Radar System Engineering

252 RADAR BEACONS [SEC.84
restricted scope. Mention should be made, however, of the more general
problem of identification, which gave rise to a system known as IFF—
Identification of Friend or Foe. This system was probably the most
important single field of application of radar beacons in the war. The
goal was to provide every friendly military ship and aircraft with a transponder
that would give an identifying reply signal in response to proper
interrogation. Since the location of the ship or aircraft in question was
almost always determined by radar, the problem was actually one of
determining the friendly or hostile character of radar targets. The IFF
interrogating equipment was thus used in the great majority of cases as
an adjunct to a radar set. The problem was enormously difficult in view
of the rapid development of many types of radar sets in both Britain and
America, the tremendous density of airplane traffic to be dealt with in
many theaters and the necessity for having replies coded with sufficient
elaborateness to prevent the effective use of captured IFF transponders
by the enemy for deception. In addition to these and other inherent
technical difficulties, there were still others of a political sort. Among
these were the problems of getting agreement among the many branches
of the British and U.S. Armed Services concerning details of desired
characteristics of systems and of planning manufacture, distribution,
installation, and maintenance of equipment in such a way that an IFF
system could actually go into effective widespread use in a theater by
some target date. It seems that problems of this sort are to be encountered
in connection with any such system that is meant to have widespread
use. In spite of all these difficulties, one such system was put
into use in nearly all theakers, and was of great help where its potentialities
were understood and its limited traffic-handling capacity was not
exceeded. It is beyond the scope of this chapter to go further into the
problems of IFF. A peace-time requirement that is likely to pose problems
of similar character, although of lesser complexity, is that of control
of air traffic in the neighborhood of airports where the traffic is likely to
be heavy.
8.4. Radar Interrogation vs. Special Interrogators.-Much of the
preceding discussion implies that beacons are to be used principally with
radar sets and to be interrogated by them. For IFF, however, because
of the great variety of radar sets at different wavelengths, it is necessary
to pick particular bands of frequencies for the IFF beacons and to supply
supplementary interrogating equipment to work with the radars. For
every proposed radar application where beacons would be of use, the
question will arise whether it is better to use radar beacons or to provide
such separate equipment to work at frequencies set aside for the purpose.
There seems to be no single correct answer. Separate cases must be
considered separately, but it is desirable that in so doing the proposed