TELE-TECH & - AmericanRadioHistory.Com

Design Of
By J. E. WOODWARD, Section Head, Dept.
of Radar and Navigation, Airborne Instruments
Lab., Inc., Mineola, N.Y. and D. R. KIRSHNER,
Supervisory Electronics Engr., Rome Air
Development Center, Griffis Air Force Base,
Rome, N. Y.
Fig. 1: PPI picture of N. Y.
International Airport (Idlewild)
as displayed on ASDE
model
Fig. 2: Irl Experimental
model of ASDE installed in
the control tower at Idle -
wild
AIRPORT Surface Detection
Equipment (ASDE) is a radar
equipment designed to permit ob-
servation and control of surface
traffic on an airport. The fundamental
requirement of such a radar
is that it display the details of an
airport with sufficient resolution
that it can supplement or replace
the visual observations of a control -
tower operator. This means that
the runways and taxiways must be
clearly defined and that objects on
these areas must be plainly visible.
Fortunately, a radar (when viewing
an airport from a somewhat
elevated position) will "see" reflections
from the areas of the airport
covered by vegetation or having the
normal rough surface of the
ground, but will not receive reflections
from the smooth surface of a
runway. The greatest part of the
airport surface will therefore be
visible on a PPI display, whereas
the runways, taxiways, and other
smooth areas will be dark. Thus,
aircraft and other objects on the
runways will be seen against a
dark background (Fig. 1).
The control of traffic on the surface
of an airport has long been
recognized as a part of the overall
problem of aircraft traffic control
and safety. Although the problem
of surface traffic control- beyond
that afforded by the control -tower
operator -has not occupied top pri-
ority in the overall program, it has
been actively pursued. At about
the end of World War II, the Air
Force (at what was then Watson
Laboratories) made a study of the
various ways in which the traffic
on an airport could be followed by
other than visual means. The report
on this study covered the use
of pressure pads, induction loops,
photocells and such devices, as well
as radar. The conclusion was
reached that, from the standpoint
of economics and practicability,
radar appeared to offer the best approach.
Based on this study, a program
was set up by the Air Force to fur-
ther investigate the use of radar
as an aid in the control of surface
traffic on an airport. This program
has led to the radar system that is
now being discussed. A very brief
history of its evolution will be
given before the details of the present
equipment are described.
It was recognized that the highest
practical radio frequency should
be used in such a radar in order to
obtain a narrow azimuth beam -
width. The 24,000 -Mc r e g i o n,
K -band, was the highest frequency
at which components were available
at that time, but it was known
that this frequency was subject to
high atmospheric attenuation. This
problem was investigated, using an
existing K -band radar, and it was
concluded that atmospheric attenuation
would not seriously impair
the operation of such a radar at the
short ranges involved.
A radar system, referred to as
Taxi Radar, was procured by the
Air Force for use in an evaluation
program. This system operated at
86 Tele -Tech & ELECTRONIC INDUSTRIES June 1956