the point you are checking.

The calculator gives the zone radius and the clearance needed.

Formulas used

  • \lambda = \frac{c}{f}
  • r_n = \sqrt{\frac{n\lambda d_1d_2}{d_1 + d_2}}
  • r_{max} = \sqrt{\frac{n\lambda D}{4}}

Worked example

With the default numbers in the calculator above:

  1. Wavelength: 0.0599585 m
  2. Radius of the zone at the point: 12.2432 m
  3. Largest radius, at the middle of the link: 12.2432 m
  4. Clearance needed at the point (60 percent of the first zone): 7.3459 m
  5. Length of the link: 10 km

Change the numbers in the calculator to see the full working, every step, for your own case.

Common questions

What is the Fresnel zone?

The ellipse-shaped region around the straight line between two antennas where obstacles affect the signal.

How much of the zone should be clear?

At least 60 percent of the first zone, as a rule for microwave links.

Where is the zone widest?

At the middle of the link.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any radio or microwave link design text (Fresnel zones).

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