c. The echo box is also used to check transmitter power and the
receiver sensitivity. Now let's look at some other applications of resonant
cavities.
27. A magnetron contains resonant cavities.
a. A magnetron is an electronic component used as a microwave
A magnetron is basically a diode tube containing a series of
resonant cavities which are excited by a rectangular pulse. The oscillating
frequency of the magnetron depends upon the size of the cavities. Part A of
Figure 83 is a picture of a typical magnetron with its interior exposed.
b. You see in Part A of Figure 83, the eight cylindrical resonant
cavities that determine the magnetron oscillating frequency.
Plungers in
the cavities are used to tune the magnetron to the desired frequency.
Notice also the loop in the cavity on the left-hand side of the magnetron.
The loop couples energy from the magnetron to the transmission line that
feeds the antenna. You will learn more about magnetrons a little later in
the course.
c. The local oscillator in a radar receiver is also a microwave
generator that has a resonant cavity. The tube in this circuit is called a
klystron.
Figure 83. Interior of Typical
Magnetron and Klystron Tube.
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