Radar System Engineering

SEC. 615] PRECISION TRACKING DURING RAPID SCAN 211
splashes of shells that miss the target can be seen on the scope of the radar.
Accurate “spotting-in” of fire both in range and in deflection is possible
with this type of set.
The antenna and scanning principle of the AN/TPG-l (which was
also designated, in various modifications, as SCR-598, AhT/MPG-l,
.lN/FPG-1) are described in Sec. 9.14, and a perspective drawing of the
antenna is shown as Fig. 9.25. The radar beam produced was about
0.55” wide in azimuth; this narrow beam, coupled with the }~ psec pulse
length used, gave the set high resolution both in range and in azimuth.
A scope photograph showing the ability of the equipment to resolve
closely-spaced targets is shown as Fig. 6.38.
FIG. 6.3S—ROW of smallships (LCI’S in formation off Honolulu) shownon micro-B of
.4N/TPG-l. Ships are less than 300 Y(I apart. (Reprinted from Eleckmics, December
1945.)
The AN/TPG-l rapid scan covered a sector 10° wide centered on the
target of interest. The antenna could be mechanically rotated as a whole
to swing the center of this sector to any desired azimuth position, or could
be rotated continuously in azimuth during search. The set incorporated
a PPI which was useful when the antenna was rotating mechanically for
search. Its other indicators were a conventional type B presentation
which presented the 10° sector covered by the rapid scan, and a micro-B
indicator. The latter is normalized at 400 ydiin. At the ranges important
in the operational use of this set, the distortion of the micro-B display
is very small. Electronic range and azimuth markers are provided on
the micro-B to aid in tracking. The azimuth error obtained in trials of
this set was less than 0.05 degrees.
The AN/MPN-l equipment, often called GCA (for ground control of
approach), is the only radar designed during the war to provide accurate