Let's talk about some basic concepts in electromagnetic wave propagation.

It can help you understand some of the phenomena we might encounter when working with antennas.

The first fundamental concept is the Huygens principle.

It simply states that every point on a wavefront can be considered as a source of new spherical waves.

The envelope of these waves become new wavefronts.

This is particularly useful when explaining our next concept, diffraction.

Diffraction is the bending of waves around obstacles or the spreading of waves when they pass through narrow openings.

Using the Huygens principle can be visualized like this.

When a wave enters an opening, it becomes a new source of spherical waves, and it seems like the original wave was spread out.

Diffraction is best observed when the size of the opening is comparable to the wavelength of the wave.

When we make the opening larger, the effect is still there, but much less dominant.

Let's move on to absorption.

Absorption occurs when the energy of an electromagnetic wave is taken up by the material the wave is passing through.

The electromagnetic wave interacts with the atoms in the material, and their energy is converted into other forms, typically heat.

In general, as the frequency of the wave increases, so does the absorption.

Also, different materials have varying degrees of absorption, so the choice of material depends on the application.

When selecting materials for pigtails and ray domes, we aim for the lowest absorption.

While for RF absorbers used in anechoic chambers, we aim for the highest.

Any transition between materials causes at least some of the electromagnetic energy to reflect.

The law of reflection states that the angle in which the wave hits the boundary is equal to the angle at which it is reflected.

This may be desired when designing antennas such as parabolic dishes, or it can be a cause of great concern when designing a ray dome where the signal reflected back into the antenna should be as low as possible.

So these were some basics of wave propagation.

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