Radar System Engineering

246 RADAR BEACONS [SEC. 8.1
beacons have sometimes been used in providing communication systems
ofamdimentary sort andalso forexercising remote control. Intelligence
has been conveyed from the radar to a beacon-carrying vehicle by modification
of the repetition rate, the length of interrogating pulses, their
spacing in groups, or the duration of the intervals of interrogation. The
replies of the beacons have also been modulated in such ways. One
200-M c/sec beacon was used for two-way voice communication while still
functioning for its normal use. For the most part, however, this use for
communications has been somewhat incidental. Much fuller use of the
channels could be made since the portion of the spectrum required for
transmission of beacon signals of a simple sort is ample for conveying
much more complicated intelligence.
Beacons of the synchronous sort just described have been variously
called “radar beacons,” ‘~responder beacons,” “racons,” and “transponders,’’
there being no essential distinctions among these terms. The
discussion hereis confinedto such beacons since other free-running types,
more like ordinary radio beacons, appear to be less useful in conjunction
with radar sets. From the free-running type, only the bearing can be
determined. Radar information is particularly useful because it gives
accurate determinations of range; it is obviously sensible to provide, as
an adjunct to radar, the sort of beacon that makes the best use of this
property.
This chapter aims to give a brief r6sum6 of the main points involved
in the use of radar beacons. The design of beacons and of systems using
them is treated at length in Vol. 3 of this series.
RADAR-BEACON
SYSTEMS
8.1. Types of Radar-beacon Systems.—In a discussion of beacons
it is convenient to classify them as fixed ground beacons, shipborne
beacons, airborne beacons, and portable beacons. All of these may be
used in conjunction with ground, ship, or airborne radar sets, or with special
interrogator-responsors. The following combinations have proved
useful so far:
Ground
Radar,
1. Shipbome beacons. This combination is of use principally for
identification of particular ships since, in general, the radar echo
from a ship is distinct enough.
2. Airborne beacons. This combination has proved to be of great
usefulness for identification and for various purposes where ground
surveillance and control of air traffic is desired. Figure 8.3 shows
the AN/APhT-19, an airborne 10-cm beacon.
.4 special system of precision bombing, known as the “ Oboe