TELE-TECH & - AmericanRadioHistory.Com

MIRROR MOTOR
,
SCREEN
TARGET SPOTS
i
By W. BLITZSTEIN
and T. LEVINE
Project Wescom,
Univ. of Pennsylvania,
Philadelphia, Pa.
PICK U.
R =h TAN
a
=h TAN 2°c
=h TAN 2'."
a 'MIRROR ANGLE
' =SPEED OF MIRROR MOTOR
Fig. 1: The targets -spots of light -are projected on a screen
Optical Simulation of Radar
THERE are two basic requirements
for any simulation of
radar. First, the generation of
targets: some entities such as voltages,
linear displacements, or rotations,
etc., must be generated in
such a fashion as to simulate the
general motion of airborne targets.
In a word, they must vary in time
to correspond to the overall trajectory
of the airborne targets.
Second, they must be adapted to
radar -like display. The varying
parameters must either be initially
in the form for radar display or
ultimately converted to the form of
radar inputs. This form of input,
of course, is a sequence of pulses
delayed in time. The delay of each
target pulse corresponds to a range
from the radar origin. Also, a way
must be devised to identify an azimuth
coordinate for each target
pulse.
There are in existence several
methods of simulation of radar.
Principal among these are:
A. Analog Computer Technique:
Targets are generated in rectangular
coordinates as voltages by means
of rotating potentiometers, and converted
to polar coordinates by
means of resolvers. By means of
electronic circuitry, the voltages
are converted to delayed pulses and
then fed to the video of a radar
display.
B. Magnetic Tape Technique: In
this technique, pulses are programmed
on a magnetic tape and
the playback is fed to the radar
video.
C. Television Technique: In this
approach, the targets are simulated
by means of spots of light projected
on and moved across a screen so
that their paths trace aircraft -type
trajectories. A television camera
detects these spots of light in rectangular
coordinates, and by means
of additional equipment the data is
converted to polar coordinates for
the radar input.
The system described in this
article is similar to the last -mentioned
system except that the TV
camera is replaced by a much simpler
and cheaper device called the
"pick-up" device. The pick -up device
detects targets in polar coordinates
as does radar itself.
Description of System
As in the television technique,
the targets are spots of light projected
on a screen, and an optical
device is used to detect these
targets (see Fig. 1).
The optical target detector is the
heart of this system and is called
the "pick-up" device (see Fig. 2).
The "pick-up" device consists
principally of a small (1x1x2 in.)
motor rotating a multi -facet mirror
in a plane perpendicular to that of
the screen. The motor and mirror
assembly is mounted on a small circular
platform (5 in. diameter)
displaced from its center by about
2 in. A fixed mirror is mounted at
the center of the circular platform
tilted at 45 °. A hollow shaft rotates
this entire assembly in a plane
parallel to that of the screen. A
light path thus exists from the rotating
mirror surface to the fixed
mirror at the center through the
hollow shaft. A 1P21 photo- multiplier
tube, located at a fixed position
at the far end of the hollow
shaft, receives the light. A lens and
very small aperture are mounted
inside the hollow shaft.
The "pick-up" device operates in
a fashion highly analogous to a real
radar set. In fact, the "pick-up"
device can be thought of as simulating
a radar which is located at
a simulated geographical position
corresponding to the projection of
the center of the "pick-up" device
onto the plane of the screen. This
is the simulated "origin" of the
radar's polar coordinate system.
Radar scans radially (fixed O and
110
Telle-Tech & ELECTRONIC INDUSTRIES June 1956