Radar System Engineering

SEC, 153] INITIAL PLANNING AND OBJECTIVES 593
output pulse powers were then low, receiver sensitivities were poor, and
system problems were not well understood. Coverage equal to or better
then that provided by the longer-wave equipment then in use or under
development appeared to be attainable only by means of extremely
high antenna gain.
As these ideas developed, microwave techniques were rapidly advancing.
Requirements forantenna gain andsize \verereduced tomderate
values, and finally computations supported by measurement showed that
a microwave system could satisfactorily meet the coverage problem.
Work was then initiated leading to the production of a ground radar,
which proved to be one of the most successful sets ever developed. Its
design characteristics were so well chosen that, even with the best
techniques available at the end of the war, it could not easily be surpassed
for air surveillance and control.
As in several other system developments involving great advances
over previous equipment, requirements on this set were not firmly
specified during the developmental stage. In many respects this freedom
from rigid requirements was advantageous. General objectives were
clear, the design men were well situated to draw freely for advice and
help on component specialists and on men familiar with operational needs,
and they were largely free to use their own ingenuity and judgment to
meet the many problems that were presented.
General Objectives.—The principal objectives can be stated simply as
follows: Coverage was considered to be important both as to maximum
detection range and as to the altitude region included, but resolution in
azimuth and in range were thought to be of comparable importance.
Where height information was desired, auxiliary height finders were to be
used; thus the radar beam could be fixed in elevation and swept continuously
in azimuth by rotation of the antenna.
Estimates of detailed requirements were difficult to make in regard to
characteristics such as (1) accuracy of range and bearing values as determined
by methods of data presentation, (2) interval between “looks”
at the target as determined by the revolutions per minute of the antenna,
and (3) traffic-handling capacity as determined by the number and type of
indicators provided. The designers, however, adopted as a general policy
the improvement or extension beyond current practice of equipment
characteristics that determined the accuracy and speed of data presentation
and use. Care was also taken in the design to permit still greater
extension of these facilities by simple changes or additions.
Beam Shape in Elevation.—A large air-surveillance set must be
located on the ground or be elevated at most by a low tower to avoid
interference by !ocal obstruct ion. The radar beam in ik 360° sweep
may look over land, over water, or over both land and water. Figure 15.4