Radar System Engineering

384 THE MAGNETRON AND THE PULSER [SEC.10.11
10.11. Miscellaneous Components. Pulse Transformers.—The development
of pulse switching tubes and of pulse loads has proceeded so
independently that usually there is little correlation between the optimum
impedance levels for best operation of these two devices. Fortunately,
satisfactory pulse transformers are available to match the impedance of
the load to that of the generator. While the elementary theory of the
pulse transformer is quite manageable, great care in design must be
exercised to preserve good wave shape with fast rates of rise, a minimum
of extraneous oscillation, and high efficiency. The ideal transformer is
shown in Fig. 10.45a; Fig. 10.45b shows the equivalent circuit of a practical
transformer (all values referred to the secondary or high-voltage
Low-voltage
end
High-voltage
end
:~~[, ;q-R[L
(a)
FIG. 10.45.—Puke transformer circuit diagram.
np RL
(.) Ideal transformer;~ = ‘; ~ = –; — = U ,
np IP n, Zo () nP
(b) Equivalent circptitof pulsetransformer.
end), exhibiting the effects of departure from the ideal case. The
symbols shown in Fig. 10.45 are defined as follows:
L1 = leakage inductance due to flux from primary current which
fails to link with secondary and represents effect of magnetic
energy stored between windings by load current.
C. = effect of electrostatic energy stored in the primary-secondary
distributed capacity. If transformer is pulsed from low-voltage
end CD must be charged through Lt.
L. = “squirted inductance” arising from nonuniform current distribution
due to the charging of Cm Current charging CDmust
HOW through L..
Cc = effect of electrostatic energy stored between primary and core.
L c = effect of magnetic energy stored in “squirted flux” which comes
from nonuniform current in primary coil arising from the
charging of Cc.
L. = effective shunt or self-inductance (input inductance with open
circuit secondary).
R. = resistance due to eddy current in iron and to hysteresis.
A good pulse transformer design attempts to maximize the shunt
inductance L. and minimize the leakage inductance L1. In addition,
undesirable oscillations arising from the series resonant circuits shown at
(b)