Radar System Engineering

SEC.10.2] THE RESONANT SYSTEM 325
magnetron with radial cathode supports. Another type of magnetron
construction, favored for the higher-frequency magnetrons where magnet
weight is of importance, is shown in Fig. 10.4b. The construction of such
a magnetron-magnet combination, or “ packaged magnetron” as it is
frequently called, is shown in Fig. 10.5. The cathode is usually supported
axially through iron pole pieces which extend quite close to the
IWa. 1O.4.—TWO types of magnetron construction: (a) radial cathode and separate magnet;
(b) axial cathode with attached magnet.
anode and thus reduce the magnetic field gap. Since the weight of a
magnet which will produce a given magnetic field strength over a given
cross-sectional area increases very rapidly with the length of the gap,
considerable magnet weight can be saved in this manner. It is customary
to supply this type of magnetron permanently attached to its magnet.
10.2. The Resonant System.—In an operating magnetron the charge
distribution in the resonant system produces electric fields which interact
with the space charge in such a way as to sustain the oscillations. Figure
10.6cz illustrates such a disposition of charge and electric field at ap
instant when the concentration of charge on the ends of the anode seg-