Radar System Engineering

196 THE GATHERING AND PRESENTATION OF RADAR DATA [SEC. 6.13
This type of height finder is free from the range limitation which
arises from the scanning loss of a rapidly scanning system. The V-beam
can, in principle, find height to any range where a search set of the came
antenna size can detect aircraft. Heights on single aircraft out to 140
miles have been recorded.
The set is shown in Fig. 6.28. The two antenna reflectors are 25 by
10 ft. The vertical sheet of radiation is obtained by three separate
transmitters feeding a horn and a series of dipoles. The slant beam uses
only two transmitters, since early-warning range is ordinarily not needed
on the slant beam which is intended for height-finding.
The results of height calibrations show that heights can be called
rapidly to an accuracy of ~ 1000 ft and, with care, to + 500 ft. If an
average is taken, better results can be obtained.
6.13. Homing.’-The use of airborne radar to guide an aircraft to its
target was extremely important during the Ivar. Long-wave radar
installed in aircraft is scarcely capable of performing an,y function more
complicated than homing, since the enormous size of an antenna giving a
beam sharp enough to produce a map-type display precludes its use in
aircraft. Fortunately for the wartime development of airborne radar,
homing is a tactically important function both in the attack of shipping
by aircraft and in the interception of hostile aircraft by defending
fighters. Sets for both purposes operating near 200 Me/see were extensively
used during the war.
Homing on a Swjace Target.—The simpler of the two problems is that
of the detection and interception of shipping by patrol aircraft. Since
targets are known to be on the surface of the sea, homing information
need be supplied only in azimuth. The first operationally successful
aircraft-to-surface-vessel, ASV, radar was the British ASV lMark II. A
counterpart of this equipment was manufactured in the United States,
being called SCR-521 by the Army and ASE by the Navy.
The SCR-521 operates at a frequent y of 176 Me/see. Two sets of
antennas are provided giving different beam patterns (Fig. 6.29); one
pattern is used for search and the other for homing. Each pattern consists
of a left and a right lobe. In the search position these lobes extend
broadside to the airplane; in the homing position they extend nearly
straight ahead, so that they overlap to a considerable extent. The exact
design of these antennas underwent a complicated series of changes. In
some equipments separate antennas were used for transmission and for
reception, and in others both functions were carried out with a common
antenna. In all cases, however, the general coverage and arrangement
of the beams were those shown in Fig. 6.29.
The radar receiver is rapidly s\vitched from the left to the right mem-
1B.vL. N. Ridenour.