Radar System Engineering

38 THE RADAR EQUATION [SEC.210
practically never depends on the detection of alone signal pulse, but on
reception, from the same range and bearing, of repeated signal pulses.
This has a profound influence on the statistical problem that we have
been discussing because, whereas thenoise fluctuations during successive
sweeps 1 are completely independent, the signal can be made to appear
at the same position in each sweep. To take advantage of this essential
difference between signal and noise it is evidently necessary to resort to
some method of information storage, or integration, which would make
use of the information contained in several sweeps. It might be possible,
Time - (b)
Time a (c)
FIG.2.6.—Outputnoiseporrer:(a) singlesmeep;(b) average
four sweeps,
of two sweeps;(c) averageof
for example, to average over a number of s~veeps—that is, to present to
the observer a single trace whose height at any time would represent the
average of the power output which was obtained in each of the several
sweeps at that same time (measured from the transmitted pulse). Now
this is substantially what many radar indicators do; it is so nearly what
they do, in fact, that quantitative conclusions drawn from a study of
the ideal process outlined are of practical significance and are surprisingly
well borne out by actual observations. Therefore, we want to
inquire more carefully into the simple averaging or integration process.
I We use the term “sweep” to mean one entireintervalbetweensuccessivepulse
transmissions. Such a termunavoidably suggestsa particulartype of display, but a
more generaland formal terminologyseemstoo cumbersome.