Radar System Engineering

SEC. 9.12] EXAMPLES OF MECHANICAL SCANNERS 287
it may be mounted and used on two trucks, this set is more commonly
based on the ground. As mobility requires, the mount is easily assembled
and disassembled in the field, and only four of its parts exceed 80 lb in
weight.
The antenna, a paraboloid made of a grid of curved }~-in. tubes, is
trimmed to an oval contour 10 ft high by 3 ft wide. The beam is therefore
of a “ beavertail” shape and since the radiation is at the 3-cm band,
the beam is 2.3° wide in azimuth and 0.7° wide in elevation. The polarization
is vertical. In the height-finding function the beam scans in
elevation between 2° below and 23° above the horizontal at a manually
controlled azimuth. For search purposes the azimuth motion may be
motor-driven at 4° per see, either boxing the compass or scanning a sector.
This azimuth rate cannot be exceeded if successive sweeps in elevation are
to cover without gaps all portions of the zone being scanned. The
“oscillating beavertail” scan which results is, however, rather slow for
search, and this function is sometimes relegated to another set with which
the AN/TPS-10 may form a team.
The main bearing of the mount is a roller-ring bearing, defining the
vertical axis of the pedestal. On the turntable are mounted the antenna
and the elevation drive, consisting of motor, gear reduction, crank, and
connecting rod. The turntable also supports the pressurized modulator
and its controls, the pressurized r-f head, and the power supply for
the receiver. The r-f head is so mounted in order to eliminate the
need for an azimuth rotary joint, and the other components named are
so mounted in order to reduce the number of slip rings on the azimuth
axis.
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Long -Range Ground Radar. The system now to be described was
designed for microwave early warning and surveillance of enemy aircraft
and the control of friendly aircraft. Two antennas (Fig. 9. 15), usually
back-to-back on a single mount, characterize this set. One is for longrange
low-angle coverage and the other, radiating a fan beam, covers
higher elevations. The set can detect single heavy bombers to above
30,000-ft altitude and 200-mile range, provided the aircraft are above the
horizon. The antennas are similar in that each has a shaped cylindrical
reflector 25 ft long, in 11 sections, fed by a linear array of dipoles at the 10-
cm band and forming a beam 0.9° wide in azimuth. The waveguide transmission
line is weatherproof, the array being housed in a Plexiglas cover.
The antennas are different in that the low-angle reflector is 8 ft high and
parabolic in vertical section, its radiation vertically polarized; whereas
the high-angle reflector is 5 ft high, of an empirically determined shape
producing an approximately cosecant-squared beam, and its radiation
horizontally polarized.
The reflectors are not perforated for the reason that the small amount