Radar System Engineering

SEC. 10.5] MAGNETRON CHARACTERISTICS 351
promise between efficiency and frequency stability and this compromise
is arrived at from a study of the Rieke diagram.
It is possible in some cases to combine with the magnetron proper a
high-Q cavity coupled to it in such a way as to reduce the pulling figure
by a large amount with little or no loss in efficiency. The ratio of the
pulling figures with and without the high-Q cavity for equivalent operating
conditions is called the “stabilization factor, ” which may be as large
as 10 but is usually between 2 and 5. The addition of this stabilizing
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FIG. 10.24.—Characteristicsof the 4J70 series.
Magnetic field = 2700gauss
Pulse current = 70 amp
Pulse duration = 0.8psec
PRF = 400ppS.
cavity has the disadvantage, however, of reducing the tuning range of
the magnetron; further, it may aggravate mode instabilities. If constant-frequency
operation is required, stabilized magnetrons should be
seriously considered.
Frequency stabilization has been incorporated into only a few magnetrons.
A good example is the 2J41, which has a pulse power output of
500 watts at 9310 Me/see and a pulling figure of 1.5 Me/see with a
tuning range of 0.7 per cent. The stabilization factor is 10. The 10-cm
series 4J70 to 4J77 is stabilized by a factor of 1.5 and the 1.25-cm 3J21
by a factor of 2. High-power magnetrons with high stabilization have
not been deveIoped.
Weight.—The development of airborne radar placed great emphasis
on the reduction in weight of all components. As a result, magnetronmagnet
combinations were produced in which every effort was made to
reduce the total weight. This development has been so successful, particularly
for the higher-frequency magnetrons, that the weight of a