Radar System Engineering

350 THE MAGNETRON AND THE PULSER [SEC. 105
is presented to the magnetron and varied in phase over at least a full half cycle
(see Fig. 10”17). The VSWR of-1.5 was selected for this definition since
it is in the range usually encountered in radar systems. Pulling figures
for magnetrons with comparable loading increase with frequency, since
the same fractional change in frequency corresponds to a larger number
FIG. 10.23.—M.agnetronwith unsymmetricaltuning cavity.
d
of megacycles at higher frequencies. Thus, similar magnetrons at 3000,
10,000, and 30,000 Me/see would have pulling figures of, say, 5, 16, and
50 Me/see. Since receiver bandwidth is not changed substantially as
the radar frequency increases, frequency stability becomes a more
important consideration at shorter wavelengths.
The effect of loading on frequency stability and methods of obtaining
various loadings have been considered in Sec. 10.4. As stated there, the
requirements of any system usually make necessary some sort of com-