7. Gallery modes

The higher the frequency, the smaller the resonator dimensions become. For example, at 30 GHz, the diameter of a resonator with relative permittivity 9, such as sapphire, is around 3 mm. With cylindrical resonators, we then use modes of higher order than the fundamental mode TE _{01 δ} , known as gallery modes, because the energy is confined to the periphery of the resonator . They are denoted ${\text{WGM}}_{\text{nm}}$