Radar System Engineering

306 ANTENNAS, SCANNERS, AND STABILIZATION [SEC.9.17
servoamplifier, and the follow-up system which includes the servomotor,
the gear train or linkage system, and a take-off actuated by the controlled
member. The gyro may be mounted on the rotating scanner or
remote from the scanner, using slip rings and resolvers to take off the
required error information. The error is fed into a servoamplifier whose
output operates the servomotor which in turn aligns the antenna with
the horizontal through a gear train or linkage system.
The gyro should preferably have either a two-speed erection mechanism
or a device to disconnect the erection mechanism when the aircraft
goes into a turn. In a turn the gyro rotor tends to align itself with the
resultant of the true gravity and the centrifugal force caused by the
acceleration in the turn, instead of with true gravity alone. This can be
minimized or eliminated by using a two-speed erection mechanism, or by
employing an electromagnetic clutch to throw out the erection system
entirely in turns.
Continuing the general classification previously referred to, stabilizers
may be further typed as stable-base, roll, or line-of-sight, depending on
the stabilization compensation afforded.
The stable-base stabilizer, as the name indicates, provides complete
stabilization of the platform upon which the antenna is mounted. This
requires use of a two-axis gyro transmitter to provide alignment or error
information for both roll and pitch axes. The gyro is usually mounted
remotely from the antenna structure in this type. In addition two
separate servoamplifiers and follow-up channels are required, one for the
roll-error component and one for the pitch-error component. Although
this provides complete stabilization, the weight of the components usually
appears excessive so that another type is preferable.
The roll stabilization referred to is stable-base stabilization with the
pitch channel removed. This requires a single-axis gyro transmitter for
the roll axis, and but one servoamplifier and follow-up channel. Roll
stabilization would be appropriate in large aircraft for which the pitch
component might be negligible or tolerable. In deciding between a roll
and a platform stabilizer the accuracy requirements must be balanced
against the weight added by the pitch channel.
The line-oj-sight method is one which maintains the axis of the beam
of radiation in a horizontal position or a fixed angular distance above or
below the horizon as the antenna rotates, scanning the horizon. This is
done by automatically tilting the antenna about an axis perpendicular to
the plane of the beam and parallel to the floor of the aircraft. Figure 9.35
shows the stabilizing attachment, A>-/.~\.15,5, mounted for photographic
test on the scanner of the A>”/.iPS-2 circular-scanning radar. The black
tubular construction of the scanner yoke can be seen, together with the
silver-plated +in. coaxial transmission line. The 29-in. paraboloid has