Radar System Engineering

210 THE GATHERING AND PRESENTATION OF RADAR DATA [SEC.6.15
Circuits have been devised and tested which provide automatic tracking
in range, as well as in angle, but it appears that the judgment of the
range operator is of definite value in the operation of this equipment.
The operator is especially useful in following a desired target in the
presence of other near-by signals, which may be due to ground objects,
other aircraft, or “window” dropped to make radar tracking difficult
(Sec. 3.10).
The proving-ground accuracy of this set is about i 25 yd in range at
all ranges, and about + 1 mill or better in angle. With good radar
maintenance, this accuracy is achieved under field conditions. This was
one of the most widely used, versatile, and generally successful of all
allied wartime radar sets.
6“16. Precision Tracking During Rapid Scan.2—.At the end of Sec.
6.12 we considered the design of systems for general air surveillance and
control which offered fairly accurate information, renewed ever,y few
seconds, on all the positional coordinates of all targets in the radar field
of view. This was claimed to be the operational ideal; and so it is, for a
radar set whose purpose is to permit the general control of aircraft. For
fire control, or for the close control of aircraft which is needed if a ground
controller is to coach a pilot through a blind landing approach, much more
precise and much more nearly continuous positional information than
that supplied by the V-beam is demanded.
The requirement of greater precision implies that narrower radar
beams must be used, and the requirement of more frequent information
implies an increase in the speed of scanning. These design changes, as
we have seen, seriously restrict the volume of space which can be covered
by the resulting radar set. However, the goal of maintaining at least a
partial situation picture by scanning, while simultaneously providing
highly accurate positional information on a particular target being
tracked, is so attractive that several equipments have been designed to
attain it. The requirement of high scanning speed has led the designers
of all such sets to use “electrical” scanners (Chap. 9).
The design limitation on the volume of space that can be covered
frequently enough to be useful is least troublesome in the case of a radar
equipment designed to deal ~rith surface targets. In this case, one is
interested only in coverage of a plane, not in searching the volume of
space that may contain aircraft. The most advanced equipment of the
rapid-scan precision-tracking type that was in field use at the end of
World War II was the AN’/TPG-l, which had been designed for the
control of shore-battery fire against ships. For the purpose of fire control
ngainst ships, a rapid-scan precision radar is most desirable, because the
1.i mil is a thousandth of a radian; thus 17.4 roils = 1’.
? By 1,. >-. Ridencmr.