Radar System Engineering

336 THE MAGNETRON AND THE P ULSER [SEC. 10.4
anode segments and thus transferring charge from the cathode to the
anode.
The r-f current set up in the oscillators isprincipally a displacement
current produced by this rotating space charge. As the spokes of the
negative space charge pass in front of an anode segment, a positive charge
is induced on its surface. Half a period later, this positive charge has
flowed around the back of the two adjacent oscillators to the two adj scent
anode segments and the spoke of the space charge has rotated to a position
in front of the next anode segment.
In addition to these displacement currents, conduction currents are
produced by the flow of electrons from space charge to the anode. Electrons
arrive at the anode at such a time as to constitute a conduction
current approximately 90° out of phase with the r-f voltage, and thus
have little effect on the oscillations.
10.4. Performance Charts and Rieke Diagrams.-Four parameters
determine the operation of the magnetron; two are associated with the
input circuit, and two with the output circuit. A typical set is H, I, G,
and B. H is the magnetic field, 1 is the anode current, and G and B are
the real and the imaginary parts of the r-f load on the magnetron measured
at some arbitrary point in the output line. The observed quantities
are three in number, usually power P, wavelength A, and voltage V.
The problem of presenting these observed quantities in terms of the four
parameters is greatly simplified by the fact that the input and output
parameters operate nearly independently of one another. Thus, it is
possible to keep G and B (the load) fixed, and study the effect of H and 1
on P, k, and V withthe assurance that the nature of the results will not
be greatly altered by changes in G and B. Conversely, H and 1 may be
fixed and the effect of G and B on P, A, and V observed. As a result of
this situation, it is customary to present the operating data on two graphs.
One is called the “performance chart,” and shows the relationship
between H, I, V, P, and X for constant load; the other is called a “ Rieke
diagram,” and shows the relationships between G, B, P, k, and V for
constant I and H.
Figure 10c16 is a performance chart for a typical magnetron with a
frequency of about 2800 Me/see.
It has been customary to plot anode voltage V as ordinate, and current
1 as abscissa. On such a graph the lines of constant H are more or
less parallel and slope upward to the right. Thus (referring to Fig.
10. 16), if the magnetron is operated at a constant magnetic field, say
2100 gauss, the relations of voltage and current are given by points on
the H = 2100 gauss line. (At 20 kv, the current drawn will be 48 amp.)
On the same chart are plotted the lines of constant power output.
These are the solid lines whose form suggests hyperbolas; they show the