Figure 2-36.Inductive magnetron tuning.
The insertion of an element (ring) into the cavity slot, as shown in figure 2-37, increases the slot
capacitance and decreases the resonant frequency. Because the gap is narrowed in width, the breakdown
voltage is lowered. Therefore, capacitively tuned magnetrons must be operated with low voltages and at
low-power outputs. The type of capacitive tuner illustrated in figure 2-37 is called a COOKIE-CUTTER
TUNER. It consists of a metal ring inserted between the two rings of a double-strapped magnetron, which
serves to increase the strap capacitance. Because of the mechanical and voltage breakdown problems
associated with the cookie-cutter tuner, it is more suitable for use at longer wavelengths. Both the
capacitance and inductance tuners described are symmetrical; that is, each cavity is affected in the same
manner, and the pi mode is preserved.
Figure 2-37.Capacitive magnetron tuning.