Radar System Engineering

290 ANTENNAS, SCANNERS, AND STABILIZATION [SEC. 9.12
pressurized all the way from the transmitter-receiver unit through a
flexible section to the scanner, the azimuth rotary joint, and the tilt
joint to the feed, which is enclosed in a hollow Styralloy ball. Parts of
the waveguide are made of nickel electrodeposited on a die-cast form
which is subsequently melted out. The scan is circular, at 30 rpm.
This scanner has an unusual feature which allows the main axis to be
adjusted to a vertical attitude despite changes in the angle of attack of
the airplane. This pitch adjustment is electrically driven and remotely
controlled by hand. A second unusual feature is the nature of the r-f
elevation joint, which allows the beam to be raised or depressed from its
normal attitude. This is merely a choke-to-flange coupling, similar to
the rigid coupling commonly employed (See Sec. 11.3), except that the
flange is slightly beveled so as to allow f 9° relative motion. This
“wobble joint” is enclosed in a flexible airtight tube.
The AN/APS-6.—The AN/APS-6 system imposes unusual requirements
on the scanner (Fig. 9.17). This radar is used for airborne detection
of aircraft under blind conditions, and therefore requires a search
over a solid angle in the forward direction. The beamwidth is about 5°.
The scan is spiral, and one turn of the spiral is described in ~ see,
which causes the plane of polarization to gyrate at this speed. The beam
is made to spiral outward from 0° (straight ahead) to 60° and back again
in 2 sec by the nodding of the antenna in relation to the yoke which forms
the forward end of the horizontal main shaft. By throwing a switch the