An antenna is a device that transmits and receives electromagnetic waves.

It's an interface between a wave traveling in a cable and flying through the air.

It's also important to understand that antennas work in both directions.

You can't have an antenna that only receives or only transmits.

Electromagnetic waves have an electrical and a magnetic component.

Two basic properties of a wave are frequency and wavelength.

Frequency says how many times a wave repeats its shape per second.

Wavelength is the distance over which the wave repeats a shape.

For example at 10 gigahertz the wavelength is roughly 30 millimeters long.

At 5 gigahertz it's roughly 60 millimeters long and at 2.4 gigahertz it's roughly 120 millimeters long and so on.

So how does an antenna work?

In order to explain that we need to break it down into the two most common types of antenna categories.

Resonant and Aperture Antennas, as the name suggests, function on the principle of resonance.

When an antenna resonates it radiates the signal that's fed to it.

The simplest example of a resonant antenna is a wire or a dipole.

The length of the dipole has to be equal to at least half of the signal wavelength in order for it to work.

This means that the radiation properties and bandwidth, which is usually quite narrow, depend on the size of the antenna.

Some examples of antennas based on resonant elements are patches, loops, and yaggies.

Aperture antennas radiate electromagnetic waves through an opening.

An example of Aperture antennas would be a horn.

The radiation diagram of an Aperture antenna depends on the size and the shape of the Aperture, but their bandwidth of operation depends on the size and the shape of the feeding structure.

This is why the radiation properties and performance of horn antennas are very stable over a very wide band.

The main parameters of an antenna are the frequency range, the shape of its radiation pattern, and its gain.

So we'll talk about some of these topics in our next video.