Radar System Engineering

344 THE MAGNETRON AND THE PULSER [SEC. 10.5
outputs of 600, 200, 80, and 0.025 kw. The single anode block at the
bottom is from a 1.2-cm 80-kw rising-sun magnetron. Figure 1020
shows one variety of a high-power (1000-kw output) magnetron. This
design has a rather long anode with heavy double-ring straps and a
coaxial output.
FIC+.1O.2O.—Ahigh-power magnetron (type 720); 10 cm, 1000-kwpulee power output.
(Courtesyof Bell Telephone Laboratories,)
Average Power.—In Sec. 10.2 it was stated that the cathodes of oscillating
magnetrons are subjected to back bombardment by some of the
electrons in the surrounding space charge. This bombardment produces
heating of the cathode surface which amounts to about 5 per cent of the
average power input to the magnetron. If this back-bombardment
power exceeds the normal heater power of the cathode (which is frequently
turned off while the magnetron is oscillating) abnormally short
tube life results. Back bombardment usually limits the average power
output. This limit can be raised by designing cathodes with very large
thermal dissipation, but the average power of magnetrons designed for
radar use rarely exceeds 0.2 per cent of the pulse power output. Table