A waveguide is a structure that borders and conveys electromagnetic waves within a path between two ends. Therefore, it is about a transmission medium for guided propagation.
The waveguides are used in the radar, radio links, phone repeaters, artificial satellites scopes and wherever, in general, extremely high frequency signals are to be transported.
Insights
In the microwave range a waveguide is in general made like a hollow metal tube with a rectangular, circular or elliptical section. It is possible that the guide be filled with a dielectic material.
Intuitively, the electromagnetic field is confined through “reflection” on the walls of the waveguide.
In the rectangular guides, whose dimensions are now normalized, the longer side A is twice the length of the shorter side B. The frequencies that can propagate in the guides must be greater than a minimum value, known as lower cut off frequency, that depends on the size of the longer side A of
the guide.
In the field of optical frequencies, waveguides are made with dielectric (non conductive) material.
They consist in a denser core lined with a less dense “shell” (cladding). The light is confined in the core through reflection on the discontinuity surface.
In integrated optics, the waveguide represents the basic element that is combined to obtain more complex functions. There are several technologies that differ mainly on the basis of the substrate and of the technique used to obtain the local increase in the refractive index.
Bibliography
http://web.tiscali.it/lukecondor/Le%20Guide%20d%27onda
htm https://it.wikipedia.org/wiki/Guida_d%27onda
