Radar System Engineering

CHAPTER 17
RADAR
RELAY
BY L. J. HAWORTH AND G. F. TAPE
INTRODUCTION
From the standpoint of the effectiveness with which a radar collects
information, the location of its antenna is of supreme importance. In
the use of the information much depends upon the location of the indicators.
“Radar relay” is a means for separating these two components
so that each can occupy the most favorable site or so that indicators can
be operated at several places simultaneously. As the name implies,
the radar data are transmitted
to some remote point by means of a radiation link.
from the source at which they are collected
17.1. The Uses of Radar Relay .-Control of aircraft in either military
or civilian applications requires the review and filtering of a mass of
information gathered from many sources, of which radar is only one.
Control centers are, therefore, located at sites chosen for their operational
convenience, whereas radar locations are chosen mainly for terrain and
coverage reasons. Sometimes it is desirable to collect the data at great
distances from one or more fixed land stations. Advantages are also
gained by obtaining the data at an airborne site with its extended horizon,
but displaying and using the data on the ground or on a ship. On the
other hand, occasions arise in which an aircraft can usefully employ
information collected from another site. In any of these cases, the
possibility of multiple dissemination of the data to many points offers
attractive
possibilities.
Prior to the advent of radar relay such transmission was done by
voice or not at all. Since the average operator can pass on only about
five data per minute this method is far too slow for any rapidly changing
complex situation, in addition to being rather inaccurate. Any really
sophisticated use of radar data at remote points therefore demands the
use of some sort of relay technique.
Two general types of situation arise: (1) those in which the data are
transmitted between jixed points on land, in which case it is possible to
use fixed, narrow-beam antennas at both ends of the relay link (or, if the
information is to be broadcast from a single antenna, to use directive
antennas at least on the various receivers); and (2) those in which one or
both sites are moving, in which case the antennas must be either omni-
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