Radar System Engineering

SEC. 614] PRECISION TRACKING OF A SINGLE TARGET 207
ing coverage of the tail cone without the necessity for scanning. The
beam \vasconically scanned by rotating the reflector about an axis which
made an angle of 2.5° ~rith its o~rn. Commutators were mounted on the
shaft of the antenna rotation mechanism so that signals from the upper
half of the scan collld be integrated and compared with those from the
lower half; similarly, signals from the left half of the scan were compared
with those from the right. The resulting error voltages were used to
deflect the spot of a CRT used as an error indicator. An automatic circuit
searched in range in the absence of a target, and locked on and
tracked a target when an echo was encountered within the 2000-yd
coverage of the set. This range circuit was used to brighten the spot
only when a target was in range, in order to distinguish between correct
pointing and the absence of a target. It also caused the target spot to
grow horizontal “wings” whose spread increased as the range grew
shorter, in order to provide an indication of range to the gunner (see
Fig. 6.13).
The axis of the conical scan was aligned with the guns so that only
point-blank fire with no lead was possible. Thk was done because the
lead required in countering the usual nightfighter approach is negligible. “
The indicator was so arranged that its display was projected into the
reflector sight, enabling the gunner to use the same technique for either
optical or radar tracking. This equipment became available so late in
the war that it had substantially no operational use, but its provingground
tests indicated that its performance would have been quite satisfact
ory. The attainable angular accuracy was about + 0.5°.
The AN/APG-15 was unusual in that a triode, the “lighthouse”
tube, was used as a pulsed oscillator. At the low pulse power used (about
500 watts), this enabled transmitter, receiver, and the necessary rectifierfilter
power supplies to be housed in one compact unit, shown in Fig. 6.36.
Automatic Angle Tracking. -Shortcomings of the SCR-268 as a firecontrol
position finder arose mainly from the use of a relatively long
wavelength which resulted in broad beams from antennas of any reasonable
size. When microwave radar became practicable with the development
of the cavity magnetron, one of the immediate applications of the
new technique was an antiaircraft position finder. The most widely used
and generally successfld of the resulting equipments was the SCR-584.
Before beginning precision tracking of a single target, a radar that is
to serve as the only equipment of an antiaircraft battery must execute a
general search in order to locate targets that are to be tracked and
engaged. No auxiliarv long-wave radar search equipment was provided
\vith the SC R-584. Instead, the 6-ft antenna reflector was helically
scanned, and targets presented on a PPI whose maximum range was
60,000 yd. A range of elevation angles up to 10° was covered by the