
Frequency standards 475
FIGURE 7.9
Basic sapphire-loaded cavity design. The sapphire cylinder (typical size: diameter 3-5 cm,
height 1-3 cm) is suspended in the metal c avity. Radio fre quency energ y is coupled into
and out of the resonator via magnetic loop pro bes. Top and bottom illustrations indicate,
respectively, the total internal reflection and field pattern for the TE
5,5,δ
mode. (Courtesy
of [655].)
A major difficulty e ncountered with s apphire WG-mode resonators is represented by
the high sensitivity to thermal fluctuations, which originates from the heavy temperature
dependence of the sapphire permittivity. To overcome this drawback, a few temper ...