Radar System Engineering

SEC. 913] THE AN/APQ-7 (EAGLE) SCANNER 291
operator can halb the nodding of the antenna, which then executes a
conical scan to permit accurate homing. A single motor, rated at 600
watts mechanical output, provides power for the nod and spin motions.
The data take-offs area 2-phase sine-wave generator for the spin angle
and a potentiometer for the nod angle, both being mounted on the main
gear case to obviate the need of slip rings. The gear case is unusual in
airborne practice in that it is oil-filled. Two r-f rotary j oints are required,
one on the spin axis and one on the nod axis.
A difficult problem in dynamic balance is presented by this scanner.
The difficulty arises from the fact that the fast (1200-rpm) rotor must
be in good balance for all attitudes of the antenna which is supported
thereon. In order to effect balance a special procedure has been evolved
whereby the correct number of standard lead weights may be attached
to each of eighteen points provided on the antenna and the main shaft.
A special type of balancing machine has becm produced for this purpose.
ELECTRICAL
SCANNERS
BY C. V. ROBINSON
No radically new principles are embodied in the mechanical scanners
discussed in the previous section. By contrast, the electrical scanners
to be discussed in the following sections have many novel features of
fundamental design and so merit a more thorough discussion.
9.13. The AN/APQ-7 (Eagle) Scanner.-The AN/APQ-7 (Eagle)
high-resolution navigation and bombing equipment was developed at
Radiation Laboratory; Bell Telephone Laboratories carried through the
production engineering. I
The antenna developed for this equipment produces at the 3-cm band
a horizontally polarized beam of radiation which has a width of 0.4° to
0.5° in azimuth and is shaped in elevation to give an approximately
cosecant-squared coverage down to 70° angle of depression. The beam
scans a 60° azimuth sector in ~ see, or 1 to-and-fro cycle in l+ sec. The
range of the Eagle system for ground-mapping is about 50 miles.
The antenna is a slender linear array 16 ft long, which fits into a
streamlined housing (vane) hung laterally beneath the aircraft that uses
it (Fig. 9.18). The body of the array consists of a fixed 16-ft extruded
aluminum channel and a movable 16-ft aluminum plate which together
form a guide of variable width (Fig. 9.19). A row of 250 dipole radiators
is mounted in the fixed channel in such a way as to draw power from the
guide formed by the two long aluminum members. A mechanism varies
I L. W. Alvarez, ‘‘ Microwave Linear Radiators, ” RL Report ATO,366, June 30,
1942; R. M. Robertson, “ Variable W“idth Jraveguide Scanners for Eagle and GC.4,”
RL Report No. 840, April 30, 1946.