2. Electromagnetic cavities

An electromagnetic cavity is an empty or dielectric-filled volume, bounded by walls of either the electrical type (interface with a conductor) or the magnetic type (interface with a high-permittivity dielectric). The former is a metallic cavity, the latter a dielectric resonator.

In principle, the cavities can have any geometric shape, but in practice they are cylindrical or parallelepipedic. Metal cavities can thus be obtained by closing rectangular or circular waveguides with metal plates perpendicular to the longitudinal axis of the guide.

If an electromagnetic field is excited inside a cavity by an appropriate means (such as an electric or magnetic antenna), standing waves can be generated when resonance conditions exist. The cavity then stores a certain amount of electromagnetic energy.

By studying the resonance...