Radar System Engineering

376 THE MAGNETRON AND THE PULSER [SEC. 10.10
been overcome. Perhaps TiOz, or some similar material of high dlelectnc
constant, will find wide use outside the low-voltage field.
Another promising approach to the condenser design problem is the
electrochemical formation of very thin insulating films on metal (such
as those employed in the electrolytic condenser) on which a layer of metal
is then deposited, High capacity per unit area results from the very
small spacing, but the insulating film must be able to withstand the
extremely high field strengths thus imposed.
Further attention to the details of mechanical design of condenser
fittings-containers, bushings, connectors, and the like—is also required.
using conventional dielectrics can
still be considerably r e d u c e d.
Figure 10.38a shows typical pulseforming
networks, the ratings for
which are given in Table 10.6.
Figure 10.38b shows a network
used in an experimental 20-Mw
pulser, the largest designed at
Radiation Laboratory. Two of
the smallest networks used are
shown for size comparison: the one
on the left has a rating of 5 kw
pulse power output; the other one is electrically equivalent to the network
(1) of Fig. 10.38a, but uses
Diaplex insulation.
The network designer has control
of pulse length and impedance
level independently of one another.
The pulse length is ordinarily
fixed by the nature of the
application, while the impedance
level is chosen to fit the characteristics
of the load, the switching
tube, and the power supply. A
pulse transformer can be inserted FIG. 10.38b.—Experimental pulse-forming
between load and pulse-forming
network.
network so that the network can be designed to use the available switching
device most efficiently. Once the pulse power output is settled and the
appropriate switching tube chosen, 20 can be determined from one of the
relations P = I; “ZO or P = V~/ZO. Usually either I, or V, is definitely
limibed for a given switch; this indicates the appropriate relation to use
in calculating Zo. It must be remembered that the voltage across the
pulse network (and hence across the switch) is twice the voltage delivered
to a matched load.