Antenas & Propagación, RF & Microwaves

Calculadora de Zona de Fresnel

Calcule el radio y la altura de limpieza de la zona de Fresnel con nuestra herramienta en línea gratuita. Asegure una fuerza de señal inalámbrica óptima evitando obstrucciones en su ruta de RF.

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Frequency (MHz)

Distance (km)

Desired Clearance (%)

What Are Fresnel Zones?

The **Fresnel Zone** is a series of concentric elliptical regions surrounding the direct line-of-sight path between a transmitter and a receiver. It's a critical concept in wireless communication because it helps us understand how radio waves propagate and ensures a strong signal. When an object, like a building, tree, or hill, obstructs this zone, it can cause signal attenuation or loss. The first Fresnel zone, which is the most important, contains about 90% of the energy from the radiated signal.

For optimal signal strength, the first Fresnel zone should be at least 60% clear of all obstructions. Without proper clearance, radio waves can reflect and cancel each other out, leading to severe signal degradation. This phenomenon, known as signal attenuation, can turn a clear line-of-sight path into a non-functional one.

Fresnel Zone Calculations and Formulas

The radius of the first Fresnel zone ($F_1$) can be calculated using the following formula:

$$ F_1 = 17.32 \sqrt{\frac{d}{4f}} $$

Where:

$F_1$ is the radius of the first Fresnel zone in meters.
$d$ is the distance between the antennas in kilometers.
$f$ is the frequency of the signal in gigahertz (GHz).

Example Calculation

Let's calculate the 1st Fresnel Zone for a link with a frequency of **5 GHz** and a distance of **2 km**. Since the formula uses frequency in GHz, we use $f=5$.

$$ F_1 = 17.32 \sqrt{\frac{2}{4 \times 5}} = 17.32 \sqrt{\frac{2}{20}} = 17.32 \sqrt{0.1} \approx 5.48 \text{ meters} $$

Common Issues and Solutions

Improper Fresnel zone clearance is a leading cause of poor wireless performance. Here are some common issues and how to solve them:

Signal Loss & Attenuation: Obstructions can cause signal power to drop significantly, even with a clear line of sight.
Solution: Raise the antenna height or relocate the antennas to achieve the necessary clearance.
Multipath Interference: Reflections from objects in the Fresnel zone can arrive at the receiver slightly out of phase, leading to signal cancellation.
Solution: Ensure the Fresnel zone is at least 60% clear, or even 80% for critical links, to minimize reflections.
Increased Packet Loss: This is a common symptom of a blocked Fresnel zone.
Solution: Use a higher frequency antenna, which has a smaller Fresnel zone, or re-engineer the link path.