Radar Horizon Calculator

What Is the Radar Horizon?

The radar horizon is the maximum distance at which a radar can see a target limited by Earth's curvature. Higher antennas see farther because the line of sight clears more of the globe. Aviation early-warning aircraft exploit this by flying at high altitude.

Radar Horizon Formula

For antenna height $h$ in meters, a common approximation with standard atmospheric refraction is:

$$d \approx 4.12 \sqrt{h}$$

where $d$ is horizon distance in kilometers. Without refraction the coefficient is about 3.57. The exact form uses Earth radius $R_E$:

$$d = \sqrt{2 \times \frac{4}{3} \times R_E \times h}$$

Maximum detection range to a target at height $h_t$ is the sum of radar horizon and target visibility distances.

Frequently Asked Questions

Why use the 4/3 Earth radius correction?

Atmospheric refraction bends radio waves slightly downward, making the effective horizon farther than pure geometry predicts. Multiplying Earth radius by 4/3 models this effect.

What is the simple formula for radar horizon?

With refraction, d ≈ 4.12 × √h km where h is antenna height in meters. Without refraction, use 3.57 × √h instead.

How does target height affect detection range?

A higher target adds its own visibility distance. Total range equals radar horizon plus target horizon distances.

Why do AWACS aircraft carry radars?

Flying at roughly 9 km altitude extends radar horizon to about 400 km, far beyond ground-based stations limited to tens of kilometers.

What is the clutter zone?

Near the surface, ground returns and atmospheric turbulence create false echoes. Low-flying targets can hide in this region below the clean detection zone.

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What Is the Radar Horizon?

Radar Horizon Formula

Frequently Asked Questions

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