Figure 39. Electric and magnetic field combination for alternate half-cycles in high-power klystron cavity.
1-40. ENERGY
SOURCES
FOR
CAVITY
cavity wall. Because of its shape, the loop acts like
EXCITATION
the primary circuit of an ordinary transformer.
Cavity excitation means that you provide
c. The ordinary transformer transfers
electrical energy to cause oscillating electric and
energy from its primary to its secondary circuit by
magnetic fields within the resonant cavity. Both
magnetic induction. Loop coupling uses the same
alternating current (ac) and direct current (dc)
principle. The energy gets from the loop to the inner
energy is required. The ac is usually microwave
wall of the cavity by magnetic induction.
(RF) power because it is already ultrahigh frequency
power when fed into the cavity. The dc is
commonly called beam energy because it is the
energy supplied to the cavity by the electron beam
focused through the drift tube.
1-41. CAVITY
EXCITATION
WITH
MICROWAVE POWER
a. There are several ways to excite the
cavity with ac (microwave) power. Some examples
are by loop coupling, probe coupling, and
waveguide or window coupling. In this text, we will
use the loop coupling method.
b. You can easily recognize when the
cavity is using loop coupling for its input (or
output), because the loop connects to a jack on one
of the cavities' four narrow walls, as shown in figure
40. The loop is simply the end of the inner
Figure 40. Coupling loop connects to jack on
conductor of an input line, bent and fastened to the
cavity's narrow wall.
344 L1
40
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