In this tutorial, we’ll explore three phenomena that can impact the propagation of radio frequency (RF) waves: refraction, scattering, and diffraction. These concepts are essential for understanding how RF signals behave in various environments, particularly in outdoor and indoor wireless setups.

Refraction

What is Refraction?

Refraction occurs when an RF wave changes direction as it passes through a medium. Imagine a wave traveling in one direction; as it encounters a new medium, it bends, altering its original path.

Think of it like this: if you place a pencil in a glass of water, it appears bent. This effect occurs because light waves from the pencil refract, or bend, as they travel from water to air. Similarly, RF waves experience refraction when they encounter different materials.

Refraction in Wireless Communication

• Outdoor Links: In outdoor scenarios, refraction can cause RF signals to bend toward or away from Earth, affecting the signal’s reach.
• Indoor Links: Indoors, glass materials like doors or windows can cause refraction. However, with modern MIMO (Multiple Input, Multiple Output) technology, refraction is often mitigated, making it less of an issue for indoor links.

The main takeaway is that when an RF signal encounters a medium, it refracts, changing its angle compared to the original path. This effect can lead to altered signal behavior, particularly in environments with varied surfaces.

Scattering

What is Scattering?

Scattering can be thought of as multiple reflections. When an RF signal encounters an uneven surface, it splits into several scattered waves, dispersing the original signal.

In essence, scattering occurs when RF waves hit reflective objects with uneven surfaces or small wavelengths, resulting in dispersed, scattered signals.

Types of Scattering

• Significant Scattering: Occurs when RF waves hit uneven surfaces like tree foliage, fences, or wall mesh, which results in signal attenuation (weakening) at the receiver. This type of scattering is disruptive to the signal.
• Insignificant Scattering: Happens when RF waves pass through media like smoke or sandstorms. In these cases, scattering may occur, but the signal typically remains strong enough to reach the receiver without significant loss.

Key Point: Scattering disrupts the original signal by creating multiple reflections, which can cause attenuation depending on the environment and surface characteristics.

Diffraction

What is Diffraction?

Diffraction occurs when an RF wave encounters an obstacle, like a building or a hill, and bends around it. This phenomenon is different from refraction; rather than passing through a medium, the wave changes direction as it wraps around the obstacle.

Visualizing Diffraction

Imagine throwing a rock into a pool of water. The impact creates ripples (waves) that move outward. If these ripples encounter a stick in the water, they bend around it rather than passing straight through. The larger the stick, the greater the diffraction effect.

In RF propagation, a similar process occurs. When a signal hits a large obstacle, it bends around it, continuing in a new direction. The larger the obstacle, the more pronounced the diffraction effect.

 

Summary

In this lesson, we discussed three key phenomena that can influence RF propagation:

1. Refraction – Bending of RF waves as they pass through different mediums.
2. Scattering – Dispersion of RF waves into multiple reflections upon hitting uneven surfaces.
3. Diffraction – Bending of RF waves around obstacles, changing the signal’s direction.