Radar System Engineering

250 RADAR BEACONS [SEC.8.2
Table 8.1 collects andsummarizes
all these applications.
Radar or
other
interrogator
TABLE 81.-SUMMARY
I
Ground
(fixed)
Shipborne
OF PRINCIPAL L’SES OF BEACONS
Beacons
.Airborne
Portable
Ground
I
Identification
Identification
Ground-controlled
precise navigation
Surveying
Shipborne
Pllotage
Identification
Control of aircraft
Homing
Life rafts
Shore bombardment
Airborne
Navigation
Blind approach
Identification
Homing
Identification
Rendezvous
Temporary marking
of points on land
Life rafts
8.2. Systems Planning.-Given a particular radar set, it is simple
enough to provide a beacon for any special use. The receiver of such a
beacon can be of narrow bandwidth and tuned to the frequency of the
radar. The reply can be either at the same frequency or at one just
different enough to permit separation of radar echoes and beacon replies,
but still receivable merely by minor adjustment of the radar receiver.
When, however, it isdesired to provide a beacon that will be useful to
many different radar sets of the same type, the problem is more complicated.
Radar sets of a given kind are usually operated at somewhat
different frequencies in order to avoid mutual interference. Thus, the
receiver of the beacon has to have sufficient bandwidth to receive the
interrogating signal from any one of the radar sets. For airborne 3-cm
radar sets, for example, the band from 9320 to 9430 Me/see was used.
This band of 110 Me/see was needed to take care of the variations of the
frequencies of the magnetrons as manufactured plus further changes to be
expected in adjustment and use in the field. The reply, however, had
to be made at some particular frequent y; that used was9310 + 2 Me/see.
Provision must be made in the radar receiver for quick and accurate
tuning to a chosen beacon reply frequency if beacon signals are to be used.
Radar sets and beacons cannot be so designed without careful planning.
If the full potentialities of radar beacons are to be realized, both
radar sets and beacons must be planned together as parts oj a unified r_adarbeacon
sgstem. Thk now seems trivially obvious, but it is not the way
that much of the existing equipment was designed. In the development
of radar, the beacons came as an afterthought. The result was that